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f\A)5/0&S- 82-^9

Biological Services Program

FWS/OBS-82/59
September 1982

Proceedings of the

Conference on Coastal Erosion

and Wetland Modification in Louisiana :

Causes, Consequences, and Options

(r-.^.

Baton Rouge, Louisiana
October 5-7, 1981

.(756

ind Wildlife Service Louisiana Universities Marine Consortium

)epartment of the Interior

State of Louisiana

The Biological Services Program was established within the U.S. Fish
and Wildlife Service to supply scientific information and methodologies on
key environmental issues that impact fish and wildlife resources and their
supporting ecosystems. The mission of the program is as follows:

• To strengthen the Fish and Wildlife Service in its role as
a primary source of information on national fish and wild-
life resources, particularly in respect to environmental
impact assessment.

• To gather, analyze, and present information that will aid
decisionmakers in the identification and resolution of
problems associated with major changes in land and water
use.

t To provide better ecological information and evaluation
for Department of the Interior development programs, such
as those relating to energy development.

Information developed by the Biological Services Program is intended
for use in the planning and decisionmaking process to prevent or minimize
the impact of development on fish and wildlife. Research activities and
technical assistance services are based on an analysis of the issues, a
determination of the decisionmakers involved and their information needs,
and an evaluation of the state of the art to identify information gaps
and to determine priorities. This is a strategy that will ensure that
the products produced and disseminated are timely and useful.

Projects have been initiated in the following areas: coal extraction
and conversion; power plants; geothermal , mineral and oil shale develop-
ment; water resource analysis, including stream alterations and western
water allocation; coastal ecosystems and Outer Continental Shelf develop-
ment; and systems inventory, including National Wetland Inventory,
habitat classification and analysis, and information transfer.

The Biological Services Program consists of the Office of Biological
Services in Washington, D.C., which is responsible for overall planning and
management; National Teams, which provide the Program's central scientific
and technical expertise and arrange for contracting biological services
studies with states, universities, consulting firms, and others; Regional
Staffs, who provide a link to problems at the operating level; and staffs at
certain Fish and Wildlife Service research facilities, who conduct in-house
research studies.

FWS/OBS-82/59
September 1982

PROCEEDINGS OF THE

CONFERENCE ON COASTAL EROSION

AND WETLAND MODIFICATION IN LOUISIANA:

CAUSES, CONSEQUENCES, AND OPTIONS

Edited by

Donald F. Boesch

Louisiana Universities Marine Consortium

Star Route, Box 541

Chauvin, LA 70344

Project Officer

Carroll L. Cordes

National Coastal Ecosystems Team

U.S. Fish and Wildlife Service

1010 Cause Boulevard

Slidell, LA 70458

Performed for

National Coastal Ecosystems Team

Office of Biological Services

Fish and Wildlife Service

U.S. Department of the Interior

Washington, DC 20240

DISCLAIMER

The findings in this report are not to be construed as an official U.S. Fish and
Wildlife position unless so designated by other authorized documents.

This report should be cited as:

Boesch, D. F., ed. 1982. Proceedings of the conference on coastal erosion and wetland
modification in Louisiana: causes, consequences, and options. U.S. Fish and Wildlife
Service, Biological Services Program, Washington, D.C. FWS/OBS-82/59. 256 pp.

PREFACE

The Conference on Coastal Erosion and Wetland Modification in Louisiana,
sponsored by the Louisiana Universities Marine Consortium and the U.S. Fish and Wildlife
Service, was held in Baton Rouge on 5-7 October 1981. The Conference was in response
to a need for a current compendium of information on the causes, consequences, and
options to deal with coastal land loss in Louisiana.

Patterns of wetlands deterioration in relation to natural geomorphic processes in
the Mississippi River delta were described as early as the I930's (Russell, R.J. 1936.
Physiography of the Lower Mississippi River delta: Louisiana Geological Survey, Lower
Mississippi Delta Geological Bulletin 8: 3-199). In the I960's systematic comparisons of
wetland areas from topographic maps indicated that the net loss of wetlands in Louisiana
was 42.7 km^ (16.5 mi /yr) (Gagliano, S.M. and J.L. van Beek 1970. Geologic and
geomorphic aspects of deltaic processes, Mississippi delta system. Louisiana State Univ.
Center for Wetland Resources, Baton Rouge. Hydrologic and Geologic Studies of Coastal
Louisiana. Rep. I. 140 pp.). Habitat mapping studies conducted in the late I970's for the
U.S. Fish and Wildlife Service and based on direct analyses of aerial imagery yielded
estimates of coastal wetland loss of 18 km /yr in the chenier plain region of
southwestern Louisiana between 1952 and 1974 (Gosselink, J.G., C.L. Cordes and J.W.
Parsons. 1979. An ecological characterization of the chenier plain coastal ecosystem of
Louisiana and Texas. U.S. Fish and Wildlife Service, Office of Biological Services.
FWS/OBS-78-9) and 83 km /yr in the deltaic plain of southeastern Louisiana between
1955-56 and 1978 (Wicker, K.M. 1980. Misissippi Deltaic Plain Region ecological
characterization: a habitat mapping study. A user's guide to the habitat maps. U.S. Fish
and Wildlife Service, Office of Biololgcal Services. FWS/OBS-79/07). Furthermore,
comparisons of land loss rates estimated for various intervals during this century indicate
a geometric increase in this rate with time, the extrapolation of which yields a 1980 rate
of 102 km /yr (39.4 mi'^/yr) for the Mississippi deltaic plain alone (Gagliano, S.M., K.J.
Meyer-Arendt, and K.M. Wicker. 1981. Land loss in the Mississippi River deltaic plain.
Trans. Gulf Coast Assoc. Geol. Soc. 31:295-300).

These revelations have heightened public and governmental concern about the
causes and consequences of the astounding rates of coastal environmental change in
Louisiana and have catalyzed action on various approaches to slow or reverse the rate of
loss. The causes are clearly complex but involve at least the senescence of the active
delta, regional and localized subsidence, leveeing of the Mississippi River, and the
effects of channelization of wetlands. Man has played a major role, in consert with
natural processes, in accelerating coastal land loss. The potential effects of these
coastal changes on living resources, state revenues and human society are massive. The
coastal wetlands of Louisiana are a major contributor to national fisheries and wildlife
resources. Given the present rates of loss, several coastal parishes have life
expectancies in the range of 50 to 100 years, and enormous social and economic
dislocations would result.

Several structural and management approaches to stemming coastal land loss have
been proposed. These range from allowing the wholesale diversion of the Mississippi
River down the Atchafalaya River to promote rapid delta building to more restrictive

iii

permitting of activities in wetlands, in recognition of the seriousness of coastal land
loss, the Louisiana Legislature in its 1981 Extraordinary Session established the Coastal
Environmental Protection Trust Fund to be applied for projects such as controlled river
diversions, barrier island stabilization, and wetlands management. The first of these
projects are scheduled to commence in late 1982.

Sound scientific understanding of the processes responsible, the effects on natural
resources, and the effectiveness of mitigative approaches will be critical to the success
of attempts to control land loss. It is to this purpose that the contributions in this
volume are addressed.

The Conference and these Proceedings are products of a cooperative Agreement
(1 4_ 1 6-0009-8 1 - 1 0 1 6) between the U.S. Fish and Wildlife Service and the Louisiana
Universities Marine Consortium related to research and informational services on
"Shoreline Erosion and Wetland Habitat Modifications in Coastal Louisiana." It reflects
the commitment of both of these organizations to address this most serious
environmental problem.

Donald F. Boesch
Cocodrie, Louisiana
September 1982

Any questions or comments about or requests for this publication should be addressed to:

Information Transfer Specialist
National Coastal Ecosystems Team
U.S. Fish and Wildlife Service
NASA-Slidell Computer Complex
1010 Cause Boulevard
Slidell,LA 70458

CONTENTS

Preface ii i

Acknowledgments viii

CAUSES: CHANGES IN DISPERSAL OF FRESH WATER

AND SEDIMENTS I

Sedimentation and Apparent Sea-Level Rise as Factors

Affecting Land Loss in Coastal Louisiana 2

R. H. Baumann and R.D. DeLaune

Assessment of Geological and Human Factors Responsible

for Louisiana Coastal Barrier Erosion 14

Shea Pen land and Ron Boyd

Mudflat and Marsh Progradation along Louisiana's Chenier

Plain: A Natural Reversal in Coastal Erosion 39

John T. Wells and G. Paul Kemp

Panel Discussion 52

Gerald G. Bordelon, Johannes van Beek, Richard Hatton,
Ron Boyd, John Wells, Clarke Lozes and
Raf)hael Kazmann

CAUSES: PHENOMENA DIRECTLY RELATED TO HUMAN ACTIVITIES . 59

Wetland Loss Directly Associated with Canal Dredging

in the Louisiana Coastal Zone 60

W. B. Johnson and J. G. Gosselink

Canals and Wetland Erosion Rates in Coastal Louisiana 73

R. Eugene Turner, R. Costanza and W. Scaife

Panel Discussion 85

Roger Saucier, Andre Delflache, James G. Gosselink,
R. Eugene Turner, Michael Lyons, Joan Phillips, and
John Woodard

CONSEQUENCES: EFFECTS ON NATURAL RESOURCES PRODUCTION 91

The Effect of Coastal Alteration on Marsh Plants 92

Robert H. Chabreck

Effects of Wetland Deterioration on the Fish and

Wildlife Resources of Coastal Louisiana 99

David W. Fruge

Some Consequences of Wetland Modification to

Louisiana's Fisheries 1 08

Barney Barrett

Wetland Losses and Coastal Fisheries: An Enigmatic

and Economically Significant Dependency 112

R. Eugene Turner

Panel Discussion 121

James G. Gosselink, Robert H. Chabreck,

David W. Fruge, Barney Barrett, R. Eugene Turner,

Mike Voisin, and John Teal

CONSEQUENCES: SOCIAL AND ECONOMIC 1 27

Legal Implications of Coastal Erosion in Louisiana 1 28

Paul Hribernick and Michael Wascom

Economic and Cultural Consequences of Land Loss

in Louisiana 1 40

Donald W. Davis

Panel Discussion 1 59

Edward W. Stagg, Paul Hribernick, Michael Osborne,
Donald W. Davis and Charles Broussard

OPTIONS: BARRIER ISLAND AND SHORELINE PROTECTION 1 63

Future Sea-Level Changes along the Louisiana Coast 1 64

Dag Nummedal

Effects of Coastal Structures on Shoreline Stabilization

and Land Loss ~ The Texas Experience 1 77

Robert A. Morton

Sand Dune Vegetation and Stabilization in Louisiana 187

Irving A. Mendelssohn

Panel Discussion 208

Charles G. Groat, Dag Nummedal, Irving A. Mendelssohn
Robert A. Morton, Johannes van Beek, Murray Hebert
and Larry DeMent

OPTIONS: LIMITATION OF DREDGING AND

FRESHWATER DIVERSIONS 213

Reversal of Coastal Erosion by Rapid Sedimentation:

The Atchafalaya Delta (South-Central Louisiana) 214

Harry H. Roberts and Ivor LI. van Heerden

Comparison of the Effectiveness of Management Options for

Wetland Loss in the Coastal Zone of Louisiana 232

J. W. Day Jr. and N. J. Craig

Panel Discussion 240

Kai Midboe, John W. Day, Horry H. Roberts,
Sherwood M. Gogliano, Peter Hawxhurst,
Samuel B. Nunez and Gerald Voisin

SUMMARY 247

LIST OF ATTENDANTS 253

ACKNOWLEDGMENTS

The Conference on Coastal Erosion and Wetland Modification in Louisiana was
planned and conducted under the able direction of a steering committee composed of
Donald F. Boesch, Louisiana Universities Marine Consortium (LUMCON); James M.
Coleman, Coastal Studies Institute, Louisiana State University (LSU); Donald W. Davis,
Nicholls State University; John W. Day, Jr., Center for Wetland Resources, LSU; Ted B.
Ford, Louisiana Department of Wildlife and Fisheries; Sherwood M. Gagliano, Coastal
Environments, Inc.; Joseph Kelley, University of New Orleans; Joel Lindsey, Coastal
Management Section, Louisiana Department of Natural Resources; Dag Nummedal,
Department of Geology, LSU; Robert Stewart, U.S. Fish and Wildlife Service (FWS); and
Michael Wascom, LSU Law Center. In addition, Charles Adams, Barney Barrett, David
Chambers, Nancy Craig, James Johnston, R. Eugene Turner and Paul Templet
contributed to the deliberations of the steering committee.

Bette Wall, Mary Katherine Politz and John Hassell of LUMCON handled the
logistical arrangements for the Conference. Mary Katherine Politz and Gloria Whitney
of LUMCON assisted in editing and revision and prepared the typescript. Carroll L.
Cordes provided patient cooperation and editorial assistance as FWS Project Officer.

Financial support for the Conference was provided by the Louisiana Universities
Marine Consortium. Prepartion and publication of the Proceedings were supported by the
U.S. Department of the Interior, Fish and Wildlife Service, National Coastal Ecosystems
Team.

CAUSES: CHANGES IN DISPERSAL
OF FRESH WATER AND SEDIMENTS

SEDIMENTATION AND APPARENT SEA-LEVEL RISE AS FACTORS
AFFECTING LAND LOSS IN COASTAL LOUISIANA

R.H. Baumann
R.D. DeLaune

Center for Wetland Resources

Louisiana State University

Baton Rouge, LA 70803

ABSTRACT

RatHS of apparent sea-level rise and marsh aggradation were determined with the
aid of Cs dating, artificial marker horizons, and water level data for the lower
Barataria and Calcasieu estauries. These marshes are not vertically accreting at a rapid
enough rate to maintain their intertidal elevation and have been subjected to net
submergence since at least the mid-1950's. This has resulted in a conversion of marsh to
open water habitats.

Rates of apparent sea-level rise at the two study areas were 1.2 and 1.3 cm/yr
from 1954 to present. Sedimentation rates through the same period were approximately
0.7 cm/yr over most of the area of investigation, though streamside marshes aggraded at
a rate of 1.35 cm/yr. The transformation of marsh to open water will be complete in a
few decades if present trends continue. A research strategy that will narrow
management alternatives is briefly outlined.

INTRODUCTION

The recognition of wetland loss as a problem in coastal Louisiana is widespread, the
consequences of wetland loss have been reasonably projected, and management agencies
and groups appear ready to commit resources towards resolution. Until the how and why
of wetland loss are understood, however, we will not know the most appropriate
mitigating procedures. The how and why are the processes of wetland loss.

Wetland loss can be viewed as the inability of wetlands to maintain themselves. In
subsiding environments, such as coastal Louisiana, the continued existence of marsh is
partially dependent on its ability to maintain its elevation within the tidal range through
vertical accretion. This must be accomplished through some combinaton of peat
formation and mineral sediment accumulation. The two can be interrelated as the influx
of sediments also supplies nutrients for plant growth (DeLaune et al. 1979). Increased
plant growth results in more material available for peat formation and increases in stem
density result in an enhanced ability to further entrap and stabilize sediment (Gleason et
al. 1979). Thus, the process appears to have a synergistic effect and a reduction in
sediment supply can result in an exaggerated effect.

We report in this paper the processes and rates of vertical accretion as determined
by Cs dating and by the use of artificial marker horizons, and relate them to apparent
sea-level rise and marsh deterioration at two sites along the Louisiana coast. The two
sites were independently studied with slightly different objectives, but the results
pertaining to wetland loss were similar.

STUDY AREA DESCRIPTIONS

The two study areas are representative of the two coastal regions of Louisiana: the
chenier and Mississippi deltaic plains. The site within the chenier plain is a brackish to
saline Spartina patens marsh known locally as the East Cove marsh, located on the south
shore of Calcasieu Lake within the Sabine National Wildlife Refuge (Figure I). The
deltaic plain site is the saline Spartina alterniflora marsh surrounding Barataria Bay
(Figure 2).

Both sites have been experiencing above average land loss rates of over 1%/yr since
the mid-1950's. A major difference between the two sites is their respective geologic
foundation. Underlying the East Cove marsh is a I to 6 m sequence of Recent sediments
(Gosselink et al. 1979) whereas in the lower Barataria basin, the Pleistocene surface lies
30 to 100 m below the marsh surface (Kolb and Van Lopik 1966). This difference in
sediment thickness suggests that the Barataria site has an inherently greater subsidence
potential. If all other factors were equal we would expect land loss rates to be
comparatively greater at the Barataria site.

METHODS

Details of sampling design, laboratory procedures, materials used, and statistical
analyses are provided in previous reports (DeLaune et al. 1978; DeLaune et al. in review;
Baumann 1980). Discussion here will be limited to a general application of various
methods and techniques as they pertain to monitoring sedimentation in Louisiana's
marshes.

The numerous techniques employed to monitor sediment accretion can be divided
into five broad categories: (I) surveys through time based on benchmarks or other
datums; (2) calculations based on sediment budgets; (3) simple mechanical devices such as
calibrated rods; (4) radiometric dating; and (5) natural and artificial marker horizons.
Categories one through three are generally unacceptable for work in Louisiana marshes
for many reasons, some of which have been discussed by Letzsch and Frey ( 1 980).

Radiometric dating can provide accurate sedimentation rate information provided
the substance being dated has been deposited in situ and the sedimentary sequence has
not been subsequently disturbed. '~^'Cs was the radioactive element used in the case
studies discussed in this report. It was first introduced into the biosphere as a product of
atmospheric nuclear testing with significant fallout levels first appearing in I95|f and
peaking in 1963 (Pennington et al. 1973). By obtaining cores and measuring the Cs
activity at regular intervals throughout the core, the average sedimentation rate from
1954 to 1963 and from 1963 to the present can be determined.

Artificial marker horizons have been extensively used in monitoring studies
involving a few years or less. Various substances have been employed, but most are not

Marsh

CAMERON
"GULF OF MEXICO

Figure 1. Location of East Cove Marsh study area,

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adequate for Louisiana's coastal marsFies because of either recognizability (color) or
density (sinkage) problems. White clay (Feldspar 26 1 -F) is one substance that is easily
recognizable from marsh sediments and is not subject to sinkage provided the organic
content of the marsh soil is less than 30% on a dry weight basis (Baumann 1980). In
Louisiana, this generally restricts its use to saline and brackish marshes.

I "^7
The combination of the ' "^ Cs and artificial marker techniques provides more

information than either technique alone can produce. The results of the two techniques

can be compared, thereby providing an additional check on method reliability. The two

techniques are compatible as some of the disadvantages of one technique are the

advantages of the other. Artificial markers do not provide information on the past

whereas Cs does. Artificial markers provide information on variability of

sedimentation rates through time, whereas Cs is generally limited to providing

average sedimentation rate information. Artificial markers can be sampled at any time

interval desired, therefore one can obtain data on possible seasonal trends, the role of

storms, etc. This frequency of sampling freedom allows one to examine processes of

sedimentation more fully, but the disadvantage is that one must wait for sedimentation

to occur.

Sea-level rise was calculated by linear regression analysis of tide gauge data
available from the U.S. Army Corps of Engineers, New Orleans District.

Land loss rates for the Barataria site were extracted from Adams et al. (1978) and
rates for the Calcasieu site were mapped and measured from available aerial photographs
using the methods described by Adams et al. (1978).

RESULTS AND DISCUSSION

Barataria Site

1 37

Cs analysis showed that marshes bordering water bodies such as lakes, bayous,

and ponds were aggrading (vertically accreting) at a rate of 1.35 cm/yr whereas marshes

more distant from water bodies were aggrading at a rate of 0.75 cm/yr (DeLaune et al.

1978). These two types of marshes are commonly referred to as streamside and inland

marshes, respectively. The difference in sedimentation rates are to be expected as

streamside marshes are closer to the source of sediments. This situation is analogous to

the levee and backswamp situation bordering many of the rivers and bayous of Louisiana

except the scale of elevation and sedimentation rate differences are much less in the salt

marshes. Density and organic carbon analysis of the core samples revealed that

aggradation occurs by both plant detritus and mineral sediment accumulation (DeLaune

et al. 1978).

Aggradation of the salt marsh as measured by artificial marker horizons from 1975
to 1979 was 1.5 cm ± 0.4 and 0.9 cm ± 0.2 for streamside and inland marshes,
respectively (Baumann 1980). The slightly higher values resulting from the artificial
marker horizon method could be due to the different time interval of sampling (5 versus
25 years), less compaction due to the shorter time interval or other unidentified
reasons. Considering the natural variability in the environment, the difference in results
between the two methods is quite small.

Apparent sea-level rise at the Bayou Rigaud tide gauge located near Grand isle was
1.3 cm/yr from 1954 to 1980 (Figure 3). Apparent sea-level rise includes both the effects
of subsidence of land, and a global, real rise in sea level which is referred to as eustatic
sea-level rise.

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1960

1970
YEARS

1980

Figure 3. Apparent sea-level rise and mean sedimentation rates for stream-
side and inland saline marshes in the lower Barataria estuary.

If we compare the apparent sea-level rise data with the sedimentation rate data it
becomes clear that since 1954 streamside marshes have kept pace with apparent sea-
level rise and, therefore, are maintaining their relative elevaton within the tidal range,
but inland marshes are not. Thus, through time flooding of inland marshes (representing
75% to 80% of the salt marsh area) increases and at some point the plants can no longer
survive (Mendelssohn et al. 1981). Once the inland marshes begin forming into ponds and
the ponds enlarge and coalesce, the streamside marshes are subject to wave attack and
they begin to erode laterally.

Examining the seasonality of sedimentation (Figure 4) with the use of the artificial
marker technique provides additional insights on why the marshes are not maintaining
their elevation. From 1975-78 most of the aggradation occurred during the winter, but
when the 1979 dataware added sedimentation appears to be equally important during
winter and summer.

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SEASONS
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Fiqure 4. Seasonality of sedimentation in the Barataria saline marsh,
1975-1978 and 1975-1979. Spring and fall values have been combined.
Values represent accumulated totals for the time period indicated.

The summer and winter sedimentation dominance has been related to storm events
(Baumann 1980). The cyclical and repetitive nature of cold front activity is responsible
for the comparatively high winter sedimentation rate. High winds re-entrain sediment in
the water column with southeasterly winds preceeding the frontal passage pushing
sediment-laden water over the marsh where the sediment is deposited. The reversal to
strong northerly winds pushes the water off the marsh and maintains high turbidity levels
in the lakes and bays (Cruz-Orozoco 1971) setting the stage for the cycle to be repeated.

Sedimentation during the summers of 1975-78 was relatively low, but increased
dramatically in 1979 due to the large scale redistribution of sediments by Tropical Storm
Claudette and Hurricane Bob. Thus, sedimentation rates during the summer can be
expected to be normally low, but episodically high depending on tropical storm activity in
this area. We expect this would also characterize the fall season, however, no major
tropical storm activity occurred over the study area during the fall during the
examination period.

Perhaps the most striking aspect is the lack of sedimentation during the spring
when the Mississippi River is in flood and carries peak sediment loads. Even the flood of
1979, which was the second largest flood since 1950 (U.S. Army Engineer District, New
Orleans 1980), did not directly result in substantial sedimentation on the study area
marshes. This lack of substantial sedimentation during the spring shows that the
Mississippi River is no longer a direct source of sediments to the study area.

The final aspect addressed in the Barataria example was an attempt to directly link
the net sedimentation deficit to land loss rates. By combining the sedimentation and
sea-level rise data with marsh elevation relative to water level data a theoretical land
loss rate could be calculated. These calculations, which are outlined in Baumann (1980),
indicated that the saline marsh in the lower Barataria Basin should have a maximum life
expectancy of nearly a century if current sedimentation rate and sea-level trends
continue in the future.

Actual land loss rates (Adams et al. 1978) indicate that maximum life expectancy is
much less even after considering the direct and intentional loss of marshes via man's
activities. This suggests that additional factors are also contributing to the land loss
problem in the lower Barataria basin.

Calcasieu Site

Both '-^'Cs profile distributions and the artificial marker techniques showed that
the East Cove marsh has been aggrading at an average rate of 0.7 cm/yr. Sampling
was not designed to compare streamside with inland accretion. The lower rate of
accretion at the Calcasieu site in comparison to the Barataria site was expected due to
the previously discussed regional differences in sediment supply and subsidence potential.

The accretion rate of 0.7 cm/yr is not sufficient to maintain the elevation of the
marsh with respect to water level. Apparent sea-level rise as measured at the nearby
Cameron tide gauge has averaged 1.2 cm/yr from 1954-80 (Figure 5). Thus, apparent sea
level has been rising at nearly twice the rate of marsh aggradation during the past
quarter-century.

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If we assume that accretion has been fairly constant throughout the period of
examination and the elevation range of the marsh is small, then the loss of marsh to open
water should parallel apparent sea-level rise (Figure 5). If present trends continue, the
East Cove marsh will complete its transformation to open water in approximately 40
years.

While the inability of the marsh to maintain its elevation with apparent sea-level
rise appears to be an important factor that is responsible for wetland loss in the East
Cove marsh, why the marshes are not keeping pace is a more difficult question to
resolve. Discharge and sediment load data suggest that the Calcasieu Ship Channel has
reduced the amount of riverborne sediment dispersed into the Calcasieu Lake system by
debouching flows directly into the Gulf of Mexico (DeLaune et al. in review). The ship
channel has also facilitated saltwater intrusion to the Calcasieu estuary which may be an
additional interacting factor in wetland loss (Gosselink et al. 1979).

Probable reductions in sediment supply and saltwater intrusion may only be a part
of the problem. The 1.2 cm/yr apparent rise in sea level at Cameron is high. One would
expect the rate to be considerably less than at Bayou Rigaud due to the inherently lower
subsidence potential, but the rates of rise at the two stations are within 0.1 cm/yr of one
another. Nearby gauges depict similar rates which seem to belie any argument that the
trends are aberrations due to gauge instability. The similarity in the rates of apparent
sea-level rise suggests that interregional factors may be an important if not dominant
factor during the past several decades.

CONCLUSIONS AND STRATEGY

In both case studies reported here, marsh aggradation has not kept pace with
apparent sea-level rise. At the Barataria site, which lies within the Mississippi deltaic
plain, basinal processes now dominate over riverine processes and it is apparent that
basinal processes cannot maintain marsh elevation given the present rate of apparent
sea-level rise. This dominance of basinal over riverine processes is characteristic of the
deterioration phase of Mississippi River deltaic cycles (Coleman and Gaglino 1964).

As an initial step towards narrowing possible management options, we need to
determine how widespread marsh aggradation deficits are. The two sites reported here
were originally chosen partially on the basis that they were experiencing high rates of
wetland loss. Thus, in addition to the small number of sample areas, the sampling is
biased.

If it is found that marsh aggradation deficits are indeed a major component of land
loss throughout the coastal zone, then it behooves us to examine why the marshes are not
keeping pace in order to propose appropriate mitigating procedures. If the marshes are
not keeping pace because canals interrupt sedimentary processes, then management
solutions may be weighted towards regulatory procedures. If fluid withdrawals have
accelerated subsidence rates, then we must look to reinjection where feasible and
possible redistribution and control of groundwater wells. If the marshes are being
sediment-starved due to levee systems, then reintroduction of sediments may help, but
this solution will be geographicaly limited to a relatively narrow corridor paralleling the
present Mississippi River. The possibility that all of these factors can be operating
simultaneously dictates that any management plan must be flexible to deal with different
causes and adaptable to change as new insights are made. But until we commit our

resources to continue to go beyond looking at effects and examine processes, we will not
know what our capabilities and limitations for management are.

ACKNOWLEDGMENT

This report is a result of research sponsored by the Louisiana Sea Grant College
Program, a part of the National Sea Grant College Program, maintained by the National
Oceanic and Atmospheric Administration, U.S. Department of Commerce. Contribution
No. LSU-CEL-81-37 of the Coastal Ecology Laboratory, LSU Center for Wetland
Resources.

LITERATURE CITED

Adams, R.D., P.J. Banas, R.J. Baumann, J.H. Blackmon, and W.G. Mclntire. 1978.
Shoreline erosion in coastal Louisiana: inventory and assessment. Louisiana
Department of Transportation and Development, Baton Rouge.

Baumann, R.H. 1980. Mechanisms of maintaining marsh elevation in a subsiding
environment. M.S. Thesis. Louisiana State Univ., Baton Rouge.

Coleman, J.M., and S.M. Gagiiano. 1964. Cyclic sedimentation in the Mississippi River
deltaic plain. Trans. Gulf Coast Assoc. Geol. Soc. 14:67-80.

Cruz-Orozoco, R. 1971. Suspended solids concentrations and their relations to other
environmental factors in selected waterbodies in the Barataria Bay region of south
Louisiana. M.S. Thesis. Louisiana State Univ., Baton Rouge.

DeLaune, R.D., R.J. Buresh, and W.H. Patrick, Jr. 1978. Sedimentation rates determined
by 13/iQs dating in a rapidly accreting salt marsh. Nature 275:532-553.

DeLaune, R.D., R.J. Buresh, and W.H. Patrick, Jr. 1979. Relationship of soil properties
to standing crop biomass of Spartina alterniflora in a Louisiana marsh. Estuarine
Coastal Mar. Sci. 8:477-487.

DeLaune, R.D., R.H. Baumann, and J.G. Gosselink. In review. Relationships among
vertical accretion, apparent sea level rise, and land loss in a Louisiana gulf coast
marsh. J. Sediment. Petrol.

Gleason, M.L., D.A. Elmer, N.C. Pien, and J.S. Fisher. 1979. Effects of stem density
upon sediment retention by salt marsh cord grass. Sporting alterniflora Loisel.
Estuaries 2:271-273.

Gosselink, J.G., C.L. Cordes, and J. W. Parsons. 1979. An ecological characterization
study of the Chenier Plain coastal ecosystem of Louisiana and Texas. 3 vols. U.S. Fish
and Wildlife Service, Office of Biological Services. FWS/OBS-78/9 through 78/1 I.

Kolb, C.R., and J.W. Van Lopik. 1966. Depositional environments of the Mississippi
River deltaic plain, southeastern Louisiana. Pages 17-61 _m Deltas and their geologic
framework. Houston Geological Society.

Letzsch, W.S., and R.W. Frey. 1980. Deposition and erosion in a Hoiocene salt marsh,
Sapelo Island, Georgia. J. Sediment. Petrol. 50:529-542.

Mendelssohn, I. A., K.L. McKee, and W.H. Patrick, Jr. 1981. Oxygen deficiency in
Spartina alternifiora roots; metabolic adoption to anoxia. Science 214:439-441.

Pennington, W., ELS. Cambray, and E.H. Fisher. 1973. Observations on lake sediments
using fallout ' -^ ' Cs as a tracer. Nature 242:324-326.

U.S. Army Engineer District, New Orleans. 1980 (and earlier years). Stages and
discharges of the Mississippi River and tributaries and other watersheds in the New
Orleans District for 1979 ( and earlier years).

ASSESSMENT OF GEOLOGICAL AND HUMAN FACTORS
RESPONSIBLE FOR LOUISIANA COASTAL BARRIER EROSION

Shea Pen land

Louisiana Geological Survey

Louisiana State University

Baton Rouge, LA 70803

Ron Boyd

Department of Geology

Dalhousie University

Halifax, Nova Scotia, Canada

ABSTRACT

Louisiana's coastal barrier systems are experiencing severe shoreline erosion and
land loss^ Between 1880 and 1980, total coastal barrier area decreased from 98.6 km"^ to
57.8 km , an overall loss of 41%. Coastal barrier land loss results from the natural
processes of deltaic transgression and marine erosion, combined with the impact of
human development. A three-stage model for the evolution of abandoned Mississippi
deltas describes deltaic transgression. Sand bodies deposited during delta building are
successfully transformed after abandonment into an erosional headland and flanking
barriers (Stage I), a transgressive barrier island arc (Stage 2), and a subaqueous
inner-shelf shoal (Stage 3). Barrier erosion trends closely correspond to the pattern of
sediment dispersal identified for each barrier evolutionary stage. Barrier islands in the
erosional headland and flanking barrier stage are essentially in a state of dynamic
equilibrium, due to the presence of a deltaic headland sand source. Transgressive barrier
island arcs do not contain such a sediment source, and hence suffer net erosion. The
principal mechanisms of transgression are subsidence combined with repeated erosion by
extratropical and tropical cyclones. Coastal barrier sediment loss, hence land loss, can
be attributed to the following mechanisms: (I) longshore loss into spits and tidal deltas,
(2) landward loss through overwash into a subsiding lagoon, (3) offshore loss due to an
inequality in offshore/onshore transport capacity, and (4) subsidence of the deltaic sand
sources. Human impacts that result in accelerated coastal barrier deterioration include
coastal structures, pipeline canals, and navigation channels. These manmade structures
disrupt sediment transport pathways and create additional sediment sinks.

INTRODUCTION

Louisiana is faced with the most serious coastal barrier erosion problem in the
United States (Figure I). Between 1880 and 1980, the total coastal barrier area of
Louisiana decreased 41%. Coastal barrier erosion and land loss results from the natural
processes of deltaic transgression and marine erosion, combined with the impact of
human development. The economic consequences of shoreline erosion and land loss are

Figure 1. Location map showing the distribution of coastal sand barriers
along the Holocene Mississippi River deltaic plain.

seen in the destruction of connmercial and residential property, the accompanying loss of
valuable coastal wetlands caused by the removal of protective storm barriers, and the
loss of fishery resources caused by intrusion of salt water into wetland nursery areas. A
new and comprehensive evaluation of shoreline change trends along 250 km of Louisiana's
barrier coastline has been made for 1922-78, using digitization of individual island areas
from the U.S. Coastal Survey charts dated between 1869 and 1969 and land cover maps
dated 1979.

DATA ACQUISITION

Analysis of shoreline change was based on two independent sets of data. Changes
in Gulf of Mexico shoreline positions were derived by the Orthogonal-Grid Mapping
System technique (Dolan et al. 1978). This technique produces a location of the
high-water line for every 100 m of shoreline, based on information that has been
summarized as an average rate of shoreline change over the period of data collection and
expressed as areas of either accretion or erosion within 5m/yr-class intervals.

The second data set was obtained by individually digitizing the surface area of each
barrier island on the Louisiana coast. This method analyzed U.S. Coast and Geodetic

survey maps for 1869-1956, together with a series of land cover maps at the scale of
1:10,000, based on 1979 aerial photography. Results are presented as a time series of
variation in coastal barrier area plotted against tropical cyclone and coastal structure
impacts.

GEOLOGICAL FACTORS RESPONSIBLE FOR COASTAL BARRIER EROSION

Deltaic evolution of the Louisiana coast is characterized by alternate periods of
land building and land loss (Figure 2). The alternation of these two activities is
determined by the balance between sediment supply and variation in relative sea level
(Curry 1964). Throughout the Pleistocene Epoch, the relative sea level has undergone
dramatic fluctuations, falling over 120 m and rising as much as several meters above

• ABBEVMLLE

^ BATON RflL'Gt **

V— ^ ""--^

\ • NEW ORLEANS

100 ^^^^

/ p^ „.,„....,.,...

'"'

Figure 2. A time series of paleographic maps depicting the evolution of the
Mississippi River deltaic plain and its depositional environments (modified
from Frazier 1967) .

present sea level. Most of this variation may be attributed to eustatic sea-level
variations related to changing volumes of ice at the polar ice caps. Since eustatic sea-
level rise ceased about 3,000 to 6,000 years BP (Coleman and Smith 1964), ongoing
subsidence resulting from a compaction and sinking of Mississippi delta sediments is the
major cause of the relative sea-level rise, and hence land loss and coastal barrier erosion,
in Louisiana.

The major factor offsetting subsidence-induced sea-level rise is sediment supplied
to the coast by the Mississippi River in a sequence of well-defined deltaic depocenters
(Fisk 1944; Kolb and Van Lopik 1958; Frazier 1967). During active sedimentation in each
depocenter, the shoreline progrades laterally as much as 120 km seaward, with the delta
plain vertically aggrading up to 5 m above mean sea level (Figure 2). Following delta
switching through upstream distributary diversion, sediment supply to the delta complex
quickly diminishes. Under these conditions, subsidence induced by substrate compaction
and dewatering becomes the dominant coastal process and deltaic transgression begins.
This period corresponds to Stage I, erosional headland and flanking barriers (Penland et
al. 1981; Penland and Boyd 1981, 1982), in which the reworking of distributary sand
bodies through shoreface retreat provides the only sand source for coastal barrier
generation (Figure 3). Shore-parallel transport distributes sand from the headland source
into downdrift marginal spits, tidal deltas, and flanking barrier islands. While sand is
being actively supplied from the erosional headland, the downdrift barrier systems in this
evolutionary stage exist in dynamic equilibrium. Subsidence gradually causes this
reworked distributary sand source to move below the reach of wave erosion and onshore
transport. With increased age and long-term subsidence, Stage 2 occurs; this barrier
system evolves into a transgressive barrier island arc, separated from the mainland by an
intra-deltaic lagoon. From this point on, sand sources no longer exist for barrier
nourishment, and the sediment dispersal pattern in this subsiding environment is the
destruction of the subaerial barrier and the formation of a subaqueous inner shelf shoal,
Stage 3. This occurs when sea-level transgression has overcome the ability of the barrier
to maintain its integrity through landward migration and vertical accretion. Geological
processes, therefore, interact in Louisiana to produce periods of rapid coastal
progradation, associated with delta building, and rapid coastal transgression, associated
with distributary abandonment and coastal barrier formation. Subsurface studies of the
Mississippi River in such areas have shown the existence of several major and minor
regressive-transgressive cycles in the past 8,000 years (Fisk 1944; Kolb and Van Lopik
1958; Frazier 1967). During the transgressive history of any one of the four abandoned
delta complexes, the following four mechanisms are identified as controlling coastal
barrier deterioration: (I) subsidence of deltaic sand source, (2) accumulation and
subsiding washover deposits, (3) infilling during migration of spit complexes and tidal
inlets, and (4) inequality in onshore-offshore sediment exchange.

Subsidence of Deltaic Sand Source

Following upstream diversion during the process of delta switching, the only source
of sand-size sediments for coastal barrier development comes from reworked distributary
sand bodies and flanking beach-ridge plains. During the evolution of an abandoned delta,
these sand sources continually subside and provide a diminishing sediment supply. The
maximum effective depth limit for erosion of deltaic sand sources is the base of the
advancing shoreface (Figure 4). Available bathymetric data locate the base of the
advancing shoreface seaward of the Bayou Lafourche headland and the Chandeleur
Islands, at a depth of around 6 to 8 m. Assuming that the estimated rates of relative
sea-level rise estimated between 0.6 and 1.5 cm/yr are correct (Kolb and Van Lopik 1958;

■o

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SUBSIDENCE OF DELTAIC SAND SOURCE

SUBSIDENCE

TRANSPORT

SHOREFACE
EROSION

15 20 25

DISTANCE (km)

Figure 4. Subsidence of distributary sand sources is the major mechanism
driving coastal barrier transgression and deltaic land loss.

Basal Portion of Ancestral
Flanking Barrier Island

500m -*

- > ,

■ \^ C^'''.^\T^^^

: ~

'-■■^-' •^■-.^-,— ^^

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Figure 5. An offshore seismic profile showing the basal portion of a spit
complex of an ancestral flanking barrier island of the Chandeleur Islands
that has been bypassed by the shoreface and is now preserved on the inner
continental shelf. The black line indicates the transgressive contact
between the overlying sandy barrier unit and the underlying St. Bernard
delta. The seismic line is shore-parallel.

Swanson and Thurlow 1973), the period of sediment supply from distributary sand bodies
is effectively limited to between 400 and 1,200 years, depending on the variation in the
subsidence rate over time. The rate of subsidence varies proportionally, according to the
thickness of the delta; thin deltas subside slowly and thick deltas subside rapidly.
Seismic data offshore from the Chandeleur Islands indicate that the St. Bernard delta
complex, which was abandoned about 1,800 years BP (Frazier 1967), is no longer
receiving an adequate sediment supply from St. Bernard distributary sand bodies through
the processes of shoreface retreat and sediment entrainment. The upper surface of the
St. Bernard delta, offshore from the Chandeleur Islands, lies two or more meters below
the base of the advancing Chandeleur Island shoreface. An offshore seismic profile
(Figure 5) reveals the base of an ancestral flanking barrier associated with the earlier
stages of coastal barrier evolution of the Chandeleur Islands. The basal portion of the
barrier has been bypassed by the shoreface and is now preserved on the inner portion of
the Louisiana continental shelf.

Accumulation in Subsiding Washover Deposits

In Louisiana, storm overwash is a major process of sediment transport during
barrier transgression (Boyd and Penland 1981; Ritchie and Penland 1982). Sea level is
subject to frequent and dramatic elevation changes on the northern gulf coast In response
to hurricane and winter frontal storms and the waves associated with them. Overwash
elevations exceeding 1.7 m may be expected to occur on the Louisiana barrier coast 10-
20 times/yr, causing washover sedimentation throughout more than 75% of most barrier
systems (Figure 6). This sediment then is stored until again reworked by the advancing
shoreface. During transgression, the site of overwash deposition in the backbarrier
lagoons, such as Chandeleur Sound or Terrebonne Bay, is continually subsiding.
Therefore, progressively greater quantities of sediment are required during transgression
for the barrier system to remain subaerial (Figure 7). For the region of active overwash
in the northern Chandeleur Islands, Penland and Boyd (1981) calculated an average
shoreline retreat rate of 5 m/yr, or 500 rnVlOO yr. A landward advance of 500 m in the
coalescing washover fans requires 2,500 m of sand per meter of fan front, assuming the
average water depth behind the Chandeleur Islands platform is 5 m. Using Kolb and Van
Lopik's average subsidence rate of 60 cm/100 yr for the St. Bernard Delta, this washover
volume will be required to increase by 300 m-^, or 12% per 100 yr. Washover sediments
become permanently lost from the barrier sediment dispersal system after the depth of
water into which the washover accumulation is advancing exceeds the nearshore depth of
the advancing shoreface.

The Infilling of Migrating Spit and Tidal Inlet Complexes

Wave-induced longshore sediment transport is a significant factor in the
development of any shoreline of an abandoned Mississippi River delta. Flanking barrier
spits and islands are supplied with sand transported alongshore by waves from erosional
headland sources. The configuration of the Bayou Lafourche headland (Caminada-Moreau
coast) indicates that sediment is transported alongshore, both to the northeast by waves
from the southwesterly quadrant, and to the west by waves from the southeasterly and
northeasterly quadrants. This has resulted in the growth of a symmetrical set of flanking
barriers, Caminada Spit and Grand Isle to the northeast, and the Timbalier Islands to the
west. Similarly, the transgressive barrier island arc configuration of the Isles Dernieres
results in bidirectional longshore transport, west toward Raccoon Point and east toward
Wine Island Pass. In contrast, the north-south orientation of the Chandeleur Island arc
results in an asymmetrical net transport pattern towards the north in response to the

METEOROLOGICAL
EVENT

STORM

SURGE (m)

OVERWASH
ELEVATION (m)

Minor Front

0 30

061

1-42 -

1-73

Major Front

061

0.90

1.73 -

2 02

East Delta

Wast Delta

East Delta

Wast Delta

Force 1 Hurricane

0 60 - 1 30

1 50

1 72 - 2.42

2-62

Western Track

Force 3 Hurricane

0 70 • 2 40

2,35

2 76 - 4.46

441

Western Track

Force 5 Hurricane

1 20 - 3.50

3 3

4 20 - 6 50

6-30

Western Track

Force 1 Hurricane

1 50 - 1 80

0 60-080

2.62 • 2 92

1 72 - 1 92

Eastern Track

Force 3 Hurricane

2 40 • 2 90

0 60 100

4 46 - 4 96

2-66 - 3 06

Eastern Track

Force 5 Hurricane

3 40 - 400

0 90 1 30

6-40 - 7.00

3 90 - 4-30

Eastern Track

Figure 6. Potential overv;ash conditions associated with extratropical and
tropical cylcones for the Louisiana coast. East delta refers to the St.
Bernard delta region, whereas west delta refers to the Lafourche delta region.
Hurricane landfall at the Lafourche delta is the western track and the eastern
track corresponds to landfall in the St. Bernard delta. Overwash elevations
are measured in meters above mean sea level.

Barrier Sands
Lagoonal Deposits

Increasing

Washover

Volume

, Overwash

Figure 7. Two modes of coastal barrier sediment loss: (1) increasing washover
storage, and (2) inequality in onshore-offshore sediment transport.

predominant wave approach from the southeast and east. Calculations from
wave-refraction analysis of longshore sediment transport along the Chandeleur Islands
indicate potential representative rates of 4 x 10"' m-^/yr to thexiorth, under 3 m high,
lO-second period, azimuth 135° wave conditions, and 3 x 10 m'^/yr, also to the north,
under 0.5 m and 5-second period, azimuth 135° wave conditions.

Active longshore transport processes on Louisiana barriers provide two further
mechanisms for permanent loss of barrier sediments: (I) spit progradation, and (2) tidal
inlet migration. As marginal spits prograde away from the shallow delta platforms by
downdrift spit accretion into deeper interdeltaic marginal basins such as Timbalier Bay,
increasing volume of sediment is required to maintain the subaerial integrity of the
system. In some instances, spits prograde into even deeper tidal inlets, and require
considerably larger sediment volumes. Examples of spit progradation into marginal
deltaic basins are found on the north end of the Chandeleur Islands, Breton Island, and at
Raccoon Point in the Isles Dernieres. Examples of progradation into tidal inlets occur at
Borataria Pass, Caminada Pass, Little Pass Timbalier, Cat Island Pass, and Wine Island
Pass. A prominent example of sediment loss into spit and tidal inlet complexes is
provided by the westward migration of the Timbalier Islands. Between 1887 and 1978,

Wine I. Timbalier isiand East Timbalier I. Boycw

_ . . . Linle Pan. LaFowcho

-10

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';" LaFourche 't; V ,\-, '_',';.;. ;,i;.'--^,'; ;LaFourche vV^ ;'c

--'•'- Delta ,; ;,',;^ 'X'-'-''-;~''--r-r''^''-;-'' ■ ''^"^ J-f-~-''^''V;

LEGEND

Timbalier Island

D
D

Shoreface

Distributary Flanli
Beach Ridge Plain

Distributary Moutti Bar

Delta Front

,--' Prodella

Backbarrier Marsh
I and Bay

Interdistributary Bay Fill

Kilometers

Figure 8. A stratigraphic strike section (top) and stratigraphic dip section
(bottom) of the Timbalier Islands showing facies relationships and the infilled
channel of Cat Island Pass offshore.

these islands migrated 6.7 km, or 74 m/yr. The average width of these flanking barriers
is approximately 900 m. Soil borings indicate an average thickness for the Timbalier
Islands of around 5 m (Figure 8). Therefore, the total volume of sediments below the
subaerial barrier is about 3.1 x 10 m-^. This figure represents a loss of 3.9 x 10 rrrlyr
of sand from the sediment dispersal system to build the Timbalier Islands. This figure
only represents the sediment stored in recurved spit deposits. A stratigraphic dip section
through the central portion of Timbalier Island and extending 800 m offshore shows an
additional sediment sink at the infilled tidal channel of Cat Island Pass (Figure 8). The
thalweg of Cat Island Pass lies seaward of the Timbalier Island shoreline and was infilled
as this inlet migrated westward. The exact volume of sediment stored in this tidal
channel is unknown, but it must be emphasized that tidal inlets in Louisiana are
significant sediment sinks. At Quatre Bauyoux Pass, the volume of sediment stored in
the ebb-tidal delta has constantly grown, due to the tidal prism increasing in size
(Howard 1982). Tidal prism enlargement is caused when land loss in the backbarrier
areas increases the bay area, making a progressively greater volume of water available
for exchange during each tidal cycle.

Another example of a migrating tidal inlet with significant sediment loss is located

6.4 km southeast from Monkey Bayou, offshore from the southern Chandeleur Islands.
Seismic information reveals the presence of relict tidal inlets infilled by southward
migrating bgrrier complexes (Figure 9). Individual tidal channel fills contain as much as

3.5 X 10 m of sand. These relict tidal inlets represent an earlier Holocene position of
the Chandeleur Island arc. The seismic sections in Figure 9 shows these sand bodies lying
in 8 to 10 m of water at the base of the advancing shoreface.

Relict Infilled
Migrating Tidal Inlet

30m

500m

Figure 9. An offshore seismic profile showing relict infilled tidal inlet
channel now bypassed by the shoreface and preserved in the inner continental
shelf. The black line indicates the transgressive contact between the over-
lying sandy barrier unit and the underlying St. Bernard delta. The seismic
line is shore parallel .

Inequality of Offshore/Onshore Transport

On most beach and barrier systems, a well-established cycle of sediment exchange
exists between the beach and shoreface in response to storm and fair weather
conditions. In general, sediment is eroded from the beach and nearshore bars under
storm conditions and stored in bars located farther offshore or deeper on the lower
shoreface. Under fair weather conditions, a variable proportion of this material may
move onshore and return to the beach, resulting in accretion. This pattern of change has
been well documented for southeastern Australian beaches (Short 1978). The proportion
of sediment returned to the beach is dependent, among other factors, on the maximum
depth from which waves can transport sediment landward under constructive fair
weather conditions, compared to the maximum depth which sediments are transported
seaward under erosive storm conditions (Figure 7).

To estimate the effectiveness of sediment return from offshore, the threshold
depth for the initiation of sediment motion was calculated for wave conditions of
A-second period, 30 cm high; 5-second period, 50 cm high; 7-second period, 200 cm high;
lO-second period, 300 cm; and 1 5-second period, 400 cm high. The first two of these
conditions represent typical constructive conditions on the Louisiana coast. The last
three conditions are typical of winter frontal storms and force l-to-3 hurricanes. For the
first two cases, 4-second and 5-second waves, the critical threshold depth offshore from
the Chandeleur Islands was 5 m and 6 m, respectively. For the 7-second, lO-second and
1 5-second waves, critical depths offshore from the Chandeleur Islands were around 40,
60, and 150 m, respectively. Murray (1970, 1972) measured near-bottom currents off the
Florida Panhandle in 3.6 m of water during the passage of Hurricane Camille and off the
southern Chandeleur Islands in depths of 20 m during winter frontal storm passage. In
both cases, the near-bottom current field velocity vectors were directed shore-parallel
and offshore during a frontal passage associated with strong, onshore winds and high
wave energy.

These data indicate the presence of a strong inequality in offshore-onshore
transport related to the storm-dominated characteristics of the wide, shallow Louisiana
continental shelf. Sediments transported offshore during these storm events under wave-
and wind-induced nearshore circulation encounter offshore- and longshore-directed
near-bottom currents. Only that sediment deposited above the 5 to 6 m depths on the
shoreface will be available for subsequent return to the barrier system. This mechanism
represents another means of permanent sediment loss from the Louisiana barrier system,
and may explain the extensive offshore sand sheets seaward from the Chandeleur Islands
reported by Frazier (1974).

THE LATE LAFOURCHE COASTAL BARRIER SYSTEM

Barrier Development

The Late Lafourche delta barrier system consists of the Bayou Lafourche erosional
headland, the Caminada-Moreau coast, and two nearly symmetrical sets of flanking
barriers, Caminada Pass spit and Grand Isle to the east, and the Timbalier Islands to the
west (Figure 10). The barriers have developed as the shoreface retreated, actively
reworking distributary sand bodies of Bayou Lafourche and the beach ridges of Cheniere
Caminada (Harper 1977). The sediment dispersal pattern consists of the longshore

LONGSHORE

TRANSPORT

DIRECTION

Figure 10. Location diagram showing the configuration of the Late Lafourche
coastal barrier system and average rates of shoreline erosion and accretion.

co;rsa-

■^l''^^°llf.»i^

vva^ChW^'"''''

Figure 11. A three-dimensional landform diagram showing barrier types found
in the Late Lafourche barrier system. Sediment availability for terrace and
dune development decreases left to right, as does shoreline stability.

transport divergence from the central erosional headland and sediment accumulation
downdrift of flanking barrier islands and tidal inlets both east and west of the erosional
headland. The Caminada-Moreau coast is a low barrier beach, approximately I m above
msl. This beach is a thin, continuous washover sheet with Holocene marsh outcropping on
the lower beach face, reflecting a negative sediment budget and rapid coastal erosion.
Increasing downdrift sediment abundance leads to the development of small channels,
washover fans, and low, hummocky dune fields which eventually coalesce further
downdrift to forma higher, more continuous offshore terrace, and eventually, a foredune
ridge (Figure I I). Downdrift flanking barrier islands migrate laterally, in the direction of
longshore sediment transport, by erosion at the updrift ends and accretion downdrift.
Washover sheets and multiple shallow breaches are common on the updrift or erosional
ends of these islands. Downdrift, longshore bars become more prominently developed in
the nearshore zone, and toward the eastern end of the system bars become attached. In
these downdrift zones, active beach ridge progradation is taking place. Recurved spit
morphology formed during the growth of Timbalier Island and Grande Isle indicates the
importance of an updrift sand source in the Caminada-Moreau erosional headland (Figure
12).

Shoreline Changes

In the erosional headland/flanking barrier stage, the greatest shoreline erosion
problems are within the erosional headland itself and on the updrift ends of the flanking
barrier islands (Figure 10). Along the Caminada-Moreau coast, erosion rates are 10 to 20
m/yr. Figure 13 shows the pattern of shoreline change from the Late Lafourche barrier
system between 1887 and 1978. Note the rapid shoreline retreat of the
Caminada-Moreau coast. Shoreline erosion and coastal spit progradation have smoothed
the earlier irregular shoreline of 1887 and closed all of the distributaries except Belle
Pass. The severest erosion is in the vicinity of Bays Marchand and Champagne. The
Orthogonal Grid Mapping System (OGMS) data from 1934-78 shows that this erosion
pattern is continuing. At Bay Champagne, the greatest rate of shoreline retreat
measured for the 44-year period was 22.3 m/yr, with erosion decreasing eastward to 9.6
m/yr at Bayou Moreau. Field measurements along the Caminada-Moreau coast made in
1979 by the Louisiana Barrier Island Project show that tropical cyclones accounted for
over 70% of the total annual erosion in that year (Figure 14).

In the Belle Pass area, erosion rates average 18.6 m/yr prior to 1954; after 1954,
the OGMS data show shoreline erosion slowing, switching to accretion sometime after
1969. The sedimentation pattern changed in response to jetty construction at Belle
Pass. Jetties 152 m long and 61 m wide were constructed at Belle Pass in 1934 to
improve the navigation channel at Bayou Lafourche. In 1968, the jetties were expanded
to 218 m long and 140 m wide, and the Bayou Lafourche navigation channel was dredged
to a depth of 6 m, width of 90 m, and extended 2 km offshore (Dantin et al. 1978). These
improvements created a formidable barrier to longshore sand transport and sediment
bypassing to the west around Belle Pass to the Timbalier Islands. The first jetty system
appears to have had little effect on the local sediment-dispersal pattern. The shoreline
continued to erode at rates averaging 18 m/yr, with no significant sand accumulation
updrift of the jetty system. In fact, the jetty system had to be extended landward
several times to keep pace with the retreating shoreline. It was after the 1968
improvements that the sedimentation began taking place along the eastern side of Belle
Pass. Accretion rates there have averaged 5.5 m/yr since 1969, representing a sink for
material that would otherwise be transported further west to the Timbalier Islands.

Grand Isle 1978

2km

Timballer Island 1978

1887

1934

2km

Sand Transport

Recurved Spit Position
Time Line

Figure 12. Recurved spit morphology of Timbalier Island and Grand Isle indi'
cate the importance of the updrift sediment source in the Caminada-Moreau
coast (see Figure 10) .

LATE LAFOURCHE BARRIER SYSTEM
SHORELINE CHANGES 1887- 1978

1887

1978

0 2

MILES

"^^ ^^-**,iiafc

:--'-■:::■'''--' ' Bay

Bdy w Champagne

Marchand '^

f.'-^' GB'^ND ISLE
L Groins -

.o»^

CAMlN^O*

1*0

^i'

Figure 13. A historical map comparison between 1887 and 1978 showing rapid
shoreline retreat along the Caminada-Moreau coast and lateral migration of
the flanking barriers of Grand Isle and Timbalier Island.

(/)

UJ
UJ

-50

-40

-30

-20

-10

+10

NET ACCRETION/EROSION-

1979
TROPICAL CYCLONE

EROSION 1979

1979 ACCRETION

TROPICAL CYCLONE
EROSION

9rK\''. FRONTAL EROSION

BAY
MARCHAND

BAY
CHAMPAGNE

Figure 14. Shoreline erosion-accretion graph illustrating the contributions
of extratropical and tropical cyclones to coastal changes along the Caminada-
Moreau coast. Tropical cyclones accounted for over 70 percent of the erosion
experienced in 1979, Extratropical cyclones (frontal erosion) accounted for
approximately 30 percent of the annual erosion.

Timbalier Islands. Timbalier Island and East Timbolier Island are the western
flanking barriers of the Bayou Lafourche headland. These barriers are composed of sand
that was transported west from the erosional headland source and that bypassed Belle
Pass (Figure 8). East Timbalier Island is a marginal recurved spit similar to the
Caminada Pass spit, and has repeatedly been detached from the erosional headland while
eroding at rates that exceed 15 m/yr. Flanking barrier islands are formed when a
marginal spit detaches from the headland. This occurrence is generally associated with
tropical cyclone landfall and barrier breaching. The updrift shoreline controls the
orientation of the newly detached island. Updrift erosion and downdrift accretion cause
rapid lateral migration and determine the stability of the island (Figure 13). Timbalier
Island, an example of a detached flanking barrier, eroded on the updrift end at an

average of 18.6 m/yr. Downdrift, the erosion decreases end switches to accretion at the
western end, averaging 17.4 m/yr.

Changes in the area of the Timbalier Island group reflect the impact of the
navigation structures at Belle Pass. Between 1887 and 1935, 19 tropical cyclones, 7 of
which were at least force-2 on the Saffir-Simpson scale (Saffir 1977), made landfall in
the vicinity of these islands, resulting in only a slight decrease in total area (Figure 15).
Between 1935 and 1956, both island areas increased, reflecting the low frequency of
tropical cyclone landfall, with just one force-2 storm occurring. Following 1956, the
area of both islands started decreasing rapidly. Hurricane frequency had increased
slightly, with five tropical cyclones impacting the coast, two of at least force-2
strength. The reduction in the island area is most likely attributed to the construction of
jetties at Belle Pass and the seawall groin system westward along East Timbalier Island,
and not to tropical cyclone impact. All of these structures have interrupted sediment
transport from the source areas within the Bayou Lafourche headland. A major factor in
reduction of longshore sediment transport appears to be the 1968 extension of the Belle
Pass jetties, as reflected by the dramatic changes in island areas during this time.
Flanking barrier islands connected to an active sediment source are dynamic and tend to
build. This appears to be the case prior to 1950 at the Timbalier Islands, when periods of
frequent hurricane impact produced little reduction in island area. These flanking
barriers, as long as they are receiving sediment input from the erosional headland, exist
in a state of dynamic equilibrium even under the conditions of rapid subsidence. The
recent land loss observed at the Timbalier Islands is directly linked to the introduction of
coastal structures in the sediment dispersal system.

Caminada Pass Spit-Grand Isle. East of the Bayou Lafourche headland lie the
downdrift barriers of Caminada Pass spit and Grand Isle. Along the Caminada Pass spit.

The Timbalier Islands Area

E 15 .__

■^^

Force 5
- Force 4

-J

Force 3 o
en

Force 2 uJ

z
<

Force 1 y
a.

Tropical 5

Storm ^

1900 1925 1950 1975

1934 - Small jetty system - Belle Pass

1950 to present

Seawal I . groin , and

breakwater construction- East Timbaher Island
1968- Jetty system and navigation channel exten-
sion - Belle Pass

COASTAL STRUCTURES

Figure 15. Changes in the area of the Timbalier Islands in relation to the
effects of tropical cyclones and coastal structures. Note the rapid decrease
in island area following construction of coastal structures updrift.

the rates of shoreline change vary west to east from 5 m of erosion, where the spit
attaches to the erosional headland, to near stability with accretional and erosional
fluctuations, adjacent to Caminada Pass (Figure 10). This pattern of shoreline change
reflects the increasing sediment abundance in the nearshore zone, downdrift toward
Grande Isle. The Caminada Pass spit has been breached several times in this century by
hurricane landfall; the major breaches were associated with Flossie in 1956 (Figure 16)
and Betsy in 1965. These breaches were unstable, infilling rapidly because of the
sediment supply from the Bayou Lafourche headland. Farther downdrift at Grand Isle,
the characteristic flanking barrier pattern of updrift erosion/downdrift accretion occurs,
as observed at Timbalier Island. Prior to 1972, Grand Isle had historically eroded on its
western end at Caminada Pass, and had accreted downdrift on its eastern end at
Barataria Pass. With construction of the jetty system on the western shore of Caminada
Pass, the western-end erosion stopped and minor accretion began, averaging
approximately 5 m/yr. Along the central shoreline of Grand Isle, erosion rates of less
than 5 m/yr are common. Farther downdrift, toward Barataria Pass, this erosional trend
again turns to accretion of 5 to 10 m/yr. Prior to jetty construction at Barataria Pass in
1958, the eastern end of Grand Isle accreted 3 to 6 m/yr, which is considered usual for
the downdrift end of a flanking barrier island. After 1958, sedimentation in this region
accelerated, producing accretion rates in excess of 10 m/yr. The U.S. Army Corps of
Engineers (1972) estimated that this jetty system traps approximately 230,000 m of sand
per year.

A time series of the total area of Grand Isle again indicates the importance of the
impact of coastal structures compared to the impact of hurricane landfall on flanking
barriers and the strategic importance of the location of the shoreline structure within
the sediment dispersal system (Figure 17). Following the placement of coastal structures
and the initiation of beach nourishment after 1950, Grand Isle increased in area from 7.8
km^ in 1956 to 8.8 km^ in 1979. This pattern is analogous to that observed in the
Timbalier Islands and indicates a marked sensitivity to coastal structures and the active
sediment dispersal system of the erosional headland and its flanking barriers. Placement
of the structures updrift of flanking barriers results in severe erosion of marginal spits
and reduction in flanking barrier island area. Placement on the downdrift ends of
flanking barriers leads to localized accretion.

Figure 16. The ebb surge of Hurricane Flossy breached the Caminada Pass spit
in 1956. Note the scour features along the shoreline formed by gulfward flow
across the spit undergoing a hydraulic jump.

10
9-

8-
7-
6 -
5
4
3
2
1 -

Grand Isle Area

Force 5

Force 4 _j

- Force 3 v)

Force 2 ^

Force 1 y

_ Tropical ^

Storm I

1951 to 1966 ■: J • Periodic groin construction

and beacti nouristiment
1958- Eastern jetty Barataria Pass
1964- Eastern letty extended ■ Barataria Pass
1972 - Western lelly - Caminada Pass

COASTAL STRUCTURES

Figure 17. Changes in the area of Grand Isle in relation to the effects of
tropical cyclones and coastal structures. Note the rapid increase in island
area following construction of coastal structures downdrift.

THE EARLY LAFOURCHE COASTAL BARRIER SYSTEM

Barrier Evolution

The isles Dernieres is the transgressive coastal barrier system associated with the
Early Lafourche Delta (Morgan 1974) abandoned 600 to 800 years ago. This barrier island
arc represents an advanced stage in evolution, resulting from extensive submergence and
reworking of the Caillou erosional headland (Figure 3). The historical map series of the
Isles Dernieres illustrates the transition from an erosional headland stage to a detached
barrier island arc stage (Figure 18). In 1853, Pelto and Big Pelto Bay separated this
barrier system from the mainland marsh by a narrow tidal channel less than 500 m wide.
By 1978, these bays had increased in size threefold and merged into Lake Pelto, and the
Isles Dernieres were located 7 km offshore. During this time period, the Isles Dernieres
shoreline retreated more than I km landward, and the original island of 1953 segmented
into four small islets.

The geological strike section running through the Isles Dernieres (west to east)
shown in Figure 19 indicates at least two distributaries and a flanking beach-ridge plain
were the principal sand sources for barrier island development. In the central portion of
the island arc a thin (I m) washover and aeolian sand unit is seen transgressing across the
backbarrier marsh. Downdrift, east and west of the island arc, sand thickness increases
at Wine Island and Racoon Point, respectively. In these spit complexes, the barrier sand
body reaches a thickness of 5 to 6 m. With subsidence of these sand bodies, the Isles
Dernieres are receiving a diminishing sediment supply. This situation is the underlying
cause for the landward retreat and segmentation of the Isles Dernieres.

' s I s s D B ' " '

Figure 18. Historical map comparison of the Isles Dernieres showing the
transition from a Stage 1 to a Stage 2 barrier system by mainland detachment.

Isles Dernieres

Whiahey
Pass

Kilometers

Figure 19. A stratigraphic strike section through the Isles Dernieres
showing facies relationships. See Figure 8 for legend.

Figure 20. Average annual erosion-accretion rates along the Isles Dernieres,

Patterns of Shoreline Change

Shoreline erosion derived from the OGMS data indicate that the highest erosion
rates within the Isles Dernieres occur along the central portion of the island arc (Figure
20). Here erosion rates in excess of I 5 m/yr are common. Downdrift, both east and west
of the central island arc, erosion rates decrease to approximately 5 m/yr. This erosion
pattern reflects the influence of barrier orientation to the dominant wave approach.
Throughout their evolution, the Isles Dernieres have faced directly into the dominant
southerly wave approach, creating a sediment transport diversion zone in the central
island arc. With sediment transported both east and west from this area, a spreading
effect results, dispersing sediments over a wider area than a more asymmetrical wave
approach, as at the Chandeleur Islands would.

Coastal structures have not been built in the Isles Dernieres barrier system;
therefore, its sediment dispersal system is undisturbed. A plot of island area versus
hurricane landfall indicates that island area has been decreasing steadily. The area of
the Isle Dernieres diminished from 34.8 km"^ in 1887 to 10.2 km'^ in 1979 (Figure 21).
Island land loss is very rapid, indicating the possible destruction of the Isles Dernieres
within 50 years. High erosion rates must be related to rapid subsidence in the area and
the lack of a substantial coarse-grained sediment imput to help maintain these barriers in
this sinking coastal environment.

ST. BERNARD BARRIER SYSTEM

Barrier Development

The Chandeleur Island system occupies the eastern margin of the St. Bernard delta,
abandoned approximately 1,800 years ago (Frazier 1967). This system represents an
advanced stage in the evolution of a transgressive barrier island arc system. The
Chandeleur Islands represent a merged system of earlier erosional headlands and flanking
barriers associated with major unidentified St. Bernard delta distributaries. Seismic and
vibracore data collected by the Louisiana Barrier Island Project indicate that shoreface
retreat can no longer penetrate through to the sand bodies associated with the St.
Bernard delta and supply coarse sediments to the island arc. These islands are presently
transgressing across fine-grained lagoonal facies of Chandeleur Islands (Figure 22). Since

20-

Isles Dernreres
Area

Force 5
- Force 4

Forces -i

Force2 "^

Force 1 <

Tropical (r

Storm ^

1975

Figure 21. Changes in the area of the Isles Dernieres in relation to the
effects of tropical cyclones. Note rapid land loss indicating the potential
destruction of the Isles Dernieres within 50 years.

1870

1978

ERROL

ISLAND

GULF OF MEXICO

Figure 22. Historical map comparison of the Chandeleur Island arc showing
its landward transgression into Chandeleur Sound.

CHANDELEUR
LIGHTHOUSE

<b°

NORTH
ISLANDS ^

NEW ' 1
HARBOR , ,

FREE \k ISLANDS ,^/jlJ ^
MASON J ..'.'^ <J.

ISLANDS >r.i a

PALOS ISLANo/y ^

BOOT ISLAND

STAKE ISLAND,
CURLEW ISLAND

GRAND

GOSIER "^

ISLAND/

BRETON
ISLAND

10-15

i/i

-. .- -

5-10

0-5

>:y^'

ssss

5-10

UJ HtM

LONGSHORE

TRANSPORT

DIRECTION

Figure 23. Average annual erosion-accretion along the Chandeleur Islands.

there is no present-day sediment source to the Chandeleur Islands, they are dinninishing
in size. The sedinnent dispersal system is recycling barrier sands within the island
complex. Storm waves transport sediment seaward into a broad inner -shelf sand sheet
and landward into backbarrier washover fans.

Patterns of Shoreline Change

The pattern of shoreline changes in the Chandeleur Islands is different from that in
the Isles Dernieres, due to differences in shoreline orientation to the dominant wave
approach. The Chandeleur Islands are oriented oblique to the dominant wave approach,
whereas the Isles Dernieres face directly into the dominant wave approach. The southern
end of the Chandeleur Islands receives the brunt of the wave attack; wave-refraction
attenuation along the shallow inner shelf increases towards the north, and is reflected in
decreasing shoreline erosion rates (Figure 23). Along the southern part of the Chandeleur
Islands, erosion exceeds 15 m/yr and is characterized by periodic hurricane destruction
followed by partial island re-emergence and rebuilding. Northward along the islands,
erosion rates decrease from 15 m/yr to around 5 m/yr at the northern end. A plot of the
area of the Chandeleur Islands versus hurricane landfalls shows the importance of periods
of high hurricane frequency to total island area (Figure 24). Between 1869 and 1924, nine
tropical cyclones made landfall in the Chandeleur Islands region, of which only two were
above force-2 strength, resulting in a slight decrease in island area. Between 1925 and
1950, five tropical cyclones made landfall; however, only one was of hurricane force; and
the remainder were tropical storm strength. For this time interval, the Chandeleur
Islands only slightly decreased in area. Between 1950 and 1969, rapid decrease in the
total island area of the Chandeleur Islands was related to a period of frequent hurricane
landfall. Five major storms impacted the island, one of which was hurricane Camille, of
force-5 strength and had deep-water wave heights measuring in excess of 20 m. As a
result of these high-intensity storms, the iota I island area of the Chandeleur Islands
decreased from 29.7 km^ in 1950 to 21 km^ in 1967. Sediment dispersal in this system
reflects the hurricane impact on barrier islands with the finite internal sediment supply
that is continually being recycled. Hurricane responses are offshore sediment transport
and barrier breaching, leading to sediment losses to the offshore and tidal delta sinks.
Sediment dispersal patterns are determined by barrier orientation to the prevailing
regional wave climate. Barrier rebuilding in the Chandeleur Island reflects the presence
of a southerly updrift sediment source supplying progradational episodes farther north.

Breton ■ Chandeleur
Island Area

---,;

Force 5

Fofce4 ^^

<
Force 3 u

- Force 2 lu
z
<

Force 1 y
cc
cr

Tropical zi

Storm ^

Figure 24. Changes in the area of the Chandeleur Islands in relation to
the effects of tropical cyclones.

CONCLUSIOhJS

1. Louisiana suffers from the most severe coastal barrier erosion and land loss problem
in the United States.

2. Patterns of natural shoreline change and erosion problems associated with coastal
structures are interpreted using the model for deltaic barrier evolution presented
here. With increasing age, coarse-grained sediments of abandoned Mississippi River
deltas first form an erosional headland and flanking barriers, Stage I, then
transgressive barrier island arc, Stage 2, and finally a subaqueous inner shelf shoal,
Stage 3.

3. Central erosional headlands and updrift ends of flanking barrier islands naturally
retreat rapidly, while downdrift, the ends of the flanking barriers accrete. The
sediment-dispersal system of an erosional headland and its flanking barriers is easily
disrupted by coastal structures. Placement of structures updrift from flanking
barriers causes severe erosion of the marginal spits and reduction of barrier island
area. Placement on the downdrift end of flanking barrier islands leads to island
accretion and downdrift erosion farther downdrift.

4. Shoreline orientation to the dominant southerly wave approach determines patterns
of shoreline change in transgressive barrier island arcs. The Chandeleur Islands,
oriented to the north/south, have progressively decreasing rates of erosion
northward in the direction of predominant sediment transport. The Isles Dernieres
are oriented east/west and are characterized by frontal retreat and island
segmentation and deterioration.

5. Tropical cyclones and extratropical cyclones are the dominant factors influencing
shoreline change in the central erosional headlands and transgressive barrier island
arcs. The placement of coastal structures predominantly influences patterns of
shoreline change in the flanking barrier systems.

RECOMMENDATIONS

1. Develop a comprehensive barrier island management plan that incorporates annual
beach nourishment in strategic locations, along with a vegetative
maintenance/research program.

2. Avoid the band-aid approach to coastal zone management. Shoreline protection
plans that address site-specific problems typically fail because their scope is too
small, not taking into account the natural working of the whole coastal system.

3. Restrict pipeline landfalls and transmission routes to environmentally sound
corridors that can be monitored and managed to reduce habitat damage. Backfill
and revegetate all existing pipeline right-of-ways in each barrier system to reduce
the breaching potential at these weak spots.

4. Avoid using coastal structures such as groin systems and rip-rap seawalls; these
protection measures have proved ineffective at critical erosion areas in Louisiana.

5. Where jetty systems and navigation cinannels are required, develop sedinnent
bypassing and recycling schennes into the design requirement. At Belle Pass and
Barataria Pass, a sediment bypassing scheme would alleviate downdrift erosion
problems. At the Houma Ship Channel, a sediment recycling scheme of the dredge
spoil could provide a source of sediment for nourishing the Isles Dernieres and the
Timbalier Islands.

6. Conduct a sand resource inventory of the entire Louisiana continental shelf.
Location, quantity, and quality of potential sediment borrows must be known before
any beach nourishment projects can be designed. Conducting small site-specific
sand resource inventories is not cost effective.

ACKNOWLEDGMENTS

Scientific results presented in this paper were sponsored by the Louisiana Office of
Coastal Zone Management through a grant to the Laboratory for Wetland Soil and
Sediments in the Center for Wetland Resources at Louisiana State University, Drs. W.H.
Patrick, Jr., and l.A. Mendelssohn, Principal Investigators. Logistical support was
provided by the Sea Grant Auxilliary. This research was conducted when Shea Penland
was with the Laboratory of Wetland Soils and Sediments and Ron Boyd was with the
Louisiana Geological Survey. Mary Penland edited the manuscript.

LITERATURE CITED

Boyd, R., and S. Penland. 1981. Washover of deltaic barriers on the Louisiana coast.
Trans. Gulf Coast Assoc. Geol. Soc. 31:243-249.

Coleman, J.M., and W.G. Smith. 1964. Late Recent rise of sea level. Geol. Soc. Am.
Bull. 75:833-840.

Curry, J.R. 1964. Transgressions and regressions. Pages 175-203 'm R.L. Miller, ed.
Papers in marine geology. Macmillan, New York.

Dantin, E.J., C.A. Whitehurst, and W.T. Durbin. 1978. Littoral drift and erosion at Belle
Pass, Louisiana. Waterway, Port Coastal and Ocean Div., American Society Civil
Engineers 104(WW4):375-390.

Dolan, R., B. Hoyden, and J. Heywood. 1978. A new photogrammetric method for
determining shoreline erosion. Coastal Eng. 2:21-39.

Fisk, H.N. 1944. Geological investigation of the alluvial valley of the Lower Mississippi
River. Mississippi River Commission, U.S. Army Corps of Engineers, Vicksburg, Miss.
78 pp.

Frazier, D.E. 1967. Recent deltaic deposits of the Mississippi River. Trans. Gulf Coast
Assoc. Geol. Soc. I 7:287-3 1 5.

Frazier, D.E. 1974. Depositional episodes: their relationship to the Quaternary
stratigraphic framework in the northwestern portion of the Gulf basin. Univ. of Texas
at Austin, Bureau of Economic Geology Geol. Circ. 74-1. 28 pp.

Harper, J.R. 1977. Sediment dispersal trends of tine Caminada-Moreau beacin ridge
system. Trans. Gulf Coast Assoc. Geol. Soc. 27:283-289.

Howard, P. 1982. Tidal deposits of Quatre Bayou Pass, LA. Pages 92-103 \n Deltaic
sedimentation on the Louisiana coast. Gulf Coast Section, Society of Economic
Petrologists and Mineralogists, Tulsa, Oklahoma.

Kolb, C, and J. Van Lopik. 1958. Geology of the Mississippi River deltaic plain,
southeastern Louisiana. U.S. Army Engineers Waterways Experiment Station,
Vicksburg, Miss. Tech. Rep. 2. 483 pp.

Morgan, J.P. 1974. Recent geological history of the Timbalier Bay area and adjacent
continental shelf. Louisiana State Univ., Museum of Geoscience, Baton Rouge, La.
Melanges 9, 17 p.

Murray, S.P. 1970. Bottom currents near the coast during hurricane Camille. J.
Geophys. Res. 74:4579-4582.

Murray, S.P. 1972. Observations on wind, tidal and density-driven currents in the
vicinity of the Mississippi River Delta. Pages I 27- 142 ]n D. J.P. Stanley, D.D.B. Swift,
and W.H. Pilkey, eds. Shelf sediment transport - process and pattern. Dowden,
Hutchinson and Ross, Stroudsburg, Pa.

Penland, S., and R. Boyd. 1981. Shoreline changes on the Louisiana barrier coast. Pages
209-219 \n Oceans. Marine Technology Society and ICCC (Oceanography Section).

Penland, S., and R. Boyd. 1982. Mississippi delta coastal sand barriers: an overview.

Pages 71-91 in Deltaic sedimentation on the Louisiana coast. Gulf Coast Section,
Society of Economic Petrologists and Mineralogists, Tulsa, Oklahoma.

Penland, S., R. Boyd, D. Nummedal, and H.H. Roberts. 1981. Deltaic barrier
development on the Louisiana coast. Trans. Gulf Coast Assoc. Geol. Soc. 31:342-346.

Ritchie, W., and S. Penland. 1982. The interrelationship between overwosh and aeolian
processes along the barrier coastline of south Louisiana. Pages 358-362 'm First
International Conference on Meterology and Air/Sea Interaction of the Coastal Zone,
The Hague, Netherlands, American Meterological Society.

Saffir, H.S. 1977. Design and construction requirements for hurricane resistant
construction. American Society Civil Engineers., N. Y. No. 2830, 20 pp.

Short, A.D. 1978. Wave power and beach stages: a global model. Pages I 1 45- 1 1 62 jn
Proceedings 16th Coastal Engineering Conference, American Society Civil Engineers.

Swanson, R.L., and E.I. Thurlow. 1973. Recent subsidence rates along the Texas and
Louisiana coast as determined from tide meausrements. J. Geophys. Res. 78:2665-
2671.

U.S. Army Corps of Engineers. 1972. Grande Isle and vicinity, Louisiana: beach erosion
and hurricane protection. New Orleans District.

MUDFLAT AND MARSH PROGRADATION ALONG LOUISIANA'S CHENIER PLAIN:
A NATURAL REVERSAL IN COASTAL EROSION

John T. Wells
G. Paul Kemp

Coastal Studies Institute

Louisiana State University

Baton Rouge, LA 70803

ABSTRACT

The chenier plain coast of southwestern Louisiana has been receiving sediment
intermittently from the Mississippi River for the last 5,000 years. A new influx of fine-
grained sediment, the first such sediment pulse in perhaps 500 to 1000 years, is leading to
localized coastal progradation along what has historically been one of the most rapidly
retreating shorelines in the United States. Carried as suspended sediment by the
"Atchafalaya mud stream," silts and clays from the Atchafalaya River are now
accumulating as mudflats along a segment of coast from Freshwater Bayou Canal to
Rollover Bayou. These transitory mudflats provide a buffer to incoming storm waves and
serve as a temporary storehouse for littoral sediments.

Process-oriented field studies initiated in 1980, together with satellite imagery,
color infrared photography, and aerial overflights since 1974, are providing insight as to
present and future trends in sedimentation. Growth of the chenier plain appears initially
to be by a series of transitory mudflats, a few of which become welded to the shoreline.
Since 1969 the pattern of mudflat sedimentation has been increasing and shifting to the
west, consistent with the direction of coastal and wave-induced currents. Accelerated
growth of the chenier plain is expected when the subaerial Atchafalaya Delta outgrows
Atchafalaya Bay, thus allowing an even greater volume of sediments to enter the
dynamic shelf region seaward of the bay and to become entrained in the mud stream.
The time scale for widespread reversal in present coastal erosion is 50 to 100 years.

INTRODUCTION

Modern man has acquired a very unstable inheritance in the coastal plain of south
Louisiana, a landscape that expands and contracts in area at rates almost unequaled
anywhere else in the world. The potentials for land building via rapid sediment
deposition and for land loss through compaction and wind/wave erosion are both large.
The degree to which these land building/land loss potentials are individually realized at
any one time, as well as the degree to which they offset each other, determine the
coastline's position on a cyclic curve of alternating progradation and retreat (Kolb and
Van Lopik 1958). The works of Morgan and Larimore (1957), Gagliano and van Beek
(1970), and Adams et al. (1978) as well as many papers in this volume, establish that
the shoreline of Louisiana, taken as a whole, is currently retreating. These authors also
point out, however, that this retreat shows a high degree of spatial variability. For

example, in the case of the modern Mississippi delta front, retreat is virtually
nonexistent and in the case of the Atchafalaya Delta complex, it is significantly
reversed. We can then draw a picture of a modern shoreline that is undergoing erosion
and transgression, but that is dynamically stable at the Mississippi River delta front and
is locally progradational near the Atchafalaya River mouth.

The 200-km section of shoreline extending west from Marsh Island to the Texas
border is distinct in plan view from the rest of the Louisiana coast (Figure I). The
complex indentations and barrier/lagoon systems that characterize the shorelines
flanking the modern Mississippi River course are not found west of Vermilion Bay. The
smooth and relatively straight form of the western half of the coast reflects a
depositional history different from that of the rest of Louisiana's coastal plain. Early
workers hypothesized that this section evolved during the Holocene as a marginal deltaic
sequence of prograding mudflats that were intermittently partially reworked into
sand/shell ridges called "cheniers" (Russell and Howe 1935; Price 1955). More recently,
Gould and McFarlan (1959) reconstructed the development of the "chenier plain" and
adjacent shelf from cores using radiocarbon dating techniques. Their interpretation
indicates that, as sea level rose from -5 m to its present level, a transgressive sequence
of marine sediments was deposited over the dissected Pleistocene Prairie Formation,
first filling estuaries, then later spreading across shallow bay and marsh environments.

During the final asymptotic stage of post-glacial rise in sea level some 5,000 years
ago, the chenier plain began to prograde rapidly, and eventually a wedge of recent
sediments 6 to 8 m thick was deposited to a width of 24 km, thus placing the shoreline
roughly where we see it today (Figure I). Pulses of sediment from the Mississippi River,
transported by coast-parallel currents, were responsible for the various stages of
progradation. At times when the Mississippi River introduced sediment in the vicinity of
the present chenier plain, the shoreline shifted seaward; during periods when its course
took the discharge farther east, sediment influx to the chenier plain was low and wave
attack was able to slow or halt the advance (Gould and McFarlan 1959). Cheniers formed
during these latter periods and now stand as "islands" in the marsh.

A new pulse of sediment, the first in some 500 to 1000 years, began adding soft
muds to the eastern margin of the chenier plain in the late I940's, coincident with the
subaqueous development of a new delta in Atchafalaya Bay (Morgan et al. 1953).
Although the delivery of sediments from the Mississippi River down the Atchafalaya
River had been in progress since the mid-1500's (Fisk 1952), it was not until the mid-
I900's that sedimentation in the bay and areas offshore became noticeable. This large-
scale introduction of silts and clays to the coast began when the inland Atchafalaya Basin
to the north became essentially sediment filled and sediment began bypassing these
basin-lakes for areas to the south. In the early I950's Morgan et al. (1953) documented
the occurrence of mud deposition along approximately 50 km of coast from Marsh Island
to Rollover Bayou which, in places, formed broad mudflats up to 2 m thick.

Nearly 30 years have passed since Morgan et al. (1953) first described these coastal
mudflats and tied their origin to the Atchafalaya River, to the east. Whereas our
understanding of the basic processes for delivering sediments to the eastern margin of
the chenier plain (Figure I) has remained the same, our ability to monitor these processes
has improved significantly. Ready access to satellite imagery, color infrared
photography, and digital current-meter data now allow us to monitor remotely shoreline
changes and the processes that govern their behavior. In the following paragraphs we
report our initial findings with respect to these questions: (I) What is the present status

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of the chenier plain relative to the cycle of land building and land loss? (2) What
connection exists between the developing Atchafalaya River delta and chenier plain
sedimentaion? and, (3) What is the future for the land building in Louisiana's western
coastal parishes?

PRESENT STATUS

Development of the chenier plain according to the broad brush model presented
above might be expected to produce a modern shoreline either uniform in character or at
least gradational from east to west. In fact, the coastline from Marsh Island to the
Texas border shows as much variability as any in Louisiana. Kaczorowski and Gernant
(1980) have recognized three distinct types of modern shorelines to which we add a
fourth. The Type I shoreline is one of perched beaches with exhumed marsh cropping out
in the surf zone (Figure 2A). Beaches consist of shell hash and sand in variable
proportions, typically fronted by a storm berm less than 0.75 m in elevation and backed
by washover deposits extending not more than 100 m into a brackish marsh back-barrier
environment. This type of shoreline fronts more than one-half of the chenier plain coast.

The Type II shoreline is one of unvegetated mudflats and can be divided into two
subcategories on the basis of sand content and origin. The first contains less than 5%
sand and shell and is composed of a fluid mud derived from an offshore source (Figure
2B). These mudflats are not permanent features and today appear to be localized in a
20-km stretch of coast extending from the mouth of Freshwater Bayou Canal west to
Rollover Bayou. The second type of "mudflat" may contain greater than 30% sand and
shell and is found updrift (east) of the jetties at Calcasieu and Sabine passes. These
essentially artificial accumulations reflect an interception of locally derived and
reworked sediments.

The Type III shoreline is a sand/shell beach which differs from the Type I in that it
represents a reactivated relict deposit (Figure 2C). Such deposits are found at intervals
along the modern coast wherever the present surf zone truncates or parallels a chenier
ridge. These beaches are most common in the western part of the chenier plain where
the spacing between ridges is closer. Coarse material eroded from deposits up to 3,000
years old is entrained in the modern longshore drift system and nourishes Type I beaches
to the west. Type III beaches exhibit a large range in morphology, show up to 4 m of
relief, and may contain relict dune fields such as that at Chenier au Tigre on the eastern
margin of the Chenier Plain.

The Type IV shoreline is one in which no continous beach exists. Brackish marsh
headlands extend into the gulf at intervals of 20 to 50 m and shelter crescentic pocket
beaches which contain minor accumulations of shell hash and organic debris (Figure 2D).
With the exception of the Type II mudflats, all of these shorelines are erosional and have
historically retreated between 3 and 10 m/yr (Adams et al. 1978). Relatively stable
sections are located at Chenier au Tigre in the east and between Calcasieu and Sabine
passes in the west.

Areas of Type II mudflat accumulation along the coast of the eastern chenier plain
were determined from color infrared photographs taken in October 1974 and October
1978 (NASA Missions 74-293 and 78-148, respectively), from 1974 orthophotoquads, and
from aerial and ground reconnaissance in 1974, 1979, and 1981. Results of these photo
and ground comparisons, together with assessments by Adams et al. (1978) for 1954-69
are shown in Figure 3.

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Three patterns have been recognized during the 12-year period from 1969-81: (I)
simultaneous erosion and accretion at the shoreline, (2) increasing length of shoreline
fronted by mudflats, and (3) shift in the locus of sedimentation to the west. No attempt
has been made to plot previous shorelines, and our contention is simply that the presence
of mudflats indicates an instantaneously prograding shoreline. The segments of coast
between mudflats are typically those that are eroding most rapidly. The processes of
erosion and accretion are cyclical in both time and space, as becomes evident from close
examination of Figure 3.

ATCHAFALAYA/CHENIER PLAIN CONNECTION

Turbid water that enters the Gulf of Mexico from the Atchafalaya River and flows
along shore as a muddy plume is herein described as the Atchafalaya mud stream. This
sediment-laden water is visible from aircraft and shows up well in LANDSAT imagery as
partially saturated returns in band 5. Mud stream dimensions vary and are controlled by
river discharge, tide stage, wind speed and direction, and residual currents. The plume
persists, however, throughout the year and trails off to the west in approximately 75% of
the images (unpublished data compiled by R. H. W. Cunningham, USACOE, New Orleans).

The well-defined seaward extent of the sediment plume on 9 February 1979 during
rising river stage is evident in Figure 4. This image is typical of many in that turbid
water is found not only in Atchafalaya Bay and offshore, but also in bays to the west.
The inset to Figure 4 shows suspended sediment concentrations taken on the day of the
satellite overpass along a transect that runs down the navigation channel and ends at the
seaward edge of the sediment plume. Suspensate concentrations, determined by
millipore filtration, are reported for surface waters only, and thus represent a
conservative estimate of sediment throughout the water column.

Within Atchafalaya Bay concentrations range from 250 to 400 mg/l (0 to 20 km.
Figure 4, inset), but increase to more than 800 mg/l seaward of the shell reef barrier (25
to 35 km). The sudden increase in concentration is perhaps a result of wave resuspension
of soft sediments that are deposited rapidly as prodelto clays seaward of the bay mouth.
Beyond this extremely turbid zone, concentrations decrease across the shelf to the plume
edge (50 to 63 km). Outside the sediment plume, concentrations are I mg/l or less.

Composition of sediment in the mud stream is the same as that in the lower
Atchafalaya River, primarily silt- and clay-sized particles with median diameters of 2 to
6 microns. Clay mineralogy is montmorillonite, illite, and kaolinite in the ratio 3:1:1.
Data reported by Roberts et al. (1980) indicate that 63% of the sediment that enters
Atchafalaya Bay is silt and clay sized. Using a mass-to-volume conversion of 425 kg/m ,
Wells and Roberts (1981) determined that this silt and clay load is 146 X 10 m-^ per year.

Evidence that sediments which enter the Gulf of Mexico from Atchafalaya Bay are
transported to the west, as indicated by satellite imagery, is also provided by current
meter moorings. Beginning in the spring of 1980, current meter data were taken at
numerous stations in and seaward of Atchafalaya Bay. Typical records of speed and
direction at three of these stations are shown in Figure 5. Data are from mid-depth
current meter moorings made with Endeco 174 ducted-impeller, magnetic recording

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Figure 4. LANDSAT band 5 image of central Louisiana coast taken on
9 February 1979. Light tones indicate high turbidity. Inset shows suspended-
sediment concentrations along transect line A-A' from lower Atchafalaya
River outlet to seaward edge of sediment plume (data courtesy R. H. II. Cun-
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current meters at the locations given in Figure 6. Thirty-five days of data were obtained
at station I, five days at station 2, and over a year of continous readings have been
obtained at station 3.

Current speeds on the inner shelf at station I are typically 10 to 30 cm/sec;
direction of flow, although setting to the northwest, is influenced strongly in this
February data set by the passage of cold fronts every 5 to 7 days, which sequentially
produce winds first from the southwest, then from the northwest. Current speeds at
station 2, just outside the bay, are 10 to 50 cm/sec and occur as well-defined pulses
related to stage of the tide. Direction, however does not fully reverse as a result of tidal
effects, but instead is dominated by river flow to the south from Atchafalaya Bay and
flow to the west from the westerly drift component of coastal waters. In Atchafalaya
Bay current speeds are substantially higher, reaching values of 40 to 80 cm/sec. Rise and
fall in current speed is coincident with tidal period in the bay. Direction of flow is
oriented down the navigation channel and does not change with stage of the tide.

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Residual currents computed from these records are shown in Figure 6. The overall
pattern is that of strong flow down the axis of the navigation channel, spreading and
reducing in speed on reaching the Gulf of Mexico, then deflection to the west on the
inner shelf. Analysis of current data taken on the shelf farther to the west (longitude
90° 30') also indicates residual flows to the west (Crout and Hamiter 1981).

First-order approximations of the sediment mass transported in the Atchafalaya
mud stream have been made by taking the product of average suspensate concentration,
cross-sectional area of the mud stream, and average drift speed of currents (Figure 6).
Conversion to volume transport is made using a density of 375 kg/m (Wells and Roberts
1981). When converted to transport per year, the volume of sediment moving in the
Atchafalaya mud stream is 53 X 10 m~^, almost half of the volume of sediment that
leaves Atchafalaya Bay. Evidence for an intimate connection between Atchafalaya delta
development and chenier plain sedimentation can be found in the good time correlation
between subaqueous deltaic sedimentation in the bay and the first appearance of
mudflats near Chenier au Tigre. Abnormally high river discharge in 1973-75 correlated
well with a renewal of mudflat development after a period of erosion in the I960's.

FUTURE FOR LAND BUILDING ALONG THE CHENIER PLAIN COAST

We have established that the chenier plain coast is a downdrift recipient of
renewed deltaic sedimentation, but that the rate of growth today is insufficient to stop
the historic trend of shoreline retreat. There is localized instantaneous progradation in
the form of ephemeral and unvegetated mudflats. Because the major effect of subtidal
muds is to attenuate incoming wave energy, conditions are being created that are
favorable for further sedimentation (Wells and Coleman 1981; Wells and Roberts 1981).
Formation of mudflats, then, is the first stage in the feedback loop between coastal
energy and shoreline response, which eventually leads to stabilization and progradation.
Volume calculations show that more sediment reaches the chenier plain via the
Atchafalaya mud stream than appears as new mudflats. For example, if a typical
mudflat has a volume of I x 10 m-' to 2 x 10° m-^, then 25 to 50 such mudflats could form
each year. Since new mudflats have not been observed to form at this rate, much of the
sediment may be spread across the inner shelf as a thin veneer over a longshore distance
of perhaps 100 km or more.

The ephemeral nature of these mudflats suggests that the localized process of
shoreline progradation has just begun to accelerate (Wells and Kemp 1981). As a result,
we hypothesize that the initial stage of coastal progradation from a new sediment pulse
is one of transitory mudflats only. As sedimentation continues, new mudflats will appear
and merge with existing mudflats. At its peak of development, the shoreline will become
"choked" with fine-grained sediment, mudflats will stabilize and grow seaward, and new
marsh vegetation will become estabished. The potential for land building by this method
should not be underestimated. The entire chenier plain region itself represents a net
coastal progradation of 25 km from the Pleistocene surface contact to the present Gulf
of Mexico shoreline. This land building took place in not more than 5,000 years during
which the many stranded beach ridges tell us that accretion alternated with erosion.
Thus, a conservative estimate of the land-building potential afforded by mudflat
accretion is on the order of 5 m/yr or close to the rate at which retreat is now
occurring. Accelerated growth of the chenier plain is expected when the subaerial
Atchafalaya delta outgrows Atchafalaya Bay, allowing a greater volume of sediments to

enter the dynamic shelf region and become entrained in the mud stream (Weils et al. in
press). The time scale for widespread reversal in present coastal erosion along
Louisiana's chenier plain is 50 to 100 years, provided that the Atchafalaya River discharge
remains relatively constant and no sediment is artifically diverted away from the mud
stream.

CONCLUSIONS

1. The chenier plain of southwestern Louisiana is presently receiving a major new
influx of fine-grained sediment from the Atchafalaya River to the east, the first such
sediment pulse in recorded history. Sediment is delivered by the Atchafalaya mud
stream, a westerly flowing band of turbid water that may extend 20 km offshore.

2. Growth of the chenier plain appears initially to be by a series of transitory
mudflats, a few of which become welded to the shoreline. The pattern of mudflat
sedimentation is increasing and shifting to the west, consistent with the direction of
coastal and wave-induced currents.

3. The Atchafalaya mud stream transports more sediment, by an order of
magnitude, to the chenier plain than can be accounted for in yearly mudflat accretion.
Much of the sediment may be spread as a thin veneer across the inner continental shelf.

4. Future development of the chenier plain will be tied intimately to the fate of
Atchafalaya Bay. Accelerated growth of the chenier plain is expected when Atchafalaya
Bay becomes sediment-filled, thus allowing an even greater volume of sediments to enter
the dynamic shelf region seaward of the bay.

5. Widespread reversal in the present erosional trend is expected in 50 to 100
years.

ACKNOWLEDGMENTS

Support for this project was provided by the Louisiana Sea Grant University
Program, a part of the National Sea Grant University Program, maintained by the
National Oceanic and Atmospheric Administration of the U.S. Department of
Commerce. Mrs. Gerry Dunn drafted the figures.

LITERATURE CITED

Adams, R.D., P.J. Banas, R.H. Baumann, J.H. Blackmon, and W.G. Mclntire. 1978.
Shoreline erosion in coastal Louisiana: Inventory and assessment. Final Report to
Louisiana Department of Transportation and Development. 139 pp.

Crout, R.L., and R.D. Hamiter. 1981. Response of bottom waters on the west Louisiana
shelf to transient wind events and resulting sediment transport. Trans. Gulf Coast
Assoc. Geo). Soc. 31:273-278.

FisU, H.N. 1952. Geological investigations of the Atchafalaya Basin and the problem of
Mississippi River diversion. U.S. Army Corps of Engineers, Mississippi River
Commission, Vicksburg, Miss., Vol. I. 145 pp.

Gagliano, S.M., and J.L. van Seek. 1970. Geologic and geomorphic aspects of deltaic
processes, Mississippi delta system. Louisiana State Univ., Center for Wetland
Resources, Baton l^ouge. Hydroiogical and Geological Studies of Coastal Louisiana
Rep. I. 140 pp.

Gould, H.R., and E. McFarlan, Jr. 1959. Geologic history of the chenier plain, southwest
Louisiana. Trans. Gulf Coast Assoc. Geol. Soc. 9:1-10.

Kaczorowski, R.T., and R.E. Gernant. 1980. Stratigraphy and coastal processes of the
Louisiana chenier plain. Field Guide, 30th Annu. Convention, Gulf Coast Assoc. Geol.
Soc. 72 pp.

Kolb, C.R., and J.R. Van Lopik. 1958. Geology of the Mississippi River deltaic plain.
U.S. Army Engineer, Waterways Experiment Station, Vicksburg, Miss., Tech. Rept. 3-
483.120 pp.

Morgan, J. P., and P.B. Larimore. 1957. Changes in the Louisiana shoreline. Trans. Gulf
Coast Assoc. Geol. Soc. 7:303-310.

Morgan, J. P., J.R. Van Lopik, and L.G. Nichols. 1953. Occurrence and development of
mudflats along the western Louisiana coast. Louisiana State Univ., Coastal Studies
Inst. Tech. Rep. 34 pp.

Price, W.A. 1955. Environment and formation of the chenier plain. Quaternaria 2:75-
86.

Roberts, H.H., R.D. Adams, and R.H. W. Cunningham. 1980. Evolution of sand-dominant
subaerial phase, Atchafalaya Delta, Louisiana. Am. Assoc. Petrol. Geol. Bull. 64:264-
279.

Russell, R. J., and H.V. Howe. 1935. Cheniers of south-western Louisiana. Geogr. Rev.
25:449-461.

Wells, J.T. and J.M. Coleman. 1981. Physical processes and fine-grained sediment
dynamics, coast of Surinam, South America. J. Sediment. Petrol. 51:1053-1068.

Wells, J.T., and G.P. Kemp. 1981. Atchafalaya mud stream and recent mudflat
progradation: Louisiana Chenier Plain. Trans. Gulf Coast Assoc. Geol. Soc. 31:409-
416.

Wells, J.T., and H.H. Roberts. 1981. Fluid mud dynamics and shoreline stabilization:
Louisiana chenier plain. Pages 1382-1401 ]n Proceedings 17th Conference Coastal
Engineering, Sydney, Australia.

Wells, J.T., S.J. Chinburg, and J.M. Coleman. In press. Development of Atchafalaya
River delta: generic analysis. Louisiana State Univ., Coastal Studies Inst. Tech. Rep.

PANEL DISCUSSION

CAUSES: CHANGES IN DISPERSAL OF FRESH WATER AND SEDIMENTS

Gerald G. Bordelon, Moderator

Johannes van Beek, Richard Hatton, Ron Boyd, John Wells,
Clark Lozes, and Raphael Kazmann, Panelists

Gerald Bordelon: The presentations ranged from a doomsday to a new birth, starting out
with a snorl<el and little worry to some good hope.

David Soileau: There has been concern about the potential adverse impacts of the
proposed Avoca Island levee extention on the marshes to the east, but the Corps of
Engineers has pointed out the potential beneficial impact on the tupelo-cypress and
bottomland hardwood areas to the north of the marshes. Dr. van Beek, what is your
opinion on this from a hydrological viewpoint?

Johannes van Beek: The hydrological issue is whether the Avoca Island levee extension
will reduce water levels in the areas north of Morgan City and in the Verret Basin.
The answer is yes it will, initially, in so far as those water levels are controlled by
the stage of the Atchafalaya River as felt at the Amelia Channel. This will only be
a temporary effect, however, because of the effects of other processes, namely
subsidence and increase in stages in the Atchafalaya River due to channel
development and delta progradation. Flooding in the basin east of the Atchafalaya
Basin is not due to backwater flooding alone, but due to backwater flooding
superimposed on tides, increased water levels due to onshore winds and large
rainfalls in the basin accelerated by channelization for the purpose of agricultural
drainage.

Joel Lindsey: Ring levees around developed areas have been proposed as an alternative
to the Avoca Island levee extension. Which would be the most cost-effective means
of flood protection?

Johannes van Beek: That is difficult to answer because of the term "cost-effective."
While we do not yet have all the answers, we have learned quite a lot about deltaic
processes and have documented changes. We have at least the nominal
understanding necessary to suggest future directions. This involves planning for land
use on a statewide basis and a commitment to those plans. It means if we have to
relocate people, we will do it. Eventually we will be forced to that anyway, because
we cannot stop what is happening along the Louisiana coast. We can buy time, but
we cannot stop delta cycles. We can initiate new ones, but this too requires human
adjustment.

David Mekasski: What would be the effect of opening the Bonnet Carre spillway on a
regular basis to marsh and shoreline accretion in western Lake Pontchartrain?

Johannes van Beek: In 1973, there was significant accretion along southern Lake
Pontchartrain and reductions of salinity lasting at least a year. In view of the
warning that the Tangipahoa swamps are giving us, I think it is necessary to consider
a major diversion into the Lake Pontchartrain system. Ideally, there would be many
smaller diversions across the Mississippi River levee through the swamps into Lake
Maurepas, but there are the major obstacles of Airline Highway and the ground level
segments of Interstate 10. Those larger diversions to the southern lake are the only
ones feasible, although Bonnet Carre may not be the only place.

John Uhl: What do you mean by small or large diversions? What types of structures are
involved?

Johannes van Beek: Small structures can convey 250 to 2,000 cfs, similar to the Bayou
Lamoque structure, and include siphons and box culverts. Large structures can
convey about 15,000 cfs and include gates and large box culvert structures.

Raphael Kazmann: We are dealing with some substantial problems in regulating the
Mississippi River flow. For one thing, the sediment available in the Mississippi River
has declined by a factor of two since the I950's. Even if we could keep the available
load from being transported off the continental shelf, there would be a deficiency in
restoring any equilibrum that might have existed. This deficiency may also cause
some poorly understood changes in sediment transport. With less sediment
transported, there is what could be called "hungry water" with more transport
energy available than there is sediment to transport. This results in bank erosion.
The nutrient flow to the Gulf of Mexico may have also decreasd as a result of
unnecessary secondary treatment of wastes.

There is much discussion of the management of the Atchafalaya River. The
Atchafalaya provides a shorter path to the gulf. This means that in the upstream
reaches of the Atchafalaya, the water level is going to degrade, that is, the high
water is going to be lower with time, thus providing land owners with the possibility
of draining the swamp. At Simmesport, for a flow of about 200,000 cfs the water
level has dropped 7 feet since the I940's. At the lower end of the Atchafalaya there
is sedimentation which is building natural levees and the water is also transporting
more sediment into the Atchafalaya Bay. This deposition will require great expense
to maintain navigation channels.

If the Old River control structure fails, most of the sediment and freshwater
will travel down the Atchafalaya. New Orleans will be on a navigable estuary (the
present Mississippi course) and all of the lower river diversion structures will simply
transmit salt water. We should adapt and accept what is happening, backoff, and
enjoy the present conditions while they exist. In this new land and new swamp that
the Atchafalaya is building, protect the new habitat. Don't consider the present
Atchafalaya Basin as a wildlife refuge; it is a wildlife death trap. Following a large
flood of 1.5 million cfs or more, there will be no deer, squirrels, etc. remaining.

There is much discussion of who is going to manage the present Atchafalaya
Basin, but you can't "manage" the area of the greatest geomorphological change in
the country. All you can do is adapt. Government policy should not encourage
people to move into the area: one such policy that is dangerous is government-
subsidized flood insurance. Further, don't build new levees at public expense or raise
existing ones. If people want to live there, let them build their own levees at their

own expense. As far as New Orleans goes, if people want to remain in New Orleans,
they had better find a new water supply because the Mississippi will eventually
abandon its course past the city, maybe in the lifetime of many in the audience.

The sediment which I indicated is no longer coming down the river is stored in
reservoirs in the Arkansas, Missouri, and Ohio rivers and their tributaries. If these
reservoirs are reasonably full at the beginning of a flood season, the entire flow of
the river will be speeded up. Where formerly the peak in flood stage would slowly
rise and persist, now the peak will rise dramatically and to higher levels. The land
accretion and erosion in the delta is just the tail end of a tremendous process in the
whole river basin which is going on now, and we do not know what the outcome will
be.

Unidentified speaker: If there is a shortage of sediments coming into marshes to offset
subsidence, has the nutrient supply also been reduced? Will freshwater diversion
increase the needed nutrient supply to allow the marshes to grow?

Richard Hatton: Many nutrients are associated with particulate sediments, but I feel
freshwater inputs would decrease saltwater intrusion which causes marsh
destruction.

Clarice Lozes: Some freshwater diversions could also serve as flood control structures to
relieve flood pressure from New Orleans by shortening the flow of river water into
Lake Pontchartrain and the Barataria Basin.

Unidentified speaker: Will these freshwater diversions carry water only during high
water periods or year-round?

Raf)hael Kazmann: High water stages carry more sediment for wetlands accretion. Also,
diversions during low stages can worsen saltwater intrusion up the river and affect
drinking water supplies. Therefore, substantial freshwater diversion must be
confined to relatively high flow periods.

Unidentified speaker: Wouldn't that present a problem in preventing saltwater intrusion
during late summer and early fall when the salinity encroachment tends to be
greatest?

Johannes van Beek: Low flow periods pose a major problem. Also salts may accumulate
in soils during episodes of high salinity flooding behind levees. Release of fresh
water, when it is available, will help leach the salts from the soils.

Walter Sikora: Long-term records in Lake Ponchartrain show highest salinity in the fall,
but do not show any long-term increase in the western lake. How then could
deterioration of freshwater swamps be attributable to saltwater intrusion?

Johannes van Beek: The break up of cypress swamps seems to be due primarily to
increased inundation rather than to increased salinity, but there may be some
critical low salinity which affects tolerance to inundation. Therefore, freshwater
diversion could increase tolerance to inundation. Also, introduction of more
sediments is required to offset the effects of subsidence on increased inundation.

Dag Nommedal: There are three major natural processes which will affect long-term
changes in south Louisiana that we cannot manage. One is the eventual diversion to
the Atchafalaya. The second is hurricanes. Thirdly, there is a tremendous amount
of evidence from tidal gauge records and climatic models that dramatic sea-level
rises have just begun. We have no means or structures to deal with these problems.
We should, thus, start discouraging development in the lowlands of Louisiana. We
can not afford to lose New Orleans, but we don't want to create other potential
traps like it.

Gary Bloize: Is there anything that can be done to protect the barrier islands? These are
very important with regard to avoiding the loss of State lands and oil and gas
resources to the Federal Government.

Ron Boyd: Instead of protecting the coastline for the purpose of saving State revenues,
Louisiana should establish an agreement with the Federal Government regarding a
fixed boundary. There are, nonetheless, a range of options for barrier island
protection, most significantly, sediment bypassing at inlets and nourishment of the
islands from the available sand sources such as in tidal deltas and nearshore zone.
This sand can be placed back on shore and stabilized by vegetation, resulting in
significantly slowing down the rate of erosion. Experience has shown that purely
structural approaches such as placement of rock walls are generally not effective.

Johannes van Beek: Although there are processes we cannot stop, barrier island erosion
is artifically accelerated by man's actions. If man can accelerate erosion rates, he
should be able to decelerate back to rates attributable to natural processes. We
must learn how best to do that in order not to be surprised by natural disasters.

Clarke Lozes: Since 1950 Plaquemines Parish has taken upon itself to initiate freshwater
diversions and presently there are three structures operating and a fourth proposed.
We are trying to improve their design and management, while at the same time, we
are taking other steps to decrease the number of new oil and gas canals in
wetlands. These may be short term approaches, effective within 100 years, but
people are living in Plaquemines Parish today. It is necessary now to take definite
action on some projects and these might hopefully lead us to a longer term
management plan.

John Uhl: What approaches can economically be taken to return the system more to
equilibrium and dominance by natural processes?

Raphael Kaznnann: The only thing we can do is build diversion structures which operate
automatically during high flows and do not cut off sediment in the Atchafalaya by
building spoil banks which keep the sediment from spreading out. But this comes
into conflict with flood protection and navigation interests.

Sherwood Gagliono: Dr. Kazmann assumes that the amount of water coming down the
Mississippi will remain the same. What are the prospects that states to the north
will divert water to other drainage basins?

Raphael Kazmann: The principal advocate of this has been Texas. If it were pure water,
it would have to be pumped 4,000 ft to use it for irrigation. Actually the sediment
loads would defeat this approach. Diverting water from Arkansas River reservoirs is
more feasible, but this river does not contribute much water to the Mississippi.

Potential diversion of 200,000 to 500,000 acre/ft/yr of water from the Missouri
River for a coal slurry pipeline is also rather negligible. Larger diversions for
irrigation in the upper Midwest may be more significant but are probably
uneconomical unless funded by the Federal Government.

Rodney Adams: If one colored on a map the areas where the projects discussed may
provide some benefits, there would be a large void between the Houma Navigation
Canal and the Barataria Waterway and in certain areas in St. Bernard Parish. We
need some more critical permitting procedures in these areas where such mitigative
approaches are infeasible.

Martha Landry: Where have the sediments which used to come down the Mississippi
River been diverted?

Raphael Kazmann: Although in the upper Missouri and Arkansas Rivers there are
reservoirs which can contain about twice the normal annual flow of the river, 25
percent of the reservoir capacity is to be used for storage of sediment. Missouri
River water used to have a tremendously high suspended sediment load which has
now been greatly reduced. They have not yet designed reservoirs which will allow
sediments to effectively bypass containment, although about 10 years ago the Bureau
of Reclaimation was optimistic about designing such devices.

Dag Nummedal: If by design or default the Mississippi was fullydiverted tothe Atchafalaya,
what would be the effect on chenier plain progradation?

John Wells: With 30 percent of the Mississippi River water and sediment flow there is
substantial progradation which should accelerate once the Atchafalaya Bay fills. If
this increased to 60 percent or more, there would be very rapid effects in about 10
years.

Walter Sikora: The sedimentation phenomena described for the lower Barataria Bay
results from reworked sediments in a saline or brackish medium. This may result in
more rapid sedimentation from water flowing into the marsh than in the case of
freshwater diversions into a marsh. The suspended sediments in the fresher water
may settle much more slowly.

Richard Hatton: When the water flows into the marsh the sheet flow rates are very slow,
such that the sediments are deposited after travelling only short distances.

John Wells: It now appears that the effect of salt flocculation has been overemphasized
and that sedimentation by organic binding of fine particles is important both in
marine and fresh waters.

Bob Gerdes: If enough small diversion structures were built along the lower river, would
that reduce the pressure on the Old River control structure during floods?

Raphael Kazmann: They would have no effect because they are too far away, up to 200
river miles. Relief spillways must be close. Even the opening of the Morganza
spillway, 10 to 12 miles away, during the 1973 flood had less of an effect than
expected at the Old River control structure.

Chris Neill: It appears that chenier plain progradation is one of the most effective
means of gaining new land. What are the pros and cons of letting more flow down
the Atchafalaya to accelerate this process?

John Wells: Certainly the building of new land and new marsh in the Atchafalaya Bay
and downdrift to the west would be a plus.

Raphael Kazmann: The negative aspects present very tough, political situations in which
compromises cannot be reached. Increasing diversion to the Atchafalaya presents
serious problems to the New Orleans water supply during low flow. Too little
diversion causes problems at Morgan City. The question becomes "Who is going to
drink salt water?"

Donald Boesch: One consequence not often discussed is the effect of river diversions on
adjacent continental shelf water, particularly increased stratification and resulting
low oxygen conditions, sedimentation, and nutrient enrichment. This should also be
considered in evaluating diversions which affect coastal and shelf waters.

Ron Boyd: Even though there may be such effects, they would not be unusual ones in the
history of the river and the adjacent continental shelf environment, because fresh
water was often discharged from more than one major distributary at a time.

John Wells: It is important to realize that land loss is only a subaerial loss; the subaerial
land that reverts to shallow water bottom also has a natural resource value. We
need to ask how much more valuable is an acre of marsh than an acre of water
bottom, as a nursery ground for shrimp or other species.

Johannes van Beek: Marshes and water bottoms are linked together. Without the input
from the marsh that acre of water bottom will not be of much good. Your question
should be modified to "What is the right combination of water and marsh?"

CAUSES: PHENOMENA DIRECTLY

RELATED TO HUMAN ACTIVITIES

WETLAND LOSS DIRECTLY ASSOCIATED WITH CANAL DREDGING
IN THE LOUISIANA COASTAL ZONE

W. B. Johnson
J. G. Gosselink

Center for Wetland Resources

Louisiana State University

Baton Rouge, LA 70803

ABSTRACT

This study addresses wetland losses directly resulting from canals, including initial
construction practices and subsequent canal bank erosion. The average actual width of
the newly dredged canals studied exceeded the width specified in the dredging permit by
13.4 m. The total width affected, including berm and spoil deposits, exceeded the
permitted canal width by an average of 81.7 m.

As canals age, they widen through erosion. The history of three old canal systems
in coastal Louisiana was examined. All these canals continue to increase in width and
differences in their patterns of widening can be explained by boat traffic, length of time
since construction, and substrate differences. The widening rate in the Leeville oilfield
is directly related to the proximity of the canal to boat traffic. Canals in areas of greatest
boat activity widened at a rate of 2.58 m/yr, while those in areas of minimal boat
activity widened at a rate of 0.95 m/yr.

INTRODUCTION

Louisiana has 30% of the Nation's coastal wetlands (Turner and Gosselink 1975), but
they are being lost at an alarming rate. Numerous investigators (Gagliano and van Beek
1970; Adams et al. 1976, 1978, 1980; Craig et al. 1979, 1980; Gagliano et al. 1981;
Baumann and Adams in press) have examined Louisiana's land loss problems. These
investigations have generally relied on large-scale mapping procedures for data
extraction, concentrating on the entire coastal zone, shoreline sections, or hydrologic
basins.

Manmade canals are a dominant feature of the Louisiana coast, and there is
considerable evidence (Craig et al. 1979, 1980; Scaife et al. in press) that this canal
network contributes significantly to wetland loss, both directly and indirectly. Direct
effects are the immediate conversion of wetland to canals and spoil banks during canal
construction (Darnell 1976), and the subsequent widening of canals as their banks erode
through time. Indirect effects (Morton 1977) are marsh deterioration from saltwater
intrusion and changes in waterflow patterns that result when deep straight canals are
dredged through wetlands. In this report we document the direct wetland loss associated
with dredging and historical erosion. Indirect effects are documented by Scaife et al. (in
press).

We first examine the relationship between proposed canal widths specified in
dredging permit applications (permitted width) and the actual wetland affected— that .o,
dredged or covered with spoil material. Secondly, we document the widening of canals
that occurs through time as their banks erode, through case studies of three old canal
systems. Finally, we show that boat traffic has a significant effect on the widening rate.

METHODS

Permit files of the U.S. Army Corps of Engineers, New Orleans District, (USACE-
NOD), provided a source of canal dimensions authorized in dredging permits. Oil and gas
well-access canals in Terrebonne and Cameron parishes, Louisiana, and the Louisiana
Offshore Oil Port (LOOP) pipeline system from the Southwest Louisiana Canal near
Leeville north to the Clovelly saltdome were evaluated. Criteria used for choosing
particular canals were accessibility, recent construction (within two years), and the
vegetation traversed. Table I summarizes canal locations, habitats, and approximate
construction dates.

Site visits were made to LOOP on 25 July 1979 and from 6 to 8 August 1979; to
Terrebonne Parish from 31 August 1979 to 3 September 1979; and to Cameron Parish
from 24 to 26 September 1979. Canal widths and elevations were measured with a Lietz
self-leveling level equipped with top and bottom stadia hairs, and a 3.7 m stadia rod with
0.1 cm graduations. Measurement locations on the LOOP pipeline were randomly
selected. At each well-access channel, two transects were sighted perpendicularly near
the well head and in the access channel.

The widths of spoil, berm, and canal were estimated. From these measurements
the total width modified by the construction and the actual canal width were
calculated. Canal depth and, where possible, canal length were measured.

Simple linear regressions were used to relate permitted canal width to the
corresponding actual canal width and to the total impact width (width of both spoil banks
and the canal). In addition, paired t-tests were used to determine if permitted berm
widths, berm depths, canal widths, canal lengths, and well head slip lengths were
significantly different from the actual dimensions measured in the field.

Evalutations were made of the widening rates of three canal systems: old oil field
navigation canals on the Rockefeller Wildlife Refuge at Grand Cheniere, Louisiana; the
Southwestern Louisiana Canal which connects Caminada Bay and Little Lake in southern
Lafourche Parish, Louisiana; and the Leeville oil field canals surrounding Leeville,
Louisiana.

Using data from Nichols (1961) on selected sites in the Rockefeller Wildlife Refuge,
we ascertained the initial canal widths at the time of construction. Nicholls also
provided the canal widths as measured in May 1958 and again in March 1961. On 26
September 1979 we remeasured the canals at the same locations.

An historical evaluation of the width of the Southwestern Louisiana Canal was
made by Doiron and Whitehurst (1974), using the original construction date and width,
aerial imagery made, and field measurements made in 1979. We updated these
measurements from Environmental Protection Agency (EPA) infared photographs made in
October 1978, scaled to 1:24,000 with a Bausch and Lomb Zoom Transfer Scope.

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The Leeville oil field was mapped from 15-minute quadrangle maps made in 1957 by
the U.S. Geological Survey, and from an October 1978 EPA infrared aerial photograph
scaled to 1:24,000 with a Bausch and Lomb Zoom Transfer Scope. Because of distortion,
it was necessary to scale small areas of the oil field independently. Canals were placed
into one of five categories, depending on their morphology and exposure to boat activity
(Table 2), and their widths were measured on both maps. Widening rates exceeded the
smallest change discernible using measurements of 0.5 mm on 1:24,000 imagery (Tanner
1978). Analysis of variance was used to test for widening rate differences among canal
types.

Table 2. Canal types in the Leeville, Louisiana oil field

Morphology

Type

Description

Major navigation canals

(MNW)

:"".':-:'i-:i'.''.:

;||;i||||i;:|||||||

:•:•:•:

\ .

WT^^

Oil field navigation
canals (OFNC)

Nonmajor canals (NMC)

Well -access canals
extending directly
off major navigation
water ways (Bayou
Lafourche and South-
western Louisiana
Canal )

Well -access canals
extending directly
off oil field naviga-
tion canals

Well -access canals
well removed from
regular boat wake
exposure

Side extensions on oil
field navigation canals
(SMNC)

Well -access areas
that are widenings of
existing navigation
canal s

r™^

Side extensions on
minor canal s (SNMC)

Well -access areas
that are widenings of
existing canals in-
frequently exposed to
boat wakes

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140 -

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TOTAL IMPACT WIDTH = 1.000 (PERMITTED CANAL WIDTH) + 81.681

1 1 [—

30 40

PERMITTED CANAL WIDTH Cm)

— r-
50

Figure 1. Relationship between proposed permitted canal widths and the total
width of the wetland corridor actually modified by construction. See Table 1
for data sources.

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f 130 H

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O 100-

r^ = Q4230
TOTAL IMPACT WDTH = 1,111 (ACTUAL CANAL WIDTH) + 68.314

— r-
25

35 45

ACTUAL CANAL WIDTH On)

Figure 2. Relationship between actual dredged canal widths and the total
width of the wetland corridor actually modified by construction. See
Table 1 for data sources.

RESULTS

The relationship between canal widths as proposed in permit applications and the
total width of the wetland corridor actually modified by construction is presented in
Figure I. Only 36.6 percent of the variation in the total width affected is explained by
differences in the permitted dimensions. Other probable sources of variability are
substrate characteristics (e.g., organic content, cohesiveness) and the care taken by
dredge operators and surveyors to adhere to permitted dimensions.

The regression relation shows that total affected width, that is the width of the
canal, berm, and both dredge material deposits, increased linearly as permitted canal
width increased; and that the actual width affected exceeded the permitted width by
81.7 m.

As might be expected the total width affecjed was slightly more closely related to
the actual dredged dimensions (Figures I and 2; r =0.423). Again, the regression slope is
nearly one. In cross section, berm and spoil deposits occupy about 68.3 m, and actual
dredged canal widths exceeded permitted widths by about 13.4 m (81.7 m compared to
68.3 m).

Analysis of the means of permitted to actual canal dimensions (as contrasted to
measurements predicted from the regression equations), showed that actual canal widths
statistically exceeded permitted canal widths by 10.9 m (Table 3). Actual berm widths
were 3 m less than permitted widths. Depth, total canal length, and slip length were not
significantly different from permitted specifications (Table 3).

Table 3. Comparisons of permitted versus actual canal dimensions, using
paired t-tests.

Actual mean

Permitted

mean

Dimension

measurement

Statistic

P > t

(m)

Depth

2.9

2.5

1 .53

0.1511

Berm width

4.6

7.6

-4.43

0.0003

Canal width

34.4

23.5

6.30

0.0001

Total canal

574.9

573.9

0.05

0.9643

length

SI ip length

112.2

106.1

1.22

0.3471

69-1

g 51-

42-

r2 : 0.82
CANAL WIDTH : 1.018 CCANAL AGE} + 21.229

1 1 r

-I \ 1 1 1 1 1 1 \ 1 \ 1 1 1 1 r

25 30 35

CANAL AGE tyrsj

Figure 3. Relationship between canal width and age in the Humble canal
system, Rockefeller Refuge, La. Locations are described in Nichols (1961).

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CANAL AGE (yrs)

Figure 4. Relationship between canal width and age in the Deep Lake-
Constance Bayou canal system. Rockefeller Refuge, La.

120 -\

I-
o

80-

40-

SOUTHWESTERN LOUISIANA CANAL

1880

1900

1950

— I r

1980

DATE

Figure 5. Relationship between canal width and age in the Southwestern
Louisiana Canal, Lafourche Parish, La. See Table 5 for raw data.

Analysis of the Rockefeller Refuge canals showed that although canals widened
linearly, the rate of increase and the zero age-intercept in the Humble canals were
different (P < 0.05) from those in the Deep Lake-Constance Bayou canals (Figures 3 and
4). In the Humble canal system, canals widened at 1.018 m/yr and 82.4% of the variation
in canal width was explained by canal age, while in the Deep Lake-Constance Bayou
system the canal widening rate was 0.704 m/yr and 78.5% of canal width variation was
explained by canal age. Widening rates for the Southwestern Louisiana Canal (Table 5
and Figure 5) were much higher than those for the Rockefeller Refuge canals (15 m/yr),
and are increasing through time.

The amount of boat traffic greatly influenced the erosion rate in the Leeville oil
field. Well-access canals (Table 2) widened faster when connected to major navigation
waterways (2.25 m/yr) than when connected to less traveled oil field navigation canals
(1.12 m/yr) or to nonmajor canals well removed from boat wake exposure (0.95 m/yr)
(Table 4). When canals were widened for well access (Table 2) the width of the widened
recess was not influenced by boat traffic density (Table 4, SMNC vs. SNMC).

DISCUSSION

The newly dredged canals examined in this study were an average of 13 m wider
than the widths specified on permit applications. In no case were they narrower. This
was expected, since the width indicated in the permit request is the minimum width at
the bottom of the canal. Canal side slopes are typically about 3:1, depending on the
solidity of the substrate, so that the surface width is greater than the permitted width.
Berms are encouraged because, although they expand the total impact width, they also
prevent spoil from backwashing and shoaling the canal, which would then require

Table 4. Numbers of observations, mean widening rate from 1957 to 1978, and
standard error for different canal types in the Leeville oil field (A) and
analysis of variance indicating differences in canal widening rates for the
period from 1957 to 1978 (B) (See Table 1 for canal types).

Canal
type

Number of
observations

Mean
(m/yr)

Standard
error

NMC
OFNC
SMNC
SNMC

13
20
34
25
12

2.58
0.95
1.12
1.20
1.16

0.
0.
0.
0.

85
13
11
15
15

Source

Canal type
MNW vs. OFNC
MNW vs. NMC
SMNC vs. SNMC

Error

Total

23.48

5.87

4,44**a

18.75

14jg**a

19.76

14.95**^

0.01

O-OINS*^

129.52

1.32

102

153.00

a **Highly significant (p < 0.01)
b NS Not significant (p > 0.05)

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premature maintenance dredging. Placement of the spoil material is constrained by tine
length of the arm on the dredge. To some extent berm width is indirectly controlled by
this. Our regression analyses showed that berm and spoil bank together generally added
68 m to the width of the wetland corridor destroyed in canal construction. When the
extra unauthorized canal width was included, the total corridor width was 81.7 m wider
than the permitted canal. For a well-access canal permitted at about 21 m (65 feet) the
total impacted width was typically about 103 m or five times the permitted canal
width. Apparently, there has been almost no policing of canal construction, nor is there
a record showing whether permitted canals are ever dredged. Since habitat loss from
canals is much greater than permit records indicate, closer adherence to permit
dimensions should be enforced. In addition, we observe that sufficient numbers of spoil
bank openings to allow the flow of water across the marsh were seldom maintained, but
sheet flow over the marsh was severely impeded by all spoil banks visited.

Boat traffic greatly influences canal widening rates as demonstrated in the analysis
of dead-end canals in the Leeville oil field. Dead-end canals off Bayou Lafourche and the
Southwestern Louisiana Canal, the two major nearby navigation routes, widened 1.46
m/yr faster than dead-end canals off oil field navigation canals and 1.63 m/yr faster than
dead-end canals some distance from boat traffic.

The re-examination of the Rockefeller Refuge and Southwestern Louisiana canals,
and information gathered in other parts of the study, provide insights into the factors
that influence the widening of dredged canals in wetlands. The specific controlling
factors that have been identified are boat traffic, geologic environment, and width of the
spoil bank. The Humble canal system has more boat traffic than the Deep
Lake-Constance Bayou system and widened about 0.3 m/yr faster. The Southwestern
Louisiana Canal, with even more exposure to boat wakes, widened at a mean rate of
almost 3 m/yr. These trends support the findings from the Leeville oil field, but part of
the dramatic difference between the widening rates of the Rockefeller Refuge and the
Southwestern Louisiana canals may be the generally firmer substrates at the Rockefeller
Refuge (Gosselink et al. 1979).

In the Southwestern Louisiana Canal, the initial period of slow widening followed by
more rapid widening may be explained by slow erosion through the consolidated spoil
banks, followed by an increased erosion rate once the canal edge reached open marsh
beyond the spoil. As shown in Table 6, a hypothetical canal permitted at 21.3 m in width
would have a berm and spoil bank 34.2 m wide on each side [=(100.6 - 32.3)/2]. At the
Initial slow widening rate of the Southwestern Louisiana Canal it would take 72 years for
the canal edge to erode through the spoil bank (compared with only 27 years at the
present rapid rate). The slower rate corresponds to the time between construction and
the dramatic increase in erosion rate of the Southwestern Louisiana Canal. Thus, we
hypothesize that once spoil banks are eroded away, one can then expect a dramatic
increase in canal widening rates. The Rockefeller Refuge canals are still eroding through
the spoils banks, as are most of Louisiana's oil field canals. Therefore, their widening
rates are relatively low and linear (Figures 3 and 4). We predict that when these canals
become 30 to 70 years old their associated land loss rates will begin to accelerate
rapidly.

Table 6. A projected history of a canal widening and width impacted from a
canal permitted to be 21.3 m wide in a saline Louisiana marsh. Construction
dimensions were estimated using the regressions and t-tests of actual con-
struction versus permitted widths. The rates of widening were estimated
using the highest and lowest rates in the Leeville oilfield.

Width (m)

Permitted

Canal 21.3

Construction

Canal 32.3

Canal and Impact 100.6

Age Width (m)

LOW (0.95 m-yr"'') HIGH (2.58 m-yr"'')

1 ^r 33.2 34.8

5 yr 37.0 45.1

10 yv 41.7 58.0

50 yr 79.7 161.2

100 yr 127.2 290.2

ACKNOWLEDGMENTS

Contribution No. LSU-CEL-81-40 of the Coastal Ecology Laboratory, LSU Center
for Wetland Resources, Baton Rouge, La. Thanks to B. Allen for a helpful review.

LITERATURE CITED

Adams, R.D., B.B. Barrett, J.H. Blackmon, 3.W. Cane, and W.G. Mclntire. 1976.
Barataria Basin: geologic processes and framework. Louisiana State Univ. Center for
Wetland Resources, Baton Rouge. Sea Grant Publ. LSU-T-76-006. I 17 pp.

Adams, R.D., P.J. Banas, R.H. Baumann, J.H. Blackmon, and W.G. Mclntire. 1978.
Shoreline erosion in coastal Louisiana: inventory and assessment. Louisiana
Department of Transportation and Development, Baton Rouge, 139 pp.

Baumann, R.H., and R.D. Adams. In press. The creation and restoration of wetlands by
natural processes in the Lower Atchafalaya River System: possible conflicts with

navigation and flood control objectives. Proceedings of the 8th Conference on
Wetlands Restoration and Creation, Tampa, Florida.

Craig, N.J., R.E. Turner, and J.W. Day, Jr. 1979. Land loss in coastal Louisiana
(U.S.A.). Environ. Manage. 3:133-144.

Craig, N.J., R.E. Turner, and J.W. Day, Jr. 1980. Wetland losses and their consequences
in coastal Louisiana. Z. Geomorph. N.F. 34:225-241.

Darnell, R.M. 1976. Impacts of construction activities in wetlands of the United
States. U.S. Environmental Protection Agency, Corvallis, Oreg. EPA-600/3-76-045.
392 pp.

Doiron, L.N., and C.A. Whitehurst. 1974. Geomorphic processes active in the
Southwestern Louisiana Canal, Lafourche Parish, Louisiana. Louisiana State Univ.,
Division of Engineering Research -RMS, Baton Rouge. Research Monographs. 39 pp.

Gagllano, S.M., and J.L. van Beek. 1970. Geologic and geomorphic aspects of deltaic
processes, Mississippi Delta system. Louisiana State Univ., Center for Wetland
Resources, Baton Rouge. Hydrologic and Geologic Studies of Coastal Louisiana. Rep.
I. 140 pp.

Gagllano, S.M., K.J. Meyer-Arendt, and K.M. Wicker. 1981. Land loss in the Mississippi
River Deltaic Plain. Trans. Gulf Coast Assoc. Geol. Soc. 31:295-300.

Gosselink, J.G., C.L. Cordes, and J.H. Parsons. 1979. An ecological characterization
study of the Chenier Plain coastal ecosystem of Louisiana and Texas, Vol. I. U.S. Fish
and Wildlife Service, Office of Biological Services. FWS/OBS-78/9. 302 pp.

Morton, J.W. 1977. Ecological effects of dredging and dredge spoil disposal: a literature
review. U.S. Fish Wildl. Serv. Tech. Pap. 94. 33 pp.

Nichols, L.G. 1961. Erosion of canal banks on the Rockefeller Wildlife Refuge.
Louisiana Wildlife and Fisheries Commission, Refuge DIv., New Orleans, (unpublished
report).

Scalfe, W., R. E. Turner, and R. Costanza. In press. Indirect impact of canals on recent
coastal land loss rates in Louisiana. Environ. Manage.

Tanner, W.F. 1978. Standards for measuring shoreline changes: a study of the precision
obtainable, and needed. In making measurements of changes (erosion and accretion).
Coastal Research. Florida State Univ., Tallahassee. 87pp.

Turner, R.E., and J.G. Gosselink, 1975. A note on standing crops of Spartina alternlflora
in Texas and Florida. Contrib. Mar. Sci. 1 9: 1 1 3- 1 1 8.

CANALS AND WETLAND EROSION RATES IN COASTAL LOUISIANA

R. Eugene Turner

R. Costanza

W. Sea if e

Center for Wetland Resources

Louisiana State University

Baton Rouge, LA 70803

ABSTRACT

Canals have increased in area from practically zero at the beginning of the century
to about 2M% of the Louisiana coastal surface area in 1978. The annual increase in canal
area is continuing to climb in 1981 as a result of new canal dredging and the widening of
existing canals. Land loss rates across the coastal zone since the 1890's, among
hydrologic units, and within areas of similar substrates and equal distances to the coast,
are all positively related to estimates of canal density. Further, estimates of land loss
at zero canal density (from regression equations) are similar to the 7,000 year coast-wide
rate of gain in land. Within 7 1/2' quadrangle maps, the new "holes" or ponds in the
marsh have appeared close to canals, not near natural channels. Coastwide, canal
surface is about 10% of the total land loss. Based on our analysis we conclude that
coastal erosion rates in Louisiana are largely an indirect result of canal dredging
activities or use. The mechanism for the effect probably involved an alteration in
wetland hydrology, but a complete understanding is presently lacking. Thus corrective
measures cannot be identified and implemented with confidence until more is known
about the mechanisms of canal and spoil bank effects on wetland hydrology.

INTRODUCTION

Canals are conspicuous features of the south Louisiana wetlands. At surface level,
in a boat, their great length, density, and diversity can go unnoticed. A few hundred feet
above the ground, however, they stand out as dominant geomorphic features. Most still
have some remnants of their original levees formed from the dredge spoil put aside
during construction. A few, notably gas pipeline canals, were filled in almost as soon as
the pipe was laid and are no longer evident; the plants there have regained their former
position in the reworked soil. Many canals are still in commercial and recreational use;
others are blocked at one or both ends. They lie straight in contrast to the twisting,
anastomotic natural channels which the canals often intersect. Water within canals rises
and falls with the tide, contains fish, and is not noticeably different from bayou water in
many respects. The linear structure of canals and the resulting effects on water and
sediment movement constitute the major difference between canals and natural drainage
systems.

These canals were largely absent at the turn of the century. Almost all were
constructed to help in the recovery of mineral deposits located thousands of meters

below ground. Canals abound in every parish, in every wetland plant community and soil
type, and have increased gradually, not suddenly, in density. In effect, a giant
experiment is being conducted and we have only to recognize it as such to evaluate the
results. The random surface distribution of canals and their differences in density over a
wide geographical area and in different geological surface substrates provides a
laboratory for the examinaton of their effects on a variety of wetland processes. This
study represents some preliminary assessments of the relationship between land loss and
canals, based on recently acquired, detailed area measurements.

The Louisiana coastal zone has grown seaward for 7,000 years at a new steady gain
of 500 to 600 ha annually. Since 1900, however, there has been a net annual loss of
land. The annual land loss rates have increased as the number of canals has increased.
The prevalent explanation for the cause of the acceleration in land loss rates usually
relies heavily on two arguments: first, that the disruptive influence of the Mississippi
River levees reduces natural overbank flooding and shunts sediments offshore, and
second, that there is a natural decay of deltas. Canals are generally considered ancillary
factors in this explanation (e.g., Gagliano et al. 1981). There is a qualitative
attractiveness to this argument, with which one of us has grappled before (Craig et al.
1980), but the data for a quantitative evaluation were limited then. Now, however, we
have new data (Wicker 1980) to support the examination of an alternative hypothesis:
that canal density is directly correlated with increased land loss rates at the local and
regional levels and through time, and that impact of canals varies with changes in soil
conditions and proximity to sediment sources. It is worth mentioning at the outset that
the point of this exercise is not to place blame on one factor or another but, instead, to
help understand what is happening and, thus, help provide for the enlightened and
effective management of these valuable renewable resources.

CANAL DENSITY

Major inventories of canals and land loss in the Louisiana coastal zone have been
conducted by Barrett (1970), Gagliano et al. (1971, 1981), Chabreck (1972), Gosselink et
al. (1979), and Wicker (1980). These are the sources we will use in the figures that
follow. The different surveys have various geographic boundaries that may not
coincide. The most extensive data set available is for the deltaic plain, which extends
from the Mississippi-Louisiana border to just west of the emerging Atchafalaya delta.
We have normalized inconsistencies in geographic boundaries by expressing the area of
canals as a percentage of annual loss based on the change from the initial to the later
conditions.

The average canal density for the whole deltaic plain has increased steadily since
1890, when we presume there were very few canals (Figure I). The canal area has
climbed geometrically with time. From 1955 to 1978, it increased from 1% to 2.4%, or
at a doubling rate of around 20 years. Including spoil banks, the total land area affected
approached 10% by 1978, a magnitude equal to the surface area one would expect the
natural drainage features to occupy in an unaltered marsh. The relationship between
natural channel density and canal surface area is an inverse one (Craig et al. 1980).
Natural channel density decreased logarithmically, while canal density increased linearly
in the vicinity of the Leeville oilfield. The natural hydrology is obviously altered by the
reduction in lateral flooding as a result of the spoil bank levees, by obstructing natural
channels, and by the linear and uniform conduit created by the canals.

o
cc

1900

1925 1950

YEAR

1975

2000

Figure 1. Canal density in the deltaic plain as determined from various
surveys (data from Chabreck 1972; Gagliano 1973; and Wicker 1980).

CANAL DENSITY AND LAND LOSS RATES

The whole coast is not uniform with respect to canal density and land loss rates.
Land loss rates for 1955 to 1978 were as low a -2% annually (a net gain of land) in the
active Mississippi River delta and in the Atchafalaya delta. Canal densities vary among
the hydrologic units as well (Table I). Some are above 3% and others are below 1%.
Canal densities have increased in the last 25 years in every hydrologic unit. There is a
general relationship between canal density and land loss rates in each hydrologic unit
(Figure 2). The point at which canal density is zero is also where land loss rates are
slightly below zero (a net gain). Further, if one looks at the historical changes in land
loss rates for the whole region, the same pattern emerges (Figure 3). Land loss is high
when canal densities are high. Both were low at the turn of the century and have
increased coincidentally since. The first estimates of land loss, for 1891 to the 1930s,
are perhaps too high, since the early maps did not delineate marsh ponds and drainage
channels. The present land loss rates are considerably more accurate and average about
0.8% annually from 1955 to 1978. Now (1982), land loss rates ore near 1% annually. This
translates to a regional "half-life" of 50 years. There is no indication that trends in
either canal density or land loss rates are changing in Louisiana.

These latter relotonships were sufficiently interesting to justify comparing land
loss rates with canal densities in individual quadrangle sheets of the coastal zone for
1955-78 (Scaife et al. in press). Subsidence rates and the substrate in each delta lobe
differ (Morgan 1963; Adams et al. 1976). One net effect of delta building is the
progradation of younger sediments over older sediments. The latter are more
consolidated and therefore more resistant to erosion. Also, wave attack and

<
>-

X
(0

LAND LOSS BY
HYDROLOGICAL UNIT
1955-1978

Y : 0.855 |X| - 0.0492

% CANAL DENSrTY
IN 1955

Figure 2. The percent annual wetland loss as related to the average canal
density for the six hydrological units of the deltaic plain (from Wicker 1980)

1.0

a
o

0.5

intercept -*

linear

regression

0.346
= 0.88

IXI - 0.0713

.1955-1978

1935-1958
1891-1935

*" historical
gain

% CANAL DENSITY

Figure 3. Land loss for three intervals between 1891 to 1978 in relation to
the average canal density for those intervals. The intercept of a simple
linear regression based on these three points is compared with the historical
net gain for the last 7000 years (Gagliano 1973; Wicker 1980; Gagliano et al .
1981).

Table 1. Canal area expressed as a percentage of land area in the
deltaic plain in 1955 and 1978 for each of seven hydrological units,
Data from Wicker (1980).

UNIT

REGION

1955 %

1978 %

Lake Pontchartrain

0.08

0.33

Breton Sound

0.79

1.82

Mississippi River Delta

2.05

3.70

Barataria Bay

1.58

3.45

Timbalier and Terrebonne

Bays

0.90

2.59

Atchafalaya Delta

1.18

3.66

Vermilion Bay

1.06

2.24

redistribution of sediments is greatest near the coast, particularly for the fine-grained
sediments of the delta tip (Coleman 1976).

We therefore assigned a delta age based on Frazier's (1967) maps and a distance to
the coast for each mapping unit. Land loss was higher nearer the coast in younger delta
substrates. But within groups of similar soils, the same pattern emerged: (I) land loss
rate was directly related to canal density, and (2) land loss rate was very near zero
when canal density was zero. An example of the analysis is shown in Figure 4. The only
exception was the Atchafalaya delta where land building is occuring. The direct
relationship otherwise holds for land areas both near and far from major sediment
sources. Proportionally, more land is lost per canal in younger rather than older deltas,
and in areas nearer the coast. New "holes" or ponds in the marsh also appear in
association with canals and away from natural channels (Figure 5).

A summary of our present linear regression analyses of canal density vs. land loss
rates is in Table 2. There is a consistent pattern within similar substrate types, among
hydrological units, and across the coast for the three survey intervals since 1890.
Further, the estimate of the land loss that would occur at zero canal density ranges from
10% of the present total land loss rate to a net gain. The average "intercept estimate"
of the three methods, (A, B, and C in Table 2) is almost exactly the same as the
historical average land increase we might expect, judging from the 7,000-year history of
land building in the coastal zone.

Put another way, the indication is that canal densities, since 1890, are high where
land loss is high and near zero where land loss is zero (except for the Atchafalaya delta
region) for areas with a variety of substrates and of varying distances from the coast.
The slopes of the regression lines vary with delta age and distance to the coast. One

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AREA DELTA SYSTEM #5
DISTANCE FROM COAST 3'

25 30 35 JO 45 50 55 60
CANAL AREA /LAND AREA « 100 (1978)

Figure 4. Land loss per 7 1/2' quandrangle for the delta system outlined
in the map. Canal area is expressed as a percent of the total land area
in 1978. This analysis and other examples are provided in detail in
Scaife et al . (in press) .

explanation might be that this relationship is the result of only the direct removal of land
by the canal dredging operations, that is, the direct loss. But this is not supported by an
analysis of the available data (Figure 6). Canal surface area accounts for less than 10%
of the total land loss from 1955 to 1978, though from the I930's to 1958 it amounted to
39%. Rather, the relationship must be explained on the basis of indirect impacts. It is
probably associated with a combination of the canal, the dredging activity, subsequent
use of the canal, and coincidental engineering (such as levees).

Given these relationships, it is worth examining the present trend in canal area
added each year (Figure 7). the Louisiana Department of Natural Resources has records
of the canal area it has permitted for the first 105 days of 1981. We prorated that
amount for 365 days. Since the actual area of a canal is 1.46 times the permitted area
(Johnson and Gosselink 1982), the amount of new canal area added each year is still
accelerating. Further, many, but not all, canals widen with age (Craig et al. 1980;
Johnson and Gosselink 1982). If the amount of canal area added each year approaches
anywhere near a 1% annual widening rate, an area equal to the permitted area should
also be added to the 1981 estimate of new canal area. The geometric increase in canal
density is thus still occurring.

NATURAL LAKES & CHANNELS

CANALS

NEW PONDS

Figure 5. "New ponds" that formed in the vicinity of Golden [^eadow, in
southern coastal Louisiana from 1969 to 1978. Ponds that coalesce to-
gether, eroding lake edges, and eroding ponds are not shown. Ponds are
black, canals are cross-hatched and the natural drainage lakes and channels
are stippled. Note that all the new ponds are in the vicinity of canals
and not near the one natural channel drainage basin draining into the north
side of Catfish Lake.

100

1955-
,• 1978

1935-
1958

1900

1925 1950

YEAR

1975

2000

Figure 6. Land loss not directly attributable to an increase in canal density
from 1890 to 1978 for three different intervals (Gagliano 1973; Wicker 1980).

Q.
M

ACTUAL
Johnson &
Gosselink,
19821

PERMITTED,

1981
preliminary
estimate, LA,
DNRl

2000

Figure 7. The area of canals added annually in the deltaic plain from 1891
based on analyses for three intervals (Gagliano 1973; Wicker 1980) extrapo-

lated to an estimate for 1981
sources permits for the first
adjusted by an actual area to
and Gosselink 1982).

based on Louisiana Department of Natural Re-
105 days (assuming 75 % in the deltaic plain)
permit area ratio of 1.46 computed by Johnson

CONCLUSION

There is strong indication that canal development is directly and indirectly related
to land loss rates. Causal mechanisms are still poorly understood, however. Canal
densities are not only increasing through time, but accelerating. As a result, land loss
rates are expected to increase as well. Since new canal dredging must now be permitted
by regulatory bodies, one might argue that regulatory action could influence further
canal density, and land loss rates. Perhaps fewer than a half-dozen of the first 2,000
dredging permits issued in 1981 by the Department of Natural Resources were denied
(although many are modified during review), and even these were subsequently approved
by the Secretary. Another solution might be to mitigate or minimize the damages of
existing and new canals. We have little data on the usefulness (or damage) of the various
mitigating techniques which have been suggested, such as weirs, backfilling, or spoil bank
design, for regional land loss reduction. River diversion schemes and current land
building in the Atchafalaya are locally important, but on a regional scale these could, at
best, reduce present total land loss rates by only 5% to 10% (Day and Craig 1982).

State Senator Nunez asked at this conference, "Would there be a land loss problem
If we had no canals?" Although natural and artificial deterioration of older delta lobes
due to wave attack and the deficit of sediment accretion compared to subsidence and sea
level rise results in localized land loss, our analyses indicate that the direct and indirect
effects of canal development have greatly exacerbated the rate and geographic extent of
land loss in Louisiana. Furthermore, existing canals, through indirect mechanisms, will
continue to encourage significant wetland loss, compounding the effects of new canals.
With canals, the historic inevitability of local delta erosion and statewide gain is altered;
local erosion has expanded statewide, and there Is a net land loss of enormous magnitude.

We have Inherited a truly major problem, but are doing little to solve it. Any
management plan that is to successfully combat coastal erosion on a meaningful level
must therefore address canal impacts and management. For example, increases in
barrier island erosion rates may be more symptomatic of the problem, than, as some have
argued, causal. As the area of wetlands behind the Islands erodes, more water Is flushed
In and out with each tide and storm. This enlarged tidal prism carries more salt water,
has greater system-wide currents, and alters sediment and water balances for plants that
bind the soil and barrier island dunes. The system-wide perturbation, caused by canals,
of estuarine salt balance, hydrology, sediment supply, and plants requires an integrated
study by a variety of experts. One grand experiment has been conducted for 90 years and
we can now see the results. Perhaps we can learn from it and proceed in a less damaging
manner in the future. The present attitude of the State of Louisiana seems to be that
the effect of canals Is ancillary or, at lease, not major. We estimate that canals are the
causal agents for at lease a majority (perhaps as much as 90%) of the present land loss,
yet the Joint Commitees of Natural Resources of the Louisiana Legislature (1981)
included no major programs for mitigation of canal effects among the $38 million In
projects recommended for the first phase of implementation of the Coastal
Environmental Protection Trust Fund Act.

ACKNOWLEDGMENTS

We thank E. Swenson for his comments, K. Westphal and C. Harrod for drafting the
figures, and Jo Paula Lantier for typing the manuscript.

LITERATURE CITED

Adams, R.D., B.B. Barrett, J.H. Blackmon, B.W. Gone, and W.G. Mclntire. 1976.
Barataria Basin: geologic processes and framework. Louisiana State Univ., Center for
Wetland Resources, Baton Rouge. Sea Grant Publ. LSU-T-76-006.

Barrett, B.B. 1970. Water measurements of coastal Louisiana. Louisiana Wildlife and
Fisheries Commission, U.S. Department of the Interior Fish and Wildlife Serv., Bureau
of Commercial Fisheries Project. 2-22-T, P.L. 88-309.

Chabreck, R. 1972. Vegetation, water, and soil characteristics of the Louisiana coastal
region. Louisiana Agricultural Experiment Station, Baton Rouge. AEA Inf. Ser. 25.

Coleman, J.M. 1976. Deltas: Processes of deposition and models for exploration.
Continuing Education Publishing Co., Inc. Champaign, III.

Craig, N.J., R.E. Turner, and J.W. Day, Jr. 1980. Wetlands losses and their
consequences in coastal Louisiana. Z. Geomorph. Suppl. 34:225-241.

Day, J.W., Jr., and N.J. Craig. 1982. Comparison of effectiveness of management
options for wetland loss in the Louisiana coastal zone. Pages 231-237 |n D.F. Boesch,
ed. Proceedings of the conference on coastal erosion and wetland modification in
Louisiana: causes, consequences, and options. U.S. Fish and Wildlife Service,
Biological Services Program, Washington, D.C. FWS/OBS-82/59.

Frazier, D.E. 1967. Recent deltaic deposits of the Mississippi River: their development
and chronology. Trans. Gulf Coast Assoc. Geol. Soc. 17:287-315.

Gagliano, S.M. 1973. Canals, dredging, and land reclamation in the Louisiana coastal
zone. Louisiana State Univ. Center for Wetland Resources, Baton Rouge. Hydrologic
end Geologic Studies of Coastal Louisiana. Rep. 14.

Gagliano, S.M., P. Light, and R.E. Becker. 1971. Controlled diversions in the Mississippi
delta system: an approach to environmental management. Louisiana State Univ.,
Center for Wetland Resources, Baton Rouge. Hydrologic and Geologic Studies of
Coastal Louisiana. Rep. 8.

Gagliano, S.M., K.J. Meyer-Arendt, and KM. Wicker. 1981. Land loss in the Mississippi
River deltaic plain. Trans. Gulf. Coast Assoc. Geol. Soc. 31:295-300.

Gosselink, J.G., C.L. Cordes, and J.W. Parsons. 1979. An ecological characterization
study of the Chenier Plain coastal ecosystem of Louisiana and Texas. Vol. I. U.S. Fish
and Wildlife Service, Office of BiologicalServices FWS/OBS-78/9. 302 pp.

Johnson, W.B., and J. G. Gosselink. 1982. Wetland loss directly associated with canal
dredging in the Louisiana coastal zone. Pages 60-70 ]n D.F. Boesch, ed. Proceedings
of the conference on coastal erosion and wetland modification in Louisiana: causes,
consequences, and options. U.S. Fish and Wildlife Service, Biological Services
Program, Washington, D.C. FWS/OBS-82/59.

Morgan, J.P. 1963. Louisiana's changing shoreline. Louisiana State Univ. Coastal Stud.
Inst., Baton Rouge. Tech. Rep. 16, Pt. D. 13 pp.

Scaife, W., R.E. Turner, and R. Costanza. In press. Indirect impact of canals on recent
coastal land loss rates in Louisiana. Environ. Manage.

Wicker, K.M. 1980. Mississippi deltaic plain region ecological characterization: a habitat
mapping study. A user's guide to the habitat maps. U.S. Fish and Wildlife Service,
Office of Biological Services. FWS/OBS-79/07.

PANEL DISCUSSION

CAUSES: PHENOMENA DIRECTLY RELATED TO HUMAN ACTIVITIES

Roger Saucier, Moderator

Andre Delfloche, James G. Gosselink, R. Eugene Turner, Michael
Lyons, Joan Phillips, and John Woodard, Panelists

Joan Phillips: The environmental community has been interested in the problem of
wetland loss in Louisiana for over 10 years. The environmental community coalesces
on the one idea of preserving renewable resources which produce revenue, food and
cultural heritage. On the other hand, non-renewable resources must also be
conserved. We must not let renewable resources be destroyed in the process of
extracting nonrenewable resources. Environmentalists have been expressing concern
and appearing before legislators on the need to protect renewable wetland resources
in the exploitation of nonrenewable resources since at least 1976. We should have
been mitigating these imjxicts since the depth of the wetlands loss problem was
recognized. We must begin the process of correcting these mistakes immediately.

We have had some progress including the adoption of a coastal zone
management program and permitting of wetlands activities under this program. But
is it working? Are new canals being shortened or eliminated where possible? Are
we using all techniques feasible and practicable to preserve and conserve renewable
resources? My concern is that we are not presently accomplishing these
objectives. Out of 1,300 coastal use permits issued thus far by the Louisiana
Department of Natural Resources, two were appealed, but a stay order to halt the
activities could not be gained before the appeals were heard by the Coastal
Commission. There is no communication on the feasibility of directional drilling to
reduce the need for wetland dredging between the Coastal Management Section and
the Office of Conservation, both within the Louisiana Department of Natural
Resources. When is the expertise and staff necessary for thorough evaluation of
permits going to be available?

The nonrenewable resources will be there in years to come if not exploited
now, thus we must stop now the destruction of renewable wetland resources in this
exploitation. Other states seem to be recognizing the importance of water
resources. For example, Florida has enacted a law placing a 5-cent sales tax on
every $100 of property sold to be used for protection of water resources. Such a
continuous source of funding is needed in Louisiana to protect water resources,
enable sound permitting and acquire important wetlands.

The environmental community will be there to at least assure that
environmental laws are implemented. We charge the scientific community to
develop the data necessary to determine what kinds of activities and in what
intensity can be allowed in wetlands without jeopardizing production of renewable
resources. We ask the public to join in our pursuit of wetlands preservation. We ask
the Legislature to fund the acquisition of knowledge and sound management and
protection of wetland resources.

JoUn Woodard: 1 am involved in tlie management of surface resources of extensive
wetlands in Terrebonne and Lafourche parishes for my company, Tenneco LaTerre.
We lease surface resources for fur trapping, alligator hunting, waterfowl and game
hunting. These uses require some activities including the placement of canals to
utilize the resources to their fullest. Many of the canals constructed for this
purpose are now wide waterways, bearing out what erosion has done. About 40 years
ago most large land owners became involved in an extensive marsh management
program mainly for hunting and trapping interests. We recognized how critical it is
to maintain stable water levels as they affect the integrity and productivity of the
marsh. These management programs have included construction of levee systems,
mud plugs, and water control structures that allow tidal exchange and have been
quite successful in reducing the impacts of later operations such as oil and gas
operations. Although the deterioration from the dredging of canals has not been
reduced to a minimum, enormous strides have been made because the land owners
have been able to work with the oil and gas operators to suggest designs which
reduce these rates of deterioration. Discussions among the land owners, oil and gas
operators, and regulatory agencies generally result in further refinement to reduce
the amount of detrimental activity required to drill a well or place a pipeline.
Energy production is very important for the State and Nation, thus we need logical
plans which allow continued energy production together with needed environmental
protection.

David Mekasski: Where wetland protection through such means as directional drilling is
not economically feasible, what are the benefits and limitations of mitigating these
effects through restoration of wetlands in another areas?

Michael Lyons: A number of companies have on the suggestion of Federal agencies or
the Coastal Management Section backfilled existing canals. We are not sure what
the benefits of backfilling are, but much more backfilling is being done today and
has been done within the last two years.

Unidentified speaker: We have seen aerial photographs of intense development of canals,
sometimes with parallel, adjacent access canals. Do oil companies cooperate and
use existing access canals where possible to reduce this effect?

Michael Lyons: In the early years of development that was more prevalent, but there is
not much of that today.

Joel Lirxlsey: There have been some problems in one company gaining access through
another's canal. There may be legal constraints. But it is very difficult now for
companies to dredge parallel canals nearby because of permitting review.

Len Bahr: Is there any technical reason for leaving wellhead access canals at their
original depth and width after the drilling barge is removed? Couldn't they be
serviced by smaller vessels requiring smaller access channels?

John Woodard: Servicing of the well with a workover rig requires nearly the same draft
as the initial drilling rig.

Johannes van Beek: Given that drilling is likely to continue, how do we determine the
processes which affect the ecosystem through hydrological modification by canals
and the procedures to mitigate adverse effects?

R, Eugene Turner: It hasn't been until recently that we have even had sufficient data
allowing the correlations which indicate the magnitude of the canal problem. The
experiences from management practices such as employed by large land owners have
not been quantified with hard data. Thus, we are presently unable to describe the
processes which will govern the effectiveness of mitigation and there is not much
effort being presently expended to do so. Experimental approaches are required to
describe the specific causes of canal-induced wetlands loss and the effectiveness of
mitigative procedures.

Joan Phillips: We have to put our money where our mouth is and develop the funding
sources which will allow us to do what Dr. Turner suggested. What we need is a
"superfund" for wetlands. There is evidence that damage is being done, thus we
should slow down development to a manageable point to allow the assessment of the
effectiveness of ways to deal with these impacts. Instead of specific mitigation on
each project, perhaps there can be a tax collected to fund investigations and
subsequent improved accretion and nourishment of wetlands.

James Gosselink: I have a little different prespective. I think we know the major
processes— subsidence accelerated with hydrological modification due to canals.
Management for specific purposes changes natural relationships; one component may
become more productive at the expense of another. An example is the extensive
canal development in wetlands in southwestern Louisiana to manage for waterfowl
and furbearers. Recent data show that land loss within these impounded areas is
accelerated. Management can not do better than nature has managed to do over
eons. We need a big plan that handles social displacement and maximizes natural
processes such as Atchafalaya delta formation. I think we are piddling around the
edges with backfilling. As important as it is in the short run, it really is not going to
address the long-run problems.

Charlotte Fremaux: Are there long-term plans being developed which include the various
piecemeal activities altering coastal wetlands? For example, does the Corps of
Engineers have a plan encompassing their various projects such as navigation
channels?

David Stuttz: To my knowledge there is no grand scheme. The Corps does not go out and
invent projects but responds to identified needs. In a limited way we address
broader scale planning through the permit process.

Sue Hones: I am with the Corps of Engineers Planning Division. As we write an
environmental impact statement we consider the impact of an activity on the area
in the context of cumulative impacts of various activities such as oilfield canals,
navigational dredging, and levee construction.

Paul Yokupzock: What effect will the deregulation of natural gas have on drilling
activities in wetlands?

Michael Lyons: The effect is uncertain. The deregulation of oil did not result in a great
increase in drilling activity in south Louisiana. The number of wells drilled per year
has gone from 1,800 in the I950's and I960's to 1,100 to 1,200 presently. This
downward trend will continue because the remaining undiscovered resources are
generally in small pockets.

Pat Mason: What is the feasibility of directional drilling in lieu of access canals in
wetlands?

Michael Lyons: Directional drilling is not generally viable because of technical and legal
problems. Exploratory wells require straight vertical drilling for geological
interpretation and intercepting several stratographic objectives. There is also the
problenn of legal disputes regarding drilling from one land owner's property to
structures under that of another. A directionally drilled well is approximately 50
percent more expensive than a straight well and this frequently makes it
uneconomical to drill the project.

Walter Sikora: I disagree with the doomsday approach expressed by Jim Gosselink.
Human activities are an important cause of land loss and good data are required in
order to deal with them. It is not acceptable to our society to stop drilling in
wetlands, thus we need to develop ways it can be accomplished without unacceptable
environmental losses.

James Gosselink: I do not disagree. In response to the short-term outlook, we need
better information but can not afford to delay action because everyone cannot be
satisfied. Nature has had a long time to optimize biological-environmental
relationships. Any human changes which interfere with them will be detrimental.
Therefore, if we do not know the consequences of an action we should take a
conservative position and try to keep as much as possible to natural landscape
features and processes. I suggest, however, that we need to look more than we have
toward the long term, where many of these short-term issues will be insignificant.

Len Bahr: I would argue that the cost differential between directional drilling and
conventional approaches involving wetlands dredging may not be that great if the
environmental costs were borne by the developer. It may be much cheaper to
society in the long run to directionally drill than to dredge new canals.

Michael Halle: Why should the oil industry be exempt from the type of regulation
imposed on strip-mining of coal with regard to restoring the land to contours enjoyed
before mining? What does it cost to backfill canals?

Michael Lyons: Backfilling wetland canals and restored strip-mined land differ in their
effectiveness. The dredged material backfilled in wetland canals will generally not
restore the original landscape. I do not know the specific cost of backfilling, but it
is less expensive than directionally drilling.

Donald Boesch: Would Dr. Saucier offer some direction regarding wetland restoration
based on his experiences in habitat development from dredged material?

Roger Saucier: It is generally unrealistic to use fine-grained material dredged with a
dragline and stored subaerially to refill a canal. The technology exists, however, and
is eminently practicable, if local geography permits, to hydraulically dredge
material from one canal to another canal or pond and create a wetland similar to
that displaced.

Donald Moore: Even though leveling of spoil banks may not be able to totally restore
wetlands displaced by a canal, it can restore the area where the spoil was placed and
return it to a coastal wetland elevation.

Roger Soocier: While it may not be practical to use material which has been in spoil
banks for a great amount of time for wetlands creation, spoil banks can be degraded
even though the material may have experienced a 50 percent volume reduction. This
reduces the effects of the spoil banks themselves, including accelerated subsidence
in the immediate area, and blockage of surface drainage and overland flow.

Murray Hebert: I hear many complaints from permit applicants that requirements are
overly broad and restrictive and, in many cases, counterproductive.

John Woodard: As a large land owner, my company is usually able to work out such
problems. Smaller land owners and independent operators may have more problems
because they lack areas in which to mitigate or the resources to accomplish
mitigation. As environmental concerns increase it has become a more difficult
process to obtain permits, but we have been generally successful if we modify the
project to obtain the permit.

Michael Lyons: I do not think regulatory programs have been overly restrictive. Often
Federal agencies suggest that the feasibility of directional drilling or backfilling
should be studied but do not absolutely require either. If these would be absolutely
required, it may be overly restrictive. Backfilling, for example, may be effective In
some areas and not others.

CONSEQUENCES: EFFECTS ON
NATURAL RESOURCES PRODUCTION

THE EFFECT OF COASTAL ALTERATION ON MARSH PLANTS

Robert H. Chabreck

School of Forestry and Wildlife Management

Louisiana State University

Baton Rouge, LA 70803

ABSTRACT

The Louisiana coastal marsh is subdivided into four vegetative types: saline,
brackish, intermediate, and fresh. The types occur in bands generally paralleling the
coastline and contain characteristic water salinity levels and plant communities.
Activities of man coupled with natural processes, such as subsidence and erosion, have
removed many natural tidewater barriers and reduced freshwater flow through the
marshes. As a result, saltwater intrusion from the Gulf of Mexico has increased and the
boundaries of vegetative types hove been altered. The saline vegetative type has greatly
increased in size and the brackish and intermediate types have shifted inland. This has
caused a drastic reduction in the size of the fresh vegetative type.

INTRODUCTION

The coastal marshes of Louisiana are one of the most productive habitats for fish
and wildlife in North America. The high production of fish and wildlife is directly
related to the abundance and diversity of photosynthetic plants produced within the
area. These plants are the basic source of energy for dependent animal populations, and
conditions enhancing plant growth serve to benefit fish and wildlife. On the other hand,
activities which alter environmental conditions can be detrimental to plants and
drastically affect fish and wildlife populations.

Activities which have had the most damaging impact on marsh vegetation are canal
construction associated with oil and gas exploration, pipelines, navigation, and flood
control; permanent drainage for agriculture, industry, and urbanization; modified
drainage patterns associated with levee and highway construction and spoil deposits; and
dredge and fill operations. The activities of man coupled with natural processes such as
subsidence and erosion have greatly altered environmental conditions and thereby
changed the distributional patterns of plants. Only with a complete understanding of the
distributional patterns and the environmental conditions necessary for optimum plant
growth can the magnitude of coastal alteration be assessed.

THE COASTAL REGION OF LOUISIANA

Marshes of the Louisiana coastal region encompass an area of approximately 1.7
million ho and span the full coastline of the State. The marshes extend inland for
distances ranging from 24 to 80 km and reach their greatest width in southeastern
Louisiana.

Water levels in these marshes are greatly affected by rainfall, tides, and local
drainage patterns. Water levels are typically within 30 cm of the marsh surface with
exceptions occurring with storm tides or during periods of excessive rainfall or prolonged
drought. The effects of tides are greater in areas nearer the Gulf of Mexico, however,
tide levels in the gulf also affect water drainage from interior marshes. In addition to its
effect on marsh water levels, tidal action in the gulf also provides a source of highly
saline water to the marshes. The daily fluctuating action causes highly saline waters to
move inland and mix with advancing fresh water to form a vast estuarine basin. The
mixing of salt water from the gulf and fresh water from inland sources provides a
horizontal stratifiction of water salinities. Water salinities range from highly saline (20
to 25 ppt) near the coastline and gradually decline inland until a zone of fresh water is
reached along the northern perimeter of the marsh region.

Penfound and Hathaway (1939) studied the coastal marsh in southeastern Louisiana
and noted that water salinity and water depth were major factors governing plant species
distribution. They subdivided the marsh into types on a basis of salt concentration of
free soil water, designated these types as saline, brackish, slightly brackish
(intermediate), and fresh, and described the plant associations within each type. The
marsh types along the entire Louisiana coast were mapped by Chabreck et al. (1968) and
Chabreck and Linscombe (1978) on a basis of the plant associations described by
Penfound and Hathaway (1939). Chabreck (1972) described the plant species composition
and soil and water characteristics of each marsh type.

DESCRIPTION OF MARSH TYPES

Marsh vegetative types along the Louisiana coast generally occur in bands
paralleling the coastline. The vegetative types are comprised of characteristic
associations of plant species with similar salinity tolerances (Table I).

Saline Vegetative Type

The saline vegetative type borders the shoreline of the Gulf of Mexico and is
subject to daily tidal fluctuations. This type forms a narrow band in the chenier plain of
southwestern Louisiana, but is very extensive in the deltaic plain of southeastern
Louisiana. The two regions combine to form a total salt marsh area of 270,000 ha
(Chabreck 1970). The saline type of the deltaic plain is dissected by numerous
embayments and tidal inlets and as a result is exposed to rapid and drastic tidal action.
The shoreline of the chenier plain is fringed by an almost continous beach deposit. The
beach restricts intrusion of gulf waters, and delays runoff of fresh water.

Water salinities average 18.0 ppt (range: 8.1 to 29.4 ppt), and soils have a lower
organic content (mean: 17.5%) than fresher types located further inland. Vegetation
within this type consists of few species. The species are salt-tolerant and dominated by
Spartina alterniflora, Distichlis spicata, and Juncus roemerianus (Table I).

Brackish Vegetative Type

The brackish vegetative type is further removed from the influence of highly saline
gulf waters than the saline type, but is still subject to daily tidal action. The brackish
type is a major vegetative type of coastal Louisiana and comprises 520,000 ha. Normal
water depths exceed that of saline marsh and soils contain higher organic content (mean:

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31.2%). Water salinities average 8.2 ppt (range: 1.0 to 18.4 ppt). This marsh type
characteristically contains numerous small bayous and lakes.

The brackish type contains greater plant diversity than the saline type but is
dominated by two perennial grasses, Spartina patens and Distichlis spicata (Table I). An
important wildlife food plant of brackish marsh, Scirpus oineyi, grows best in tidal marsh
free from excessive flooding, prolonged drought, and drastic salinity changes. The
species is, however, often crowded out by the domiant grasses, [xirticularly S. patens.

Intermediate Vegetative Type

The intermediate vegetative type lies inland from the brackish type and occupies
an area of 280,000 ha. This type receives some influence from tides and water salinities
average 3.3 ppt (range: 0.5 to 8.3 ppt). Water levels are slightly higher than in the
brackish type, and soil organic content averages 33.9%. Plant species diversity is high
and the area contains both halophytes and freshwater species used as food by a wide
variety of herbivores. Sporting patens dominates the intermediate type as it does the
brackish type, but to a lesser degree. Other common plants are Phragmites communis,
Sagittaria falcata, and Bacopa monnieri (Table I).

Fresh Vegetative Type

The fresh vegetative type occupies the zone inland from the intermediate type and
south of the Prairie formation and Mississippi River alluvial plain. In many areas the
fresh type is adjacent to or intermixed with forested wetlands (swamp). The fresh
vegetative type encompasses an area of 530,000 ha and is equal to the brackish type in
size. The type is normally free from tidal influence and water salinities average only 1.0
ppt (range: 0.1 to 3.4 ppt). Because of slow drainage, water depth and soil organic
content (mean: 52.0%) are greatest in the fresh type. In some fresh marshes, soil organic
matter content exceeds 80% and the substrate for plant growth is floating organic
matter referred to as flotant by Russell (1942). The type also supports the greatest
diversity of plants and contains many species which are preferred foods of wildlife.
Dominant plants include Panicum hemitomon, Eleocharis spp., Sagittaria falcata, and
Alternanthera philoxeroides. ~~~ ~~"

COASTAL ALTERATIONS

Stratification of the Louisiana coastal marshes into distinct vegetative types has
historically been maintained naturally by surface features and hydrological processes.
The advance inland of saline gulf waters was usually restricted by natural barriers, such
as beaches, cheniers, low marsh ridges, and natural levees along streams and lakes. The
meandering and shallowing of coastal streams as they moved inland reduced their
capacity to carry large volumes of salt water. The discharge of fresh water from inland
sources through coastal streams also served to dilute and prevent the inland advancement
of saline tide waters.

Activities of man including leveeing, canal dredging, and stream channelization
coupled with natural processes, such as subsidence and erosion, have reduced the
effectiveness of saltwater barriers and altered hydrological processes. Canals and
channelized streams which connect tidal saltwater sources to inland marshes of lower
salinity function in two ways to alter vegetative types. During low tides in the Gulf of

Mexico, the canals flush fresher water from interior marshes and lower water levels.
Then, with high tides in the gulf, salt water is able to move farther inland. The process
is gradual, and a period of several years may be necessary for the effects to become
evident.

As water salinity increases in an area, plants unable to tolerate the higher salinity
die and are gradually replaced by species adapted to the new salinity regimes. Greatest
damage to plants takes place when fresh marsh containing high levels of soil organic
matter is subjected to water of much greater salinity and strong tidal action. Plants in
the area are killed by increased water salinity, and the organic substrate becomes loose
and disorganized without plants roots to hold it together. As tide water moves through
the area, small amounts of organic matter are picked up by the current and flushed out
through tidal channels. Before new species can become established, marsh elevations
may drop 10 to 20 cm over broad areas. Open ponds and lakes thus develop and
productive marshland is lost. Thousands of hectares of marsh in the deltaic plain of
southeastern Louisiana have been thus affected. The chances of such areas again
supporting emergent plant growth is very unlikely unless corrective action is taken on a
large scale.

Prior to levee construction along the Mississippi River, overbank flooding would
send vast quantities of fresh water and alluvium down former channels of the river and
other streams emptying into the gulf on the deltaic plain. In many areas flood water
from the Mississippi River would reach the Gulf of Mexico via sheet flow over the
marshes.

As a result of overbank flooding, a tremendous area of fresh marsh was developed
and maintained. Also, nutrient-rich sediment was added to the marsh, thus enhancing
productivity and promoting land building.

Because of several disastrous floods, the Mississippi River Commission was formed
in 1879, and levee construction for flood control began in 1882. Completion of the levee
system required many years, but today the levee system extends southward to the active
delta (approximately 100 km south of New Orleans). Approximately one-third of the
Mississippi River flow is diverted through the Atchafalaya River during flood stage. The
remainder is carried through the leveed channel of the Mississippi to the Gulf of Mexico.

CHANGES IN VEGETATIVE TYPES

A comparison of studies by Penfound and Hathaway (1939), O'Neil (1949) and
Chabreck (1970) disclosed that the plant species composition within vegetative types
changes very little over a period of several decades. Environmental conditions or
successional stages may cause certain species to become abundant locally. On a
coastwide basis, however, the species composition of individual types has remained
relatively stable. Changes most noticable were the decline of three-cornered grass
(Scirpus oineyi) in the brackish type (Palmisano 1967) and sawgrass (Cladium jamaicense)
in the intermediate and fresh types (Valentine 1977). In recent years, smooth beggartick
(Bidens laevis) has greatly increased in the fresh vegetative type (Kinler et al. 1981).

Although little modification has taken place within vegetative types, considerable
change has been noted among vegetative types during the past three decades. This
change was caused by coastal alteration which resulted in increased saltwater intrusion
and general shifts in the boundaries of vegetative types.

The location of vegetative types in the Louisiana coastal nnarsh was delineated
during previous investigations by O'Neil (1949), Chabreck et al. (1968), and Chabreck and
Linscombe (1978). Each investigation represented a different time period and provided a
base from which temporal changes in vegetative types could be evaluated.

Changes in the location of the saline and brackish vegetative types over a period of
approximately 25 years were determined by comparing the vegetative type map by O'Neil
(1949) with that by Chabreck et al. (1968). The saline type in the chenier plain in
southwestern Louisiana changed very little over the period and occupied a narrow zone
about 0.8 km wide adjacent to the Gulf of Mexico. Comparisons of the saline types in
the deltaic plain showed a different situation, however. Measurements from the earlier
study may revealed that the saline vegetative type extended inland for an average of 9.3
km from the gulf shoreline, but the 1968 map placed this type 12.7 km inland, an
encroachment averaging 3.4 km over the 25-year period.

The brackish vegetative type was also compared on the two maps. Measurements
revealed that the brackish marsh extended inland an average of 14.5 km during the 1941-
45 period (O'Neil 1949) and 15.6 km in 1968, a retreat of only I.I km. Considerable
differences were noted, however, between the chenier plain and deltaic plain marshes.
The O'Neil map shows the deltaic plain brackish type extending inland for an average of
20.0 km; but, in 1968, the northern boundary of this type was 26.1 km inland. In contrast,
the brackish type of the chenier plain extended inland for a mean distance of 9.0 km
during the O'Neil study, but by 1968 the northern boundary of this type had advanced
seaward to a line only 5.2 km inland.

Since the saline vegetative type maintained essentially the same position over the
years in the chenier plain, the seaward advancement of the northern boundary of the
brackish type represents a reduction in the width of this type. In fact, O'Neil (1949)
shows the chenier plain brackish type as a strip 8.2 km wide, while Chabreck et al. (1968)
shows this same type 4.2 km wide, a reduction of about 47 percent. The brackish type in
the deltaic plain, however, actually widened during the 25-year period. During the
earlier period, this type was 10.6 km wide, but by 1968, the average width had increased
to 13.4 km.

The widening of the saline and brackish vegetative types in the deltaic plain
resulted from saltwater intrusion from the Gulf of Mexico into the intermediate and
fresh vegetative types. Increased canal dredging and stream channelization, coupled
with subsidence and erosion, were major factors in the change. The reduction in the
width of the brackish type on the chenier plain reflected a reduction in water salinities in
that area. Factors operating to reduce water salinities during the 25-year interval
included the discharge of large amounts of fresh water by the Atchafalaya River into the
area plus construction of levees and water control structures to prevent saltwater
intrusion.

Changes in the size of vegetative types in the Louisiana coastal marshes were
determined for a 10-year period by comparing the size of types mapped by Chabreck et
al. (1968) with those mapped by Chabreck and Linscombe (1978). Chabreck and
Linscombe (in press) computed the size of vegetative types and areas where types had
changed to either saltier or fresher conditions. They found that vegetative types had
changed on 3,730 km'^ or 21.9% of the State's coastal marshland over the 10-year
period. This represented a change to saltier vegetative types on 13.7% of the area and to
fresher types on 8.2% of the area with a net change to saltier conditions on 5.6% of the
entire coastal marshes or 950 km^.

In 1968 the fresh vegetative type encompassed 5,260 knn'^, but by 1978 it hod been
reduced to 4,900 knn^ (6JB%). During the sanne time period, the saline vegetative type
increased from 3,768 km^ to 4,105 km^ (8.9%). Only slight changes in size were noted in
the brackish and intermediate types from 1968 to 1978; thie brackish type increased 96
km^ (1.8%) and the intermediate type decreased 73 km^ (2.6%). The brackish and
intermediate types are actually transitional zones between the saline and fresh types. As
a result of coastal alteration, salt water moved further inland during the 10-year
interval. This caused the saline vegetation type to expand in size and the transitional
zones (brackish and intermediate types) to retreat further inland with very little
modification in size. Consequently, the fresh vegetative type was reduced in size, and
the inland advancement of the saline vegetative type was mostly at the expense of the
fresh type.

LITERATURE CITED

Chabreck, R.H. 1970. Marsh zones and vegetative types in Louisiana coastal marshes.
Ph. D. Dissertation. Louisiana State Univ., Baton Rouge. I 13 pp.

Chabreck, R.H. 1972. Vegetation, water and soil characteristics of the Louisiana
coastal region. La. Agric. Exp. Stn. Bull. 664. 72 pp.

Chabreck, R.H., T. Joanen, and A.W. Palmisano. 1968. Vegetative type map of the
Louisiana coastal marshes. Louisiana Wildlife and Fisheries Commission, New Orleans.

Chabreck, R.H., and G. Linscombe. 1978. Vegetative type map of the Louisiana coastal
marshes. Louisiana Department of Wildlife and Fisheries, New Orleans.

Chabreck, R.H. and G. Linscombe. In press. Changes in vegetative types in Louisiana
coastal marshes over a 10 year period. Proc. La. Acad. Sci.

Kinler, N.W., G. Linscombe, and R.H. Chabreck. 1981. Smooth beggartick, its
distribution, control and impact on nutria in coastal Louisiana. Worldwide Furbearer
Conference Proceedings, Frostburg State College, Frostburg, Md. 1:142-154.

O'Neil, T. 1949. The muskrat in the Louisiana coastal marshes. Louisiana Department
of Wildlife and Fisheries, New Orleans. 159 pp.

Palmisano, A.W. 1967. Ecology of Scirpus oineyi and Scirpus robustus in Louisiana
coastal marshes. M.S. Thesis. Louisiana State Univ., Baton Rouge. 145 pp.

Penfound, W.T., and E.S. Hathaway. 1939. Plant communities in the marshlands of
southeastern Louisiana. Ecol. Monogr. 8:1-56.

Russell, R.J. 1942. Flotant. Geogr. Rev. 32:74-98.

Valentine, J.M. 1977. Plant succession after saw-grass mortality in southwestern
Louisiana. Proc. Annu. Conf. Southeast. Assoc. Game Fish Comm. 30:634-640.

EFFECTS OF WETLAND DETERIORATION ON THE
FISH AND WILDLIFE RESOURCES OF COASTAL LOUISIANA

David W. Fruge

U.S. Fish and Wildlife Service

P.O. Box 4305

Lafayette, LA 70502

ABSTRACT

The vast wetlands of the Louisiana Coastal Region (LCR) are of national
importance to fish and wildlife. These wetlands are winter habitat for one-fourth of the
North American dabbling duck population, a large portion of the Mississippi Flyway's
diving ducks, and over 400,000 geese. Coastal Louisiana also supports numerous other
migratory birds, many of which nest in its wetlands. The LCR marshes produce the
largest fur harvest in North America, and support the largest volume of
estuarine-dependent fish and shellfish landings in the United States. Fish and wildlife
related recreation in the LCR is also extensive, including over 5 million man-days of
saltwater fishing in 1975 and 676,000 man-days of waterfowl hunting during the 1977-78
season.

Prior studies documented an annual land loss rate of over 42.7 km^(l6.5 mi )/yr in
the LCR. More recent investigations indicate that this rate of wetland loss has more
than doubled since 1956. Wetland deterioration, which is partially attributable to natural
causes, has been greatly accelerated by human influences such as navigation channel
excavation, agricultural drainage, and construction of mainline Mississippi River levees
that have prevented freshwater and sediment overflow into adjacent subdelta marshes.
Continued wetland deterioration may lead to serious declines in estuarine-dependent fish
and shellfish harvest, fur catch, waterfowl habitat, and related fish and wildlife
productivity.

The U.S. Fish and Wildlife Service has long advocated freshwater diversion for
habitat improvement in the Mississippi deltaic plain region and is presently participating
in the evaluation of several freshwater diversion sites being investigated by the U.S.
Army Corps of Engineers. It is anticipated that marsh restoration measures involving
freshwater diversion and other approaches will also be financed by the State of Louisiana
through its Coastal Environmental Protection Trust Fund.

INTRODUCTION

Area Setting

The Louisiana Coastal Region (LCR) contains a vast expanse of valuable wetlands.
Chabreck (1972) estimated that this area contained approximately 1 million ha (2.5
million acres) of fresh to saline marsh, 0.7 million ha (1.8 million acres) of ponds and

lakes, 0.9 million ha (2.2 million acres) of bays and sounds, and over 50,000 ha (125,000
acres) of bayous and rivers in 1968. The LCR has been divided into two main
physiographic units (Morgan 1973): the deltaic plain of the central and eastern portions
and the chenier plain of the western portion. Both of these regions have been developed
over the past 5,000 years by a series of prograding and overlapping deltaic lobes composed
of sediments transported by the lower Mississippi River and its distributaries. Both
the deltaic plain and the chenier plain have been the subject of extensive ecological
characterization efforts by the U.S. Fish and Wildlife Service's National Coastal
Ecosystems Team. Approximately 74% of Louisiana's coastal marshes occur in the
deltaic plain, while 26% are found in the chenier plain.

Importance to Fish and Wildlife

Fisheries. Louisiana consistently leads the United States in volume of commerical
fishery landings. Nearly 3.7 billion kg (1.7 billion lb) of commercial fish and shellfish,
worth approximately $190 million at dockside, were landed in Louisiana during 1978
(National Marine Fisheries Service 1979). The bulk of this catch is composed of
estuarine-dependent species including menhaden, Atlantic croaker, seatrout, spot, red
drum, blue crab, brown shrimp, white shrimp, and American oyster. The LCR also
supports a large recreational fishery. Approximately 580,000 persons expended over 5
million saltwater angling days in the area in 1975, spending over $35 million (U.S. Fish
and Wildlife Service 1977). Approximately 373,000 man-days were spent sport shrimping
in the LCR in 1968 (U.S. Fish and Wildlife Service 1976), and present effort is believed to
be much higher.

Wildlife. The Louisiana coastal marshes are of great importance to migratory
waterfowl, providing winter habitat for more than two-thirds of the entire Mississippi
Flyway waterfowl population in recent years (Bellrose 1976). Palmisano (1973) noted
that one-fourth of the North American puddle duck population winters in these wetlands,
with peak numbers of over 5.5 million of these birds recorded during December 1970.
Coastal Louisiana's wetlands also support over one-half of the continental mottled duck
population, with fall populations of 75,000 to 120,000 birds reported (Bellrose 1976).
Diving ducks are also abundant in the Louisiana coastal marshes and adjacent waters
during fall and winter. More than 90% of the Mississippi Flyway's 870,000 lesser scaup
winter in Louisiana, primarily in its coastal zone (Bellrose 1976). In addition, nearly 38%
of the canvasbacks that winter in the Mississippi Flyway occur in Louisiana, mostly in Six
Mile and Wax lakes of the lower Atchafalaya basin and Atchafalaya delta (Bellrose
1976). Many ducks present in fall and spring are transients that utilize the LCR for
feeding and resting enroute to or from Central and South America (Palmisano 1973). The
Louisiana coastal marshes and adjacent ricefields have supported 369,000 lesser snow
geese and 55,000 white-fronted geese in recent years (Art Brazda, U.S. Fish and Wildlife
Service, Lafayette, Louisiana, personal communication).

The LCR wetlands provide important habitat to numerous other migratory birds.
Common game species include clapper rail, king rail, sora, common snipe, purple
gallinule, and common gallinule. Non-game migratory species are also abundant in the
area. A total of 148 nesting colonies of seabirds, wading birds, and shorebirds
representing 26 species and over 794,000 nesting adults were inventoried in the LCR
during 1976 (Portnoy 1977). In addition, approximately 14 active bald eagle nests were
recorded by Fish and Wildlife Service personnel in the LCR during 1980, representing the
largest nesting concentration of this endangered species in the south-central United
States.

TOO

Because of its extensive coastal wetlands, Louisiana has been the leading
fur-producing area in North America as long as records have been kept (Lowery 1974).
The Louisiana fur harvest accounted for nearly one-third of the Nation's fur take in the
19^9-70 season (U.S. Fish and Wildlife Service 1971). According to the Louisiana
Department of Wildlife and Fisheries (1978b), over 3.2 million pelts worth more than $24
million were taken in Louisiana during the 1976-77 season. Muskrat and nutria, primarily
coastal species, accounted for nearly 90% of the pelts harvested during that period.

In recent years, alligator numbers in the LCR have exceeded 500,000, thus
permitting controlled hunting in much of the area. In 1979, 16,300 alligators worth
approximately $1.7 million were harvested in the LCR (Louisiana Department of Wildlife
and Fisheries 1980).

The LCR supports extensive sport hunting and other wildlife-oriented recreation.
For example, an estimated 676,000 man-days were spent waterfowl hunting in the LCR
during the 1977-78 season (Louisiana Department of Wildlife and Fisheries 1978a), and
the 1980 demand for nonconsumptive wildlife-oriented recreation in the LCR was
projected at 1.14 million man-days (U.S Fish and Wildlife Service 1976).

MAGNITUDE OF WETLAND DETERIORATION IN COASTAL LOUISIANA

]rly studies by Gagliano and van Beek (1970) documented a net annual land loss
42.7 km (16.5 mi ) in the LCR. This estimate was based on a comparison of

Ear
rate of k^.i Km- \\b.o mi-; in rne ll,k. mis esTimare was Dasea on a compar
maps covering the periods 1931-42 and 1 948-67. Recent studies of wetland loss have been
conducted in the chenier plain ecosystem of southwest Louisiana and southeast Texas
(Gosselink et al. 1979). Based on these studies, it was estimated that approximately
1,800 ha (4,400 acres)/yr of marsh were converted to open water, spoil deposits, or
agricultural or urban uses between 1952 and 1974 in the Louisiana portion of the chenier
plain. A recent study (Wicker 1980) of the Mississippi Deltaic Plain Region (MDPR)
conducted for the Fish and Wildlife Service's National Coastal Ecosystems Team and the
U.S. Bureau of Land Management produced dramatic results. Data obtained from
planimetering habitat maps prepared for this study revealed that approximately 188,000
ha (465,500 acres) of coastal marsh were lost in the Louisiana portion of the MDPR
betweeri 1955-56 and 1978, for an annual loss rate of about 8,300 ha (20,600 acres) or
32.3 mi^/yr. Combining this estimate with the estimated marsh loss rate of 1,800 ha
(4,400 acres)/yr in the chenier plain, it is estimated that the marshes of the entire LCR
are being lost at an approximate rate of 10,000 ha (25,000 acres)/yr or 100 km^(39
mi )/yr. This is more than twice the rate of 42.7 km^ (16.5 mi^)/yr reported by Gagliano
and van Beek (1970).

CAUSES OF WETLAND DETERIORATION

Wetland deterioration in the LCR is attributed to land loss and salt water
intrusion. According to Craig et al. (1979) land loss in the LCR results from an
interaction of natural and man-induced impacts. Natural land loss occurs through
subsidence, compaction, and erosion of the substrate following cessation of active deltaic
deposition (Morgan 1973). Barrier islands and tidal inlets buffer coastal marshes from
storm energy and regulate salinities. The erosion of barrier islands and widening of tidal
inlets have also been identified as causes of land loss (Craig et al. 1979). Numerous
man-induced alterations have accelerated natural wetland loss. Federally financed

101

navigation channels, mainline Mississippi River levees, and upstreann diversions and flood
control reservoirs have virtually eliminated overbank flooding along the lower Mississippi
River. Consequently, most of the riverborne sediments ore being transported past
formerly active deltas and into the deeper Gulf of Mexico (Gagliano and van Beek
1970). This loss of sediment input has, except in Atchafalaya Bay, prevented large-scale
delta building, and has accelerated subsidence and erosion of existing marshes. Other
human causes of wetland loss include canal dredging and associated spoil disposal and
drainage of wetlands for agricultural purposes (Gagliano 1973). Gagliano (1973)
attributed approximately 25% of the total land loss in coastal Louisiana during the
previous 30 years to oil and gas industry dredging.

Saltwater intrusion, another major cause of wetland deterioration, is occurring in
many areas of the LCR. Saltwater intrusion has wide-ranging adverse effects, such as
allowing encroachment of the predaceous southern oyster drill (Thais haemastoma) onto
productive oyster reefs and conversion of fresher marshes to more saline types or to open
water.

FISH AND WILDLIFE IMPLICATIONS OF WETLAND DETERIORATION

Fisheries

The marshes of the LCR are extremely important to the maintenance of its
estuarine-dependent sport and commerical fisheries. These wetlands produce vast
amounts of organic detritus, an important trophic component of estuarine fish and
shellfish productivity. The marshes and associated shallow waters of the LCR are also
important as nursery habitat for many estuarine-dependent species. This importance has
been documented by numerous authors, such as Herke (1971), White and Boudreaux
(1977), Rogers (1979), and Chambers (1980). There is growing evidence that the amount
of marsh is the most important factor influencing estuarine-dependent fishery
production. Turner (1979) reported that Louisiana's commercial inshore shrimp catch is
directly proportional to the area of intertidal vegetation, and that the area of estuarine
water does not seem to be directly associated with shrimp yields. He further noted that
the loss of wetlands in Louisiana has a direct negative effect on fisheries. Although the
effects are masked by large annual variations in yield, wetland losses in the LCR
reported by Craig et al. (1979) are equivalent to 2.86 million km^ (6.31 million lb) of
shrimp harvest "lost" over the past 20 years (Turner 1979). Lindall et al. (1972) presented
evidence that shrimp and menhaden are being harvested at or near maximum substainable
yield. These species accounted for nearly 99 percent of the total volume of Louisiana's
commerical fish and shellfish landings in 1976. Further evidence that this is occurring
was presented by Harris (1973), who noted that any substantial decreases in marsh
habitat will result in decreased estuarine-dependent fishery production. An analysis of
the dependence of menhaden catch on wetlands in the LCR was conducted by Cavit
(1979). The findings of this analysis suggest that menhaden yields are greatest in those
LCR estuarine basins having the highest ratio of marsh to open water. Based on the
evidence cited above, continued wetland loss in the LCR could lead to serious declines in
its estuarine-dependent fishery.

Wildlife

Wildlife dependent on the LCR marshes face serious habitat declines as a result of
future land loss and saltwater intrusion. Losses of fresh to intermediate marsh or

102

conversion of these wetlands to more saline types will adversely affect nnigratory puddle
ducks, OS relative abundance of these waterfowl in the LCR is highest in the fresher
marsh types (Palmisano 1973). Based on rather conservative projections of declines in
habitat quality and abundance in the LCR, it has been estimated that demand for
waterfowl hunting will exceed available supply by 454,000 man-days by the year 2020
(U.S. Fish and Wildlife Service 1976). Habitat quality and quantity for other marsh birds
such as rails, gallinules, American coot, and various wading birds will also be reduced by
continued wetland deterioration. Nutria comprised roughly 70% of Louisiana's total fur
harvest between 1970 and 1975 (O'Neil and Linscombe 1975). Nutria catch per acre is
highest in fresh marsh, declining progressively in the intermediate, brackish, and saline
marsh types (Palmisano 1973).

Alligator populations also reached peak levels in fresh to intermediate marshes
(McNease and Joanen 1978). Accordingly, continued wetland deterioration can be
expected to result in declines in fur harvest and alligator populations, especially as land
loss and saltwater intrusion reduce fresher marsh acreage.

DISCUSSION OF MEASURES TO REDUCE WETLAND DETERIORATION

Except for regulation of development, the primary measures investigated to date
for control of wetland deterioration in the LCR have involved diversion of Mississippi
River water into adjacent marshes and estuarine areas for salinity control and creation
of new subdeltas. A plan for introduction of Mississippi River water into the subdelta
marshes of southeast Louisiana was submitted by the Fish and Wildlife Service to the
U.S. Army Corps of Engineers in 1959 (U.S. Fish and Wildlife Service 1959). This plan
included a recommendation for the construction of four water control structures, having
a combined discharge capacity of 620 m-^/sec (24,000 cfs), to divert Mississippi River
water for salinity control. The structures would have benefited an estimated 107,000 ha
(264,500 acres) of marsh and estuarine waters. The annual benefits of this plan in
increased oyster yields, furbearer harvest, and waterfowl utilization were estimated at
$841,600, exceeding costs by 62%. That plan, now known as the "Mississippi Delta
Region, Louisiana" project, was authorized by Public Law 89-298 on 27 October 1965.
Detailed planning of one of the four authorized diversion structures was initiated in 1969,
but was suspended when local interests failed to furnish economic justification for their
requested change in the location of that structure (U.S. Army Corps of Engineers 1975).
It should be noted that, despite the obvious need for the project to mitigate the adverse
effects of the Mississippi River mainline levees, the project is classified as
"enhancement", making local Interests responsible for 25% of the project costs. This has
been cited by local interests as one reason for their reluctance to participate in the
project. Now there is renewed local Interest, however, in one of the four diversion
structures (Caernarvon site), and a new letter of assurance is reportedly forthcoming
from the State of Louisiana to the Corps of Engineers indicating a willingness to assume
25% of the project cost. The most comprehensive treatment of measures for arresting
land loss and saltwater intrusion in the LCR is contained In a report prepared by Gagliano
et al. (1973b) under contract to the U.S. Army Corps of Engineers. That study was
conducted in conjunction with a broad evaluation of the LCR by on ad hoc interagency
group and evaluated two primary measures for addressing wetland deterioration,
including:

(I) controlled introduction of Mississippi River water into adjacent estuarine
marshes and bays for salinity control and nutrient input; and

103

(2) creation of subdeltas along the lower Mississippi River through controlled
freshwater diversion into adjacent shallow bays.

A multi-use monagennent plan for south-central Louisiana was subsequently
developed (Gagliano et al. 1973a). This plan recommended certain developmental
controls, management and maintenance of barrier islands, erosion control, and surface
water management of existing runoff surpluses and controlled subdelta building with
diverted Mississippi River water and sediments.

Despite the virtually universal recognition of the seriousness of the wetland
deterioration problem in the LCR and the existence of plans to address that problem, no
major federally financed measures have been implemented. Two ongoing Federal water
resource studies being conducted under the leadership of the U.S. Army Corps of
Engineers offer considerable promise, however, for large-scale supplemental freshwater
introduction into the subdelta marshes of the LCR. These include the Louisiana Coastal
Area Study and Mississippi and Louisiana Estuarine Areas Study. With regard to the
latter study, preliminary estimates by the U.S. Fish and Wildlife Service indicate that
between $4.4 and $5.2 million in annual benefits to fish and wildlife can be realized with
a single large-scale diversion into the Lake Pontchartrain-Lake Borgne area of southeast
Louisiana (Fruge and Ruelle 1980).

In 1979, the Louisiana Legislature enacted legislation directing the Secretary of the
Louisiana Department of Transportation and Development to prepare a freshwater
diversion plan for Louisiana. Components of that plan are being formulated and are
expected to complement any freshwater introduction measures implemented by Federal
agencies. More recently, Louisiana Governor Dave Treen signed legislation providing $35
million for studies and projects to address coastal erosion problems. The funding will be
obtained from the newly designated Coastal Environmental Protection Trust Fund. It is
anticipated that a portion of these funds will be expended on marsh restoration measures
such as freshwater diversion projects.

It is clear that the important fish and wildlife resources of the LCR are threatened
by rapid, continued degradation of its wetland habitat through land loss and saltwater
intrusion. This problem is widely recognized by natural resource managers, scientists,
and the public at large, and positive measures have been proposed to address it.
Definitive action must be taken, however, to implement these measures at the earliest
possible date.

LITERATURE CITED

Bellrose, F.C. 1976. Ducks, geese and swans of North America. A Wildlife Management
Institute book sponsored jointly with Illinois Natural History Survey. Stackpole Books,
Harrisburg, Pa.

Ccvlt, M.H. 1979. Dependence of menhaden catch on wetland habitats: a statistical
analysis. Unpublished report submitted to U.S. Fish and Wildlife Service, Ecological
Services Field Office, Lafayette, La. U.S. Fish and Wildlife Service, Office of
Biological Services, National Coastal Ecosystems Team, NSTL Station, Miss. 12 pp.

104

Chabreck, R.H. 1972. Vegetation, water and soil characteristics of tPie Louisiana
coastal region. La. Agric. Exp. Stn. Bull. 664 72 pp.

Chombers, D.G. 1980. An analysis of nekton communities in the Upper Barataric Basin,
Louisiana. M.S. Thesis. Louisiana State Univ., Baton Rouge. 286 pp.

Craig, N.J., R.E. Turner, and J.W. Day, Jr. 1979. Land loss in coastal Louisiana. Pages
227-254 ]n J.W. Day, Jr., D.D. Culley, Jr., R.E. Turner, and A.J. Mumphrey, Jr., eds.
Proceedings of the Third Coastal Marsh and Estuary Management Symposium.
Louisiana State Univ., Div. of Continuing Education, Baton Rouge.

Fruge, D.W, and R. Ruelle. 1980. Mississippi and Louisiana estuarine areas study. A
planning-aid report submitted to the U.S. Army Corps of Engineers, New Orleans
District, New Orleans, Louisiana. U.S. Fish and Wildlife Service, Division of
Ecological Services, Lafayette, La. 86 pp.

Gagliano, S.M. 1973. Canals, dredging, and land reclamation in the Louisiana coastal
zone. Louisiana State Univ., Center for Wetland Resources, Baton Rouge. Hydrologic
and Geologic Studies of Coastal Louisiana. Rep. 14. 104 pp.

Gagliano, S.M., P. Culley, D.W. Earle, Jr., P. King, C. Latiolais, P. Light, A. Rowland, R.
Shiemon, and J. L. van Beek. 1973a. Environmental altas and multiuse management
plan for south-central Louisiana, Vol. I. Louisiana State Univ., Center for Wetland
Resources, Baton Rouge. Hydrologic and Geologic Studies of Coastal Louisiana. Rep.
18. 132 pp.

Gagliano, S.M., P. Light, and R.E. Becker. 1973b. Controlled diversions in the
Mississippi delta system: an approach to environmental management. Louisiana State
Univ., Center for Wetland Resources, Baton Rouge. Hydrologic and Geologic Studies
of Coastal Louisiana. Rep. 8. 146 pp.

Gagliano, S.M., and J.L. van Beek. 1970. Geologic and geomorphic aspects of deltaic
processes, Mississippi delta system. Louisiana State Univ., Center for Wetland
Resources, Baton Rouge. Hydrolgoic and Geologic Studies of Coastal Louisiana. Rep.
I. 140 pp.

Gosselink, J.G., C.L. Cordes, and J.W. Parsons. 1979. An ecological characterization
study of the Chenier Plain coastal ecosystem of Louisiana and Texas. U.S. Fish and
Wildlife Service, Office of Biological Services. 3 vol. FWS/OBS-78/9 through 78/1 1.

Harris, A.H. 1973 Louisiana estuarine dependent commercial fishery production and
values (regional summary WRPA-9 and WRPA-IO analysis of production and habitat
requirements). Report prepared for U.S. Department of Commerce, National Marine
Fisheries Service, Water Resources Division. St. Petersburg, Florida. 36 pp.

Herke, W.H. 1971. Use of natural, and semi-impounded, Louisiana tidal marshes as
nurseries for fishes and crustaceans. Ph. D. Dissertation. Louisiana State Univ., Baton
Rouge. 264 pp.

Lindall, W.N., Jr., J.R. Hall, J.E. Sykes, and E.L, Arnold, Jr. 1972. Louisiana coastal
zone: analysis of resources and resource development needs in connection with
estuarine ecology. Section 10 and I3~fishery resources and their needs. Prepared for

105

U.S. Department of the Army, New Orleans district, Corps of Engineers, Contract 14-
17-002-430. National Marine Fisheries Service Biological Laboratory, St. Petersburg
Beach, Fla. 323 pp.

Louisiana Department of Wildlife and Fisheries. 1978a. 1977-1978 waterfowl survey.
Baton Rouge. 1 2 pp.

Louisiana Department of Wildlife and Fisheries. 1978b. Wildlife resources of
Louisiana. Wildl. Educ. Bull. 93. Baton Rouge. 34 pp.

Louisiana Department of Wildlife and Fisheries. 1980. News release 80-48. 8 August.

Lowery, G.H., Jr. 1974. Fur in Louisiana. Pages 21-45 in The mammals of Louisiana and
its adjacent waters. Louisiana State Univ. Press, Baton Rouge.

McNease, L., and T. Joanen. 1978. Distribution and relative abundance of the alligator
in Louisiana coastal marshes. Proc. Annu. Conf. Southeast. Assoc. Fish and Wildl.
Agencies. 32:182-186.

Morgan, J. P. 1973. Impact of subsidence and erosion on Louisiana coastal marshes and
estuaries. Pages 217-233 |n R.H. Chabreck, ed. Proceedings of the Second Coastal
Marsh and Estuary Management Symposium. Louisiana State Univ., Div. of Continuing
Education, Baton Rouge.

National Marine Fisheries Service. 1979. Fisheries of the United States, 1978. Curr.
Fish. Stat. 7800. NOAA-S/T 79-183.

O'Neil, T., and G. Linscomb. 1975. The fur animals, the alligator, and the fur industry in
Louisiana. Louisiana Wildlife and Fisheries Commission, New Orleans. Wild. Educ.
Bull. 106. G6 pp.

Palmisano, A.W. 1973. Habitat preference of waterfowl and fur animals in the northern
gulf coast marshes. Pages 163-190 |n R.H. Chabreck, ed. Proceedings of the Second
Coastal Marsh and Estuary Management Symposium. Louisiana State Univ., Div. of
Continuing Education, Baton Rouge.

Portnoy, J.W. 1977. Nesting colonies of seabirds and wading birds—coastal Louisiana,
Mississippi, and Alabama. U.S. Fish and Wildlife Service, Biological Services
Program. FWS/OBS-77/07. 126 pp.

Rogers, B.D. 1979. The spatial and temporal distribution of Atlantic croaker,
Micropogon undulatus, and spot, Leiostomus xanthurus, in the upper drainage basin of
Barataria Bay, Louisiana. M.S. Thesis. Louisiana State Univ., Baton Rouge. 96 pp.

Turner, R.E. 1979. Louisiana's coastal fisheries and changing environmental conditions.
Pages 363-370 ]n J.W. Day, Jr., D.D. Culley, Jr., R.E. Turner, and A.J. Mumphrey, Jr.,
eds. Proceedings of the Third Coastal Marsh and Estuary Management Symposium.
Louisiana State Univ., Div. of Continuing Education, Baton Rouge.

U.S. Army Engineer District, Corps of Engineers, New Orleans, Louisiana. 1975.
Mississippi Delta Region Salinity Control Structure, Louisiana, condition of
improvement, 30 June 1975. Page 3-I7A jn Project maps, vol. 2: Flood control,
Mississippi River and tributaries.

106

U.S. Fish and Wildlife Service. 1959. A plan for freshwater introduction from the
Mississippi River into sub-delta marshes below New Orleans, Louisiana, as part of the
Mississippi River and Tributaries Review. U.S. Fish and Wildlife Service, Division of
Ecological Services, Lafayette, La. 48 pp.

U.S. Fish and Wildlife Service. 1971. Fur catch in the United States, 1970. Wild. Leaf!.
499. Washington, D.C. 4 pp.

U.S. Fish and Wildlife Service. 1976. Fish and wildlife study of the Louisiana coastal
area and the Atchafalaya Basin Floodway. Appendix D., part 3: sport fish and wildlife
harvest. U.S. Fish and Wildlife Service, Division of Ecological Services, Lafayette,
La. 61 pp. Unpublished.

U.S. Fish and Wildlife Service. 1977. 1975 National survey of hunting, fishing and
wildlife associated recreation. Washington, D.C. 91 pp.

White, C.J., and C.J. Boudreaux. 1977. Development of an areal management concept
for gulf penaeld shrimp. Louisiana Wildlife and Fisheries Commission, Oysters, Water
Bottoms and Seafoods Division, Tech. Bull. 22. New Orleans. 77 pp.

Wicker, K.M. 1980. Mississippi Deltaic Plain Region ecological characterization: a
habitat mapping study. A user's guide to the habitat maps. U.S Fish and Wildlife
Service, Office of Biological Services. FWS/OBS-79/07.

107

SOME CONSEQUENCES OF WETLAND MODIFICATION
TO LOUISIANA'S FISHERIES

Barney Barrett

Louisiana Department of Wildlife and Fisheries

Box 14526

Baton Rouge, LA 70898

ABSTRACT

Agencies of State and Federal Governments as well as local interests have long
recognized that Louisiana's wetlands are undergoing adverse ecological changes. These
changes are the result of both natural processes and the works of man.

The dominant ecological change taking place in the coastal area is habitat
alteration— wetlands are eroded and replaced by water. Now there are many proposals to
reduce erosion rates which include freshwater introduction, jetties, and additional
restrictions on activities.

Freshwater introduction may be the most efficient means of reducing land loss
rates. Fresh water, particularly from the Mississippi River, would reduce saltwater
intrusion and contribute nutrients and sediments to the estuaries and wetlands. Changes
in water regimes, however, could drastically alter animal populations as occurred in
Sabine Lake. The water cycle was changed by the construction of the Toledo Bend
reservoir and dam which resulted in a drastic reduction in shrimp harvest in this lake.

RECOGNITION OF THE PROBLEM

We are not just learning about land loss. There was a realization that flood control
projects on the lower Mississippi River were causing adverse ecological changes prior to
oil and gas activity in south Louisiana. With the leveeing of the Mississippi River along
with industrial development and its accompanying channelization and dredging, the
problem was intensified and the rate of habitat destruction increased.

The Louisiana Wildlife and Fisheries Commission and its predecessors, as well as
the affected parishes and other local interests, have recommended repeatedly, since as
early as 1900, that Mississippi River water be directed into adjacent subdelta marshes to
maintain habitat.

U.S. Fish and Wildlife Service (1959) stated "Loss of fertility, formerly maintained
at a high level by overflow water from the Mississippi River is reducing the value of the
subdelta marshes as nursery and rearing grounds for all fish and wildlife forms". These
observations made 22 years ago remain true today.

The problem of land loss is much more serious today because of the rate of loss now

108

taking place— 10,205 ha (25,216 acres) per year according to Gagliano (1981). The actual
rate of habitat loss may be greater than these calculations indicate, as these figures may
not include wetlands removed from their historic use because of drain and fill activities,
and it may not include vast areas surrounded by hurricane protection levees, road beds or
other structures which essentially block off or disrupt drainage patterns. This separation
of wetlands inhibits the flow of nutrients and aquatic life from one system to another
end, therefore, that area of marsh is lost for any significant contribution to fishery
production. Additionally, the land loss rates do not include areas which cannot be
exploited for living resources because of pollution. For instance, the State Health
Department prohibits the harvest of oysters east of the Mississippi River in areas which
are exposed directly to Mississippi River waters from siphons and other water control
structures.

Society is irreversibly committed to the protection of life and property by
maintaining levees along the Mississippi and other rivers. Therefore, efforts to build new
lands are basically limited to controlled freshwater introduction from the rivers at
selected sites. The overall effects need to be carefully projected and evaluated in
advance because such effects could be more damaging than beneficial. Even if the rivers
were allowed to seek natural courses, the present sediment load would not be adequate to
compensate for land loss rates due to the trapping of sediments by impoundments
upstream. It required approximately 6,000 years to form Louisiana's coastal area by
natural processes. If the present coastal area is considered to be 2,400,000 ha (6,000,000
acres) of land and shallow water bodies then the accretion rate for the past 6,000 years
was 400 ha (1,000 acres) per year. We are presently losing coastal wetlands at the rate
of 10,205 ha per year (Gagliano 1981). Therefore, natural accretion rates would not be
adequate to maintain our coastal area. It is obviously misleading to calculate accretion
rates over a 6,000-year period, but any way the numbers game is played, the task of
appreciably reducing present land loss rates is monumental.

In addition to having only limited resources to build new land, we are also limited in
protecting existing wetlands as many of the forces and processes which reduce the
coastal land area are not presently controllable. The freeze of 1961-62 resulted in the
destruction of the black mangroves, large fish kills, reduced oyster harvest, and the 1962
shrimp harvest was one of the lowest of record. The impact of this freeze, which formed
ice in the lower part of Barataria Bay, was short-lived on the animal population. It took
approximately 7 years for the black mangroves to come back, however. These mangroves
are important to the area as they reduce erosion and aid in land building by trapping
sediments in their root systems. The passage of hurricane "Betsy" in 1965 resulted in the
immediate loss of entire islands and caused hundreds of feet of coastline and shoreline
recession. Uncontrollable natural subsidence also is a major factor in land loss. To a
limited extent, subsidence due to mineral extraction is controllable.

FISHERIES MANAGEMENT OPTIONS

Any proposed use of large amounts of river water for land building should be
carefully considered. The reduction of the discharge of fresh water at the river mouth
may affect biological processes in the adjacent estuaries and the nearshore Gulf of
Mexico. Spawning and migration patterns may be severely impacted if the flow of the
river is altered.

Fishermen should take an interest in efforts to maintain our coast as the industry

109

cannot long survive at the present land loss rate. Additionally, the fishing industry may
be damaged by measures taken to reduce this rate.

Saltwater intrusion, as a result of reducing the discharge of fresh water, can
severely affect shrimp production. Reduction of the brackish zone limits the shelter and
food available to maturing shrimp. The increase in estuarine salinities as a result of land
loss and concomitant saltwater intrusion may increase shrimp harvest over a short period
because of enlarged nursery grounds (Barrett 1975). A point will be reached, however,
when there are no longer enough marshes to nourish the historic nursery grounds; then,
shrimp harvest will decline permanently.

As 75 to 85 percent of the species of fishes and macroinvertebrates inhabiting our
coastal areas are estuarine dependent, changes in our estuaries, such as salinity increases
and loss of detritus from marsh reduction, would damage these stocks.

A case in point is the effect of the Toledo Bend Reservoir on the marine animal
communities in Sabine Lake (Whitehead and Perret 1974). Seasonal pulses of fresh water
into this lake prior to flow control consisted of high discharges during early spring and
low discharges during the summer. This water cycle is normal for Louisiana streams, and
apparently ideal for shrimp and other marine species. Since 1967, high freshwater
discharges into Sabine Lake occur throughout the summer as a result of control structure
operation. The impact of this change in water cycles has been dramatic on shrimp
production in this lake. Prior to 1967, annual shrimp catches in Sabine Lake were as
large as 385,000 kg (850,000 lb). Since 1967, annual shrimp catches in the lake were
31,000 kg (67,000 lb) with an average annual catch of 9,000 kg (20,000 lb) between 1967
and 1977.

Oyster populations are reduced as higher salinities resulting from coastal erosion
allow inhabitation by predators and pathogens. An instance which demonstrated the
advantages of freshwater introduction to oyster production was reported by the Louisiana
Wildlife and Fisheries Commission (I960). The Bayou Lamoque structure, which was
completed in 1956 for the purpose of improving oyster habitat east of the Mississippi
River, discharged 6 X 10° m^ (500,000 acre-feet) of river water into the adjacent
marshes in 1957. Following this discharge, oyster yields increased about 100% and
survival of young oysters improved because of a reduction in predators and pathogens and
an increase in nutrients.

Many of the uses of our marshes result in impacts which physically destroy and
reduce the quality of these marshes. Users of the marshes are regulated by licenses and
permits, however, the rate of land loss with its related adverse effects on animals and
habitats continues to increase.

Management of an animal population is an effective tool for preserving end
propagating fish and wildlife— for example, the alligator has now been taken off the
endangered species list in Louisiana. Years ago the alligator was becoming endangered
primarily because of overhunting. Laws were then enacted which prohibited the taking
of alligators. During the period that these animals were protected, populations
increased. The protection of animals can easily be accomplished by establishing seasons,
bag limits and methods of kill.

The habitat of the various animals using the marshes and estuaries is not well
protected; habitat maintenance is as important to the survival and well being of fish and

110

wildlife as hunting and fishing regulations. Sea turtles are endangered primarily because
of habitat loss and predation on eggs and young. The brown pelican population was
eliminated locally because of the poor quality of habitat and the accumulated presence
of pesticides in its foods. The fisherman, trapper, and hunter are subjected to
enforceable regulations and limits. These regulations and limits are changed frequently
to accommodate changes in animal population. We do not have adequate regulations for
habitat preservation. Discharges of pollutants into coastal waters are generally policed
by the industry; requirements for dredging activities are difficult to enforce; and
apparently many dredging permits have been approved with little modification.

There is a pressing need to begin activities which would reduce land loss rates. In
our haste to reduce these rates, however, we should be very careful to not duplicate the
impact which occurred in Sabine Lake as a result of changes in the water regime.
Although efforts to reduce land loss rates will be expensive, the loss of 10,209 ha (25,216
acres) during the next 12 months will result in the loss of millions of dollars to the State
and its citizens. A stepwise approach should include measures to stabilize or retard
erosion initially in critical areas while carefully planning future development. All phases
should be approached on on interdisciplinary basis to utilize the best possible expertise to
achieve the desired results, both short- and long-term.

LITERATURE CITED

Barrett, B.B. 1975. Environmental conditions relative to shrimp production in coastal
Louisiana. La. Dep. Wildl. Fish. Tech. Bull. 15.22 pp.

Gagliano, S.M. 1981. Special report on marsh deterioration and land loss in the deltaic
plain of coastal Louisiana. Presented to Frank Ashby, Secretary, Louisiana
Department Natural Resources and Jesse Guidry, Secretary Louisiana Department
Wildlife and Fisheries. Coastal Environments, Inc. Baton Rouge, La. 13 pp.

Louisiana Wildlife and Fisheries Commission. I960. Eighth biennial report Louisiana
Wildlife and Fisheries Commission 1958-1959. Louisiana Wildlife and Fish.
Commission, Div. of Education and Publication. New Orleans.

U.S. Fish and Wildlife Service. 1959. A plan for freshwater introduction into sub-delta
marshes below New Orleans, Louisiana as part of the Mississippi River and Tributaries
Review. U.S. Fish and Wildlife Service, Division of Ecological Services, Lafayette,
La. (>(i pp.

Whitehead, C.J., and W.S. Perret. 1974. Short term effects of the Toledo Bend project
on Sabine Lake, Louisiana. Proc. Annu. Conf. Southeast Assoc. Game Fish Comm.
27:710-721.

Ill

WETLAND LOSSES AND COASTAL FISHERIES:
AN ENIGMATIC AND ECONOMICALLY SIGNIFICANT DEPENDENCY

R. Eugene Turner

Center for Wetland Resources

Louisiana State University

Baton Rouge, LA 70803

ABSTRACT

Louisiana's coastal fishing industry landings are limited by the area of coastal
wetlands, not open water. The relationship is not sufficiently understood, but is
demonstrable through the life history patterns of all the commercially important species,
organism density in the vicinity of altered and natural wetland-water edges, experiments
in predation, and correlation analysis of landings data and wetland quantity and quality.
The management implications are that wetland area should be conserved in order to
maximize for the largest potential fisheries yields. The impact of previous wetland
losses are not well documented because of lack of good landings data that accounts for
both year-to-year environmental influences and a changing fishing effort. At a projected
1% wetland loss rate over the next 20 years, the commerical fishing industry will
experience a potential one billion dollar loss spread throughout the industry (exclusive of
the recreational value). Thus with a mere 10% reduction in the present loss rates, the
annual savings would be 5 million dollars.

CORRELATION OF FISHERIES AND WETLANDS

Across the broad geographic perspective of coastal environments it seems quite
clear that where wetlands and estuaries are large in area there are likely to be
substantial fishing industries nearby. To be sure, many fishing operations are nowhere
near wetlands, for example, the tuna and anchovy fisheries; but it is generally true that
if one can find a good-sized coastal wetland-estuary on the map and a suitable harbour
nearby that there is commerce in locally-caught fish and invertebrates.

This correlation is easily shown with species such as penaeid shrimp whose
worldwide price is stable and high. Within an area, such as Louisiana, coastal wetland
area is directly correlated with the commerical landings of shrimp caught in inshore
waters (Figure I). Since the annual inshore catch is a fairly uniform percentage of the
total annual catch, the relationship is true for all landings vs. wetland area in Louisiana.
Worldwide, the weight caught per area wetland does vary within the geographic limits of
distribution of penaeids (Figure 2). We might show similar graphs for blue crab landings
(Turner and West, unpublished) or, if we had the landings data, for many species whose
life history involved a period of migration between coastal wetlands and open water. The
relationship between landings and open water, in contrast, is not a statistically
significant one, though it appears to be negative (Turner 1977). Furthermore, for shrimp,
at least, it is also true that the species of shrimp landed is directly related to the kinds
of vegetation present in the estuary. Brown shrimp in Louisiana, for example, are

112

O)
CO

250

500

10^ ha

Figure 1. The relationship between the area of wetland vegetation in each
hydrologic unit in south Louisiana and the commercial yields of shrimp
caught therein (adapted from Turner 1977).

1000

100

<
I

Coeficient of Determination (R^) - 0.54

_,„ -.07(x)
y-1 57e ' '

20
LATITUDE

Figure 2. The relationship between the yield of penaeid shrimp per area
of coastal vegetation (kg/hectare) and latitude. Only commercial quanti-
ties were evaluated; the areas are for states in the U.S. and various
countries throughout the world (adapted from Turner 1977).

113

100

liJ

Q-co 80
SZ

I*"
c/)0 60

8^20

UJ<

0 10 20 30 40 50

PERCENT SALINE PLANT COVER

IN EACH HYDROLOGICALUNIT

Figure 3. The relationship between the percent of brown shrimp caught in
Louisiana's coastal hydrologic units and the type of vegetation in that
unit (adapted from Turner 1977).

prevalent where saline wetland vegetation is proportionally high (Figure 3). In summary,
then, a coastal fisheries species whose life cycle involves use of the estuary for the
juveniles is considered estuarine-dependent; in Louisiana this amounts to essentially all
of the landings (McHugh 1966; Chambers 1980). The area of wetlands, not that of open
water, seems to be the factor limiting the local species abundance.

Coastal wetlands are very productive ecosystems as a result of abundant water,
nutrient supplies, and tidal flushing. In comparing animal production in various
ecosystems, where plant production is high, animal production is generally also high
(Table I). The greater grazing efficiency in aquatic ecosystems further increases animal
production relative to plant production. In wetlands, the percent consumption of plant
matter by animals averages 8% and is similar to that of animals in most terrestrial
systems. The renewal of animal biomass is twice annually. The net result is that
wetlands are excellent natural protein "factories" (Turner 1982).

Attempts to distinguish between animal production in "wet" land and that in the
overlying water are problematical, since wetlands are, by definition, dependent on the
hydrological regime for the maintenance of ecosystem integrity. Sediments, nutrients,
and gases move from wetland to water and back again in very complex ways, which we
are only now beginning to describe in detail (e.g. Pomeroy and Wiegert 1981). Our
terrestrial experience in desert, forest, and grassland ecosystems has often led us to
assume conveniently (and erroneously) that, in wetlands, water is also functionally

114

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115

distinct from land. This assumption has resulted in confusion, for example, about
whether some aquatic animals are actually wetland-dependent and, therefore, should be
included in estimates of wetland animal production, though they live primarily in the
open water. There is little dispute on this point if the animal lives, feeds, and reproduces
within wetlands. But what about the temporary resident, the migrating waterfowl
arriving in south Louisiana from Canada? What about the larval fish and shrimp, which
are spawned offshore and enter the estuary to live for only a tenth of their life cycle?
Fish, birds, and some invertebrates make long and involved migrations between feeding
ground and "nursery area". Penaeid shrimp spawn in deep oceanic zones, and may arrive
simultaneously with waterfowl in coastal wetlands to grow. River prawns of southeast
Asia move downstream to estuaries to spawn. In South America some fish move both
upstream and downstream to wetlands during their life cycle (Welcomme 1979). A
common denominator of these life history patterns is the considerable distance between
the habitat where the adults feed and the wetland where they began life or spent the
critical early stages of it.

This nursery value of wetlands is a result of both the food found there and the
refuge value it affords prey. Wetland "edge" is an important locus for both functions.
The organic content of sediment adjacent to a natural marsh and that of sediment
separated from the marsh by a bulkhead, or levee are compared in Figure 4. The edge
next to the marsh has a much greater organic content than the edge without a marsh, and
this is typical. The same author found higher animal densities within the natural edge
than in the edge altered by a levee (Figure 5).

Aquatic organisms suffer high predation when young. Wetland habitats limit the
access of larger predators simply because the zone is shallow. Prey species exploit the
micro-environment among the vegetation in order to avoid predators. Charnov et al.
(1976) conducted a simple experiment documenting this (Figure 6). When insect larvae
were placed in an aquarium together with a predator, they quickly hid in the darkened
corners. Wetlands are analogous to the corners of the aquarium: they provide both hiding
places and a source of food for larvae. Vince et al. (1976) documented a field example of
this for a temperate salt marsh. There the saltmarsh killifish, Fundulus heteroclitus,
preys upon two amphipods at the marsh/water interface. The dense, small stems provide
cover for the prey and reduce successful predation. As a consequence the size
distribution and abundance of the prey are directly dependent on the vegetation density.

Because of these strong relationships between wetlands and coastal fisheries
species, it is possible to predict adult abundances if the environmental conditions during
juvenile life stages are known. Mortality is proportionally greatest while the species is
small; thus the available potential value of wetland habitat is modified by annual
climatic changes, e.g., temperature, flooding, and salinity (Condrey 1979; Barrett 1975;
Turner 1979). Wetlands are productive, and the fisheries couplings with wetlands are
known to exist. The mechanism of the couplings are not clear, however; the animal's life
history is an expression of the evolutionary adaptation to an exploitable habitat, be it
edge, food or both.

CONSEQUENCES OF WETLANDS LOSS

For management purposes it is a lot to know that wetlands areas, not water surface
area, limits commerical fishing yields. Based on the available information one can firmly

116

LU
O

LU
O.

1001
80
60-^

40
20

NATURAL MARSH
note "edge effect "

TOTAL ORGANICS

80 ft.

B
ALTERED MARSH

TOTAL ORGANICS

80 ft.

DISTANCE FROM SHORE

Figure 4. Example of qualitative change in the land-water interface, with
and without wetlands (Mock 1967). The percent organic material in the
estuarine sediments immediately adjacent to a natural marsh (A) increased
peripheral to the marsh, whereas no such increase was found adjacent to an
altered marsh (B) which had an artificial levee between the normal low-water
line and the higher wetland.

<
oc

liJ 500
Q.

t-
liJ

^ 250
V)

895

UJ
CD

CONTROL ALTERED
SITE AREA

SHORE

50 ft. 100 ft.
OFFSHORE

LOCATION

Figure 5. Mean catch of juvenile shrimp per trawl sample at various dis-
tances from a wetland with and without an artificial levee (Mock 1967)

117

W 80

o
o

1 tt' t

\ i

\ 1

10 20

TIME imin.

Figure 6. Predator avoidance by mayfly nymphs, indicated by their distri-
bution in the corners of a chamber depending on whether a fish predator was
present (upper line) or absent (lower line) (Charnov et al . 1976). The
corners in these experiments are analagous to refuge provided by vegetation
within shallow wetland zones.

conclude that the present high coastal wetland losses in Louisiana will eventually
translate into a reduction in commercial and recreational fish yields. The natural
potential fish yields are decreasing, not increasing. This decline is not yet apparent in
the fisheries statistics of landings for at least two reasons. First, the annual variations
in landings are large in relation to the wetland loss rates. For example, the commercial
shrimp and blue crab fishing efforts have, at times, been steady from one year to the
next. The landings one year might be twice that of the next year, however. In
comparison the land loss rates, hence wetland loss rates, are about 1% annually over the
last 25 years (Wicker 1980). Secondly, fishing effort in Louisiana has increased
dramatically in the last 25 years. Double-rigged shrimp trawling was introduced in the
mid-1950's and not completely adopted by all the fleet for several more years. Larger
vessels with more horsepower have been added every year, and some industries, like the
menhaden industry, have added more fishing vessels (and spotter planes) almost
continuously throughout the I960's and I970's. The hidden, cumulative effect of land loss
on Louisiana's fisheries is distributed over a long period amongst many fisherman. With
the combination of increased fuel costs, inflation, and a now nearly full fishing industry,
the effects of land loss rates will be felt dramatically in the coming years; this will be
especially true as the loss rates continue to accelerate beyond 1% annually. Doi et al.
(1973) documented an example of the effects of coastal habitat losses on fisheries in the
Seto inland sea in Japan. As the area of intertidal land was lost to land reclamation, the
shrimp catches declined proportionately and sharply.

If we assume that a 1% decline in the potential fishery yield is equivalent to the 1%
per year wetland loss, then the cumulative loss in dockside dollar value over the next 20
years is equal to twice the present value ($190 million dollars in 1978) of the entire
commercial landings, or $380 million. At least 50% of this value is a result of the high

118

volume and price of the commercial shrimp harvest. Recreational catches are
considerable, but not included in this estimate. The actual total economic value is three
times higher than the dockside value as a result of value added during processing and
delivery (Jones et al. 1974). Thus over the next 20 years the present expected wetland
loss rate of at least 1% annually could result in a cumulative commercial fishing
economic loss of I.I billion dollars to Louisiana. A substantial proportion of the current
wetlands loss is a direct result of new human activities (Craig et al. 1980). If wetland
loss were reduced by only 10% over the next 20 years (an average 0.9% loss rate average)
the general savings in fishing catch value would be worth 5 million dollars annually, or a
total of 100 million dollars over the 20 years. Small percentage changes in large
numbers, when accumulated over two decades become a very significant number. It is a
number worth considering when the long-term benefits are weighed against the
immediate costs of a quick recovery of non-renewable resources. A small investment in
the future now may have potentially less painful consequences later.

ACKNOWLEDGMENT

This report is Publication CEL-SG-82-OIO of the Coastal Ecology Laboratory
Center for Wetland Resources, Louisiana State University.

LITERATURE CITED

Barrett, B.B. 1975. Environmental conditions relative to shrimp production in coastal
Louisiana. La. Dep. Wild. Fish. Tech. Bull. 15. 22 pp.

Chambers, D.G. 1980. An analysis of nekton communities in the upper Barataria Bay
Basin, Louisiana. M.S. Thesis. Louisiana State Univ., Baton Rouge. 286 pp.

Charnov, E.L., G.H. Orians, and K. Hyatt. 1976. Ecological implications of resource
depression. Am. Nat. 110:247-259.

Condrey, R.E. 1979. Draft environmental impact statement and fishery management
plan for the shrimp fishery of the Gulf of Mexico, United States waters. Louisiana
State Univ., Center for Wetland Resources, Baton Rouge.

Craig,N.J., R.E. Turner, and J.W. Day, Jr. 1980. Wetland losses and their consequence
in coastal Louisiana. Z. Geomorph. N.F. 34:255-241.

Doi, T., K. Okada, and K. Isibashi. 1973. Environmental assessment on survival of
Kuruma prawn, Penaeus japonicus, in tideland. I. Environmental conditions in Saizyo
tideland and selection of essential characteristics. Bull. Tokai Reg. Fish. Res. Lab.
76:37-52.

Jones, L.L., J.W. Adams, W.L. Griffin, and J. A. Allen. 1974. Impact of commercial
shrimp landings on the economy of Texas and coastal regions. Tex. Agric. Exp. Stn.
Publ. TAMU SG-75-204. 18pp.

McHugh, J.L. 1966. Management of estuarine fishes. Am. Fish. Soc. Spec. Publ. 3: 133-
154.

119

Mock, C.R. 1967. Natural and altered estuarine habitats of penaeid shrimp. Proc. Gulf
Caribb. Fish. Inst. 19:86-98.

Pomeroy, L.R., and R.G. Wiegert (eds.) 1981. The ecology of a salt marsh. Springer,
New York. 271 pp.

Turner, R.E. 1977. Intertidal vegetation and commercial yields of penaeid shrimp.
Trans. Am. Fish. Soc. 106:41 1-416.

Turner, R.E. 1979. Louisiana's fisheries and changing environmental conditions. Pages
363-370 jn J.W. Day, D.D. Culiey, R.E. Turner, and A.J. Mumphrey, eds. Proceedings
of the Third Coastal Marsh and Estuary Management Symposium. Div.of Continuing
Education, Louisiana State University, Baton Rouge, La.

Turner, R.E. 1982. Protein yields from wetlands. Pages 405-415 |n B. Copal, R.E.
Turner, R.G. Wetzel and D. F. Whigham, eds. Wetland ecology and management.
International Science Publishers, Jaipur, India.

Vince, S., I. Valiela, and N. Backus. 1976. Predation by the salt marsh killifish Fundulus
heteroclitus (I.) in relation to prey size and habitat structure: consequences for prey
distribution and abundance. J. Exp. Mar. Biol. Ecol. 23:255-266.

Welcomme, R.L. 1979. Fisheries of African floodplain rivers. Longman, New York. 318
pp.

Whittaker, R.H., and G.E. Likens. 1973. Carbon in the biota. Pages 281-300 jn G.M.
Woodwell and E.R. Pecan, eds. Carbon and the biosphere. USAEC Symp. Series No. 30.
Washington, D.C.

Wicker, K.M. 1980. Mississippi Deltaic Plain Region ecological characterizations: a
habitat mapping study. A user's guide to the habitat maps. U.S. Fish and Wildlife
Service, Office of Biological Services. FWS/OBS-79/07.

120

PANEL DISCUSSION

CONSEQUENCES: EFFECTS ON NATURAL RESOURCES PRODUCTION

James G. Gosselink, Moderator

Robert H. Chabreck, David W. Fruge, Barney Barrett,
R. Eugene Turner, Mike Voisin and John Teal, Panelists

James Gosselink: Let me ask Mr. Voisin and Dr. Teal if they have any comments before
we have a general discussion.

Mike Voisin: Do we want to maintain the coastal marshes as they were in 1940, 1950,
I960, 1970 or let them to continue to degrade before taking action? Being in the
oyster industry, I would hope we try to save them as they are today. We are very
satisfied with the existing conditions, even though we do have some problems.
Oyster fishermen were the first to feel the loss of marshes and barrier islands.
Oyster supplies dwindled in terms of catch per boat while the total catch remained
the some. In the I930's and I940's oysters were fished up to 10 to 15 miles offshore.
Oysters are dependent on brackish water of 5 to 15 ppt, but with salt water intrusion
oystering has moved inshore.

Oysters are good indicators of environmental quality; they don't move and they
can't lie. If we manage the environment to maintain oyster production, as it is today
we will also be preserving valuable coastal environments. As oyster production
moved inshore, the pollution of coastal waters with human wastes has moved down
toward the coast. The convergence of intruding salt water and the pollution line is
reducing available habitat for oyster production and harvest. Other problems facing
the oyster industry are oil company exploration, salt-dome leaching for petroleum
storage and the proposed Avoca Island levee extension, which would limit the
introduction of fresh water into the west Terrebonne marshes, one of the State's
leading oyster grounds. Production east of the Mississippi River is declining and
oyster growth rates have slowed there because of marsh deterioration. Production is
shifting to Terrebonne, Lafourche, Vermilion and Iberia parishes where the
Atchafalaya River supplies fresh water and nutrients. If we can save the oyster as it
is today, we will save the coast as it is today.

John Teal: In the over twenty years I have been a student of salt marsh ecology in
Georgia and New England, I have witnessed the evolution of research and
understanding and also the development of concern about the destruction of coastal
marshes. Louisiana has more marshes than any other state in the United States and
most of the problems associated with marshes. I won't say you also have most of the
understanding about how marshes work, but you obviously have a lot of it in
Louisiana. In New England the marshes are small and we can isolate inputs and
outputs and thus have advantages in some of the ways one can do research.

The general problems of wetland destruction and, in a broad sense, the
consequences to fish and wildlife are understood. The consequences of actions taken

121

to restore or protect wetlands and estuaries must be understood, consequently the
processes which support productivity must also be understood. Correlations between
wetland characteristics and natural resource production provide an indication of the
overall relationships, but more detailed information on actual processes is required.
This requires experimental approaches to marsh ecology. Improved cooperation
from fisherman and other natural resource harvesters, who are often reluctant to
provide detailed information on their harvests, offers the potential of extensive and
meaningful data if treated properly.

The changes in Louisiana's coastal environments provide an experiment on a
very large scale, which can provide insight to the relationship of wetlands and
natural resource production. If this can be combined with sufficient long-term
support of scientific enterprises to describe processes in detail, sound natural
resource management strategies may result.

James Gosselink: In the Calcasieu estuary where wetland loss has been rapid, inshore
shrimp yields have increased. How can this be interpreted?

Barney Barrett: Erosion and saltwater intrusion may in the short run increase shrimp
production by increasing the area of nursery grounds with salinity above 10 ppt.
Calcasieu Lake is somewhat saltier than it was years ago, but, as marsh habitat loss
proceeds, shrimp production will decline.

Eugene Turner: The inshore yield is a fairly constant proportion of the total catch
(including the offshore catch) on a statewide basis. Thus the inshore catch statistics
in the Calcasieu estuary are probably also representative of the contribution of the
estuary to the offshore catch. In the Calcasieu estuary, freshwater has been
diverted to rice fields, causing an increase in salinity, and consequently short-term
increases in shrimp yield. Fishing effort has also increased.

James Gosselink: Is fossil peat, released by wetland erosion, important as a food source?

Eugene Turner: Natural channels are continuously reworked and release peat. I do not
think that the accelerated wetland loss causes a great increase in peat released.

John Teal: Organic matter which accumulates in marsh sediments below the top few
millimeters is quite resistent to degradation and I doubt that it is an important food
source.

Donald Boesch: For particular important fishery species such as shrimp, we can relate
production to a number of variables, such as the area of saline marsh, the amount of
natural marsh edge, mixture of open water and marsh, and critical temperature
conditions. Do we satisfactorily know what these optimum conditions are for any
particular species? If not, what do we need to know?

Barney Barrett: The brackish zone of the marsh estuaries is being compressed and
reduced. This may result in a series of rather salty estuaries extending to the
Intracoastal Waterway and an abrupt transition to freshwater. The objective is to
maintain a broad brackish habitat rather than management for a particular fishery
species.

Donald Boesch: Limiting considerations to one species for the moment, couldn't the

122

shrimp nursey value of a system be enhanced by controlling salinity regime and
water-marsh edge habitat?

Eugene Turner: The issue is more complex than one salinity zone or the length of edge.
Conditions beneficial to brown shrimp may not be benefical to white shrimp, for
example.

Donald Landry: Shrimp production is not a function of the area of saline marsh but of
total estuarine area, which is a function of rainfall, riverflow, etc.

Barney Barrett: An area with a great amount of saline marsh and marsh edge may have
higher shrimp production than one with less, but there will be considerable year-to-
year fluctuatious due to rainfall, river discharge, temperature and the amount of
nursery area.

Eugene Turner: The long-term average is a function of nursery ground area, which is
wetlands, not open water ~ for brown shrimp it is saline marsh, for white shrimp it
is brackish and fresh marsh. On top of that, of course, there will be year to year
variation.

Mike Voisin: Because shrimp migrate and vary so much, oysters are a better gauge of
estuarine productivity.

DcxKild Boesch: The point of my original question is to lead to the question of how do we
manage the various hydrological units of coastal Louisiana for multi-species
production. In some large units (e.g. Terrebonne-Timbalier basin) we may be able to
maintain a range of conditions suitable for shrimp, oysters, etc. In smaller areas or
areas where freshwater input overwhelms tidal effects (e.g. Atchafalaya Bay) it may
be unrealistic to expect production of all these living resources. Should we have a
conscious strategy of managing these large systems with salinity gradients for
multiple resources and other systems for a single resource?

David Fruge: For managing large basins we should plan on freshwater diversion managed
to retard wetland loss, not necessarily change wetland types. We have also proposed
diversions along the lower Mississippi River to create new subdeltas and new marsh.

Donald Boesch: Then you would manage for maximum wetland vegetation rather than for
a particular harvestable resource?

David Fruge: The resources will occupy the niches that are provided for them.

Donald Boesch: You would like to manage for grass and Mike Voisin for oysters, that's
my point.

David Fruge: I believe controlled freshwater diversions can do both by promoting marsh
growth and protecting oysters from predators. The primary areas being considered
for diversions are at Caernarvon, upper Barataria Basin and subdeltas at the river
mouth. There isn't yet much opposition to these diversions. Perhaps an oyster
fisherman in the immediate vicinity of a diversion would lose production due to
pollution or the fresh water itself. Most management agencies, however, are
supporting freshwater diversion.

123

Mike Voisin: That's right, the biggest problem with freshwater diversion is with the
oyster industry. But the oyster industry is the best organized of the fishermen
groups. Oyster growers are for freshwater diversion in some situations and against
it in others. An oyster grower may have invested time and money or inherited a
lease and the Corps of Engineers might destroy it by opening up the Bonnet Carre
spillway or the Morganza spillway. The oyster fishermen are vocal and unified and
have more political impact than other fishermen groups.

Helen Kennedy: Couldn't the oyster fisherman just move his grounds farther from the
source of freshwater diversion as salinity shifts?

Mike Voisin: There are two oyster fisheries in Louisiana — a private fishery and a public
fishery. There are 800,000 acres set aside for the public fishery and 250,000 acres
of oyster grounds are privately leased. The leases do not shift with the salinity.

Wendili Curole: The main problems confronting freshwater diversion are economic and
social. There are relatively few areas where freshwater can be economically
diverted, thus our attention should be practically focused on these areas. Secondly,
there are some social effects such as the dislocation of oyster growers as has been
discussed.

Ray Varnell: In the case of the Bayou Lamoque structure, the purpose for this diversion
was to ameliorate some of the predation problems affecting adjacent oyster beds.
Some of the beds have been silted in, but a much larger area was opened to
production. On the other hand, the oyster growers are plagued by a pollution
problem as a result of poor river water quality.

James Gosselink: Since the main source of fresh water is the Mississippi River, can that
pollution problem be solved?

Ray Varnell: There are structural designs which will allow the introduction of water
through marshes which act as a filters for pollutants.

John Teal: That mechanism depends on what the pollutants are. It is not very effective
for compounds which are soluble in water.

Ray Varnell: Most of the Mississippi River pollutants are adsorbed on particulate
material which settles in the marshes.

Scott Liebowitz: Aren't we fighting an uphill battle with lower river diversions, when the
natural tendency of the river is to shift to the Atchafalaya River and rapidly build a
delta? Might not we gain more by diverting more flow down the Atchafalaya and
concentrating on building that delta cheaply and effectively?

David Fruge: I don't think lower river diversions are futile. These diversions can
markedly slow the rate of marsh loss and modification. The Atchafalaya delta
should be managed also and activities which interfere with the active marsh growth
in that area (such as the Avoca Island levee extension) should be avoided.

Donald Landry: I represent Terrebonne Parish, an area greatly affected by the
Atchafalaya River. The issues surrounding flood control, navigation, and land
building are very complex. The rapid building of land at the mouth of the

124

Atchafalaya will have tremendous detrimental impacts which are not socially or
economically acceptable at thus time. The eventual changes will require substantial
changes including movement of people, and new technology must be developed to
deal with it. The lower river diversions are of small magnitude which do not
intefere with what is occurring at the mouth of the Atchafalaya.

Don Moore: With regard to the earlier issue of optimal conditions in wetlands for living
resources, a good objective would be to maximize the area of brackish marsh. Saline
marsh is a good brown shrimp nursery and intermediate marsh is good white shrimp
nursery, while brackish marsh provides good nursery conditions for both.

Paul Yakupzack: Who is the savior of the marsh? Is it a State agency, Federal agency?
Many agencies are involved, but none seems to be the leader or even a clearing
house of information.

Darryl Clark: The Coastal Management Section of the Department of Natural Resources
is not the "savior". We are often put in the position of many regulators of being
attacked from all sides ~ industry, fishermen, academics, environmentalists. We
must balance these competing interests. This is difficult because of the lack of hard
knowledge available and the dynamic nature of our coastline. We are trying a
number of approaches including marsh creation. Coastal protection projects have
been recommended to the Legislature and are proposed for funding.

Mike Voisin: It boils down to politics. If enough people become aware of the problem,
then the politician will become the savior, because that's what he wants to be.

Murray Hebert: No one person or group can be the savior of the coast. What we are
doing today is certainly a step in the right direction. Certainly, education is critical
at this point ~ education of the public and legislators. The Joint Committees on
Natural Resources have recommended spending $38 million on projects, which in
many cases are just to maintain the status quo. If the State can move forward, the
Federal agencies will fall in line. For the first time, I believe we are moving in that
direction.

Donald Landry: Who is going to do it? We are. The educated public. We must save
ourselves through public awareness.

Linda Deegan: If fish and wildlife resources are worth about $190 million annually, how
can these concerns compete with the petroleum industry, worth over $10 billion
annually?

Donald Landry: You don't have to compete, because the two resources are not
incompatible. They both can co-exist and be beneficial. For example, the major
land companies which own 90 percent of wetlands in Terrebonne Parish and develop
oil and gas resources are very interested in protecting the marshes. Renewable and
nonrenewable resource interests must work together.

125

CONSEQUENCES: SOCIAL AND ECONOMIC

127

LEGAL IMPLICATI0h4S OF COASTAL
EROSION IN LOUISIANA

Paul Hribernick
Michael Wascom

Sea Grant Legal Program

Law Center

Louisiana State University

Baton Rouge, LA 70803

ABSTRACT

Erosion in the coastal zone of Louisiana has serious legal consequences for all
property owners — private, State and Federal. When a private property owner and the
State are placed in an adversarial position, the general rule of Louisiana law dictates
that erosion works against the private property owner's interest and works in favor of the
State's interest. When the State and the Federal Government are placed in an
adversarial position, the general rule of law dictates that erosion works against the
State's interest and works in favor of the Federal Government's interest. Following
these general rules, if the forces of nature work to erode a private property owner's land,
he may lose title of that land which erodes, and its valuable mineral resources, to the
State. Similarly, if the forces of nature work to erode the coastline of Louisiana, the
State may lose to the Federal Government, title to land in the Outer Continental Shelf in
an amount corresponding to the number of acres of coastline that has eroded. At stake
are invaluable mineral resources which pass with the ownership of the land.

THE LEGAL IMPLICATIONS OF COASTAL EROSION IN LOUISIANA

The weathering effects of natural forces in the coastal zone contribute to endless
alteration of the landscape. The physical causes of this erosion and its ramifications are
currently objects of intense scientific inquiry. Science is not the only discipline studying,
and reacting to, the severe changes worked by erosive forces in the coastal environment
of Louisiana, for in addition to habitat loss, hydrological modification, adverse effects on
fisheries, and myriad other physical manifestations, erosion presents significant legal
consequences for landholders in the coastal zone. This paper will examine the legal
implications of erosion to coastal property owners in Louisiana. First, how erosion
changes the relationship between an individual private property owner and the State will
be explored. Later, the relationship between the State Government and the Federal
Government as property owners will be examined to illustrate potential changes in legal
ownership directly attributable to coastal erosion.

128

EROSION, STATE WATER BOTTOM OWNERSHIP, AND THE PRIVATE
PROPERTY OWNER

Ownership of property is an ancient and fundamental legal right in western
civilization.' In addition to exclusive rights to the surface, private property owners may
possess preeminent rights in subsurface minerals and even the airspace above the
land"^. The measure of the property owner's rights is tied to the surface area of his
holdings and boundaries established on the surface serve as a convenient method
delineating the rights of adjoining proerty holders.

Just as any person may own property in his individual capacity, the State may own
property and exercise all normal proprietary functions over its domain. In the
celebrated 1845 case. Pollard's Lessee v. Hagan," the U.S. Supreme Court determined
that each state owned the lands underneaTE navigable waters within the state. The Court
reasoned that because the original 13 states owned the land under their navigable waters,
all states subsequently entering the union should take ownership of equivalent water
bottoms because the Constitution promised them "equal footing" at statehood. Because
Pollard's Lessee v. Hagan involved only the tidewaters of Mobile Bay, and was further
complicated by a deed of cession from the State of Georgia to the United States, the
case did not make clear whether the equal footing doctrine gave the states title to the
beds of inland navigable waters not affected by the tide. Subsequent Supreme Court
decisions, however, held that the states did own the bottom of inland navigable waters,
(such as the upper Mississippi)". Still later, the Supreme Court decided that state law--
rather than Federal common law—controlled the disposition of navigable water bottoms,
including what general rules of law would apply when such lands eroded." Therefore, in
Louisiana's coastal wetlands, Louisiana property law dictates the consequences when a
private landowner's property erodes under the forces of nature.

Since the State of Louisiana owns the beds of navigable bodies of water, a key
inquiry that must be made before the legal consequences of erosion can be determined is
whether or not the body of water abutting the private landowner's property is
"navigable." Louisiana courts have essentially adopted the Federal admiralty definition
of navigability.'^ The Daniel Ball,' ' a U.S. Supreme Court case, defines navigable
rivers in the following manner:

"Those rivers must be regarded as public navigable rivers in law
which are navigable in fact. And they are navigable in fact when
they are used, or are susceptible of being used, in their ordinary
condition, as highways for commerce, over which trade and travel
are or may he conducted in the customary modes of trade and travel
on waters."

Using this definition, Louisiana courts have determined that historical commercial
use '-^ or actual present commerical use may adequately demonstrate navigability for
property law purposes.

Once navigability has been determined, the legal consequences which result from
erosion depend on where the erosion is occurring. Louisiana property law recognizes
three distinct types of shoreline: lakeshore; banks of rivers, bayous and streams; and
seashore. Similar types of erosion in each of these areas can have widely differing legal
consequences for the private property owner.

129

Lakeshore Erosion

Article 500 of the Civil Code prevents the riparian " landowner from taking any
property rights in land exposed by the gradual receding of a lake (dereliction) or in the
gradual buildup of sediment on the lakeshore (alluvion). At the same time, Articles 450
and 452 hold that the bottoms of navigable water bodies are public things and incapable
of private ownership. Because the courts have ruled that the State owns the bottom of a
navigable lake up to the high watermark, Louisiana law, in effect places the private
property owner abutting a navigable lake, in a "no win" situation. If the lake shrinks due
to imperceptible natural causes, his property is separated from the water by a strip of
state-owned land. If his shoreline is eroding or his land is subsiding, the State takes title
to any land that is inundated by the expanding lake waters.

It has already been noted that the equal footing doctrine requires that the state be
given title to all land under navigable waters when it enters the union. When Louisiana
was admitted to the Union in 1812, it was given ownership to all land beneath navigable
waters up to the high water mark. Because Article 500 prevents the State from losing
any land to the private riparian landowner, the threshold question of navigability assumes
critical importance when assessing the property law implicatons of shoreline erosion in a
coastal lake. If the water body was navigable in 1812, Article 500 dictates that the limit
of such navigable waters in 1812 is an immutable line in favor of the State. ''^ That is,
irrespective of the waterway's present navigability, the State will always own as much as
was navigable in 1812. Furthermore, erosion on lake shorelines serves to increase state
land ownership in direct proportion to the decrease in private property ownership.

The Louisiana Supreme Court in Miami Corp. v State, '^^ summarized the rule:

"It apppears to be the rule that where the forces of nature-
subsidence and erosion—have operated on the banks of a navigable
body of water, regardess of whether it is a body of fresh water or
the sec, or an arm of the sea, the submerged area becomes a portion
of the bed and is insusceptible of private ownership."

Furthermore,

"The mere fact that a portion of the bed of a navigable body of
water may have been formed by the action of natural forces does
not change the situation, for the rule is, that when submersion
occurs, the submerged portion becomes a part of the bed or bottom
of the navigable body of water in fact, and therefore the property of
the SJxite, by virtue of its inherent sovereignty, as a matter of
law."'^^

Under this rule, the determination that a body of water was navigable in 1812 will
dictate the legal consequences of erosion in a lake 170 years later.

If the water body was not navigable in 1812 a different set of legal consequences
occurs. In such a case, the lake bottom is a private thing "^ and may be held by the
private property owner. Therefore, if subsidence creates a lake on private property after
1812 or enlarges (or shrinks) an existing but non-navigable lake, the owner does not lose
title to the land. If the lake that was non-navigable in 1812, becomes navigable due to
natural forces, the Civil Code and the jurisprudence of Louisiana provide no definite

130

answer as to the ownership of the lake. A literal reading of Article 450 woulcLrequire
that ownership of the bed must go to the State, but this view has been criticized.

Bank Erosion of Rivers, Bayous, and Streams

Deltaic river systems are much more dynamic than lakes and different laws govern
the ownership effects of erosion on private property adjacent to rivers, bayous, and
streams. Navigability is still important, but the "immutable line" concept of lakeshore
erosion does not apply in the riverbank erosion situation. Rather, the courts adhere to
the concept implicit in the Code that navigabUity and its relationship to property law
must reflect the nature of Louisiana's rivers.^ Generally, the courts apply the same
navigability tests for rivers as for lakes and if a river is deemed navigable, the equal
footing doctrine grants title of the bed to the State. But unlike lakes, portions of rivers
can rapidly become navigable, while other segments may become non-navigable. Because
of this, the concept of navigability as applied to rivers must more accurately reflect the
changing nature of Louisiana's rivers.

If a river is determined to be navigable. State law limits the state-owned bed to
such lands covered by mean low water as measured on both banks. If the river is found
to be non-navigable, the bed may be held in private ownership.^'

The critical question that governs the Louisiana courts' inquiry into the legal
consequences of riverbank erosion is not navigability, but rather the nature of change
brought about by erosive forces. If the change is gradual and imperceptible, erosion
creates one set of legal consequences, but if erosion is sudden and avulsive, another set
of consequences arise.

There are four imperceptible changes on navigable rivers that are specifically
recognized under Louisiana law: erosion, accretion (or alluvion), dereliction and the
creation of islands and sandbars. As a general rule, the riparian landowner loses to the
State any land that is eroded by a navigable river, but gains from th&.State any alluvion
that is deposited on his bank which causes his property to accrete. This rule is h^t
summed up by the Louisiana Supreme Court in Succession of Delachaise v^ Maginnis;

"In ... [a] . . . sense it may be said that rivers give or take away,
like change or fortune. If it takes away the owner must bear the
loss; if it gives, justice affords him the gain.""^^

The Louisiana courts have determined that since the Civil Code dictates that the
beds of navigable rivers are insusceptible to private ownership, erosion creating new
riverbed must work in favor of the State because "once a body of water is found to be
navigabJe, it follows that the bed or bottom must be held to be the property of the
State."-^'

•JO

The Civil Code specifically sets out the rules for accretion or alluvion.-^^ Article
499 simply states that "the alluvion belongs to the owner of the bank . . ." It must be
noted, however, that although the banks of navigable streams may be held in private
ownership, Article 499 reserves to the public the right to occupy such banks for
necessary purposes (e.g., wharfs, boat landing, drying of nets).

Dereliction, the imperceptible drying up or retreat of a navigable river, is treated
similarly to accretion. Ownership of newly exposed land belongs to the riparian,

131

subject to the Code provision which reserves some uses of the exposed bonk to the
public.

Ownership of newly formed islands and sandbars is controlled by Article 505. If an
island or sandbar arises in the channel of a navigable river, ownership goes to the State.
If a sandbar does not arise independently in the channel, but rather grows out from the
shore, it is treated as an accretion and ownership goes to the riparian.-^-' Litigation over
the ownership of sandbars invariably turns on which side can prove how the sandbar was
created.-^^

If erosive forces cause a sudden, or avulsive change, the legal implications are
quite different from those of imperceptible changes. The general rule with avulsive
changes, as directed by the Civil Code, is that the State will exchange ownership of the
old bed for ownership of the new bed.-^' If a river suddenly changes course, abandoning
its original bed and inundating the land of a former riparian, the State takes ownership of
the new bed and the landowner (who now has a river running iicross his former riparian
estate) takes the original bed. In Fitzsimmons v. Cassity, the Louisiana Court of
Appeal expressed the rule this way:

" When a river changes its course and for this purpose appropriates
private property for its new bed, the lawmaker, out of a spirit of
justice and fairness, has wisely ordained, in effect, that the owner of
the appropriated land shall be compensated for his loss by becoming
owner of the abandoned bed." "

The court makes it clear that even though the old channel may still be navigable, the bed
nonetheless goes into private ownership.^*^ The Code provides, however, that if the river
ever resumes its original channel, all parties shall retake their former lands.

If an avulsive action of a river cuts off riparian land and creates an island, the Civil
Code provides that the ownership of the island does not change.^^ This provision works
in conjunction with Article 504 which provides for the exchange of bed ownership when a
river changes course to insure predictable legal consequences in the wake of an avulsive
change.

Seashore Erosion

The legal effects of erosion along the seashore are similar to those of erosion along
a lakeshore except that navigability is of little importance. The Submerged Lands Act
granted Louisiana paramount rights to the seabed from the mean ordinary low tide line
seaward to the three-mile territorial limit. Civil Code Article 450, in addition to
recognizing ownership of the territorial seabed, grants the State ownership of the
seashore.

Seashore is defined in the Code as "the space of land pver which the waters of the
sea spread in the highest tide during the winter season."^^ This definition has been
interpreted to require more than mere tidal influence to demonstrate that waters are
actually part of the sea. In thus way, the courts have limited "seashore" to the actual
coast and "arms of the sea". -^ Working with this definition and the guidance of the
Code, Louisiana courts have held that ownership of any seashore that erodes to become
sea bottom is transferred to the State. "Moreover, any accretions along the seashore
are property of the State. ^' The littoral^" landowner is placed in a "no win" situation

132

similar to that of the lakeshore landowner: if his land is eroding, he loses ownership to
the State; if his land is accreting, he becomes separated from the ocean by a strip of
state-owned land.

Reclamation Process

The potentially immense value of oil beneath a landowner's property is generally
calculated on the basis of surface land ownership. Erosion, and subsequent transier of
ownership to the state, may mean significant losses in future royalty revenue^" to a
property owner whose land is eroding. In an effort to address this problem, the State
Legislature acted in 1978 to create a process by which a property owner can reclaim
lands lost to the state by erosion.-*^ The Louisiana Consitiution provides that:

"The legislature shall neither alienate nor authorize the alienation
for the bed of a navigable water body, except for p>urposes pf
reclamation by the owner to recover land lost through erosion."

(emphasis added).

The legislature exercised the option granted to them in the Constitution and
provided a mechanism whereby a property owiier con earn back land he lost to erosion
and thereby protect potential oil revenue. The landowner must apply to the

Department of Natural Resources (DNR) and provide them with a professional survey
showing the exact extent of the land claimed to be lost by erosion. DNR will review the
application and seek the input of the Attorney General, the Department of
Transportation and Development, the Department of Wildlife and Fisheries, and any
other State agency or local government who jriay have an interest in the reclaimed
area. If all parties consent to the application, -^ the landowner will be give a two-year
permit to reclaim the land. The gravity of the coastal erosion problem is highlighted by
the fact that the statute specifically encourages coastal landowners to reclaim lands out
to the baseline decreed by the U.S. Supreme Court in the 1975 Tidelands decision.

STATE WATER BOTTOM OWNERSHIP AND THE FEDERAL GOVERNMENT

Although the State generally inherits a superior legal positon in relation to the
private landowner when erosion destroys private lands, when State lands are being
eroded, the state's legal position ultimately proves to be inferior to the Federal
Government's paramount rights.

Relying on Pollard's Lessee v. Hagan,-*-^ the states always assumed that the equal
footing doctrine applied to lands beneath the three-mile territorial sea. With the advent
of commercially practical offshore drilling technology in the late I940's and the
subsequent discovery of huge oil reserves on the Outer Continental Shelf, the states
looked forward to lucrative oil revenue from production in the territorial sea. This
scenario wa^ shattered in 1947 by the U.S. Supreme Court in United States v^
California.^^ That decision held that the United States maintained paramount rights in
the land seaward of the low water mark. The outcry from coastal states convinced
Congress that remedial action was necessary. A political solution was forged in 1953
with the passage of the Submerged Land Act.^' This act effectively reversed the
Supreme Court's United States v. California decision by deeding title to the seabed, for
the width of the territorial sea, to the adjacent coastal State.

133

In an effort to maximize its terr

cumbersome series of Supreme

litigation culminated in 1969 with Uni

two questions of critical importance for understanding the legal implications of coastal
erosion. First, the Court decided that international law must be applied to determine
Louisiana's coastline. The net effect of this decision was to minimize Louisiana's
offshore claims. Second, and more important, the Court declared Louisiana's coastline
to be ambulatory. This means Louisiana's baseline (from which the territorial sea is
measured) can move landward as the coast erodes, depriving Louisiana of substantial
offshore oil revenue. This fact is made clear in the June 1981 decree ° where the
Supreme Court implies that if the coastline recedes due to erosive forces, the United
States would have the right to seek a more favorable boundary with the state in court.

CONCLUSIONS

When a Louisiana private property owner's lands are subjected to erosion, he is
placed in an adversarial position with the State. If the private property abuts a navigable
river, the riparian loses to the State any property which erodes, but gains ownership of
any alluvion that builds up along his river bank. If the private property abuts a navigable
lake or the coastline, the littoral owner is placed in a "no win" situation. Any portion of
his land which erodes is lost to the State and ownership of any new land created between
his property line and the water vests in the State, cutting the littoral owner off from the
water by a strip of state-owned land. However, State law generally allows the private
land-owner to reclaim any land lost to erosion.

When the State's coastline is subjected to erosion, the State is placed in an
adversarial position with the Federal Government. As erosion forces the coastline
landward, the State's territorial sea theoretically moves a corresponding distance
landward. Unlike the private landowner, the Federal Government does not give the
State a chance to reclaim lands lost to erosion. As a result, Louisiana may untimately
lose valuable offshore mineral rights to the Federal Government if the courts are ever
asked to recompute the State's coastline which is the baseline for measurement of the
territorial sea.

ACKNOWLEDGMENTS

This publication is a result of research sponsored by the Louisiana Sea Grant
Program, part of the National Sea Grant Program maintained by the National Oceanic
and Atmospheric Administration, United States Department of Commerce. The Federal
Government is authorized to produce and distribute for government purposes
notwithstanding any copyright notation that may appear hereon.

FOOTNOTES

1. The right of an individual to hold private property is of such significance that it is a
specifically protected right in U.S. Constitution. See, U.S. CONST, amend. V

2. See generally. Mineral Code, La. Rev. Stat. Ann. Section 31:4 et seq.

134

3. See e.g., Herrin v. Sutherland, 74 Mont. 587 (1925), City of Newark v. Eastern
TJFlines, I59F. Supp. 750(1958)

4. As a general proposition, established oil field rights can be conceptualized as being in
direct proportion to surface area owned in a declared field. See generally, La. Rev.
State. Ann. Sections 3 1 :9- 1 1

5. AUBRY AND RAU, CIVIL LAW TRANSLATIONS, Vol. II Sections 169, 170 (7th ed.
1961)

6. 44 U.S. (3 How.) 212 (1845)

7. The Court's reasoning in Pollard's Lessee v. Hagan was that because the lands under
navigable waters were not specifically granted to the United States by the
Constitution, they were thereby reserved to the original 13 States. The Court then
concluded that Article IV, Section 3 of the Constitution (which controls the formation
of new states) and Article I, Section 8, clause 16, (which was interpreted by the Court
at that time to prevent Federal control over lands other than the District of Columbia
and military reservations) read together, demanded that newly created states be
admitted on the same terms ("equal footing") as the original 13 States. Therefore all
states own the land under their navigable waters. See also, La. Civ. Code Ann. art.
450

8. See, Shively v. Bowlby, I 52 U.S. I, (1893); Eldridqe v. Trezevant, 160 U.S. 452 (1895)

9. See, United States v. Chandler-Dunbar, 229 U.S. 53, ( 1 9 1 3); Oregon ex rel State Land
Board v. Corvallis Sand and Gravel Co., 429 U.S. 363 (1977)

10. See generally, YIANNOPOULAS, LOUISIANA CIVIL LAW TREATISE, 42 (2d ed.
\98W~

11. 77 U.S. (10 Wall.) 557 (1870)

1 2. jd., at 563

13. See, State v. Aucoin, 206 La. 787, 20 So 2d 136, (1944). See Also, Id. at 158,
(Fournet, J., dissenting); Amite Gravel Sand Co. v. Roseland Gravel Co., l58'La. 704,
87 So. 718 (1921); State v. Jefferson Island Salt Mining Co., 183 La. 304, 163 So. 145
(1935)

14. State ex rel Atchafalaya Basin Levee District v. Capdeville, 146 La. 89, 83 So. 421
(1919); State v. Jefferson Island Salt Mining Co., supra, note 13

15. The threshold question of whether or not a body of water is a lake or a river is
generally dictated by the physical characteristics of that water body, which the
courts will examine on a case by case basis. Some factors the court looks to are the
size of the water body, source of its water (is it primarily drainage or river flow?),
presence or absence of current, flow within well-defined banks, amount of sediment
load carried by the water. See, Slattery v. Arkansas Natural Gas, 138 La. 783, 70 So.
806 (1916); Amerda Petroleum Corp. v. State Mineral Board, 203 La. 473, 14 So. 2d 61
( 1 943); State v. Placid Oil Co., 200 So. 2d 154 (La. 1974)

135

16. Riparian refers to those things related to, or located on, the bank of a natural
watercourse.

17. State V. Placid Oil Co., 300 So. 2d 154 (La. 1975), cert, denied, 419 E.S. 1110
(19731

18. Miami Corp. v. State, 186 La. 784, 173 So. 315 (1937), overruling State v. Erwin,
l73La. 507, 136 So. 84(1931)

19. See, YIANNOPOULAS, supra, note 10. As can be imagined, the proof problems in
establishing what was navigable in 1812 are enormous. Most, if not all water bottoms
were unsurveyed at that time. Although the burden of proving navigability rests with
the state, it is not a task of such insurmountable magnitude as to nullify State claims
to newly inundated lands.

20. Supra, note 18

21. ]d., at322

22. ]d., at 323

23. La. Civ. Code Ann. art. 453

24. See, La. Civ. Code Ann. art. 506. See also, La. Civ. Code Ann. arts, 499-505 See,
YIANNOPOULAS, supra, note 10. TKis criticism is lent indirect support byTRe
Supreme Court's recent decision in Kaiser Aetna v. United States, 444 U.S. 164
(1979). In that case, the Court held that a non-navigable pond that was artificially
connected to the sea could not be ruled open to public navigation without paying its
private owners compensation under the Eminent Domain Clause of the Fifth
Amendment to the U.S. Constitution. The courts in Louisiana may be willing to
extend this rule and require the State to compensate a private landowner if the State
takes title to the bed of a formerly non-navigable lake on the landowner's property.

25. See, La. Civ. Code Ann. art. 506. See also. La. Civ. Code Ann. arts. 499-505

26. See, Smith v. Dixie Oil Co., 156 La. 691, 101 So. 24(1924)

27. La. Civ. Code Ann. art. 506. See State v. Aucoin, supra, note 13; Bank of
Coushatta v. Yarborough, 139 La. 510, 71 S. 784(1916)

28. See, Esso Std. Oil v. Jones, 233 La. 9 1 5, 98 So. 2d 236 ( 1 957), State v. Capdeville,
supra, note 14. It should be noted in this situation that land loss experienced by one
land owner will be accompanied by a deposition of alluvion and a corresponding gain
to some other landowner, usually on the opposite bank. Therefore, although the State
stands to gain greatly from erosion of private property, the laws of nature dictate
that the State's water bottom holdings remain relatively constant. This is not
accurate, however, when both banks of a navigable river are eroding. In that case,
the State's gain is absolute.

29. 44 La. Ann. 1043, I I So. 715 (1892)

30. Id., at 716

136

31. State V. Capedeville, supra, note 14 at 425. See also, Miami Corp. v. State, supra,
noteTS

32. La. Civ. Code Ann. arts. 499-501

33. Esso Standard Oil v. Jones, supra, note 25

34. Lo. Civ. Code Ann. art. 499

35. jd.

36. See, Butler v. State, 244 So. 2d 888 (La. App. 1971), writ denied 246 So. 2d 680.
Before accurate survey records were kept, the burden of proving how a sandbar
evolved was immense. With modern scientific mapping and satellite observation
technique, proof problems will be minimized in the future.

37. La. Civ. Code Ann. art. 504

38. l72So. 824(La. App. 1937)

39. ]d., at 829

40. Louisiana Courts are apparently disposed to grant all the former bed— including
sandbars attached to land—to the landowner whose property is now inundated by the
river, See, Stephens v. Drake, 134 So. 2d 674 (1961). The court apparently decides
that Article 504 overrules Article 499 when the two come into conflict.

41. La. Civ. Code Ann. art 504

42. La. Civ. Code Ann. art 503

43. 43 U.S.C.A. Sections 1301 et seq. See text accompanying notes 54 to 63, infra

44. La. Civ. Code Ann. art 451

45. An "arm of the sea" is generally considered any body of water immediately
adjacent to, or directly connected with the sea. See, Buras v. Salinovich, 154 La. 495,
97 So. 748 (1923) citing Morgan v. Negodich, 40 La. Ann. 246, 3 So. 636 (1887) with
approval. Lake Pontchartrain has always been held to be an arm of the sea.

46. New Orleans Land Co. v. Board of Levee Comm'rs., 171 La. 718, 132 So. 121
(l9Jn

47. Ruch V. New Orleans, 43 La. Ann. 275, 9 So. 473 ( 1 89 1 )

48. Littoral refers to those things related to, or located near, the coastline.

49. If the eroded lands are presently subject to a lease, the State will take ownership
of those lands subject to any existing leases. The legislature has provided that the
landowner will not lose any presently valid lease. See, La. Rev. Stat. Ann. Section
9:1 151. This limits the landowner's loss to royalty revenue derived from a discovery

137

of minerals subsequent to his loss of the land due to erosion.

50. l978La. Acts, 645

51. La. CONST, art 9, Section 7

52. La. Rev. Stat. Ann. Section 41:1702. This statute specifically gives the landowner
the right to recover all oil, gas and mineral rights in addition to the actual land
surface.

53. Although the statute is not precisely clear, Sections (D) and (H) of La. Rev. Stat.
Ann. Section 41:1703 would appear to give each one of these agencies and local
governments veto power over the proposed reclamation.

54. The state loses relative to the Federal Government both when state land and any
private landowner's property is eroded. The reason is that the baseline, or coastline,
from which the three-mile territorial sea (the bottom of which belongs to the state) is
computed, is measured from the points of land that extend farthest into the Gulf of
Mexico, be they privately owned or state owned. If state lands erode, the baseline
(and therefore territorial sea) moves landward. Similarly, when private lands erode,
even through the state gains onwership of the new bottom, the baseline moves
landward and the states gain from the private landowner is offset by its loss to the
Federal Government.

55. supra, note 6

56. 332 U.S. 19(1947)

57. supra, note 43

58. United States v. Louisiana, 339 U.S. 699 (1950) (applies U.S. v. California rule to
Louisiana); 354 U.S. 516 (1957) (Louisiana attempts to litigate its territorial sea, but
Supreme Court rules that Alabama, Florida, Mississippi, and Texas are necessary
parties and must be joined); United States v. Louisiana, et. al, 363 U.S. I (May I960)
(Supreme Court rejects Louisiana's claim to a nine-mile territorial sea and grants only
three miles); United States v. Louisiana, et. al, 364 U.S. 502 (Dec. I960) (Final decree
defining coastline at ordinary low water); United States v. Louisiana, 382 U.S. 288
(1965) (Court rejects Texas' attempt to use artificial jetties to enlarge its territorial
sea); United States v. Louisiana, 394 U.S. I I (1969), See text accompanying notes 54-
56; United States v. Louisiana, 420 U.S. 529 (l973r(Court overrules Louisiana's
objections to special master's report); United States v. Louisiana, et al., 422 U.S. 1 3
(1975) (Court supercedes 1965 baseline it had established and orders an accounting of

oil revenue); United States v. Louisiana, U.S. 49 U.S. L.W. 4825 (1981)

(Final decree setting ambulatory coastline and territorial sea; Court orders a final
accounting due I December 1981).

59. The Constitution vests original jurisdiction in the Supreme Court when a state
sues the United States directly. In such cases, the Supreme Court is the trial court of
first instance. Because of the time-consuming nature of such cases, the Court will
generally appoint a special master to hear the case and make recommendations to
it. Of course, the Court is free to disregard the findings of the special master.

138

60. 394 U.S. II (1969)

61. For example, Louisiana had claimed that Breton and Chandeleur islands delineated
the baseline of Louisiana and that the territorial sea must be measured out three
miles from their shore. International law disapproves such a claim, granting a coastal
state only a three mile ring around islands that are greater than three miles
offshore. See, Guste and Ellis, Louisiana Tidelands Past and Future, 21 Loy. L. Rev.
817, at lli

62. United States v. Louisiana, U.S. , U.S.L.W. 4825 (1981)

63. Id., at 4825

139

ECONOMIC AND CULTURAL CONSEQUENCES
OF LAND LOSS IN LOUISIANA

Donald W. Davis

Earth Science Department

Nicholls State University

Thibodaux, LA 70310

ABSTRACT

Louisiana's coastal lowlands are facing a serious dilemma. The problem is related
directly to man's interference with the Mississippi River's flow regime and the effects of
erosion induced by natural processes— winds, waves, currents, and tides. As a result, the
wetlands are out of balance. Progradation has been superseded by erosion with land
disappearing at an alarming rate. Approximately 103.6 km'^/yr (40 mi^/yr) are being
destroyed—changing from barrier island and protected marshes to open water.

The next 200 years are critical, since a large portion of Louisiana's coastal zone
will be eroded away. In the process an important nursery ground and habitat for
migratory waterfowl, fur and hide-bearing animals and fisheries will be lost. "High" land,
already scarce, will be at a premium and the cumulative economic effect will be
measured in the billions of dollars.

New Orleans will lose its natural defense against a hurricane-induced storm surge.
With parts of the "Crescent City" 6.1 m (20 ft) below sea level, it cannot afford to be at
the mercy of an unimpeded tropical cyclone. Without the surrounding marshes, the first
line of defense will have vanished.

Trappers will lose the habitat preferred by muskrat and nutria. The Nation's
preeminent fur-producing region, producing from $2 million to $24 million in annual pelt
sales, will be gone. Additional renewable resources, such as shrimp, oysters, crab, and
menhaden, worth hundreds of millions of dollars annually, will no longer have a habitat
that supports more than 25% of the country's commercial fisheries. Concomitant with
the decline in these industries will be the partial demise of the nearly $200 million
recreational industry.

Probably the most important single loss to the State will be Louisiana's land/water
boundary. As this line retreats, the limit of Louisiana's offshore zone moves shoreward.
The end result is the forfeiture of millions of dollars in oil royalties— at least $20 million
for each mile of coastal retreat. Further, the multibillion dollar infrastructure
associated with the petroleum industry also faces the loss of valuable "high" ground; thus
a number of favorable advantages of living and working in Louisiana are changed.

Unique lifestyles will also be altered or lost. Centuries-old traditions will die. The
cultural heritage of the region will be diluted and the economic resources responsible for

140

billions will be gone. The final question is: "Can we afford the loss of Louisiana's
wetlands?"

INTRODUCTION

South Louisiana's 6.5 million acres of coastal wetlands account for 40% of the
Nation's nnarsh ecosystems (Gosselink 1980). The region is defined by elevation and the
absence of trees. Where the land is at least 0.5 m (18 inches) above sea level, a swamp
forest will be evident. The marsh, on the other hand, is a conspicuous lowland—literally
a sea of grass.

The physical and biological complexities of this unique physiographic province are
the subject of numerous technical reports, papers, and monographs. The initial work of a
multitude of wetland scientists established the guidelines for subsequent research. These
individuals contributed significantly to the systematic examination of alluvial
environments. Their interdisciplinary studies provided insight into the surface and
subsurface elements that comprise the various marsh habitats. From this foundation,
interest in the coastal lowlands proliferated.

Early investigators discovered the vast expanse of marsh is larger than Connecticut
and Delaware combined and a product of the wandering distributaries and alluvial
processes of the Mississippi River. With each channel change river-borne sediments were
diverted into new areas. The Mississippi River, therefore, created this large extensive
band of coastal property. Prior to the late 1800's, south Louisiana experienced at least
6,000 years of deltaic progradation.

Unfortunately, Louisiana's coastal zone is presently out of balance— a great natural
catastrophe is occurring. Land is disappearing. For the entire Louisiana coast, marsh
losses in 1980 exceeded 10,000 ha (25,000 acres)/yr— a rate that is increasing
geometrically and not arithmetically. With I million ha (2.5 million acres) of fresh to
saline marsh, 700,000 hectares (1.8 million acres) of ponds and lakes, and 900,000
hectares (2.2 million acres) of bays and estuaries, there is now more water than land
(Fruge 1981). Land building in the deltaic plain has been replaced by a projected rate of
loss of approximately 100 km (40 mi )/yr (Gagliano, et al. 1981), coupled with a rise in
sea level estimated to be 30 cm (I ft) per century, the wetlands are in serious danger. By
comparison, on the national level approximately 400,000 ha (I million acres) of coastal
marshes have been lost since 1954 at a rate of 15,000 ha (38,000 acres)/yr (Gosselink
1980). In Louisiana, at least 300,000 ha (800,000 acres) have been lost in the last 80
years with more than half of this occurring since 1950 (Gagliono 1981).

These land loss figures are staggering, since Louisiana's wetlands provide a habitat
for more than two-thirds of the Mississippi Flyway's wintering waterfowl, the largest fur
and alligator harvests in North America, and more than 25% of the country's commercial
fisheries. Few states can compete with Louisiana in the production of renewable and
nonrenewable resources; yet due to land loss, they are threatened and may vanish.

The land that is eroding at a record rate is a result of sediment deposition
associated with the Mississippi River. For centuries, sediment laden water has fanned
out along the coast, creating two distinct zones: the deltaic and chenier plains, east and
west, respectively, of Vermilion Bay.

141

THE DELTAIC PLAIN

The deltaic plain is the site of a series of seven deltaic lobes extending seaward at
different times during the last 6,000 to 7,000 years. Except for the modern "bird's foot"
delta, each lobe advanced into the shallow waters of the continental shelf and was
distinguished by numerous distributaries. These channels continued to bifurcate, thus
aiding the distribution of the river sediments and progradation of the coast. Through
time, the recurring channel changes created the intricate "horse's tail" pattern of levee
fingers extending into the wetlands. Fluvial-marine materials deposited in the prodelta,
interdistributary and intradelta environments built up an estimated 75% of the deltaic
plain (Kolb and Van Lopik 1958; Frazier 1967). Most of this land is an abandoned subdelta
composed of alluvial ridges, beaches, marsh and water surface, where accretion has been
replaced by subsidence and erosion.

in the paludal environments, the organic bulltongue (Sagittaria) and other grass-
derived materials develop in place. They are not altered by alluvial deposits. In these
tracts organic material continually decays and accumulates as peats, in effect, building
the marsh "down" rather than "up." Decomposition maintains an organic layer that
thickens with subsidence to a depth of 3 to 6 m (10 to 20 ft) (Russell 1942; Kolb and Van
Lopik 1958).

On a regional basis, some southeastern Louisiana surfaces may sink as much as 5 m
(17 ft) per century (Kolb and Van Lopik 1958). In many areas aggradation simply cannot
keep pace with subsidence. Small ponds often develop that expand rapidly as wind-driven
waves attack the poorly consolidated sediments that make up the shore (Gagliano and van
Beek 1970).

Further, the construction of flood levees and the dredging of drainage, navigation,
petroleum, and logging canals upset the sedimentation balance, influenced salt water
intrusion, and disrupted the natural flow regimes. Consequently, the Mississippi's natural
processes were altered and erosion began to overshadow deposition. Sediments are now
channeled off the continental shelf. This waste of sediments deprives the coast of the
"material" that sustained the balance and prevents the building of new marshes. There is
nothing available that can offset the rapid rate of wetland loss (Fruge 1981). Salt water
moves inland and kills the root mat that "holds" the marsh together^ In the I90p's this
reversal in the natural cycle has accelerated from a loss of 17.3 km /yr (6.7 mi /yr) in
1913 to nearly 104 kmVyr (40 miVyr) in 1980 (Gagliano 1981).

THE CHENIER PLAIN

On southwestern Louisiana's near -sea -I eve I grasslands the surface is broken by a
series of long, narrow sand ridges, locally called cheniers (Howe et al. 1935). Referred to
as the chenier plain, the area was formed by wave action pushing sand up onto shore
(Russell and Howe 1953; Price 1955). Each chenier marks the position of a once active
shoreline (Schou 1967). When the Mississippi occupied one of its western courses, clays,
muds, and sands were carried westward by littoral currents advancing the chenier plain
as a mud coast. Interruptions in the progradation process allowed coarser particles to
accumulate as a ridge. An increase in sedimentation caused the shoreline to advance
leaving the conspicuous, oak-covered chenier as the region's most impressive and
continuous topographic feature (Howe et al. 1935).

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"Prairie marshes" associated with the 3,000 km'^ (1,200 mi ) of chenier plain have
an old and firmer foundation (Coleman 1966). Subsidence is not q% important in the
ecology of these marshes as it is in the newer formation to the east (O'Neil 1949). The
region is subjected to uninterrupted wave attack that rapidly erodes the shoreline. Like
the deltaic plain, it is also facing a serious land loss problem.

ECONOMICS OF ENDANGERED MARSH: LOSS OF MORE THAN JUST LAND

Built by the Mississippi and eroded by natural processes often accelerated by man,
Louisiana's marshes nevertheless nurture and support a vast natural resource that is
threatened by the cumulative effects of marsh deterioration.

Since the late I930's the wetlands complex has experienced rapid economic growth
and development. Much of this growth is a result of the hydrocarbons extracted onshore
and, more recently, offshore. Oil and gas account for a multibillion dollar industry.
Agriculture, seafood, trapping, and recreation are multimillion dollar industries. In
addition, Louisiana's largest city and the Nation's leading seaport. New Orleans, is
directly or indirectly tied to the economics of the marsh. Land loss affects each industry
differently, but in the long term, it is not in the State's best interest, since it will have a
cumulative effect on Louisiana's economy.

To understand the complexities of the land loss problem as it relates to the
cultural/economic intricacies of the wetlands, six topics will be discussed: New Orleans,
trapping, fisheries, recreation, hydrocarbons and land use.

New Orleans: The Sea Level City

When people think of Louisiana, they think of New Orleans. The city is synonymous
with the State. It is Louisiana's largest city and has recently become the country's
largest seaport. Like the rest of south Louisiana, New Orleans is a product of the
Mississippi. From early cotton packets, to modern petrochemical industries that flank its
course from Baton Rouge to New Orleans, the Mississippi provided the principal impetus
for regional growth.

To make New Orleans the city that it Is required extensive drainage and
reclamation programs. When the area was surveyed in 1720, each block was circled with
canals. These channels established New Orleans' dependence on a drainage network.
Levee construction began as early as 1718. Ten years later, a manmade embankment 1.6
km (I mile) long protected the "Vieux Carre." By 1735, it totaled 64 km (40 mi) (Davis
and Detro 1980). In 1743, an ordinance required property owners to complete their
levees or forfeit their lands (Schneider 1952). It was apparent that this settlement would
always face drainage problems, a battle yet to be won (Samuel 1959).

To insure that settlers confronted the drainage problem. Governor O'Reilly, in
1770, issued regulations: "To every family coming to settle in the province, a tract was
to be granted... on condition that the grantee should within three years, construct a
levee. ..finish a highway..., with parallel ditches towards the levee,..." (Martin 1882).
These regulations guaranteed Louisiana's lowlands would be adequately drained. As a
result, drainage and reclamation has become an integral part of New Orleans' growth. In
the process, the "Crescent City" is the only North American city that has, for more than
two and a half centuries, fought a continuous battle with flooding.

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With parts of the city more than 6 m (20 ft) below sea level, New Orleans depends
on levees and drains to protect the populace. A single pump failure, or levee crevasse
can be disastrous. The city has learned to cope with these problems(Schneider 1952); yet
it was not added to the Orleans Parish Levee District until 1950. With city funds, levees
were built on the river.

After the disastrous flood of 1927, the need for flood control became apparent. To
save New Orleans, the levee was blown up creating an artificial crevasse (Simprich
1927). The Army Corps of Engineers began to construct the Mississippi's "guide levees."
In modern Louisiana these manmade embankments protect cities, towns, villages,
farmland, and industrial complexes. In retrospect, they have allowed New Orleans to
reclaim commercial, industrial, and residential property. With much of this "new" land
below sea level, rain runoff and groundwater seepage is pumped uphill.

Levee systems are essential to keep flood waters out. Pumps operate continually
to remove the excess. With continued urban/industrial expansion into the wetlands, there
is a constant problem with subsidence. When drained, the peat land shrinks and subsides
by as much as 75%. Developments, therefore, must withstand 3.5 m (12 ft) of subsidence
during the first 50 years after drainage and the levees must provide protection from high
tides, rains, and hurricanes (Wagner and Durabb 1976).

As the marsh deteriorates the buffer zone between the Gulf of Mexico and New
Orleans narrows. This "cushion" is the city's first line of defense. It serves many useful
purposes. As a site for the urbanite to engage in outdoor recreation, it is without
parallel. For the people in New Orleans, however, it buffers against a hurricane's storm
surge. When this barrier has eroded away, the city is in a most precarious situation,
since it has no manmade defenses that can compare to the marsh. With parts of New
Orleans more than 6 m (20 ft) below sea level, flooding is a constant problem. Even
though the area is drained, the natural system is superceded by an artificial one that, at
times, cannot accommodate the torrential rainstorms of the summer months. With its
"foreland" eroding, the city is in a dubious position. Since two of the city's immediate
marsh neighbors, Plaquemine and St. Bernard parishes, have projected land loss rates in
1980 of 3,574 ha/yr (8,831 acres/yr) and 685 ha/yr (1,695 acres/yr), respectively, their
marsh's life expectancy are 52 and 152 years (Gagliano 1981). Consequently, the
"cushion" is disappearing at an astonishing rate. The data clearly suggest Louisiana's
largest urban agglomeration will require substantial new flood protection measures
within the next 50 to 100 years, particularly as the area becomes more exposed to open
water.

The Settlers and Their Occupations

Louisiana's coastal zone has been the site of continuous human occupancy for at
least 12,000 years. From prehistoric Indians, to modern communities of French-speaking
"Cajuns," the alluvial wetlands have supported a range of cultures and settlements.
Numerous ethnic groups colonized the aquatic lowlands, locating their homes and villages
on protected and well-drained land, near navigable waterways, and not too far from their
fishing, hunting, trapping, and agricultoral areas (Detro and Davis 1974). They
established also the region's dependency on wetland resources.

Unlike New Orleans, the settlers within the wetlands were French farmers,
trappers, and fishermen. They regarded the semiaqueous terrain as an attractive
location for their new "marsh villages." In addition to the French, a group of Yugoslavian

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oyster fishermen settled along the bayous, bays, and lakes southeast of New Orleans. In
time they were joined by other Balkan immigrants (Evans 1963). Germans, Irish, Italians,
Spanish, Lebanese, Filipinos, and Chinese settled within the coastal wetlands. These
"folk" became farmers, laborers, oystermen, shrimpers, trappers, and truck farmers. As
a result, the regional economy was established by the diverse ethnic mosaic that typifies
the coastal zone. The mixing of nationalities resulted in a milieu that is absolutely
unique in the United States (Evans 1963) and a subsistence lifestyle based on the folk
occupations established by these original settlers— trapping, fishing (both for sport and
profit) and farming.

Trapping; A Multimillion Dollar Industry

Few people recognize that North America's most productive fur-producing region is
Louisiana's alluvial wetlands. The fur business dates to the I 700's, but the State did not
become a significant fur producer until the twentieth century. At its height, the
trapping industry provided employment for at least 20,000 people. Now less than a third
of that number are licensed trappers. Severance tax records reveal these individuals
account for nearly half of the Nation's fur harvest. In less than 50 years, the marsh
dweller transformed Louisiana's alluvial lowlands into the country's pre-eminent fur-
producing region, with an annual yield often greater than that of the remainder of North
America. This extensive near-sea-level habitat has been responsible for as much as 65%
of the country's yearly fur harvest (Davis 1978).

In the early 1800's, alligator (Alligator mississippiensis), mink (Mustela vison), and
raccoon (Procyon lotor) were valuable hide and furbearing animals^ These species,
although important, did not account for the state's spectacular growth. Two small
mammals are the industry's principal furbearers—the muskrat (Ondatra zibethicus) and
nutria (Myocastor coypus). For more than 50 years, the muskrat was the largest fur
producer; in a good season, more than 5 million animals would be trapped. Unlike the
indigenous muskrat, the nutria was accidentally introduced into the wetlands; it is an
exotic. This Argentinian rodent is a prolific animal that diffused throughout the State.
In less than 30 years, it supplanted the muskrat and became Louisiana's most important
furbearer.

Trappers harvest approximately 1.5 to 2.5 million nutria annually; since the early
I940's, more than 100 million have been removed from the marsh. Originally considered
worthless, the animals' presence has resulted in a multimillion dollar industry. With
yearly pelt sales that vary from $2 million to $24 million. The fur industry generates
inconsistent income since between two successive seasons, pelt sales can differ by as
much as $12 million. Although muskrat and nutria are the backbone of the industry,
trappers also add to their income by harvesting raccoon, mink, otter and, since
reclassification, the alligator. Each of these animals contributes to the economic
survival of the remaining trappers within the coastal zone. Consequently, trapping is an
important "folk" industry that continues to be a significant source of income.

The fur business is tied to the marsh, which Penfound and Hathaway (1938)
conveniently divided into four vegetative types: saline, brackish, intermediate, and
fresh. Various maps (O'Neil 1949; Kolb and Van Lopik 1958; Chabreck et al. 1968)
document the elongate patterns of these vegetation assemblages. In general, the bands
parallel the coast in an east-west direction. The areol limits are not stationary, but
change with various edaphic factors, disrupting the vegetation and contributing to a
decline in the furbearing population.

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As the coast retreats, the saline marsh will expand reducing the range of the
brackish and intermediate marsh's three-cornered grass (Scirpus oineyi) that provides
90% of the muskrat's food supply (O'Neil 1949) and accounts for "the most productive fur
habitat along the northern gulf coast" (Palmisano 1972). Continued land loss will
eventually influence the canouch (Panicum hemitomon) and alligator grass (Alternanthera
philoxeroides) that are a nutria favorite. Ultimately, this renewable resource will be
lost. As a result, an industry that has been an important part of the marsh dweller's
winter subsistence activity will be lost. A part of the region's cultural heritage will die
and a unique lifestyle will be lost.

Fishing; By Weight or Value, the Wetlands Are a Seafood Factory

Each year Louisiana fishermen catch more than 680 million kg (1.5 billion lb) of
estuarine-dependent fish and shellfish, primarily menhaden, oysters, shrimp, and the
nearly ubiquitous blue crab, representing more than one-quarter of the country's total
catch (National Oceanic and Atmospheric Administration 1975). The region's biological
wealth has provided a means of subsistence for its human inhabitants since prehistoric
times. Fishing is an important part of the region's cultural heritage. In the seasonally
oriented economy of the wetlands, the trapper finishes the fur harvest in February and by
May he has prepared his boat for opening day of the shrimp season. Though wetland
inhabitants long considered the marsh low in monetary value, they always profited from
an abundant seafood harvest. With time and increased demand, Louisiana's seafood catch
has escalated in value to more than $190 million annually; thus, the State is number one
by weight and second in value (Ringold and Clark 1980; Aquanotes 1981).

This harvest is directly related to Louisiana's coastal wetlands. The State's
economicaly important fish species spawn or migrate into the coastal estuaries to take
advantage of the rich food supply, protective habitat, annual changes in meteorological
conditions and other favorable factors. Flooding and salt stress are particularly
important, since they determine the length of the growing season and the marsh's
productivity. This influences the fisheries resource, in as much as they are dependent on
the wetland's abundant food supply (Gosselink 1980). The reduction of this productive
habitat through land loss affects the commercial fisheries. This is particularly true in
the shrimp industry, where the yields are directly associated with the wetland area.

The commercial seafood industry developed with the exploitation of shrimp and
oysters, harvested commercially since the late I800's. These two species account for
nearly half of the State's annual fisheries income, with shrimp landings representing from
20%-30% of the total shrimp harvest in the United States.

Shrimp. Two species of shrimp are harvested: brown (Penaeus aztecus) in the
spring and white (P^ setiferus) in the fall. These penaeid shrimp spawn and hatch
offshore, but grow to a marketable size in the region's estuarine environments.
Louisiana's extensive area of intertidal vegetation provides the necessary environmental
factors to insure the shrimp's survival. The estuarine-dependent shrimp need the
marshes, not open water to mature into a marketable size. Current changes from marsh
to open water will affect the resource by reducing the harvestable shrimp considerably.
Originally harvested by cast nets and haul seines, commercial fishermen now use a
Lafitte skiff outfitted with an otter trawl or poupier (butterfly net). With the
introduction of the otter trawl in 1915, the shrimping industry was revolutionized
completely. A larger area could now be harvested with fewer men, thus yielding a
greater production per man because of the increased efficiency of the gear (Padgett

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I960). By 1920, Louisiana's total shrimp catch was 14.5 million kg (32 million pounds) —
nearly twice as great as the preceding year (Viosca I 920; Padgett I 960).

Prior to the availability of ice and modern freezing techniques, shrimp caught in
southeast Louisiana's fishing grounds were taken to one of the numerous drying platforms
to be dried, packaged, and sold. Although plagued by frequent hurricanes and a declining
market, Barataria, Timbalier, Terrebonne, Caillou, and Atchafalaya bays, as late as 1962,
supported 23 shrimp drying platforms (Pillsbury 1964). Three years later, a mere 16
remained. Less than 5 now survive and operate only intermittently (Davis 1976).

With more sophisticated boats and equipment, the shrimp harvest has grown
rapidly. Expansion of the industry resulted in the shrimp becoming the most valuable
seafood in Louisiana. The catch is second only to menhaden in quantity, but first in
dollar value. Since 1880, Louisiana has led the gulf states in shrimp catch 69% of the
time (Barrett and Gillespie 1973). This catch is worth from $100 to $140 million annually
(Larson et al. 1980).

Despite a fairly stable commercial shrimp harvest, the yearly catch per fisherman
has declined. Recent data suggests that the catch is directly related to the available
marsh vegetation. Loss of this vegetation has a direct negative impact on this fishery.
In short, loss of marsh reduces shrimp production and with time the industry appears to
be in danger (Fruge 1981). One of the country's richest nursery grounds may be lost and a
centuries old fishing tradition will disappear.

Oysters. The oyster industry relies almost totally on one species, the American
oysterTCrassostrea virginica Gmelin). Other species do not contribute significant
amounts to the catch. Since 1939, when Louisiana's oysterman harvested more than 5.8
million kg (13 million pounds) (Lyies 1967), the catch statistics have fluctuated
dramatically, with a general decline in production (Van Sickle et al. 1976; Dugas 1977).
Louisiana currently leads the gulf states in production, with an average yield of about 4
million kg (9 million pounds) of meat yearly. This figure has remained constant over the
last 20 years with only severe environmental catastrophies influencing the harvest.
Although environmental problems occasionally affect production, such as diverting the
sediment-laden waters of the Mississippi through the Bonne Carre Spillway into Lake
Pontchartrain. Louisiana generally ranks second nationally (after Maryland) in yields.
Dockside value of Louisiana's oyster harvest is between $3 million and $4 million annually
(LyIes 1967; U.S. Department of Commerce 1968-1975).

As oystermen are "farmers of the sea", they must contend with a number of forces
that can destroy the crop (Gunter 1955). The oyster has a number of enemies. The
oyster drill, or boring snail (Thais haemostoma and 1_. floridana) locally known as a
"conch" and the saltwater drum (Pogonias cromis) are at the top of the "unwanted list"
(McConnell and Kavanagh 1941; Waldo 1957; Van Sickle et al. 1976; Dugas 1977). The
deadly drill occurs over a wide area in Louisiana's oyster bedding waters, but it must
have high salinities to survive (Burkenroad 1931; Goltsoff 1964). The saltwater drum is
another unwanted predator that congregates in large schools whose collective appetite
can destroy a bedding ground in a single night (Van Sickle et al. 1976). Both predator
problems are saltwater dependent.

Although oyster culture is plagued by a number of problems, the oyster fisherman
continues to be the backbone of this commercial fishing industry. Along the bayous of
south Louisiana oyster luggers are part of the waterfront landscape. They represent a
commitment to harvesting the oyster in much the same way as the Lafitte skiff relates

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to the shrimp fishermen. Through time, the oystermen has learned to live with all his
problems. In 1913, there were at least 1,700 people involved in Louisiana's oyster
industry (Hart 1913). Today, there are more than 2,000 liscensed oystermen, each of
whom pays a small lease fee to stake out an oyster bed. In 1912, there were almost 7,000
ha (17,000 acres) leased to oystermen (Hart 1913). Currently, there are more than 80,000
ha (200,000 acres) involved in the fishery (Dugas 1977).

The industry is thriving, but its future will depend, in part, on the environmental
changes taking place along the coast. The distribution of the oyster depends on the
salinity content within the estuarine and nearshore areas. Salinity in many of the
interdistributary basins is increasing as a result of the coastal deterioration that has
accompanied land subsidence and canalization (Chapman 1968; Barrett 1970; Morgan
1972; Davis 1973). With increases in salinity, and if more firm substrata are available,
oyster populations could actually increase. If the land that encloses the estuarine
environments is lost, however, and the area becomes open water, then the industry will
decline and another renewable resource will be gone.

Menhaden . The third valuable commercial marine resource is the menhaden
(Brevoortia patronus), or "pogie." The first landings of menhaden were reported in the
region around 1940, although commercial exploitation of the species can be traced back
to the early 1800's along the Atlantic coast (Lyies 1967; Christmas and Etzold 1977; Frye
1978). Since then, menhaden has become the principal industrial fish taken in
Louisiana. The reason for its apparent late development is that the oily flesh of the
species is not suitable for human consumption, but when processed it is a valuable source
of oil and animal feed.

Catch statistics reveal that the first landings were in West Florida. In 1880, less
than 450 kg (1,000 lb) were harvested. Since this small beginning, the industry has
expanded considerably. Although variability exists in the catch record, landings have
increased steadily since the 1 950's (Christmas and Etzold 1977). The production curve
reached its peak in 1971 when Gulf of Mexico ports processed 700 million kg (1.6 billion
lb). Since this record year, landings have exceeded 450 million kg (I billion lb) annually
(Christmas and Etzold 1977).

Louisiana's "pogie" fleet annually harvests from 270 to more than 450 million kg
(600 million to I billion lb) of this industrial fish. With the area located in and around the
Mississippi delta as particularly productive, combined with improvements in fishing gear,
menhaden fishermen harvest a catch worth, in most years, in excess of $10 million
(Perrett 1968; St. Amant et al. 1973; Wheeland and Thompson 1975).

Although "shrimp is king" in Louisiana, by weight the menhaden industry is the
State's most important fishery. Consequently, the menhaden catch has made the ports of
Cameron, Empire-Venice, and Dulac-Chauvin among the top five fishing ports in the
United States. Combined, these ports account for a fisheries harvest greater than 390
million kg (850 million lb), which represents more than $80 million in annual fisheries
income. With continued emphsis on providing protein meal to the underdeveloped
countries, the future of the menhaden industry looks favorable. It is, however, necessary
to maintain the estuarine environments used by the young fish in the early stages of their
development (Rientjes 1970; Dunham 1972). If this habitat is lost, then the menhaden
could be seriously impacted.

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The habitat changes that would result from land loss would mean that Louisiana's
position as the Nation's number one "seafood factory" would vanish. In addition, the jobs
directly and indirectly associated with these renewable resources would also disappear.

Recreation; The Favorite Pastime of Coastal Sportsmen.

With one out of every two Americans involved in outdoor recreation, and with
water serving as the largest single attraction, the water bodies and biologic resources of
coastal Louisiana attract both resident recreationalists and out-of-state tourists in
rapidly increasing numbers. The income generated by the recreation/tourist trade plays
an important role in the region's economic structure.

Grimes and Pinhey (1976) noted that by the year 2000, Louisiana wetlands will be
needed to meet the recreational demand of the State's expanding population. With two-
thirds of Louisiana's inhabitants located within 2 hours driving time of the marshlands,
the coastal zone and associated offshore waters are already available to a large
population for day or overnight use.

In 1970, Louisiana's deltaic wetlands supported an estimated 10 million man-days of
recreational activity annually (Martin 1972). If this figure increases to 25 million user
days by 1985, as expected, Louisiana's deltaic wetlands will be worth in excess of $55
million/acre/yr (assuming a user-day value of $l5/day). The onshore and offshore
recreational areas are utilized at a relatively intense rate due to their accessibility and
because they are free of high user fees and other use-inhibiting factors. With 90% of the
land lost in freshwater marshes, however, the preferred winter habitat of puddle ducks is
being reduced. By the year 2000, the "recreational ledger" will show a deficit of more
than 360,000 user-days. There will not be enough marsh to meet the hunter demand
(Fruge 1981).

Nevertheless, the coastal marshes provide outdoor enthusiasts with year-round
recreational opportunities. In fall and winter, hunters, trappers, and fishermen harvest
ducks, muskrat, nutria, alligator, and numerous fresh- and saltwater fish. In contrast,
spring is the season to shrimp, crab, crawfish and fish for spotted seatrout (Cynoscion
nebulosus), largemouth boss (Micropterus salmoides), and red snapper (Lutianus
campechanus). From the beginning of spring until the first cold front moves througn the
area, fishing and boating are the principal elements in the use-cycle. By late September,
the gallinule (Gallinula choropus) season is open, followed by quail, dove, rail, snipe,
duck, and geese (Chabreck and Joanen 1966).

Hunting and fishing; the principal recreational activities. Louisiana is a wintering
area for between 6 million to o million waterfowl per year; approximately 75% to 80%
concentrate in the coastal marsh (Burts and Carpenter 1975). The 36 waterfowl species
that winter in Louisiana make hunting an extremely important and popular recreational
activity (St. Amant 1959).

Sportsmen take advantage of the birds migratory cycle and have utilized the
chenier and deltaic plains as a major waterfowl hunting locale, bagging 2.8 million water
fowl in the 1977-78 season. In that same season, the coastal parishes contributed 63% of
the total State waterfowl harvest (Gauthier 1978).

Wetland hunting is a traditional winter sport activity. As a renewable resource, the
migratory populations are maintained by properly managing the wetlands. This is

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accomplished by closely regulating hunting activity during breeding, migration, and
wintering activities (Duffy and Hoffpaeur 1966; Herring 1974). In short, habitat
preservation is the key to maintenance of the waterfowl resource and an annual recurring
income that in most years exceeds $80 million (Larson et al. 1980).

Species diversity of fresh- and saltwater fish and shellfish in the coastal lowlands
results in fishing generating the highest participation rates of all the recreational
activities. As a year-round leisure-time activity that varies with the breeding cycle of
the various fish species, water levels, fishing pressure, and habitat productivity (Lambou
1963), fishing-related expenditures exceed $40 million annually (International Marine
Expositions 1978). More than 1 1,000 km (7,000 mi) of wetland shoreline provide more
than 390,000 resident fishermen with extensive recreational opportunities. Since 1950,
the number of resident licenses in the coastal marshes has increased by more than
100,000. This indicates that sport fishing is a popular recreational pastime and one that
will continue to grow in popularity. Consequently, Louisiana will need more fishing
areas, not less.

Along Louisiana's coast there are 60 species of fish that are associated with the
estuarine or marine environments (Mclntire et al. 1975). Freshwater fisherman seek a
diversity of fish species, especially largemouth bass (considered the top gamefish),
catfish, "sac-a-lait" or crappie, and bluegill or bream. The black bass (largemouth bass)
Is considered the state's most sought-after game fish. Whereas, saltwater fisherman
primarily catch spotted seatrout, Atlantic croaker (Micropogon undulatus), one of the
most abundant commerical fish along the gulf coast (Rogillio 1975), redfish (Sciaenops
ocellata), sometimes referred to as "bull" or "rat" reds, and black drum (Pogonias
cromis). The spotted seatrout is the main species caught, representing 40% of the daily
saltwater fish catch (Louisiana Wild Life and Fisheries Commission 1970).

In addition, offshore there are more than 2,500 oil and gas platforms that serve as
artificial reefs for fish communities. The fishing activity near the "rigs" is often
excellent. To take advantage of this clustering, 40 to 50 charter boats ferry saltwater
anglers to these sites.

It is apparent that the recreational sportsman benefits greatly from Louisiana's
wetlands. The area is a recreational resource of inestimable value. It has been utilized
throughout this century to meet the leisure-time needs of the State's inhabitants and
others. Those who take advantage of this unique environment recognize its value, since
they provide millions of recreational efforts per year. Unfortunately, as the area is lost,
the habitats perferred by the game birds and fish will dwindle, thus affecting an industry
that contributes an estimated $200 million to Louisiana's economy. Loss of this revenue
will result in the collapse of the infrastructure that is supported by the industry. Also
affected will be the number of unhappty individuals who can no longer profit from a
marsh that provides the water-oriented sportsman with unexcelled recreational
opportunities.

FROM AGRICULTURE TO OIL: THE CHANGE IN LAND USE PATTERNS

Throughout Louisiana's history, agricultural activities have occupied an important
position in the wetland's social and economic environment. The wealth gained from
hydrocarbons, commercial fishing and trapping, industrial development and tourism do
not overshadow the value of agricultural products. The favorable climate and fertile

150

alluvial soils allow almost every crop indigenous to the western hemisphere to be raised.
Arable land, however, is limited in this region because of poor drainage and the
availability of land suitable for agriculture. For more than 200 years the Nation's
marshlands were thought to be of no economic value; they were considered worthless.
Nevertheless, in New England and the Middle-Atlantic states many wetland grasses were
harvested for livestock. Lamson-Scribner (1896) reported hay production of up to I ton
per acre, with hay stacks dotting the coastal lowlands. For more than half of the
twentieth century the marsh was not developed for its intrinsic value. It was reclaimed
to satisfy the needs of an expanding population (Allen and Anderson 1955). The
agricultural lessons learned on the eastern seaboard were apparently forgotten or
ignored.

Today, the alluvial wetlands are recognized as a valuable and highly productive
environment, whose productivity can easily outstrip the best cultivated land. It is a
renewable resource; one that operates with minimum capital expenditures and is
epitomized in Louisiana.

Those who originally entered coastal Louisiana were explorers, hunters, trappers,
and fishermen. Travel records and archaeological investigations reveal that these "folks"
depended on the land for their subsistence. English, French, Acadian, and Creole farmers
followed and created scattered communities along the natural levees of the region's
bayous.

By 1822, the coastal zone's population was scattered along the main cheniers,
coteaux, hummocks, islands, and natural levees. This "high ground" supplied farmer-
trapper-fisher "folk" with the essential requirements for their economic existence and
became the focal point of human occupancy. In a sense, these communities are
considered a homogenous unit, since people consider a bayou settlement, regardless of
length, as a single entity with varying degrees of continuity.

Farming was practiced throughout the region. Many areas that were farmed are
now underwater or so small and isolated that they can no longer be used for row-crop
agriculture. Most of these tracts are composed of mineral and organic soils firm enough
to support cattle, but not suitable for farming by traditional methods. Consequently,
marsh dwellers for more than 100 years have been grazing cattle within the marsh. They
have learned to live with a serious problem and yet maintain a way of life that serves as
a link to the past and is an important part of the region's cultural heritage. Since
approximately 20% of Louisiana's cattle graze the wetlands, it is a unique industry.
Proper and often inventive management techniques allow the herds to survive. The
marshes are a recognized cattle producing region, that will continue only if careful
management of the region continues.

Traditionally, arable natural levee land has been used to produce sugar cane. With
mills closing and price uncertainties, the future of the business is in question, however.
Farmers are selling their land. The form and intensity of land use competition with sugar
cane are perhaps most visible. Since the region has become more populous, more
prosperous, more urbanized, and more industrialized since World War II, land is at a
premium.

The dynamic nature of the growth trend is derived essentially from the long-term
development of the area's vast hydrocarbon resources. Extensive service base expansion
at the expense of agricultural production, commercial fishing, and trapping activities,

151

the relatively low average cost of living, a favorable tax structure, an attractive climate
and the unique cultural/recreational annenities also contribute to the region's growth. A
recent source of land use competition Is associated with hydrocarbon development: oil
and natural gas wells, pipeline pumping stations, and natural gas processing plants.
Individually, these uses occupy relatively small plots of land. Together, although precise
estimates are not available, the total area Involved is substantial. Few farmers refuse to
sacrifice a portion of their cropland to gain the potential income from an oil or gas well
or the proceeds from a long-term oil lease.

Suburban expansion is apparent also throughout the sugar region and the population
of the entire coastal zone is growing at an annual rate of approximately 5% (University
of New Orleans 1977). Competitive land uses associated with urbanization are often
directly linked to the petroleum Industry.

Sailors exploring the coast of Louisiana and Texas in the I600's recorded seeing a
black slick floating on the sea. This seepage provided a small clue to the vast storehouse
of hydrocarbons trapped in a geosyncline stretching from Mississippi, through Louisiana
and into the coastal provinces of Texas. The resource was not drilled until 1901 when a
wildcatter completed the first producing well in south Louisiana (Postgate 1949). In
developing this resource more than 28,000 wells have been drilled in the coastal zone.

In 1947 the search for recoverable hydrocarbons moved offshore and a new chapter
was added to the history of the petroleum industry (Londonburg 1972). Since the
successful completion of Kerr-McGee's, Phillips Petroleum's and Stanolind Oil's first
offshore well on the continental shelf, the oil Industry has drilled more than 20,000 wells
in the open waters of the Gulf of Mexico. Currently, more than 2,500 platforms are
pinned to the Gulf's floor. With the ever-increasing demand for hydrocarbons, oilmen are
drilling in areas previously considered economically unfavorable. Working in the coastal
marsh and then farther and farther offshore, drilling crews are now drilling on leases
more than 241 kilometers (150 miles) from logistic support bases In water greater than
304 meters (1,000 ft) deep.

Largely as a result of this activity, Louisiana produces at least 35% of the Nation's
natural gas and 25% of its oil. As production has Increased, so have support Industries
such as storage yards, pipe suppliers, and pipeline contractors. The needs of the oil
Industry have spurred growth in ship-building and all kinds of marine supply businesses
that vend everything from diving equipment to fast-food, shore-to-ship, catering
services.

The dynamic growth of oil and gas exploration during the last three decades has
placed an entirely different demand on the relatively few "chunks" of high-and-dry real
estate in the coastal zone; the demands for solid ground now include much more than
having a firm place to anchor a drilling platform. The need for onshore support bases,
platform fabricators, pipe supply yards, ship yards, and service facilities have Increased
exponentially. Today, virtually every community that borders the bayous of south
Louisiana serves as headquarters for one or more support services needed by the oil and
gas industry. Because land is at such a high premium, some firms have built extremely
compact facilities to handle the large and complex operations needed to build ships,
offshore platforms, and other complicated pieces of machinery. Refiners and
petrochemical manufacturers compete for the few large plots so they can install plants
as close as possible to the source of their required hydrocarbons. As a result, population
clustering has created a heterogeneous mixture of residential, commercial, industrial,

152

and transportation properties. Settlennents are agglomerated into strips because of the
reciprocal relationship between each and the natural environmental restraints placed on
urban and built-up land. The strips are limited by a finite quantity of arable property,
reflected in land use patterns and threatened by continued land loss.

As the petroleum business is a multibillion dollar industry, land loss will have a
dramatic effect on the region's oil- and gas-related economy. Logistic support sites will
be lost, thus complicating the movement of men and equipment to production sites.
More importantly, as the land erodes, so does the State's land/water boundary;
consequently, the outer limit of Louisiana's offshore zone moves shoreward. The end
result is Louisiana's oil royalties decrease by at least $20 million per mile of coastal
retreat and a highly significant source of revenue is changed. This is probably the single
most important immediate result of land loss and one that can change a number of
favorable advantages of living and working in Louisiana.

CONCLUSIONS

By nature coastal regions are the most continually changing zones on earth; they
represent one of the most viable and complex regions on the globe. Within this
environment there is a never ending interplay between the great forces and processes of
nature that are constantly resculpting the region's topography. Man has had relatively
little effect on these agents; he has no control over the natural processes that have for
centuries influenced the coast. He has, however, promoted directly and indirectly some
coastal modifications. The manmade elements that have altered flow regimes, sediment
patterns and vegetative "assemblages have created a problem. The problem is related
directly to man's interference with the Mississippi's flow regime. As a result, the
wetlands are out of balance. Land loss forces now supersede constructive forces thus
threatening the jobs, industries, and lifestyles of the people whose lives are tied directly
or indirectly to the coast. The final question is: "Can we afford the loss?"

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155

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157

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158

PANEL DISCUSSION

CONSEQUENCES: SOCIAL AND ECONOMIC

Edward W. Stagg, Moderator

Paul Hribernick, Michael Osborne, Donald W. Davis and
Charles Broussard, Panelists

Charles Broussard: I can best illustrate how regulations can interfere with environmental
use or nnanagement by relating a case study. One of the earliest attempts to acquire
a permit for deterring saltwater intrusion was in Vermilion Parish. Hurricane Edith
in 1971 caused six openings allowing tidal transport of brackish water into the
Mermentau Basin. The maintenance of the Mermentau Basin as a freshwater area
for rice farming, fish and wildlife habitat, and navigation was mandated by Federal
law. The act, however, did not allow the Corps of Engineers to expend Federal funds
except for control structures. The State Office of Public Works, therefore, funded a
project to close these breaches and bids were advertised in October 1972. Section
404 of the Clean Water Act became effective in 1972 and I thought it would be a
great assistance in protecting our coastal environment. It has had the opposite
effect in this case, however. Letters of concurrence were sought and obtained from
a large number of State and Federal agencies, including the U.S. Fish and Wildlife
Service, for this project. The National Marine Fisheries Service, however, objected
to the closure of the breaches saying this is a saltwater estuarine area. To this day,
there has still been no permit issued and there are now 167 attachments to the
original application.

The intent of the laws related to coastal zone management is not being
realized. Rice farming has been driven out of the area. Waterfowl populations
declined because of a reduction in millet, or wild rice, from 80,000 acres to a few
thousand acres. Duck populations declined from more than a million to less than
200,000. Hardness of ground water in the region has increased due to saltwater
intrusion from negligible amounts of 12 grains/gallon in deep wells in 1930 to 70 to 90
grains/gallon, which is not fit for rice farming or human consumption.

Donald Landry: The Houma Navigation Canal was built with Terrebonne Parish funds but
is maintained by the Corps of Engineers. It has now widened beyond the 700 ft
right-of-way. What is the legal responsibility of the assuring local agency to the
property owners?

Paul Hribernick: Similar problems exist with the Houma Navigation Canal and the
Mississippi River Gulf Outlet. The law is unclear with regard to bodies of water
made navigable. If the bottom is found to be in State ownership, normal erosion
rules would apply, and land owners may be able to reclaim land damages for which
they haven't received compensation from the government. The law does not say who
pays for restoration, however. The land owner may be able to sue in a tort for
compensation in which case the liability of the government would be limited to fair
market value of the lost property.

159

Michael Osborne: The legal liability may depend on the stated responsibility in the
assuring agreement.

John Uhl: This question has been recently raised with the Corps of Engineers in regard to
the Harvey Canal.

Clcorke Lozes: Assurances require that the Federal Government be held harmless and
safe from damages and require State and local government maintenance.

Rod Emmer: In preparation of an environmental impact statement for the Almonaster-
Michoud Industrial District in New Orleans, we identified, as an impact, accelerated
erosion of the Mississippi River Gulf Outlet and recommended implementation of
structural measures to offset this erosion. The responsibility for protecting the
shoreline may be identified beforehand in this case.

Michael Osborne: It seems to me that the parish could make a strong legal argument
that, in the case of navigation canals designed or constructed by the Corps of
Engineers, that if the canal widened beyond the right of way, the Corps inadequately
designed the project for its 50-year life.

John Uhl: What can be done to streamline the permit process?

Charles Broussard: There should be limits to the time allowed for response to permit
applications. There should be clarification of the role of State agencies in the
review process. For example, in the Mermentau Basin case, the National Marine
Fisheries Service would not accept the Louisiana Department of Wildlife and
Fisheries report. Also, there should be limits to the time for interagency conflict
without resolution.

John Uhl: We tried to include in the Jefferson Parish coastal zone management program
time limits for reasonable responses and discussion of 6 months to one year. This
was met with some consternation.

Charles Broussard: The Secretary of the Army has the right to make a decision even
when a conflict is not resolved, but such decisions are politically difficult.

Michael Osborne: There is some confusion of these past procedures and problems under
Corps of Engineers administration of Sections 10 and 404 with the present State
adminstered coastal use permit system begun in October 1980. Often the blame for
these environmental conflicts belongs with the people who engineered the project
for not anticipating these problems of conflicts in water resource uses.

Charles Broussard: In the Mermentau Basin case, a broad view of multiple resources was
held from the beginning and was the reason for developing the project. Replacement
of the Vermilion Locks has begun at a cost to the Federal Government of $36.8
million. This project is being developed to maintain the integrity of the Mermentau
Basin, yet within a stone's throw we are not allowed to close the breaches in order to
prevent saltwater intrusion.

Paul Hribemick: Section 404 is an attempt to effect multdisciplinary decisionmaking
but, in the political compromises needed to pass the act, effective veto power was

160

given to agencies which serve different constituencies. For example, the National
Marine Fisheries Service represents commercial fishing interests, the Corps of
Engineers represents navigation interests, and the Fish and Wildlife Service
represents wildlife and recreation interests. We need better administrative solutions
to resolve the conflicts which develop among the constituencies. The State coastal
zone management program is set up to assist in the resolution of these conflicts.
The Coastal Management Section must make permit decisions within 42 days from
receipt of application unless inadequate information is included in application. In
the short existence of the coastal use permit program, 800 decisions were issued in
an average of 56 days including delays because of Inadequate information. The
possibility of general use permits is also being considered to further streamline the
process. The State program also includes coordination meetings with Federal and
State agencies during which individual projects are reviewed.

Unidentified speaker: A recent memorandum of understanding between the Corps of
Engineers and Environmental Protection Agency sets up a process for special
treatment of hardwood bottomlands. Can anyone explain this process?

Michael Osborne: The Avoyelles Sportsman's League case led to an argument regarding
which agency has the right to decide what is a wetland. The agreement to which you
refer is an attempt to establish this responsibility.

George Robichaux: The Department of Health and Human Resources is engaged in an on-
going flood plain management program and one consideration is specific prohibition
of habitation within flood plains. Beyond immediate intransigence, what will be the
long-term social and cultural impacts of that type of prohibition?

Donald Davis: There would definitely be cultural impacts because many residents have
occupied these areas for many generations. It is difficult to tell someone that they
can not live where their grandfather did and most people will refuse to move. If it is
a question of no longer offering them subsidized flood insurance, I think that most
people would still resist moving.

Donald Landry: The Federal flood insurance program is being reviewed and the total
elimination of subsidized flood protection in coastal areas is being considered.

Charles Broussard: If we are not allowed to protect our barrier islands, land loss will
accelerate to unbelievable rates throughout south Louisiana.

Donald Landry: Does land accreted on a barrier island go to the property owner?

Paul Hribernick: Land accreted on a barrier island goes to the State. Receding shoreline
can be reclaimed by private land owners at their own expense.

161

OPTIONS: BARRIER ISLAND

AND SHORELINE PROTECTION

163

FUTURE SEA LEVEL CHANGES
ALONG THE LOUISANA COAST

Dag Nummedal

Department of Geology

Louisiana State University

Baton Rouge, LA 70803

ABSTRACT

The relative elevation of sea and land has been changing throughout time in
response to two fundamentally different groups of factors. Global factors include
changes in the volume of the ocean basins due to tectonic processes and changes in the
total amount of ocean water due to glaciation. Local factors include subsidence of
continental margins and the compaction of recent sediments. During this century, global
sea level (eustatic) appears to have been rising at a rate of 1.2 mm/yr. Along the south-
central Louisiana coast the land surface appears to be sinking at a rate of about
8 mm/yr.

Recent global climatic modelling strongly suggests that we are about to enter a
period of rapid warming due to increased amounts of carbon dioxide (CO2) in the
atmosphere. As a consequence, eustatic sea-level rise is predicted to accelerate both
because of steric expansion of the ocean water and continued melting of polar ice caps.
For the next 40 years the eustatic sea-level rise may average 10 mm/yr. The local
relative sea level in coastal Louisiana would therefore rise at about twice its present
rate over this time period. At this rate local sea level will, in the year 2020, stand some
70 to 75 cm higher than now.

INTRODUCTION

Sea level, that universal elevation datum, is neither level nor constant. Spatial and
temporal fluctuations in sea level occur at all scales and frequencies.

Global sea-level variations on the geologic time scale of tens of millions of years
occur in response to tectonically controlled changes in the volume of the ocean basins
(Hays and Pitman 1973). The actual change in location of the shoreline on a continental
margin becomes a function of the rate of global (eustatic) sea-level change relative to
the rate of margin subsidence, sedimentation (or erosion), and a number of local
factors. On passive continental margins (as the U.S. Atlantic and Gulf of Mexico coasts)
the rates of tectonically controlled changes in the relative elevation of sea and land are
quite slow, typically a few mm per 1,000 years (Pitman 1978, 1979). Furthermore, the
slow yet persistent subsidence of a continental margin geosyncline is generally
compensated by landward mantle flow and uplift of the coastal plain. Evidence for this
is seen in progressively older, uplifted strata in a landward successsion away from the

164

present Atlantic and Gulf of Mexico shorelines (Oaks and DuBar 1974).

Superimposed on these essentially tectonic sea-level changes are higher-frequency
fluctuations of a multitude of origins. Periodic formation of continental ice sheets and
attendant deglaciations have, at least since the Pliocene and possibly throughout the
Cenozoic (Matthews and Pore 1980), been responsible for major sea-level changes on a
typical time scale of 10,000's of years. Present sea level appears to be at an elevation
comparable to that reached during earlier major interglacials. The latest low stand of
sea level occurred at the peak of the late Pleistocene Wisconsin glaciation some 18,000
years ago. Early sea level curves (Curray 1965; Milliman and Emery 1968) indicated that
this low stand was as much as 130 m below present sea level. Recent work by Dillon and
Oldale (1978) and Blackwelder (1980), however, strongly suggests that sea level may have
risen much less than 100 m since the late Wisconsin low (Figure I).

a.
Q

100-

150

® Fixed samples
• Mobile samples
— Proposed sea-level
curve; U. S. East Coast

Years BP X 10^

Figure 1. Sea-level curves for the late Quaternary inferred from radio-
carbon-dated samples along the east coast of the U. S. (Dillon and Oldale
(1978). The most recent curve (dashed) suggests a late Wisconsin low stand
of less than 100 m below present sea level.

Regardless of the absolute magnitude of sea-level rise over the last 18,000 years,
this "Holocene transgression" is responsible for the existence of a multitude of coastal
sedimentary sequences (deltas, fluvial channel fills, marsh deposits, tidal channel fills) on
the present shelf floor (Curray 1965; Swift 1976; Field et al. 1979; Pilkey et al. 1981). At
the time of maximum ice retreat, global sea level rose at a rate of about I m/century, a
rate which is about four orders of magnitude faster than the long-term tectonically
induced global sea-level changes.

Because the relative abundance of stable oxygen isotopes in deep-sea sediments is a
measure of global oceanic temperatures, one can reconstruct a paleo-temperature time
series from analysis of deep-sea cores (Figure 2). This curve suggests the existence of
numerous glaciations on a time scale of about one every 100,000 years throughout the
Pleistocene (Shackleton and Cita 1979).

165

+ 4 0 "^ o-

+ 3 0 » Worm

-^ ^ ^ ^ f55 ioO 50 b Depth below sea floor (m)

4n..y. 2.4 my. 2 m.y. 1 m.y.

Approximale Age

Pliocene Plelilocene

Figure 2. Oxygen isotopic record for the Pliocene and Pleistocene in Deep
Sea Drilling Project Site no. 397 in the Atlantic Ocean off northwest
Africa (modified from Shackleton and Cita 1979). Highe^^O values indicate
periods of global cooling and formation of continental ice sheets.

RECENT GLOBAL SEA LEVEL CHANGES

Sea-level fluctuations on the time scales discussed have controlled the time-
stratigraphic evolution of continental margin sedimentary sequences. They also provide
some hints of what factors should be considered in trying to explain present short-term
sea level fluctuations (lO's of years) and they may guide our modelling efforts in
attempts to predict the future, in the following discussion of present and near-future
sea-level changes, a clear distinction has been made between eustatic factors (i.e.,
factors which affect the global sea level) and local factors (which include subsidence and
local oceanographic effects).

Recent data increasingly support the view that sea level did not rise in a smooth
and continuous fashion during the Holocene transgression. The rise appears to have been
characterized by a series of oscillations with an amplitude of a few meters on a typical
time scale of lOO's of years. Data supporting this view are mostly archaeological (Figure
3A, Brooks et al. 1979), yet historical data in Europe suggest that there has been a one-
meter sea-level fluctuation within the last millenium (Figure 3B, Rhode 1978). The most
recent sea-level minimum coincides with the peak of the "little ice age" at the end of
medieval time.

Over the last century an increasing number of tide gauges have been installed in
harbors around the world. Records from such gauges yield information about the local
relative change in level of the sea and the land upon which the gauge is placed. All such
records demonstrate large fluctuations in mean annual sea level; generally, however,
these fluctuations are superimposed on a secular trend. The annual fluctuations derive
from long-term meteorological tides (atmospheric pressure variations), continental run-
off and winds (Fairbridge and Krebs 1962). The longer term (decades) trend is more
controversial yet of paramount significance to human efforts at developing the coastal
zone.

Attempts to derive the rate of global sea-level rise from such tide gauge records
have generally been based on various trend analysis techniques applied to the "average"
of records from a number of stations. Records from stations known to be subject to
rapid sinking (Galveston, Texas; Louisiana coast) or rising due to glacioisostatic rebound
(Scandinavia, parts of Canada) or underthrusting of an oceanic plate (Oregon,

166

Washington, Alaska, and Japan) are customarily excluded in such trend analysis. Yet
little is really known about continental subsidence rates at the remaining tide gauge
stations.

6 5

4 3 2

YEARS BPX 1000

YEARS AD

Figure 3. A. Sea-level fluctuations on the central South Carolina coast
over the last 4000 years (modified from Brooks et al . 1979). Curve is based
on radiocarbon dated archaeological samples and basal peats. B. Sea-level
fluctuations on the North Sea coast of Germany since 650 A.D. (modified from
Rhode 1978). The curve is based on hisitorical data.

In view of these complications it is remarkable that five independent analyses of
sea-level rise have arrived at nearly identical global rates. Gutenberg (1941) appears to
have been the first to identify a world-wide rise in sea-level since the mid-1800's at a
rate of about I mm/yr. Analysis of a larger number of stations by Fairbridge and Krebs
(1962) yielded a rate of rise of 1.2 mm/yr between 1900 and 1950. A comprehensive
analysis of all reliable U.S. tide gauge data by Hicks (1978) gave a relative rise (with
respect to North America as a whole) of 1.5 mm/yr (Figure 4A) for a 36-year period from
1940 through 1975. Emery (1980) found that the sea levels at 247 tide gauge stations of
the world did exhibit a rise of about 3 mm/yr since 1940. The most recent study (Gornitz
et al. 1982) which is based on more than 700 tide gauge stations. All geographic regions
of the world experienced a sea-level rise (after correcting for uplift or subsidence of the
land when known), and the global rate of rise is 1.2 mm/yr (Figure 4B)(Gornitz et al.
1982). This study (Gornitz et al. 1982) may come the closest yet to actually having
identified global eustatic sea-level change.

167

90
80
70
60
50

- 40

- 30

■ 20

■ 10
0

E
E

-D

1940

1950

1960

1970

Figure 4. A. Average sea-level time series for all U. S. tide gauge
stations with the exception of Alaska and Hawaii (Hicks 1978). B. Global
mean sea-level trend from tide gauge data (modified from Gornitz et al. 1982)

Mean sea-level fluctuates seasonally (Pattullo \966; Nummedal and Humphries
1978). Along the U. S. gulf coast the annual amplitude is about 25 cm (Marmer 1952).
Sea level is maximum in early fall due to the steric effect (thermal expansion of
seawater above the thermocline). Other factors affecting seasonal sea level include
freshv^ater runoff from the continent (Meade and Emery 1971) and persistent winds
(Behrens et al. 1977).

To test whether the thermal expansion of water also could have a long-term effect
on rising sea level, Gornitz et al.(l982) correlated the global mean sea-level trend for the
last century and the global mean temperature curve for the same time period derived by
Hansen et al. (1981). Using 5-year running means of both parameters they obtained a
correlation coefficient of 0.8. Best regression fit was obtained for a time lag of 18 years
between the temperature and sea-level rise curves. This lag time is of the same order as
the thermal relaxation time of the upper layer of the ocean. The findings suggest that at
least part of the observed global sea-level rise is attributable to the thermal seawater
expansion. A simple one-dimensional model of the heat flux into the ocean and the
attendant thermal expansion suggests that only about half of the observed rate of global
sea-level rise can be attributed to steric expansion; the balance may reflect a slow, but
steady, melting of polar ice sheets as well as lowering of global groundwater levels.

PREDICTION OF FUTURE CHANGES IN GLOBAL SEA LEVEL

Sea-level studies have traditionally been historical and empirical. The derived sea-
level curves have been so variable (Bloom 1977) as to make trend extraction and future
predictions all but impossible. Yet scientifically based estimates of future sea levels
should be a key component in decisions regarding the use and protection of low-lying
coastal lands. The findings reviewed above now permit such a prediction.

168

From the analysis presented in this paper, temperature emerges as the key control
on sea level. It directly controls steric water expansion and the mass balance of the
polar ice sheets. It indirectly controls global surface- and groundwater budgets. The
global mean temperature record over the last century can best be explained in terms of
the combined effects of natural climatic cycles and a warming trend from addition of
CO7 to the atmosphere ("greenhouse effect") due to the burning of fossil fuels (Broecker
1975).

An extension of Broecker's analysis has been made in Figure 5 with temperature
data updated through 1980 and the model of Hansen et al. (1981) used as a basis for the
predicted C02-related warming trend. The figure demonstrates that observed
temperatures essentially fall within the range predicted from the two component trends
for most of the century. Global temperatures over the last few years, however, have
risen significantly above the predicted trend.

"le natural temperature cycles used in this analysis are based on analysis of stable
; (0) in ice cores from Camp Century in Greenland (Dansgaard et al. 1971).

Thf
isotopes

Whatever the origin of the climatic cycles observed in the Greenland ice cores, the
pattern has been essentially stable during the last 1,000 years. Two cycles appear to be
inherent in the Camp Century temperature record, one of 80-year and another of 180-
year duration. The curve in Figure 5 is the composite of these two cycles. Because of
the regular harmonic pattern this natural temperature curve can easily be extended and
thus provide one element in the predicton of future global temperature trends.

It is well documented that the COn
steadily increasing in this century (Si
modelling of the atmospheric response to
Wetherald (1975) and Hansen et al. (198!
in the atmosphere from "pre-industrial"
increase global temperatures by 2.4°C to
atmospheric CO2 content because this
throughout the world.

content of the terrestrial atmosphere has been
egenthaler and Oeschger 1978). Numerical
an increase in its COt contents by Manabe and
) suggested that a doubling of the CO2 content

levels of about 300 ppm to 600 ppm would
3.5°C. A major unknown, is the rate of rise of

is largely controlled by industrial patterns

Natural Cycles

Observed Globol Mean

COj Worming

Predicted Temperature Trend

1900
Year

Figure 5. Global temperature variations. The predicted temperature trend
is the composite of that due to C02-induced warming and natural temperature
cycles. Observed global temperatures and predicted COp warming from Hansen
et al . (1981). Figure design modeled after Broecker (1975),

169

According to the model of Hansen et al. (1981) for slow energy growth (1.5% annual
growth in energy consumption) one would expect an increase in global temperature of
about l.5°C at the end of the next century. Using the thermal expansion model (Gornitz
et al. 1982) for sea water, the steric effect alone would cause a corresponding increase in
global sea level (eustotic) of about 30 cm. If the steric effect has been responsible for
half of the observed sea-level rise over the last century and this same ratio should
continue under a regime of further global warming, then total eustatic sea-level increase
for the next century would be 60 cm. Eustatic sea-level rise over the last century was
only about 12 cm. This predicted five-fold increase in the rate of eustatic sea-level rise
should be attributed both to the increased atmospheric CO2 and the fact that for the
next 40 years the earth will experience the warming phase of the natural (Camp Century)
temperature cycles (Figure 5). Because of cyclicity of the natural temperature
variations, sea level is likely to increase in a step-wise rather than linear fashion over
the next century. The next 40 years (1980-2020) will probably be the period of the most
rapid rate of sea-level rise. The eustatic rate of rise could conceivably be as high as
I cm/yr during that time. That rate corresponds to the most rapid post-glacial rise some
I 1 ,000 to 1 2,000 years ago.

Without intending to be alarmist, another consequence of the predicted global
warming must be mentioned for the sake of completeness. This concerns the West
Antarctic ice sheet. This ice sheet is grounded below sea level making it vulnerable to
rapid disintegration and melting in case of a general warming (Hughes 1973; Mercer
1978). Since the present summer temperature in its vicinity is about -5°C a global
warming of 2.5°C might seem insignificant. All global atmospheric models stress,
however, that the magnitude of polar temperature fluctuations exceed those of the
global mean because of albedo-related positive feedback. A global warming will reduce
high-latitude snow cover, reduce the surface albedo, and thus heat that region more
rapidly than low-latitude zones (Manabe and Stouffer 1980). A 2°C global warming may
cause a temperature rise of about 5°C in Antarctica and thus induce melting of the West
Antarctic ice sheet. The response to that event would be an increase in global sea level
of between 5 and 6 m (Mercer 1978). This rise would not be uniform across the globe,
however, because of changes in the gravitational attraction exerted by the ice sheet on
the surrounding ocean, the Earth's immediate elastic response to the unloading, and the
long-term response due to viscous flow within the mantle (Clark and Lingle 1977).
Furthermore, the time scale of ice sheet disintegration is presently unknown.

SEA-LEVEL CHANGES IN LOUISIANA

Local relative sea-level rise includes eustatic and local components. Prediction of
future sea-level changes along the Louisiana coast, therefore, requires knowledge about
land subsidence. In view of a "eustatic" sea-level rise of 1.2 mm/yr, it is clear that most
of the local sea-level rise observed on the Louisiana coast is due to subsidence (Swanson
and Thurlow 1973).

Figure 6 presents three tide gauge records from the central Louisiana coast as well
as a longer time series from Galveston, Texas, all of which document a history of rapid
local relative sea-level rise. The longer Galveston record documents well the temporal
changes in observed rates of sea-level rise. For example, if the entire Galveston record
is averaged one finds a rate of rise of 5.5 mm/yr. If one only considers the 20-yr time
span from 1950 to 1970, the rate then was 2.5 mm/yr. The rapid local change in sea-
level at Galveston between 1940 and 1945 (Figure 6) might be due to man's activities in

170

Humble
Oil -A'

Figure 6. Yearly mean sea-level series for four stations along the north-
central gulf coast. Data from tide gauges at Galveston, Eugene Island (at
the entrance to Atchafalaya Bay), Bayou Rigaud (Grand Isle), and Humble Oil
Platform "A" (13 km off Grand Isle). Data from Hicks and Crosby (1974) and
Baumann (1980).

the area, although sea-level curves from as far away as Pensacola show a rapid increase
during the same period. In view of these rapid temporal changes, the predicted
subsidence rates in the following paragraph should be considered very tentative.

From Humble Oil "A" and the Bayou Rigaud tide gauge records (Figure 6), one finds
a rate of local sea level rise of between 1.0 and I.I cm/yr for the period of duration of
the two records. By subtracting a rate of 1.2 mm/yr for eustatic rise, one arrives at a
subsidence rate of about 9 mm/yr for the south-central Louisiana coast. Farther west, at
Eugene Island, at the entrance to Atchafalaya Bay, one finds a subsidence rate of 7.3
mm/yr. A longer-term average subsidence rate can be derived from a C-based local
relative sea-level curve determined for the Caminada-Moreau beach ridge plain in
southern Lafourche Parish (Gerdes 1982). Gerdes' data suggest that local relative sea
level in that region has risen a total of 2.75 m during the last 1,000 years (Figure 7). This
corresponds to an average rate of 2.75 mm/yr. If one compensates for a eustatic rise of
1.2 mm/yr (assuming this rate to be valid for the last 1,000 years), then one finds a local
long-term subsidence rate of 1.55 mm/yr. This is a much lower rate than that derived

171

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a.

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\ 26 ^

^^^

RIDGE PLAIN DATES

'1 \*^^

l-OH

\r.

1 -

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CREVASSE

SPLAY

ORGANICS

\
\

-^REWORKING 1 39 |

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\ h5h new dates— this study
\ ^8 & vibracore location

nin DATES REPORTED BY OTVOS (1969)

1 1 1 1 1

1000

2000

3000

4000

5000

6000

7000

C AGE (YEARS B.P.)

Figure 7. Inferred relative sea-level rise at the Caminada coast of
Lafourche Parish (Gerdes 1982). The curve is based on radiocarbon-
dated basal peats and in situ, articulated shells of Crassostrea virqinica.

from local tide gauges, an observation which has two alternative interpretations: (a)
natural processes of subsidence in coastal Louisiana are highly tinne dependent, or (b) the
rapid subsidence over the last few decades is largely man-induced. Whichever cause is
the dominant, however, neither is likely to alter the current subsidence rate dramatically
over the next 40 years. A linear extrapolation of current subsidence rates would predict
a cumulative subsidence over the next 40 years of 36 cm for the Grand Isle area and 29
cm at Eugene Island. The numbers are high; however, both are less than the predicted
eustatic rise (40 cm) for the same period. Table I summarizes the predicted amounts of
eustatic rise, subsidence, and local relative sea-level rise for the Louisiana coast over
the next 40 and 1 00 years.

Table I. Predicted future changes in sea level on the Louisiana coast based on data from
Bayou Rigaud (Grand Isle) and Eugene Island (Atchafalaya Bay).

Year

2020
2080

Eustatic
rise (cm)

40
60

Subsidence
(cm)

29-36
73-90

Local relative
sea-level rise (cm)

69-76
133-150

172

CONCLUSIONS

It has often been assumed in past writings that changes in sea level are too slow
and imperceptible to play a significant role in shoreline changes on time scales of
concern to human development. This paper has demonstrated that, contrary to this
belief, sea level is likely to rise at a fast and accelerating pace in the very near future.

Now, local relative sea-level changes along the Louisiana coast appear to be
dominated by subsidence. The rate of subsidence is more than five times as high as the
average rate of eustatic sea-level rise for the last century. Eustatic sea level is directly
controlled by global mean temperature through changes in the specific volume of near-
surface water and melting of polar ice sheets. The global mean temperature, in turn, is
affected by periodic natural climatic cycles and a C02-induced "greenhouse effect".
Using conservative estimates for the rate of CO2 release, one finds that the global
warming over the next decades may cause a eustatic sea level rise of about I cm/yr
between the years 1980 and 2020. This rate exceeds the local subsidence rate of coastal
Louisiana implying that global eustatic sea-level changes will be our greatest concern in
the next few decades.

The estimated eustatic rise plus subsidence may amount to about a 75-cm local
relative sea-level rise over the next 40 years along the Louisiana coast. With that rate
of rise, it is imperative that plans for development and protection of the Louisiana coast
take sea-level changes into account.

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Behrens, E.W., R. L. Watson, and C. Mason. 1977. Hydraulics and dynamics of New
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Blackwelder, B. W., O. H. Pilkey, and J. D. Howard. 1979. Late Wisconsin sea levels on
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Gerdes, R. G. 1982. Stratigraphy and history of development of the Caminada-Moreau
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Gornitz, V., S. Lebedeff, and J. Hansen. 1982. Global sea-level trend in the past
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Gutenberg, B. 1941. Changes in sea-level, postglacial uplift, and mobility of the earth's
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Hansen, J., D. Johnson, A. Lacias, S. Lebedeff, P. Lee, D. Rind, and G. Russell. 1981.
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Hays, J. D., and W. C. Pitman. 1973. Lithospheric plate motions, sea-level changes and
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Hicks, S. D. 1978. An average geopotential sea-level series for the United States. J.
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Manabe, S., and R. J. Stouffer. 1980. Sensitivity of a global climate model to an
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Manabe, S., and R. T. Wetherald. 1975. The effects of doubling the CO2 concentration
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Meade, R. H., and K. O. Emery. 1971. Sea-level as affected by river runoff, eastern
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Pitman, W. C. 1978. The relationship between eustacy and stratigraphic sequences of
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Rhode, H. 1978. The history of the German coastal area. Die Kuste 32:7-29.

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176

EFFECTS OF COASTAL STRUCTURES ON SHORELINE STABILIZATION
AND LAND LOSS - THE TEXAS EXPERIENCE

Robert A. Morton

Bureau of Economic Geology

The University of Texas

Austin, TX 78712

ABSTRACT

Recent studies indicate that Texas is losing about 120 ha (300 acres) of wetlands
and 40 ha (100 acres) of gulf-front property annually. Although total land losses in Texas
are considerably less than those in Louisiana, they are still substantial and the reason
many shoreline protection structures have been erected. The structures have not always
produced the desired effects, however. Instead, some have accelerated erosion of nearby
beaches. Groins have generally been ineffective because sand supply is inadequate where
beaches are eroding. With one exception, seawalls built on Gulf of Mexico beaches have
failed or have been severely damaged during storms. Most bulkheads and seawalls have
protected the adjacent property, but at the expense of publicly-owned recreational
beaches that are eroded by the reflected wave energy. Because of similarities in
geologic setting and physical processes along the gulf coast, the effects of these
structures can be evaluated and the results applied to Louisiana where shoreline
stabilization is being considered to mitigate land loss.

INTRODUCTION

Public and private property worth millions of dollars is lost annually from coastal
environments around the world including areas of south Louisiana and Texas that border
the Gulf of Mexico (Figure I). Some of these land losses are natural products of
shoreline erosion and submergence of the land surface; other losses commonly result
from surface modifications such as dredging, river control, and building coastal defense
structures.

The coastlands of Louisiana are dominated by extensive deltaic plain marshes and
bays bordered by minor barrier islands in the east and a broad chenier plain in the west,
all associated with construction and abandonment of the Mississippi River delta (Figure
I). In contrast, the Texas coast is characterized by much smaller oceanic deltas (Rio
Grande, Brazos-Colorado) and intervening barrier-strandplain features, bays, and minor
marshes (Figure I). Despite these proportional differences in coastal environments, the
similarities in physical processes, geologic setting, and human activities between the
areas make the shoreline responses to coastal structures in Texas applicable to similar
settings In Louisiana. In both states, coastal structures are being used to mitigate land
loss along migrating barriers that are remarkably similar In origin and geologic setting.
For example, the gulf beach and barriers (East Timbolier Island and Grand Isle), that
front the Lafourche subdelta are comparable in many respects to the gulf beach and
barriers (East Matagorda Peninsula, Follets Island, Galveston Island) that front the
Brazos-Colorado delta (Figure I).

177

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SUMMARY OF LAND LOSSES IN TEXAS

In this century alone land losses along the Texas gulf shoreline have amounted to
nnore than 4,000 ha (10,000 acres) and average rates of loss have increased from about 14
ha (35 acresVyr near the turn of the century to nearly 160 ha (400 acres)/yr over the past
decade (Morton 1977). Accelerating land losses of substantially greater magnitude
(10,000 ha/yr) have also been reported for the Louisiana coast (Gogliano et al. 1981). The
magnitude of land loss in Texas is illustrated in Figure 2 which shows nearly 320 m of
beach retreat with erosion rates averaging between 7 and 8 m/yr. Although land losses in
the bays and lagoons have not been quantified in detail, they probably represent
additional losses of about 120 ha (300 acres)/yr. These high rates of land loss have led to
the emplacement of numerous breakwaters, jetties, groins, bulkheads, and seawalls in on
attempt to hold back the sea or at least delay the retreat of the shoreline.
Unfortunately these structures have not always accomplished their intended purposes and
in some instances they have actually caused increased beach erosion.^

Bays and Lagoons

Shorelines bordering the bays and lagoons are typically low clay bluffs, wetland
marshes, or sand and shell beaches. Each shoreline type formed under different
geological conditions and each responds differently to present-day processes.

The clay bluffs are composed principally of Pleistocene fluvial-deltaic sediments
that form the upland areas of the adjacent Coastal Plain. Of the three shoreline types,
clay bluffs exhibit the greatest disequilibrium with extant coastal processes and,
therefore, are the most vulnerable to wave attack and undercutting. As a result,
essentially all clay bluffs are retreating at rates up to 7 m/yr.

Coastal marshes that fringe the bays of the upper Texas coast are decreasing in
area not only because of shoreline erosion, but also because of sediment compaction and
attendant submergence. These wetland losses caused by sediment compaction are fewer
in Texas when compared to Louisiana owing to the smaller area of delta-plain and bay-
margin marshes where this process occurs. The loss of wetlands in Texas is primarily a
function of shoreline retreat which averages 3 to 5 m/yr in many areas. By comparison,
sand and shell beaches are relatively stable although their rate oif retreat is commonly on
the order of 0 to 2 m/yr.

Gulf Shoreline

In contrast to historical changes in the bay shorelines that are complex (McGowen
and Brewton 1975; White et al. 1978), changes in the Texas gulf shoreline are fairly
systematic and beach erosion is most severe in three areas (Figure I): between Sabine
Pass and Rollover Pass, between San Luis Pass and Brown Cedar Cut (vicinity of the
Brazos River delta. Figure 2), and on South Padre Island (vicinity of the Rio Grande
delta). Each of these areas is characterized by thin sand beaches that are retreating
over marsh and delta-plain muds at average rates of 3 to 5 m/yr regardless of storm
frequency and intensity. In each of these areas, ocean waves have consumed hundreds of
acres and have destroyed numerous beach houses in the past 20 years. Despite the
hazards of storm overwash, flooding, and shoreline erosion, permanent residence and
recreational development continues to increase in these areas and structural methods are
being used in an attempt to reduce land losses and to provide storm protection.

179

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MAJOR CAUSES OF LAND LOSS

The three primary causes of land loss in Texas and elsewhere are (I) reductions in
sediment supply, (2) relative sea-level rise and (3) human activities; although listed
separately the third category directly affects the other two (Figure 3). Of foremost
importance is the natural decrease in sediment supply that accompanied climatic changes
over the past few thousand years. Simply put, the major coastal rivers and nearshore
currents are no longer delivering the volume of sediment that they once did. This natural
decrease in sediment supply has been aggravated to varying degrees by dam construction
and entraining of rivers and emplacement of jetties, groins, and seawalls that
compartmentalize the coast and disrupt the longshore transport of sand. Hence, these
structures have locally contributed to shoreline erosion and their contribution to land loss
may be even greater in the future.

SOURCES
riverine discharge
shoreline erosion
onshore transport
eolian processes

SINKS

shoreline accretion
storm wQshover
tidal inlets
coostol structures
eolian processes
offshore transport
resource extraction

subsurfoce fluid withdrawal
river basin development
maintenance dredging
beach maintenance
coastal structures
artificial passes
dune alterations
highway construction

temperature

evapotranspirotion

precipitation

wove climate
longshore currents
riverine discharge
valley aggradation,
or incision
tides
wind
storms

tectonic subsidence
compoctionol subsidence
eustatic sea level changes
secular sea level changes

Figure 3. Interaction of factors affecting land losses. Arrows point toward
the dependent variables: the number of arrows originating from or terminating
at a particular factor indicates the relative degree of independence or inter-
action. For example, human activities are independent of the other factors,
but they affect sediment budget, coastal processes, relative sea-level condi-
tions, and. perhaps, climate (Morton 1977).

181

Relative sea-level rise refers either to rising of the water level or sinking of the
land surface; both processes produce the same effect and both may act simultaneously.
The end result is that the land becomes submerged and the shoreline retreats, inland.
Along the Texas and Louisiana gulf coast relative sea-level rise in recent years averaged
between 0.5 and I m per century (Hicks 1972). Again both natural processes and human
activities are involved. The land surface sinks naturally as the underlying sediments
compact, but withdrawal of subsurface fluids (ground water and hydrocarbons) locally
accelerates the process and leads to increased land surface subsidence. Added to this is
the possible worldwide (eustatic) rise in sea level caused by melting of the polar ice
caps. Recent studies indicate that this sea-level rise may also be accelerating because
of the "greenhouse effect" produced by COo (Emery 1980) and other gasses that are
released to the atmosphere. When viewed collectively, these processes suggest that the
long-term outlook for coastal areas is not good because land losses will likely continue to
be widespread and vast areas may become submerged.

REVIEW OF COASTAL STRUCTURES IN TEXAS

Bays and Lagoons

Shoreline stabilization projects in Texas bays and lagoons are principally of two
types: (I) numerous, relatively low-cost structures such as wooden bulkheads, concrete
seawalls, riprap, and small groins that are designed to protect a single waterfront lot or
(2) a few expensive reinforced concrete bulkheads designed to protect an entire
development. The former group of structures are generally short lived (less than 25
years) because of the materials employed and the exclusion of physical processes from
the project design. In contrast, the latter group of structures has only been used for
slightly more than a decade and their longevity is uncertain. Common causes of
bulkhead/seawall failures are deterioration of the wood, corrosion of the tie-backs, or
flanking, overtopping, and undercutting by storm waves and nearshore currents. These
processes as well as slope failures are responsible for reducing the effectiveness of most
rubble revetments. In addition, most groins are rendered ineffective for bay shore
protection because of inadequate sand supplies in the littoral drift system. Effects
common to these structures are the acceleration of erosion along adjacent, unprotected
shorelines as well as disruption of the offshore bar system and loss of the beach along
sandy bay shores.

Gulf Shoreline

Serious attempts to stabilize the gulf shoreline, especially at harbor entrances,
began in the mid-1800's when safe navigation into the shallow bays was becoming
important to the coastal economy. Perhaps the most famous structure is the Galveston
seawall (Figure 4) that was erected not to halt beach erosion, but to prevent overwash
and flooding from storms such as the 1900 hurricane that claimed more than 6,000 lives.
The seawall has adequately protected the city of Galveston from erosion and storm
waves, but in so doing the recreational beach was sacrificed. This is most noticeable
along the western part of the seawall where visitors drove on a wide sand beach prior to
1965. Now the seawall toe is protected by riprap, but the adjacent unprotected beach
has eroded landward of the seawall and is retreating at fairly high rates.

Other seawalls built on the Texas coast are less massive than the Galveston seawall
and they also have been less effective in preventing land loss. Seawalls built by

182

Figure 4. Western part of massive seawall
sand beach seaward of the seawall.

on Galveston Island. Note lack of

'nyu.y

Figure 5. Remnants of seawall on South Padre Island that failed during
Hurricane Beulah.

183

individuals or corporations on South Padre Island, North Padre Island, and Sargent Beach
(Figure I) have completely failed or have been so severely damaged that costly repairs
were required to maintain them. A representative example is found on South Padre
Island (Figure 5) where a privately built seawall constructed in 1962 was destroyed by
Hurricane Beulah in 1967. This seawall was built by the landowner after a previous
seawall, constructed seaward, foiled in the early I960's. The position of the former
seawall is now completely submerged by the open gulf. Furthermore, continued erosion
has removed the beach in front on the second seawall (Figure 5).

The most recent examples of extensive seawall damage occurred on North and
South Padre islands during Hurricane Allen (1980). The fact that a large seawall built
with corporate funds did not survive the storm (Figure 6) is important for several
reasons. First of all, the seawall failed even though (I) the storm center was more than
130 km (80 mi) away and (2) at landfall the storm was relatively weak by hurricane
standards. Secondly, considerable damage occurred on the landward side of the seawall
owing to overtopping by storm waves and the hydrostatic head (back pressure) developed
by flood waters as the storm surge subsided. Thirdly, this massive and expensive
structure needed extensive repairs less than 15 years after it was built to protect a
resort development.

Figure 6. Seawall on North Padre Island damaged during Hurricane Allen,

184

In summary, except for the Galveston seawall built at public expense, most
concrete shoreline protection structures erected on the Texas coast in recent years have
failed or have been severely damaged. These structures have finite lives, are expensive
to construct and maintain, and they commonly transfer the erosion problem elsewhere by
locally eliminating the sediment supply. For these and other reasons the U.S. Army
Corps of Engineers recommended the use of nonstructural methods, such as beach
nourishment, sand bypassing, and dune construction, when feasible for shoreline
stabilization projects.

CONCLUSIONS

Attempts to mitigate land loss through the use of permanent structures may not be
successful because (I) land losses in adjacent areas will probably accelerate, (2) initial
project costs plus maintenance expenditures may exceed the value of the protected
property, and (3) the temporary abatement of land loss and attendant sense of security
may inadvertently lead to further economic development and the potential for future
losses of even greater magnitude. This is analogous to flood-plain development
downstream of dams that impound upstream flood waters, but do not prevent severe
downstream flooding caused by intense rainfall throughout the drainage basin.
Implementation of multiple individual shoreline stabilization projects that (I) lack
integration into a more regional plan and (2) are designed without full knowledge of the
local geologic setting and coastal processes may prove to be inadequate as long-term
solutions to coastal land loss.

ACKNOWLEDGMENT

Publication was authorized by the Director, Bureau of Economic Geology, The
University of Texas at Austin.

LITERATURE CITED

Emery, K.O. 1980. Relative sea levels from tide-gauge records. Proc. Natl. Acad. Sci.
U.S.A. 77:6968-6972.

Gagliano, S.M., K.J. Meyer-Arendt, K.M. Wicker. 1981. Land loss in the Mississippi
River Deltaic Plain. Trans. Gulf Coast Assoc. Geol. Soc. 31:295-300.

Hicks, S.D. 1972. On the classification and trends of long period sea level series. Shore
and Beach 40:20-23.

McGowen, J.H., and J.L. Brewton. 1975. Historical changes and related coastal
processes, gulf and mainland shorelines, Matagorda Bay area, Texas. Univ. of Texas at
Austin, Bureau of Economic Geology Spec. Publ. 72 pp.

Morton, R.A. 1977. Historical shoreline changes and their causes, Texas gulf coast.
Trans. Gulf Coast Assoc. Geol. Soc. 27:352-364.

Morton, R.A., and M.J. Pieper. 1975. Shoreline changes in the vicinity of Brazos River
Delta (San Luis to Brown Cedar Cut). Univ. of Texas at Austin, Bureau of Economic

185

Geology Geol. Circ. 75-4. 47 pp.

White, W.A., R.A. Morton, R.S. Kerr, W.D. Kuenzi, and W.B. Brogden. 1978. Land and
water resources, historical changes and dune criticality: Mustang and North Padre
Islands, Texas. Univ. of Texas at Austin, Bureau of Economic Geology, Report of
Investigations 92. 46 pp.

186

SAND DUNE VEGETATION AND STABILIZATION IN LOUISIANA

Irving A. Mendelssohn

Laboratory for Wetland Soils and Sediments

Center for Wetland Resources

Louisiana State University

Baton Rouge, LA 70803

ABSTRACT

The sandy barriers that fringe the Louisiana deltaic plain are dynamic and
ephemeral coastal features. In terms of development, management, and conservation,
these landforms pose many problems unique to the Mississippi River deltaic
environment. The abandonment of a major delta by the Mississippi River initiates the
development of a Louisiana barrier system. Nearshore marine processes and subsidence
become the dominant mechanisms of shoreline evolution. Marine processes erode the
abandoned delta and concentrate a restricted quantity of coarse-grained sediments into
highly mobile barrier islands, spits, and beaches which overlie unconsolidated delta silts
and clays. Subsidence, due to the compaction of these unconsolidated sediments, in
concert with a eustatic increase in sea level, generates a rapid apparent sea-level rise,
equivalent to I m/ 100 yr. This combination of sea-level rise and limited coastal sand
supply has produced the most serious barrier island erosion problem in the United States.

The use of hard structures, such as groins, jetties, and seawalls to control or reduce
barrier island erosion in Louisiana has met with limited success. The use of vegetation to
stabilize substrates offers a sound alternative to the hard structure approach to erosion
abatement. This paper introduces Louisiana's barrier dune vegetation and qualitatively
describes the use of this vegetation for dune building and stabilization on Timbalier
Island, Louisiana.

INTRODUCTION

Critical components of many coastal systems are the low-lying strips of land called
barrier islands or beaches that make up the seaward boundary of the estuary and protect
it from the direct onslaught of the sea (Godfrey 1976). The combination of an
accelerated sea-level rise, due to local deltaic subsidence, and a limited coastal sand
supply has produced in Louisiana the most serious barrier island erosion problem in the
United States. Louisiana's barrier islands (Figure I) are migrating landward at rates as
high as 50 m/yr while losing total land area at a rate of 65 ha/yr (Mendelssohn et al.
1982).

The environmental and economic consequences of shoreline erosion in Louisiana are
immense because of the important functions that barrier islands perform. (1) Barrier
islands protect marshes and create estuaries by acting as a marine buffer zone to

187

Suboeftal Sandy Ekirnen

■n^

a 10 20 30 40 50

I I 1 J 1 -I

Figure 1. Location of Louisiana's barrier islands.

saltwater intrusion, hurricane stornn surge, and deep water wave attacks . In this way,
Louisiana's barrier islands help to support a finfish and shellfish industry which accounts
for over 25% of the total U. S. commercial catch each year. (2) Barrier islands provide
habitat for wildlife and shelter for endangered or threatened species. (3) Barrier islands
provide protection for mainland areas, including oil and gas facilities which generate
considerable tax revenues for Louisiana. (4) Since the three-mile boundary for
Louisiana's territorial waters is measured from the barrier islands, the State is concerned
with the problem of continued landward migration of the barrier islands as this migration
could result in a reevaluation of the State's three-mile boundary and a net loss of oil and
gas leases to the Federal Government. (5) Barrier islands offer recreational
opportunities and aesthetic qualities unique to this system.

The use of hard structures (groins, jetties, seawalls) to control or reduce barrier
island erosion in Louisiana has met with limited success (Penland and Boyd 1981). In the
case of groins and jetties, accretion may result at the updrift side of the structure, e.g.,
the east end of Grand Isle, but accelerated erosion often occurs at a downdrift location,
e.g., the Grand Terre islands. The inherent problems with structures like groins and
seawalls are now being recognized (Leatherman 1980). Seawalls, for example, only
protect what is landward; accelerated beach erosion often occurs seaward of these
structures (Silvester 1977). In addition, these structures destroy the aesthetic qualities
that attract so many people to these ecosystems. Sand dune building and stabilization
offer a sound alternative to the hard structure approach to erosion abatement.

188

The objectives of this report are to (I) describe the vegetation of the dune
community of Louisiana's barrier islands; (2) indicate plant species that may be used for
dune stabilization in Louisiana; and (3) qualitatively discuss an attempt to build and
stabilize a foredune ridge on Timbalier Island, Louisiana.

FUNCTION OF STABILIZED DUNES

How do dunes aid in reducing barrier island erosion? Firstly, coastal dunes provide
a reservoir of sand to the beach during storm events. Not only does the dune system
nourish the beach during storms, but the building of an offshore storm bar from dune
sands has the effect of reducing the slope of the beach and lengthening the surf-swash
zone so that the maximum energy dissipation of storm waves is achieved (Leatherman
1979a). Both effects tend to reduce erosion of the beachface. Secondly, continuous sand
dunes act like levees, retarding overwash and island breaching. Because one of the
primary causes of sand loss to an island is due to breaching and subsequent inlet dynamics
(Leatherman 1979b), the role of sand dunes in strengthening the island against breaching
is very important in controlling the overall erosion of the island. Thirdly, a well-
vegetated dune provides a source of vegetation to recolonize overwashed and breached
dunes after storms. This vegetation is important in initiating new sand accumulation and
dune-building processes.

Some coastal investigators have questioned the function of barrier dunes during
storm conditions. Dolan (1972) maintained that large stabilized dunes are detrimental to
the long-term stability of. the barrier system since they were believed to interfere with
beach dynamics by (I) constricting the swash zone so that wave energy is dissipated over
a narrower area, resulting in increased turbulence and concommitant beach erosion, and
(2) functioning as seawalls and thus concentrating wave energy to increase the scour of
adjacent sand beaches. Based on this hypothesis for which no hard data were collected,
the U. S. National Park Service has argued that dunes are detrimental to the stability of
barrier islands, and in some locations should possibly be breached artificially by
bulldozers. As Leatherman (1979b) points out, "This management approach is rather
startling, considering that dune conservation programs are essentially ubiquitous
worldwide."

Thus, the question exists: Do stabilized barrier dunes increase barrier island
erosion? Leatherman (1979a, b, c), who has intensely investigated this question,
concluded that Dolan's hypothesis is not substantiated by field measurements or by
results from previous research:

"From laboratory tests and field observations during storm
conditions, it has been shown that the barrier dune does not result in
steepening of the upper beach foreshore. Instead, the profile continues
to flatten asymptotically until a critical minimum value is achieved.
Seaward migration and building of the outer storm bar can provide for
a wide enough surf-swash zone to achieve maximum energy dissipation
and thus define a new equilibrium profile. Dolan's (1972) emphasis on
the importance of the subaerial beach profile in energy dissipation and
wave reflection neglects the full range of interactions. The presence
of a dune line cannot constrict the energy dissipation process since the
seaward boundary (storm bar) is not a static feature.

189

"It is very tempting to draw an analogy between a seawall and an
eroding barrier dune. The essential difference appears in their
response: static vs. dynamic. Unless a sand dune is essentially
structurally controlled by rip-rap or caissons as a seawall, it is free to
erode or accrete depending on the environmental conditions. It has
long been argued by the U. S. Army Corps of Engineers (1974) that
dunes serve as a sand reservoir for beach nourishment in times of need
(during storm conditions). In fact, it has been clearly shown that a
high sand dune will reduce foreshore erosion during a storm since a
greater amount of sand is available to fill the offshore profile and
buildup the outer bar to provide sufficient width to dissipate the wave
energy (Van der Meulen and Gourlay I 969).

"The case against barrier dunes, artificially induced or totally
natural, is not convincing from either a beach or barrier dynamics
viewpoint. Much more work needs to be done along these lines,
particularly in the case of storm generated beach dynamics"
(Leather man 1979b).

DUNE STABILIZATION IN THE UNITED STATES

There exists a long history of the use of vegetation to retard the erosion of dunes in
the United States. Attempts at coastal dune stabilization were made as early as 1703
when colonists of Cape Cod used grasses to control sand erosion due to their own
deforestation of sandy areas (Westgate 1904).

In the early I900's, intense efforts to vegetate existing dunes along the Pacific
Northwest coast began. Primarily, European beach grass, Ammophila arenaria, and
American dunegrass, Elymus mollis, were planted. These plantings proved to be
successful to the point that the dominant dune plant in the Pacific Northwest is European
beach grass.

Along the Atlantic coast, large scale planting by the Civilian Conservation Corps
(CCC) occurred along the North Carolina coast from 1934-36. American beachgrass,
Ammophila breviligulata, was planted extensively in the Bodie Island area of the outer
banks. Between 1936-40, the CCC and the Works Progress Administration (WPA), under
the direction of the National Park Service, erected almost I million meters of sand
fencing to create a continuous barrier dune along the outer banks, including Hatteras,
Pea, and Bodie islands (Dolan et al. 1973).

After a series of strong hurricanes impacted the Atlantic coast starting in 1954
with "Hazel", new interest in dune erosion control was stimulated. The National Park
Service and the Soil Conservation Service began testing various species of grasses on
North Carolina's Outer Banks in the late I950's. Beach grasses, especially American
beachgrass, have been planted extensively on the outer banks during the I950's and
I960's. With the establishment of the Cape Hatteras National Seashore in 1957, the
National Park Service felt it was important to protect the dunes making up the park from
eroding. Thus, extensive dune plantings continued which augmented the I930's effort at
dune construction. After this effort, an almost continuous vegetational cover existed on
these barrier islands making up the outer banks.

190

Vegetation has been used to stabilize dunes to varying degrees along the Northeast,
Middle and Southeastern Atlantic shorelines, Florida, the northern coast of the Gulf of
Mexico, and Texas. Although the New Orleans District of the U. S. Army Corps of
Engineers and the Soil Conservation Service initiated some dune plantings on Grand Isle
in the past, the use of vegetation to build and stabilize dunes along the Louisiana coast
has been generally overlooked.

SAND DUNE COMMUNITY

Sand dunes are windblown accumulations which form in the shape of mounds,
ridges, and/or bands when a supply of sand is available. Although dunes may be
completely unvegetated, such as large mobile dunes which continually move as dictated
by eolian forces, the majority of dunes on barrier islands have some degree of plant cover
which may vary from exceedingly sparse to highly dense.

Vegetation aids in building dunes by first reducing wind velocity in its lee and this
causes the deposition of sand grains. As more and more sand is deposited, these sand
grains accumulate into small mounds. Secondly, the roots of dune plants bind the sand
which results in varying degrees of substrate stability, depending on root density. In
response to newly accreted sands, which provide a fertilizing effect, vegetational growth
is stimulated. In many grasses, horizontal rhizomes give rise to tillers which greatly
increase the vegetative spread of the plant. As more tillers are produced, more sand is
accumulated until the vegetation may be nearly buried. When burial is even more rapid,
shoots are killed and rhizomes stop extending laterally, but continue growing vertically
until the new surface is reached, when again tillering takes place. This process allows
the vegetational growth to keep pace with sand accumulation and create partially
stabilized embryo or hummock dunes. As these dunes increase in number, they begin to
coalesce to form a dune line. Hence, a foredune is created. The configuration and
height of a dune line is a function of the sand supply and intensity and direction of
prevailing winds relative to the orientation of the barrier beach. Onshore winds normally
form large dunes while alongshore or offshore winds form dune lines which are more open
and lower in physiognomy.

The above dune-building processes primarily occur on the backshore (i.e., the
horizontal or gently sloping part of the beach that is inundated only by storm waves and
extremely high tides) of Louisiana's barrier islands. This zone of the beach often
contains small hummock dunes and sparse vegetation. Densely vegetated dunes have
been estimated to occupy less than 3% of the total Louisiana barrier island area
(Mendelssohn et al. 1982), although the sandy backshore-dune-swale zones account for
approximately 18% of the islands' area. Since vegetated sand dunes are important
sources of sediments to these islands after storm events, it is clear that in their present
state, the barrier islands and beaches of Louisiana only have a limited source of
sediments in the form of back beach and dune deposits.

The dunes of Louisiana's barrier islands are poorly developed as a result of a limited
amount of eolian transported sand and the high frequency of overwash resulting from
hurricanes and storms. Most of Louisiana's barrier islands and beaches have only one
primary dune line which is relatively low in profile and only moderately vegetated.
Barrier islands without well-developed dunes, such as in Louisiana, have limited sand
reserves and, thus, a limited mechanism of reducing net beach erosion. Since vegetation
aids in building of dunes and is essential for sand stabilization, dune vegetation plays a
key role in maintaining this important source of sediments on the barrier islands.

191

The sand dune is a relatively inhospitable environment for vegetation
establishment. Environmental factors such as salt spray from saline waters of the Gulf
of Mexico, soil moisture deficiencies, limited nutrient supply, and soil instability may all
negatively affect coastal dune vegetation.

Salt spray occurs when effervescence in the surf generates droplets into the air
where they are concentrated and transported inland by the wind (Boycel954).
Impingement on vegetation may result in chlorosis and subsequent death of plants. The
active agent of the salt spray is the chloride ion which enters the windward portions of
plant parts through cracks and lesions in the epidermis. The degree of injury is related to
the windspeed above the critical value of 7 m/sec where an abrupt increase in salt spray
intensity occurs as turbulent air flow increases. In addition to affecting growth, it has
been demonstrated that airborne salt spray is the primary environmental factor
determining the distribution, shape, and zonation of maritime plant species (Wells and
Shunk 1937; Costing and Billings 1942; Art 1971). Many of the grasses that grow on
foredunes are resistant to salt entry and hence can survive the intense spray zones of the
beach. Those plants that are less adapted are found in the lee of dunes or other
vegetation. Salt spray is an important factor preventing the establishment of annual
plants on the foredunes (Van der Valk 1974). As found along the Atlantic coast of the
United States, the salt spray effect only allows those plants specifically adapted to this
environment to inhabit the gulfward edge of Louisiana's barrier islands.

The question of whether the dune environment presents a water deficiency to
plants has been greatly debated. Although the top few centimeters of a dune may be
completely dry, the sand below this level is often moist. It has been hypothesized that
the dry surface sand acts as a vapor trap which prevents deeper drying of the substrate.
The water table, per se, which depends on the size of the dune and may be several meters
from the active rooting zone, acts as an indirect source of water via vapor phase
diffusion upward to the rooting zone. Since the capillary rise of water from a free water
surface even in a very fine sand is not more than about 40 cm, the water table in a dune
only a few meters high can make no direct contribution to the moisture requirements of
most dune plants. Both rainfall and the condensation of soil water vapor provide
important sources of water to dune vegetation, but their relative contribution is
unknown.

The dune plants themselves play an active role in controlling their water
requirements. This may be done by controlling water loss at the leaf surface, as in the
shallow rooting pennywort, Hydrocotyle bonariensis, by accumulating large amounts of
water in succulent tissue as in the dune elder, lva~imbricata, or by producing roots which
penetrate deep into the substrate, as in some of the dune grasses, e.g., Panicum, Uniola.

Dune sands are generally deficient in nutrients essential for plant growth. The
major inputs to the dune system are salt spray and precipitation. The mineralization of
organic matter in the dunes is of limited importance since eolian processes remove most
lightweight organic matter. Fertilizer-addition tests have demonstrated that inorganic
nitrogen is the primary nutrient controlling the growth of dune vegetation (Woodhouse
and Haines 1966; Dahl et al. 1974). Phosphorus may become secondarily deficient after
the nitrogen deficiency has been ameliorated. Although nutrients would appear to be in
limited supply, some dunes support lush, productive stands of vegetation. Recently, it
has been demonstrated that dune grasses possess sand grain sheaths (rhizosheaths) around
their roots. Nitrogen fixation, a process by which microorganisms fix atmospheric
nitrogen into plant-available ammonia, is specifically associated with these sheaths

192

(Wullstein and Pratt 1980) and may be a primary pathway by which nitrogen is provided
to dune plants. In addition, some plants such as beach pea, Strophostyles helvola, possess
nitrogen-fixing nodules which serve the same function as rhizosheaths.

Soil instability is another problem that dune vegetation must overcome. Plants
have a more difficult time establishing themselves in shifting windblown sand than in a
stable substrate. In addition, vegetation is often buried by drifting sand. Dune plants
have adapted to this environment by having the capacity to grow upward through
considerable accumulations of sand. Burial has a stimulatory effect on the growth of
dune grasses; too much sand burial can cause plant death, however. The resistance to
sand burial varies with species. The grasses are most resistant, while dicotyledonous
plants are more susceptable to sand burial. On the outer banks of North Carolina, sand
burial was the major factor preventing the establishment of most annual plants on the
foredune or any other area of shifting sand (Van der Valk 1974). These plants can survive
sand burial of no more than 16 cm. Accumulations of 20 to 30 cm are normal in this
foredune.

In Louisiana, the dominant dune vegetation includes salt meadow hay, Spartina
patens, bitter panicum, Panicum amarum, seashore dropseed, Sporobolus virginicus, and
beach morning glory, Ipomea stolonifera. Of secondary importance, as indicated by their
frequency of occurrence, are beach tea, Croton punctatus, seashore paspalum, Paspalum
vaginatum, dune elder, Iva imbricata, seaside goldenrod, Solidago sempervirens, sea oats,
Uniola paniculata, and pennywort, Hydrocotyle bonariensis. Figures 2, 3, and 4
demonstrate the distribution of these and other species on three Louisiana barrier
systems.

Certain species of dune plants are more efficient dune builders than others. For
example, in Louisiana species such as panicum, croton, and sea oats can build dunes from
I to 5 m high, while salt meadow hay normally generates dunes of relatively low profile,
less than I m. Also, the shape of the dune produced can vary depending upon the
vegetation type. For example, beach tea and dune elder produce large hummock dunes,
while panicum more frequently generates dune ridges. Even different species of grasses
produce different dune forms. For example, in North Carolina, American beachgrass
produces a gently sloping dune while sea oats generates a steep dune front; panicum
builds a dune intermediate in shape (Woodhouse et al. 1977).

Although most of Louisiana's dune vegetation is ubiquitous, found on all of
Louisiana's barrier islands and beaches, there are two notable exceptions. Sea oats is
primarily found on the barrier islands east of the Mississippi River delta, specifically the
Northern Chandeleur Islands. Sea oats is almost completely absent west of the delta,
except for three small populations on the Camlnada-Moreau coast and a few plants on
Grand Isle. On the other hand, panicum is very prevalent on Louisiana's barrier islands
west of the Mississippi delta, but almost nonexistent on the Chandeleur islands. The
reasons for these disjunctions are unclear. There are two plausible hypotheses for why
sea oats is not appreciably found west of the delta. Since the islands west of the delta
are of a much lower profile than the northern Chandeleurs, these islands tend to be
overwashed more frequently. Sea oats may not be able to recover from the effects of
overwash as rapidly as other species and hence has lost its prominence on these low-lying
islands. Because sea oats growing on dunes of lower elevation are closer to the
watertable, it has been hypothesized that this plant, which is apparently highly adapted
to dry beach sands, is stressed by excess soil moisture which reduces its vigor. The
reasons for the panicum disjunction is an even greater mystery. Nonetheless, both plants
are potentially good dune builders and sand stabilizers.

193

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CAMINDA - MOREAU BEACH (EAST)

CAMINADA PASS BERM

DUNE

SWALE

MARSH

SOUND

Panlcum fpun*

Spartint pafnt

Pmnlcum amarum

Andropogon tcoparlut

Sporobolu* virglnlcut

Hydrocotyla bonarlantit

Satuvlum portulaeattrum

Solldago tamparvlrana

Croton punctatua

Strophoatylaa halvola

Baceharia hallmlfolla

Hatarothaea aubaxlllaria

LIppla nodltlora

Flmbrlatylla tpadleaa

Cypania atrlgoaua

DIchromana eolorata

Agallnia marltlma

torrlehia frutaacana

LImonlum naahll

Chloria patraaa

Sabatia atallaria

Selrpua amarleaiHia

Avlcammla garmlnaaa

Juneua ap.

Salleofitla bigalorll

30m

Figure 3. Vegetational distribution-dune profile on the Caminada-Moreau barrier
beach east section.

TIMBALIER ISLAND

Spartlna patens

Avicennia germinans

Andropogon scoparlus

Sporobolus virglnicus

Flmbrlstylis spadlcea

Strophostyles helvola

Solldago sempervirens

Paspalum vaglnatum

Eustoma exaltatum

Sabatia stellaris

GULF

BERM BEACH

DUNES

SWALE

30m

■■■■

Figure 4. Vegetational distribution-dune profile on Timbalier Island.

VEGETATION FOR DUNE STABILIZATION IN LOUISIANA

Although approximately 462 species of plants inhabit Louisiana's barrier islands and
beaches (Montz 1981), only a small percentage of these are suitable for dune building and
stabilization. Plants suitable for dune stabilization must of course, be able to grow and
procreate where dunes are naturally located, in the path of blowing sand parallel to the
high tide line of the backshore. To grow well in this environment along the shoreline of
the Gulf of Mexico, a plant must be able to tolerate sand burial, sand impingement, salt
spray, saltwater flooding, drought, heat, and low nutrient supply. In addition, these
plants must be able to trap and hold sand against wind and wave erosion. The following
plants which inhabit Louisiana's coastal dunes meet these requirements.

Spartina patens, salt meadow hay (Figure 5), is a creeping rhizomatous plant (0.5 to
1.5 m tall) forming in small clusters or singly. This plant is distributed in North America
along the eastern coast from Quebec to Florida, Texas, and the eastern coast of Mexico
and is present in a few localities in Michigan and New York, on islands in the Caribbean,

196

and is also know in Europe in France, Corsica, and Italy. Salt meadow hay flowers mostly
from May to September, but occasionally throughout the growing season. Viable seed is
produced in early September.

This perennial grass is the most widespread plant on Louisiana's coastal dunes.
While this species is more productive on moist sites, it is often found as the sole
dominant on low-lying dunes and washover flats. The grass spreads to make dense stands
by a network of slender rhizomes. The aboveground stems are slender and up to I m tall
with rolled to semirolled leaves less than 0.6 cm wide. Salt meadow hay can be dominant
in all three of the major barrier island habitats: dune, swale, and salt marsh (high
marsh).

For use along the Louisiana coast, this plant may be thinned from existing stands or
ordered from horticultural supply houses. Although the viability of naturally occurring
seed has not been tested in Louisiana, if it is similar to what has been found in the
Carolinas (Seneca 1969; Graetz 1973), this plant may be suitable for propagation by
seed. Plantings of vegetative material can be made in late winter and early spring.
Planting stock consists of several stems rooted at the base, preferably with a section of
rhizome attached. In vegetating sand flats, the stock is planted 46 cm apart in the
center of the planting area, spreading out to I to 1 .2 m apart at the edges. This
graduated planting allows sand to penetrate to the center of the grass in the first two
seasons making a wider, flatter dune. Planting depth is about 10 to 13 cm.

Panicum amarum, bitter panicum (Figure 6), has culms 0.3 to 2 m tall that form
large or small clumps or solitary plants from rhizomes. This plant is distributed in North
America on the Atlantic and gulf coasts from Connecticut to Florida and Texas, in the
West Indies, and on the eastern coast of Mexico. Bitter panicum flowers from September
to November. According to Gould (1975), P. amarulum, seashore panicum, seems "to
represent no more than a growth form or variety of a single species," Panicum amarum.
This conclusion agrees with the analysis of Palmer (1975). Therefore, P. amarum should
be used as the scientific name for this plant in Louisiana.

Bitter panicum is an important perennial of foredune areas in Louisiana and is a
good grass for dune stabilization. Since this plant produces no viable seed, its only means
of colonization and propagation is by rhizome. The leaves of bitter panicum are smooth
and bluish in color. Seed heads are narrow, compressed, and most often sparsely
seeded. The plants grow to an average height of I to 1.2 m.

In Louisiana, planting stock may be obtained from cuttings of existing populations
or purchased from commercial sources. Planting stock consists of a single stem cut at
the base to include a node, a stem with part of the rhizome attached, or 20- to 30- cm
lengths of the rhizome without the aboveground parts. The latter must contain at least
two nodes per piece of rhizome. Bitter panicum is best planted in the spring through
early summer at a depth of 15 to 25 cm for stem material and 10 cm for rhizome. Plants
should be spaced at 46 cm.

Sporobolus virginicus, seashore dropseed (Figure 7), is a perennial, strongly
rhizomatous plant arising singly or in clusters. In general, this plant is distributed along
the eastern coast from Virginia to Florida and Texas, and southward through the West
Indies and the Caribbean to Brazil. Sporobolus flowers from May to October,
occasionally to December.

197

Figure 5. Spartina patens, salt meadow hay.

Figure 6. Panicum amarum, bitter panicum,

198

Seashore dropseed, although not a dominant dune plant in Louisiana, is frequently
found in scattered patches colonizing newly accreted sand. This species often forms
embryo dunes gulfward of the primary dune line and invades washover sites with salt
meadow hay. Sporobolus has an extensive fibrous root system making it suitable for sand
stabilization. This low growing, perennial grass spreads by rhizomes and occasional
stolons. Culms are stiff and 15 to 20 cm tall. Leaves are numerous and 5 to 10 cm long.

Propagation of this plant is generally by pieces of rhizomes which root readily.
Since this plant towers prolifically in Louisiana, however, the potential for the
production of viable seeds is present and plant establishment by seed may be an
alternative propagation methods. Seashore dropseed should be planted in early spring
either as transplants or rhizome pieces. Plants should be spaced at 46-cm centers and be
planted at a depth of approximately 10 cm.

*^ ^^

Figure 7. Sporobolus virginicus, seashore dropseed.

199

Paspalum vaginatum, seashore paspalum (Figure 8), is a perennial plant with culms
10 to 60 cm tall arising from an extensive system of long, slender rhizomes in coastal
sands. Its distribution is from North Carolina to Florida and Texas, south to Argentina,
and also in the Old World tropics. Paspalum flowers between late summer and winter.

In Louisiana, seashore paspalum, occupies environments similar to seashore
dropseed, i.e., sand flats and embryo dunes. Both species can also be found in sandy,
wetter interdunal areas protected from salt spray effects. Although this species is not a
dominant dune plant in Louisiana, its fibrous root system makes it a prime candidate for
dune stabilization trials.

Seashore paspalum is a low, creeping grass, resembling coastal bermuda grass,
(Cynodon dactyl on), that spreads by runners as well as rhizomes. The flowering culms of
this plant are usually less that 0.3 m high. Although seashore paspalum can endure on
very wet sites, even salt water inundated, this plant also builds small hummock dunes on
dry flats.

Seashore paspalum can easily be propagated by transplanting runners or rhizomes.
Optimum planting time and depth are similar to seashore dropseed. Transplants should
be 46 cm apart.

Uniola paniculate, sea oats (Figure 9), is a perennial plant with 1.2 to 2 m tall stout
culms arising singly or in small clusters from long, thick rhizomes. This species is found
on dunes and sandy flats along the ocean from Virginia to Texas, northern West Indies,
and eastern Mexico. Sea oats flowers from June to December, but mostly in late summer
and early autumn.

Although sea oats is the most important and widespread grass on coastal dunes in
the Southeast United States (Craig 1976), its importance in Louisiana is limited. Sea oats
is found on Louisiana's Chandeleur islands, but with the exception of a few small isolated
populations, is almost completely lacking on the barrier islands and beaches west of the
Mississippi River Delta. The dominance of sea oats is not reestablished until the area of
Padre Island, Texas. The reason for this disjunction is unclear, although factors such as
the lack of a large seed source, impact of frequent washover events due to hurricanes,
and dune formations which are too low in elevation to prevent plant roots from entering
the water table are possible causes.

Although sea oats produces viable seeds, which are important in colonizing new
areas (Woodhouse et al. 1968), the plant spreads primarily from long extended rhizomes.
Sea oats leaves are narrow, pale green, and die back in the winter in more northerly
latitudes. The leaves are normally rolled inward. The stems of this plant are slender and
up to I m tall. The seed heads are compressed spikelets borne at the end of stiff culms.
Seeds mature in the fall.

Seed germination is not high, and seedling survival is low (Seneca 1969; Graetz
1973). Thus propagation via transplants will provide the highest success. In Louisiana,
sea oats cannot be thinned from existing populations since these populations are already
too small. Sea oats transplants can be obtained, however, from commercial supply
houses for dune stabilization measures in Louisiana. When replanting, the transplants are
set at least 0.3 m deep and packed in tightly. The basal part of the leaves may be buried,
but deep planting is desired to keep the roots moist.

200

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The best time for planting sea oats is fronn late winter to early summer. Depth of
planting should be 20 to 30 cm. Each plant should be transplanted at 46-cm centers.
Plantings can be spaced at 0.6 to 1.2 m intervals at the edges of the planting area to
allow for sand penetration into the center of the planting area. Sea oats usually take 2
years to stabilize a dune and hence should be used in conjunction with faster sand
stabilizing plants, such as bitter panicum.

Croton punctatus, beach tea (Figure 10), is a woody-based perennial, commonly
wide-spreading, and up to 45 cm high. This species inhabits coastal dunes from North
Carolina to Florida and Texas, and flowers from March to December or in some cases all
year. Seeds, glossy gray with darker mottlings, ripen in October through November.

Beach tea is only sporadically found along the Louisiana coast. Where it is present,
e.g., on the Northern Chandeleur islands, this species builds up large hummock-like dunes
and is a significant member of the dune community. Beach tea primarily spreads by seed
and is characterized by its silvery-colored leaves and pubescence. The stems are tan
with cinnamon-colored spots.

This plant can be propagated by planting the seed 2.5 to 5 cm deep during the late
fall and up to early spring. Beach tea should only be used for the purposes of dune
stabilization with grasses having a more fibrous root system.

Iva imbricata, dune elder (Figure II), is a woody-based perennial about 60 cm high
with fleshy leaves. Dune elder is found on sand dunes of the Atlantic and gulf coasts
from Virginia to Florida and Texas, and flowers from August to September.

Dune elder has a similar growth habit to that of beach tea, and thus, forms
hummock-like dunes. In specific areas of Louisiana, this plant is a dominant of the dune
community. Dune elder has a strong system of rhizomes which allow it to spread and
form colonies. In addition, roots develop along the stems if they are buried by sand. The
leaves of this plant are fleshy, narrow, and lance-shaped, growing to about 6 cm long.
Dune elder is highly adapted to the dune environment. Its thick fleshy leaves are
impervious to salt spray and the plant spreads upward and outward as sand accumulates
around it.

This plant may be propagated with seed or with stem cuttings. Seed collected,
cleaned, and planted in the fall has a good chance of success (Graetz 1973). In cleaning
the seed, care must be taken in rubbing away the chatty bracts so as not to injure the
fragile seed coats. Seedlings also can be found naturally near the parent plant and can
easily be transplanted in the spring. Stem cuttings root easily in peat pots and can be
used as transplant stock. Cuttings should be planted in the late winter or early spring, 10
to 1 5 cm deep.

The best dune-forming plants have both vertically and horizontally elongating
stems and a fibrous root system. These characteristics enable the plants to grow
vertically through accumulating sand, to spread laterally increasing plant density and
cover, and to most efficiently bind sediments. These characteristics plus the ability of
dune vegetation to survive and reproduce under relatively harsh environmental conditions
makes the above plants nearly perpetual agents for stabilization.

202

TIMBALIER ISLAND DUNE STABILIZATION PROJECT

At this time there is only one relatively large-scale dune building and stabilization
project along the Louisiana coast. This project, located on a washover terrace of
Timbalier Island (Figure 12), is a joint effort of Texaco Corporation, U.S. Soil
Conservation Service, and Louisiana State University's Center for Wetland Resources.
The objective of this pilot project was to determine the feasibility of building and
stabilizing dunes along the Louisiana coast without using beach nourishment. This is an
important consideration since beach nourishment alone can cost from 2 million to 3
million dollars per linear mile of beach while dune building and stabilization via sand
fence and vegetation ranges from $30,000 to 60,000 per mile, 50 to 100 times less
expensive. In addition, any beach nourishment project will require sand fencing and
vegetation to keep the sand in place, thus, making the expense for the total beach
nourishment project even greater.

The Timbalier Island study was initiated in May of 1981 on a 335-m long relatively
flat washover channel containing almost no existing vegetation (Figure 13). Sand fencing
was first installed to attempt to trap sand and build a small dune. Sand fencing was
arranged to test whether diagonal sand fencing accumulated more sand than sand fencing
oriented parallel to the beach. Perpendicular side spurs were also tested (Figure 14). In
late May, 5,000 bitter panicum transplants, thinned from populations on the Caminada-
Moreau barrier beach, were planted to a width of 7.6 m along this 335 m length of
backbeach. Percent survival of these transplants after six weeks was good and averaged
84%, ranging from 69% to 93%. Tillering from a single transplant after 6 months was
prolific with 8 to 12 new tillers originating from each original culm.

The bitter panicum transplants were only one-third of the total number of plants to
be established in this area. Since a mixed planting would provide a greater potential for
success, two other species were also established: sea oats and seashore paspalum.
Because neither of these species are found in great enough abundance to be thinned from
natural populations in Louisiana, they were purchased from a commercial source in
Florida. The two species were transplanted in October and November 1981 which
resulted in a total of 13,200 plants spaced evenly at approximately 46-cm centers.
Survival rates for the seashore paspalum have been estimated at 37% after 7 months and
for sea oats at 28% after 6 months.

Fertilizer was added to the transplanting site once during the first growing season
in late September at a rate of 227 kg of sodium nitrate and 68 kg of 0-20-20 phosphorus-
potassium fertilizer.

As of this writing, a maximum of I to 1.2 m of sand has accumulated within the
test site depending upon the presence and orientation of the sand fencing (Figure 15).
The sand fencing was essential in accumulatng relatively large amounts of sand in a short
period. Vegetation, alone, only trapped small quantities of sand. Preliminary data
indicated the sand fencing with perpendicular side spurs accumulated the greatest
amount of sand on this beach. Bitter panicum, during the first year of this project, has
been the most successful of the three species planted. (Figure 16).

203

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205

CONCLUSIONS

The use of vegetation for dune building and stabilization in Louisiana offers an
erosion control method that is compatible with natural coastal processes and is relatively
inexpensive. This method has its best chance of success on islands undergoing some
degree of accretion and dune building. But even in transgressive environments,
vegetative stabilization in combination with sand fencing and/or beach nourishment
offers a viable means for reducing coastal erosion.

ACKNOWLEDGMENTS

The author expresses his appreciation to the Coastal Energy Impact Program of the
Louisiana Office of Coastal Zone Management for its financial support of the research
from which this manuscript is derived; to F. Monteferrante, M. Hester, D. Carlock, and
graduate students of the Department of Marine Sciences, Louisiana State University for
carrying out much of the field work; to Mr. J. Jordan of Texaco Corporation; to Mr. C.
Starkovich and Ms. F. Talbot of the Soil Conservation Service for coordinating and
participating in field plantings on Timbalier Island; and to Texaco Corporation for
funding this field planting effort.

LITERATURE CITED

Art, H. 1971. Atmospheric salts in the functioning of a maritime forest ecosystem.
Ph.D. Dissertation. Yale University, New Haven, Conn.

Boyce, S. G. 1954. The salt spray community. Ecol. Monogr. 24:29-67.

Craig, R. M. 1976. Grasses for coastal dune areas. Proc. Fla. State Hort. Soc. 89:353-
355.

Dahl, B. E., B. A. Fall, A. Lohse, and S. G. Appan. 1974. Stabilization and
reconstruction of Texas coastal foredunes with vegetation. Gulf Universities
Research Consortium Rep. 139. Galveston, Tex.

Dolan, R. 1972. Barrier dune system along the outer banks of North Carolina: a
reappraisal. Science 176:286-288.

Dolan, R., P. J. Godfrey, and W. E. Odum. 1973. Man's impact on the barrier islands of
North Carolina. Am. Scientist 61:1 52- 1 62.

Godfrey, P. J. 1976. Barrier beaches of the east coast. Oceanus 19:27-40.

Gould, F. W. 1975. The grasses of Texas. Texas A&M Univ. Press, College Station. 653
pp.

Groetz, K. E. 1973. Seaside plants of the Carolinas. University of North Carolina. Sea
Grant Publ. UNC-SG-73-06.

206

Leatherman, S. p. 1979a. Barrier dune systems. A reassessment. Sediment. Geo I. 24:1-
\6.

Leatherman, S. P. 1979b. Barrier island handbook. National Park Service, Cooperative
Research Unit, The Environmental Institute, Univ. of Massachusetts, Amherst. 101 pp.

Leatherman, S. P. 1979c. Beach and dune interactions during storm conditions. Q. J.
Eng. Geol. 12:281-290.

Leatherman, S. P. 1980. Barrier island management. Pages 1470-1480 jn Proceedings of
the Conference-Coastal Zone '80, Hollywood, Florida.

Mendelssohn, I. A., P. S. Penland, W. H. Patrick, Jr. 1982. Louisiana barrier islands and
beaches. Report to the Louisiana Office of Coastal Zone Management. (In
preparation).

Montz, G. N. 1981. Final report annotated checklist of plants on the coastal beaches,
islands, and barrier islands of Louisiana. U.S. Army Corps of Engineers, New Orleans,
La. 43 pp.

Oosting, H. J., and D. W. Billings. 1942. Factors affecting vegetational zonation on
coastal dunes. Ecology 23:131-142.

Palmer, P. G. 1975. A biosystematic study of the Panicum amarum - P. amarulum
complex (Gramineae). Brittania 27:142-150.

Penland, P. S., and R. Boyd. 1981. Shoreline changes on the Louisiana barrier coast.
Oceans. September: 209-219.

Seneca, E. D. 1969. Germination response to temperature and salinity of four dune
grasses from the outer banks of North Carolina. Ecology 50:45-53.

Silvester, R. 1977. The role of wave reflection in coastal processes. Pages 639-654 |n
Proceedings of Coastal Sediments 77.

U. S. Army Corps of Engineers. 1974. Shore protection manual. Coastal Engineering
Research Center, Ft. Belvoir, Va.

Van der Meulen, T., and M. R. Gourlay. 1969. Pages 70 1 -707 ]ri Proceedings of the I Ith
International Coastal Engineering Conference, London.

Van der Valk, A. G. 1974. Environmental factors controlling the distribution of forbs on
coastal foredunes in Cape Hatteras National Seashore. Can. J. Bot. 52:1057-1073.

Wells, B. W., and I. V. Shunk. 1937. Seaside shrubs: wind form vs. spray forms. Science
85:499.

Westgate, J. M. 1904. Reclamation of Cape Cod sand dunes. U. S. Dep. Agric. Bureau
Plant Ind. Bull. 65:407-41 I.

Woodhouse, W. W., Jr., and R. E. Haines. 1966. Dune stabilization and vegetation on the
outer banks of North Carolina. Department of Soil Science, North Carolina State
Univ. at Raleigh. Soil Sc. Ser. 8.

207

PANEL DISCUSSION

OPTIONS: BARRIER ISLAND AND SHORELINE PROTECTION

Charles G. Groat, Moderator

Dag Nummedal, Irving A. Mendelssohn,
Robert A. Morton, Johannes van Beek, Representative Murray J. Hebert

and Larry DeMent, Panelists

Charles Groat: State Representative Murray Hebert has joined the speakers as a
panelist. Representative Hebert is from Terrebonne Parish which has an extensive
border with the gulf, lined with barrier islands. Consequently, he has been among
the most active legislators in matters of shoreline erosion and barrier island
protection.

Murray Hebert: First, I want to express my appreciation to LUMCON for holding this
conference. It's a good idea for the scientific community to interact with the others
representing diverse responsibilities and attitudes regarding the issues of coastal
erosion.

As a member of the House Natural Resources and Ways and Means committees
I have made coastal restoration my top legislative priority. In Terrebonne Parish
alone we have lost 200 mi of marsh and barrier island in the last 40 years. With the
possible exception of Plaquemines Parish, Terrebonne and Lafourche parishes are the
ones most affected by coastal erosion. One of the ways we used to get legislators
concerned about coastal erosion is to prepare some simple map overlays which
highlight the area of land loss. For example, this segment of the western Isles
Dernieres contained 1,180 acres of barrier island in 1953 and 476 acres in 1978 for a
loss of 60 percent. East Timbalier Island suffered a 42% reduction in size in the
same period.

The Joint Committees on Natural Resources have recommended projects to
slow coastal erosion costing $38 million, including island restoration and
stabilization projects, mainly in the Terrebonne-Lafourche area. Also recommended
are freshwater diversions in Plaquemines and St. Bernard parishes and shoreline
protection and wetlands management projects in southwestern Louisiana. Another
project recommended for testing is marine accretion, a process by which calcium
carbonate is built on wire through which a weak current is passed. This can be done
economically for about one cent per pound in place.

Some projects recommended probably will not work, but the Legislature feels
that with the severity of the problems and diverse opionion about what can be done,
we will have to go with trial and error. Thus we will need the scientific community
to monitor these projects and determine which ones will work and which ones will
not.

208

Mock Mathis: I have been involved in the construction of most of the coastal structural
projects discussed here, including the Belle Pass jetties, the Grande Isle jetties, the
East Timbalier project and the Holly Beach project.

I do not agree with some of the things said about East Timbalier Island. We
began working there in 1965 and it has been virtually an annual experiment financed
by Gulf Oil Company. Where were you experts when I needed you? There was a lack
of any one willing to make a commitment as to what would work. Gulf made a
commitment of between $15 million and $25 million. We have followed the advice of
world experts on this project. I do not agree that the riprap seawall has not
protected the island; there is a lot of island left. One of our errors was scraping
sand from the low dunes of +5 feet to +3 feet msl on the island. This caused some
washover channels. Much of the sand has gone to the back protection dike built to
an elevation of +6 feet and hard enough for trucks to run on. Another error is the
permeable nature of the rock structure, which has allowed tidal flow to erode behind
the rocks. Nonetheless, these experiences should now serve as valuable experiments.

Charles Groat: Several speakers brought up the point of the relative sand starvation of
the Louisiana barriers. The Legislature's recommendations included geophysical
exploration of offshore sand sources which could be used for nourishment.

Dag Nunrimedal: The Corps of Engineer's Coastal Engineering Research Center has had a
successful project to identify sand sources along the east coast. Some sources do
exist off the Louisiana coast which could be used. However, if we remove too much
sand from these ar^as disequilibrium will result and the sand may be transported
back into these holes.

Murray Hebert: I agree with Mr. Mathis that if it were not for the rocks protecting East
Timbalier Island we would have much less of that island remaining.

Jay Combe: I disagree that seawall structures such as the Galveston Seawall cause
erosion. If there were no erosion in the first place, there would have been no need
for the seawall. Without the seawall the shoreline would have eroded farther into
the sand dunes.

Dag Nummedal: That is not true. Most seawalls are erected to protect the land. Any
natural shoreline, even if it recedes, maintains a beach.

Robert Morton: The Galveston seawall was built in response to the loss of lives. It has
been documented that locally the increased shoreline erosion is attributed to the
seawall.

With regard to offshore sand sources, we have surveyed the Texas inner shelf
using high resolution seismic methods. In an area off Galveston our seismic survey
indicated a lack of viable sand supplies. The Corps of Engineers subsequently looked
more intensely only to find a thin veneer of relict sand over Pleistocence mud; an
insufficient source of sand for beach nourishment. Offshore sand supplies must be
both extensive enough and located near the site of beach nourishment.

Irving Mendelssohn: Sand nourishment should be followed by vegetative stabilization
because, in the past, unstabilized sand has often been washed away.

209

David Stuttz: The Corps of Engineers has had a beach nourishment project at Grand Isle
where we have found sufficient offshore sand supplies one-half mile offshore. The
dunes created will also be vegetated.

Jake Valentine: When I was a U.S. Fish and Wildlife Service refuge manager at
Chincoteague, Virginia, we built a 15-mile dune line with sand fence and vegetation
over a period of 5 to 6 years. One January in the early I960's, a northeaster blew for
5 days and washed the dune line away. I watched the Chandeleur Islands for the last
20 years, including the effects of Hurricane Camille, its subsequent build-up and
partial destruction by Hurricane Frederick. Beach erosion control has made more
mistakes than virtually any other occupation, primarily because of failure to take
into account natural geological processes. Everyone says we must do something and
normally, as in the case of the Timbaliers, we do it wrong.

Robert Morton: I have been asked to address the Senate Natural Resources committee in
Texas to testify about the mineral accretion process. I would like to ask
Representative Hebert to comment about the plans to employ this process in
Louisiana.

Murray Hebert: The process works by passing a weak current through a wire and placing
an anode in the vicinity, and, like an oyster secretes a shell, the mineral builds up on
the negative. This may cut the cost of conventional methods of 70% to 80% in
place.

Our intention would be to put out three test projects under different conditions
and with different goals. The mineral can accrete as fast as 3h inches in 12 days, but
at this rate the material is soft and weak. Normally material of a strength of 4,200
psi, one-third stronger than concrete, can be grown at a rate of one inch on a single
strand over a 2'k- to 3-month period. In addition to trapping sand, this process has
great potential for protection of metal from corrosion in marine and oil field
applications.

Dag Nummedal: It is my understanding that the two field sites where this marine
accretion process has been tried are the boot basin of the University of Texas
laboratory at Port Aransas and a quiet lagoon in St. Croix. Can this material be
accreted fast enough to survive on a relatively high energy beach?

Murray Hebert: I really do not know. We may want to apply this inside islands. But this
is why I have suggested a test project, rather than a full-scale application. We
definitely need to develop some new technologies for shoreline protection.

H. Dickson Hoese: After the 1973 flood a Corps of Engineers report noted the large
biological cost of maintaining levees and suggested that it be included in cost-
benefit analyses. Now we realize there is a significant geological cost of the levee
system. Is there a study of these long-term costs in existence, and if not, why not?

Larry DeMent: I do not necessarily believe that the leveeing of the river is the
fundamental problem. Most accretion takes place near the river when it overtops its
banks and relatively little accretion results in a basin at some distance from the
source. In fact, we can look at the area between Venice and the Head of the Passes
in which there are no levees. There has been tremendous land loss from 1952 to
1971 and significant losses between 1971 and 1978. These losses cannot be

210

attributed to the construction of levees. Otiier areas suffering land loss were
abandoned delta lobes long before the construction of artificial levees. The Corps is
faced with making an overall evaluation of each individual project with regard to its
potential contribution to coastal erosion.

Donald Landry: The Corps of Engineers performed a study of the barrier islands in the
I960's and concluded that the cost-benefit ratio did not justify expenditures for
barrier island protection. However, this analysis did not take into account the
benefits regarding protection of marshlands inside the islands. Of what benefit are
the islands in protecting interior wetlands from erosion?

Murray Hebert: From admittedly unscientific studies of land-loss maps it does appear
that where barrier islands have been eroded away the interior marsh has eroded
much more rapidly than where it is still protected by barrier islands.

I have the feeling that the islands absorb a tremendous brunt of the sea. For
instance, where a gap has opened between Timbalier and East Timbalier islands one
can almost see a channel opening through Lake Barre to Montegut. A community of
600 Indians in this area is now cut off by road just on a high tide.

Dag Nummedal: It is possible that this is mainly an effect of subsidence. A numerical
model study of Moriches Inlet, Long Island, concluded that the change in storm surge
would be imperceptible given the quadrupling of the size of an inlet. A similar study
in Galveston Bay related to deepening the entrance channel for deepwater draft
vessels also concluded that it would have little or no effect on flooding in the bay.

Johannes van Beek: The opening of large bays behind the islands has increased the rate
of erosion of interior wetlands because of increased fetch for wind waves. This
would be happening even if the barrier islands remained as they are .

Charles Groat: Subsidence, then, is a double villain because in addition to directly
causing erosion of wetlands it may have the effect of increasing the water depth and
thus the erosive powers of waves generated in the bays.

Irving Mendelssohn: The lack of ability to answer the simple question of the degree to
which island erosion affects marsh erosion illustrates the need for more research on
basic processes. Unfortunately, we hear that legislators say we have enough studies
and action is what we need. I feel this is a short-sighted viewpoint and I think our
inability to answer this question exemplifies that.

Murray Hebert: Perhaps in place of studies we can use monitoring. People themselves
have gotten tired of the word "studies" and legislators, because they represent
people, have also become tired of the word. Nonetheless we need to continue to
work with the scientific community to monitor our efforts and to better understand
the main causes of erosion.

I might add that there are over 2,000 oil and gas wells inside the barrier islands
in Terrebonne Parish. If the barrier islands erode there structures will become
vulnerable to the sea, because they were not designed as offshore structures. Some
of these fields are old and it would not be feasible to place offshore type platforms
in these areas. Because there are about 15,000 jobs in Terrebonne Parish directly or
indirectly resulting from the oil industry, the problem is of tremendous importance
to our economy.

211

Frank Atkinson: In Europe, a decision was made on the position of a fortification line
and money was spent on shoring up that line, if Louisiana is going to spend money on
coastal protection, we have to decide where that fortification line is going to be and
then decide how to protect that line. Where is that fortification line going to be?

Johannes von Beek: We have been evaluating that in relation to the rates of land loss
being experienced. It is evident that the line must be a considerable distance inward
from the present coast. There are two major conditions for the determination of
that line: (I) where are the major investments and population centers and (2) where
are the major natural levee deposits in order to build structures necessary for
permanent protection. Taken together, one can fairly well draw a line along Bayou
Teche through Houma to Bayou Lafourche.

Murray Hebert: By their recommendation of $17 million dollars in island stabilization
projects, the Joint Natural Resources Committees decided the line will be the
barrier islands. With the tremendous amount of revenues which have been generated
in Louisiana, it would certainly be a shame if we left a legacy of depleted natural
resources, depleted fisheries, an eroding coastline, and a depleted treasury. I would
certainly hope that we can get more people involved in solving these problems.

Dag Nummedal: Because there are people and investments which need protection, we
obviously need to take some steps, even if short-term to slow the rate of erosion.
However these efforts need to be tied into regional or statewide plans for ultimate
land use. We need to keep productive resources, but should not build structures
which will bring a lot of new people into the threatened areas. The European
experience has been different because that coastline is stable. The Louisiana coast
is subsiding an order of magnitude faster than the German or Dutch coast.

Irving Mendelssohn: I can not say where the line should be drawn; that is largely a socio-
economic and political question. However, to draw the line at the barrier islands is
really not looking at the facts. There is no way to permanantly protect some barrier
islands which are subsiding, without discovery of huge sand supplies and spending
billions of dollars to continuously replenish the islands. We can draw such lines
temporarily, but we need a commitment to research on the processes which must be
understood for long-term planning.

Larry DeMent: In my mind, we might need two or three fortification lines rather than a
single line. The first line may be the barrier islands, which we know are highly
dynamic. This may require pumping sand behind the islands in order to maintain a
moving line without having the islands disappear. Another line may be inland and
aimed at protecting population centers and wetlands.

Johannes van Beek: Even though we have been talking about a line I think that to some
extent we can still have the best of both worlds. A line can be drawn and planned
for, then we can afford to manage the system outside the line as a dynamic system
and reap its benefits.

Charles Groat: Thus, it may be that there are short-term benefits which justify short-
term Investments which are not long-term answers. But ultimately we have also to
strive for the long-term answers.

212

OPTIONS: LIMITATION AND MITIGATION
OF DREDGING AND FRESHWATER

DIVERSIONS

213

REVERSAL OF COASTAL EROSION BY RAPID SEDIMENTATION:
THE ATCHAFALAYA DELTA (SOUTH-CENTRAL LOUISIANA)

Harry H. Roberts
Ivor LI. van Heerden

Coastal Studies Institute and Departnnent of Marine Sciences

Louisiana State University

Baton Rouge, LA 70803

ABSTRACT

In early I950's Atchafalaya Bay began experiencing sedimentation, which marked
the initiation of a new major delta lobe In the Mississippi River Delta complex. This new
era will be characterized by rapid progradation and marshland growth In parts of coastal
Louisiana that have been typified by coastal retreat for hundreds of years. Although the
Atchafalaya River has long been a distributary of the Mississippi, it was not until the
early I950's that the Atchafalaya Basin had filled sufficiently to allow significant
quantities of sediment to be transported to the bay. The I950's and I960's marked the
period of subaqueous growth when the bay bottom accreted with prodelta clays and silty
clays. As a product of the abnormally severe 1973 flood, the Atchafalaya Delta became
a subaerial feature characterized by sand-rich lobes which are prograding at a rapid
rate. During 1972-77 approximately 32.5 km^ (12.6 mi ) (above low tide level) of new
marshland was added to Atchafalaya Bay as a product of sedimentation from Lower
Atchafalaya River Outlet. Similar orocesses are occurring at the mouth of Wax Lake
outlet, where, by early 1976, 2.20 km (0.85 mi ) of new land existed.

Systematic monitoring of changes within the delta system over the last 4 years has
shown that delta growth responds directly to flood volume and duration. The years 1976
through 1978 can be characterized as average in terms of discharge. Analysis of
LANDSAT imagery reveals that Wax Lake suffered a net loss of subaerial expression
during this period owing to the combined effects of subsidence, compaction, and winter
erosion. Comparison of aerial photographs for a section of eastern Atchafalaya Delta
reveals a similar trend. Land loss was reversed during the major flood in 1979.

The delta has evolved by channel bifurcation and bar fusion, processes by which
coarse distributary-mouth bars fuse into larger sand bodies through selective elimination
of the delivery network. These processes are accomplished by rapid growth of
mid-channel bars and sealing of feeder channels by subaqueous levee growth. The
presence of deltas at Lower Atchafalaya River and Wax Lake outlets has elevated water
levels near the coast during floods (backwater effect), causing sediment-rich water to be
transported into surrounding marshes. A similar response results from setup prior to
cold-front passage. The net effect is marsh aggradation and restoration in flood areas.
Rapid sedimentation since the I950's has reversed the traditional trend of coastal erosion
in the vicinity of Atchafalaya Bay and is now initiating a new growth phase of the
downdrift chenier plain.

214

INTRODUCTION

During the Holocene, the broad Mississippi River deltaic plain was built by "delta
switching" (Figure I). This fundamental land-building mechanism resulted in a net
progradation of the shoreline over the past 6,000 to 8,000 years. The depositional history
consists of construction and abandonment of large and complex delta lobes on a time
scale of about 1,000 years for each major sedimentation event. During the regressive
phase of a delta lobe's history, local progradation of the shoreline and the building of new
marshland are maximized. Domination by fluvial processes over marine processes, as is
the case in the Mississippi Belize delta lobe, results in rapid progradation of
distributaries and associated facies, causing a complicated channel geometry. Between
and along the flanks of major feeder channels relatively thin wedges of rapidly deposited
sediments create bay fills, which are initiated, fill the bay with marshlands, and
deteriorate to an open-bay condition once again on a time frame of generally less than
200 years. At some point, however, the major delivery system diverts sediment and
water through a more efficient and generally shorter route to the receiving basin. As
diversion takes place the formerly active lobe is starved of sediment. The effects of
sediment dewatering and compaction, as well as regional subsidence associated with
northern Gulf of Mexico depocenter, become dominant and a phase of rapid land loss is
initiated. Since there is generally only one major locus of deposition or active delta lobe
along the coast at any given time, the remaining coastal areas ore in various stages of
retreat, depending on their relative ages. In deltas such as the Mississippi which have
been constructed by deposition of dominantly fine-grained sediment in a receiving basin
with low wave-current energy, the coastline is always in a state of dynamic change.

The modern Belize "delta lobe has been the locus of Mississippi River deposition for
the past 600 to 800 years. This delta-building event has resulted in a thick sequence of
both subaerial and subaqueous sediments that have prograded onto the Continental
Shelf. Because of this extensive progradation and other geological factors, the modern
river course has reduced its gradient and general flow efficiency to a point that upstream
diversion is favored. Fisk (1952) predicted abandonment in favor of the more efficient
Atchafalaya River course by the mid-1970's if the diversion were not controlled. From
the point at which the two rivers meet, north of Baton Rouge, the Atchafalaya course to
the sea is 307 km shorter and, therefore, is favored by its steeper gradient. Although
Mississippi River flow down the Atchafalaya course has been documented as far in the
past as the 1500's (Fisk 1952), it was not until the early I950's that significant quantities
of sediment started to arrive at the coast. Shiemon (1975) and Roberts et al. (1980)
discussed the basin-filling phase prior to the arrival of abundant prodelta clays in
Atchafalaya Bay and along the downdrift coasts. At this time a new phase of delta
building in the Mississippi River delta complex was initiated, and areas that have
experienced coastal retreat for literally hundreds of years entered a new era of coastal
accretion. This paper describes the early stages of Atchafalaya delta growth and the
implications of this event with reference to Louisiana's problems of land loss and coastal
retreat.

DELTA HISTORY

Delta development in Atchafalaya Bay can be divided into two major stages,
subaqueous and subaerial. The subaqueous phase was initiated as deposition in the
intricate network of lakes and swamps of the Atchafalaya Basin reached a point such
that sediments were fluxed through the system to the coast. This natural catchment

215

CD -I- +J

S- n3 c

3 4-1 OI

CJli — O

-.- cu cj

Ll_ "O i-

216

basin filled for hundreds of years, but it was not until the early I950's that swamp floors
and lake bottoms had accreted to a point that fine-grained sediments were transported to
the coast in significant quantities. In addition to basin filling, flood-control levees in
Atchafalaya Basin have increased the hydraulic efficiency of the river, which is
responsible for delivering proportionately higher loads of both fine and coarse sediment
to the coast. Starting in about 1952, accelerated sedimentation in Atchafalaya Bay
marked the beginning of subaqueous delta growth (Shiemon 1975). From that time to
1973 prodelta clays and silty clays aggraded the bay bottom seaward of both the Lower
Atchafalaya River Outlet and the Wax Lake Outlet, an artificial channel dredged in 1942
(Figure I).

As a product of the abnormal 1973 flood, a disproportionate quantity of sediment
was transported to Atchafalaya Bay. Prior to this time only a few small shoals were
exposed at low tide, and these areas were primarily composed of dredge spoil from the
navigational channel which is maintained from the Lower Atchafalaya River Outlet
through the Point Au Fer shell reefs. After the massive 1973 flood (Figure 2), however,
numerous coarse subaerial lobes appeared on both the eastern and the western sides of
the river outlet. This event initiated the sand-rich subaerial phase of delta
development. Since that time sands have been prograding over finer prodelta clays and
silts. As a product of subaerial delta growth, marshlands expanded rapidly in
Atchafalaya Bay.

69 ' 70 ' 71 ' 72 ' 73 ^ 74 ' 75 ' 76 77

Figure 2. Mean monthly discharge for the Atchafalaya River at Simmesport,
Louisiana, for 1956-1981. The dotted line represents average annual peak
flow, which is approximately 400,000 ft^/s. Note the abnormal discharge
years 1973, 1975, and 1979.

217

WATER AND SEDIMENT INPUT

Thirty-four years of hydrographic data collected on Atchafoloya River flow at
Simmesport, Louisiana, show that the average annual flow over the sample period (1938-
72) was 5,126 rn^/s (181,000 U^/s) (U.S. Army Corps of Engineers 1974). Within this data
collection period, the average annual peak flow that occured in the spring was
approximately I 1,300 m-^/s (400,000 U^/s). About 70% of this flow arrived at the coast
through the Lower Atchafalaya River Outlet, while the remainder was transported
through the man-made Wax Lake Outlet. During the years of subaqueous delta growth
(early I950's to 1972), flood levels only occasionally exceeded the I 1,300 m-'/s (400,000
ft /s) level (Figure 2); from 1973 to 1980, however, this level was significantly exceeded
three times, in 1973, 1975, and 1979. These abnormal floods also transported a
proportionately higher-than-average sediment load to Atchafalaya Bay. Flow velocities
during flood are such that the coarsest particles available (generally fine-sand size) can
be transported as suspended load (Roberts et al. 1980). In response to abnormally high
discharge during the 1970's, deposition and subsequent subaerial growth of the
Atchafalaya Delta have been impressive, as is illustrated by a 1976 photomosaic (Figure
3). The most recent flow measurements (1979-81) made in the lower reaches of
Atchafalaya River and in the main arteries of the newly formed delta indicate that
approximately 67% of the water and sediment transported from the Lower Atchafalaya
River mouth goes down the western branch (dredged navigation channel), while about
27% is conducted through the eastern branch (Figure 3). Minor passes near the river
mouth account for the remaining 6% of the flow.

Roberts et al. (1980) present a sediment budget for the Atchafalaya system from
1967 to 1975; the annual suspended sediment load nearly doubled during the three
high-water years of the early 1970s. It was estimated that much of the suspended-load
sand was derived from scouring and resuspension of previously deposited sediments in the
Lower Atchafalaya River course. The net change in the dominance of sediment reaching
the bay from clay and silt to silt and fine sand over the last 30 years has resulted in the
construction of sizable sand-rich sediment lobes that have been rapidly colonized by
marsh plants as soon as they build to the low-tide level.

SPATIAL-TEAAPORAL CHANGES IN MARSH LAND

Bathymetric changes in Atchafalaya Bay have been impressive. The 1967
bathymetric map shows distributary-mouth bar deposits whose limits are roughly
represented by the 4-ft (1.2-m) depth contour. At this time these deposits were
beginning to prograde into the bay, forming broad, shallow platforms which front the
natural channels of Lower Atchafalaya River and Wax Lake outlets (Figure 4). By 1972
the distributary-mouth bar platform had extended over most of the bay (Roberts et al.
1980). The natural channel of the Lower Atchafalaya River mouth showed a pronounced
seaward extension and development of a major bifurcation to the east.

The 1977 bathymetric map of Atchafalaya Bay (Figure 5) emphasizes the
tremendous volume of predominantly coarse-grained material deposited in the decade
1967-77. An extensive network of distributary-mouth bar deposits formed in both the
complex Wa>eLake and Atchafalaya delta lobes. Roberts et al (1980) estimated that 16
km^ (6.55 mi^) of new land had developed above mean sea level by 1977. When estimated
from the low tide level, a net land gain of 32.5 km^ (12.6 mi ) over the same period was
calculated (Rouse et al. 1978).

218

y^ DEER ISLA ■*»-5'

^'-' -

^ -■''^^F?^

rrss-

;.^:*

-/^■•4

y^:

2 '

'i %
: i

0 500 1000 1500

Aerial photo
mosaic flown
12 October 976.

Figure 3. Photomosaic of Atchafalaya delta (12 October 1976).

219

Figure 4. Bathymetric map of Atchafalaya Bay in 1967 (Roberts et a1 . 1980)

[ 1 Atea above MSL
[.'^"^ "J l0'-20' below. MSL

Figure 5. Bathymetric map of Atchafalaya Bay in 1977 (Roberts et al . 1980).

220

The extent and evolving pattern of new subaerial marsh in the Atchafalaya delta
lobe is illustrated in Figure 6. Unusual hydrologic conditions during the first 3 years of
subaerial exposure played an important role in the rapid development of this dynamic
phose of Atchafalaya Delta growth. Rouse et al. (1978) showed that by early 1976, 19.0
km (7.3 mi ) of new Iqnd had forrned above mean sea level, corresponding to an average
growth rate of 4.75 km /yr (1.8 mi^/yr) (Figure 7). Through aerial-photo mapping of the
eastern half of the delta, van Heerden (1980) confirmed the dramatic growth rate in
1973, 1974, and 1975 and the major flood in 1979. During average floods the growth rate
is somewhat reduced, however.

Through analysis of LANDSAT imagery a growth curve has been developed for Wax
Lake delta lobe (Figure 8). Unpublished data (Susan Chinburg, Coastal Studies institute,
Louisiana State University, Baton Rouge, 1981, personal communication) suggest that the
Atchafalaya Delta exhibits the same growth trends, although on a larger scale. Subaerial
expression of new marsh land increased steadily from 1973 to 1976, but decreased during
1977 and 1978. This reduction in surface area reflects the average-sized floods during
these years, but more importantly reveals the dynamic effects of wind-wave-induced
erosion during the passage of winter cold fronts (van Heerden and Roberts 1980a). The
cumulative effects of the passage of cold fronts spaced at approximately I -week
intervals are erosion and denudaton of new marsh surface. During minor floods this loss
may not be completely replenished. During major floods, however, the marsh surface
aggrades significantly, offsetting any land loss resulting from cold-front-related erosion.

DELTA LOBE RESPONSE CHARACTERISTICS

Systematic monitoring of land accretion, changes in channel cross sections, and
sediment characteristics have shown that delta growth responds directly to flood volume
and duration. Reductions in channel cross section are most dramatic during major floods
(van Heerden and Roberts 1980b). Distributary channels experience mid-channel shoaling
and bar formation at their seaward ends (Figure 9). This bifurcation mechanism results
in a complex network of sand lobes, separated by branching distributaries, characteristic
of deltas whose river mouths are frictionally dominated and are generally building into
unstratified, low-energy, shallow-water environments (Welder 1959; Wright and Coleman
1974).

As the fluvial effluent passes from the confined distributary channel to the shallow,
unconfined bay, it rapidly experiences a reduction in velocity. Associated with the
frictional deceleration of the flow is a reduction in turbulence and the coarsest part of
the suspended load is deposited, initiating a mid-channel bar (Figure lOa). Once
initiated, shoaling hxiyward of the mouth causes an increase in the friction-induced
deceleration and effluent spreading, which in turn increases the shoaling rate (Bates
1953; Wright 1977). The overall effect of the differential sedimentation is a branching of
the channel into two distributaries (Figure I Ob). Velocities also decrease away from the
center line of the divergent current field. Deposition occurs at the outer edges of the
effluent plume, giving rise to subaqueous levees. The levee ridges flare away from the
mouth, reflecting the divergent current field that results from the abrupt transition to
unconfined flow (Figure lOc). The same process may then be repeated on the two newly
formed channels (Figure lOd). In the above manner, the subaerial components of the
emergent delta have evolved into a complex network of sand lobes separated by
branching distributaries.

221

Figure 6. Areas of subaerial exposure obtained from LANDSAT images and aerial
photographs depicting progressive evolution of the Atchafalaya delta.

222

1972

1973

1974

1975

1976

Figure 7. Exposed area (above msl ) of the Atchafalaya delta (modified from
Rouse et al . 1978).

3 r

1972

1974

1976

1978

Figure 8. Exposed area (above msl) of the Wax Lake delta
imagery analysis.

1980

Data from LANDSAT

223

Width (ft.:

2000

West
Bank

Vert. Exag. 250x

T I r

78 79

Year

PROFILE DATE CROSS SECTIONAL AREA fl? (n? )

Tl AUG'77
T2 JAN' 79
T3 JUL '79

18.732.4 (1,740.30)

12.936.5 (1,201.84)
10,870.3 (1,009.86)

Figure 9. Profile of cross section in East Pass (see Figures 3 and 11 for
location) showing the development of a mid-channel bar.

■"?-

' RIVER MOUTH
BAR

MID CHANNEL
BAR

(b)

OI^^nO/^-

^^1 Suboeriol natural levee
[ ,~ ""I Suboqueous natural levee
CZH Bors
Marsh

Figure 10. Schematic diagram of delta development,

224

Generally one of the channels formed in a bifurcation is smaller than the other.
The smaller slowly loses hydrodynamic efficiency and eventually seals owing to
subaqueous levee formation. Thereafter it fills with fine-grained sediment and fuses
with adjacent lobes. Thus larger lobes form as a result of coalescence of numerous
smaller distributary-mouth bars and adjacent channels (Figure 1 1).

IMPLICATIONS OF DELTA BUILDING

Diversion of Mississippi River fresh water and sediment to the central coast of
Louisiana will steadily influence the future character of coastal environments in the
immediate vicinity of Atchafalaya Bay and its adjacent downdrift coasts, in conjunction
with man-made flood control measures, filling of the Atchafalaya Basin, a natural
sediment sink, has promoted transport of sediments in significant quantities to the coast
since the early I950's. The initial sediments to impact the central Louisiana coast from
this progression of events associated with "delta switching" were fine grained. They
started a regressive phase that will replace the traditional erosional trends that have
characterized central and western Louisiana coasts for hundreds of years.

In addition to simply supplying sediment to nearshore depositional sites, aggraded
bay bottom and resulting delta development have influenced the hydrography of
surrounding marshlands. For example, flood levels at Morgan City and in adjacent
marshes average over 0.3 m (1.0 ft) higher than in pre-delta years (U.S. Army Corps of
Engineers 1974). This change has resulted from the inefficient dispersal of flood waters
because of the obstructive effects of deltas at the mouths of both the Lower Atchafalaya
River and Wax Lake outlets. Elevated flood levels have the net effect of driving
sediment-laden water into marshes lying generally between the Grand Lake-Six Mile
Lake complex and the coast (Baumann and Adams in press). It is suggested that this
process tends to cause an increased increment of yearly sedimentation which results in
aggradation of the marsh surface at a higher rate than in pre-delta years.

Another set of processes, winter cold-front passage, also accounts for abnormal
elevation of water levels in coastal marsh areas surrounding Atchafalaya Bay. Figure 12
illustrates a record segment (January 1978) from a tide gauge located at the Amerada
Hess platform (Figure 3) on the western side of the Atchafalaya Delta. Water level
changes in the bay associated with a cold-front passage and tidal effects are shown on
this figure. Winds preceding a cold front generally blow from a southerly quadrant,
which promotes setup or water-level elevation in the bay (Figure 12, up to 2100 hr on 16
January). It is during this phase in cold-front-related events that local wave action
suspends sediments and high water levels force turbid water into the coastal marshes. As
the cold front crosses the area from northwest to southeast, winds switch to a northerly
quadrant and cause rapid setdown (Figure 12, after 2100 hour on 16 January). Swift
movement of water out of the bay, coupled with wind-wave action, is responsible for
erosion and redistribution of sediment within the delta (van Heerden and Roberts 1980a).

The similarity of water level response to cold-front passages at three sites in
Atchafalaya Bay is illustrated in Figure 13. The magnitude of the mean fluctuations
decreases from Eugene Island to the Lower Atchafalaya River mouth. Maximum average
water levels at Deer Island, near the mouth, were nearly 92 cm (3.0 ft) above mean sea
level during this study period (January 1979-April 1980). These elevated coastal water
levels initiate overbank flooding of surrounding marshes, which promotes aggradation of
the marsh surface.

225

Position of profile

Figure 11. Aerial photograph of an eastern delta area showing coalescence
of delta lobes and position of cross section in East Pass (Figure 9).

226

1200

U Jan 78

2400

1200

15 Jan 78

2400

1200

16 Jan 78

2400

1^00
17 Jan 78

1* in hours

Figure 12. A tide gauge record segment from the western side of the

Atchafalaya delta (Amerada Hess platform, Figure 3) showing the setup

and setdown of bay water levels associated with cold-front passage
(14-17 January 1978).

Figure 14 summarizes the suggested sedimentological impacts that diversion of
fresh water and sediment down the Atchafalaya system will have on the central and
western coasts of Louisiana. One of the initial effects of sedimentation in the bay
(I950's) was to diminish and finally eliminate a once-productive oyster fishery, Point Au
Fer and Marsh Island oyster reefs. With increased sedimentation of highly organic clays
and silty clays both in the bay and on the inner continental shelf, the shrimp fishery
potential is steadily increasing, however.

As the deltas from both Lower Atchafalaya River and Wax Lake outlets continue to
fill the bay and build onto the shallow continental shelf, delta lobes will merge to form
extensive new marsh lands that wilL protrude into the marine environment. At the
present rate of nearly 3 km (1.16 mi ) of new marshland added above mean sea level to
the Atchafalaya deltas yearly (average 1975-81), by the end of this century, it is
estimated, bay filling will be complete and the subaerial delta will be prograding onto the
continental shelf. The mean drift system, as well as the wave-induced longshore drift, in
this part of the northern Gulf of Mexico favors an east-to-west transport direction. It is
safe to assume that the major areas of coastal progradation will be in the immediate
vicinity of the delta and along the downdrift coasts. New data concerning the important
effects of significant currents generated after the passage of cold fronts suggest that the
coarse facies (fine sands) may be skewed somewhat to the southeast after the delta
starts supplying coarse sediment to the continental shelf (Adams et al., submitted for
publication). However, even assuming that cold-front effects will modify coarse-
sediment transport on the shelf, the clays, silty clays, and silts will be spread in front of
the prograding subaerial delta and along the chenier coasts to the west (Figure 14). In
the short time since the I950's coastal progradation has replaced coastal retreat in many
downdrift sites. Sedimentation rates should increase in these areas as Atchafalaya Bay
fills and the delta progrades onto the shelf.

227

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IVOR'S ISLAND

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DEER ISLAND

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AVERAGE LEVEL
EUGENE ISLAND

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HOURS AFTER FRONT PASSAGE (WIND SHIFT)

Figure 13. Mean water levels in Atchafalaya Bay following cold fronts.
These data are summarized for 35 cold fronts between 1 January 1979 and
30 April 1980.

Additional effects associated with water-level elevation near the coast will tend to
offset marsh deterioration caused primarily by the numerous processes collectively
described as subsidence. These "backwater effects" are caused by deltas at the mouths
of major flood-water outlets at the coast. This process, plus similar effects produced by
water-level elevation during the passage of cold fronts, provides a new supply of
sediment to the marshes, causing aggradation of the surface.

In summary, diversion of Mississippi River water and sediment to the coast through
the Atchafalaya system has led to the following conclusions concerning impacts on
central and western Louisiana coasts:

(1) New marsh lands are being added in the vicinity of the active Lower
Atchafakiya River and Wax Lake Deltas at an average rate of about 3 km /yr
(1.16 m^lyr) (average 1973-81). This trend will continue as long as present flow
levels are maintained.

(2) Downdrift coastlines are starting to accrete as a product of advected clays and
silty clays from the Atchafalaya River source. The rate of coastline
progradation should increase as the delta builds onto the continental shelf and
makes sediments more available to the downdrift areas.

(3) "Back-water effects" result from water-level elevation during cold-front
passages and inefficient dispersal of sediment-rich flood waters at the coast

228

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229

owing to delta building at the Lower Atchafalaya River and Wax Lake outlets.
These processes encourage marsh restoration.

ACKNOWLEDGMENTS

This research was supported by the U.S. Army Corps of Engineers, Contract No.
DACW 29-77-C-0I63, and the Coastal Sciences Program, Office of Naval Research,
Arlington, Virginia 22217. Part of the research was also supported by the Louisiana Sea
Grant Program, a part of the National Sea Grant Program, maintained by the National
Oceanic and Atmospheric Administration, U.S. Department of Commerce. Special
recognition should be given to R.H.W. Cunningham, R.D. Adams, and R.H. Baumann, who
collected and processed data from reports and files of the U.S. Army Corps of Engineers,
New Orleans District. Some of these data appear in this paper. Mrs. G. Dunn is cited for
her drafting of figures and Mr. K. Lyie for photography.

LITERATURE CITED

Adams, C.E., Jr., J.T. Wells, and J.M. Coleman. Submitted for publication. Sediment
transport on the central Louisiana Continental Shelf: implications for the developing
Atchafalaya River Delta. Contrib. Mar Sci.

Bates, C.C. 1953. Rational theory of delta formation. Bull. Am. Assoc. Petrol. Geol.
37:2119-2161.

Baumann, R.H., and R.D. Adams. In press. The creation and restoration of wetlands by
natural processes in the lower Atchafalaya River system: possible conflicts with
navigation and flood control objectives. Proceedings, 8th Conference Wetland
Restoration and Creation, Tampa, Fla., May 8-9, 1981.

Fisk, H.N. 1952. Geological investigation of the Atchafalaya Basin and the problem of
Mississippi River diversion. U.S. Army Corps Engineers, Mississippi River Commission,
Vicksburg, Miss. v. I. 145 pp.

Kolb, C.R., and J.R. Van Lopik. 1966. Depositional environments of the Mississippi River
deltaic plain - southeastern Louisiana. Pages 17-61 ]n Deltas in their geologic
framework. Houston Geological Society.

Roberts, H.H., R.D. Adams, and R.H. W. Cunningham. 1980. Evolution of the sand-
dominant phase, Atchafalaya Delta, Louisiana. Bull. Am. Assoc. Petrol. Geol. 64:264-
279.

Rouse, L.J., Jr., H.H. Roberts, and R.H.W. Cunningham. 1978. Satellite observation of
the subaerial growth of the Atchafalaya Delta, Louisiana. Geology 6:405-408.

Shiemon, R.J. 1975. Subaqueous delta formation - Atchafalaya Bay, Louisiana. Pages
209-221 ]n M.L. Broussard, ed.. Deltas. Houston Geological Society.

U.S. Army Corps of Engineers. 1974. Preliminary draft environmental impact statement,
Atchafalaya Basin floodway. New Orleans, La.

van Heerden, I. LI., and H.H. Roberts. 1980a. The Atchafalaya Delta: rapid progradation
along a traditionally retreating coast (south-central Louisiana). Z. Geomorph. N.F.,
34:188-201.

230

van Heerden, I. LI. and H.H. Roberts 1980b. The Atchafalaya Delta: Louisiana's new
prograding coast. Trans. Gulf Coast Assoc. Geol. Soc. 30:497-506.

Welder, F.A. 1959. Processes of deltaic sedimentation in the Lower Mississippi River.
Louisiana State Univ., Coastal Studies Inst., Baton Rouge. Tech. Rep. 12. 90 pp.

Wright, L.D. 1977. Sediment transport and deposition at river mouths: a synthesis. Bull.
Geol. Soc. Am. 88:856-868.

Wright, L.D., and J.M. Coleman. 1974. Mississippi river mouth processes: effluent
dynamics and morphologic development. J. Geol. 81:751-778.

231

COMPARISON OF EFFECTIVENESS OF MANAGEMENT OPTIONS
FOR WETLAND LOSS IN THE COASTAL ZONE OF LOUISIANA

J.W. Day, Jr.
N.J. Craig

Center for Wetland Resources

Louisiana State University

Baton Rouge, LA 70803

ABSTRACT

The coastal wetlands of Louisiana, an area of 14,000 krrc (5,400 mi ), are currently
experencing an overall net loss of approximately 130 km /yr (50 mi /yr). Various
management options have been suggested to combat the problem of wetland loss. This
paper examines the effectiveness of three management options: (I) management of the
current land building of the Atchafaiaya River, (2) controlled diversion schemes on the
lower Mississippi River and (3) strict regulatory control of canals within the coastal
zone. 5trict regulatory control of new canalicould reduce future land loss rate by 30 to
40 km /yr. This compares with ! to 3 km /yr for controlled diversion plans, and 18
km /yr for the land-building processes of the Atchafaiaya River. We conclude that if the
problem of wetland loss is to be properly addressed by regulatory agencies, they must
make a serious attempt to control canal construction.

INTRODUCTION

The coastal wetlands of Louisiana, an areo of approximately 14,000 km^, are
experiencing an overall net loss of about 130 km /yr. This includes a loss rate of 102
km /yr in the Mississippi deltaic plain (Gagliano 1981) and 26 km /yr in the chenier plain
along the southwest Louisiana coast (Gosselink et al. 1979) (see Figure I). The loss is
cumulative resulting from both natural and artificial causes. Natural causes include land
subsidence, the deterioration of abandoned river deltas, and erosion by wave energy and
storms. Human-induced land losses result from flood control practices, impoundments,
and the dredging of canals and channels (Craig et al. 1979). Wetland loss in turn creates
significant problems: (1) hydrologic changes in the wetland-estuarine system which
exacerbates saltwater intrusion and eutrophication; (2) losses in the storm buffering
capacity of the wetlands; (3) a decrease in waste assimilating capacity of wetlands; and
(4) a diminished nursery area for Louisiana's coastal finfish and shellfish (Craig et al.
1979; Hopkinson and Day 1979; Kemp and Day in press).

The objectives of this study are to describe the factors leading to wetland loss in
the Louisiana coastal zone and to evaluate several different management options for
dealing with the problem.

232

Figure 1. Major geomorphic provinces in Louisiana.

Notural Factors Leading to Land Loss

The Mississippi deltaic plain is a large area of dynamic geomorphic change. Over
the past several thousand years Mississippi River sedimentation has formed the coastal
wetlands of Louisiana, building seven major deltaic lobes since the stabilization of sea
level. Within this process of overall growth were large-scale cycles of land growth and
decay of land.

In an active delta, sedimentation exceeds erosion and there is a net land gain.
Land building occurs at the mouth of the river's channel, through overbank flooding, and
through sedimentation in older deteriorating marshes (Baumann and Adams 1982). But
as its channel lengthens, the Mississippi seeks a new, shorter course to the Gulf of
Mexico and ultimately abandons the older channel. During this phase, active land
building ceases in the old delta and there is a net loss of land from erosion and
subsidence. Historically, land loss in old Mississippi River deltas was compensated for by
land gain in the active delta.

There are three major natural mechanisms involved in the process of land loss: (I)
Gulf of Mexico beach retreat, (2) lateral erosion of streamside marsh shores, and (3)
gradual sinking of inland marshes. Wave action is the primary cause of shoreline retreat

233

and erosion. Inland nnarsh loss is caused prinnarily by lack of sufficient sedimentation to
offset apparent sea level rise. Studies done by DeLaune et al. (1978) and Baumann (1980)
showed that only streamside marshes are accreting fast enough to offset the effects of
subsidence.

Artificial Causes of Land Loss

Flood control, navigation improvements, agricultural impoundments, and
canalization interact with natural geologic processes to accelerate wetland loss. Lack of
adequate sediment supply is caused largely by the construction of levees along the
Mississippi; these have almost eliminated overbank flooding and caused the closure of a
number of minor distributaries. The modern delta has grown out to the edge of the
continental shelf and most of the river's sediment load is deposited in deep Gulf of
Mexico waters. These flood control measures have interrupted the balance between
riverine and marine processes which built and stabilized marsh and swamp areas. The
only significant land building along the Louisiana coast is in Atchafalaya Bay where a
new delta is being formed (Roberts et al. 1980).

Canals constructed for such activities as oil exploration and recovery, navigation,
and drainage significantly contribute to wetland loss. Aerial photography of coastal
Louisiana gives a stunning image of wetlands densely webbed by canals. The

construction of canals leads directly to land loss through dredging and spoil deposition.
Indirect influences include such factors as changes in hydrology, saltwater intrusion, and
altered sedimentation patterns (Craig et al. 1979; Cleveland et al. 1981). The highest
rates of marsh erosion occur in areas with the highest density of dredged canals
(Blackmon 1979; Craig et al. 1979; Turner et al. 1982).

MANAGEMENT OF WETLAND LOSS

A number of management approaches have been suggested to combat the problem
of wetland loss. The creative use of riverine sediments to help build new wetland areas
or infill decaying marshes is one mitigation technique that has been suggested. This
could be accomplished through controlled diversions along the lower Mississippi River
(Gagliano and van Beek 1974), and through proper management of sediment flows into the
newly forming Atchafalaya delta region. Another management option is stricter
regulatory controls on canal construction within the coastal zone. In this paper, we will
assess the effectiveness of these various approaches in reducing wetland loss rates.

Atchafalaya Delta

The Atchafalaya River is a major distributary of the Mississippi and carries about
30% of the total flow. It is currently creating new wetlands in the Atchafalaya Bay
Delta, as well as restoring deteriorating wetlands in adjacent areas. There is also a
measurable accretion of sediments along the chenier plain associated with the deposition
of fine sediments from the Atchafalaya River. The amount of sediment required to fill
Atchafalaya Bay could be deposited in a 60-year period given the flood regimes of the
period 1851 to 1967. If abnormally high floods of 1970-77 are included in this long-term
average (i.e. 1951-77) the estimated time for this to occur is 42 years. The recurrence in
the I980's of the extremely high flood stages of 1970-77, would reduce the time needed
to fill the bay to less than a decade (Baumann and Adams 1982).

234

Before the emergence of the Atchafalaya delta during the floods of the I970's,
existing wetlands adjacent to the lower Atchafalaya River were deteriorating at a rapid
rate. During 1972-78, the loss rate was reversed and the wetland area grew. Baumann
and Adams (1982) examined quadrangle maps for the area and found a net loss during
1955-72 of 7,805 ha (4.88 kmVyr). The interval between 1972 and 1978, by contrast, had
a much reduced rate of land loss and some areas experienced wetland gain (Baumann and
Adams 1282). Nonflotant marsh in the examined area experienced a net gain of 1,676 ha
(0.28 kmVyr) during 1972-78, with 1,277 ha (0.21 kmVyr) attributable to formatiop of
the new delta in Atchafalaya Bay. The same area lost a total of 6,736 ha (0.42 km /yr)
of wetlands from 1955 ta 1972. The marshes peripheral to Atchafalaya Bay experienced
a reversal from 0.42 km /yr loss to a 0.07 km^/yr gain (Baumann and Adams 1982). In
summary, the net wetland gain in the Atchafalaya Bay area is caused by two factors: (!)
the creation of new land in Atchafalaya Bay in the form of the new delta and (2) the
reversal of land loss in deteriorating marshes adjacent to the bay by infilling with
riverine sediment.

Table 1. Effects of different mitigation techniques for reducing land loss
(see text for derivation).

Activity Reduction in land loss rate

(km^/yr)

Atchafalaya River

New delta growth 11.9

Reversal of chenier plain beach retreat^ 1.1

Infilling of older marshes 4.9

TOTAL 17.9

Controlled diversions lower

Mississippi River 1-3

Regulatory control of new canals 30-40

^This value assumes that the present net rate of shoreline retreat will be
arrested. The net rate of retreat was calculated as the algebraic sum of
shoreline changes for each interval along the chenier plain as given in
Adams et al . (1978).

235

An additional impact of Atchafalaya River sediments is the reduction of beach
retreat along the chenier plain coast west of Atchafalaya Bay. During most of this
century, there has been a net shoreline retreat in this area (Adams et al. 1978). Fine-
grained sediments from the Atchafalaya are now being deposited along this coast,
however, and it is estimated that within 50 years there will be a net growth (Wells and
Kemp 1981).

Future growth of the Atchafalaya delta, assuming the flow regimes of 1851-1977,
will take place at the rate of I 1.9 km /yr (Baumann and Adams 1982). The infilling of
older marshes adjacent to the Atchafalaya as previously discussed, is occurring at 4.9
km /yr (Baumann and Adams 1982). A reversal of the chenier plain beach retreat, which
will stabilize the situation and result in no net loss for that area, is occurring at a rate of
LI km /yr (Adams et al. 1978; Wells and Kemp 1981). Therefore, the accretion from
Atghafalaya River sediments is responsible for a total reduction in land loss of 17.9
km Vyr (Table I).

Controlled Diversions

As a means of introducing river water and sediment to offset wetland loss, plans
have been developed for controlled diversions of the Mississippi River. "Basically, it
would re-establish the overbank flow regime of the deltaic plain, presently disrupted by
flood protection levees, and restore more favorable water quality conditions to the highly
productive deltaic estuaries" (Gagliano and van Beek 1974). According to Gagliano et al.
(1971), the feasibility of controlled diversion is indicated by the relatively small input of
energy and materials needed to build a subdelta. Several sites for controlled diversions
are presently being developed along the lower Mississippi River. According to Gagliano
(I98IJ the potential reduction in land loss rate using controlled diversion is between I and
3 km /yr.

Regulatory Control of New Canals

The highest rates of marsh loss occur in areas with the highest density of canals.
Land loss rates were determined for the seven management basins in Louisiana and it was
estimated that when canal, spoil area and indirect Josses were included (Craig et al.
1979), 44% to 54% of the total annual loss of 102 km"^ (39.4 mi^) in the deltaic plain was
caused by canals.

Canals contribute to wetland loss both directly and indirectly. The direct impact
of canals can be easily measured. For example, unpublished data from U.S. Fish and
Wildlife Service records show that 397 permits for dredging of Louisiana marshes were
granted to oil companies in 1975, with a direct loss of 772 ha (1,907 acres) of marsh; in
1976, 435 permits resulted in a direct loss of 981 ho (2,424 acres); and during the first 6
months of 1977, 206 permits were issued resulting in a direct loss of 524 ha (1,295
acres). Thus, in 2.5 years there was a direct loss of 2,227 ha (5,626 acres) of Louisiana
marsh just to the petroleum industry (Lindall et al. 1979). Spoil deposition from canal
construction is generally two to three times greater than the canal area itself. Craig et
al. (1979) estimated that the indirect impacts of canals can cause wetland loss in an area
three to four times the initial canal area. Therefore, the total loss of wetlands caused by
industrial access canals for the 2.5-year period mentioned above will ultimately be 6,000-
8,000 ha (15,000 to 20,000 acres). One of the mechanisms by which this additional loss
takes place is the widening of canals with time. Annual increases in canal widths of 2%
to 14% in the Barataria Basin have been documented, indicating width doubling rates of 5

236

to 60 years (Craig et cl. 1979).

As a regional network, canals result in: (I) higher rates of wetland loss (Craig et
al. 1979); (2) increased saltwater intrusion, which further exacerbates the wetland loss
problem (Van Sickle et al. 1976); (3) changes in the hydrology of the wetland system
(Hopkinson and Day 1979, 1980a, 1980b; Craig et al. 1979; Kemp and Day in press); (4) a
reduction in capacity for wetlands to buffer the impacts of large additions of nutrients
(Hopkinson and Day 1979, 1980a, 1980b; Kemp and Day in press); (5) a loss in storm
buffering capacity; and (6) loss of important fishery nursery grounds (Turner 1977; Lindall
et al. 1979; Chambers 1980).

Turner et al. (1982) have recently extended the analysis of the relationship of canal
density and wetland loss by examining U.S. Fish and Wildlife Service habitat maps for
1955 and 1978. The change in marsh as shown by 260 quadrangle mops in the deltaic
plain and the extent to which canals attributed to this change were examined. Again, a
strong relationship between canal density and wetland loss was found. Turner et al.( in
press) have estimated that if no additional canals were constructed in the wetlands, that
the loss rate would be 30 to 40 km^/yr less over the next 20 years.

ADVANTAGES AND DISADVANTAGES OF DIFFERENT
MANAGEMENT OPTIONS FOR CONTROLLING WETLAND LOSS

In managing the Atchafalaya River's contribution to wetland gain, a large area of
the Louisiana coast — from western Terrebonne Parish to the Texas border — will benefit
and a minimum amount of engineering aid will be required to accomplish land building.
The disadvantages are that this sediment nourishment is area-specific and does not seem
to be effective in flotant marshes (Baumann and Adams 1982).

Controlled diversions of the Mississippi River have several advantages: (I) the
areas affected have high wetland loss rates; (2) there will be a possible improvement in
fisheries; and (3) advanced planning can be done and operational experience can be
gained. The disadvantages of controlled diversions are that: (I) they are area-specific
and can affect only the lower Mississippi River; (2) engineering costs are high; and (3)
there would be pollution problems associated with toxic substances in the Mississippi
River.

Regulatory control over canals has the advantages of: (I) affecting all areas of the
coastal zone; and (2) addressing the major human cause of wetland loss. The
disadvantages are: (I) the opposition to such strict regulation by the political and private
sector; and (2) lack of complete information on the relationship between canals and
wetland loss.

CONCLUSIONS

Comparison of the effects of the different management options and mitigation
techniques for reducing wetland loss in Louisiana reveal that regulatory control of new
canals could reduce the loss rates approximately 30 to 40 km /yr, in contrast to
I to 3 km'^/yr for controlled diversion plans, and approximately 18 km /yr for land
building by the Atchafalaya River. If the problem of wetland loss is to be properly
addressed by regulatory agencies, they must make a serious attempt to control the
construction of canals (see Table I).

237

To combat wetland loss, we advise: (I) management of the Atchafaiaya River for
maximum land building; (2) use of controlled diversions along the Mississippi River; and
(3) strict regulatory control of canals within the Louisiana wetland system.

ACKNOWLEDGMENT

This work was partially supported by funds from the Louisiana Department of Natural
Resources, Coastal Resources Unit. This is contribution no. LSU-CEL-82-22 of the
Coastal Ecology Laboratory, Center for Wetland Resources, L.S.U.

LITERATURE CITED

Adams, R., P. Banas, R. Baumann, J. Blackmon, and W. Mclntire. 1978. Shoreline
erosion in coastal Louisiana: inventory and assessment. Final Report to Louisiana
Department Transportation and Development. 139 pp.

Baumann, R.H. 1980. Mechanisms of maintaining mcrsh elevation in a subsiding
environment. M.S. Thesis. Louisiana State Univ., Baton Rouge.

Baumann, R., and R. Adams. 1982. The creation and restoration of wetlands by natural
processes in the Lower Atchafaiaya River System: possible conflicts with navigation
and flood control objectives. Proceedings Eighth Annual Conference on Wetlands
Restoration and Creation. 8:1-24.

Blackmon, J. H., Jr. 1979. A detailed analysis of marsh deterioration for selected sites
in the Barataria Basin. Pages 21 1-226 m J.W. Day, Jr., D.D. Culley, Jr., R.E. Turner,
and A.J. Mumphrey, Jr., eds. Proceedings Third Coastal Marsh and Estuary
Management Synmposium. Louisiana State Univ., Div. of Continuing Education, Baton
Rouge.

Chambers, D.G. 1980. An analysis of nekton communities in the upper Barataria Basin,
Louisiana. M.S. Thesis. Louisiana State Univ., Baton Rouge.

Cleveland, C, C. Neill, and J. Day. 1981. The impact of artificial canals on land loss in
the Barataria Basin, Louisiana. Pages 425-435 in W. Mitsch, R. Bosserman, and J.
Klopatek, eds. Energy and ecological modelling. ETsevier Scientific Publ., New York.

Craig, N.J., R.E. Turner, and J.W. Day, Jr. 1979. Land loss in coastal Louisiana (USA).
Environ. Manage. 2:133-144.

DeLaune, R.D., WJH. Patrick, Jr., and R.J. Buresh. 1978. Sedimentation rates
determined by '■^' Cs dating on a rapidly accreting salt marsh. Nature 275:532-533.

Gagliano, S.M. 1981. Special report on marsh deterioration and land loss in the deltaic
plain of coastal Louisiana. Presented to Frank Ashby, Secretary, Louisiana
Department Natural Resources and Jesse Guidry, Secretary, Louisiana Department
Wildlife and Fisheries. Coastal Environments, Inc. Baton Rouge, La. 13 pp.

Gagliano, S.M., P.P. Light, and R.E. Becker. 1971. Controlled diversion in the
Mississippi River Delta system: an approcah to environmental management. Louisiana

238

State Univ., Center for Wetland Resources, Baton Rouge. Hydrologic and Geologic
Studies of Coastal Louisiana Rep. 8. 146 pp.

Gagliano, S.M., and J.L. van Beek. 1974. An approach to multiuse management in the
Mississippi Delta systems, delta models for exploration. Houston Geological Society.

Gosselink, J.G., C.L. Cordes, and J.W. Parsons. 1979. An ecological characterization
study of the Chenier Plain coastal ecosystem of Louisiana and Texas. 5 vol. U.S. Fish
and Wildlife Serivce Office of Biological Services. FWS/OBS-78/9 thru 78/ II.

Hopkinson, C.S., and J.W. Day, Jr. 1979. Aquatic productivity and water quality upland
estuary interface in Barataria Basin, La. Pages 291-314 |n R.L. Livingston, ed.
Ecological processes in coastal marine systems. Plenum Press, New York.

Hopkinson, C.S., and J.W. Day, Jr. 1980a. Modeling hydrology and eutrophicatlon in a
Louisiana swamp forest ecosystem. Environ. Manage. 4:325-334.

Hopkinson, C.S., and J.W. Day, Jr. 1980b. Modeling the relationship between
development and storm water and nutrient runoff. Environ. Manage. 4:315-324.

Kemp, G.P., and J.W. Day. In press. Nutrient dynamics in a Louisiana swamp receiving
agricultural runoff in cypress swamps. Univ. of Florida Press, Gainesville.

Lindall, W., A. Mager, G. Thayer, and D. Ekberg. 1979. Estuarine habitat mitigation
planning in the southeast. ]n Mitigation Symposium: a National Workshop on
Mitigating Loss of Fish and Wildlife Habitat. Colorado State Univ., Ft. Collins, Colo.
GTRM-65.

Roberts, H., R. Adams, and R. Cunningham. 1980. Evolution of sand dominant subaerial
phase, Atchafalaya Delta, Louisiana. Am. Assoc. Petrol. Geol. Bull. 64:264-279.

Turner, R.E. 1977. Intertidal vegetation and commercial yields of penaeid shrimp.
Trans. Am. Fish. Soc. 106:41 1-416.

Turner, R., R. Costanza, and W. Scaife. 1982. Canals and wetland erosion rates in
coastal Louisiana. Pages 73-84 ]n D.F. Boesch, ed. Proceedings of the conference on
coastal erosion and wetland modification in Louisiana: causes, consequences and
options. U.S. Fish and Wildlife Service, Biological Services Program, Washington,
D.C. FWS/OBS-82/59.

Van Sickle, V.R., B.B. Barrett, T.B. Ford, and L.J. Gulick. 1976. Barataria Basin:
Salinity changes and oyster distribution. Louisiana State Univ., Center for Wetland
Resources, Baton Rouge. Sea Grant Publ. LSU-T-76-002.

Wells, J.T., and G.P. Kemp. 1981. Atchafalaya mud stream and recent mudflat
progradation: Louisiana chenier plain. Trans. Gulf Coast Assoc. Geol. Soc. 31:409-
416.

239

PAhEL DISCUSSION

OPTIONS: LIMITATION AND MITIGATION OF DREDGING
AND FRESHWATER DIVERSI0^4S

Kai Mi<t>oe, Moderator

John W. Day, Harry H. Roberts, Sherwood M. Gagliano, Peter Hawxhurst,
Senator Samuel Nunez and Gerald Voisin, Panelists.

Kai Midxje: We will now be joined by two additional panelists, State Senator Samuel
Nunez and Mr. Gerald Voisin of Louisiana Land and Exploration Company. Senator
Nunez represents St. Bernard and Plaquemines parishes and obviously has a vital
concern over land loss and is Chairman of the Senate Natural Resources Committee.

Samuel Nunez: Of course I have many reasons to try to protect St. Bernard and
Plaquemines parishes which are disappearing at a. rapid rate. That is now recognized
in the Legislature and at a local level. In 1964 the people of one of my parishes
passed a special bond issue to fund a freshwater diversion structure at Caernarvon,
which has not been built yet, but I think we can solve that.

This week we will present a report from the Joint Natural Resources
Committees to the Legislature and the Governor on what we should do about the
problem of coastal land loss. We asked the Mineral Board to estimate the effect of
a retreat of one-half mile of the coast on State revenues from oil and gas
production. They indicated a loss of at least $52,000/day. It is vital to protect our
coastal environments, not only from the standpoint of revenues to the State, but also
from the standpoint of recreational value, commercial seafood industry, and
protection of our estuaries.

Our report is based on extensive expert testimony and recommends the
expenditure of revenues to the Enhanced Mineral Trust Fund, which is set aside as a
percentage of State oil and gas revenues. I can think of no better use of those funds
than the protection of the resource which produced them.

The approach the Committees have taken is to propose specific projects and
estimate their costs. Our recommendations include as a beginning: freshwater and
sediment diversion at Caernarvon, barrier island revegetation in Terrebonne,
Jefferson and Lafourche parishes, cybernetic architecture or artificial creation of
reefs, rock structures and jetties and sand restoration on barrier islands, beach
protection at Holly Beach, and wetland management programs. These programs
total over $38 million. But given the loss of natural resources and revenues, this has
to be only a beginning. If we do not take some of the revenue from coastal oil and
gas production and dedicate it to the restoration of marsh lands and protection of
the fragile estuarine system and coastline we will be doing ourselves and our
grandchildren an injustice.

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Gerald Voisin: The property Louisiana Land and Exploration Company owns is located in
nine coastal parishes in southeastern Louisiana. The company adopted a marsh
management plan in 1952 in cooperation with the U.S. Soil Conservation Service.
Following this plan we have constructed 385 water control structures or weirs, dams,
earthen plugs, and shoreline stabilization structures. These management approaches
have been successfully applied to freshwater, intermediate, and brackish marshes. I
wholeheartedly support plans for freshwater diversion which is the only answer to
improving the marsh. The proof is the rapid accretion of marsh in western
Terrebonne Parish. On the other hand, in lower Plaquemines Parish there is serious
saltwater intrusion and rapid subsidence where there has been a reduced river input.

Unidentified speaker: Senator Nunez, how much of the $38 million do you think will
become available?

Samuel Nunez: Hopefully all of it. We are probably not asking for enough but we are
trying to be realistic.

Linda Deegan: What will be the effects of the pollutants present in high concentrations
in Mississippi River water in the wetlands receiving freshwater diversions?

Samuel Nunez: Oysters do very well in areas where fresh water is diverted in
Plaquemines Parish and they are monitored by the Board of Health. The only
problem seems to be increased coliform bacteria counts during certain periods.
Improvements in sewage treatment along the lower river will hopefully clear this up.

Sherwood Gagliano: Water quality can be monitored and the structure can be closed in a
short period of time. Furthermore, the structures only operate during high flow
conditions when water is generally better. The Nation is committed to achieving
certain water quality standards and by agressively using the water for environmental
management purposes we help force the issue of meeting those water quality
standards.

Michael Halle: Some of the techniques proposed in the Legislature's report are
questionable, based on the opinions of scientists and the presentations made at this
conference, including cybernetic architecture, groins and jetties. Why were
scientists not used to draw up plans that will work?

Samuel Nunez: We are not going to be married to any particular plan. We invited many
scientists before the committees for their advice. Many of the projects are of the
pilot scale to determine whether they will work. Our recommendations include
pilot- and full-scale projects in five different approaches: freshwater and sediment
diversion, nourishment and revegetation of beaches, artificial reef structures, rock
structures, and wetlands management.

Unidentified speaker: Mr. Voisin, would you clarify your company's policy on backfilling
canals?

Gerald Voisin: We have no problem with backfilling, but do with a blanket policy
requiring backfilling. Not every marsh type can support backfilling. In some
circumstances it is useless and may destroy more marsh than if the canal were left
alone. We agreed with the Coastal Management Section to backfill two canals in
every marsh type in which we work and study the effectiveness of these.

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Samuel Nunez: Comprehensive pipeline crossing legislation previously passed was also
meant to look into this, but funding of implementation of this program was vetoed.

Walter Sikora: Because there are areas where the shoreline will retreat and others, such
as the Atchafalaya delta, where the shoreline will prograde, could we enter an
agreement with the Federal Government to fix the Federal-State boundary?

Samuel Nunez: The courts have decreed that the boundary is ambulatory and subject to
judicial review, but I agree that it would be good to fix a boundary.

Kai Mi(ft>oe: With a net land loss of 40 mi^/yr, the Federal Government has little
incentive to negotiate a fixed boundary.

R. Eugene Turner: I am pleased by the approach of experimental backfilling canals which
Mr. Voisin described. 1 believe that generic investigations and projects on marsh and
canal management should be included in the coastal protection program Senator
Nunez described.

Unidentified speaker: Based on John Day's comparisons of the effectiveness of various
approaches to slow land loss, should management focus only on canal impacts
because the effects of freshwater diversions are inconsequential?

John Day: We can save more land by better regulating canals than can be gained by
Atchafalaya delta building or freshwater diversion. Canals are widespread whereas
controlled or natural diversions are site specific. If we do not address the issue of
canals we will not address the main cause of land loss, but all of these approaches
should be used in combination.

Joan Phillips: Directional drilling can reduce the need for canals, however, industry
spokesmen indicate it is impractical or too expensive. The Coastal Management
Section does not have the expertise to evaluate this claim and reportedly cannot
solicit the advice of the Office of Conservation of the Department of Natural
Resources. If the Office of Conservation cannot advise the Coastal Management
Section on this matter, the Coastal Management Section should develop its own
expertise in this field.

Michael Lyons: Generally a directional hole costs 50% more than a straight hole.
Straight holes can more effectively reach the several stratigraphic objectives of an
exploratory well. Directional drilling would clearly save marsh land, but would not
reduce the needed number of wells. Most offshore drilling is directional because of
the large investment of the platform from which a number of directional wells can
be drilled.

Lirxla Deegan: Then the decision of whether to use directional drilling is based solely on
economics, but these economics exclude environmental costs.

Kai Midboe: Can a distinction be made between those canals near the ocean and those
farther inland?

R. Eugene Turner: The relationship between canal density and land loss is more severe
the closer to the coast and the newer the delta.

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Samuel Nunez: If we had no canals at all would we still have a problenn? Would not
subsidence still result in land loss?

R. Eugene Turner: I think that at least 50% of the wetland loss is directly or indirectly
attributable to canals. Disruption of the natural hydrology seems to be the primary
mechanism causing wetland loss indirectly as a result of canals.

Donald Moore: A recent presentation was made concerning the use of hovercraft for
accessing oil and gas locations in wetlands in order to reduce the need for canals.
Several companies are ready to build such craft, but apparently no one in the
industry is willing to make a commitment to use them.

Kai Midboe: When 1 worked with the House Coast Guard Subcommittee we studied the
use of hovercraft by the Coast Guard. Hovercraft are very expensive to build and
operate. This is probably the main reason for the reluctance to use them for oil and
gas activities.

Donald Moore: Hovercraft are already being used in oil and gas development on the
North Slope of Alaska. I think they are certainly worth looking at in this instance.

Sue Hones: Regarding the effects of major Corps of Engineers projects compared to oil
field canals, while reviewing a 5-mile canal in the Barataria Basin we found nearly
56 miles of oilfield canals within a small triangular area. The Corps does build some
canals, but oilfield canals are so much more extensive.

Samuel Nunez: The Corps' Mississippi River Gulf Outlet is probably the largest canal I
have ever seen dredged.

Peter Howxhurst: The Corps only builds canals when asked to, they don't do it on their
own. To get these constructive efforts, such as river diversion, off the ground is
going to take a concerted and coordinated effort by Federal, State and local
government as well as the users of the marsh areas. We need to view our activities
in a broad context with respect to resources. As was mentioned earlier, we need to
evaluate the social costs of individual activities. For example, an oil company
wishes to dredge a canal because it is cheaper than directional drilling. We need to
set limitations on activities, such that all the quantifiable costs and less readily
identifiable social costs are considered in cost-benefit analysis. At one time the
Corps could consider such social well-being costs, but I understand revised
regulations under the Reagan administration will make that more difficult.

Charlotte Fremoux: What agency will resolve whether privately owned lands will be used
for a purpose such as river diversion?

Gerald Voisin: Right now we have to deal with about 14 agencies, but no one has
proposed a better marsh management plan than that we developed with the Soil
Conservation Service in 1952. The regulatory agencies operate independently,
sometimes with different objectives.

Sherwood Gogliono: The property right considerations depend on the type and magnitude
of the project. The existing freshwater diversions on the east side of the river are
cooperative efforts between local land owners and local government and, to some

243

extent, the State government. The Violet experience suggests that works very well
provided there is a framework for discussion of problems. The coastal zone
management framework is good for that because it includes local xidvisory
committees, parish and State government and interfaces with the Federal
Government. Larger projects are public works projects which have to be
inplemented much as an interstate highway, including taking of properties and
easements. The mechanisms for this are very well established and should not be an
obstacle for implementing an environmental management project. There is a
framework for compensating individuals whose ownership or use is displaced.

Kai Midboe: Having worked so heavily on the Governor's Atchafalaya Basin plan, I can
tell you though, that the land-use issue is probably the most politically difficult.
Even though the mechanisms such as eminent domain are there, they are politically
difficult to exercise.

Samuel Nunez: The large land owners in the wetlands seem to be willing to cooperate
because they will benefit. For example, the Delacroix Corporation will donate or
give easements for the Caernarvon structure. Many of these corporations lease
these lands for trapping and hunting and, furthermore, when their land erodes it
reverts to State ownership.

Tommy Michot: Would anyone care to speculate on what the shape of the coastline will
be in 50 or 100 years given the absence of man-made structures or control?

Sherwood Gagliano: It would take quite a while for a diversion to the Atchafalaya to
occur. The river might maintain its present course, at least partially, for a long
time. Commonly more than one river distributary has been functioning at the same
time during the history of the delta. The Atchafalaya Delta will continue to grow
and should produce a large delta lobe because the continental shelf is shallow and
the underlying land is relatively stable. The chenier plain would expand
significantly. The intervening areas between the active delta areas would continue
to deteriorate.

Joan Phillips: i would hope Senator Nunez's committee would remain active and begin
planning how we would like the coastal zone of Louisiana to be in the future and how
this can be achieved.

Samuel Nunez: Presently we have addressed mainly short-range goals. We cannot afford
to quit longer-term efforts when we have been told that Plaquemines Parish will
disappear in 49 years. If the wheat fields of Kansas were disappearing at the
alarming rate experienced by the marshes of Louisiana, it would be declared a
national disaster.

John Day: I would like to reiterate that two things, which are not in Senator Nv.. az's list,
that have to be addressed are the management of canals and the Atchafalaya delta.

Samuel Nunez: Would you care to elaborate on how to deal with canals? Do we stop new
canals all together? How do we deal with existing canals?

John Day: I would like to know what would happen if there were a near-blanket
prohibition of new canals? I have a feeling that we would get all of the oil out of
the ground that we could anyway.

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Samuel Nunez: I am not going to disagree with you, but I will simply point out that these
current efforts represent what we can realistically gain legislative approval for. If,
as was indicated earlier, canals account for 50% of the land loss, we are trying to
address the other 50%. The Legislature will eventually address the issue of canals,
but if we prohibited them today we would run into difficulties related to concern
about energy shortages. Rather than going forward, I am concerned we would go
backward.

Linda Deegan: The approaches to backfilling Mr. Voisin mentioned constitute a
constructive proposal to deal with the issue of canals. This is the type of positive
approach which could be included in the Legislature's recommendtions.

Samuel Nunez: Perhaps backfilling should hove been a condition for permitting 50 years
ago. I agree we have to address the canal problem. I have addressed the pipline
problem by passage of an act for which the funding was vetoed. This program could
help address the canal issue.

Lee Black: It is probably too late to amend the report prior to the Special Session three
weeks away. Therefore we should support the plan and develop efforts for other
projects for subsequent legislative sessions.

Kai Midboe: The Enhanced Mineral Trust Fund has probably been spent 100 times over, so
a concerted effort is required to obtain these funds for coastal erosion.

Samuel Nunez: There is no better way to spend funds generated from mineral extraction
in coastal Louisiana than to use them to protect the area from which they come, if
the extraction is acknowledged to be part of the cause of the problems. The oil
industry is important to Louisiana and generates 30% to 40% of State revenues and
provides much employment. As a legislator I must balance all these benefits and
detriments.

Len Bahr: Most issues have two sides, an environmental cost and an economic cost.
Quantifying the environmental cost is a prime area of research. There are exciting
new techniques for placing a dollar cost on environmental effects. When the
environmental costs of dredging a canal can be expressed in dollars, then political
and regulatory decisions will become clearer.

Sherwood Gogliano: Senator Nunez said that the Legislature's program is a start. It is
more than that. It is a turning point. The coastal zone management plan was an
important first step, but this is the second step in which we are making a
commitment to manage renewable resources based on substantial funding. The
program is a package of approaches which we can start implementing and
monitoring. Clearly not everything will work, but we will never know until we try.
At the present rates of deterioration we can not afford to wait any longer.

Peter Hawxhurst: The efforts to implement programs and publicize the coastal erosion
problem are necessary to generate the grass roots support needed to attract State
and Federal funding.

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SUMMARY COMMENTS OF PANEL MODERATORS

CAUSES: CHANGES IN DISPERSAL OF FRESH WATER AND SEDIMENTS

Mr. Gerald G. Bordelon, Chairman, Louisiana Coastal Commission

The various alterations which man has made to Louisiana's coastal environment for
flood protection, navigation, and mineral resource extraction have had many
consequences which were not perceived when they were undertaken. This has largely
resulted from interruptions of the natural flow of water and sediment on which our
estuarine and coastal areas depend.

The most pervasive alterations have been the control of the Mississippi River flow.
Including impoundments up in the watershed, which have reduced to half the previous
sediment load of the lower river; leveeing of the river for flood protection, which has
prevented the flux of sediments and fresh water in the interdistributary basins adjacent
to active delta lobes; and regulated division of the river between the Atchafalaya River
and the Mississippi River proper. Over the years, we have also taken various steps to
control the coastline Itself, such as jetties and seawalls, some of which we now discover
have had some serious negative consequences. All of these alterations have been made
to benefit mankind, but now we find that there are also eventual human costs as well. At
the same time, nature takes its course, where It takes away it can also give, as in the
case of the rapid progradatlon of the Atchafalaya River delta and the chenier plain
coast.

The coastal wetlands of Louisiana need good supplies of fresh water and sediments
to maintain their integrety and vitality. We have seen in presentations and discussions,
that marshes need a continued sediment supply to offset subsidence and sea-level rise.
This is a particularly profound observation, given the possibility of increased sea-level
rise in the future. Furthermore, wetlands and estuaries need fresh water, literally the
life blood of Louisiana. Fresh waters carry sediments and nutrients, but are particularly
needed to maintain the salinity gradients In the estuaries. Saltwater intrusion has caused
serious problems for the oyster industry and has caused rapid deterioration of freshwater
wetlands.

Various approaches have been discussed to deal with the problem of restoring fresh
water and sediment supplies to our coastal areas. These range from river diversions of
various scales, either for maintenance of salinity levels or wetlands accretion, to
management of the Atchafalaya delta to maximize the creation of productive habitats,
and to nourishment of sand-starved barrier Islands. Although the panelists and audience
differed widely in their preferred approaches, all seemed to agree that whatever Is done
should be In concert with natural processes rather than in vain attempts to defeat them.

In summary, natural processes exacerbated by alterations to freshwater and
sediment flows have caused major problems which have such significant consequences
that we as a society must challenge them. It appears that we need to take Immediate
action on a number of necessary long-range plans and accomplish the societal
adjustments which will be required.

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CAUSES: PHBvlOMENA DIRECTLY RELATED TO HUMAN ACTIVITIES

Dr. Roger Saucier, U.S. Army Engineer Waterways Experiment Station

I would like to depart from strictly summarizing the excellent presentations made
in the session I moderated and present my reflections on the underlying common concerns
which I heard voiced during many of the conference discussions.

A great deal of concern has been expressed about the formidability and
inevitability of certain natural processes. We are not likely to do anything about the
processes of regional subsidence and sea-level rise; however this is not justification for a
defeatist attitude. Many natural and man-induced processes are controllable, and
perhaps even reversible. I am quite impressed, not just about what we know about these
processes, but how we have taken steps to apply this knowledge. In the past, our
management decisions have been made, all too frequently, not out of ignorance of the
processes, but more often out of disregard of them, perhaps influenced by the thought
that we could do nothing about them.

Several concepts for erosion control have been discussed, such as freshwater
diversion and marsh creation. I am particularly impressed by the potential of these,
because they are not brute force, man-against-nature approaches. They recognize what
nature, itself, has done and can do with assistance by man. This view is obviously
influenced by my background in geography, a science once referred to by a prominent
geographer as human ecology. This definition recognizes man as part of the ecosystem,
rather than a force apart from the ecosystem. Man, thus, should optimize his use of
natural resources ~ in this case water and sediment — to achieve those conditions and
values he desires. There may come a time when man has to turn exclusively to concrete
and steel approaches, but I do not think we are near this point. Concrete and steel now
have their place, but as means of influencing natural processes, not of preventing them.

In the near future, I see the need to field-test and demonstrate rather than
procrastinate. As scientists, we believe certain things can work, but decisionmakers and
the public have to be convinced. Also, rough spots on the road between theory and
practice have to be smoothed out.

We must realize that coastal Louisiana of tomorrow will not be the same as today.
But certainly today it was not the same as it was yesterday or the day before. Man often
reacts adversly to change, feeling the present is optimal. We can look to the future with
optimism, but it would help if we can continue to investigate the consequences of the
change. I fear that while we will be able to dramatically influence erosion and land loss,
vast geomorphic changes nevertheless are taking place. We must probe the consequences
of these, which may be profound on a regional scale, insofar as climate, ocean currents,
marine fisheries, waterfowl migration, and many other factors are concerned.

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CONSEQUENCES: EFFECTS ON NATURAL RESOURCE PRODUCTION

Dr. James G. Gosselink, Center for Wetland Resources, Louisiana State University

There was general agreement among panelists that wetland loss has resulted in
changes in vegetation and changes in secondary consumers, such as waterfowl, alligators
and furbearers that use the marsh directly. In fact there was not much argument that
estuarine-dependent fish and shellfish resources have also already been affected. The
key to this estuarine dependence is habitat availability. If the habitats are available and
healthy, then their associated living resources will also be. The question then becomes
how to deal with the loss and change of habitat.

I will not present a complete and coherent summary, but will highlight some of the
questions raised. What are the prospects for freshwater diversions? The prospects are
good for limited areas and for controlling saltwater intrusion but there appear to be
socio-economic limitations. What is the optimum marsh-water edge interface ratio and
can this be engineered in canal design? More broadly, can we manage the marshes for
improved habitat? What is the optimum type of marsh (e.g., brackish marsh) and can we
engineer to maximize this type of marsh? Who is the savior of the wetlands, in the sense
of their conservation and management? The feeling I get is that it better be all of us,
from the grassroots to the politicians and decisionmakers.

In the long run, abandoned deltas will erode away. Is it economically sound to pour
money into them for freshwater diversion, etc., or would it be better to develop plans for
replacing eroding wetlands with new areas, such as in the Atchafalaya delta?
Considering, the relative value of wildlife and petroleum resources, how can
environmentalists hope to compete in the political arena of environmental conservation?

I do not know how to answer all these questions, therefore I will try to relate my
personal perspective on our current situation as reflected in the conference. There is a
growing change in attitude toward the environment, which translates to political reality
in a new conservatism. Previously, environmentalists were on the defensive and
considered radicals. Resources were abundant and the popular and dominant paradigm
was that development was good, and that natural resources were plentiful and free, the
burden was on the environmentalist to show that an activity was destructive to the
environment and should be terminated. A new more conservative view is that as
nonrenewable resources are rapidly depleted, and reliance on renewable resources in
Louisiana becomes increasingly important, thus we must conserve and foster them. The
onus of environmental modification thus lies with the developer. He is now on the
defensive, must prove that the change is environmentally safe and must pay for the
whole cost of the change.

CONSEQUENCES: SOCIAL AND ECONOMIC

Mr. Edward W. Stagg, Council for a Better Louisiana

The Council for a Better Louisiana and I have for sometime been interested in
water resource problems in Louisiana, particularly with regard to ground water and
surface water. These concerns share common ground with those concerns about coastal
erosion. In the past, our water problems were primarily two-fold: one, to get rid of it,
and secondly, to pray that we did not have a hurricane to give us too much. I believe,

249

however, we are moving into a new era because of our population growth and the type of
industries we now have, where we are much more concerned about water conservation.
One of the brightest people I have ever known, told me 10 or 12 years ago that in the
future of Louisiana, we would be without our cheap natural energy resources — oil and
gas. He said that for the eventual development of Louisiana, the one unique resource, if
we conserved it, would be water. The utilization and conservation of water is of great
long-term importance.

In our panel deliberations, we first considered property rights. If I could summarize
that discussion, I would say that individual property rights are in danger, in so far as
water is concerned. Erosion tends to work against the private owner and against the
State in favor of the Federal Government. State law allows private land owners to
restablish claims to eroded land if, at his own expense, he rebuilds it. This is, of course,
an expensive proposition. Thus my impression is that the interest of private land owners
ore in considerable jeopardy in coastal Louisiana.

Furthermore, there is a lack of property rights to water in Louisiana. We have
some riparian rights established in law, but there is nothing comparable to the mineral
code for oil and gas in so far as water is concerned. This is principally a concern
regarding ground water, where a well drilled on other property may deplete ground water
under an individual's property. We do not have protection regarding groundwater rights
and it is an issue the legal and academic communities should investigate.

Other legal issues related to coastal erosion concern regulations, which may have
been erected to protect the environment, but which also may become an impediment to
activities designed to control erosion or saltwater intrusion. We heard a horror story
about an attempt to erect control structures initiated in 1972, which has been held up by
permitting problems through 1981. The environmental assessment process should be
streamlined by shortening the time of review by Federal and State agencies.

The economic and social impacts of continued coastal erosion in Louisiana are
indeed likely to be enormous. Dr. Davis developed sobering scenarios about the
tremendous economic costs of declining renewable natural resources, and increased flood
protection and how this may affect society in south Louisiana.

OPTIONS: BARRIER ISLAND AND SHORELINE PROTECTION

Dr. Charles Groat, Louisiana Geological Survey

Barrier islands are literally at the forefront of the coastal erosion problem, being
out in front of the land mass. It is necessary to consider options available to slow barrier
island erosion within the frame work of the natural processes which have created and are
destroying the islands. Barrier islands are as much, if not more than other parts of the
coast, a part of the death process of a delta. Any attempt to stop erosion must face up
to that process of dying and the options available must be carefully considered in that
context.

Having considered the processes which form and destroy Louisiana's barrier islands,
speakers then discussed various attempts which have been made in the past in Louisiana,
Texas, and other parts of the world to stop shoreline erosion and preserve the integrity of
barrier islands. We considered structural methods such as groins to pin down the ends of

250

the islands, rock jetties, seawalls, etc., and some of the nnore passive nnethods, such as
vegetation stabilization and sand fences, intended to maintain the sand which is there.
One of the problems faced in shoreline and barrier islands preservation is the
maintenance of sediments there, either by preventing sediment from escaping the system
or by furnishing new supplies.

We also found the dichotomy that I believe is present throughout the conference.
Members of the academic community offered the opinion that the barrier islands and
coastal processes are not as well understood as is necessary. In order to develop ultimate
solutions which are long-term as well as short-term, economically justifiable, and,
effective, coastal processes must be much better understood. On the other hand, others
including Representative Murray Hebert, stated that people in Louisiana know there Is
an erosion problem, many studies have been conducted, many people are living along
eroding shorelines and near marshes which are disappearing. They feel that, particularly
with the money which may be available from the State, it is time to take some action.
They don't necessarily deny that more studies are needed, but feel that we ought to do
the best we can based on the information available.

In fact it is the approach of immediate action which is being taken. The Louisiana
Joint Natural Resources Committees of the Louisiana Legislature have recommended a
program, a large portion of which deals with stabilizing and slowing the erosion of
Louisiana's barrier islands. On the other hand. Representative Hebert, speaking for the
Legislature, admitted that we don't know everything we need to know. While conducting
these immediate, short-term approaches to protecting barrier islands, we also need to
conduct studies to help understand the ultimate possibilities and long-term strategies for
coastal protection.

The long-term coastal conditions and methods to deal with them have to be
considered in light of global phenomena. Dr. Nummedal suggested we may be facing
major sea-level rises that could make many of our attempts to stop shoreline erosions
very difficult. Are we facing other overwhelming natural forces, such as rapid
subsidence attributable to natural destruction of some parts of the delta system. We
must sort out and understand these large-scale phenomena.

To summarize, the need to do something is very apparent in a political sense and in
the eyes of the people who live in coastal Louisiana. In the eyes of the academic
community, we need to know much more than we do. Perhaps we will also learn much
from our initial attempts, which no one claims are going to solve all our coastal
problems. Some attempts will not work, but they may teach us as much as those that
do. Undoubtedly because of the highly dynamic nature of the barrier islands, much
attention must be focused on these environments in the future.

OPTIONS: LIMITATION OF DREDGING AND FRESHWATER DIVERSIONS

Mr. Kai Midboe, Governor's Office of Intergovernmental Affairs,

It is difficult to quickly summarize the presentations and discussions of such
complex subjects, particularly when one is not an expert, but must summarize experts.

The panel basically addressed the question of what activities would be most
effective in retarding or correcting coastal land loss. The three primary activities

251

discussed were the delta building of the Atchafalaya River, freshwater diversions along
the Mississippi River, and control of canals in wetlands.

The Atchafalaya River is building a large lobate delta in the Atchafalaya Bay and
also causing land accretion along the coast of southwestern Louisiana. The question is
how do we realize the maximum benefits from these natural processes. Interestingly, the
new delta has been built since 1950, rhost of it since 1970. There have been three 100-
year floods during that period, however. Is this phenominal delta growth, in fact, unusual
and will it continue at the recent rates?

There were three main issues discussed in reference to freshwater diversion: (I)
how to recreate the natural overflow patterns which cause land accretion and retard
saltwater intrusion; (2) how to initiate new areas of delta growth; a delta lobe is really a
series of small lobes which can be recreated with selective freshwaters diversions; (3)
how can water and sediment brought over or through the levee be managed and be
directed to the interior of wetlands where they are needed. With regard to freshwater
diversions, the point was made, which I think is a very good point, that enough research
has been done to allow implementation. Granted, further research will occur in the
future, but we are far enough along to allow affirmative action. Dr. Gagliano made the
very good point that we are wasting a very valuable resource in Louisiana by allowing the
shunting of most of the Mississippi River's fresh water and silt off the edge of the
continental shelf by confining it until it reaches the active distributary system at the
river's mouth.The water, sediments, and nutrients are the bases of our agriculture, marsh
development, and most of our natural resources.

Two problems related to freshwater diversions were raised. An important one
which cannot be overlooked is the concern of the people impacted by the diversion. The
benefits which may accrue because of the diversion may not accrue to the communities
and local governments impacted. There have been occasions where local governments
have actively resisted plans for freshwater diversion because of this. Another problem is
that control structures upriver have been very effective, there is much less sediment
transported by the river available for diversion.

An issue that I was really surprised about is the degree to which the coastal erosion
problem is a result of canal dredging. Gene Turner estimated that at least 50% of the
coastal land loss is a direct or indirect result of canal dredging for the oil and gas
industry, navigation, and other purposes. If this is so, how can we better manage these
activities, where must they be stopped, etc.

Senator Nunez discussed the study recommendations made by the Joint Natural
Resources Committees of the Louisiana Legislature. They make specific

recommendations for projects to stem coastal erosion and estimate the costs of these
activities. The Corps of Engineers is also working on a series of studies regarding
implementation of freshwater diversion. Clearly the "bottom line" in all these efforts is
one which appears consistently in government, and that is dollars. How will we pay for
it? How does it fit in with competing needs for these funds? The Governor and
Legislature now appear ready to devote considerable sums of State resources from the
Enhanced Mineral Trust Fund for coastal protection.

This briefly summarizes our delibrations. I want to complement the panelists for
excellent presentations and discussion and the audience for their provocative questions.

252

LIST OF ATTENDANTS

Rodney D. Adams, Center for Wetland Resources, Louisiana State University
D. Jane Allan, Louisiana State University
Frank Atkinson, Tri-Lock Erosion Control
Peggy Autin, Louisiana Geological Survey
Whiitney J. Autin, Louisiana Geological Survey

Lloyd Baehr, U.S. Army Corps of Engineers

Len Bahr, Center for Wetland Resources, Louisiana State University

Buddy Baker, Louisiana Cooperative Fisheries Unit

Barney Barrett, Louisiana Department of Wildlife and Fisheries

Joy Bartholomew, Louisiana State Planning Office

Ronald E. Becker, Center for Wetland Resources, Louisiana State University

Heino Beckert, U.S. Bureau of Land Management

Vernon Behrhorst, Louisiana Intracoastal Seaway Association

C. Lee Black, Louisiana State University

Bob Blackmon, Coastal Management Section, Louisiana Department of Natural Resources

Gary Blaize, Terrebonne Parish Coastal Advisory Committee

Gerald Bodin, U.S. Fish and Wildlife Service

Ed Bodker, Louisiana Department of Transportation and Development

Donald F. Boesch, Louisiana Universities Marine Consortium

Donald Bollinger, Secretary, Louisiana Department of Public Works

Gerald Bordelon, Louisiana Coastal Commission

Ron Boyd, Louisiana Geological Survey

Joseph C. Branco, U.S. Soil Conservation Service

Charles E. Broussard, Flying J. Ranch

Toni Brown, Louisiana Department of Wildlife and Fisheries

Bill Burke, Coastal Managment Section, Louisiana Department of Natural Resources

Janet Burt, League of Women Voters of Louisiana

Jane Caffrey, Center for Wetland Resources, Louisiana State University
David F. Carney, Louisiana Department of Wildlife and Fisheries
Keith L. Casanova, Center for Wetland Resources, Louisiana State University
Jim Catallo, Center for Wetland Resources, Louisiana State University
Robert Chabreck, School of Forestry and Wildlife Management, Louisiana State

University
David Chambers, Coastal Management Section, Department of Natural Resources
Gary W. Childers, Southeastern Louisiana University
Susan Chinberg, Coastal Studies Institute, Louisiana State University
Darryl Clark, Coastal Management Section, Department of Natural Resources
Danny S. Clement, U.S. Soil Conservation Service

James M. Coleman, Coastal Studies Institute, Louisiana State University
Jay Combe, U.S. Army Corps of Engineers

Will Conner, Center for Wetland Resources, Louisiana State University
Carroll L. Cordes, U.S. Fish and Wildlife Service
Windell Curole, South Lafourche Levee District
Mary Curry, Jefferson Parish

253

Jack Daggett, Louisiana Deaprtment of Tranportation and Development
Thonnas Davidson, Departnrient of Geography, Louisiana State University
Donald W. Davis, Earth Sciences Department, Nichoiis State University
John Day, Center for Wetland Resources, Louisiana State University
Linda Deegan, Center for Wetland Resources, Louisiana State University
Ronald DeLaune, Center for Wetland Resources, Louisiana State University
Larry DeMent, U.S. Army Corps of Engineers
John D. deMond, Louisiana Department of Wildlife and Fisheries
Andre Delflache, Lamar University

Tom Denes, Center for Wetland Resources, Louisiana State University
Chris Dionigi, Department of Biology, University of Southwestern Louisiana
Ronnie Duke, T. Baker Smith and Son

Mary-Ann Eames, Department of Marine Science, Louisiana State University

Rod E. Emmer, Coastal Environments Inc.

Betty Everitt, Department of Zoology and Physiology, Louisiana State University

Doris Falkenheimer, P.L.U.G.

Monica Farris, U.S. Army Corps of Engineers

Michael Flynn, Department of Biology, University of Squthwestern Louisiana

Paul Fournier, Terrebonne Parish School Board

Charlotte Fremaux, League of Women Voters of Louisiana

Sherwood M. Gagliano, Coastal Environments, Inc.

Albert Gaude, University of Southwestern Louisiana

Bob Gerdes, Louisiana Geological Survey

Linda Glenbeski, U.S. Army Corps of Engineers

Laurel Gorman, Louisiana Geological Survey

James Gosselink, Department of Marine Science, Louisiana State University

C.G. Grant, Louisiana Geological Survey

Christana Haas, Center for Wetland Resources, Louisiana State University

Michael Halle, Sierra Club

Sue Hones, U.S. Army Corps of Engineers

Richard Hatton, Department of Geology, Louisiana State University

Peter Hawxhurst, U.S. Army Corps of Engineers

John L. Haydel, Terrebonne Parish School Board

Murray Hebert, Louisiana House of Representatives

Mike Hess, Louisiana State University

Mark Hester, Center for Wetland Resources, Louisiana State University

Eileen Hill, Coastal Information Repository, Louisiana State University

Rocky Hinds, Louisiana Department of Wildlife and Fisheries

H. Dickson Hoese, Department of Biology, University of Southwestern Louisiana

Richard Hoogland, National Marine Fisheries Service

Norman Howden, Center for Wetland Resources, Louisiana State University

Paul Hribernick, Law Center, Louisiana State University

Mary Hungate, U.S. Fish and Wildlife Service

James G. Johnson, Louisiana State University
James B. Johnston, U.S. Fish and Wildlife Service
Claire Joller, Terrebonne Magazine

254

Brenda Jones, U.S. Fish and Wildlife Service

Richard Kaswa, Jr., Department of Marine Science, Louisiana State University

Raphael Kaznnann, College of Engineering, Louisiana State University

Peggy M. Keney, National Marine Fisheries Service

Helen Kennedy, Center for Wetland Resources, Louisiana State University

Cory W. Kerlin, Anninoil USA, Inc.

Eric Knudsen, Louisiana Cooperative Fisheries Unit, Louisiana State University

Wilfred Kucera, U.S. Fish and Wildlife Service

Donald P. Landry, Terrebonne Parish Police Jury

Martha Landry, Terrebonne Parish Police Jury

Francisco Ley, Center for Wetland Resources, Louisiana State University

Michael Lindsay, Louisiana State University

Joel L. Lindsey, Coastal Management Section, Department of Natural Resources

Michael Loden, Jefferson Parish

Astrid Lolan, Louisiana Senate Staff

Clarke L. Lozes, Plaquemines Parish

Michael Lyons, Mid-Continent Oil and Gas Association

Chris Madden, Center for Wetland Resources, Louisiana State University

Brian Marotz, Louisiana Cooperative Fisheries Unit, Louisiana State University

Pat Mason, Louisiana Coastal Commission

Michael Materne, U.S. Soil Conservation Service

Paul I. Mathemeier, Department of Microbiology, University of Southwestern Louisiana

Mack Mathis, Anthony J. Bertucci Construction Company

Amy Maynard, Department of Geology, Louisiana State University

Karen L. McKee, Center for Wetland Resources, Louisiana State University

David A. Mekasski, St. Charles Parish

Earl Melancon, Biology Department, Nicholls State University

Irving A. Mendelssohn, Center for Wetland Resources, Louisiana State University

Charlie Mestarer, Louisiana Department of Wildlife and Fisheries

Kai Midboe, Louisiana Governor's Office

Thomas C. Michot, U.S. Fish and Wildlife Service

Carolyn Miller, Center for Wetland Resources, Louisiana State University

Frank Monteferrante, Center for Wetland Resources, Louisiana State University

Donald Moore, National Marine Fisheries Service

Timothy Morrison, Louisiana Department of Wildlife and Fisheries

Bob Morton, Bureau of Economic Geology, University of Texas

Chris Neill, Center for Wetland Resources, Louisiana State University
Dag Nummedal, Department of Geology, Louisiana State University

Michael Osborne, National Wildlife Federation

Robert Parker, Freeport Sulphur

Elaine Parton, Center for Wetland Resources, Louisiana State University

Shea Penland, Center for Wetland Resources, Louisiana State University^

Susan Peterman, Center for Wetland Resources, Louisiana State University

Joan Phillips, Sierra Club

Amy Prior, Coastal Studies institute, Louisiana State University

255

Rene Randon, Louisiana Land and Exploration Company
Steve Risotto, Center for Wetland Resources, Louisiana State University
Harry H. Roberts, Coastal Studies Institute, Louisiana State University
George Robichaux, Louisiana Department of Health and Human Resources

Roger Saucier, Waterways Experiment Station, U.S. Army Corps of Engineers

Harry Schafer, Louisiana Department of Wildlife and Fisheries

Freda Schnitzler, Department of Biology, University of Southwestern Louisiana

Walter B. Sikora, Center for Wetland Resources, Louisiana State University

Terry Slattery, U.S. Fish and Wildlife Service

Chris Smith, Center for Wetland Resources, Louisiana State University

Albert So, Department of Geography, Louisiana State University

David Soileau, U.S. Fish and Wildlife Service

Ronald S. Sonegut, Louisiana Deparment of Wildlife and Fisheries

Edward Stagg, Council for a Better Louisiana

David Stuttz, U.S. Army Corps of Engineers

Victoria Sullivan, Department of Biology, University of Southwestern Louisiana

Eric Swenson, Center for Wetland Resources, Louisiana State University

Laura J. Swilley, U.S. Army Corps of Engineers

Kenneth G. league. Center for Wetland Resources, Louisiana State University

John Teal, Woods Hole Oceanographic Institution

Paul H. Templet, Coastal Environments Inc.

R. Dale Thomas, Department of Biology, Northeast Louisiana University

Bruce Thompson, Center for Wetland Resources, Louisiana State University

Dana W. Toups, Bradley Matierals

Drukell B. Trahan, Louisiana Geological Survey

R. Eugene Turner, Center for Wetland Resources, Louisiana State University

Denny Ufuell, Louisiana State University

John Uhl, Jefferson Parish Coastal Zone Management

Jacob M. Valentine Jr., U.S. Fish and Wildlife Service

Johannes L. van Beek, Coastal Environments, Inc.

Jack Van Lopik, Center for Wetland Resources, Louisiana State University

Virginia Van Sickle, Louisiana Geological Survey

R.J. Varnell, Plaquemines Parish

Gerald Voisin, Louisiana Land and Exploration Company

Michael Voisin, Louisiana Oyster Growers and Dealers Association

Paul W. Wagner, Burk and Associates

Flora Wang, Center for Wetland Resources, Louisiana State University
John T. Wells, Coastal Studies Institute, Louisiana State University
Mike Windham, Louisiana Department of Wildlife and Fisheries
John Woodard, Tenneco LaTerre Company

Paul Yakupzack, U.S. Fish and Wildlife Service

Cathy Zapel, Department of Geology, Louisiana State University

256

50272-101

REPORT DOCUMENTATION
PAGE

l._ REPORT NO.

FWS/OBS-82/59

4. Title and Subtitle

Proceedings of the Conference on Coastal Erosion and Wetland
Modification in Louisiana: Causes, Consequences, and Options

7. Author(s)

D. F. Boesch, ed.

3. Recipient's Accession No.

5. Report Dale

September 1982

8. Performing Organization Rept. No.

9. Performing Organization Name and Address

Louisiana Universities Marine Consortium
Star Route, Box 531
Chauvin, Louisiana 70344

10. Project/Task/Work Unit No.

11. Contract(C) or Grant(G) No.
(C)

(G)

12. Sponsoring Organization Name and Address

U.S. Fish and Wildlife Service
Office of Biological Services

13. Type of Report & Period Covered

14.

15. Supplementary Notes

16. Abstract (Limit: 200 words)

This volume contains 16 papers and panel discussions from a conference held in
Baton Rouge, La., 5-6 October 1981. The presentations consider the causes and conse-
quences of coastal erosion and wetland modification in Louisiana and the mitigative
options available to slow or reverse the rapid rate of coastal land loss. Detailed
habitat mapping studies have allowed accurate estimates of coastal habitat change and
land loss through 1978. Projections from these rates of change indicate an annual rate
of land loss in coastal Louisiana in the early 1980' s of approximately 130 kmVyr
(50 m^/yr) .

The projected effects of wetland modification on the bountiful living resources of
coastal Louisiana (fisheries, fur and hide bearers and waterfowl) are major because of
the close dependence of these resources on estuarine wetlands. These changes and others
related to flood protection, transportation and ownership of mineral resources are
projected to have extensive social and economic consequences.

Options proposed to slow coastal land loss include major and minor diversions of
the Mississippi River, barrier island and shoreline restoration and protection, hydro-
logical management of wetlands and more restrictive permitting of dredging activities.

17. Document Analysis a. Descriptors

Louisiana, wetlands, coastal, erosion, management, causes and effects

b. Identifiers/Open-Ended Terms

Wetlands, erosion, management, Louisiana

c. COSATI Field/Group

IB. Availability Statement

Unlimited

19. Security Class (This Report)

Unclassified

20. Security Class (This Page)

Unclassified

21. No. of Pages

viii + 256

22. Price

(See ANSI-Z39.18)

*US GOVERNMENT PRINTING OFFICE 1982-574176

See Instructions on Reverse

OPTIONAL FORM 272 (4-77)
(Formerly NTIS-35)
Department of Commerce

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W H 0 I

DOCUMENT

COLLECTION

®<D

LEGEND

Headquarters - Office of Biological
Services, Washington, D.C.
National Coastal Ecosystems Team,
Slidell. La.
Regional Offices

U.S. FISH AND WILDLIFE SERVICE
REGIONAL OFFICES

REGION 1

Regional Director

U.S. Fish and Wildlife Service

Lloyd Five Hundred Building, Suite 1692

500 N.E. Multnomah Street

Portland, Oregon 97232

REGION 2

Regional Director

U.S. Fish and Wildlife Service

P.O.Box 1306

Albuquerque, New Mexico 87103

REGION 3

Regional Director
U.S. Fish and Wildlife Service
Federal Building, Fort Snelling
Twin Cities, Minnesota 55111

REGION 4

Regional Director
U.S. Fish and WildUfe Service
Richard B. Russell BuiJding
75 Spring Street, S.W.
Atlanta, Georgia 30303

REGION 5

Regional Director

U.S. Fish and Wildlife Service

One Gateway Center

Newton Corner, Massachusetts 02158

REGION 6

Regional Director

U.S. Fish and Wildhfe Service

P.O. Box 25486

Denver Federal Center

Denver, Colorado 80225

REGION 7

Regional Director
U.S. Fish and Wildlife Service
1011 E.Tudor Road
Anchorage, Alaska 99503

' — r;;^ — \

FISH AWILDl IKK
SERVICE

DEPARTMENT OF THE INTERIOR

U.S. FISH AND WIIDIIFE SERVICE

As the Nation's principal conservation agency, the Department of the Interior has respon-
sibility for most of our nationally owned public lands and natural resources. This includes
fostering the wisest use of our land and water resources, protecting our fish and wildlife,
preserving th&environmental and cultural values of our national parks and historical places,
and providing for the enjoyment of life through outdoor recreation. The Department as-
sesses our energy and mineral resources and works to assure that their development is in
the best interests of all our people. The Department also has a major responsibility for
American Indian reservation communities and for people who live in island territories under
U.S. administration.

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