(ary airs alae: Cug. kes Cor. leck. Kep. GENE
COASTAL GEOLOGY AND GEOTECHNICAL PROGRAM
. TECHNICAL REPORT CERC-92-4
US Army Corps
of Engineers GEOMORPHIC VARIABILITY
IN THE COASTAL ZONE
by
Joann Mossa
Department of Geography
University of Florida
Gainesville, Florida 32611
and
Edward P. Meisburger, Andrew Morang
Coastal Engineering Research Center
DEPARTMENT OF THE ARMY
Waterways Experiment Station, Corps of Engineers
3909 Halls Ferry Road, Vicksburg, Mississippi 39180-6199
May 1992
Final Report
Approved For Public Release; Distribution Is Unlimited
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May 1992 Final report
4. TITLE AND SUBTITLE 5. FUNDING NUMBERS
Geomorphic Variability in the Coastal Zone
6. AUTHOR(S)
Joann Mossa
Edward P. Meisburger
Andrew Morang
7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)
Department of Geography, University of Florida
Gainesville, FL 32611
USAE Waterways Experiment Station, Coastal Engineering Research
Center, 3909 Halls Ferry Road, Vicksburg, MS 39180-6199
9. SPONSORING/ MONITORING AGENCY NAME(S) AND ADDRESS(ES)
8. PERFORMING ORGANIZATION
REPORT NUMBER
Technical Report
CERC-92-4
10. SPONSORING / MONITORING
AGENCY REPORT NUMBER
US Army Corps of Engineers, Washington, DC 20314-1000
11. SUPPLEMENTARY NOTES
Available from National Technical Information Service, 5285 Port Royal Road,
Springfield, VA 22161
12b. DISTRIBUTION CODE
12a. DISTRIBUTION / AVAILABILITY STATEMENT
Approved for public release; distribution is unlimited
13. ABSTRACT (Maximum 200 words)
The coastlines of the world’s oceans encompass a tremendous variety of geomorphic and geologic
structures. They range from rocky cliffs to sandy barrier beaches to low-lying swampy wetlands. The
geomorphic forms were created by the interaction of antecedent geology, physical dynamic processes,
and man-made intervention. Variable features are usually composed of unconsolidated materials that
respond rapidly to changes in the dynamic environment. More stable features are usually associated with
consolidated rock or occur in quiescent environments. The geologic history of shorelines can be inferred
from a careful study of geomorphic structures, coupled with additional data on physical processes and
historic events. Many of the study techniques are relatively simple, consisting of analysis of existing
maps and historical sources.
An understanding of the processes which have shaped the shore is crucial to the design of coastal
structures and to the intelligent management of coastal resources and habitats. In addition, understanding
of the form/process relationships between geomorphology and dynamics may allow coastal scientists to
more accurately predict the results of construction or other modifications along the shore.
14, SUBJECT TERMS 15. NUMBER OF PAGES
Barrier beach Coastal geology Dunes Geomorphology
Beach rock Coastline Erosion Longshore transport 16. PRICE CODE
Cliff Delta i iability Tidal inlet aa,
17. SECURITY CLASSIFICATION | 18. SECURITY CLASSIFICATION | 19. SECURITY CLASSIFICATION | 20. LIMITATION OF ABSTRACT
OF REPORT OF THIS PAGE OF ABSTRACT
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Contents
Contents
POL ACS se. as eh A SR ERE lt ae otet ra Let Maat ix
Conversion Factors, Non-SI to SI (Metric) Units of Measurement . . x
(="TntrOGUC EO MS ey ke saves eetatta te Merete te tan a) ay neon acrt tes lates fereemist tet cele tat Fe 1
Backeoroutidies eh hit hiss cc Ms Scala MONS, po 0. SlSH AR MG cer go otetates 1
Scope: isc chock Secxcupd teens, PIA ita peerret EA attra sitar te ae tae 2
Goastal*Glassificatiomiay Gyles Vas vats cee el titer ete rotet Seats or at er 2,
ANfOTMAtIOMFSOURCES ey pes eset ee sees etetie volte (a) fella raeiemietia an 2
2—Relevant Processes and Factors .........----0++- ee 4
Climates id Aaah Bais oh eis ee i els Se oe a ee oe 5
Wir diss net eet wy hose tt teto ayh cocncin Gaba le» encase, Ze) Ge Geeta asenta) 7
Cyclonic Disturbances: oc... 03. s Ses ee oh 8
WIA WES? SSaee SUR sian SON aan rlce 2 AINE Sicutrctte, tates om aMesantal es oi 10
STRECES) cs RNCE A Letiee, MARR Nah Nm nee tease. dentate eee 14
(GUPRENES seek, oe ee law coins Newco yout tesevion ous oneos eke teins 17
Storm: Sure estes) sree Aihara EMA ght eee Mae al Stars a's 18
STRAITS Potente, PR testo be alloc Give aeons eee site tiantentes surat sates 20
Relative: Seaeleeveliatpricssts anc ciecel cia eirstecneit Went) cinekerten relists. 20
Lithology and Weathering . 2.04.6 ee ele lee tw ee ee es 22
Opeanismswpeyes cs SKS AMS. ee 2 Wea ae eden one ane at eg 3s = 24
Mass Wasting and Mass Transport .......--.---++e++005 27
Sedimenta@hanactermparcs ser desuas crews) teteyiciee atwrciclsiecel aiken) cee os 29
Sediment Supply and Human Activity...........--5504- 33
3=VariableGoastalukeatures: 2. mecca. 6 cle ete ties a oc ol oe 36
Beach-anduNearshore;Zone. «9. cidlses sae ce sw es 38
Lithified Coasts: Cliffs:and Platforms ...:........-2+..-- 44
Organic Recs, cteny oie sia wae oo Son eee arse ele nearer 46
GoastaleOunes meee us ede owen ce ko resem monet or siege ee cueiant= 47
Back Barrieriand Lagoons... 0.0.52 cee ee ee sees 50
Mudflats, Salt Marshes, and Mangrove Coasts ..........-. 51
TIS ee weave ob: Goole AUPE sD eeu 0 OMRO Rens Blctoratolatd, cwcdoanie 52
Inletsenc een aries errands) cneeeeeeae
Shelf Shoal startet ces sates er nee oe
ID Gltastyetrahe eosin cme ee ete etic ok sie Sian ae ede?
WiavedDatacuce xen Sree nian cma ee
Water Wevellayy cies neces ce re es a
GUrrentS aan eee ee we pee eee te ane
5—Investigation of Geomorphic Factors ......
Nature of Geomorphic Changes .........
Historical Charts and Aerial Photographs ...
Airborne Scanners and Satellite Data ......
Remote Sensing by Ocean Vessel ........
Field Survey, Mechniques!. 345 6 - ee eo
Sedimentological and Stratigraphic Techniques
PhysicaliModels ays.) cen sees oa eyes al srenete ais
Numerical Models ese ee aes
6—Summary and Conclusions ............
IRGLerencesee ne weeny eee ee ne See ete an ou pres eka
Contents
Contents
Figures
Figure 1.
Figure 2.
Figure 3.
Figure 4.
Figure 5.
Figure 6.
Figure 7.
Changes in barometric pressure, wind speed, wind
direction, wave height, wave period, and surge as a
cyclone passes laterally offshore along a north- and
south-facing coastline in the Northern Hemisphere ... .
Distinctive zones of wave action and morphologic
characteristics of the littoral:zone:: sj 4 ach. ee:
Wave refraction surrounding headlands and bays
and over submarine morphologic features .........
Appearance and classification of breaking waves
according to Galvin (1968) combined with beach slope
and wave height to water depth ratio as discussed by
Street and! Camfielde@i966) 94. 2 amid Ce 2s. Sse.
Macroscale morphology of microtidal, mesotidal, and
macrotidalfcoasthimesin miei havens at oeusin. putens oc
Wave-induced nearshore currents as determined by
breaker angle. Cell circulation pattern with well-
developed rip currents occurs when the breaker angle
is close to zero. Asymmetric circulation with
longshore currents feed rip currents when breaker
angle is small. A longshore noncirculatory pattern
occurs with an oblique wave approach and large
breakersan gle: Site ana yee cer reece
Some aspects of geomorphic variability attributable
to lithology, structure, and mass movement along
semi-consolidated and consolidated coasts in cross
SEChIOMy WLM oce Tent Wiha aI ear adh) a elite GLa: SG
10
11
12
13
16
19
23
vi
Figure 8.
Figure 9.
Figure 10.
Figure 11.
Figure 12.
Figure 13.
Figure 14
Figure 15.
Figure 16.
Figure 17.
Aerial photograph of Pta. de la Garita, Cabo de la
Aguja, Columbia. A pocket beach has formed
between two resistant headlands. To the right of the
headlands, waves approach the coastline at a steep
angle, causing longshore currents which transport
sediments away from the headland. Photograph
taken from an altitude of 600 m; distance between
the headlands is about 0.5 km. (Photo by Andrew
Morang lO St) iyi iieaccn a a cous enn on tinge camcae aps tars
Outcrops of Pleistocene coquina rock of the
Anastasia Formation on a beach in East Florida.
Erosion of such rocks contributes sediment particles
toithevbeach ote ote. eae ee ae ate, Le eae.
Conditions for erosion, transportation, and deposition
of particles in water according to Hjulstrom........
Inlet through a barrier stabilized by jetties. Note the
large amount of sand trapped by the larger jetty and
recession of the shore across the inlet............
Beach protection structures, Cartagena, Columbia.
Although the city is built on the barrier beaches
which protected the original Spanish anchorage, the
present shoreline suffers from a lack of sand, and the
beaches are narrow or are entirely missing in some
areas (Photograph by Andrew Morang 1981) .......
Beach backed by seawall near Galveston, TX. Note
riprap added for further protection..............
Surface and subsurface environments and
variations of barrier islands, strand plain coasts,
and itidalflats oei25 on is Pa: «Rak. Se esse cans
Three-dimensional morphodynamic classification of
beaches and selected associated attributes .........
Three models of shoreline response to sea
bevelttiser able Mice: Oyated opens Serene Nes mbmennes Cem yer ae
A variety of cliff morphologies in cross section.
Plunging cliff is steeply sloping and possibly shows
a notch. Cliff with shore platform may develop from
increased notch development and mass movement of
overlying material. Cliff base beach may develop
from cliff with shore platform if sediment supply
exceeds transport of material§ oy ik ne SS ws aa
25
26
28
34
34
35
37
41
43
45
Contents
Contents
Figure 18.
Figure 19.
Figure 20.
Figure 21.
Figure 22.
Figure 23.
Figure 24.
Figure 25.
Figure 26.
Figure 27.
Figure 28.
Figure 29.
Partly vegetated coastal sand dunes. Eastern
Alabama near Florida/Alabama state line (March
1991). This area was devastated by Hurricane
PM rederiG im 197 Oi ay ise eA ee vetoes eee magenta on 2
Rhizomes help hold sand in place and spread the
colonization of dune grasses. Eastern Alabama near
Florida/Alabama state line (March 1991) ..........
A three-dimensional view of some features commonly
associated with a barrier island system, including
the back barrier, overwash fans, and lagoons .......
Aerial view of unstabilized barrier inlet showing
shallow parts of the flood and ebb tidal deltas.......
Linear shoals on the New Jersey coast. Note the
abundance of shoreface-connected shoals throughout
and the isolated shoals which are most abundant off
the:Brigantinearcageeeuatss Byeesieeeteis Sieroe cheeks ©
Cape-associated shoals off Canaveral Peninsula, a
large cuspate foreland on the Florida Atlantic coast.
Note shoreface-connected linear shoals north of
False:‘Capeu, seacitsnte-aciseitincuater ails varies Saadienecs
Bottom-mounted Sea Data™ 635-12 directional wave
gage mounted in tripod using railroad wheels as
COPEL, WEIDHtS'y Sas srecahiruta nt en eis Se chk set ee..
Deepwater wave hindcasting curves .............
Littoral Environmental Observation forms used by
the volunteer observers participating in the
EE Oro gram “sacc4y chs tes es) wee ese ee ne
Monthly water level changes at Juneau, AK. High
water typically occurs October-December. Data
from Lyles, Hickman, and Debaugh (1988) ........
Monthly water level changes at Galveston, TX.
High water occurs twice per year: April and
SEpleMmber-NOVEMMCI ean cua wetaeal eel ae aan es
Yearly mean sea level changes at Juneau, AK, from
1936-1986. The overall fall in sea level shows the
effects of isostatic rebound. Data from Lyles,
IHickman,and:Debaughi(1988)' <0 2.5 Ga. ee
47
49
51
56
59
61
67
67
68
70
70
71
Vil
vill
Figure 30. Yearly mean sea level changes at Galveston, TX,
from 1908-1986. Subsidence of the land around
Galveston may be caused by groundwater withdrawal
ANd COMPACHOMs iio shes cilia sy chan aie oieetame ames ee
Figure 31. Late Quaternary sea level curves inferred from
radiocarbon-dated samples along the U.S. coastlines
(modified from Dillon and O’Doyle (1978) ........
Figure 32. Net shoreline movement of a portion of the South
Carolina coast based on historical maps surveyed
between:1 857 and? 19838 sy Be ee Bee.
Figure 33. Morphologic indicators of littoral drift along natural
and modified shorelines. Natural features such as
rock headlands show accretion on the updrift side.
and erosion on the downdrift side (A), tidal inlets
and spits show extension in a downdrift direction (B-
C), and beach ridge headlands show successive
growth on the updrift end influenced by the
development of coastal cells, which form shoreline
irregularities (D). Coastal engineering structures
including groin fields, jetties, seawalls, attached
breakwaters, and detached breakwaters (E-I)
generally show accumulation of sediment on the
updrift side, and reduced sediment supply on the
dOwnaritt Sides eo. le es Eas Re IO
Figure 34. Principles of obtaining subbottom seismic data ......
73
AP
79
80
83
Contents
Preface
Preface
The study reported herein results from research performed by the Coastal
Engineering Research Center (CERC) of the US Army Engineer Waterways
Experiment Station (WES) under Work Unit No. 32538, "Survey of Tech-
nologies in Coastal Geology," Coastal Geology and Geotechnical Program,
authorized by the US Army Corps of Engineers (USACE). Mr. John Sanda
was USACE Technical Monitor. Ms. Carolyn M. Holmes was the CERC
Coastal Program Manager.
This report was prepared by Dr. Joann Mossa, Department of Geography,
University of Florida, under the US Army Summer Faculty Research and
Engineering Program and by Messrs. Edward P. Meisburger and Andrew
Morang, Coastal Geology Unit, Coastal Structures and Evaluation Branch
(CSEB), Engineering Development Division (EDD), under the general
direction of Mr. Thomas W. Richardson, Chief, EDD, and Ms. Joan Pope,
Chief, CSEB. Director of CERC during the investigation was Dr. James
Houston, and Assistant Director was Mr. Charles Calhoun, Jr. Peer review
was provided by Dr. Donald Stauble, Ms. Joan Pope, and Mr. J. B. Smith,
WES.
At the time of publication of this report, Director of WES was
Dr. Robert W. Whalin. Commander and Deputy Director was
COL Leonard G. Hassell, EN.
Conversion Factors, Non-SI to SI (Metric) Units of Measurement
Non-SI units of measurement used in this report can be converted to
SI (metric) units as follows:
[mites ft" | tonsa
miles per hour 1.609347 kilometers per hour
Conversion Factors Table
1 Introduction
Background
Many geomorphic features are relatively stable and changes in their form
occur slowly; others are less stable and are subject to comparatively rapid
change in response to dynamic environmental factors. Variable features are
usually composed of unconsolidated or friable materials that react rapidly to
changes in the dynamic environment. More stable features are usually associ-
ated with consolidated rock and/or the absence of potent geological processes.
Few geological environments contain a greater variety of dynamic
geomorphic features than the coastal zones of oceans and large lakes. Because
of the many variable features, complex processes, and submerged areas, study
and description of coastal areas present special problems that do not arise
when examining more stable environments. In general, study of coastal areas
requires a process-oriented approach and a larger database than are usually
needed for study of more stable and accessible environments. The large
database is needed for two principal reasons. First, time series data collection
on many variable geomorphic features is needed to determine the range of
temporal variability. Second, selection of representative data points and
projection of data by visual observation and aerial photography are not possi-
ble in submerged parts of the coastal zone. Consequently, a dense data matrix
is needed for an adequate and reliable representation of bottom morphology
and sediment distribution.
Temporal variations in coastal geomorphology occur in: (a) cyclic
patterns; (b) as a result of intermittent noncyclic events; or, (c) as long-term
trends. Cyclic variations occur on a periodic or repetitious basis and are
generally related to processes like astronomical tide and seasonal sea and swell
patterns. Intermittent events are noncyclic occurrences such as large storms
or earthquakes. They are of relatively short duration but often have lasting
consequences for coastal morphology. Long-term trends include gradual
changes in relative sea level or climatic patterns which, in turn, cause slow
but often significant changes in coastal features or processes. Over the time
scales of modern process studies, they are considered noncyclic, although over
geologic time scales they may have a periodic component. The detection of
such long-term trends is often difficult, but they may be discovered by
Chapter 1 Introduction
comparative analysis of historical maps, charts, and aerial photographs that
show changes over decades or centuries.
Scope
This report identifies and briefly discusses variable coastal features, the
processes and factors that affect them, and the available technology and
techniques for their study. The features discussed here are, for the most part,
associated with the direct effects of marine and lacustrine processes.
Terrestrial features and processes that occur inland of the coastline are
discussed briefly in the following section. They are described in greater detail
in many standard texts dealing with geomorphology, physical geography and
physical geology (Chorley, Schumm, and Sugden 1984; Strahler and Strahler
1987; Bloom 1991).
Coastal Classification
Shorelines are influenced by a combination of nonmarine and marine
processes. Shepard’s (1963) genetic classification of coasts reflects the
dichotomy of nonmarine and marine influences. Primary coasts, according to
his classification, are essentially nonmarine in origin and are shaped mainly by
land erosion, subaerial deposition, volcanism, and diastrophism. Secondary
coasts are shaped by marine processes, including wave erosion, marine
deposition, and organic/biologic modification.
Primary shorelines have yet to be appreciably modified by marine pro-
cesses. Land erosion coasts include: (a) drowned river valleys; (b) drowned
glacially eroded coasts, including fjords; and (c) drowned karst topography.
Coasts of subaerial deposition include: (a) those principally reflecting river
deposition with either deltas of various forms or alluvial plains; (b) those
reflecting glacial deposition, with partially submerged moraines, drumlins, or
drift features; (c) wind deposition with active or fossil dunes, or sand flats;
and (d) those reflecting landslide deposition and perhaps other forms of mass
wasting. Volcanic coasts include those influenced by lava flows, tephra or
volcanic ash, and volcanic collapse or explosion. Coasts may also be shaped
by diastrophic movements, which produce faulted and folded coasts of various
types, and coasts with sedimentary extrusions such as salt domes and diapirs.
Information Sources
The most direct and accurate means of obtaining information on the vari-
ability of coastal features in an area is by conducting repetitive surveys over a
Chapter 1 Introduction
period of time. This period must be sufficient to cover the main cyclic events
associated with the seasons. Repeated surveys should cover each of the
seasons of a yearly cycle. In addition, survey density and timing suitable to
document the effects of extreme events, such as major storms, floods, and
hurricanes, are also desirable. Study of long-term cycles by repetitive surveys
is not widely practiced because of the expense and continuing commitment
needed to obtain sufficient data.
Historical maps, charts, and aerial photographs are important sources of
geologic information. A valuable source of these items is the National Ocean
Service (NOS) and its predecessors. Survey data extending back 150 years
are available for many areas, and preliminary charts of considerably larger
scale and detail than the published versions can be obtained from the NOS
archives. These historic sources are of great value in revealing long-term
trends. Some sources for historical and recent aerial photography and maps
are listed in Fulton (1981).
Data on intermittent noncyclic events are usually difficult or impossible to
obtain. In particular, baseline data of conditions immediately before the event
are often nonexistent because there is typically insufficient advance warning to
organize and conduct an adequate survey. However, aerial photographs can
often be obtained even with fairly short notice and are valuable in showing
conditions before an event, especially in the shore zone. Post-event surveys
should be conducted as soon as the affected area becomes accessible.
Information regarding past events can often be found through a com-
bination of field and laboratory tests. These include a variety of stratigraphic
and sedimentologic techniques, such as the analyses of sedimentary structures,
grain size, sediment composition, heavy minerals and fossils, and the
radiometric dating of organic remains in sediment deposits and of other iso-
topes of natural and human-derived sources. These techniques, in addition to
archeologic and pedologic ones, are of value in working out past environmen-
tal changes and events over a variety of time scales, although some parts of
the geologic record may have been obliterated.
Literature sources on coastal features and processes, many containing
historical information, are abundant, but a considerable research effort is
needed to cull out pertinent works. In a recent computer-assisted literature
search, over 1,400 items were listed under the key words "coastal geology,"
"coastal geography," "coastal geomorphology," and "coastal classification."
Most had been published since 1970. Selected key sources of coastal
engineering information, including meteorology and climatology, water levels,
wave and currents, ice, beach erosion and littoral transport, topography and
bathymetry, and geology and geomorphology, are described in Chu, Lund,
and Camfield (1987). Historical geomorphic data can also be acquired from a
variety of sources (Trimble and Cook 1991). Local records such as tax
assessments, deeds, and local surveys may also be useful (Fulton 1981). Fur-
thermore, there are many unpublished sources of coastal information that can
be sought from government agencies, universities, and private firms.
Chapter 1 Introduction
2 Relevant Processes and
Factors
From both a temporal and spatial perspective, the geomorphic variability of
a coast reflects a balance between forces that promote change and materials
that resist change. Forces promoting change include atmospheric,
oceanographic, biologic, and terrestrial processes that act individually and in
combination. Some of these are important locally and others are important
regionally, over short- and long-term periods. The processes and products of
the interaction of the various factors in coastal environments are complex, and
it is often advantageous for a researcher to adopt a holistic approach.
Because the coast lies at the boundary between the atmosphere, ocean, and
land, processes within each of these environments are important in promoting
coastal change. In the atmosphere, factors operating on varying spatial and
temporal scales include climate, wind, and cyclonic disturbances. Oceanic
processes that influence coasts include waves, tides, currents, storm surges,
tsunamis, and sea level (eustatic) changes. Terrestrial processes may be inter-
nally driven, such as by tectonic factors, or externally driven, by climatic and
meteorologic agents such as running water, groundwater, and ice. Biologic
processes may also come into play, influencing both the shape and material of
coastal environments. Interactions between many of the major processes are
described briefly in subsequent pages.
Materials in coastal environments have varying properties, which charac-
terize their ability to resist deformation by stresses, their ability to resist
weathering and abrasion, and their ability to resist transportation by a fluid
agent. The strengths of materials depend on the nature of the solids that
comprise them, the nature of the voids (whether filled, or partly filled, with
water or with air), and the forces holding the aggregates together. Some
factors that characterize resistance to shear include rock strength, state of
weathering, and the spacing, width, and continuity of joints and voids.
Frictional and cohesive strength, mineral hardness, and fabric also cause mate-
rials to vary in their resistance to erosion by abrasion, fluid stresses,
corrosion, and plucking. Materials vary in their resistance to entrainment and
transportation by fluids according to their volume, density, and friction with
the bed. Because coastal sediments display a range of characteristics from
consolidated to unconsolidated, gravel to clay, terrigenous to biogenic, they
show great variety in their resistance to natural forces. The nature and
Chapter 2 Relevant Processes and Factors
resistance of inland materials, which can be transported to the coast by
terrestrial processes, also contribute to the geomorphic variability of coasts.
Climate
Climate and weather are terms used to describe a broad group of interre-
lated atmospheric processes. Weather characterizes the overall state of the
atmosphere on short time scales of minutes to months. Climate, in contrast,
characterizes the long-term conditions of an area, using averages together with
measures of dispersion and frequency.
Several interrelated climatic factors such as temperature, pressure, wind,
and moisture have a great influence on the development of the coastal zone.
These factors may change as long-term trends, and also display cyclic and
noncyclic variations. Distinctive cyclic variations include seasonal and daily
changes associated with the revolution and rotation of the earth. Regional
variations in paleoclimatic and modern climatic factors also contribute to the
spatial variability of coastal geomorphic features. Of the various climatic
factors, wind most strongly influences modern process and geomorphic vari-
ability of coasts, both directly and indirectly. Wind is discussed subsequently
in a Separate section.
Evidence from stratigraphic, paleontologic, palynologic, radiometric,
pedologic, and archeologic data shows that many climatic changes of global
and regional scale have occurred throughout geologic time. While the long-
term paleoclimatic history of the earth is not well known, paleoclimatic data
assist in characterizing general aspects of the many profound and widespread
changes that have occurred throughout geologic time.
Most evidence indicates that over the last 500 million years, the earth was
warmer than present, with the poles being ice-free most of this time (Frakes
1979; Lamb 1982). About 55 million years ago, global climate began a long
cooling trend, which led to the development of the high-latitude ice sheets.
Superimposed upon this trend, over the last 1 to 2 million years during the
Quaternary period (Pleistocene and Holocene epochs), are a number of alter-
nating glacial and interglacial episodes. In the Northern Hemisphere, these
episodes were characterized by widespread waxing and waning of the ice
sheets into the mid-latitudes. Falling and rising temperatures in both hemi-
spheres accompanied glacial advance and retreat. During cooler periods,
more widespread glaciation of high altitudes was also common.
These climatic changes were accompanied by large fluctuations in sea
level. During glaciations, water was withdrawn from the ocean basins and
stored in ice sheets and mountain glaciers. During interglacial periods, it
returned to the ocean basins. Many of the large inland lakes also may have
Chapter 2 Relevant Processes and Factors
expanded during the colder climates of glaciations, perhaps in response to
reduced evaporation. Crustal depression occurred with ice advance over the
continents; crustal rebound followed deglaciation, further complicating the
history of relative sea level changes along coastlines.
Because of changes in relative sea level, even those coasts not directly
glaciated have been affected to some degree. But coasts were affected in
differing ways by these processes and events, adding to their geomorphic vari-
ability. Such eustatic, climatic, and crustal changes are still occurring to
varying degrees in different parts of the world. This subject will be further
discussed in the section on relative sea level later in this part of the report.
Variations in paleoclimate and glacial activity account for much of the vari-
ability in geomorphic landforms and processes along coasts. Examples of
erosional coasts include fjords, which were produced by the erosive activity of
mountain glaciers in conjunction with relative sea level changes. The erosive
activity of the mid-latitude North American ice sheets was also integral in the
formation of the Great Lakes basins (Hough 1968). As characterized by
Shepard (1963), depositional glacial coastlines may consist of tills, moraines,
and drumlins. The north shore of Long Island Sound, extending from
Connecticut to Massachusetts, displays these features.
Modern climatic conditions have been well-documented by systematic and
accurate meteorological observations in many parts of the world. In some
places, such records exist for periods as long as 2 centuries. These form a
foundation for a reasonably accurate model of the earth’s present climatic
patterns and of anticipated trends. The use of satellites for remote sensing of
the atmosphere and the development of general circulation models are assist-
ing in the interpretation of past and the prediction of future climates.
Coasts are directly and indirectly affected by modern climatic conditions.
Differences in temperature and precipitation influence organisms, vegetation
type, and biomass production (Whittaker and Likens 1975). Climatic varia-
tion also affects the type and intensity of weathering and the rates of denuda-
tion (Langbein and Schumm 1958; Knighton 1984), which in turn influence
geomorphic features along coasts. Atmospheric conditions are intimately
linked to oceanographic conditions, so that a change in one will cause a
change in the other.
Climatic factors need not operate directly in the coastal zone to be
relevant. For example, wind-generated waves in remote offshore areas can
eventually reach and affect the coast, and precipitation in inland areas is
important in producing and transporting sediment that enters the coastal
system. The assessment of climatic factors therefore requires consideration of
climatic data from outside, as well as within, the coastal zone.
Chapter 2 Relevant Processes and Factors
Wind
Wind has a considerable influence on the coastal zone. This influence may
be direct, since wind is an agent causing erosion and transportation. Near the
coast, winds often have a predominant onshore-offshore orientation. If winds
are blowing offshore, sediments may be eroded and transported from inland
areas and then deposited in the coastal zone. Sediments from within the coast-
al zone, particularly the dry sand of dunes and beaches,.may be eroded and
transported offshore directly by wind.
The influence of wind is also indirect because wind stress causes the
formation of waves and oceanic circulation. Over large areas and long time
scales, predominant wind velocities and durations affect wave climate,
whereas over shorter time scales, storm winds generate waves capable of great
geomorphic activity. Waves generated by wind, in turn, often approach the
coast at an angle, leading to longshore currents. Strong onshore winds, if
sustained, may also cause increased water levels or setup.
Wind is caused by a pressure gradient, or horizontal differences in pressure
across an area. This, in turn, may be created by differences in temperature,
as the pressure, temperature, and density of gases are interrelated. Depending
on the scale of the pressure and temperature variations, atmospheric
phenomena range from those of global scale, which are generally persistent, to
those of local scale and short duration, such as storms.
On a global scale, the wind systems occur in characteristic belts, being
named for the direction from which they blow. Near the earth’s surface, the
zone about 5° to 25° poleward of the equator is characterized by the northeast
trades in the Northern Hemisphere, and by the southeast trades in the South-
ern Hemisphere. Wind direction is predominantly westerly between about 30°
and 60° in both hemispheres, whereas easterly winds are predominant pole-
ward of 60°. While these belts shift somewhat over the year, these create
characteristic wind patterns and intensities, which affect wave energy and
predominant wave directions, oceanic circulation, and sediment transport by
both wind and water.
Seasonal shifts in wind also occur in some regions, notably in southeast
Asia where monsoon winds occur. The monsoon brings strong seasonal
onshore winds, which influence the wave environment and circulation of the
Indian Ocean (Davies 1980). The monsoon is accompanied by abundant pre-
cipitation caused by moist maritime air masses. Other local winds of note
include the katabatic winds in cold climates, mountain and valley winds, and
the sea and land breezes (Hsu 1988).
The sea breeze and land breeze are common phenomena that occur because
of diurnal temperature differences between land and water. During the day,
especially in the summer, the land warms more rapidly than the water. The
Chapter 2 Relevant Processes and Factors
air expands and rises as it warms, forming a belt of lower pressure along the
coast. The pressure gradient between the water and land causes a sea breeze
in which air from the sea blows landward. The opposite happens at night.
The land cools more rapidly because it is less efficient than water at storing
heat. The air over the sea has lower pressure, resulting in vertical
convection. The convection causes the land breeze to flow seaward.
Cyclonic Disturbances
Centers of relatively low atmospheric pressure, also known as cyclones,
are associated with windy, cloudy, and wet weather. In contrast,
anticyclones, or high pressure weather patterns, are generally associated with
calm, dry weather. Cyclones occur in many sizes and forms, including
continental-size extratropical cyclones, tropical cyclones of varying intensity,
and tornadoes. All are capable of causing significant geomorphic change,
because of the winds, waves, and storm surges associated with them. The
intensity of cyclonic winds is controlled by the pressure gradient, or change in
pressure measured along a line at a right angle to the isobars. Low pressure
may also occur as elongated troughs, which range in scale from a few hundred
kilometers to continental.
Extratropical cyclones, also known as wave or mid-latitude cyclones, are
transient features that develop in various stages. Initially, they develop along
the polar front, a narrow zone separating the cold, polar easterly winds from
the warmer, mid-latitude westerly winds. A wave or indentation forms
between the cold and warm air masses, causing the cold air to invade warmer
territory and the warm air to enter colder territory along sharply defined
fronts. The cold air masses, being denser, force up the warm air as they
move along the surface, whereas the lighter warm air masses move over the
colder air masses. The cold air masses eventually dominate the surface after
all of the warm air is forced off the ground. This cuts off the source of
moisture and energy, causing the system to die.
Central pressures in extratropical cyclones vary greatly, with lows of
940 mb* (compared to average sea level pressure of 1013.2 mb), although
typically they do not fall below 980 mb. In both hemispheres, the most
intense extratropical cyclones occur in the winter, with less intense systems
developing in fall and spring. Cyclonic winds blow counterclockwise in the
Northern Hemisphere, and clockwise in the Southern Hemisphere. Thus,
depending upon the relationship of the storm orientation and track to the
coast, there are several possible wind sequences (e.g., onshore winds followed
by offshore winds) that affect wave, current, and sediment transport patterns
(Niedoroda et al. 1984). Typically, the systems are transported with the
westerly flow and move toward the east, although their tracks depend on
*
A table of factors for converting non-SI units of measurement to SI (metric) units is presented on page x.
Chapter 2 Relevant Processes and Factors
upper air circulation. They usually pass an area within a day or two, although
sometimes they remain stationary over an area for several days.
Tropical cyclones, in contrast, are believed to originate from pre-
existing disturbances called easterly waves, which are found in the tropical
oceans in the 8° to 15° latitude band. The conditions that promote their for-
mation include low level cyclonic vorticity, a Coriolis force, minimal vertical
changes in velocity, sea surface temperatures warmer than 27°C, unstable
lapse rates, and high humidities at mid-tropospheric heights (Riehl 1979).
Such disturbances do not form in oceans such as the southern Atlantic, which
do not meet these conditions.
If the storm intensifies and average wind speed increases, tropical
cyclonic disturbances become tropical depressions, tropical storms, and finally
hurricanes, with average wind speeds in excess of 75 mph. Increasing wind
speeds are caused by an increased pressure gradient, where central pressures
in severe hurricanes can fall below 900 mb. The great majority of tropical
cyclones develop in the late summer and early fall in both hemispheres. As
with other cyclones, meteorologic events follow a characteristic sequence
(Figure 1) that affects coastal geomorphic features, depending upon the rela-
tionship of the storm orientation and track to the coast (i.e., Penland and Suter
1984).
The geomorphic activity of tornadoes and waterspouts, because they are
small in size and develop and die rather quickly, is not on the same scale as
other cyclones. Tornadoes are associated with cumulonimbus or thunderstorm
clouds, and are most common in zones where air masses of contrasting
temperature and moisture meet, such as the interior of the United States.
Occasionally, tornadoes and waterspouts affect coastlines, with most damage
being caused by high wind speeds; wind duration and fetch are typically insuf-
ficient to develop large waves.
The relative influence of extratropical cyclones compared to tropical
cyclones depends largely on latitude. Closer to the tropics (e.g., the
U.S. Gulf coast and southern U.S. Atlantic coast) tropical cyclones have a
higher frequency of occurrence than farther poleward. Farther poleward,
(e.g., in the northern U.S. Atlantic coast) extratropical cyclones and
associated fronts occur more frequently and typically exhibit greater
magnitudes. In the lower mid-latitude climates where both may occur, an
issue of some debate concerns the relative importance of these storms, as it is
unknown whether the higher frequency-lower magnitude extratropical cyclones
have a greater geomorphic impact than the lower frequency-higher magnitude
tropical cyclones.
Chapter 2 Relevant Processes and Factors
10
SOUTHERLY WESTERLY NORTHERLY
ye eT
OFF SHORE SURGE ONSHORE
WAVE
PERIOD
SOUTHERLY WESTERLY NORTHERLY
Laat Aree
ONSHORE SURGE
OFFSHORE
TRACK
MAP VIEW (IME SSERIES
Figure 1. Changes in barometric pressure, wind speed, wind direction,
wave height, wave period, and surge as a cyclone passes
laterally offshore along a north- and south-facing coastline in
the Northern Hemisphere (adapted from Carter 1988)
Waves
Waves are of great importance in the formation and variability of coastal
geomorphic features. They are especially effective in the shore and shoreface
areas, where they are capable of moving sediment directly or by generation of
longshore currents. Wind waves, the most common type, are generated by
wind stress on the water surface. The height and energy of wind waves
increase with increasing wind velocity, fetch (the extent of water over which
the wind blows), and wind duration.
Waves impinging on a coast are not necessarily produced by local winds in
coastal waters. They may be produced by distant weather systems and reach
the coast after traveling some distance, up to thousands of kilometers, outside
the area in which they were generated. Such waves are called swells, while
waves still within the area of generation are called seas. Swells have a longer
period, or time of passage between two successive wave crests, and move
faster than locally generated waves. Swells undergo a decay process in which
the height becomes progressively less with distance traveled, although they
Chapter 2 Relevant Processes and Factors
still retain most of their energy, and the wave period becomes longer. Two
sets of long-period waves approaching the coast with slightly differing
wavelengths may produce a resultant pattern, known as surf beat, that displays
a periodic variation in height. Waves change character as they enter progres-
sively shallower water, causing a variety of wave and breaker types, as well
as several distinctive zones of wave action (Figure 2).
LITTORAL ZONE
NEARSHORE ZONE OFFSHORE ZONE
BACKSHORE ORESHORE INSHORE SHOREF ACE —|
BERMS SWASH BREAKER
= CaN AON EUR a ee NATE Gey Su ag
TRANSITION ZONE
. .\* , LONGSHORE BAR>
TROUGH ae
*RUNNEL’ 2
Figure 2. Distinctive zones of wave action and morphologic characteristics of the littoral
zone
Waves approaching a coast undergo a transformation of certain characteris-
tics which is called shoaling, because they have progressed into water depths
in which frictional interaction with the bottom affects their motion. Signifi-
cant transformation begins to occur when a wave enters water depths equal to
about one half the wave length. This transformation causes the wave speed
(celerity) to decrease, the wavelength to decrease, and the wave height to
increase, since more energy is packed into a smaller area. The wave front
may bend or change in direction as waves approach a shoreline and are
affected by bottom topography. This phenomena is known as wave refraction.
Because of variations in bathymetry from place to place, the trans-
formation of a given deepwater wave is site-specific and must be calculated on
the basis of local bathymetric characteristics, bottom friction, and coastal con-
figuration. Wave refraction bends the wave front, so that it becomes more
nearly parallel with the bottom contours with decreasing water depths. For
this reason orthogonals generally converge on headlands and diverge in bays
(Figure 3). However, when waves cross irregular bathymetry, the waves may
be refracted upon themselves.
Chapter 2 Relevant Processes and Factors
VPA
+
| |
\ | |
|
|
ecw ee
FA Pp
waves [SUBMARINE RIDGE ee
in —— Pilon \ a
| ay
L
oie
=e I ERE SIL Se tet SUBMARINE CONTOURS
-=— =" REAAGONALS
Figure 3. Wave refraction surrounding headlands and bays and over submarine
morphologic features
AS waves continue to enter shallower water depths, they may become un-
stable and break, becoming substantially distorted in shape from their
deepwater form. Breaking waves follow a continuum that has been classified
by Galvin (1968) into spilling, plunging, collapsing, and surging breakers. In
general, steep deepwater waves and onshore winds approaching gentle slopes
produce spilling breakers, where water spills down the steepened shoreward
wave face (Figure 4). Plunging breakers are associated with long, low deep-
water swells and intermediate slopes. Flatter waves breaking on a steeply
sloping shore surge or collapse, with the base of the wave surging forward
and the crest collapsing or disappearing.
Chapter 2 Relevant Processes and Factors
NON- BREAKING
REFLECTION
SURGING
COLLAPSING
Beach slope (tan®)
“7'~
u
w
w
S
a
u
ro)
Y
w
a
ig
ni
ie
U
3
wu
faa
SPILLING
NON-BREAKING
TOTAL DISSIPATION
0.4 0.8
Initial wave height to
water depth ratio (H;/d,)
Figure 4. Appearance and classification of breaking waves
according to Galvin (1968) combined with beach slope
and wave height to water depth ratio as discussed by
Street and Camfield (1966) (adapted from Carter 1988)
Chapter 2 Relevant Processes and Factors
14
Once the waves break, a surf zone is generated in which much smaller
waves are projected toward the foreshore and beach face. Upon breaking, the
motion of the water particles in a wave changes from orbital to linear. The
presence and the width of a surf zone are controlled by beach slope and tidal
phase (Ingle 1966). Beaches with gentle slopes, which are typically composed
of fine sand, are characterized by wide surf zones, whereas beaches with steep
slopes, which are composed of shingle and cobble, often lack surf zones.
Beaches of intermediate slope may have a surf zone at low tide, when wave
action is over flatter portions of the beach profile, but may lack a surf zone at
high tide when the waves break closer to shore over the steeper beach face.
The landward component of this linear motion, which surges onshore
at a high velocity, is known as swash, while the lower-velocity return flow,
which is driven by gravity, is known as backwash. As waves approach the
beach at an angle, the oblique upward rush of swash, succeeded by the return
of backwash down the beach, results in a longshore movement of sediment.
Deepwater wave characteristics can be estimated by an analysis of weather
map data over the period of interest, a process known as hindcasting (Coastal
Engineering Research Center (CERC) 1984). Waves may be observed from
shipboard or shore, or can be measured by gages deployed on buoys, struc-
tures, or on the sea bottom. Refraction analyses can be performed manually
by the orthogonal or wave-front method, or by computer methods when the
offshore relief, wave approach direction, and wave period are known.
In addition to energy from incident waves, some energy may be transferred
to secondary wave motions called edge waves, which develop at right angles
to the shoreline. Edge waves have a maximum amplitude at the shoreline and
decline seaward. They develop differently on shorelines of differing
gradients. Many coastal forms and processes have been linked to edge wave
characteristics (Holman 1983; Carter 1988).
The overall wave field at a site is typically formed by a combination of
waves from several different sources, some local and some distant. Longer
waves associated with storms reach deeper parts of the shoreface profile than
do shorter waves associated with calmer conditions. In order to be useful in
understanding the development and modification of coastal features and effects
on coastal engineering works, data collected by the methods described above
must cover a sufficient time span to record seasonal cyclic patterns and the
occurrence of intense storms.
Tides
Tides are characterized by a rhythmic rise and fall, or flood and ebb, of
sea level over a period of several hours. Because tides are generated by the
gravitational forces associated with the moon and the sun, changes in the
Chapter 2 Relevant Processes and Factors
declination of the moon and sun with the earth, and the relative position of
these three astronomical bodies, influence the pattern and magnitude of tides.
The timing and magnitude of high tide and low tide at any given location can
be closely predicted by changes in these and other astronomical constituents.
Three major types of tides can be distinguished, based upon the pattern and
frequency of occurrence of high and low tides during a tidal day. Tidal
bulges form on both sides of the earth in response to a balance of forces
associated with gravity, centripetal acceleration, and gravitational attraction
(Komar 1976). The earth rotating on its axis typically produces semidiurnal
tides, with two tidal maxima and minima every 24 hr and 50 min. This
period exceeds the length of a solar day because of the advance of the moon’s
orbit. Diurnal tides display, on the average, one maximum and one minimum
each day. Diurnal tides occur where the typical cycle is complicated by other
astronomical factors. A combination of these characteristics, where two high
and low tides having large diurnal inequality occur daily, are known as mixed
tides. Mixed tides are commonly classified as being predominantly semi-
diurnal or diurnal (Defant 1958). Important tide-generating constituents, ex-
pressed as a ratio of the major components influencing diurnal tides to those
influencing semidiurnal tides, are used to measure these variations.
In general, tidal range is highest when the moon is full or new, and when
the moon, sun, and earth are in alignment, or syzygy. These alignments
produce the spring tides, in which the high tide is higher and the low tide is
lower than average. Tidal range is lowest during the first and third quarters,
when the moon and sun align perpendicularly with the earth, a condition
known as quadrature. These less-pronounced high and low tides are col-
lectively known as neap tides. The sequence from spring to neap to spring
takes about 28 days, or one lunar month. Both spring and neap tides are
affected by drag forces, which cause tidal range to lag syzygy and quadrature
by up to 1.5 days.
Longer period cycles are generated by varying lunar and solar distances,
caused by the ellipticity of both the moon’s orbit around the earth, the earth’s
orbit around the sun, and the sun’s declination. The moon’s orbit around the
earth is by far the more important of these. From perigee, when the moon is
closest to the earth, to apogee, when it is farthest, represents a change in
distance of about 13 percent. The earth is closer to the sun in early January
by about 3 percent than its farthest position in early July, causing tidal range
to be slightly greater in the Northern Hemisphere in the winter and fall than in
the spring and summer.
Tidal range or magnitude is strongly affected by the depths and configura-
tion of the land masses encountered. Davies (1964) introduced coastal
classification divisions based on the spring-tide range, namely microtidal
(< 2 m), mesotidal (2-4 m), and macrotidal (> 4 m). Tidal magnitude is
influenced by the depths and configuration of the land masses encountered in
crossing the continental shelves, which cause local resonances and reflections
at land boundaries.
15
Chapter 2 Relevant Processes and Factors
The type and frequency of occurrence of a wide variety of coastal
landforms have been related to the tidal range (Hayes 1980) (Figure 5).
Microtidal ranges occur on open ocean coasts and in certain landlocked seas.
They are conducive to the development of river deltas, barrier islands, and
spits. The Gulf of Mexico is an example of a microtidal environment.
Macrotidal ranges occur where the tide is dissipated across a wide, shoaling
slope, or confined to estuaries and gulfs whose land boundaries cause local
resonances and reflections. They are conducive to the development of funnel-
shaped estuaries, mudflats, and salt marshes. Locations with mesotidal ranges
include features found in both microtidal and macrotidal environments, but are
also well-known for well-developed tidal deltas.
MICROTIDAL MESOTIDAL MACROTIDAL
DELTAS
BARRIER
ISLAND/
STRANDPLAIN
INLETS
TIDAL
DELTAS
RIDGES
TIDAL
FLATS
LIKIHOOD OF OCCURRANCE
SALT
MARSH
ESTUARY
Sra
0 =—MICROTIDAL—= 2 =—MESOTIDAL —> 4=—— MACROTIDAL —= 6
TIDAL RANGE (M)
Figure 5. Macroscale morphology of microtidal, mesotidal, and macrotidal coastlines
(modified from Hayes 1980)
16
Chapter 2 Relevant Processes and Factors
Because tides are influenced by many factors and show great temporal and
spatial variation, they play an important role in the variations of both
processes and landforms in the coastal zone. The length of the drying period
of the intertidal zone, changes in the water table of beaches, and the intensity
and duration of tidal currents are all influenced by the type and magnitude of
tides. Tides also influence the timing of morphologic changes, since cliff
erosion and beach building may occur only intermittently at high tide. Long-
term tidal variations, including solar semi-annual and 18.6-year components,
may also be related to cycles of progradation and stabilization by mangroves
on fluid mudflat coasts (Wells and Coleman 1981b).
Several landforms showing geomorphic variability are strongly influenced
by tides. Tidal flats are depositional surfaces, alternately flooded and
exposed. The formation, dimensions, and spacing of inlets are related to the
total volume of water or tidal prism. Flood and ebb deltas, as well as asso-
ciated features at inlets, are controlled by tidal current hydraulics. Tidal
channels of various types, including intertidal channels, tidal creeks, and tidal
rivers, are influenced to differing degrees by tides.
Currents
Near the coast, currents are effective agents of erosion and transport of
sediments and, consequently, have an impact on the geomorphic variability of
coasts. Mechanisms responsible for the generation of coastal currents include
winds, waves, and tides.
Wind-driven currents, in combination with density currents, comprise
much of the large-scale oceanic circulation, as well as much of the circulation
in marginal seas. These currents, generated by the drag of wind on the ocean
surface, are deflected up to 45 deg as a result of the Coriolis effect, although
appreciably less in shallower waters. Ocean circulation following the parallels
is predominantly wind-driven, whereas circulation following the meridians is
largely density-driven (Mosetti 1982). Wind-driven currents show greater
influence on geomorphic variability in marginal seas than oceans, because
sediment transport and beach modification are facilitated by shallower depths.
Wave-generated currents can influence any part of the shore, shoreface,
and Continental Shelf; however, the most important currents for coastal
development are longshore currents. Longshore currents are generated
between the breaker zone and shore by waves approaching the shore at an
angle. The wave height, period, direction of approach, and bottom slope are
important in determining the direction and characteristics of longshore cur-
rents. Flow velocities of longshore currents are typically around 30 cm/sec,
but can be substantially higher. While such velocities are often unable to
entrain materials, suspension by concurrent waves may greatly increase the
effectiveness of sediment transport.
Chapter 2 Relevant Processes and Factors
17,
In some places, the hydraulic head of water carried onshore by waves may
return across the surf zone as a concentrated jet, known as a rip current (Bow-
en 1969; Bowen and Inman 1969). Rip currents are relatively narrow and
strong, capable of moving sediment seaward through the breakers and the in-
shore bar field. Although near-bottom flow usually dissipates rapidly, surface
flow may persist for greater distances. The geologic signature of rip currents
can be seen on the seafloor well seaward of the surf zone (Morang and
McMaster 1980). Rip currents tend to be found at positions of lowest breaker
height.
The existence of rip currents, and the manner in which they are fed,
depends upon whether the nearshore current system is dominated by a cell cir-
culation system or a longshore current. Typically, both situations are present
simultaneously (Shepard and Inman 1950). In the cell circulation system, the
rip currents are fed by a series of longshore currents that increase in velocity
from a minimum midway between two adjacent rips to a maximum just before
turning seaward into the rip (Figure 6). If the wave approach angle is large,
at least 5 deg to 10 deg, a strong longshore current will be generated that is
continuous along the shoreline. The intermediate condition with a smaller
breaker angle is known as general circulation. General circulation may result
in an asymmetrical current pattern, with velocities at their minimum level
updrift from the rip current and increasing to a maximum before turning
seaward to the next rip current (Komar and Inman 1970).
Tidal currents are horizontal water movements caused by the rhythmic
rise and fall of the sea surface. Their magnitude generally increases with
increasing tidal range. Tidal currents force water to move both at the surface
and at depth, and generally have the greatest velocities during the flood and
ebb, at mid-stage between high tide and low tide. In the open ocean, tidal
current velocities rarely exceed 1 m/sec. In restricted passages and shallow
coastal shelves, however, velocities are greater and can exceed 4 m/sec in
some channels.
Storm Surges
Sustained and strong wind stresses on a water body, often developed under
tropical and extratropical storm systems, not only create waves but also pro-
duce a horizontal flow of water in the general direction of the wind. When
this flow approaches a coast and is affected by shoaling, there is a sustained
increase in the water levels, known as a storm surge. Storm surges may be as
much as 3 to 6 m during major hurricanes or extreme seiches on the Great
Lakes, and may be augmented by decreases in atmospheric pressure. This
anomalously high water level can cause flooding of the beach, dunes, and
Chapter 2 Relevant Processes and Factors
CELL CIRCULATION (,*0°)
rip
current
ASYMMETRIC CIRCULATION (SMALL &, )
ieee eae
()4
longshore
current
LONGSHORE NON-—CIRCULATORY PATTERN (LARGE &_)
x breaker zone
longshore
current
Figure 6. Wave-induced nearshore currents as determined by breaker angle. Cell
circulation pattern with well-developed rip currents occurs when the
breaker angle is close to zero. Asymmetric circulation with longshore
currents feeds rip currents when breaker angle is small. A longshore
non-circulatory pattern occurs with an oblique wave approach and large
breaker angle
Chapter 2 Relevant Processes and Factors
1s)
20
inland areas, can extend the zone of wave attack inshore, and can increase
hazards and damage. Strong offshore winds can similarly produce decreased
water levels.
Storm surges, as products of the weather, can be studied by hindcast
methods from historical weather charts in the same general manner as waves.
The magnitude of water-level change is dependent upon wind velocity and
direction, fetch, depth of water, and slope of the inner shelf (Shore Protection
Manual 1984), as well as the orientation of the storm system in relation to the
coast. As with tides, the configuration of the coast may influence water
levels, with increased elevations being particularly common in embayments.
In many cases more direct records of storm surge can be obtained from
tide gages and measurement of high-water marks following the storm. In
recent years, there has been an increasing volume of work in storm surge
modelling and prediction. The Sea, Land and Overland Surges from Hurri-
canes (SLOSH) model (Jelesnianski and Chen 1982) and the Special Program
to List the Amplitudes of Surge from Hurricanes (SPLASH) models
(Jelesnianski 1972) are among the most widely used.
Tsunamis
Tsunami is a Japanese term used widely in the scientific literature to refer
to a train of progressive long waves generated by an impulsive disturbance
either in the ocean or a small body of water. A tsunami is usually caused by
a severe earthquake. Tsunami waves have periods of several minutes to
several hours and can move at speeds of 700 to 900 km/hr in the open ocean,
depending upon water depth. Upon approaching shallow water, their speed
decreases but their wave height increases dramatically.
While tsunamis are rare, they have the potential to cause extreme
geomorphic change and damage to structures. Crustal movements around the
Pacific basin are likely to cause tsunamis. Islands in the center of the Pacific
basin, such as Hawaii, can receive effects from multiple sources, and are
particularly vulnerable.
Relative Sea Level
Changes in relative sea level occur when there is (a) a general eustatic
variation of sea level, (b) uplift or subsidence of a coastal landmass, or (c) a
combination of the two. The net gain or retreat of land along coasts is
influenced by the combination of sea level changes and changes in erosion or
accretion over time (Bloom 1965). Transgression, the landward migration of
the shoreline, usually occurs with rising relative sea level unless a high rate of
Chapter 2 Relevant Processes and Factors
deposition can offset this tendency (Curray 1964). Regression, the seaward
migration of the shoreline, typically occurs with falling relative sea level,
unless high rates of erosion offset this tendency (Payton 1977).
Eustatic changes are primarily the result of changes in the volume of water
in the oceans or changes in the dimensions of ocean basins. Although there
are many reasons for variations in ocean volume, the growth, or waxing, and
decay, or waning, of large continental and alpine glaciers have been the
primary causes of fluctuations in the past 2 million years (the Pleistocene and
Holocene Epochs) (Emery and Aubrey 1991). During glacial episodes,
enormous amounts of water were locked up in the massive continental and
widespread alpine glaciers, causing a substantial reduction in the volume of
oceanic water and a reduction of sea level to more than 100 m below the
present level. During interglacial episodes, the amount of meltwater that
returned to the ocean caused a rise in sea level that at times exceeded the
present elevation by more than 80 m.
The last major glaciation, known as the late Wisconsin age in North
America, reduced sea level to over 100 m below the present. The waning of
that glaciation precipitated a rapid rise of sea level commencing about
18,000 years ago, reaching near the present level about 4,000 years ago,
when sea level became more or less stable. Because large glaciers still exist
in Antarctica, Greenland, and some mountainous areas, the present sea level is
below that of some prior interglacial periods when a more extensive melting
of glacial ice occurred.
The fluctuations of sea level during the Pleistocene and Holocene Epochs
have caused the shoreline to migrate back and forth, alternately exposing and
submerging large parts of the present continental shelves and areas inland of
the present shoreline. These transgressive and regressive events have left
depositional features of terrestrial origin in marine environments, and features
of marine origin in terrestrial environments.
Studies of historical tide records in recent years indicate that a rise in sea
level is taking place in many locations (Hicks 1978; 1983; Gornitz, Lebedeff,
and Hansen 1982). This rising trend, which some scientists believe may
accelerate in the future, has been attributed by some to the general warming of
the planet accompanied by glacial melting, possibly caused by increased
concentrations of carbon dioxide (CO,), methane (CH,), and other gases in the
earth’s atmosphere which trap longwave-electromagnetic radiation. Projection
of future trends based on past sea level history is difficult because of the
relatively short time that widespread accurate data have been systematically
collected, because of problems in correcting for vertical earth movements, and
because of difficulties in projecting trends.
Local and regional changes in relative sea level also occur where coastal
landmasses are uplifted or depressed as a result of tectonic activity, sediment
compaction, or unloading and loading by glacial ice or water. These move-
ments may increase or decrease the effects of eustatic sea level fluctuations,
Chapter 2 Relevant Processes and Factors
Zl
22
and may result in local horizontal transgressions or regressions of sea level or
vertical submergence or uplifting of terraces.
Tectonic movements may be so slow that they have little influence on
geomorphic variability. On the other hand, they may occur as dramatically
and suddenly as in the Great Alaskan Earthquake of 1964, which caused
upward displacement of 10 m in places, and downward displacement of 2 m
in others, over a period of only a few months (Hicks 1972). In general, these
movements tend to be greatest at margins of tectonic plates and, in particular,
at converging plates.
Consolidation and dewatering, which cause a reduction in volume, are
particularly prominent in areas which experience rapid sedimentation, such as
the Mississippi Delta of southeastern Louisiana. Surface and subsurface sedi-
ments, which are poorly consolidated and include organic-rich materials, may
experience very high rates of compaction. In general, the rates of sediment
consolidation decrease with increasing depth. They also decrease with
increasing age, especially in environments of recent sedimentation.
Unloading and loading of the lithosphere by glacial ice and water may also
produce vertical and horizontal movements, further complicating the history of
relative sea level changes along coastlines. Isostatic depression of the litho-
sphere, which occurs with glacial advance over the continents, is proportional
to the ratio between the density of ice and that of the mantle (Andrews 1974).
Isostatic or crustal rebound follows deglaciation. Rates of uplift, estimated
from raised shorelines, may exceed 20 mm/yr (Smith and Dawson 1983).
Although much slower rates of isostatic compensation are attributed to ero-
sional unloading, these rates may be sustained over longer periods.
Lithology and Weathering
The nature of rocks and sediment deposits is of great importance in
determining the inherited morphology and the development and modification
of coastal features. The lithologic factor having the greatest effect on coastal
features is the degree of consolidation. This governs the ability of rock
material to be eroded and transported, which, in turn, influences the form and
stability of geomorphic elements occurring in the coastal zone.
Consolidated rock coastlines are often hilly or mountainous, with the
exception of reefs, which are generally low-lying. The inherited morphology
is usually prominent, with erosional features being more numerous than
depositional features. Some geomorphic variability is attributable to rock
type, interbedding, jointing, and dip and strike of strata (Figure 7). Temporal
geomorphic variability is not as great as on unconsolidated coasts because con-
solidated rocks are highly resistant. However, in some places, rocky coasts
may be modified by depositional features. These include locations where
Chapter 2 Relevant Processes and Factors
LITHOLOGY AND STRUCTURE
INTERBEDDED
WEAK AND
RESISTANT
STRATA
WEAK STRATA
FAULTED COASTLINE
IGNEOUS CLIFFS
JOINTING AND DIP
WELL JOINTED DIPPING STRATA
MASS MOVEMENT
MUDFLOWS LANDSLIDES
Figure 7. Some aspects of geomorphic variability attributable to lithology,
structure, and mass movement along semi-consolidated and
consolidated coasts in cross section
rivers deliver sufficient quantities of sediment for the construction of extensive
spits and baymouth barriers, or where erosion of cliffs or reefs exceeds
transport of sediments by marine processes.
Chapter 2 Relevant Processes and Factors
23
24
Unconsolidated or poorly consolidated materials are found in low-lying
coastal plains and deltaic complexes. Along coasts of unconsolidated
materials, large amounts of sediment typically are available and morphologic
variations can occur rapidly. Relict geomorphic features are readily altered in
this environment. Depositional features are likely to be more numerous than
erosional features. A detailed description of coasts composed of uncon-
solidated sediments follows in a section on sediment character.
Both lithology and jointing influence the resistance of a rocky coastline to
weathering and erosion. Additional factors are susceptibility to weathering
(mechanical or chemical), hardness of the constituent minerals and cementa-
tion, the nature and density of voids, and climatic conditions. Mechanical
weathering involves the breakdown or disintegration of rock without any sub-
stantial degree of chemical change. Examples are processes such as tempera-
ture change, crystallization by salt or frost, wetting and drying, changes in
overburden, and organic activities. Chemical weathering involves the decom-
position or decay of minerals because of hydration and hydrolysis, oxidation
and reduction, solution and carbonation, chelation, and/or biochemical
changes.
In a given area, weathering or erosion may occur at different rates.
Various rock types may be more or less susceptible to erosion by waves,
tides, and currents. As a result, differential weathering and erosion may
produce uneven coastlines where headlands are formed of resistant materials
and bays occur in less resistant materials (Shepard and Grant 1947)
(Figure 8). Small-scale effects of differential weathering cause rocks to have
uneven pitting or surface characteristics. Coastal configuration at differing
scales may also be influenced by terrestrial agents that cause erosion, such as
running water, ice, wind, and groundwater.
Organisms
Marine organisms may play either a destructive or constructive role in the
formation of coastal sediment deposits. Some organisms, including species of
algae, mollusks, echinoids, worms, and sponges have the ability to bore into
rock for protection against predators or to obtain anchorage on the bottom.
The resulting weakening and breakdown of the rocks makes them more
susceptible to wave erosion. Physical and chemical weathering generally
break down and dissolve organically produced or biogenic materials more
rapidly than clastic sediments.
Biological activity also plays a constructive role in the formation of coastal
sediment deposits. Although biogenic materials are more easily destroyed
than terrestrial clastics, new sources are continually being provided. Many
organisms that inhabit the submerged part of the coastal zone contain hard
parts, usually composed of calcium carbonate. Upon the death of the
Chapter 2 Relevant Processes and Factors
Figure 8. Aerial photograph of Pta. de la Garita, Cabo de la Aguja, Columbia (Feb 1981).
A pocket beach has formed between two resistant headlands. To the right of
the headlands, waves approach the coastline at a steep angle, causing longshore
currents which transport sediments away from the headland. Photograph taken
from an altitude of 600 m; distance between the headlands is about 0.5 km.
organism, the hard materials become part of the bottom sediments. Mollusks,
calcareous algae, barnacles, bryozoa, and foraminifera are important elements
of coastal sediment deposits in many places.
In most places, mollusks are the principal organic shell contribution to
coastal sediments. Breakdown of the larger shells into sand and granule-size
material usually occurs where shells are exposed to boring organisms and the
action of waves and currents. Some organisms have segmented shells that
separate into smaller particles soon after death. Common examples of this are
certain calcareous algae such as Halimeda sp. and barnacles. Both of these
organisms are made up of numerous parts, which are composed of calcium
carbonate.
In areas of high biological production and/or low input of terrestrial
sediment, biogenic sediment particles may exceed the inorganic particles in
number. In certain environments, such as coral reef areas, biogenic material
is dominant, and sometimes the sole material type. Accumulation of biogenic
material in sediments seems to be more important in offshore areas than in
beach and dune sediment, presumably because of the higher destruction rate of
Chapter 2 Relevant Processes and Factors
shell material in the turbulent beach environment, especially where the shell
material is mixed with substantial amounts of quartz sand.
It is not uncommon to encounter shell material that has been produced in
an earlier time under different environmental circumstances than the present
(relict material). From North Carolina to Florida, relict material may be a
significant element in coastal deposits. One way in which coastal deposits
may be preserved is by secondary diagenetic changes. An example is the
formation of beach rock, which involves the consolidation of beach sand by
interstitial cement composed chiefly of calcium carbonate (Higgins 1968). For
example, the Anastasia Formation beach rock, a coquina limestone, may
outcrop in the surf zone as nearshore reefs or as a low cliff in the berm area
(Figure 9).
In addition to contributing sediment particles, several organisms are
capable of building reefs on the sea floor. Corals are the best known reef
builders and usually produce the largest reef structures. However, various
types of worms, mollusks, bryozoa, and coralline algae are also capable of
reef construction.
Figure 9. Outcrops of Pleistocene coquina rock of the Anastasia Formation on a beach in
East Florida. Erosion of such rocks contributes sediment particles to the beach
Chapter 2 Relevant Processes and Factors
Coral reefs are best developed in subtropical and tropical climates but
certain species of coral can tolerate colder water temperatures. The actual
amount of coral in a reef varies. It can be relatively small, providing a
framework that fills out with the hard parts of plants and animals that flourish
in the typical coral reef environment. Coralline algae are important in reef
construction because they form calcium carbonate crusts that help hold the dif-
ferent reef materials together.
Mass Wasting and Mass Transport
Once clastic and biogenic materials are broken apart by mechanical and
chemical weathering, they are more susceptible to downslope movement under
the influence of gravitational processes. These processes, collectively termed
mass wasting, may vary in scale, occurring either slowly or quickly in a
number of parent materials. Causes and mechanics of mass wasting are
variable, but depend in part on slope, soil moisture, and physical properties.
While most attention is given to subaerial mass wasting, submarine failures
occur on deltas and on the Continental Shelf (Prior and Coleman 1978).
The shape of failures and distribution of debris may take on a variety of
forms. Thus, in coastal settings, mass wasting may directly influence
geomorphic variability (Figure 7). Along cliff coasts, especially in unconsoli-
dated material, gravity movement is important and is often aided by wave
undercutting of the base. Waves and currents are important in removing mass
wasting debris, thus reexposing the cliff face to wave attack (Figure 8).
Mass wasting of hillslopes, whether at the coast or inland, may also fa-
cilitate sediment supply. Mass wasting directly by gravity is distinguished
from other gravity-induced movements in which the material is carried by
transporting agents such as running water, groundwater, ice, snow, and air.
Direct movement by these agents is termed mass transport, although, in
nature, mass wasting and mass transport merge into each other so that in some
cases the distinction becomes arbitrary. Abrasion or mechanical wear of
materials by solid particles transported in fluids, and corrosion or chemical
wear from the reaction of rocks with substances in water are additional
processes involved in the erosion of materials.
Materials may be transported in one of three major modes within a fluid
(dissolved load, suspended load, or bed load). The dissolved load consists of
material transported in solution. The suspended load consists primarily of fine
particles, which are entrained and maintained into the flow primarily by
turbulent mixing processes. In bed load transport, particles move by rolling,
sliding, or saltating at velocities less than those of the surrounding flow.
The great majority of material is transported from inland areas to coasts by
running water. The magnitude of sediment yield by running water is con-
2
Chapter 2 Relevant Processes and Factors
trolled by five main groups of factors: (a) precipitation and runoff
characteristics; (b) soil resistance; (c) basin topography; (d) vegetation cover;
and (e) land use. Of these, most consider mean annual precipitation or runoff
to be the most important variable. Although studies show great disparity, the
greatest sediment yields occur in semi-arid regions and very humid regions
(Knighton 1984). Only a small proportion of the sediment mobilized from in-
land areas on a given occasion will reach the coast, while most is stored
temporarily in the basin. There is large geographical variability in concentra-
tion and distribution of sediment carried from sources to the coast by running
water.
In a fluid, the entrainment, transport, and deposition of sediment particles
are often defined as functions of sediment diameter and mean fluid velocity.
In flowing water, the Hjulstrom curve indicates that the threshold velocity is
at a minimum for medium size quartz sand particles, and that higher velocities
are necessary to entrain both finer and coarser sediments (Figure 10), for
reasons to be discussed shortly. Greater velocities are required to transport
materials of similar size in wind as opposed to water (Bagnold 1941).
Velocity alone does not control the capacity of a fluid to entrain particles.
Other characteristics include the viscosity of the fluid, the nature of the fluid
motion, the character and shape of the bed materials, and the impact of
saltating or bouncing grains.
SS tf) Vv TRL
~~ Velocity
“<n
i?)
SS
E
YS
>~
FES
rs)
2
oO
>
Transportation
Sedimentation
VY
Z\- Fall
Velocity
Clay and silt Fine sand Sand Gravel and boulders
0.001 ea | eal | |
Ae) 10
0.001 0.01 0.1 100
Size (mm)
Figure 10. Conditions for erosion, transportation, and deposition of particles in water
according to Hjulstrom (1935)
Chapter 2 Relevant Processes and Factors
Fine, cohesive sediments respond differently to hydrodynamic forces than
do non-cohesive sediments. Fine sediments are made up largely of clay min-
erals with an interlayered crystal structure, and normally have a negative
surface charge. Cohesion results from inter-particle surface attractions
between clay minerals, which are promoted in sea water, and then reinforced
by organic secretions. Thus, for noncohesive sediments, the main stabilizing
force is the particle weight, whereas cohesive sediments are stabilized by
interparticle adhesion and organic binding.
The relative importance of running water, wind, ice, or groundwater in
transporting materials from inland areas to the coast varies greatly with local
conditions. Running water is most important for transporting solid and
dissolved materials where large rivers meet the coast. Locally, smaller rivers
may be important, and reworking of ancestral river deposits is also often
significant. As with running water, groundwater may be important for trans-
portation of solutes or dissolved materials. Wind is important in arid areas,
although not necessarily more important than running water. Transportation
by ice is much slower than by water and wind, so that ice is probably only
important over long-term periods at high latitudes.
Between the offshore and coastal zones, mass transport may take place by
a variety of mechanisms. Erosion and transport of offshore sediments are
chiefly accomplished by waves and wave-generated littoral currents in the
shore and upper shoreface areas. Considerable difficulties arise when attempt-
ing to apply sediment movement thresholds in oscillatory flow, as the water
particles under waves reverse their direction of flow and accelerate and
decelerate under each pulse. The threshold condition for movement appears
to be better related to the ratio between grain diameter and orbital diameter of
the water particles (Komar and Miller 1973).
Storm-generated waves and currents can effectively erode and transport
material in deeper waters of the continental shelf, and it is likely that they
play a role in modifying and moving large sediment features, such as shelf
shoals. Mass transport has both a longshore component, parallel to the shore,
and a cross-shore component, which may be onshore or offshore. Lower-
energy events mostly transport sediment onshore, while larger events transport
sediment offshore and sometimes onshore, if overwashing and overtopping
occur.
Sediment Character
Unconsolidated coastal sediments may be composed of a variety of mate-
rials, which range in size and shape, mineralogy, density, and other proper-
ties. Clastic sediments are comprised of rock detrital grains, whereas biogenic
sediments are comprised primarily of calcium carbonate grains from shells,
skeletons, and invertebrates. The characteristics of these materials account for
Chapter 2 Relevant Processes and Factors
29
30
much of the geomorphic variability of clastic shorelines and provide informa-
tion that may assist in interpreting past processes or in predicting the transport
potential of sediments.
Sedimentary particles show a range in size and are classified according to
diameter, assuming the particles are roughly spheroid in shape. These sizes
are divided into several major classes, in order of increasing diameter, being
clay, silt, very fine to very coarse sand, granule, pebble, cobble, and boulder
(Table 1). Generally, clay minerals are cohesive, being held together by
electrolytic forces. Coarser sediments, which make up the bulk of coastal
sediments, are considered noncohesive or cohesionless.
The type of sediments found in a location depends on the source and
supply of materials and the energy of the environment. If the nature of the
source and supply are held constant, coarser sediments are deposited in high-
energy environments and produce beaches of steeper slope, whereas finer
sediments are deposited in low-energy environments and are associated with
beaches of gentler slope. Mixtures of differing populations of sediments are
common, including combinations of coarse and fine, clastic and biogenic, and
differing source regions. These contribute further to the geomorphic variabil-
ity of coasts.
Sandy coastlines are predominant worldwide. Sand may be supplied by
rivers, by adjacent parts of the coasts including beaches, headlands and cliffs,
by offshore sources, or by wind. Silt and clay coastal sediments occur in
generally lower energy settings such as lagoons and back barriers. Near large
rivers (Wells and Coleman 1981a) and in glaciolacustrine settings, silts and
clays may dominate coastal materials.
Pebble and cobble coastlines, called shingle beaches in Britain, are more
common in areas of glacial and fluvioglacial sediments (Bird 1969; King
1982), in areas where coastal rock formations yield debris of appropriate size
(Bird 1969), and in localized areas where rivers deliver coarse materials to the
shore. Beaches of granule-sized particles are rare (King 1982).
Cobbles and pebbles on beaches have a variety of characteristic shapes,
including disks, rods, and spheres, which are found in characteristic zones of
the beach profile. The distribution of the various sediment shapes on beach
profiles is controlled largely by selective sorting (Bluck 1967). Contrary to
usual descriptions, marine abrasion appears not to be the predominant cause of
the disk shape, in that the largest oblate disks are found near the high tide
mark and thus are least worked by the sea.
Beaches of terrigenous origin generally have quartz as the most abundant
mineral, accompanied by varying proportions of feldspar, mica, other light
minerals, and heavy minerals. Quartz is dominant because it is the most
abundant mineral in the earth’s crust, as well:as being mechanically durable
and chemically inert (Jackson 1970). Pebble and cobble beaches have highly
varied mineralogy, depending upon the nature of the source. Clay minerals
Chapter 2 Relevant Processes and Factors
Table 1
Sediment Particle Sizes
Unified Soils Classification | ASTM Mesh No. [wi size «| PHI Size Wentworth Classification
4096.00
256.00 él
Cobble 128.00 d
107.64 Cobble
90.51
76.00
64.00 i
58.82
45.26 6
38.00
Coarse Gravel 32.00 :
26.91 d
22.63
19.00 E
16.00 ¢ Pebble
13.45 i
11.31 .
9.51
Fine Gravel d 8.00 4
6.73 é
: 5.66 ;
4.76 :
4.00 d
3.36 ;
Coarse Sand 2.85 : Granule
2:35 5
2.00 A
1.68 ;
1.41 : Very Coarse
1.19 }
Medium Sand 1.00 E
0.84 f
0.71 Xu Coarse
0.59 [
| 0.50 i
0.42 :
0.35 :
0.30 ;
0.25 A
0.210 :
Fine Sand 0.177 ; Fine
0.149 A
0.125 :
0.105 zi
0.088 fe Very Fine
0.074
0.0625 f
0.053 ;
0.044 :
Silt 0.037 ‘
0.031 :
0.0156 i
0.0078 :
0.0039 (
0.0020 101,
0.00098 Clay
Clay 0.00049
0.00024
0.00012
0.00006 Colloid
Chapter 2 Relevant Processes and Factors
32
also have varied composition, the most common being kaolinite, smectite,
illite, and chlorite.
Shell fragments, coral debris, algal material, and oolites are common on
tropical coasts and islands, in temperate regions where shelly organisms are
abundant offshore, or along coasts with calcareous cliffs. The mineralogy of
the fragments is primarily calcareous, although dolomitic, phosphatic, and
siliceous materials may be present. Most calcium carbonate grains are
biogenic since they are made up largely of shells, skeletons, and invertebrates.
In some tropical areas where the water is super-saturated with calcium
carbonate, non-biogenic precipitates of calcium carbonate called oolites may
form.
Along volcanic coasts, such as Hawaii and the north shore of Martinique,
black sand beaches of basalt and pumice may be dominant. Driftwood and
timber are common, particularly in the vicinity of lumbering areas, although
they can be found on virtually any coast. Along cliff coasts, logs may
facilitate erosion by abrasion. Other organic materials, such as peats, are
common coastal materials. They are formed in low-energy areas such as
vegetated marshes and swamps.
Characteristics of the sediments can provide clues to their origin and
depositional environments. Size analysis can help distinguish beach, dune,
and eolian flat environments (Mason and Folk 1958), and the shape, inclu-
sions, and optical characteristics of a sediment may also assist in determining
its geologic origin. The mineralogy of the materials and heavy minerals can
be used as a tracer to indicate the source or provenance of sediments. Heavy
minerals typically form a minor constituent of the original rock and have a
specific gravity greater than quartz or feldspar, with a density of
2.8 gm/cu cm being a generally accepted lower limit (Brenninkmeyer 1978).
Because of their greater density, heavy minerals respond differently to the
sorting and concentration that occur in marine processes. The utility of
various heavy minerals in determining provenance varies according to their
occurrence (common to very rare) and their stability. Statistical techniques,
including factor analysis (Clemens and Komar 1988; Komar et al. 1989), may
be useful in determining dispersal patterns and sorting of heavy minerals.
Just as rocky coasts may produce significant zones of unconsolidated
sediment because of erosion, coasts of unconsolidated sediments can develop
lithified zones because of diagenetic changes. One of the most common sec-
ondary diagenetic changes is the formation of beach rock, involving the con-
solidation of beach sand with an interstitial cement composed chiefly of
calcium carbonate (Higgins 1968). Beach rock develops best on tropical and
subtropical coasts, although it has also been reported on temperate coasts.
Most researchers think that the formation of beach rock takes place under-
ground, near the top of the water-saturated zone of the beach. Thus, beach
rock is generally not visible unless shoreline recession has occurred and the
overlying sediment has been washed away.
Chapter 2 Relevant Processes and Factors
Sediment Supply and Human Activity
Sediment supply at a given coastal segment can be a critical factor in the
morphology of unconsolidated coastal features such as beaches, deltas, and
capes. The volumetric accounting of the material lost or gained constitutes a
sediment budget. Longshore transport out of or into an area is the chief cause
of loss or gain along mainland coasts and most barrier beaches (Bowen and
Inman 1966). Other important reasons for gains include river transport, sea
cliff erosion, onshore transport, biogenic deposition, hydrogenic deposition,
wind transport into an area, and beach nourishment. Significant losses are
caused by wind transport out of an area, offshore transport, solution,
abrasion, dredging, and mining. Human modifications along the coast,
including engineering structures, dredging, and beach nourishment, can
profoundly influence the patterns and amounts of losses and gains. Human
modifications of river basins can also change the amounts and patterns of the
supply of incoming materials.
An analysis of sediment supply may involve the investigation of input at a
relatively great distance from a given project site. The relationships of supply
and transport are complex, in that littoral sediments supplied by one factor,
such as river sources, may be transported or removed by another, such as
longshore processes. A multitude of techniques including field measurements,
charts, maps, photographs and documents, numerical analyses, and computer
simulations can be employed. Sometimes, analyses can be facilitated by
breaking up the coast into a series of compartments, or cells, to assist in
identifying sources and sinks (Carter 1988). The time scale over which data
are collected is important, as sediment budgets also reflect the geomorphic
variability of coasts, and may be influenced by cyclic and noncyclic changes
and long-term trends.
Engineering structures often create obstruction to alongshore sediment
transport. Structures most commonly affecting alongshore sediment move-
ment are groins and jetties (Figure 11). Groins are constructed for the pur-
pose of obstructing or retarding alongshore sediment transport to mitigate the
effects of erosion. However, they usually cause accelerated erosion of
downdrift beaches by cutting off or reducing the amount of material that
reaches them (Figure 12). If spaced incorrectly, groins can also cause
localized erosion. Offshore breakwaters are being used in some places to
reduce the effects of wave erosion, while at the same time allowing along-
shore transport processes to continue.
Other engineering structures may create an obstruction to onshore-offshore
sediment transport. Seawalls and bulkheads are often built to protect cliffs
and dunes from being eroded by direct storm wave activity or by slumping
(Figure 13). Where cliffs are composed of unconsolidated material they are
an important source of sediment both to the adjacent shore and to the
Chapter 2 Relevant Processes and Factors
33
Figure 11. Inlet through a barrier stabilized by jetties. Note the large amount of sand
trapped by the larger jetty and recession of the shore across the inlet
Figure 12. Beach protection structures, Cartagena, Columbia (1981). Although the city is
built on the barrier beaches which protected the original Spanish anchorage, the
present shoreline suffers from a lack of sand, and the beaches are narrow or are
entirely missing in some areas
Figure 13. Beach backed by seawall near Galveston, TX. Note riprap added for further
protection
alongshore transport system. Therefore, protecting the cliffs can cause net erosion of the
adjacent and downdrift beaches.
Structures and activities in river basins also affect the availability of sediment
supply to the coast. Sediment supply can be greatly reduced by the building of dams and
reservoirs in watersheds because sands, silts, and clays are impounded behind the dams.
Therefore, when the rivers ultimately reach the coast, they transport lower sediment loads
than they did before the dams were built. As an example, recent erosion of the Nile Delta is
attributed to the construction of the Aswan High Dam (Carter 1988). Other structures, such
as revetments which reduce bank caving, and levees, which prevent rivers from overtopping
their banks, also reduce sediment supply to coastal and wetland areas. Stream diversion,
whether a natural event or by design, can cut off important sources of sediment to the coastal
areas formerly receiving sediment from those sources. In some circumstances, diversion of
streams may supply sediment to an area that formerly had been bypassed. Land-use changes
in watersheds, including deforestation, agriculture, and urbanization, may affect the fluxes
and timing of sediment supply to coasts.
Chapter 2 Relevant Processes and Factors
35
36
3 Variable Coastal Features
Coastal features can be examined at a variety of scales. As features are
examined in progressively smaller area and greater detail, the morphologic
characteristics generally reveal more rapid changes and greater complexity.
Some major coastal environments are described herein, with large-scale
morphological features being given most attention. These are examined from
a variety of perspectives including profile, plan-view, and three-dimensional.
Morphological features of smaller scale, such as bedforms, are described in
sections where they are often found, including the beach and nearshore zone
and tidal inlets.
Various types of geomorphic changes take place in varying environments
of the coastal zone, depending upon materials and which processes are locally
more important. Large-scale coastal forms generally encompass a wide
variety of environments, each exhibiting distinctive processes and responses.
For example, the sediments near a barrier island may represent shelf,
shoreface, beach/foreshore, dune, back barrier flat, and lagoon environments,
each morphologically distinctive (Figure 14). Strandplain coasts and tidal flats
contain some, but not all, of the same environments (Figure 14). Coasts
strongly influenced by terrestrial fresh water and/or sediment input, e.g., near
estuaries and deltas, also have a unique suite of processes, environments, and
characteristics.
Material type also affects coastal form. In locations where unconsol-
idated sediments are available, beaches may form if materials are predomi-
nantly sand-sized or coarser, although the processes and characteristics of
sand-sized beaches and coarse clastics are distinctive. If abundant sand supply
is available, coastal dunes may form, If there are significant storms, over-
washing, overtopping, and associated features may occur. Mudflats, marshes,
and mangrove swamps may form if materials are predominantly fine-grained.
Lithified materials coasts also show distinctive processes, with large-scale
morphologies typically including cliffs and shore platforms. Locations where
organic deposition occurs typically develop hard, shallow reefs, with forms
differing from those found in clastic sediment environments.
Chapter 3. Variable Coastal Features
BARRIER ISLAND
BACKSHORE
BACK BARRIER DUNE
FLAT
LAGOON MARSH FORESHORE/BEACH
SHOREFACE
FORESHORE /BEACH
SHOREFACE
TIDAL FLAT
TIDAL CHANNELS TIDAL MUD
TIDAL SAND FLAT
SALT MARSH \
AY. IW
HT
Figure 14. Surface and subsurface environments and variations of barrier islands, strand plain
coasts, and tidal flats
37,
Chapter 3 Variable Coastal Features
38
Beach and Nearshore Zone
Beaches are accumulations of unconsolidated sediment extending shoreward
from the mean low tide line to the inland limit of the littoral zone, where
vegetation or a change in relief begins to develop (i.e., coastal sand dunes,
beach ridges, terraces, or a cliff line) (Komar 1976). Beaches are among the
most variable coastal geomorphic features and the most widely distributed of
any of the coastal sedimentary environments (Dolan et al. 1972). Extensive
beach development occurs on low-lying coasts where great quantities of
sediment are available, primarily at barrier coasts, with the remainder occur-
ring in pocket beaches, lakes, and rock headlands (Davis 1985). Beach
sediments generally range from fine sand to cobbles. Finer materials are
present on few ocean beaches, because waves create turbulence which keeps
fine materials in suspension.
Beaches may hug the coastline or show a number of large-scale detached
forms. Barrier islands, which are totally disconnected from the mainland
shoreline, are typically fronted by beaches (Nummedal 1983), and separated
from the mainland by lagoons, wetlands, or tidal marshes. Spits are quasi-
linear subaerial landforms caused by longshore deposition in which beaches
separate from the main coastline and project into the deeper waters of estuary
mouths or bays. If a spit extends across a bay, it is known as a baymouth
barrier. Cuspate forelands are seaward-projecting accumulations of materials.
Wave refraction around an offshore island may lead to the development of a
tombolo, a beach connecting the mainland with the island.
The beach surface can be divided into two major zones, the
backshore, which extends inland from the normal high-tide level, and the fore-
shore, which is equated with the intertidal zone (Figure 2). The beach and the
nearshore zone, which extends from the low-tide level to the seaward limit of
bar-and-trough topography, are closely related but show markedly different
forms and processes.
Generally, most of the backshore consists of one or more berms or beach
ridges, which are flat to gently landward-sloping accumulations of wave-
deposited sediments. Gravel and cobble beaches may show one or more
storm ridges in the backshore. According to Carter (1988), a beach ridge is a
berm that has survived erosion, and there is no real morphological or sedi-
mentological distinction between them. In this study, two types of beach
ridges were distinguished, one which was controlled by runup, and one which
was the result of ridge stranding. The seaward limit of the backshore is
marked by the berm crest, at which the slope changes along a more steeply
inclining beach face. Eroding beaches may show a continuous upper
foreshore-to-backshore slope and a slightly concave-upward profile.
Morphologic features of the foreshore are more variable and numerous
than in the backshore. For example, the beach face slope may be inclined
Chapter 3. Variable Coastal Features
from 1 deg to 30 deg, depending upon the sediment character of the foreshore
and the processes acting upon it. Steeper beach faces generally occur with
coarse materials and in higher energy environments. A small and sometimes
subtle step, typically marked by a concentration of shell debris and/or coarse
sediments, may be present at the line where the waves plunge before surging
up the beach face. A sandbar and landward trough, known as a ridge-and-
runnel system, may also be present at times (Figure 2). The ridge-and-runnel
system is most common on _ beaches with an abundance of sand. Seaward of
the ridge near the low-water line, there may be a nearly horizontal morpho-
logic zone called a low tide terrace.
Rhythmic topography changes also occur in varying scales on the fore-
shore. Beach cusps (spacing of 10-30 m) and giant cusps (spacing of
100-200 m) are examples. Both cusp features have a similar morphology and
a non-tidal genesis, with beach cusps being related to accretionary processes
during swell conditions, and giant cusps being formed during storms under
erosional wave conditions. Spacing of beach cusps may be related to rip
current spacing, the wavelength of edge waves, and the spacing between
waves arriving at the beach from different directions. Larger rhythmic fea-
tures called beach protuberances (100 m-100 km) are characterized by subtidal
components and sandbar movements. Non-rhythmic morphologic features,
forming aperiodic protuberances, may also occur at the shoreline, often in
response to the longshore drift patterns associated with cells. Other non-
rhythmic features, such as salients, may form in sheltered areas behind rock
outcrops or offshore breakwaters.
Morphologic features of the nearshore zone include a number and variety
of stable and ephemeral subtidal bar forms. These often show relationships to
beach topography. The formation of submarine bars is favored by, but not
entirely dependent on, a gentle shoreface slope, low tidal range, ample sedi-
ment supply, and a low incidence of long swell waves. Bars are absent only
where these factors are lacking, and are less stable in shallow water than in
deeper water.
Several types of submarine bars have been recognized. They are differen-
tiated mainly on the basis of plan view shape, alignment, and continuity.
Longshore bars are the most common, consisting of a 1- to 4-meter relief
linear ridges aligned parallel to shore. Their continuity is broken only by
narrow rip channels which may migrate alongshore. The origin of longshore
bars is believed to be related to breaking waves, and most bars seem to be
located at the breaker line (Miller 1976). Where multiple longshore bars
exist, their positions are often associated with the breaker lines at high- and
low-tide stages, multiple breaker lines, or breaker positions for various wave
characteristics.
In the nearshore zone, crescentic bars are the next most common form.
They are shaped convex-seaward, and may be in-phase or out-of-phase with
shoreline protuberances. Lunate bars form a half crescent, with the bar
initially extending from the shore protuberance, then bending to a more or
Chapter 3 Variable Coastal Features
39
40
less shore-parallel orientation pointing in the direction of the longshore
current. Transverse bars are oriented perpendicular to shore and are attached
at beach protuberances.
Process-response mechanisms in the beach and nearshore environment have
been integrated into a number of distinct morphological states, ranging from
dissipative to reflective with several transitional morphodynamic regimes
(Wright et al. 1979; Short 1979; Wright and Short 1983). The system
interrelates waves, currents, morphology, sediment size and sorting, and sedi-
ment transport (Figure 15). Dissipative profiles are characterized by low
gradients and wide surf zones, multiple parallel bars, and suspended load
transport. Reflective systems have steep beach faces with surging breakers,
edge waves and widespread cusps, bed load transport, and an absence of
nearshore bars and rip currents. Intermediate regimes incorporate elements of
both domains, progressing through the transitional intermediate states from
longshore bar and trough to rhythmic bar and trough, to traverse bar and rip,
to ridge and runnel.
On predominantly sandy coastlines, beaches and the nearshore region con-
tinually respond to ever-changing winds, waves, tides, and currents by
showing adjustments in profile and morphologic features according to beach
type and environmental conditions. The day-to-day changes can be notable.
On the beach and nearshore, when wave energy is low or moderate, there is
overall net onshore transport and constructional activity.
As energy increases, long-period, steep-profile storm waves may produce
considerable erosion of the beach and nearshore environment. Longshore
bars, for example, can shift position quickly, moving offshore at rates of 30 m
daily. In response to less steep waves, bars move more slowly (Birkemeier
1985; 1987). Many types of morphologic changes respond to tidal cycles.
One example is the migration of erosion and accumulation zones on a diurnal
or semidiurnal basis with tidally driven water table changes (Duncan 1964).
In addition to the day-to-day fluctuations in beach morphology, longer term
cyclic and unidirectional effects occur on sandy beaches. The principal cyclic
effects are usually related to seasonal variations in dynamic factors, which in
turn create distinct cyclic changes in beach morphology and sediment char-
acteristics. Thus, survey data should ideally cover different seasons in order
to indicate the range of values that may be encountered during a year.
During periods or seasons when frequent or severe storms occur, (typically
winter), sand is eroded from the beach, causing the profile to become lower
and narrower. Offshore bars may develop or enlarge due to the addition of
material from the beach. With the return of fair weather conditions, the beach
tends to recover and all or a part of the material in offshore bars may return
to the beach. Occasionally, overtopping and overwashing occur on sandy
coastal barriers, when water and sediment may pass over the barrier crest and
settle on the landward side. Overwashing events are generally noncyclic,
preventing the beach from recovering to its initial condition. It is rare that
Chapter 3. Variable Coastal Features
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Chapter 3 Variable Coastal Features
42
material moves from the back to the front of a barrier. However, seaward-
flowing currents may cross barriers if landward water levels become elevated,
a phenomenon sometimes termed the storm surge ebb-residual flow (Hayes
1967).
Coarse-grained clastic beaches are distinctive in terms of their grain size,
wave energetics response, and profile characteristics, but are also distinctive
in sediment transport and coastal evolution. Such beaches are usually morph-
ologically reflective, dominated by plunging breakers with no surf zone,
strong longshore bedload transport in the swash zone, and seepage as a major
process (Carter 1988). While sand beaches undergo tidal and seasonal
changes, gravel beaches have arrested swell profiles, which are maintained
through most storm periods but can show aseasonal responses. Coarse clastic
beaches may show alongshore grading. Sediment transport processes are
poorly understood in these cases, but are likely related to the wave parameters
as on sand beaches.
Longer term cyclic and noncyclic events affecting beach and nearshore
morphology may extend over a period of decades or centuries. Variations in
climatic patterns, wave characteristics, sediment supply, and relative sea level,
as well as the lasting effects of coastal engineering works, inlets, and extreme
events may cause long-term cyclic and noncyclic changes. Studies of histor-
ical maps, charts, and aerial photographs are valuable to show relatively long-
term trends of such factors as shoreline or shoal migration, and bathymetric
changes that should be considered in project design.
If a beach has been subject to environmental forces for an adequate period,
the beach profile will respond to both the long-term and short-term changes in
a manner that tends to restore an equilibrium profile. In equilibrium, the
amount of sediment deposited by waves and currents will be balanced by the
amount removed by them. Some researchers have proposed that the slope of
natural profiles fits the following equation: h(x) = Ax™, where A is a scale
factor primarily dependent upon sediment characteristics and m is a shape
factor, proposed to be 2/3 (Bruun 1954; Dean 1977; Dean and Maurmeyer
1983). While the equilibrium profile may be disturbed by unusual and
exceptional conditions, such response models can assist in predicting future
shoreline positions and in interpreting shoreline history.
Over historic, and particularly over longer time scales, shoreline response
to sea level rise may follow one of three generalized models (Figure 16). The
erosional response, or Brunn Rule model, assumes offshore dispersal of
eroding shoreline materials such that the rates of sea level rise and sea bed
rise are commensurate. In the rollover model, a transgressive barrier moves
landward at a rate controlled by the rate of sea level rise (Dillon 1970). The
barrier overstepping model suggests that the barrier may be drowned, remain-
ing on the shoreface, as sea level rises above it.
Chapter 3 Variable Coastal Features
(A) EROSIONAL RESPONSE (The Bruun Rule)(Offshore transport)
el Rie
Eroded <
volurte. .
“Deposited volume «oe
Close out
|.____________ x
(B) ROLLOVER (transport)
ke RL—+
(C) OVERSTEPPING (No transport)
Figure 16. Three models of shoreline response to sea level rise:
(a) Erosional response model/Brunn rule assumes off-
shore dispersal of shoreline materials; (b) Island rollover
model assumes barrier migrates landward according to
rate of sea level rise; (c) Barrier overstepping model
assumes submergence in place with barrier remaining on
shoreface (after Carter 1988)
43
Chapter 3 Variable Coastal Features
44
Lithified Coasts: Cliffs and Platforms
Rocks and sediments that are semi-consolidated or consolidated may form
vertical or steep cliffs that constitute a marked break in slope between the
hinterland and the shore. If marine processes are given adequate time, the
cliff may be fronted by a gently sloping shore or intertidal platform where
debris may rest (Figure 17). The slope and recession rates of the cliff faces
depend on a number of terrestrial and marine processes, as well as the
geotechnical properties of materials comprising them, including grain size and
degrees of consolidation. Recent volcanic or loosely consolidated Quaternary
sediments show the greatest erosion rates (Sunamura 1983).
Marine processes remove cliff materials directly by attack at the cliff base,
and indirectly by undercutting, causing failure or mass wasting of the overly-
ing rock. The debris produced by these processes may then be transported by
a variety of marine processes. Resulting accumulation, erosion, or cliff
modification depends on the relationship between the relative rates of supply
and removal at the shoreline (Pethick 1984).
If marine processes are capable of removing slope debris much faster than
the rate of debris supply, then, in most cases (depending upon the structure
and lithology of the rock) the slope will retreat parallel to itself. When the
supply of debris far exceeds the capacity for removal, basal debris will
accumulate at the angle of repose (the maximum angle of slope at which loose
cohesionless material rests). Between these extremes, a variety of slopes
ranging from debris angle of repose to vertical faces are possible.
Typically, profiles of steeply sloping shorelines are highly reflective,
whether the materials are consolidated or unconsolidated. Currents are shore-
parallel and unidirectional, and bars are generally absent. Longshore sediment
transport rates are high, and most materials are moved away by currents.
Thus, along cliff coasts, the rates of supply must generally exceed those of
lower slope coasts to produce beaches.
As with beaches, lithified coasts show irregular shorelines. Headlands and
bays may be related to the submergence of a hilly or mountainous topography
by arise in sea level. Differential erosion and weathering may also lead to
the development of alternating headlands and bays on rocky cliff coasts. Once
formed, the presence of prominent headlands on rocky coasts influences waves
and tides, sediment dispersal and deposition, and shoreline evolution.
Headlands influence refraction, causing wave ray convergence. Recent
research has shown that headlands may protrude into tidal flows, causing tidal
eddies, and in some cases providing a stagnation zone where offshore shoals
can form. These, in turn, can alter the wave energy environment, creating
nonuniform wave attack, and altering the spatial patterns of cliff erosion
(Carter 1988).
Chapter 3 Variable Coastal Features
SHORE
PLATFORM
PLUNGING CLIFF CLIFF WITH CLIFF BASE BEACH
SHORE PLATFORM
Figure 17. A variety of cliff morphologies in cross section. Plunging cliff is steeply sloping
and possibly shows a notch. Cliff with shore platform may develop from
increased notch development and mass movement of overlying material. Cliff
base beach may develop from cliff with shore platform if sediment supply
exceeds transport of materials
Coasts of consolidated materials resist wave attack because of compressive,
tensile, and cohesive properties. Thus, because they are primarily erosional
rather than depositional in nature, they show distinctive morphologic features
in comparison with unconsolidated coastal sediments. Sustained wave attack
may etch notches in rock, the deepest notches occurring where dynamic
pressures are greatest. Multiple notches may form if there are various
dynamic wave horizons, most likely associated with changing water levels.
Notches may become sea caves along zones of structural weakness. Varia-
tions in resistance may also lead to the development of sea stacks and sea
arches seaward of the cliffs.
Coastal slope recession typically leaves behind a shore platform, a surface
that is quasi-horizontal or of low slope angle, marking the lowest level to
which the erosion reached. Maximum width of such platforms is about 1 km
(Flemming 1965), and their profiles may be linear, concave, or convex. A
variety of processes act on platform surfaces, including abrasion, mechanical
wave erosion, weathering, and solution, which vary depending upon the
nature of the processes, rocks, structure, tides, age, and history.
Abrasion from sand and shingle is concentrated on the upper shoreward
section of the platform since these abrasive materials are generally absent on
the lower levels (Robinson 1977; Trenhaile 1980). Considered by some to be
the most important, mechanical wave erosion may assist in breakup and plat-
form surface lowering by wave shock, wave hammer, air compression, and
other forms of dynamic pressure release (Trenhaile 1980). Several weathering
processes may also be involved, particularly those associated with alternate
45
Chapter 3 Variable Coastal Features
46
wetting and drying of the platform surface. This water-layer weathering
includes physical processes such as expansion, swelling, and salt
crystallization, and chemical processes such as hydration and oxidation. Wave
erosion may proceed more rapidly in weathered material, with subaerial pro-
cesses at the water table level possibly coming into play. In tropical calcare-
ous areas, solution of rocks and bioerosion appear to be important processes
in shore platform development.
While the complexities of platform morphology are not well understood,
the shore platform functions as a dissipator of wave energy and as a pathway
for sediment transport at the cliff edge. The platform slope may thus influ-
ence the cliff, in that steep slopes would create increased longshore sediment
transport and promote cliff recession, whereas gentle slopes would not allow
sufficient longshore transport and beach progradation would result (Bradley
and Griggs 1976). The critical platform slope would be dependent upon the
shear stress at the bed by wave forces and the strength of materials making up
the shore platform.
Organic Reefs
Reefs, which are formed mainly from biogenically produced carbonates,
are important structures in tropical waters. Like lithified coasts, they form
hard bottoms, but several unique forms develop in such environments. Sever-
al types of marine organisms are capable of precipitating calcium and other
carbonates in skeletal and non-skeletal forms, but reefs of coral skeleton are
the most common. Corals grow most successfully in shallow, warm, mud-
free waters of moderate salinity, characteristically between latitudes of 30° N
and 30° § where such conditions occur.
Four major forms of large-scale reefs have been identified: (a) fringing
reefs, (b) barrier reefs, (c) atolls, and (d) table reefs (Stoddart 1969).
Fringing reefs are connected with the land, whereas barrier reefs are separated
from land areas by a lagoon which may be several kilometers wide. Minor
reef shapes include ring-shaped forms on banks and shallows, and reef knolls
or patch reefs growing in lagoons. Like barrier reefs, atolls rise from deep
water, enclosing a lagoon, but unlike barrier reefs, they do not enclose land
within them. Table reefs rise from the sea floor as a shallow bank, being
capped with reef growths that appear different from the other forms.
The reef surface has a high roughness, and will change local
morphodynamics by affecting the energy of incident waves and by increasing
turbulence. Reef form and structure are considered to be linked largely to
wave climate, and may show process gradients. Studies on the Grand
Cayman reefs show that the outer reef is dominated by wind-driven currents,
the inner by high-frequency waves, and the lagoon by deepwater waves and
tides (Roberts, Murray, and Suhayda 1975).
Chapter 3 Variable Coastal Features
Coastal Dunes
Coastal dunes (Figure 18) occur where there is a sufficient sediment
source, onshore winds of sufficient velocity to transport the available material,
and a flat or low-relief space inland of the coastline to accommodate dune
formation. Sources of dune material are usually the dry portion of sandy
beaches. The wider the beach, the greater the surface area exposed to wind
transport and, consequently, the greater the volume of material available to
form dunes. Flat, dissipative shorelines, where large volumes of sand are
stored subaerially at low water, are highly suited for foredune development
(Short and Hesp 1982).
Figure 18. Partly vegetated coastal sand dunes. Eastern Alabama near Florida/Alabama
state line (March 1991). This area was devastated by Hurricane Frederic in
1979
Chapter 3. Variable Coastal Features
47
48
Tide range and type can be of considerable importance in beach-dune
interactions. On beaches where tide ranges are high, more sand is uncovered
at low water, effectively increasing the size of the source area. Tide type is
also important because the wind velocity necessary to move sediment is
significantly increased when the sediment is moist or wet. Because of this,
more sediment is available in areas where diurnal tides occur, since a longer
period of time is available for the foreshore sand to dry out between high tide
stages.
Effective transportation of sediment by wind occurs when the wind reaches
a threshold velocity that is determined not only by sediment characteristics,
but by moisture content, slope, radiation and energy balance factors, chemical
precipitates, and vegetation (Carter 1988). The threshold velocity is signifi-
cantly increased for moist material. Also, the seaward slope of the beach
surface increases threshold values in accordance with the steepness, because
the particles must move upslope to reach the dune area. Sand transport from
the beach to dune areas occurs only when wind blows in an onshore direction,
whereas sand transport from major inland sources occurs only when wind
blows in an offshore direction. Thus, the frequency of onshore and offshore
winds, their relation to local sources, and their velocity, are important factors
in dune development.
Dune formation requires an open space inland of the coastline that can be
reached by windblown sand from the beach. A relatively high cliff or steep
slope at the coastline can prevent dune formation by blocking the transport
path. In such cases, windblown material may accumulate at the base of the
cliff or slope, but this material will be periodically eroded during high water
levels, and it will develop into true dunes.
The stability of dunes varies greatly and depends primarily on the amount
of vegetation cover. Dunes found in arid climates are usually not vegetated
and tend to be mobile. Coastal dunes in non-arid climates are likely to
support some vegetation cover and be more stable. However, unvegetated and
thinly vegetated dunes can occur in any climate. Colonization of dunes by
vegetation not only depends on whether an area has sufficient moisture, but
whether the grasses and other plants are salt-tolerant and can respond to
conditions of rapid sand accumulation. The types of dune grasses found in an
area show spatial variety according to the types of species in an area, and
rapid temporal successions are often present (Carter 1988; Chapman 1964;
Goldsmith 1985; Woodhouse 1978).
Vegetation cover is a factor in the stability of dunes because the plants can
both decrease the mobility of sediments and increase the likelihood of deposi-
tion by changing local aerodynamic conditions. Many dune plants have long
roots, rhizomes, and runners that help hold sand in place (Figure 19). The
presence of dense vegetation, in turn, at normal wind speeds can displace the
aerodynamic boundary of the wind velocity profile upwards. This process
then provides a net downward momentum flux, which promotes sediment
trapping.
Chapter 3 Variable Coastal Features
Figure 19. Rhizomes help hold sand in place and spread the colonization of dune grasses.
Eastern Alabama near Florida/Alabama state line (March 1991)
Because dunes are effective in sediment stabilization and trapping, dune
vegetative cover and form are interrelated and can be classified as such (Short
and Hesp 1982). Densely vegetated dunes are associated with fixed, shore-
parallel dune ridges. As vegetation decreases, dune patterns range from
discontinuous ridges to hummock dunes to small blowouts. Minimally
vegetated dunes show residual knolls, barchanoid forms with crescent shapes
and downwind horns, and transverse blowouts or hollows.
Dune vegetation can be damaged or destroyed by various diseases and
natural and human-induced disturbances. Climatic and meteorologic stresses,
particularly droughts and storms, fire, grazing by wildlife and domesticated
Chapter 3 Variable Coastal Features
49
50
species, and foot and vehicular traffic can alter the morphologic and ecologic
conditions of dunes.
Because dunes help protect inland areas from storm damage, many
communities promote dune stabilization and protection. For dune
construction, beach nourishment is often practiced in conjunction with mea-
sures to stabilize and trap sediments, (e.g., fencing, vegetative planting, or the
placing of other obstacles). These measures, as well as the construction of
walkways to reduce trampling, are also used for dune stabilization and
protection.
Lithified or fossil dunes occur in some places where there are calcium
carbonate particles in the dune material. Climatic factors promote leaching
and reprecipitation of calcium carbonate, which may allow dunes to lithify
under favorable conditions. Modern coastal dunes that have become lithified
occur largely in tropical climates where there is a high level of calcium
carbonate in the coastal sediments and alternating wet and dry periods.
Back Barrier and Lagoons
During storms and high water levels, the sea may breach a dune ridge,
bringing sediment from the coastal area further inland. Some scientists call
the phenomenon overwash, and the product is called washover (Carter 1988).
Overwashing may result in a distinctive set of breach-throat-fan landforms,
forming a washover channel through the dune and a washover fan. This
washover fan develops on the landward side of a barrier and spreads over
parts of the backshore, back barrier flat, back barrier marsh, or shallow
lagoon (Figure 20). Storm frequency, overwash volume, dune susceptibility,
and barrier height are important factors in the development of washovers.
Low-lying or low-profile barriers in areas of frequent, severe storms have
numerous washovers. Storm surge ebb-residual flow, which occurs more
infrequently than overwash, may result in seaward currents and landforms.
Washover channels are distinguished from inlets in that their elevation is
above mean sea level. The patterns of breaches may be related to a combina-
tion of marine or non-marine processes. Washover deposits provide an
important mechanism by which marine transgression may take place, not just
for sand-dominated, but also for gravel-dominated barriers (Carter and Orford
1984). Overwash features are particularly common in the Gulf of Mexico
coast and eastern seaboard of the United States. These areas experience
severe extratropical and tropical cyclones with some frequency.
Coastal lagoons are shallow water bodies, often running parallel to the
coast and connecting to the open sea with an inlet. Lagoons differ from tidal
flats in that they remain water-filled even at low tide and are separated from
the open sea by sand bars, barrier islands, or reefs. Lagoons have been
Chapter 3. Variable Coastal Features
WASHOVER
re
ade Z INLET ae
FLOOD-TIDAL
SHOALS
\ Gp \ BARRIER
: \ BEACH
COMPLEX
Figure 20. A three-dimensional view of some features commonly associated with a
barrier island system, including the back barrier, overwash fans, and
lagoons
classified according to hydraulic balance, where inflow is equal to, greater
than, or less than outflow. The volume of water being exchanged is known as
the tidal prism (Carter 1988). The salinities of lagoons are highly variable,
depending upon water exchange with sea water and the amount of inflowing
fresh water. Sediment brought into lagoons may be washed over from the
barrier island, blown into the lagoon from the barrier island, introduced by
tidal currents through inlets, or transported from the mainland areas by rivers.
Generally, the coarsest sediments are found closest to the barrier.
Mudflats, Salt Marshes, and Mangrove Coasts
Mudflats, despite their name, are not entirely flat, nor do they consist
entirely of mud. They occur predominantly in areas of medium to large tidal
range, areas sheltered from the effects of wind-driven waves, or in areas of
abundant suspended sediment supply (Pethick 1984), including in the vicinity
of deltas. Mudflats show a marked break in slope about mid-tide level, below
which the surface slopes steeply toward the low-water mark. Moving seaward
and downslope, sediment size increases, with upper mudflats being replaced
by sandy mudflats at slightly lower levels. These sandy mudflats in turn
change into more steeply sloping sand flats below mid-tide level. Fine-
Chapter 3 Variable Coastal Features
5
grained sediments may be supplied from marine, coastal cliff, fluvial, or
estuarine sources.
Mudflat morphology is related to tidal and sediment processes, and the
break in slope at mid-tide generally reflects the position of the maximum tidal
velocity (Pethick 1984). The upper part of the mudflat surface progressively
increases in height due to the accretion of sediments, so that the period of
inundation of each tide is successively reduced. Eventually, the mudflat may
become exposed long enough to allow vegetation to colonize, leading to the
development of salt marshes.
Salt marsh development usually begins with the deposition of mud on a
sand surface followed by the establishment of algae salt-tolerant plants like
Spartina Patens, Spartina Alternifora, and eelgrass near the high-water mark.
The vegetation and seaweed may assist in trapping increasing amounts of
sediment. Increased vegetative sediment trapping leads to the upward and
outward building of hummocks, and to reduced wave heights and energies.
Rates of marsh sedimentation are controlled by sediment availability and
vegetative trapping, and also by the magnitude and frequency of various
factors affecting water level elevation, including waves, tides, and surges.
With increasing elevation, however, there will be decreased frequency of
inundation, and thus reduced rates of upward accretion during storms.
Salt marshes are well-developed during periods of relative sea level stabili-
ty, and typically occur on marine delta plains, behind barrier beaches, in
depressions, embayments, and other irregularities of the coast. Salt marshes
trap muddy sediments in low-energy tidal situations along protected sections of
extratropical coasts, comprising 1- to 2- km bands along the Atlantic and gulf
coasts of the United States. Numerous organisms are uniquely adapted to
such conditions, and the salt marsh substrate records contain many details that
are of significance in paleoecology and environmental reconstruction.
Mangrove swamps occupy Settings similar to salt marshes, except that they
occur in lower latitudes, between 30 deg N and 30 deg S. Mangroves include
several species of low trees and shrubs, and are characterized by an entangle-
ment of arching prop roots that facilitates trapping of fine sediment.
Typically, they are composed of higher amounts of organic debris than
marshes. Mangrove growth is favored by tidal submergence and high tidal
range, low coastal relief, saline or brackish water, abundant fine sediment
supply, and low wave energy. The most notable area of mangrove develop-
ment in the United States is in southwest Florida.
Estuaries
Estuary definitions vary, but all estuaries share several important attributes.
They are semi-enclosed water bodies in which tidal exchange and fresh water
Chapter 3 Variable Coastal Features
from land drainage combine, typically resulting in hydrodynamic, turbidity,
and salinity gradients. In contrast with deltas, estuaries occur at the mouths
of rivers that have low sediment loads in comparison with dissipative forces
(Nichols and Biggs 1985). Lagoons behind barrier islands are also classified
as estuaries.
Estuaries may develop under a variety of climatic and topographic condi-
tions, including valleys and coastal embayments that have been submerged.
Many estuaries were formed mainly during the most recent deglaciation and
associated sea level rise. These include most of the coastal plain estuaries,
some of which have been closed by barrier beaches. Fjords are a special class
of estuaries created by the scouring action of glaciers. Fault-block estuaries
may be controlled by local or regional structure.
Estuaries function mainly as sinks or traps, although those that are largely
filled may be sources of sediment. Their long-term survival depends on
changes in the volumetric capacity for storage (due to eustatic and tectonic
factors) and on sedimentation rates from inland and coastal sources. Estuarine
sediments are derived from a number of sources including the watershed, the
Continental Shelf, local erosion, biological activity, and the atmosphere.
Sedimentary processes in estuaries are controlled by tides, waves, and meteo-
rological forces, as well as river inflow. Within an estuary, the processes
may be dominated by estuarine-fluvial, estuarine, or estuarine-marine activity.
As in other parts of the coast, estuaries show temporal variations with cyclic
and noncyclic processes, and spatial variations in process, material, and form.
Estuaries have been classified according to the mixing processes caused by
the density differences between fresh- and saltwater masses (Pritchard 1967).
Salt wedge estuaries are highly stratified, with fresh water from river dis-
charge floating over the denser saltwater, a condition manifested by near-
horizontal isohalines. The freshwater layer thins oceanward, and vertical
advection is the primary mechanism for mixing across the freshwater/saltwater
interface. A partially mixed estuary shows increased tidal influence, to the
point where river discharge does not dominate circulation. Mixing is caused
by both vertical advection and the increased turbulence associated with tidal
currents. The differences between surface and bottom salinities are approx-
imately constant over the estuary, and the isohalines are at an angle. A fully
mixed estuary is vertically homogeneous because tidal mixing eliminates
vertical density stratification.
Shoreface
The shoreface is just seaward of the surf zone, and appears as a concave-
upward surface with a slope on the order of 1:200 (Niedoroda, Swift, and
Hopkins 1985). The shoreface configuration, particularly the upper part,
plays an important role in the modification and transformation of waves
Chapter 3 Variable Coastal Features
54
approaching the shore. In addition, data from many areas suggest that under
certain circumstances, there is an interchange of sediments between the upper
shoreface and the beach. Although the interchange occurs on a seasonal basis,
it may be unidirectional at times.
Because of the cost and difficulty of obtaining data and sediment samples
from offshore areas, less is known about the shoreface zone than the adjacent
shore and coast. However, repetitive profiles indicate that shoreface
morphology is variable over the long term (Moody 1964), and that episodic
sediment transport, with suspension of sediments at least 1 m above the sea
floor, occurs in response to changes in waves and currents (Young et al.
1982; Vincent, Young, and Swift 1983).
Everts (1978) analyzed 49 composite shoreface profiles based on 441 mea-
sured profiles from the Atlantic and gulf coasts of the United States. Of the
49 composite profiles, only three, all from northwestern Florida, did not
contain a definable shoreface slope. In general, the profiles show the shore-
face to have a concave-upward slope and to be significantly steeper than the
usually planar shelf floor, perhaps representing a cutoff point of significant
active modification of the profile by waves and currents.
Shoreface variability is more pronounced on the upper shoreface because of
the decrease in wave and current forces with increasing depth. The most
pronounced short-term effects appear to be seasonal, with the more energetic
winter regimen tending to move material from the beach to the shoreface and
summer fair weather conditions tending to move material onshore. Lower
shoreface deposits are disturbed less often and probably become active only
during major storms.
On many transgressing barrier coasts, the barriers are overriding their own
back-barrier deposits, which may crop out on the beach or the shoreface.
Evidence of outcropping back-barrier deposits on transgressive coasts include
blocks of salt marsh peat and shells of back-barrier fauna such as Crassostrea
virginica (Gmelin). Most back-barrier sediment is fine-grained and tends to
move rapidly offshore to deeper water where it is more stable. Coarser sand
may also occur in back-barrier deposits in the form of storm washover
deposits and flood-tidal shoal complexes adjacent to relict inlets. In most
cases this material was originally derived from beach sediments moving in the
alongshore drift or from relict river channel deposits. Thus, these deposits
are more stable and are not likely to increase shoreface recession rates.
Usually, shoreface areas are primarily composed of unconsolidated sands.
However, many shoreface zones are underlain by consolidated material such
as rock or reefs, glacial till, or clay. These shorefaces may be more stable
and may not follow the equilibrium profiles of primarily depositional shore-
faces or of those underlain by ancient unconsolidated material. Admixtures of
silt and clay are not uncommon, especially on the lower shoreface, where
outcrops of fine-grained back-barrier deposits often occur on transgressive
coastlines.
Chapter 3 Variable Coastal Features
Generally, sediment grain size of shoreface deposits decreases in an
offshore direction because of wave energy distribution along the profile.
Exceptions occur where coarse materials that occur in deeper shoreface areas
are left as finer sediments and moved onshore, or where outcrops of relict
substrate material are exposed on the sea floor.
Inlets
An inlet is a small, narrow opening, recess, or indentation into a coastline
or a lake through which water penetrates into the land (Bates and Jackson
1980). Although inlets range in size from the narrow short breaches in sandy
barrier islands to the wide entrances of major estuaries, most geologic studies
concern tidal inlets, which are interruptions in barrier beaches maintained by
tidal flow (Fisher 1982). Tidal inlets are most characteristic of sand-domi-
nated barriers, and may originate as natural interruptions in a developing
barrier beach or baymouth spit, or as breakthroughs caused by storm waves
(Fisher 1982). Gravel-dominated barriers tend to lack inlets and tidal passes
because they have greater structural stability and more seepage than do sandy
barriers (Carter and Orford 1984).
Tidal inlets usually consist of a gorge or throat, and several shoals includ-
ing a shallow one flanking the gorge, a landward flood-tidal delta shaped
mainly by flood-tidal currents, and a seaward ebb-tidal delta shaped mostly by
ebb-tidal currents and waves. Sand in the alongshore drift system, which is
intercepted by the inlet tidal currents, supplies the inlet shoals (Figure 21).
Nevertheless, some material may bypass the inlet. Morphological features
associated with tidal deltas include small tidal spits and topographically high
semicircular ridges, which extend across the breadth of the sandbank as flood
or ebb shields (Hayes 1980).
Inlets exchange water between the ocean and back barrier during each tidal
cycle. Therefore, several aspects of inlet morphology are related to tidal
processes. Inlet spacing, for example, decreases with increasing tidal range,
and inlet migration is influenced by tides and the quantity of littoral drift.
Microtidal barrier inlets tend to be widely spaced and ephemeral, migrating
rapidly with the longshore drift direction. The primary process is by erosion
of the updrift margin of the inlet and deposition on the downdrift margin
(Galloway and Hobday 1983). Deeper mesotidal inlets are less subject to
longshore migration, especially if they are incised into harder underlying
strata. At some sites, updrift inlet migration has been noted (Aubrey and
Spear 1984; Carter 1988).
Variations in tidal delta morphology can also be related to differences in
tidal range, and thus the tidal prism, and to differences in wave-energy flux
impinging upon an inlet (Boothroyd 1985). Microtidal areas are thought to
Chapter 3 Variable Coastal Features
55
56
Figure 21. Aerial view of unstabilized barrier inlet showing shallow parts of the flood
and ebb tidal deltas
Chapter 3. Variable Coastal Features
have poorly developed ebb-tidal deltas and relatively larger flood-tidal deltas
because of the dominance of wave energy over the small tidal prism. Along
mesotidal areas, ebb-tidal deltas are more prominent, but are more elongated
and extend farther seaward in areas of lower wave energy.
On a smaller scale, variations in bedforms, or deviations from a flat bed,
and accompanying sedimentary structures are associated with inlet hydrody-
namics including the effects and interaction among tidal currents, wave char-
acteristics, and longshore drift. Bedforms show varying wavelengths and
amplitudes, and have been divided into categories largely on the basis of
wavelength. Ripples are small bedforms with spacings to 60 cm, which can
be generated by both waves and currents.
In the past, terminology for large-scale bedforms has been confusing and it
has recently been suggested that Jarge bedforms be called subaqueous dunes
(Ashley 1990). First-order descriptors of such subaqueous dunes include size
and shape. Descriptors based on spacing include small (0.6-5 m), medium
(5-10 m), large (10-100 m), and very large (> 100 m) dunes with cor-
responding heights. Shape is distinguished by two-dimensional and three-
dimensional descriptors. Second-order descriptors should be used where
feasible to characterize superposition (simple or compound bedforms) and
sediment type (size and sorting). Third-order descriptors characterize bedform
morphology, bedform behavior, and flow.
Bedforms are sensitive to flow velocity and somewhat independent of
depth, which allows them to serve as a powerful tool in estimating flow
velocities in estuaries when field current measurements are not possible
(Boothroyd 1985). The shape of bedforms can also vary in response to
increasing flow strength (Hayes and Kana 1976). The orientation of these
shapes and associated slipfaces also provides clues to flow direction.
Inlet stability plays an important role in coastal geomorphic variability.
The effects of inlets on coastal hydraulic and sedimentation patterns may
extend to areas lying some distance from the inlet itself. Historical studies
have shown that barrier inlets are ephemeral features, which may be closed or
created at susceptible places by storm overwash during the course of a single
storm. Newly breached inlets may be temporary or may be maintained by
tidal currents and may persist for many years. Inlet shoals also are not fixed,
and changes in form and dimensions occur as a result of varying currents,
waves and sediment supply factors.
Barrier inlets and associated shoals are of great importance in barrier
sedimentation because they act as sinks for sediment in the longshore transport
system. The opening of an inlet can thus greatly reduce downdrift sediment
supply by trapping large amounts of sediment moving in the longshore drift
pattern and storing it in inlet shoal complexes. This loss of nourishment to
downdrift beaches can result in serious erosion and shoreline regression as the
sediment supply decreases. Inlet closure can restore downdrift sediment
supply and ebb-tidal delta materials may gradually return to the alongshore
Chapter 3 Variable Coastal Features
57
58
transport paths, but the flood-tidal delta materials remain virtually undisturbed
in the lee of the restored barrier.
Many barrier inlets are important navigation channels, affording access to
back-barrier lagoon complexes from the open sea. For this reason, it has
become common practice to stabilize inlets and thus prevent migration and
reduce shoaling of main channels with sediment. The chief means of stabili-
zation has been the building of jetties and structural stabilization of the banks
of the inlet throat. Since the jetties partly or wholly block alongshore
transport, they may effectively trap some sediments that would formerly have
migrated across the ebb-tidal shoals and reached the downdrift shore. Thus,
jetties may create serious sand starvation in downdrift areas.
In recent years, various methods have been adopted to artificially bypass
sand in inlet areas to prevent its loss into the inlet-associated shoals or its
accretion on the updrift side of jetties. All require a detailed knowledge of
local sediment transport and rates and pathways to materially affect inlet navi-
gation, yet emulate the natural sediment transport processes.
Shelf Shoals
Large ridge-like shoals with a relief of up to 10 m or more that extend for
tens of kilometers are common features of the continental shelf. They are
especially well-developed and numerous in the Middle Atlantic Bight region,
where extensive shoal fields occupy much of the shelf area. Similar shoals
have been described on the shelf off Argentina and in the North Sea off
Germany (Swift et al. 1978). Other shoals occur on the Mississippi River
delta plain (Penland et al. 1989).
Shoals have attracted considerable attention because of questions regarding
their origin and development and because most that have been investigated
contain large amounts of clean fine- to coarse-grained sand and gravel poten-
tially useful for beach fill or construction aggregate (Anders and Hansen
1990). Only a small number have been investigated in any detail as yet, using
methods such as seismic reflection, profiling, and coring (Duane et al. 1972;
Ludwick 1975; Coleman, Berquist, and Hobbs 1988; Meisburger and Duane
1971; Meisburger and Field 1975; Meisburger and Williams 1980; 1982).
Much remains to be learned about the origin, nature, sediment characteristics,
and variability of shelf shoals.
Linear shoals on the Atlantic Shelf exhibit at least 3 m of relief between
the crest and the surrounding surface. Two types are recognized: shoreface-
connected and isolated (Duane et al. 1972) (Figure 22). Shoreface-connected
shoals show a seaward excursion of the 10-m depth contour, and isolated
shoals occur farther seaward on the shelf floor. Isolated linear shoals are
thought to have originated as shoreface-connected shoals during the Holocene
Chapter 3 Variable Coastal Features
|
74°10
Harvey if
Cedarsf
Contours in Fathoms
SCALE
5
Brigantine
Figure 22. Linear shoals on the New Jersey coast. Note the abundance of shoreface-
connected shoals throughout and the isolated shoals which are most abundant off
the Brigantine area (from Meisburger and Williams 1982) ~
Chapter 3. Variable Coastal Features
S}s)
60
transgression that were detached by coastal retreat as sea level rose and
flooded the shelf. Though nearshore processes were responsible for their
formation, isolated shoals are maintained and modified by storm-generated
shelf currents and waves.
Over 200 large shoals have been identified on the Atlantic Shelf, showing
modal depths over the crest of 6 to 9 m, 12 to 15 m, and 24 m, mean shoal
axis azimuths of 32 deg, and northward-opening angles of 10 to 35 deg
between the shoreline and shoal axis (Duane et al. 1972). Seismic reflection
profiles indicate that these shoals rest on a near-horizontal surface of the shelf
floor. Cores of shoal material are primarily composed of mud-free, well-
sorted medium sand or sand and gravel mixtures. In many cases, cores pene-
trating the shoal base have recovered mud, peat, and/or shells having a
radiocarbon age of early to mid-Holocene.
Arcuate-shaped shoals, which occur in coastal areas, may be associated
with estuaries or capes (Duane et al. 1972). Shoals may form near the
mouths of estuaries and sounds where littoral drift material is intercepted and
distributed by tidal currents. Cape-associated shoals (Figure 23) occur off
cuspate forelands where convergence of littoral drift has resulted in the deposit
of low-lying salients which protrude from the coast. Remnants of both
estuary- and cape-associated shoals that were formed and abandoned during
the Holocene transgression may extend well out on the shelf. These features
in aggregate have been called shoal retreat massifs (Swift et al. 1972). They
can be traced shoreward to modern arcuate shoals in estuaries and off capes.
The shapes and sizes of arcuate shoals and shoal retreat massifs are
variable because of the influence of waves, and tidal and storm-generated
currents. For example, Field and Duane (1974) found evidence that a shoal
field off Canaveral Peninsula on the Florida Atlantic coast had been reworked
by waves and currents. Sediments as deep as 4 m below the sediment-water
interface showed evidence of recent abrasion. In addition, comparison of
historical bathymetric surveys revealed that between 1898 and 1965, shoal
crests accreted several meters and migrated over 300 m to the southeast.
Similarly, studies of bathymetric charts of the past century by Granat and
Ludwick (1980) indicate that shoals in Chesapeake Bay entrance changed
shape and position during the time covered. Although relict in having origi-
nated in past times, most shoal retreat massifs have been influenced by
subsequent shelf processes, often leading to radical changes in their form and
orientation (Swift et al. 1972).
Deltas
Deltas are subaerial and subaqueous accumulations of river-derived sedi-
ments deposited at the coast. Sedimentation occurs when streams decelerate
by entering and mixing with larger bodies of water (Wright 1982). Deltaic
Chapter 3 Variable Coastal Features
SHOAL C
HETZEL SHOAL
SHOAL
D
CAPE CANAVERAL
Scale Nautical Miles —
Contour Interval: 5 Feet 30! go" 20
Figure 23. Cape-associated shoals off Canaveral Peninsula, a large cuspate foreland on the
Florida Atlantic coast. Note shoreface-connected linear shoals north of False
Cape (from Field and Duane 1974)
Chapter 3 Variable Coastal Features
61
62
morphology, sediment distribution, and stratigraphy are the result of numerous
factors related to the action and interaction of fluvial and marine or lacustrine
processes and structural controls. Deltas develop when streams deliver more
sediment to the coast than coastal processes can erode and transport away.
Deltas form under a wide variety of environmental conditions. A major
prerequisite is the existence of a major river drainage system that carries sub-
stantial quantities of clastic sediment. Drainage basin climate, geology, relief,
and area are all critical determinants of river discharge and sediment load. In
addition to fluvial processes, marine processes (waves, tides, and currents)
and tectonic and deformational forces influence delta formation and form.
Though numerous factors tend to produce great variability in active deltas, it
is generally agreed that the interaction of river, wave, and tide regimes is the
major factor influencing delta morphology and sediment types (Galloway
1975). Littoral drift and offshore slope also control sand body geometry.
Subaqueous zones of deltas include the prodelta, the seawardmost element
consisting of an apron of fine-grained sediments, and the more landward delta
front, usually consisting of coarser silt and sand. The subaerial delta plain lies
above the low tide level. It can be divided into a lower delta plain, where
marine or lacustrine influence is active, and an upper delta plain, which lies
above tidal or other marine or lacustrine influence and is dominated by
riverine processes and features.
Active and abandoned zones occur on both the subaqueous and subaerial
deltas. Active delta zones are accreting, and on the delta plain are occupied
by functioning distributary channels, which develop from the deposition of
bed material at channel mouths. Abandoned deltas occur where distributary
channels became blocked or lost flow to other channels, causing them to fill
with silts and clays. Abandonment can also result from upstream channel
avulsion, in which the river occupies an alternative course with steeper
gradient. Such events are attributed to seaward growth of the delta and the
associated reduction in hydraulic head, a process which occurs about every
1,000 to 1,500 years in the Mississippi Delta Plain (Kolb and van Lopik
1966).
Depositional environments in deltaic areas can thus be distinguished
according to which processes influence sedimentation. Although the nature of
sediment supply may vary, the coarsest materials are deposited near the
channel and mouth, while deposition of fine sediments occurs in environments
of lower energy. The prodelta consists of fine-grained sediments deposited
from suspension. On the delta front, features may include distributary mouth
sands, distal-bar silts, tidal ridges, and shoreface beach deposits. On the delta
plain, deposits associated with the distributary channel and margins include
channel bed, channel fill, natural levee, and crevasse splay deposits. Inter-
distributary sediments are deposited in swamps, marshes, lakes, bays and
lagoons, and are primarily laminated or bioturbated fine sediments. At the
seaward edge, delta plain sediments of various kinds may be reworked into a
Chapter 3 Variable Coastal Features
variety of environments more characteristic of coastal processes described
elsewhere, including beaches, inlets, beach ridge plains or dune fields.
Once an active delta is abandoned, marine, estuarine, and paludal processes
take over the landscape. Such abandoned deltas may prograde or remain
stable if marine processes provide sufficient sediment. More likely, they may
deteriorate because of marine reworking, increased subsidence and compaction
inland, and decreased fluvial sedimentation rates. The Mississippi Delta Plain
has undergone such transformations, where the sands of abandoned deltas
have been reworked into barrier headlands and flanking barrier islands by
marine processes. As the marsh behind these barriers subsides, barrier island
arcs are left standing in open water. Through continued marine reworking
and subsidence, the barrier islands progressively disintegrate to form inner
shelf shoals. Transformation from one form to another may take several
decades or hundreds of years, while delta abandonment to shoal formation
may take a few thousand years to complete.
A delta plain, such as that of the Mississippi River, has unique environ-
ments that are highly vulnerable to both natural events and human activities.
Because of storms such as tropical and extratropical cyclones, transgression of
the low-profile barriers is rapid, with erosion rates over 5 m/year in places.
In wetlands, many factors are involved in relative sea level rise and
subsidence, including eustatic factors and consolidation of Quaternary and
older sediments. In Louisiana, land loss has averaged over 100 sq km per
year. Decreased sediment supply to wetlands because of levee building along
the rivers and in the marshes, as well as decreased sediment loads due to
trapping of sediments by reservoirs upstream, has prevented accretion of the
marsh surface as sea level rises. Brine discharges, and dredging of canals and
channels for navigation and oil-drilling activities are some other human
activities that influence land loss.
Strand Plains: Ridges and Cheniers
On coasts where there is an abundant supply of unconsolidated sediments,
and in wave-dominated settings, including in the vicinity of river mouths, it is
common to find beach ridge plain coasts and chenier plain coasts. Both are
called strand plains and display shore-parallel ridges, which represent succes-
sive seaward accretion and reworking (Figure 14). Ridges are shore-parallel
bodies of coarse materials, with ridge crest elevations well above mean high
tide and troughs near the mean low tide level. Ridges originate primarily due
to marine processes, caused by several possible mechanisms. They generally
develop immediately behind the active beach as a flood-level ridge, as an
eolian accumulation, or by water deposition below and eolian deposition
above.
Cheniers are shore-parallel bodies of sand and shell enclosed by prograding
marsh and mudflat deposits. They develop in response to fluctuating supplies
Chapter 3 Variable Coastal Features
63
64
of clastic sediment, typically in the vicinity of major river deltas. During
episodes of reduced longshore sediment supply, coastal reworking occurs with
deposition of coarse-grained material at the marine edge. During periods of
accelerated fine-grained sediment supply, such as when delta lobes occur in
proximity to these coasts, the coarse deposits are stranded inland behind
seaward-building mudflat deposits.
Chapter 3 Variable Coastal Features
4 Investigation of
Environmental Factors
Geomorphic variability is chiefly caused by the work of dynamic envi-
ronmental factors that vary over time and space. The most important of these
factors are waves, tides, and currents which continually affect the shore and
upper shoreface. During periodic storms, these factors affect a much wider
zone, producing large-scale changes in geomorphic features. Because of this,
data on geomorphic variations in the coastal zone are much more valuable
when accompanied by wave and current observations for the same time period
so that process-response relationships can be examined. This portion of the
report concerns the equipment and techniques used to gather wave and current
data.
Wave Data
Methods of obtaining wave data include gages, hindcasting from weather
maps, shipboard observations, and littoral environment observations. Gages
are the most accurate of these methods, but their relative cost often restricts
their use to short-term deployments for the purpose of validating data col-
lected by observation or hindcasting methods. Multiple gages across the shore
zone in both shallow and deep water can be used to determine the accuracy of
wave transformation calculations for a specific locale.
Wave gages can be separated into two general groups: directional and
non-directional. In general, directional gages are more expensive to build,
deploy, and maintain than non-directional gages. Because wave direction is
an important parameter in applications such as sediment transport analysis and
calculation of wave transformation, the additional expense is often necessary.
Wave gages in both categories can be installed in buoys, placed directly on the
sea or lake bottom, or mounted on existing structures, such as piers,
navigation aids, and offshore platforms.
Buoy-mounted non-directional gages are accurate and relatively easy to
deploy and maintain. Data are usually transmitted by radio from the buoy to
Chapter 4 Investigation of Environmental Factors
65
66
an onshore receiver and recorder. Bottom-mounted pressure gages measure
wave parameters by sensing the pressure changes with the passage of each
wave. They can be either self-recording or can be connected to onshore
computers and recorders with cables. Divers must retrieve data periodically
from self-recording gages.. Both types of systems require regular
maintenance. Structure-mounted wave gages are the most accessible of the
non-directional gages, allowing convenient maintenance. Unfortunately,
offshore structures are not always located near project sites.
Directional wave gages are used mainly in buoys or bottom mounts of
single units (Figure 24) or multiple arrays in a fixed configuration.
Directional buoy-type wave gages are often designed to measure other
parameters, especialiy meteorologic ones. Pressure-type gages can measure
wave direction using an accompanying electromagnetic current meter or by
combining multiple synoptic pressure measurements from individual gages in a
known geometric array.
Wave hindcasting is widely used for obtaining wave statistics by analysis of
weather maps using techniques developed from theoretical considerations and
empirical data (Coastal Engineering Research Center 1984) (Figure 25). Over
the last several decades, since wave hindcasting came into common use,
numerous improvements have been made in the technique and reasonably
reliable information on wave climate in given areas can be computed (Abel
et al. 1989; Hubertz and Brooks 1989; Jensen, Hubertz, and Payne 1989;
Corson et al. 1987; Corson and Tracy 1987). Advantages of hindcasting
include the long-term database associated with weather maps and the useful
statistical information.
A large amount of wave data is available in the form of visual wave
observations from ships at sea and from shore stations along the coasts of the
United States. Although observations are less accurate than measured data,
experienced persons can achieve reasonably accurate results and the large
database of available observations makes it a valuable resource. Shipboard
wave observations have been compiled by the US Navy Oceanographic
Research and Development Activity in the form of sea and swell charts and
data summaries such as the Summary of Shipboard Meteorological
Observations. Areal coverage by these sources is extensive, but the greatest
number of observations come from shipping lanes.
The second important source of observations has been collected by CERC
under the Littoral Environmental Observation (LEO) program (Schneider
1981; Sherlock and Szuwalski 1987). The program, which was initiated in
1966, makes use of volunteer observers who make daily reports on conditions
at specific sites along the coasts of the United States (Figure 26). A variety of
data from over 200 observation sites are available from CERC. As shown,
LEO data include more than wave parameters, and encompass information on
winds, currents, and some morphologic features. LEO data are best applied
to a specific site, and do not provide direct information regarding deepwater
statistics.
Chapter 4 Investigation of Environmental Factors
Figure 24.
WIND SPEED ¢km/h)
Figure 25.
Bottom-mounted Sea Data™ 635-12 directional wave gage mounted in tripod
using railroad wheels as corner weights
FETCH LENGTH ¢km)
20, ' 100: 200 500 10002000 5000 10000
/
fe
200 500 1000 2000 53000
FETCH LENGTH (mid
HEIGHT OF WAVE (<m)
DURATION OF WIND CONDITIONS Chours>)
Deepwater wave hindcasting curves (from Bretschneider 1959)
Chapter 4 Investigation of Environmental Factors
WIND SPEED (<mi/h)
67
SITE NUMBERS
[2S SS
WAVE PERIOD
Record the time in seconds for
eleven (11) wave crests to pass a
stationary point. If calm record O.
WAVE ANGLE AT BREAKER 22 23 24
Bee
Record to the nearest degree the
direction the waves are coming from
using the protractor on the reverse side. O if calm.
WIND SPEED
Record wind speed to the nearest
mph. If calm record O.
FORESHORE SLOPE
Record foreshore slope to the
nearest degree.
LONGSHORE CURRENT
CURRENT SPEED
Measure in feet the distance the dye ae
patch is observed to move during a one (1)
minute period; If no longshore movement record O.
RIP CURRENTS
LITTORAL ENVIRONMENT OBSERVATIONS
RECORD ALL DATA CAREFULLY AND LEGIBLY
DAY
Jo Record time
using the 24
hour system
BREAKER HEIGHT
Record the best estimate of the
average wave height to the nearest
tenth of a foot.
WAVE TYPE
0 - Calm 3 - Surging
| - Spilling 4 - Spill / Plunge
2 — Plunging
WIND DIRECTION - Direction the wind ae
is coming from.
KN 2S = Bey Soe Sie 7 = WieniO!=iGalm (i)
2-NE 4-SE 6-SW 8-NW
WIDTH OF SURF ZONE
Estimate in feet the distance from
shore to breakers, if calm record O.
DYE 36 37 38
Estimate distance in feet from
shoreline to point of dye injection.
3132 33 34
CURRENT DIRECTION
QO No loagshore movement
+1 Dye moves toward right
- | Dye moves toward left
so Si Se
If rip currents are present, indicate spacing ( feet). If spacing is irregular
estimate average spacing. If norips record O.
BEACH CUSPS
If cusps are present, indicate spacing ( feet)
estimate average spacing. If no cusps record O.
PLEASE PRINT:
SITE NAME
54 55 56
If spacing is irregular
OBSERVER
Please Check The Form For Completeness
REMARKS:
CERC 113-72
8 Mor 72 Make ony additional remarks, computations or sketches on the reverse side of this form.
Figure 26. Littoral Environmental Observation forms used by the volunteer observers
participating in the LEO program (from Schneider 1981)
Chapter 4 Investigation of Environmental Factors
While a considerable amount of data exist on the coastal and oceanic pro-
cesses of the US coasts, there are few field studies in which data on
geomorphic changes and relevant processes were obtained concurrently. Such
data are critically needed for many areas in order to validate existing models
of process/response relationships under a variety of conditions.
Wave data is one of several components required to characterize the
process-response framework of the coastal zone. Important wave parameters
include wave height, period, and steepness, and breaker type. The estimated
height is often given as the significant wave height (H ,,,), the average of the
highest one-third of waves, or as the maximum height (H ,,,9), the average of
the highest one-tenth of the waves. Significant wave height may be used to
compute other wave statistics (Shore Protection Manual 1984).
Certain wave characteristics are strongly related to morphologic variables.
Wave steepness, for example, is an important variable in determining fore-
shore slope, which explains changes in beach profile characteristics from
summer to winter (Shepard and LaFond 1940; Saville 1950; Bascom 1954).
Other wave characteristics, including the surf scaling factor and breaker type
are important in determining beach profile characteristics (Wright et al. 1979;
Huntley and Bowen 1975). Other parameters, such as shore-normal currents
and sediment grain size, should also be considered in conjunction with wave
variables in order to thoroughly understand beach profile development (Sonu
and van Beek 1971; Iwagaki and Noda 1963; Komar 1976).
Wave climate data can also be used in conjunction with bathymetric data to
construct wave refraction diagrams, which provide an indication of how
bottom topography can affect the bending of waves approaching a shoreline.
Such studies can help in determining mass transport and longshore transport of
sediment, which in turn can assist in predicting morphologic changes, and in
design of coastal engineering projects. Wave refraction analysis can also be
used for hypothetical scenarios, for instance, how wave energy and associated
littoral conditions would be affected by the dredging of an offshore shoal or
offshore placement of dredged material.
Water Level
Water level measurements represent the combined effects of tides, setup or
setdown by onshore or offshore winds, eustatic changes, and vertical crustal
displacements Figures 27-31). Short-term variations, particularly those
associated with storms, are important in increasing the effective wave base.
This allows erosion to take place farther inland than during mild weather
periods. Long-term variations in sea level, while of much lower intensity than
surf processes, can be important in predicting erosion or accretion and
changes in beach profile response (e.g., Wells and Coleman 1981b; Hands
1983).
Chapter 4 Investigation of Environmental Factors
69
70
A
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2)
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Figure 27. Monthly water level changes at Juneau, AK. High water typically occurs
October-December. Data from Lyles, Hickman, and Debaugh (1988)
| MEAN: 1908 - 1986 | 1908 - 1986
ELEVATION (FT) ABOVE ORIGINAL DATUM
Figure 28. Monthly water level changes at Galveston, TX. High water occurs twice per
year: April and September-November
Chapter 4 Investigation of Environmental Factors
=
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1910 1920 1930 1940 1950 1960 1970 1980 1990
YEAR
Figure 29. Yearly mean sea level changes at Juneau, AK, from 1936-1986. The overall
fall in sea level shows the effects of isostatic rebound. Data from Lyles,
Hickman, and Debaugh (1988)
ELEVATION (FT) ABOVE ORIGINAL DATUM
1910 1920 1930 1940 1950 1960 1970 1980 1990
YEAR
Figure 30. Yearly mean sea level changes at Galveston, TX, from 1908-1986. Subsidence
of the land around Galveston may be caused by groundwater withdrawal and
compaction
Tz
MILLIMAN AND
EMERY 1968
_.-PBOPOSED........
SEA LEVEL
CURVE: U.S.
—!
Ww
=
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WW
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-25 -20 -15 -10 -5
YEARS BEFORE PRESENT
(Thousands)
Figure 31. Late Quarternary sea level curves inferred from radiocarbon-dated samples
along the U.S. coastlines (modified from Dillon and Oldale 1978)
Over shorter time scales, tides and storm surges are important in under-
standing geomorphic changes. In order to obtain continuous data at a specific
site, water level recorders have to be deployed. If fewer data are required,
high and low tidal predictions can be obtained from tide recording stations.
However, in some locations, the discrepancy between predicted and actual
tides on coastal areas only a short distance apart may be considerable. A
method for tidal adjustment between predicted tides at a station and those at a
nearby study area can be obtained even if only short-term site measurements
are available (Glen 1979).
Sea level also shows pronounced seasonal changes, with some locations
differing by 1 m annually from the highest to the lowest monthly values
(Komar 1976). Around the United States and in most locations worldwide,
for example, sea level is lowest in the spring months and highest during the
late summer and autumn. A number of factors are responsible for these
seasonal deviations, including changes in water temperature, salinity, atmo-
spheric pressure, river runoff, and longshore winds.
The National Ocean Service of the National Oceanic and Atmospheric
Administration (NOAA) is responsible for monitoring sea level variations at
115 stations nationwide (Hicks 1972b). The Corps of Engineers District
offices located near the coast also collect tidal elevation data at additional
locations. Daily readings are published in reports that are entitled "Stages and
Discharges of the (insert location) District."
Chapter 4 Investigation of Environmental Factors
Trends of sea level series over decades have been examined for the United
States and elsewhere, in some cases dating back to the beginning of the
century (Hicks 1972b; 1978; Gornitz, Lebedeff, and Hansen 1982). In the
analysis of long-term data, Hicks (1972b) found that series exhibited yearly
variability and apparent secular trends, which might either be nonperiodic
phenomena or segments of very long oscillations. Yearly variability is due to
variations in the meteorological and oceanographic parameters of wind, direct
atmospheric pressure, river discharge, currents, salinity, and water
temperature. In one case, extreme unidirectional change was caused within a
few months by the Alaskan earthquake in 1964 (Hicks 1972a). Apparent
secular trends result from longer term glacioeustatic, tectonic, climatologic,
and oceanographic influences.
In some cases, it is important to dampen the effects of yearly variability so
that the nature of secular trends will become more pronounced. A weighting
array may sometimes be applied to reduce yearly effects. Least-squares
regression methods are typically inadequate, as the secular trends often show
pronounced nonlinearity (Hicks 1972b). It is also important to examine
periodic effects in the long-term series, such as the 18.6-year nodal period,
which Wells and Coleman (1981b) concluded was important for mudflat
stabilization in Surinam. In some cases, such as on the Great Lakes, water
level changes in conjunction with existing models can be used to predict
erosion and changes in the shore and offshore profile (Hands 1983).
The geomorphic response of the shoreline to sea level rise may follow one
of several scenarios. Applicability of the erosional response model or Bruun
Rule has been discussed by Hands (1983). The onshore migration or rollover
model often applies to barrier coasts where washover is an important process
(Dillon 1970). In other locations where coastal forms change slowly, features
may drown in place without transport occurring (Carter 1988). Depending on
the location and time scale involved, the geomorphic effects can be studied
with a variety of techniques including historic data, seismic data, and strati-
graphic methods.
Currents
Speed and direction of longshore and cross-shore currents are also impor-
tant for understanding coastal changes. Direct measurements of the velocity
and direction of current flow can be made by instruments deployed on the
bottom or at various heights in the water column. Lagrangian methods such
as floats, bottom drifters, drogues, and dye are also used, especially in the
littoral zone where current meter data (as well as the current meters) are
adversely affected by turbulence.
Current measurements may be Lagrangian, following the motion of the
flow in its spatial and temporal evolution, or Eulerian, defining the motion at
Chapter 4 Investigation of Environmental Factors
74S:
74
a fixed point and determining its temporal evolution. Lagrangian current-
measuring devices are often used in circulation studies, pollution studies, and
for monitoring ice drift. For Eulerian or fixed current meters, proper place-
ment is essential for adequately determining sediment transport pathways.
Several types of current sensors are in common use including impeller,
electromagnetic, acoustic, acoustic Doppler, laser Doppler, and inclinometer
types (Fredette et al. 1990). Impeller current measurements are acquired by
means of a propeller device which is rotated by current flow. Impeller
devices are considered to be the least expensive and have been widely used for
a considerable time (Teleki, Musialowski, and Prins 1976). They are subject
to snaring, biofouling, and bearing failure, but are more easily repaired in the
field and more easily calibrated than other types (Fredette et al. 1990).
All the other current meters have several features in common, although
they operate on different principles. Each has no moving parts, has rapid
response, is self-contained, can be used in real-time systems, and can be used
to measure at least two velocity components. The degree of experience of the
persons working with the instruments probably has more to do with the
performance of the current meters than does the type of meter used (Fredette
et al. 1990).
In addition to direct current measurements, indirect current estimates of
current speed and direction can also be made from bedforms, particularly in
shallow water. The deviations from a flat bed and associated sedimentary
structures are associated with coastal hydrodynamics, including the effects and
interaction among tidal currents, wave characteristics, and longshore drift,
particularly at inlets and estuaries. Bedforms reflect flow velocity, but are
generally independent of depth (Clifton and Dingler 1984; Boothroyd 1985).
Bedform can vary in response to increasing flow strength (Hayes and Kana
1976). Bedform orientation and associated slipfaces also provide clues to flow
direction.
Knowledge of the magnitude and direction of currents at the coast allows
the prediction of sediment movements and thus is basic to an understanding of
landform development. Information concerning cross-shore (shore-normal)
currents and sediment transport can assist in predicting beach profile change.
Longshore (shore-parallel) currents and associated transport can assist in
predicting beach planview changes. The combined effects of both types of
currents, generating cell circulation, may explain or assist in identifying
regularly spaced features along many coasts. The longshore migration of such
cells can also cause landform migration associated with the spatiotemporal
migration of higher energy nodes.
Conversely, the configurations of the shoreline can provide information
regarding littoral currents. Shoreline proturberances, particularly in the
vicinity of structures, headlands and barriers, and tidal inlets are useful
indicators of the prevailing littoral sediment drift (Komar 1976). Such
indicators cannot generally be used for quantitative estimates of the sediment
Chapter 4 Investigation of Environmental Factors
transport rate because the shoreline eventully tends to reach an equilibrium
condition.
Some types of currents, such as rip currents, may be controlled in spacing
by other parameters; i.e., edge waves or other wave height variations along
the shore, or the surf zone width. However, irregular nearshore topography,
which also may be manifest by shoreline protuberances, can produce
nearshore circulation (Sonu 1972). In such cases wave height variations may
not exist. Aerial photography may be helpful in assessing the location of
some types of currents, their patterns, and possibly their movement. Loca-
tions of rip currents can sometimes be detected using side-scan sonar if
characteristic channels have been scoured in the seafloor (Morang and
McMaster 1980).
Chapter 4 Investigation of Environmental Factors
7k)
76
5 Investigation of Geomorphic
Factors
Nature of Geomorphic Changes
Techniques for investigating geomorphic features and coastal evolution can
provide useful information for coastal engineering design. Such techniques
can include field surveys, analysis of historical maps and aerial photographs,
airborne remote sensing, waterborne remote sensing, and sedimentologic and
stratigraphic techniques depending on the spatial scale and the time scale of
the data needed. Collection and comparative analysis of time series data
showing dimensions, elevations, and configuration of coastal features over an
extended period of time are effective ways of identifying temporal geomorphic
changes and trends. In most cases, the use of multiple techniques will provide
a useful balance of information regarding a site.
At the interface where marine and lacustrine processes interact with the
land, coastal features are highly variable. For effective management, cyclic
patterns, intermittent noncyclic events, and long-term trends must be
considered. In mild weather, the morphological changes that take place on a
day-to-day basis are relatively small and often compensate for each other, so
that little net effect is apparent. During storms, a wider zone of the coast may
be exposed to coastal processes and large geomorphic changes can occur in
only hours or days.
In many places, distinct changes in coastal geomorphic features occur on a
seasonal basis. A common example is a winter-summer cycle, in which
winters are times of more intense and frequent storms than the summer
seasons. An example of seasonal cycles in coastal morphology is the changes
that occur in beach profiles. The more severe wave climate of winter causes
erosion of the shore, with the eroded material usually transported seaward to
the upper shoreface, where it often forms submarine bars. With the return of
milder conditions in the summer months, this sand usually returns to the beach
and a period of milder weather prevails. This cycle may be interrupted by
hurricanes in summer and early fall, which greatly disrupt the normal summer
Chapter 5 Investigation of Geomorphic Factors
shore characteristics and often penetrate well inland of the shore zone because
of high waves and storm surges.
In addition to cyclic seasonal patterns, many areas are being affected by
long-term unidirectional trends in a particular environmental factor, which
causes continuous adjustments in morphology. For example, a rising relative
sea level usually results in shore erosion and progressive landward retreat of
the shoreline. Evidence of past or ongoing changes, and the rates of these
changes, need to be taken into account for planning and management of
engineering activities.
A rapid change in coastal morphology, due to an intense storm or other
event that causes a feature to be out of equilibrium with the prevailing envi-
ronmental factors can lead to significant long- and short-term trends.
Unidirectional trends are observed until the normal balance or equilibrium is
restored. In some cases, the effects of an extreme event may become
permanent because normal processes are unable to restore the old equilibrium.
Several types of unidirectional trends caused by extreme events are
possible. For example, beach and dune sands lost to storm overwash deposits
cannot be returned because there is no process that can move the material
back toward the shore, except for minor eolian transport. Thus, most of the
material will not reenter the shore area unless barrier recession eventually
reexposes it on the seaward side. Also, if island breaching occurs during
storms, inlets may develop and enlarge unless littoral drift processes work to
close them.
The identification and analysis of trends in coastal geomorphic processes
and features are of great importance in the planning and design of coastal
engineering efforts and of long-range management plans. Indeed, in many
cases, the purpose of coastal engineering works may be to modify or com-
pensate for some trend that is producing undesirable effects. Since each
location is unique geomorphically, exhibiting different types of changes,
management and structural techniques that are appropriate for a given site
might not be appropriate for others. In summary, although coastal
geomorphology displays many general trends, unique conditions at each
location must be identified and evaluated before initiating engineering projects
or long-term management practices.
Historical Charts and Aerial Photographs
Detection of long-term trends is often difficult because these processes are
often relatively slow on human time scales. However, trends may be
identified by comparative analysis of historical maps, charts, and aerial
photographs that show changes over a period of decades or centuries.
Historical charts and aerial photographs of many areas have been periodically
Chapter 5 Investigation of Geomorphic Factors
TT,
78
resurveyed and fairly accurate surveys, going back in some cases 150 years or
more, are available for most US coastal areas.
The primary source of chart data is the NOS and its predecessor, the
U.S. Coast and Geodetic Survey. Archive material for all past surveys of
these agencies is available from NOS, a division within NOAA. Much of this
data can be obtained in the form of preliminary plots that are of a larger scale
and contain more soundings and bottom notations than the published charts
made from them. Some of these data were used for regional studies of net
shoreline movement (Anders, Reed, and Meisburger 1990) (Figure 32). A
great variety of additional documentary evidence may also be available, as
described by Fulton (1981). This includes such items as local records and tax
assessments, which might be incorporated in background investigations of a
site if sufficient time exists to find these materials.
Aerial photographs are another useful and economic technique for examin-
ing details of coastal features above the water line. The general turbidity of
coastal waters inhibits the application of photographic data of the offshore
bottom; however, in relatively clear shallow water, the crests of submarine
bars and shoals may be visible. Sources of aerial photography data are
numerous, including Federal, state, county, and local government agencies.
Aerial photography of coastal areas has been collected for about 60 years;
thus, it often can provide useful time series data on changing conditions.
Also, the effects of major events can be documented by aerial photography
because the necessary equipment and airplanes can be rapidly mobilized to
reach areas that are not easily accessible on the ground.
Applications of aerial photographs include assessments of short-term and
long-term, as well as mesoscale and macroscale, coastal changes. The type of
information that can be derived depends in part upon the scale of the
photography, and also upon the historical nature of the database. The relative
accuracy of the surveys, maps, or aerial photographs will depend largely on
the scale of the initial photography; horizontal and vertical error increases
with smaller scale (Tanner 1978).
Much information regarding local processes can be derived from maps and
aerial photographs. One example is the longshore movement of sediment, an
item of paramount interest to geologists and engineers because of its impor-
tance in coastline evolution. The geometry of coastlines in the vicinity of
headlands, tidal inlets and streams, and coastal structures is one key to
determine the directions of littoral transport (Figure 33). Storm impacts,
including island breaches, occurrence of overwash features, and changes in
inlets, vegetation, and dunes can be determined with time-series photography.
Problems with siltation of tidal inlets, river mouths, estuaries, and harbors can
also be examined using photographs.
Large data sets of historical aerial photographs and maps can be used for
interpretating regional geomorphic changes in coasts. Using detailed historical
data, Dolan and Hayden (1983) were able to assess that shore processes and
Chapter 5 Investigation of Geomorphic Factors
NOILVIASO GYVONVLS
NoIsous
(JA/W) INSWSAOW LAN JDVYSAV
Figure 32. Net shoreline movement of a portion of the South Carolina coast based on
historical maps surveyed between 1857 and 1983 (from Anders, Reed, and
Meisburger 1990)
80
HEADLAND TIDAL INLET OR STREAM
GROINS JETTIES
SEAWALL BREAKWATER OFFSHORE BREAKWATER
Figure 33. Morphologic indicators of littoral drift along natural and modified shorelines.
Natural features such as rock headlands show accretion on the updrift side and
erosion on the downdrift side (A), tidal inlets and spits show extension in a
downdrift direction (B-C), and beach ridge headlands show successive growth
on the updrift end influenced by the development of coastal cells, which form
shoreline irregularities (D). Coastal engineering structures including groin fields,
jetties, seawalls, attached breakwaters, and detached breakwaters (E-1)
generally show accumulation of sediment on the updrift side, and reduced
sediment supply on the downdrift side
landforms assume systematic, as opposed to random, patterns both along and
across the coast. Large storms caused severe erosion in the same locations as
previous storms of lower severity. Long-term erosion rates can be examined
even over large areas (Dolan, Hayden, and May 1983). Such studies can then
be used to assign temporal probability levels to the distribution of coastal
change rates and thus predict shoreline positions several years beyond the data
set (Dolan et al. 1982; Dolan and Hayden 1983). Clues regarding the influ-
ence of natural and human-induced wetland changes can also be found by
interpretation of historical maps and photographs (May and Britsch 1987).
Chapter 5 Investigation of Geomorphic Factors
If detailed historical mapping of shorelines or inland areas is attempted,
care should be taken to reduce photographic distortion error. Aerial
photography should be corrected photogrammetrically to reduce sources of
error such as tilt, yaw, and parallax. If data are taken from maps using
different projections, the maps need to be geometrically corrected to conform
to the same grid. Once these corrections are made, allowance should be made
for tidal and seasonal changes. Good reference points should be chosen.
These are usually readily available in populated areas or areas with strong
human imprint, but can be difficult to establish along non-populated coasts.
Sampling intervals must also be chosen to avoid systematic errors associated
with rhythmic features. Extrapolation errors should also be avoided, so that
long-term erosion rates are not projected from short-term data sets.
Airborne Scanners and Satellite Data
Multispectral scanners and remote sensing devices mounted on aircraft and
satellites can provide various types of data that in some cases exceed the
capability of conventional photography. The resolution of scanner data is
generally not as good as aerial photography, with each data cell or pixel
(picture element) having a size from a few meters (on low-altitude aircraft
scanners) to several hundred meters on a side. Depending on the system and
flight altitude, the aerial coverage on one image is typically far more extensive
than on photographs. Also, the coverage may extend to parts of the electro-
magnetic spectrum invisible to the human eye, including the near and thermal
infrared and radar bands. With digital data collected from scanners, the
capability for quantitative analysis is far superior to aerial photography, and
the data in some cases may be suited to numerical modelling studies. Time-
sampling capabilities at a given location include several passes per month by
different satellites, allowing repetitive changes to be examined. The timing,
however, is not at the discretion of the user.
Applications of satellite remote sensing are especially good for assessing
large-scale changes in the surface of the coastal zone. In the vicinity of del-
tas, estuaries, and other sediment-laden locations, the determination of spatial
patterns of suspended sediment concentration can be facilitated with remote
sensing. In shallow-water portions of non-turbid water bodies, some features
of the bottom, including the crests of submarine bars and shoals, can be
imaged. On a relatively crude level, satellites may assist in monitoring tidal
changes, particularly where the land-sea boundary changes by several
hundreds of meters. In deeper waters, satellites can also provide data on
ocean currents and circulation (Barrick, Evans, and Weber 1977). Aircraft-
mounted radar data also show promise in the analysis of sea state.
Chapter 5 Investigation of Geomorphic Factors
81
82
Remote Sensing By Ocean Vessel
Depth-sounders, side-scan sonar, and subbottom profilers are three major
ways to collect data on subaqueous environments from an ocean vessel. All
require the use of high resolution positioning systems. Fathometers are the
most common devices used for acoustic depth-sounding to conduct
bathymetric surveys. Side-scan sonar provides an image of the aereal distri-
bution of sediment, surface bedforms, and larger features such as shoals and
channels, and thus can be helpful in mapping directions of sediment motion.
Subbottom profilers and seismic techniques are used to examine the near-
surface stratigraphy below the seafloor.
Bathymetric surveys are required for many studies of geomorphic
variability in coastal waters. Survey-quality fathometers include many devices
to improve accuracy, including correction for change in tide, change in draft
with vessel speed, and speed of sound. Even so, the maximum accuracy is
estimated to be + 0.2 m (Morton, Stewart, and Germano 1984); thus, such
errors should be considered in volume change measurements of features.
Survey lines are typically parallel and are run at an appropriate spacing
depending on the survey’s purpose and the scale of features to be examined.
Side-scan sonar permits the collection of surface characteristics data for the
seafloor. The resulting image of the bottom is similar to a continuous,
oblique aerial photograph, with lower frequency scanners providing less detail
but greater range than higher frequency scanners. Detailed information,
including the spacing and orientation of bedforms, and grain size differences
in seafloor sediments, can generally be distinguished on side-scan, as can
larger individual features. It is generally recommended that bathymetry be
run in conjunction with side-scan, because detailed information on the relief of
bottom features is valuable during the interpretation of side-scan sonographs.
The side-scan system is sensitive to vessel motion, making it suitable only for
work during calm conditions.
The principles of subbottom seismic profiling are fundamentally the same
as in acoustic depth sounding. Subbottom seismics employ a lower frequency,
higher power signal to penetrate the seafloor. The signal is reflected from
interfaces between sediment layers of different acoustical impedance
(Figure 34). Coarse sand and gravel are often difficult to penetrate with
conventional subbottom profilers, resulting in poor records. New equipment
is helping to overcome such problems, although the data are of lower
resolution. Spacing and grid dimensions are usually the same as those used
for bathymetric and side-scan surveys, being dependent upon the nature of the
investigation.
Chapter 5 Investigation of Geomorphic Factors
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tigation of Geomorphic Factors
Chapter 5 Inves
84
Field Survey Techniques
The most direct and accurate means of assessing geomorphic variability is
to conduct periodic surveys for the express purpose of obtaining time-series
data. However, as a practical matter it is usually not feasible to carry out
repeated surveys for a sufficient length of time for reliable and comprehensive
information because of expense and because the lead time for projects often
does not allow sufficient time to obtain the needed data. Nonetheless, a set of
surveys spanning over a year or more can be of substantial help in learning
more about the prevailing seasonal changes.
Field surveys of coastal features show that the most active zones are the
shore and upper shoreface. Submerged interior parts of previously subaerial
features, such as relict shore and dune deposits formed during earlier stages of
development, are distant from the modern shoreline and are likely to be
affected by marine or lacustrine processes only during large storms. Large-
scale aerial photographs and topographic maps of these interior areas are
usually available and are adequate for study purposes.
Information on the active, more variable shore and shoreface zones is
usually obtained by direct field survey. The preferred surveying technique
involves collecting a series of shore-normal profile lines. The profile lines
should extend landward of the influence of inundation by moderate storms,
usually behind frontal dunes. The preferred closure depth is at the toe of the
shoreface, often defined as a selected depth contour where variability becomes
minimal. Profile lines should be spaced at intervals close enough to show any
significant changes in lateral continuity. Profile lines are connected with a
surveyed shore-parallel baseline from which position and elevations of each
profile origin can be determined.
Resurveying control profile lines at selected intervals of time can reveal
seasonal patterns. In addition, special surveys can be made after significant
storms and events to determine whether these events affect the local beach
system. As previously noted, however, lead time and expense do not usually
allow for an extended period of monitoring profiles. At a minimum, summer
and winter profiles are recommended to identify seasonal variability.
A permanent or semi-permanent benchmark, or set of benchmarks, is
required for reoccupying a profile site over successive months or years. Ona
rapidly transgressing coast, these benchmarks should be located near the
landward end of the profile line in order to minimize storm damage, although
locations which might experience dune burial should be avoided. Ona
regressive coastline, the benchmarks can be placed closer to the shoreline. In
both cases, care should also be taken to reduce the visibility of benchmarks so
that they will not be damaged by vandals.
Chapter 5 Investigation of Geomorphic Factors
Onshore portions of profiles are surveyed using standard land survey
techniques and equipment. Extending profile lines offshore beyond wading
depths requires a boat or amphibious vehicle. Positioning offshore can be
accurately and rapidly established by one of several high-precision navigation
systems now available. Fathometers can be used for continuous profiling of
the area seaward of the breaker zone but the signals are disrupted by breaking
waves in the zone. Further, boats suitable for offshore use cannot approach
close enough to the shore to connect directly to the land profile. Amphibious
vehicles are better suited to this task because they can traverse the sea-land
boundary and establish the continuity of profile lines.
In waters relatively close to shore during favorable weather conditions, one
survey platform that is often used is a sea sled, consisting of a long upright
stadia rod mounted vertically on a base frame with sled-like runners
(Clausner, Birkemeier, and Clark 1986) or a mast with a prism for use by
total station survey techniques (Fredette et al. 1990). The sled is towed,
winched, or otherwise propelled along the profile lines (self-propelled,
remote-controlled sea sleds are currently being developed) while frequent
depth and position data are determined using onshore instruments. Because
neither the sea sled nor the onshore survey and positioning equipment are
floating, elevations are not subject to wave or tide variations, thus providing a
more accurate comparison between repeated surveys. At present, bottom
samples must be obtained from a boat or amphibious vehicle working in
conjunction with the sea sled. The technique is currently limited to use within
4 km of the coast and water depths of 12 m, less than the height of the sled
mast.
Sedimentological and Stratigraphic Techniques
In addition to examining large morphological features, examination of
small-scale morphology can provide much information on the variable nature
of coastal forms and processes. A number of techniques exist that enable
collection of data on present and past processes at a site, using information on
the characteristics of sediments and surface stratigraphy.
Knowledge of sediment characteristics may be useful for predicting
sediment movement during storms, the nature of seafloor features, and the
geologic history of the area of investigation. Sediment transportation is
influenced by properties such as size, shape, and composition, with grain size
being most important. Differential transport of coarse and fine, angular and
rounded, and light and heavy grains leads to grading. There are several
samplers for determining the movement of sediments (McCave 1979; Seymour
1989). Sediment traps are a direct means of estimating sediment movement
(Kraus and Dean 1987). Bed surface sediments are typically collected with
grab samplers and then analyzed using standard laboratory procedures as
described in other sources (Fredette et al. 1990; Buller and McManus 1979).
Chapter 5 Investigation of Geomorphic Factors
85
86
For acquiring undisturbed samples or samples at greater depths, some type of
coring device must be employed.
Cores allow retrieval and examination of the subsurface material in the
area of investigation. From the recovered sediment sequence, much informa-
tion regarding history of the depositional environment and processes can be
determined. Depending upon the information required, the types of analyses
performed on the core may include grain size, sedimentary structures, the
occurrence of shells and minerals, organic content, microfaunal identification,
x-radiographs, age dating, and engineering tests. If it is important to under-
stand much about the geologic history of a site, vibratory corers will be
necessary, which may retrieve samples exceeding 12 m in length. Even
deeper cores can be recovered with rotary drilling equipment. If only infor-
mation regarding recent processes is necessary, then a box corer, which
samples up to 0.6-m depths in the sediment and provides detailed information
regarding sedimentary structures, will likely be adeqate.
Standard surveying techniques or large-scale aerial photographs are
preferable to side-scan sonar for acquiring bedform data on exposed sand
banks at low water. Dimensionless parameters of ripples and other bedforms
can indicate depositional environment (Tanner 1967). Flow directions can be
assessed in terms of the trace of the crestline (Allen 1968). Wave-formed
structures reflect the velocity and direction of the oscillatory currents, plus the
length of the horizontal component of orbital motion and the presence of
velocity asymmetry within the flow (Clifton and Dingler 1984). The flow
strength for inter-tidal estuarine bedforms can also be estimated for a given
flow depth by a velocity-depth sequence of bedform development (Boothroyd
1985).
Heavy minerals may provide information regarding sources, processes, and
other aspects of geomorphic variability in the coastal zone. Pronounced sea-
sonal variations in heavy minerals may also occur in the beach and nearshore
samples, with foreshore samples showing higher concentrations in winter than
summer, and samples outside the surf zone showing lower concentrations in
winter than summer. An explanation for this phenomenon is that light
minerals are transported from the beach foreshore to deeper water during the
winter, and are transported back again during the summer (Inman 1953;
Nordstrom and Inman 1975).
Physical Models
The use of physical models can also shed light on the geomorphic variabil-
ity of coasts. Physical models require scaling and calibration, and significant
time and expense to set up initially. Once in operation, however, they allow
for direct measurement of process elements, and the study and isolation of
variables that are difficult to assess in the field. Some examples of physical
Chapter 5 Investigation of Geomorphic Factors
model experiments, conducted principally in wave tanks, that help elucidate
geomorphologic variability of coasts include studies of littoral drift blockage
by jetties (Sireyjol 1965), breaker type classification (Galvin 1968), experi-
ments of cliff erosion (Sunamura 1983), relationships of storm surge or short-
term water level changes to beach and dune erosion, and studies of suspended
sediment concentration under waves (Hughes 1988). Physical models are
considered invaluable for many coastal engineering studies. (A detailed
description of the types and results of such models is beyond the scope of this
report.)
Numerical Models
The use of numerical models in assessing changes in coastal geomorph-
ology is rapidly increasing in sophistication. Models include those that
perform wave refraction and longshore transport computations, those that
estimate beach profile response and coastal flooding, and those that examine
shoreline change and storm-induced beach erosion (Dean and Maurmeyer
1983; Komar 1983; Birkemeier et al. 1987; Kraus 1990). While a detailed
description of such models is beyond the scope of this report, such studies can
greatly assist the understanding of coastal processes and landforms in the
vicinity of a study site. In turn, prior characterization of local geomorphology
based on independent data sources can provide an invaluable check on the
reasonableness of such models’ results.
Chapter 5 Investigation of Geomorphic Factors
87
88
6 Summary and Conclusions
Coastal environments show great geomorphic diversity over space and over
time. Spatial diversity occurs because coastal landforms develop in a variety
of terrestrial and marine environments, composed of materials that include a
variety of rocks and sediments. In addition, environmental factors, such as
coastal winds, waves, tides, currents, storms, sea level, tectonics, and
sediment supply show geographical variation. Temporal diversity in
landforms and materials occurs largely because environmental factors show
temporal variations. Temporal variations may be cyclic, noncyclic, or
unidirectional over the time period examined. The geomorphic variability of
coasts reflects the multiplicity of geomorphic and geologic responses over a
variety of time scales.
Types of geomorphic zones include (a) beaches and the nearshore zone,
(b) coastal dunes, (c) the shoreface, (d) inlets, (e) shelf shoals, (f) deltas,
(g) estuaries, (h) reefs, (i) mudflats and mangroves, (j) strand plains, and
(k) cliff coasts. It is an important aspect of engineering and geologic studies
to assimilate and interpret evidence regarding geomorphic variability over the
multiple time scales that occur in these wide-ranging coastal environments.
Study of the geomorphic variations of coasts can be approached over a
variety of time scales. Three principal time scales that are important in
assessing geologic and geomorphic changes in coasts include the following:
(a) modern studies based largely on field data or laboratory and office
experiments regarding environmental processes; (b) historic studies based
largely on information from maps, photography, archives, and other sources;
and, (c) paleoenvironmental studies based largely on stratigraphy and
associated geological and paleoenvironmental principles. In actuality,
however, these general time scale approaches show overlap. Further, within
each of the categories, certain time scales may be of particular importance for
influencing coastal changes. For example, tidal and seasonal changes are
significant in modern studies and Holocene sea level history is important in
paleoenvironmental studies.
Many coastal geomorphic features are temporally variable and tend to
change form with changes in certain critical environmental factors. Some of
these changes are cyclic and relate mainly to seasonal variations in wave
climate; others are the result of rare intermittent events such as major storms
Chapter 6 Summary and Conclusions
or long-term unidirectional trends that may be climatic or related to changes in
relative sea level and/or sediment supply. The planning and design of coastal
engineering projects and the long-term management of coastal areas require a
basic knowledge of the likely geomorphic variations that can be expected to
occur during the lifetime of the project. Thus, before planning and designing,
some study of the environmental and geomorphic features of the coastline to
be engineered, and its relation to adjacent coastlines, should be given detailed
attention.
Many types of processes occur in the coastal zone. Inland of the coastline,
terrestrial processes are dominant, except during severe storm surges and
where the coastline is on a barrier backed by marginal marine features such as
lagoons, sounds, bays, and marshland. The shore and shoreface are the main
focuses of coastal marine processes: waves, currents, tides, and storm surges.
Seaward of the shoreface, inner Continental Shelf features such as linear and
arcuate shoals may change because of interaction with large waves and storm-
generated shelf currents. Other important causes of change in coastal zone
features are changes in relative sea level, increase or decrease of sediment
supply, and construction of engineering projects. Processes acting on
consolidated rock are usually much slower to bring about significant
morphological change, and some features may remain relatively unchanged for
centuries. Also, some changes such as relative sea level may take place so
slowly that they are difficult to detect and measure.
Data collection on temporal changes in coastal features and environmental
factors is often difficult and expensive. Ideally, time-series data should cover
periods of several years, but this is rarely possible because of required lead
time and funding constraints. In some cases, there are historical resources in
the form of earlier hydrographic surveys, aerial photography, and prior
studies that can provide information about past temporal changes, but many
are deficient in detail, quality, time span, or frequency of observations and
measurements.
It is important to obtain data on the processes, such as waves and currents,
that affect coastal features and, insofar as possible, gain an understanding of
the connection between processes and variable geomorphic features. Many
instruments are now available for acquiring time-series data on waves,
currents, winds, and other dynamic factors of the environment. Although
capable of obtaining high quality data, these techniques of data collection can
be expensive if used alone. With good historical sources such as weather
charts, much can be learned concerning factors such as waves and storm
surges by hindcasting, and instruments may be more economically used in a
limited role to verify data. The difficulty in measuring many environmental
factors is primarily economic rather than technical.
The geomorphic variability of the coast requires that a range of factors be
considered in the management and engineering of coasts for storm protection
and navigation. Environmental and geomorphic factors cause the rates, scale,
and nature of change in coastal environments to be highly variable, and the
Chapter 6 Summary and Conclusions
89
90
interaction of these various factors is generally complex. Coastal scientists
and engineers will be more successful in planning and designing coastal
projects by determining the geomorphic variability of the coastal zone over
short and long time scales.
Chapter 6 Summary and Conclusions
References
Abel, C. E., Tracy, B. A., Vincent, C.L., and Jensen, R.E. 1989.
"Hurricane Hindcast Methodology and Wave Statistics for Atlantic and
Gulf Hurricanes from 1956-1975," WIS Report 19, U.S. Army Engineer
Waterways Experiment Station, Vicksburg, MS.
Allen, J. R. L. 1968. Current Ripples: Their Relation to Patterns of Water
and Sediment Movement, North Holland, Amsterdam, Netherlands.
Anders, F. J., and Hansen, M. 1990. "Beach and Borrow Site Sediment
Investigation for a Beach Nourishment at Ocean City, Maryland,"
Technical Report CERC-90-5, U.S. Army Engineer Waterways
Experiment Station, Vicksburg, MS.
Anders, F. J., Reed, D. W., and Meisburger, E. P. 1990. "Shoreline
Movements, Report 2: Tybee Island, Georgia to Cape Fear, North
Carolina: 1851-1983," Technical Report CERC-83-1, U.S. Army Engineer
Waterways Experiment Station, Vicksburg, MS.
Andrews, J. T., ed. 1974. Glacial Isostasy, Dowden, Hutchinson and Ross,
Stroudsburg, PA.
Ashley, G. M. 1900. "Classification of Large-Scale Subaqueous Bedforms:
A New Look at an Old Problem," Journal of Sedimentary Petrology,
Vol 60, pp 160-172.
Aubrey, D. G., and Speer, P. E. 1984. "Updrift Migration of Tidal Inlets,"
Journal of Geology, Vol 92, pp 531-545.
Bagnold, R. A. 1941. The Physics of Blown Sand and Desert Dunes,
Methuen, London, UK.
Barrick, D. E., Evans, M. W., and Weber, B. L. 1977. "Ocean Surface
Currents Mapped by Radar," Science, Vol 198, pp 138-144.
Bascom, W. H. 1954. “Characteristics of Natural Beaches," Proceedings of
the Fourth Conference on Coastal Engineering, pp 183-190.
References
91
92
Bates, R. L., and Jackson, J. A. 1980. Glossary of Geology, 2nd ed., Amer-
ican Geological Institute, Falls Church, VA.
Bird, E. C. F. 1969. Coasts, Massachusetts Institute of Technology Press,
Cambridge, MA.
Birkemeier, W. A. 1985. "Storm-Induced Morphology Changes During
Duck 85," Coastal Sediments 87, American Society of Civil Engineering,
New Orleans, LA, pp 834-847.
Birkemeier, W. A., Kraus, N. C., Scheffmer, N. W., and Knowles, S. C.
1987. “Feasibility Study of Quantitative Erosion Models for Use by the
Federal Emergency Management Agency," Technical Report CERC-87-8,
U.S. Army Engineer Waterways Experiment Station, Vicksburg, MS.
Bloom, A. L. 1965. "The Explanatory Description of Coasts," Zeitschrift fur
Geomorphologie, Vol 9, pp 422-436.
. 1991. Geomorphology: A Systematic Analysis of Late Cenozoic
Landforms, Prentice Hall, Englewood Cliffs, NJ.
Bluck, B. J. 1967. "Sedimentation of Beach Gravels: Examples from South
Wales," Journal of Sedimentary Petrology, Vol 37, pp 128-156.
Boothroyd, J. C. 1985. "Tidal Inlets and Tidal Deltas," Coastal Sedimentary
Environments, R. A. Davis, Jr., ed., Springer-Verlag, New York,
pp 445-532.
Bowen, A. J. 1969. "Rip Currents, 1: Theoretical Investigations," Journal
of Geophysical Research, Vol 74, pp 5467-5478.
Bowen, A. J., and Inman, D. L. 1966. "Budget of Littoral Sands in the
Vicinity of Port Arguello, California," Technical Memorandum No. 19,
U.S. Army Engineer Waterways Experiment Station, Vicksburg, MS.
1969. "Rip Currents, 2: Laboratory and Field Investigations,"
Journal of Geophysical Research, Vol 74, pp 5479-5490.
Bradley, W., and Griggs, G. 1976. "Form, Genesis, and Deformation of
Central California Wave Cut Platform," Bulletin of the Geological Society
of America, Vol 87, pp 433-440.
Brenninkmeyer, B. M. 1978. "Heavy Minerals," The Encyclopedia of
Sedimentology, F. W. Fairbridge and J. Bougeois, eds., Dowden,
Hutchinson and Ross, Inc., Stroudsburg, PA, pp 400-402.
Bretschneider, C. L. 1959. “Wave Variability and Wave Spectra for Wind
Generated Gravity Waves," U.S. Army Beach Erosion Board Technical
Memorandum No. 113, Vicksburg, MS.
References
Bruun, P. 1954. "Coast Erosion and the Development of Beach Profiles,"
U.S. Army Beach Erosion Board Technical Memorandum No. 44,
Vicksburg, MS.
Buller, A. T., and McManus, J. 1979. “Sediment Sampling and Analysis,"
Estuarine Hydrography and Sedimentation, K. R. Dyer, ed., Cambridge
University Press, Cambridge, UK.
Carter, R. W. G. 1988. Coastal Environments: An Introduction to the
Physical, Ecological, and Cultural Systems of Coastlines, Academic Press,
London, UK.
Carter, R. W. G., and Orford, J. D. 1984. "Coarse Clastic Barrier Beaches:
A Discussion of the Distinctive Dynamic and Morphosedimentary
Environments," Marine Geology, Vol 60, pp 377-389.
Chapman, V. J. 1964. Coastal Vegetation, MacMillan Co., New York.
Chorley, R. J., Schumm, S. A., and Sugden, D. E. 1984. Geomorphology,
Methuen, London, UK.
Chu, Y., Lund, R. B., and Camfield, F. E. 1987. "Sources of Coastal Engi-
neering Information," Technical Report CERC-87-1, U.S. Army Engineer
Waterways Experiment Station, Vicksburg, MS.
Clausner, J. E., Birkemeier, W. A., and Clark, G. R. 1986. "Field
Comparison of Four Nearshore Survey Systems," Miscellaneous Paper
CERC-86-6, U.S. Army Engineer Waterways Experiment Station,
Vicksburg, MS.
Clemens, K. E., and Komar, P. D. 1988. "Oregon Beach-Sand Compositions
Produced by the Mixing of Sediments Under a Transgressing Sea," Journal
of Sedimentary Petrology, Vol 58, pp 519-529.
Clifton, H. E., and Dingler, J. R. 1984. "“Wave-Formed Structures and
Paleoenvironmental Reconstruction," Marine Geology, Vol 60, pp 165-
198.
Coleman, S. M., Berquist, C. R., Jr., and Hobbs, C. H. 1988. "Structure
and Origin of the Bay-Mouth Shoal Deposits, Chesapeake Bay, Virginia,"
Marine Geology, Vol 83, pp 95-113.
Corson, W. D., Abel, C. E., Brooks, R. M., Farrar, P. D., Groves, B. J.,
Payne, J. B., McAneny, D. S., and Tracy, B. A. 1987. "Pacific Coast
Hindcast, Phase II Wave Information," WIS Report 16, U.S. Army
Engineer Waterways Experiment Station, Vicksburg, MS.
References
I3
94
Corson, W. D., and Tracy, B. A. 1987. "Atlantic Coast Hindcast, Phase II,
Wave Information: Additional Extremal Estimates," WIS Report 15,
U.S. Army Engineer Waterways Experiment Station, Vicksburg, MS.
Curray, J. R. 1964. "Transgressions and Regressions," Papers in Marine
Geology, R.L.Miller, ed., Macmillan, New York, pp 175-203.
1965. "Late Quaternary History of Continental Shelves of the
United States," The Quaternary of the United States, H. E. Wright and D.
G. Fyre, eds., Yale University Press, New Haven, CN, pp 723-735.
Davies, J. L. 1964. "A Morphogenetic Approach to World Shorelines,"
Zeitschrift fur Geomorphologie, Vol 8, pp 127-142.
1980. Geographical Variation in Coastal Development, Longman,
London, UK.
Davis, R. A., Jr., ed. 1985. "Beach and Nearshore Zone," Coastal
Sedimentary Environments, Springer-Verlag, New York, pp 379-444.
Dean, R. G. 1977. “Equilibrium Beach Profiles: U.S. Atlantic and Gulf
Coasts," Technical Report No. 12, University of Delaware, Newark, DE.
Dean, R. G., and Maurmeyer, E. M. 1983. "Models for Beach Profile
Response," CRC Handbook of Coastal Processes and Erosion, P. D.
Komar, ed., CRC Press, Inc., Boca Raton, FL, pp 151-167.
DeFant, A. 1958. Ebb and Flow, the Tides of Earth, Atmosphere, and
Water, University of Michigan Press, Ann Arbor, MI.
Dillon, W. P. 1970. "Submérgence Effects on a Rhode Island Barrier and
Lagoon and Inferences on Migration of Barriers," Journal of Geology,
Vol 78, pp 94-106.
Dillon, W. D., and Oldale, R. N. 1978. "Late Quarternary Sea Level
Curve: Reinterpretation Based on Glacio-Eustatic Influence," Geology,
Vol 6, pp 56-60.
Dolan, R., Hayden, B., Hornberger, G., Zieman, J., and Vincent, M. 1972.
"Classification of the Coastal Environments of the World," Technical
Report No. 1, ONR Contract 389-159, University of Virginia,
Charlottesville, VA.
Dolan, R., and Hayden, B. 1983. "Patterns and Predictions of Shoreline
Change," CRC Handbook of Coastal Processes and Erosion, P. D. Komar
ed., CRC Press, Inc., Boca Raton, FL, pp 123-149.
>
References
Dolan, R., Hayden, B., and May, S. 1983. "Erosion of the U.S.
Shorelines," CRC Handbook of Coastal Processes and Erosion, P. D.
Komar, ed., CRC Press, Inc., Boca Raton, FL, pp 285-299.
Dolan, R., Hayden, B., May, S., and May, P. 1982. "Erosion Hazards
Along the Mid-Atlantic Coast," Applied Geomorphology, R. Craig and
J. Craft, eds., Allen and Unwin, London, UK.
Duane, D. B., Field, M. E., Meisburger, E. P., Swift, D. V. P., and
Williams, S. J. 1972. “Linear Shoals on the Atlantic Inner Continental
Shelf, Florida to Long Island," Shelf Sediment Transport, D. J. P. Swift,
D. B. Duane, and O. H. Pilkey, eds., Dowden, Hutchinson and Ross,
Inc., Stroudsburg, PA, pp 447-489.
Duncan, J. R. 1964. "The Effects of Water Table and Tidal Cycle on
Swash-Backwash Sediment Distribution and Beach Profile Development,"
Marine Geology, Vol 2, pp 186-197.
Emery, K. O., and Aubrey, D. G. 1991. Sea Levels, Land Levels, and Tide
Gages, Springer-Verlag, New York.
Everts, C. H. 1978. "Geometry of Profiles Across the Inner Continental
Shelves of the Atlantic and Gulf Coasts of the United States," Technical
Report CERC-78-4, U.S. Army Engineer Waterways Experiment Station,
Vicksburg, MS.
Field, M. E. 1979. "Sediments, Shallow Bottom Structure, and Sand
Resources of the Inner Continental Shelf, Central Delmarva Peninsula,"
Technical Paper No. CERC-79-2, U.S. Army Engineer Waterways
Experiment Station, Vicksburg, MS.
Field, M. E., and Duane, D. B. 1974. “Geomorphology and Sediments of
the Inner Continental Shelf, Cape Canaveral, Florida," Coastal Engineering
Research Center Technical Memorandum 42, Vicksburg, MS.
Fisher, J. J. 1982. "Inlets and Inlet Migration," Encyclopedia of Beaches and
Coastal Environments, M. L. Schwartz, ed., Hutchinson Ross Publishing
Co., Stroudsburg, PA, pp 486-488.
Flemming, N. C. 1965. "Form and Relationship to Present Sea Levels of
Pleistocene Marine Erosion Features," Journal of Geology, Vol 73,
pp 799-811.
Frakes, L. A. 1979. Climatic Changes Through Geologic Time, Elsevier,
Amsterdam, Netherlands.
References
96
Fredette, T. J., Nelson, D. A., Miller-Way, T., Adair, J. A., Sotler, V. A.,
Clausner, J. E., Hands, E. B., and Anders, F. J. 1990. "Selected Tools
and Techniques for Physical and Biological Monitoring of Aquatic Dredged
Material Disposal Sites," Technical Report CERC-D-90-11, U.S. Army
Engineer Waterways Experiment Station, Vicksburg, MS.
Fulton, K. 1981. "A Manual for Researching Historical Coastal Erosion,"
California Sea Grant College Program, Report No. T-CSGCP-003.
Galloway, W. E. 1975. "Process Framework for Describing the
Morphologic and Stratigraphic Evolution of Deltaic Depositional Systems,"
Deltas: Models for Exploration, M. L. S. Broussard, ed., Houston
Geological Society, Houston, TX, pp 87-98.
Galloway, W. E., and Hobday, D. K. 1983. Terrigenous Clastic
Depositional Systems, Springer-Verlag, New York.
Galvin, C. J. 1968. "Breaker Type and Classification on Three Laboratory
Beaches," Journal of Geophysical Research, Vol 73, pp 3651-3659.
Glen, N. C. 1979. "Tidal Measurement," Estuarine Hydrography and
Sedimentation, K. R. Dyer, ed., Cambridge University Press, Cambridge,
UK.
Goldsmith, V. 1985. "Coastal Dunes," Coastal Sedimentary Environments,
R. A. Davis, Jr., ed., Springer-Verlag, New York, pp 303-378.
Gornitz, V., Lebedeff, S., and Hansen, J. 1982. "Global Sea Level Trend in
the Past Century," Science, Vol 215, pp 1611-1614.
Granat, M. A., and Ludwick, J. C. 1980. "Perpetual Shoals at the Entrance
to Chesapeake Bay: Flow Substrate Interactions and Mutually Evasive Net
Currents," Marine Geology, Vol 36, pp 307-323.
Hands, E. B. 1983. "The Great Lakes As a Test Model For Profile
Responses to Sea Level Changes," CRC Handbook of Coastal Processes
and Erosion, P. D.Komar, ed., CRC Press, Inc., Boca Raton, FL, pp 167-
189.
Hayes, M. O. 1967. "Hurricanes as Geological Agents: Case Studies of
Hurricanes Carla, 1961 and Cindy, 1963," University of Texas, Bureau of
Economic Geology, Report No. 61.
Hayes, M. O. 1980. "General Morphology and Sediment Patterns in Tidal
Inlets," Sedimentary Geology, Vol 26, pp 139-156.
Hayes, M. O., and Kana, T. W. 1976. “Terrigenous Clastic Depositional
Environments," Coastal Research Division, Department of Geology,
University of South Carolina, Technical Report No. 11-CRD.
References
Hicks, S. D. 1972. "Changes in Tidal Characteristics and Tidal Datum
Planes," The Great Alaskan Earthquake of 1964: Oceanography and
Coastal Engineering, National Academy of Sciences, Washington, D.C.
Hicks, §. D. 1972b. "On the Classification and Trends of Long Period Sea
Level Series," Shore and Beach, Vol 40, pp 20-23.
. 1978. "An Average Geopotential Sea Level Series for the U.S.,"
Journal of Geophysical Research, Vol 83, pp 1377-1379.
. 1983. "Sea Level Variations for the United States: 1855-1980,"
U.S. Department of Commerce, National Oceanic and Atmospheric
Administration, National Ocean Service, Rockville, MD.
Higgins, C. G. 1968. "Beach Rock," Encyclopedia of Beaches and Coastal
Environments, M. L. Schwartz, ed., Hutchinson Ross Publishing Co.,
Stroudsburg, PA, pp 70-73.
Hjulstrém, S$. 1935. "Studies of the Morphological Activity of Rivers as
Illustrated by the River Fyris," Bulletin of the Geological Institute, Univer-
sity of Upsala, Vol 25, pp 221-527, Upsala, Sweden.
Holman, R. A. 1983. "Edge Waves and the Configuration of the Shoreline,"
CRC Handbook of Coastal Processes and Erosion, P. D. Komar, ed.,
CRC Press, Inc., Boca Raton, FL, pp 21-34.
Hough, J. L. 1968. "Great Lakes," Encyclopedia of Geomorphology, R. B.
Fairbridge, ed., Dowden, Hutchinson and Ross, Inc., Stroudsburg, PA,
pp 499-506.
Hsu, S. A. 1988. Coastal Meteorology, Academic Press, Inc., San Diego,
CA.
Hubertz, J. M., and Brooks, R. M. 1989. "Gulf of Mexico Hindcast Wave
Information," WIS Report 18, U.S. Army Engineer Waterways Experiment
Station, Vicksburg, MS.
Hughes, S. A. 1988. “Laboratory Measurement of Spatial and Temporal
Suspended Sediment Concentration Under Waves," Miscellaneous Paper
CERC-88-1, U.S. Army Engineer Waterways Experiment Station,
Vicksburg, MS.
Huntley, D., and Bowen, A. 1975. "Comparison of the Hydrodynamics of
Steep and Shallow Beaches," Nearshore Sediment Dynamics and
Sedimentation, J. Hails and A. Carr, eds., Wiley, London, UK.
Ingle, J. C., Jr. 1966. "The Movement of Beach Sand," Developments in
Sedimentology, Vol 5, Elsevier, Amsterdam, Netherlands.
97
References
Iwagaki, Y., and Noda, H. 1963. "Laboratory Study of Scale Effects on
Two Dimension Beach Processes," Proceedings of the Eighth Conference
on Coastal Engineering, pp 174-210.
Inman, D. L. 1953. “Areal and Seasonal Variations in Beach and Nearshore
Sediments at La Jolla, California," U.S. Army Beach Erosion Board,
Technical Memo 39, Fort Belvoir, VA.
Jackson, K. C. 1970. Textbook of Lithology, McGraw-Hill Book Company,
New York.
Jelesnianski, C. P. 1972. SPLASH (Special Program to List the Amplitudes
of Surges from Hurricanes): I. Landfall Storms, NOAA Technical
Memorandum NWS TDL-46, Washington, D.C.
Jelesnianski, C. P., and Chen, J. 1982. SLOSH (Sea, Land and Overland
Surges from Hurricanes), Techniques Development Laboratory, NOAA,
National Weather Service, Silver Springs, MD.
Jensen, R. E., Hubertz, J. M., and Payne, J. B. 1989. "Pacific Coast
Hindcast, Phase III, North Wave Information," WIS Report 17,
U.S. Army Engineer Waterways Experiment Station, Vicksburg, MS.
King, C. A. M. 1982. “Shingle and Shingle Beaches," Encyclopedia of
Beaches and Coastal Environments, M. L. Schwartz, ed., Hutchinson Ross
Publishing Co., Stroudsburg, PA, pp 751-752.
Knighton, D. 1984. Fluvial Forms and Processes, Edward Arnold, Inc.,
New York.
Kolb, C. R., and van Lopik, J.R. 1966. "Depositional Environments of
Mississippi River Delta Plain, Southeastern Louisiana," Deltas in Their
Geological Framework, M. L. Shirley, ed., Houston Geological Society,
Houston, TX, pp 13-61.
Komar, P. D. 1976. Beach Processes and Sedimentation, Prentice-Hall,
Inc., Englewood Cliffs, NJ.
. 1983. "Computer Models of Shoreline Changes," CRC Handbook
of Coastal Processes and Erosion, P. D. Komar, ed., CRC Press, Inc.,
Boca Raton, FL, pp 205-216.
Komar, P. D., Clemens, K. E., Li, Z., Shih, S-M. 1989. "The Effects of
Selective Sorting on Factor Analyses of Heavy Mineral Assemblages,"
Journal of Sedimentary Petrology, Vol 59, pp 590-596.
Komar, P. D., and Inman, D. L. 1970. "Longshore Sand Transport on
Beaches," Journal of Geophysical Research, Vol 75, pp 5914-5927.
98
References
Komar, P. D. and Miller, M. 1973. "The Threshold of Sediment Movement
Under Oscillatory Waves," Journal of Sedimentary Petrology, Vol 43,
pp 1101-1110.
Kraus, N. C., and Dean, J. L. 1987. "Longshore Sand Transport Rate
Distribution Measured By Sediment Trap," Coastal Sediments ’87,
American Society of Civil Engineers, New Orleans, LA, pp 891-896.
Kraus, N. C., ed. 1990. "Shoreline Change and Storm-Induced Beach
Erosion Modeling: A Collection of Seven Papers," Miscellaneous Paper
CERC-90-2, U.S. Army Engineer Waterways Experiment Station,
Vicksburg, MS.
Lamb, H. H. 1982. Climate, History, and the Modern World, Methuen,
New York.
Langbein, W. B., and Schumm, S. A. 1958. “Yield of Sediment in Relation
to Mean Annual Precipitation," Transactions of the American Geophysical
Union, Vol 39, pp 1076-1084.
Lyles, S. D., Hickman, L. E., Jr., and Debaugh, H. A., Jr. 1988. "Sea
Level Variations for the United States 1855-1986," U.S. Department of
Commerce, National Oceanic and Atmospheric Administration, National
Ocean Service, Rockville, MD.
Ludwick, J. C. 1975. "Tidal Currents, Sediment Transport and Sand Banks
in Chesapeake Bay Entrance," Estuarine Research, L. E. Cronin, ed.,
Academic Press, New York, Vol 2, pp 365-380.
Mason, C. C., and Folk, R. L. 1958. "Differentiation of Beach, Dune, and
Aeolian Flat Environments by Size Analysis, Mustang Island, Texas,"
Journal of Sedimentary Petrology, Vol 28, pp 211-226.
May, J. R., and Britsch, L. D. 1987. "Geological Investigation of the
Mississippi River Delta Plain: Land Loss and Land Accretion," Technical
Report GL-87-13, U.S. Army Engineer Waterways Experiment Station,
Vicksburg, MS.
McCave, I. N. 1979. "Suspended Sediment," Estuarine Hydrography and
Sedimentation, K. Dyer, ed., Cambridge University Press, Cambridge,
UK.
Meisburger, E. P., and Duane, D. B. 1971. "Geomorphology and Sediments
of the Inner Continental Shelf, Palm Beach to Cape Kennedy, Florida,"
U.S. Army Coastal Engineering Research Center, Technical Memorandum
No. 34.
References
100
Meisburger, E. P., and Field, M. E. 1975. "Geomorphology, Shallow
Structure, and Sediments of the Florida Inner Continental Shelf, Cape
Canaveral to Georgia," U.S. Army Coastal Engineering Research Center,
Technical Memorandum No. 54.
Meisburger, E. P., and Williams, S. J. 1980. "Sand Resources on the Inner
Continental Shelf of the Cape May Region, New Jersey," Miscellaneous
Report CERC-80-4, U.S. Army Engineer Waterways Experiment Station,
Vicksburg, MS.
1982. "Sand Resources on the Inner Continental Shelf Off the
Central New Jersey Coast," Miscellaneous Report CERC-82-10,
U.S. Army Engineer Waterways Experiment Station, Vicksburg, MS.
Miller, R. L. 1976. "Roles of Vortices in Surf Zone Prediction:
Sedimentation and Wave Forces," Beach and Nearshore Sedimentation,
R. A. Davis, Jr. and R. L. Ethington, eds., Society for Economic
Paleontologists and Mineralogists Special Publication 24, Tulsa, OK,
pp 92-114.
Milliman, J. D., and Emery, K. O. 1968. "Sea Levels During the Past
35,000 Years," Science, Vol 162, pp 1121-1123.
Moody, D.W. 1964. "Coastal Morphology and Processes in Relation to the
Development of Submarine Sand Ridges Off Bethany Beach, Delaware,"
Ph.D. Dissertation, Johns Hopkins University, Baltimore, MD.
Morang, A., and McMaster, R. L. 1980 "Nearshore Bedform Patterns
Along Rhode Island From Side-Scan Sonar Surveys," Journal of
Sedimentary Petrology, Vol 50, No. 3, pp 831-840.
Morton, R. W., Stewart, L. L., and Germano, J. D. 1984. "Results of
Monitoring Sites at Cap Sites 1, 2, and the FVP Site in Central Long
Island Sound and a Classification Scheme for the Management of Capping
Procedures," Contribution No. 38, prepared for the U.S. Army Engineer
Division, New England, Waltham, MA.
Mosetti, F. 1982. "Currents," Encyclopedia of Beaches and Coastal
Environments, M. L. Schwartz, ed., Hutchinson Ross Publishing Co.,
Stroudsburg, PA, pp 346-349.
Moslow, T. F., and Heron, S. D., Jr. 1978. "Relict Inlets: Preservation
and Occurrence in the Holocene Stratigraphy of Southern Core Banks,
North Carolina," Journal of Sedimentary Petrology, Vol 48, pp 1275-1286.
Nichols, M. M., and Biggs, R. B. 1985. "Estuaries," Coastal Sedimentary
Environments, R. A. Davis, Jr., ed., Springer-Verlag, New York,
pp 77-186.
References
Niedoroda, A. W., Swift, D. J. P., and Hopkins, T. S. 1985. "The
Shoreface," Coastal Sedimentary Environments, R. A. Davis, Jr., ed.,
Springer-Verlag, New York, pp 533-624.
Niedoroda, A. W., Swift, D. J. P., Hopkins, T. S., and Ma, C-M. 1984.
"Shoreface Morphodynamics on Wave-Dominated Coasts," Marine
Geology, Vol 60, pp 331-354.
Nordstrom, C. E. and Inman, D. L. 1975. "Sand Level Changes on Torrey
Pines Beach, California," U.S. Army Coastal Engineering Research
Center, Fort Belvoir, VA.
Nummedal, D. 1983. "Barrier Islands," CRC Handbook of Coastal
Processes and Erosion, P. D. Komar, ed., CRC Press, Inc., Boca Raton,
FL, pp 77-121.
Payton, C. E., ed. 1977. Seismic Stratigraphy - Applications to Hydrocarbon
Exploration, American Association of Petroleum Geologists, Tulsa, OK.
Penland, S. and Suter, J. R. 1984. “Low Profile Barrier Island Overwash
and Breaching in the Gulf of Mexico," Proceedings of the Nineteenth
Coastal Engineering Conference, pp 2339-2345.
Penland, S., Suter, J. R., McBride, R. A., Williams, S. J., Kindinger, J. L.,
and Boyd, R. 1989. "Holocene Sand Shoals Offshore of the Mississippi
River Delta Plain," Transactions of the Gulf Coast Association of
Geological Societies, Vol 36, pp 471-480.
Pethick, J. 1984. An Introduction to Coastal Geomorphology, Edward
Arnold, Inc., New York.
Prior, D. B., and Coleman, J.M. 1978. "Submarine Landslides on the
Mississippi Delta-Front Slope," Geoscience and Man, Louisiana State Uni-
versity School of Geoscience, Vol 19, pp 41-53.
Pritchard, D. W. 1967. "Observations of Circulation in Coastal Plain
Estuaries," Estuaries, G. H. Lauff, ed., American Association for the
Advancement of Science Publication 83, Washington, D.C., pp 3-5.
Riehl, H. 1979. Climate and Weather in the Tropics, Academic Press, New
York.
Roberts, H. H., Murray, S. P., and Suhayda, J. N. 1975. "Physical
Processes in a Fringing Reef System," Journal of Marine Research, Vol
33, pp 233-260.
Robinson, L. A. 1977. "Marine Erosive Processes at the Cliff Foot,"
Marine Geology, Vol 23, pp 257-71.
101
References
Saville, T. 1950. "Model Studies of Sand Transport Along an Indefinitely
Straight Beach," Transactions of the American Geophysical Union, Vol 31,
pp 555-556.
Schneider, C. 1981. “The Littoral Environment Observation (LEO) Data
Collection Program," Coastal Engineering Research Center Technical Aid
81-5, Vicksburg, MS.
Selby, M. J. 1985. Earth’s Changing Surface, Clarendon Press, Oxford,
UK.
Seymour, R. J., ed. 1989. Nearshore Sediment Transport, Plenum Press,
New York.
Shepard, F. P. 1963. Submarine Geology, 2nd ed., Harper and Row, New
York.
. 1973. Submarine Geology, 3rd Ed., Harper and Row, New York.
Shepard, F. P., and Grant, U. S., TV. 1947. "Wave Erosion Along the
Southern California Coast," Geological Society of America Bulletin, Vol
58, pp 919-926.
Shepard, F. P., and Inman, D. L. 1950. "Nearshore Circulation Related to
Bottom Topography and Wave Refraction," Transactions of the American
Geophysical Union, Vol 31, No. 4, pp 555-65.
Shepard, F. P. and LaFond, E. C. 1940. "Sand Movements Near the Beach
in Relation to Tides and Waves," American Journal of Science, Vol 238,
pp 272-285.
Sherlock, A. R., and Szuwalski, A. 1987. "A Users Guide to the Littoral
Environment Observation Retrieval System," Information Report CERC-
87-3, U.S. Army Engineer Waterways Experiment Station, Vicksburg,
MS.
Shore Protection Manual. 1984. 4th ed., 2 Vols, U.S. Army Engineer
Waterways Experiment Station, Coastal Engineering Research Center,
U.S. Government Printing Office, Washington, D.C.
Short, A. D. 1979. "Three Dimensional Beach Stage Model," Journal of
Geology, Vol 87, pp 553-71.
Short, A. D., and Hesp, P. A. 1982. "Wave, Beach and Dune Interactions
in Southeastern Australia," Marine Geology, Vol 48, pp 259-284.
Silvester, R. 1962. “Sediment Movement Around the Coastline of the
World," Proceedings of the Conference on Civil Engineering Problems
Overseas, Paper No. 14, London, UK, pp 289-304.
102
References
Sireyjol, P. 1965. "Communication sur la Construction du Port de Contonou
(Dahomey)," Proceedings of the Ninth Conference on Coastal Engineering,
American Society of Civil Engineers, New York.
Smith, D. E., and Dawson, A. G. 1983. Shorelines and Isostasy, Academic
Press, London, UK.
Sonu, C. J. 1972. "Field Observation of Nearshore Circulation and
Meandering Currents," Journal of Geophysical Research, Vol 77, pp 3232-
3247.
Sonu, C. J., and van Beek, J. L. 1971. "Systematic Beach Changes in the
Outer Banks, North Carolina," Journal of Geology, Vol 79, pp 416-425.
Stoddart, D. R. 1969. "Ecology and Morphology of Recent Coral Reefs,"
Biological Reviews, Vol 44, pp 433-498.
Strahler, A. N., and Strahler, A. H. 1987. Modern Physical Geography,
John Wiley and Sons, New York.
Sunamura, T. 1983. "Processes of Sea Cliff and Platform Erosion," CRC
Handbook of Coastal Processes and Erosion, P. D. Komar, ed., CRC
Press, Inc., Boca Raton, FL, pp 233-266.
Swift, D. J. P., Kofed, J. W., Saulsbury, F. P, and Sears, P. 1972.
"Holocene Evolution of the Shelf Surface, Central and South Atlantic Shelf
of North America," Shelf Sediment Transport, D. J. P. Swift, D. B.
Duane, and O. H. Pilkey, eds., Dowden, Hutchinson, and Ross,
Stroudsburg, PA.
Swift, D. J. P., Parker, G., Lanfredi, N. W., Perillo, G., and Figge, K.
1978. “Shoreface-Connected Sand Ridges on European Shelves: A
Comparison," Estuarine and Coastal Marine Science, Vol 7, pp 257-273.
Tanner, W. F. 1967. "Ripple Mark Indices and Their Uses," Sedimentology,
Vol 9, pp 89-104.
Tanner, W. F., ed. 1978. “Standards for Measuring Shoreline Change,"
Coastal Research, Tallahassee, FL.
Teleki, P. G., Musialowski, F. R. and Prins, D. A. 1976. "Measurement
Techniques for Coastal Waves and Currents," Information Report CERC-
76-11, U.S. Army Engineer Waterways Experiment Station, Vicksburg,
MS.
Trenhaile, A. S. 1980. "Shore Platforms: A Neglected Coastal Feature,"
Progress in Physical Geography, Vol 4, pp 1-23.
103
References
Trimble, S. W., and Cooke, R. U. 1991. "Historical Sources for
Geomorphology Research in the United States," The Professional
Geographer, Vol 43, pp 212-227.
Vincent, C. E., Young, R. A., and Swift, D. J. P. 1983. "Sediment
Transport Along the Long Island Shoreface, North American Atlantic
Shelf: Role of Waves and Currents in Shoreface Maintenance,"
Continental Shelf Research, Vol 2, pp 163-181.
Wells, J. T., and Coleman, J. M. 1981a. "Physical Processes and Fine-
Grained Sediment Dynamics, Coast of Surinam, South America," Journal
of Sedimentary Petrology, Vol 51, pp 1053-1068.
. 1981b. "Periodic Mudflat Progradation, Northeastern Coast of
South America: A Hypothesis," Journal of Sedimentary Petrology,
Vol 51, pp 1069-1075.
Whittaker, R. H., and Likens, G. E. 1975. "Net Primary Production and
Plant Biomass for the Earth," The Primary Production of the Biosphere,
H. Reith and R. H. Whittaker, eds., Springer-Verlag, New York,
pp 305-328.
Woodhouse, W. W., Jr. 1978. “Dune Building and Stabilization With
Vegetation," SR-3, U.S. Army Engineer Waterways Experiment Station,
Vicksburg, MS.
Wright, L. D. 1982. "Deltas," Encyclopedia of Beaches and Coastal
Environments, M. L. Schwartz, ed., Hutchinson Ross Publishing Co.,
Stroudsburg, PA, pp 358-68.
Wright, L. D., and Short, A. D. 1983. "Morphodynamics of Beaches and
Surf Zones in Australia," CRC Handbook of Coastal Processes and
Erosion, P. D. Komar, ed., CRC Press, Inc., Boca Raton, FL, pp 35-64.
Wright, L. D., Chappell, J., Thom, B. G., Bradshaw, M. P., and Cowell, P.
1979. “Morphodynamics of Reflective and Dissipative Beach and Inshore
Systems, Southeastern Australia," Marine Geology, Vol 32, pp 105-140.
Young, R. A., Merrill, J. T., Clarke, T. L., and Proni, J. R. 1982.
"Acoustic Profiling of Suspended Sediments in the Marine Bottom
Boundary Layer," Geophysical Research Letters, Vol 9, pp 175-178.
104
References
Appendix A
Glossary of Geologic Terms
ANGLE OF REPOSE The maximum slope at which cohesionless sediments
are stable.
ARCH A rock feature in the form of an arch lying close offshore. The form
and isolation are products of marine erosion.
AVULSION A tearing away. Often refers to a rapid change in a river’s
course.
BACK BARRIER Pertaining to the lagoon-marsh-tidal creek complex in the
lee of a coastal barrier island, barrier spit, or baymouth barrier.
BARCHAN DUNE A dune of crescentic shape with the convex side facing
the prevailing wind.
BEACH CUSPS One of a series of low mounds separated by crescentic-
shape troughs spaced at regular intervals along a beach.
BEDFORMS Any deviation from a flat bed that is readily detected by eye,
e.g., ripple marks, sand waves.
BIOEROSION Erosion of rocks or sediment created by biological activity,
especially boring organisms.
BIOGENIC Of biological origin. Usually sediments composed of the hard
parts of plants or animals and organic reef masses.
BIOTURBATION The disturbance of sediment bedding by the activities of
burrowing organisms.
BLOWOUTS Places in vegetated dunes or sand flats where bare spots occur
and are subjected to wind erosion.
BRYOZOA Invertebrate belonging to the Phylum Bryozoa and characterized
by colonial growth and a branching, twiglike skeleton.
Al
Appendix A Glossary of Geologic Terms
A2
BYPASSING The movement of sediment across a natural or manmade
barrier to alongshore sediment movement.
CARBONATION A chemical weathering process involving the
transformation of calcium, magnesium, potassium, and sodium minerals
into carbonate and bicarbonates of these metals by carbon dioxide
contained in water.
CHELATION The taking up or release of a metallic ion by an organic
molecule.
CLASTIC Sediment or rock composed of particles of pre-existing rocks or
minerals that have been transported out of the place of origin.
CONTINENTAL SHELF The broad shallow submarine plain that fringes
many continental coasts.
CORALLINE Pertaining to the large group of hard, calcareous, external
skeletal, bottom-dwelling marine coelenterates of class Anthozoa.
CORIOLIS EFFECT The apparent deflection of moving objects from a
straight path caused by earth rotation. Moving bodies appear deflected to
the right in the Northern Hemisphere and to the left in the Southern
Hemisphere.
CREVASSE Splay deposit Deposits laid down by river water emerging from
a break or rupture in a river’s levees. The deposits sometimes resemble a
small delta.
CYCLONIC Pertaining to an atmospheric system that is characterized by
low pressure and counterclockwise winds north of the equator and
clockwise winds to the south.
DIAGENESIS Changes undergone by sediments after their initial deposition.
The term often refers to compaction, cementation, and replacement.
DIAPIR Structure in which the core of an anticline breaks through overlying
rocks.
DIASTROPHISM The deformation of large masses of rock.
DIP The angle of a bedding plane to the horizontal.
DISTRIBUTARY A branch of a stream flowing out of another stream.
Distributaries are most common in deltas.
DOLOMITIC Containing dolomite, a calcium magnesium carbonate.
Dolomite is both a mineral and rock name.
Appendix A Glossary of Geologic Terms
DRUMLIN A glacial feature usually consisting of a large mound of glacial
drift.
EBB TIDAL DELTA Shoal formed on the seaward side of inlets by ebb
tidal currents.
ECHINOIDS A class of free-moving echinoderms, mostly with rigidly plated
bodies.
EUSTATIC Refers to worldwide changes in sea level due to changes of the
volume of water in the ocean or a change in the volume capacity of the
basins.
FJORD A glaciated valley that has been partly drowned by relative sea level
changes or as a result of overdeepening by the glacier that formed it.
FLOOD TIDAL DELTA A shoal complex on the landward side of an inlet
deposited by flood tidal currents.
FORAMINIFERA Protozoans characterized by tests of one to many
chambers composed of calcite or of agglutinated particles.
FRIABLE Weakly consolidated or weathered rock that is easily broken up.
GEOMORPHIC Pertaining to landforms.
GLACIAL DRIFT Sediments associated with glacial deposition.
GLACIOISOSTATIC Vertical crustal movement including depression of a
land area due to the weight of overlying glacial ice or elevation of the land
due to unloading of glacial ice.
GLACIOLACUSTRINE Pertaining to glacial deposition or erosion in a
lake.
GROINS Low structures oriented perpendicular to the shore. They are
intended to trap or retard alongshore movement of beach material.
HOLOCENE EPOCH The latest epoch, which began about 10,000 years
before present, following the last glaciation.
HYDRATION Absorption of or chemical reaction with water.
HYDROLYSIS A decomposition reaction involving water, usually between
silicate minerals and aqueous solution.
IGNEOUS Said of rock or minerals which solidified from molten or partly
molten materials. Granite is a common example.
A3
Appendix A Glossary of Geologic Terms
A4
ISOBARS Lines of equal barometric pressure on a weather map.
ISOHALINES Lines of equal salinity on a chart of saltwater bodies.
KARST A limestone terrain of very irregular topography due to extensive
solution of the limestone rock.
KATABATIC WIND Any wind blowing down an incline. If the wind is
cold, it is known as a foehn; if it is cold, it may be a fall or gravity wind.
LACUSTRINE Pertaining to a lake.
LAGOON A shallow body of water behind a coastal barrier island, barrier
spit, or baymouth barrier. Also applied to the water bodies inland of coral
reefs and atolls.
LAPSE RATE The adiabatic rate of change of a meteorological element
(such as temperature) associated with a change in height.
LITHIFIED Refers to rocky or hardened sediments.
LITHOLOGIC Pertaining to the character of rock.
LITHOLOGY The general characteristics of a rock or sediment.
LITHOSPHERE The solid portion of the earth, usually referring to the crust
and upper part of the mantle (about 100 km in thickness total).
LONGSHORE CURRENT A current flowing alongshore, primarily inshore
of the outer breaker line.
LONGSHORE DRIFT Sediment moving alongshore on the foreshore and
adjacent breaker zone due to waves and wave-generated currents.
MARGINAL SEAS A partly enclosed sea bordering a continental landmass.
MASS WASTING The movement of soil and sediments downslope due to
gravity.
MORAINE Accumulation of glacial till left by melting of glaciers. Material
is deposited directly by the ice.
MORPHODYNAMIC A concept introduced by Wright, Short, and
coworkers which represents the integration of seemingly disparate
hydrodynamic and morphologic factors into a coherent morphologic model
with distinct states or stages.
MORPHOLOGY In geology, the visual shape of landscape features, either
singly or as a group in a given area.
Appendix A Glossary of Geologic Terms
NATURAL LEVEE A natural embankment along the shore of a stream
deposited by overflow during floods.
ORBITAL WAVE MOTION The orbital displacement of water as a wave
passes.
ORTHOGONAL A line perpendicular to a wave crest.
OOLITE Calcareous rounded particles ranging from egg-shaped to button-
shaped that are precipitated directly from sea water.
PALEOENVIRONMENT An ancient environment that is reconstructed by
the evidence of fossils, bedding and sediment, or rock characteristics.
PALEONTOLOGY The study of past geological history, primarily by
analysis of fossil remains of organisms.
PALUDAL Pertaining to low water-covered land, such as swamps and
marshes.
PALYNOLOGY The study of spores and pollen. Often used to help
reconstruct past environments.
PARALLAX The apparent displacement of an object due to a change in the
position of the observer.
PEDOLOGY The science of soils.
PHOSPHATIC Containing phosphate, usually in combination with other
elements, to form minerals.
PLEISTOCENE A subdivision of the Quarternary period. The Pleistocene
encompasses the ice ages.
QUATERNARY The period following the tertiary period and containing the
Pleistocene and Holocene epochs.
RADIOCARBON DATE Age of a carbonaceous material derived from the
radioactive changes in carbon 14 through time.
RADIOMETRIC Chronological age determined by study of suitable
radioactive substances.
RELATIVE SEA LEVEL The level of land and sea in respect to one
another. Changes in relative level may be due to eustatic sea level changes
or the vertical movement of the landmass.
SALTATION The movement of sediment particles in a series of short jumps
from the bottom.
Appendix A Glossary of Geologic Terms
A5
A6
SALT DOME A diapir of salt that breaks through overlying rocks or
sediment. Hydrocarbon-bearing strata are often associated with salt domes.
SEDIMENTOLOGICAL Pertaining to the science of sedimentary rocks and
their formative processes.
SEISMIC REFLECTION A geophysical method of obtaining sonic
representations of subbottom stratification. Seismic reflection surveys are
performed on land and at sea.
SELECTIVE SORTING The process in sediment transport of differential
response of sediment particles due to differences in size, shape, and
specific gravity.
SETUP Elevation of a water surface due to onshore mass transport of water
by wind and waves.
SHORE The border of a landmass with the sea.
SHOREFACE A sloping bottom zone between the shore and the inner
continental shelf.
SILICEOUS Containing silica.
SINK A process that subtracts sand from a littoral compartment.
SLIP FACE The steeply sloping lee side of a dune or sand wave.
SPIT A long narrow ridge of sand usually extending from a headland parallel
to the general trend of the coast.
STACK A rock column isolated offshore by coastal erosion.
STRATIGRAPHIC Pertaining to the study of stratified rocks and sediments.
STRIKE The orientation of the line of intersection of a bedding fault plane
with a horizontal plain.
STORM SURGE A rise of water level above normal due to wind stress on
the water surface.
SUBAERIAL Pertaining to the land surface as contrasted with subaqueous,
i.e., below the water surface.
SUPERPOSITION A geological concept that a rock or sediment overlying
another layer is younger in origin, provided no structural deformation
exists that would reverse the sequence.
TECTONIC Pertaining to structural movements of rock masses.
Appendix A Glossary of Geologic Terms
TECTONIC PLATES A large part of the earth’s crust that moves as a unit
with respect to other plates.
TEPHRA Clastic material that has been ejected from a volcano.
TERRESTRIAL Pertaining to land as opposed to the ocean.
TILT Sideways inclination of an aircraft or spaceship.
TSUNAMI A long-period wave caused by an underwater disturbance such as
an earthquake. Tsunamis are often highly destructive if they reach a coast.
TIDAL PRISM The total amount of water that flows into a lagoon, harbor,
or estuary and out again with the rise and fall of the tide.
WAVE STEEPNESS The ratio of wave height to wave length.
WEATHERED The condition of rocks that have undergone physical and/or
chemical alterations due to exposure to the elements.
YAW Refers to an aircraft’s or spaceship’s turning by angular motion about
a vertical axis.
Appendix A Glossary of Geologic Terms
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Geomorphic variability in the coastal zone / by Joann Mossa and Ed-
ward P. Meisburger, Andrew Morang ; prepared for Department of the
Army, US Army Corps of Engineers.
120 p. : ill. ; 28 cm. — (Technical report ; CERC-92-4)
Includes bibliographic references
1. Coast changes. 2. Geomorphology. 3. Submarine topography. |.
Title. Il. Meisburger, Edward P. Ill. Morang, Andrew. IV. U.S. Army
Engineer Waterways Experiment Station. V. United States. Army.
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