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Technical Report CERC-93-5
March 1993
US Army Corps
of Engineers
Waterways Experiment
Station
Technologies for Assessing the Geologic
and Geomorphic History of Coasts
by Andrew Morang
Coastal Engineering Research Center
Joann Mossa
University of Florida
Robert J. Larson
Geotechnical Laboratory
Approved For Public Release; Distribution Is Unlimited
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Saw PRINTED ON RECYCLED PAPER
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Technical Report CERC-93-5
March 1993
Technologies for Assessing the Geologic
and Geomorphic History of Coasts
by Andrew Morang
WANN
o 0301 AME 5
MO
Coastal Engineering Research Center
U.S. Army Corps of Engineers
Waterways Experiment Station
3909 Halls Ferry Road
Vicksburg, MS 39180-6199
Joann Mossa
Department of Geography
University of Florida
Gainesville, FL 32611
Robert J. Larson
Geotechnical Laboratory
U.S. Army Corps of Engineers
Waterways Experiment Station
3909 Halls Ferry Road
Vicksburg, MS 39180-6199
Final report
Approved for public release; distribution is unlimited
Prepared for
Under Work Unit 32538
U.S. Army Corps of Engineers
Washington, DC 20314-1000
US Army Corps
of Engineers
Waterways Experiment
Station
GEOTECHNICAL |
LABORATORY
COASTAL ENGINEERING
RESEARCH CENTER
oN I oe it } FOR INFORMATION CONTACT :
ENVIRONMENTAL Ry | H yy W PUBLIC AFFAIRS OFFICE
LABORATORY <4 » HL) A U. S. ARMY ENGINEER
y x f WATERWAYS EXPERIMENT STATION
3909 HALLS FERRY ROAD
VICKSBURG, MISSISSIPPI 39180-6199
PHONE : (601)634-2502
STRUCTURES
eer LABORATORY
JE S
tC}
AREA OF RESERVATION = 2.7 sq km
Waterways Experiment Station Cataloging-in-Publication Data
Morang, Andrew.
Technologies for assessing the geologic and geomorphic history of coasts /
by Andrew Morang, Coastal Engineering Research Center, Joann Mossa,
Robert J. Larson ; prepared for U.S. Army Corps of Engineers.
173 p. : ill. ; 28 cm. — (Technical report ; CERC-93-5)
Includes bibliographical references.
1. Geomorphology — Methodology. 2. Coast changes. |. Mossa, Joann.
Il. Larson, Robert J. Ill. United States. Army. Corps of Engineers. IV.
Coastal Engineering Research Center (U.S.) V.U.S. Army Engineer Water-
ways Experiment Station. VI. Title. VII. Series: Technical report (U.S. Army
Engineer Waterways Experiment Station) ; CERC-93-5.
TA? W34 no.CERC-93-5
Contents
PRCEACC APES, tosses poi cape ase xs easel ER EE oe EN ECS PR SSC PENS fe) ix
Conversion Factors, Non-SI to SI Units of Measurement ........... x
1 IMtFOGUCHION Bae, ws oy eee eae eaeiin, ty ose vente Meee pero eae ae ere 1
Back round cpeit ts hat caper Peet aetna: cli: ceical aye. 1a diy aiik MOM 1
Environmental and Geologic Factors Affecting Coasts .......... 4
SCOPE REY es cel mcd actuate NEES Bie po R AR a TER REL ER AMPED SOMCET EE BIS oR od U
2—Sources of Existing Coastal Information ................... 9
Wei teratlinesS OULCES ene vimmeu el Aa ye p aici Meera aa ede SL Ml ais i 9
Meteorologicallandi€limatic: Data) eG2ne See ae oo eee 11
NENA DEL Vili aie es or Wales (2G pet Sa tene Mcrae pen nen, Ueety | Ua a eMC RL Sea 11
WiatereveliDataling! artis art paler cee 3g eT, alten ee AO 8 12
Geologiciand! Sediment) Datay (3.25) ma aie eee eet ae 19
Saurces) of7Aerialsehotographyarws eee ee eee 22
Satellite RemotelysSenseduD ataieaew wwii aren een ness 23
Mopographic.and)BathyimetricyDatayeisiae eee ean ore 27
Shoreliney@hangey Manse stacy eeu tee ees ec acetic swear oure remus 27
3—Field Data Collection and Observation .................... 29
Site Inspection and Local Resources ...................... 30
Photographsandihime:Sequencessaruneia-n eee eer 31
Wave Measurements and Observations .................... 31
Water Level Measurements and Observations ................ 35
Current Measurements and Observations ................... 36
Grab Sampling and Samplers ......................000% 4]
Stratisraphic Sampling girs esse cise scour contr eee ate hic eae yes 42
Sediment Movement and Surface Forms ................... 46
Navigation and Positioning Equipment .................... 55
Geophiysicaliihechniquesay aera aye a aa acai a nls 56
MorphologicrandsBathymetricsProfilessy. = 0) sere aie eneieny oa 62
ErOtotypemNiOnitorin gpm etre, nse nen ce ane er es tsedi cut 65
4—Laboratory Techniques and Approaches ................... 66
Laboratory Observationiand Experiment 9.05.22. - - «eee ole 66
Phy sicalpModels) 525 ois... rserons eyes Ghakesokane ye, ©) eee mena 76
5—Analysis and Interpretation of Coastal Data ................. 80
Wiave Records! soc. = ayaa Rate ole ae Oia ane ss ene sy Oueieads (oun 81
Water eveluRecords) ii. Gee. is ieee et oo tac) eRe ow or enn: 92
Current RECO‘dS: 3.3 fo le aR ae a 35
Maps' and) Photographsisne yar teenies es ce cis cree 105
Topographic;and! Bathymetsic) Data) eens i eye 109
Coastal Data Interpretation with Numerical Models ........... 120
6—Summary and) Conclusions) serene ee eee eee 124
References! 2 ai th.09s aed aids. 5: acces pene 2 Cie ee 127
AppendixvAs# Glossany) cece, sen a: ane aeons re mete eiieo cas oeinetio nt Al
Appendix B: List of Wave Information Studies (WIS) Reports ...... Bl
Appendix C: List of Selected Sources for Aerial Photography and Other
Remote SensingyData:.gn 50). 2h. cp cematrre es reer eter os see Gil
Appendix D: Addresses of Government Agencies Producing Maps ... D1
Appendix E: List of Journals That Contain Articles Pertaining to the
Geologic and Geomorphic History of Coasts ............... El
Appendix F: Field Reconnaissance for Coastal Erosion Study, Site Visit
Checklist 2.2 Ses So Gale yeh seas Oe ne Ce ne Fl
List of Figures
Figure 1. Some techniques for studying geomorphic changes of coasts
OVER ivaniousitime/Scalesiars eae een eee 3
Figure 2. A three-dimensional view of some features commonly
associated with a barrier island system, including the back
barrier, overwash fans, and lagoons ................ 4
Figure 3. Surface and subsurface environments and variations of barrier
islands, strand plain coasts, and tidal flats ............ 5
Figure 4.
Figure 5.
Figure 6.
Figure 7.
Figure 8.
Figure 9.
Figure 10.
Figure 11.
Figure 12.
Figure 13.
Figure 14.
Figure 15.
Figure 16.
Figure 17.
Figure 18.
Figure 19.
Figure 20.
Morphology of microtidal, mesotidal, and macrotidal coastlines
(modified@iromi Hayes) (1976)) Raa so ented oo nies eeen 6
Littoral Environmental Observation forms used by the
volunteer observers participating in the LEO program ..... 13
Late Quaternary sea level curves inferred from radiocarbon
dated samples along the U.S. coastlines. ............. 14
Monthly water level changes at Juneau, AK ........... 16
Monthly water level changes at Galveston, TX ......... 16
Yearly mean sea level changes at Juneau, AK, from 1936-1986 17
Yearly mean sea level changes at Galveston, TX, from 1908-
1986 RGR de PSB. lt ae A BONING. MR REE it7/
Typical tide curve for Oregon coast ................ 19
The reference zero point for IGLD 1985 at Rimouski, Quebec
is shown in its vertical and horizontal relationship to the Great
Lakes-St. Lawrence River System ................. 21
SPOT satellite image, Atchafalaya Bay, LA ........... 24
Northeast Gulf of Mexico, February 1990. NOAA 10 satellite,
AWHRR: Channels secon CRN eh ok haces ie esa seve de 25
Spectral resolution and approximate spatial resolution of sensors
on LANDSAT, SPOT, and NOAA satellites ........... 26
Bottom-mounted Sea Data! 635-12 directional wave gage
mounted in tripod using railroad wheels as corner weights .. 34
Tidal elevations from seven stations in Choctawhatchee Bay
andavicinity Florida: sic 3). 2 eke eee ake SR ee 37
Trench excavated in the edge of a sand dune, eastern Alabama
near Alabama/Florida state line ................... 44
OMA DABS pee deus 9 aa com Cl Pea IE Bie eis Ro eee: 46
Rotary drilling operations under way in the estuary of the
GuayacanyRiver “Ecuadoni a tec cin erate mos acs ss 48
vi
Figure 21.
Figure 22.
Figure 23.
Figure 24.
Figure 25.
Figure 26.
Figure 27.
Figure 28.
Figure 29.
Figure 30.
Figure 31.
Figure 32.
Figure 33.
Figure 34.
Figure 35.
Figure 36.
Figure 37.
Figure 38.
Side view of steel frame and polyester mesh sediment trap used
at Duck, NC, by Kraus (1987) during CERC’s DUCK-85 field
Experiments) *s Wve, see coerce Tet ee ones meee aie 49
Plan view of basic ripple types (modified from Allen 1968) .. 52
Two- and three-dimensional bed forms .............. 33
Velocity-grain size relationships for subaqueous bed forms .. 54
Principles of obtaining subbottom seismic data.......... 60
Side-scantsonarin(operationiesry amet yeee ea ieee 61
Sample form for core description of sedimentary environments 71
Photograph of a portion of the Los Angeles/Long Beach
Harbor physicalémodel vcs, styeee eee ces cue ass a) enrc0 Seem ee 78
Comparison of wave gage pressure measurements recorded at
Long/Beachistawltand:2) 284) Sn. He ee eee Se 79
Example of continuous wave pressure record and wave burst
Samplingyotapressurerdatale syn ae neme nen nee er 82
Pressure data collected by two gages mounted on a tripod off
Mobile: Bay, ‘Alabamai/'2!. ees, ee. bey ies eee 84
Example of a single wave burst of 1,024 pressure
points from the same gages that produced the records
in‘Figure’31" | 2 See ea A, Geena 84
Analyzed wave data from Burns Harbor, Indiana ........ 85
Pressure data from Burns Harbor, Indiana,
April:6} 1988iaaw 23208.) Pe SOSH BOD NE BESS. La 86
Example of tabular summary of wave data from offshore Fort
WaltonvBeachs:Floridaw sky nae i ah ee ee ee 90
Plots of wave height, peak period, and peak direction from
offshore Fort Walton Beach, Florida................ 91
Coastal currents measured off Fort Walton Beach, Florida
Panhandlets:. vniztzs 0c) AT. Wy: TOR. BOR Be eee 97
Current measurement stations in East Pass Inlet, Destin,
Florida during October 1983 hee ae cine 99
Figure 39.
Figure 40.
Figure 41.
Figure 42.
Figure 43.
Figure 44.
Figure 45.
Figure 46.
Figure 47.
Figure 48.
Figure 49.
Figure 50.
Figure 51.
Example of hand-written field notes listing times and data
values of East Pass current measurements ............ 100
Time series plots of current speed (bottom) and direction (top) 101
Morphologic indicators of littoral drift along natural and
modified: shorelines: 255.50 even cele cane oe sos yee 6 106
Changes in shoreline position near St. Marys entrance, Florida-
Georgia (from Kraus and Gorman 1993) ............ 107
Example of a hand-annotated hydrographic map from a Florida
PTOJOCE Site oye. serierectrcishy hee oud syenhs Aen anager Fils art cama 110
Digitally collected hydrographic data from a Florida project
Sit tue es coches, copra net ee ta ete te Ut ea ie Uke rare oer 112
Surface grid computed by CPS-3 based on the data shown in
Ri QUT 44s eis i iacst aru Pree NE icc eR RRA irae esi 113
Contoured bathymetry of the same area shown in Figures 44
BNGAS oo open hes Ray Arcee etait R oma: POU IN L 11e AP tc 115
Overall growth of an ebb-tidal shoal over 24 years is shown by
theyadvanceiofithesl5-ftisobathweas ei ees eee 116
Isopach map showing overall changes in bottom configuration
between 1967 and 1990 at East Pass, Florida ......... 117
Growth of the ebb-tidal shoal at East Pass, FL......... 118
Classification of beach change models (Kraus 1989) ..... 121
Flowchart for studies of coastal geology............. 125
List of Tables
Table 1.
Table 2.
Table 3.
Table 4.
Tidal Datums and Definitions, Yaquina Bay, Oregon...... 20
Low Water (chart) Datum for IGLD 1955
Andel GIED AMOS aioe hese ae i tuaeler Fo ce panera eee alecccateat 21
Self-Contained and Cable-Telemetry Wave Gages;
Advantages and Disadvantages ................... 33
Wave Gage Placement for Coastal Project Monitoring ..... 35
vii
viii
Table 5.
Table 6.
Table 7.
Table 8.
Table 9.
Table 10.
Table 11.
Table 12.
Table 13.
Table 14.
Table 15.
Subaqueous Soil Sampling Without Drill Rigs
and!Casing ect: eRe ae ernest rate eee eee eens
Maximum Allowable Errors for Hydrographic Surveys
Allowable Horizontal Positioning System Criteria.......
Example of Beach Fill Area Profile Survey Scheme ....
Sediment:Particle:Sizes* 202 See ee eee
Minimum Weight of Sample Required Given Maximum
Particle Sizeuin bopulatione 1-2 tenet tet eee
Wave Data Sampling Intervals, Typical CERC Projects ....
Sea. State:Parameters . 223.2 hs a ees
Reporting Conventions for Directional Environmental
Measiirements) 72:02 ie taken te fla eR cok Ene Pee
Short-Term Sea-Level Changes Along Open Coastlines
Long-Term Causes of Changes in Relative Sea Level ...
Preface
This report is based on research carried out at the Coastal Engineering
Research Center (CERC) and the Geotechnical Laboratory (GL) of the
U.S. Army Engineer Waterways Experiment Station (WES) under the "Survey
of Technologies in Coastal Geology" Work Unit 32538, Coastal Geology and
Geotechnical Program, authorized by the U.S. Army Corps of Engineers
(USACE). Messrs. John H. Lockhart, Jr., John G. Housley, Barry W.
Holliday, and David A. Roellig were USACE Technical Monitors.
Ms. Carolyn Holmes is CERC Program Manager.
This report was prepared by Mr. Andrew Morang, CERC, Dr. Joann
Mossa, Department of Geography, University of Florida, while under contract
at CERC through the U.S. Army Summer Faculty Research and Engineering
Program, and Mr. Robert J. Larson, GL, Earthquake Engineering and
Geosciences Division (EEGD), Geologic Environments Analysis Section.
Dr. Mossa and Mr. Morang worked in the 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. Mr. Larson was under the
general direction of Dr. Lawson M. Smith, Chief, Engineering Geology
Branch, and Dr. Arley G. Franklin, Chief, EEGD. The report was reviewed
by Mr. Steve Chesser, U.S. Army Engineer District, Portland,
Mr. Danny W. Harrelson, GL, and Dr. Paul F. Hadala, GL.
Director of CERC during the investigation was Dr. James R. Houston,
and Assistant Director was Mr. Charles C. Calhoun, Jr. Director of the
Geotechnical Laboratory during the investigation was Dr. William F.
Marcuson III, and Assistant Director was Dr. Paul F. Hadala. Director of
WES during publication of this report was Dr. Robert W. Whalin.
Commander was COL Leonard G. Hassell, EN.
Conversion Factors, Non-SIl to
SI Units of Measurement
Non-SI units of measurement used in this report can be converted to SI units
as follows!:
Ca
Oe
Gre
a
1 Some data examples are presented in English units, in accordance with the units used
during the original data collection.
1 Introduction
Background
Coastal environments display great geologic and geomorphic! diversity
over space and time. Spatial diversity occurs because coastal landforms
develop in a variety of terrestrial and marine environments from a variety of
rocks and sediments. Environmental factors, such as coastal winds, waves,
tides, currents, storms, sea level, tectonics, sediment supply, and human
influences, cause vast geographic variation. Temporal diversity in landforms
and materials occurs largely because environmental factors fluctuate over
time. These environmental variations may be cyclic, noncyclic, or
unidirectional over the time period examined. As a result, the geologic and
geomorphic history of a coastal area is a response to a multiplicity of
environmental factors over a variety of time scales.
The assimilation of evidence and the interpretation of geologic and
geomorphic history of a coastal area require an understanding of the system’s
dynamics and its response to temporal and spatial environmental changes.
Each facet of the coastal system is constantly changing and each altered facet
influences subsequent changes to the system. Data which indicate the rates,
magnitude, and frequency of phenomena such as the effects of storms, sea
level rise, coastal erosion, or the subsidence of continental margins, are
important for understanding the history and current status of geologic systems.
The understanding is significant to a variety of issues, including predicting
and planning for coastal hazards and engineering design of coastal structures.
Three principal time scales are important in assessing the geologic and
geomorphic changes of coasts. These include: (1) modern studies, which are
based largely on field data or laboratory and office experiments of
environmental processes; (2) historic studies, which are based largely on
information from maps, photography, archives, and other sources; and
(3) studies of paleoenvironments, which are based largely on stratigraphy and
1Geomorphic refers to the description and evolution of the earth’s topographic features -
surficial landforms shaped by winds, waves, ice, flowing water, and chemical processes.
Chapter 1 Introduction
associated geological principles (Figure 1). These general categories overlap.
Furthermore, 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. Tidal fluctuations are
difficult to detect in studies of paleoenvironmental changes, and sea level
typically changes too slowly to be an important factor in modern process
studies.
Several lines of inquiry are available to assess the geologic and geomorphic
history of coasts. One means of acquiring coastal data is through field data
collection and observation. These data may be numerical or non-numerical,
and may be analyzed in the field, laboratory, or office. Laboratory studies
are used to collect data through physical model experiments, such as in wave
tanks, or to analyze geological properties of field data, such as grain size or
mineralogy. Office studies include interpretation of historic maps,
photographs, and references, as well as analyses and numerical simulation of
field, laboratory, and office data. Typically, the best overall understanding of
environmental processes and the geologic history of coasts is acquired through
a broad-based combination of techniques and lines of inquiry.
The quality of the results depends on several factors. Among these is the
use of existing data. If secondary data sources (i.e. existing maps,
photography, and literature sources) are limited or unavailable, assessing the
geologic history will be more difficult, more costly, and typically more
inaccurate. Consequently, before initiating detailed field, laboratory, or office
studies, thorough literature review and search for secondary data sources
should be conducted. This report lists sources and agencies that can be con-
sulted in searches for secondary data of various types.
The quality of the research equipment, techniques, and facilities also
influences the quality of the evaluation of geologic and geomorphic history.
For example, echo-sounding and navigation instruments used to conduct
bathymetric surveys have recently been improved. If such equipment is
available, the mapping of geologic and geomorphic features can be extended
further seaward to a higher degree of accuracy than was previously possible.
It is important that the coastal geologist and engineer stay abreast of new
techniques and methods, such as remote sensing and geophysical surveys,
computer software and hardware developments, and new laboratory methods.
For example, recent developments in Geographic Information Systems (GIS)
enable the coastal scientist to analyze and interpret highly complex spatial data
sets. This report describes some recent developments and techniques that are
used in the analysis of coastal data sets.
Scientists must recognize certain problems and assumptions involved in
data collection and analyses and make adjustments for them before making an
interpretation. It is critical to account for various sources of error in
preparing estimates of coastal changes and acknowledge the limitations of
Chapter 1 Introduction
= Thermoluminescence-=
—— Cy, —e
—— Paleoecology —————_=
—=Paleomagnetism=
=~ Soils Geomorphology =
—= Dendrochronology=
—=— Csi7—e
= Pb 210
=a Lichenometry =
—=— Archeology —————__»>—
Timescale, years
——__ Archives —£-_ ——————o
—=—_—— Maps —__ >
—=— Satellite Images —=—
—=— Aerial Photos —=
—
10m
(53 Min)
—=—- Geophysical Systems———=—
—=——- Currents ————_=
=< Salinity, Temperature ——____9/)/_ __
Suspended/Bedload
Sediment Concentration
=_—_ Wves
—=——— Meteorology ————____=
10-6 y
32 . e 0
ee) Observation & Historical Documents Geological/Paleoecologic
Experimentation Reconstruction
Figure 1. Some techniques for studying geomorphic changes of coasts over various time
scales. Arrows indicate the approximate time span during which a particular
study technique can be used
interpretations and conclusions when these are based on data covering a short
time period or a small area.
Chapter 1 Introduction
Environmental and Geologic Factors Affecting
Coasts
Broad classifications of morphologic type can be identified at coastlines
around the world. A partial listing includes barrier, strand plain, deltaic, mud
flat, volcanic, rocky, reef-fringed, and estuarine! coasts (Carter 1988; Mossa,
Meisburger, and Morang 1992). Within each of these major groups,
however, a number of distinctive environments can be distinguished when
examining the coast in cross section and in plan view. Some of these environ-
ments are common to many types of coasts. Figures 2, 3, and 4 show exam-
ples of the types of environments found at coasts within some of the
morphologic groups.
Washover
Fan
Spit
Ebb—Tidal
Shoals
Flood—Tidal
Shoals
Figure 2. A three-dimensional view of some features commonly associated
with a barrier island system, including the back barrier, overwash
fans, and lagoons
The geomorphic variability and geologic evolution of the coast are influ-
enced by an array of environmental factors. A partial listing of the factors
that influence coasts over varying time scales includes climate, wind, and
cyclonic disturbances, waves, tides, storm surges, currents, relative sea level,
lithology and weathering, erosion and transportation, sediment supply, coastal
1 Geologic terms are defined in Appendix A, "Glossary," at the end of this report.
Chapter 1 Introduction
BARRIER ISLAND
Backshore
Back Barrler Dune
Flat
Lagoon Marsh Foreshore/Beach
Shoreface
STRAND PLAIN
Beach Ridge/
Forshore/Beach
Shoreface
Shelf
TIDAL FLAT
Tidal Channels Tidal Mud
Flat Tidal Sand Flat
Salt Marsh
Figure 3. Surface and subsurface environments and variations of barrier islands, strand
plain coasts, and tidal flats
Chapter 1 Introduction 5
MICROTIDAL MESOTIDAL
VEGETATED
AND i
UNVEGETATED |°
RIVER
DELTAS
BARRIER
ISLAND/ 3
STRANDPLAIN
INLETS
TIDAL
DELTAS
LIKIHOOD OF OCCURRANCE
ESTUARY
0 —— MICROTIDAA —= 2—— MESOTIDAL ——™= 4—-— MACROTIDAL —= 6
TIDAL RANGE ¢M)
Figure 4. Morphology of microtidal, mesotidal, and macrotidal coastlines (modified from
Hayes (1976)). Stipple pattern represents the likelihood that a particular land
form is found along a stretch of the shoreline subject to the tide range indicated
on the x-axis
materials, and human activities. The factors vary in magnitude or energy and
in frequency and duration. Coastal materials may differ in structure,
lithology, size, and consolidation, causing differences in their resistance to
erosive forces.
Assessment of the geologic and geomorphic history of coasts is complex
because a multiplicity of environmental factors affect the coast simultaneously,
and coastal features can change immediately or slowly in response to these
factors. Throughout the Pleistocene and Holocene periods, there have been
significant fluctuations of sea level, continental tectonic uplift and subsidence,
Chapter 1 Introduction
and climatic changes, causing the zone of constant wave action to transgress
or regress. Investigations of the geologic history of coasts thus may extend
beyond the narrow zone of present shorelines to cover much wider areas over
which coastal processes have acted during the geologic past.
Scope
This report describes technology and procedures for obtaining and
analyzing evidence that can be used to interpret the geologic history of coasts.
Three principal investigation time scales are discussed; namely, modern,
historic, and paleoenvironmental. Some techniques used to collect and
analyze data from the field, laboratory, and office can in some cases be
applied to different time scale groups. For example, aerial photographs can
provide information regarding both modern processes and historical changes
of coasts. For this reason, this report is divided according to the differing
locations where data are collected and analyzed, rather than according to the
time scale of the investigation.
Chapter 1 provides an introduction and review of this report. Chapter 2
describes the coastal zone morphologies and environmental factors responsible
for temporal and spatial variations of coasts, and discusses potential secondary
sources of information for coastal studies. In Chapter 3, field data collection
and observation are discussed. Chapter 4 summarizes recent laboratory tech-
niques and approaches, both for analysis of field data and for controlled
studies using physical models. Chapter 5 reviews a variety of approaches
used for office analysis and interpretation of data from both primary and
secondary sources. Chapter 6 summarizes and gives an overview of the
application and availability of technology for assessing the geologic history of
the coastal zone. Appendix A is a glossary of geologic terms, Appendix B is
a listing of Wave Information Studies (WIS) reports, and Appendix C is a list
of sources for aerial photography and other remote sensing data. Appendix D
contains addresses of government agencies that produce maps, and Appen-
dix E is a list of journals that contain articles pertaining to the geologic and
geomorphic history of coasts. Appendix F is a site visit checklist for a coastal
erosion study.
In reviewing technologies for assessing the geologic and geomorphic
history of coasts, this report covers a breadth of information. Many of the
techniques used to monitor processes and structures in the coastal zone are
exceedingly complex. This report outlines some of the many errors that can
occur when the inexperienced user deploys instruments or accepts without
critical appraisal data from secondary sources. The text is not intended to be
so pessimistic that it dissuades coastal researchers from continuing their
investigations, but rather is intended to guide them to other references or to
specialists where expert advice can be obtained. The reader should also con-
sult basic references regarding coastal geology, geomorphology,
Chapter 1 Introduction
sedimentology (i.e., Boggs 1987; Komar 1976; Schwartz 1982; Pethick 1984;
Davis 1985; Carter 1988), as well as references which discuss secondary
sources (i.e., Chu, Lund, and Camfield 1987) and available techniques and
technologies (Goudie 1981; Shore Protection Manual 1984; Horikawa 1988).
Chapter 1 Introduction
2 Sources of Existing Coastal
Information
Literature Sources
Information pertinent to the geologic and geomorphic history of coasts can
be obtained and/or interpreted from libraries, universities, and Federal, state,
and local government agencies (Fulton 1981). The following provides details
on some of these sources:
a. University and college departments and libraries. In many instances,
the collections of books, periodicals, dissertations, theses, and univers-
ity faculty research project reports contain data. This especially
occurs when the institutions are in coastal areas, where research is
funded by Federal or state government agencies (i.e. Sea Grant),
where the university has graduate programs and faculty active in
research in appropriate fields, and at universities where one or more
members of the faculty are coastal specialists. Major universities also
have government documents repositories where Federal and state
government publications are housed.
b. Local sources. These are often overlooked, but can provide detailed
and sometimes unique data pertinent to the locale. Such sources
include the local newspaper, courthouse records, historical diaries,
lighthouse records, local journals, engineering contract records, land
transactions, and museums.
c. Government agencies. Geologic coastal data may be available from
government agencies at the Federal, state, and local level
(Appendices C and D). Federal agencies with data archives include
the U.S. Geological Survey (USGS), the U.S. Coast and Geodetic
Survey (USCGS), the National Oceanographic and Atmospheric
Agency (NOAA), the U.S. Army Corps of Engineers (USACE),
(including the U.S. Army Engineer Waterways Experiment Station
(WES), the Coastal Engineering Research Center (CERC), and
USACE District and Division offices), the U.S. Department of
Chapter 2 Secondary Sources of Coastal Information
10
Transportation (DOT), the U.S. Environmental Protection Agency, the
U.S. Fish and Wildlife Service, and the Naval Research Laboratory
(NRL). At the state level, agencies with relevant coastal information
include the state geological surveys (or bureaus of geology),
departments of transportation, departments of environmental resources
and/or water resources, and state planning departments.
Industry. Energy (oil and gas) companies often keep records, which
may be accessible to scientists, of coastal processes in conjunction
with their offshore drilling operations. Construction companies have
records in files on their construction projects. Environmental and
engineering firms may also have data from projects that were per-
formed for government. Some of these data are in the public domain.
Environmental impact reports from nuclear power plants built in
coastal areas contain extensive coastal process and geologic data.
Journals. Most large university libraries have holdings of national
and international scientific journals. Most of the scientific literature
associated with the geologic history of coasts will be in the realm of
geology, oceanography, marine science, physical geography, atmo-
spheric science, earth science, and polar studies. Most research
studies will be in the specific fields of coastal sedimentology, coastal
geomorphology, and marine geology. A listing of pertinent journals is
given in Appendix E.
Conference Proceedings. Most large national and international confer-
ences produce proceedings of papers presented at symposia. The
conference proceedings can be obtained from university libraries.
Proceedings, abstracts, etc. are also published by scientific
organizations. These publications may also include announcements of
symposia, grants awarded, and other announcements that may lead to
environmental and geologic information.
Computerized Literature Searches. Most major university and govern-
ment agency libraries have access to computerized literature databases.
The databases contain information that may be acquired by key terms,
subjects, titles, and author names. Computer-operator assistance may
be needed because access to the system and an understanding of its
nuances are critical to a successful search. A clear and complete list
of key words is important to the computer operator. It is also
necessary to link terms to avoid getting extraneous/erroneous listings
of information sources.
Chapter 2 Secondary Sources of Coastal Information
Meteorological and Climatic Data
Meteorological and climatic data are often useful for characterizing signifi-
cant environmental processes and for revealing the characteristics of severe
storms. Significant climatic and storm events are important in analyzing and
interpreting the geologic and geomorphic history of coasts. Major storms or
long-term variations in storminess strongly affect coastal morphology. This is
manifested, for example, by the changes on barrier beaches associated with
winds, waves, and high water levels which may cause overtopping and
overwashing during storms.
Meteorological and climatic data can be compiled from secondary sources
or through an original data collection program in the field using instruments
and observations. As with most of the important environmental factors, most
secondary information pertains to studies over historic and modern time
scales. Published data are plentiful and include data from many sources
throughout the world. The National Climatic Data Center and the National
Hurricane Center within NOAA are important sources of meteorological and
climatic data. For selected coastal sites, data collected through CERC’s
Littoral Environmental Observation (LEO) program may also provide helpful
information. The titles of several important publications and addresses for
agencies that collect meteorological and climatic data in the United States are
listed in Chu, Lund, and Camfield (1987).
Wave Data
Wave data are required to characterize the process-response framework of
the coastal zone. Important wave parameters include wave height, period,
steepness and direction, and breaker type. Of special interest is the character
of waves inside the breaker zone, where it is estimated that 50 percent of
sediment movement takes place, mostly as bed load (Ingle 1966). Wave data
can be: (a) collected from secondary sources; (b) estimated in the office using
hindcast techniques from weather maps, shipboard observations, and littoral
environment observations; or (c) measured in the field using instrumented
wave gages.
Wave gage data are collected by Federal and state agencies and by private
companies. For research projects that require wave data, analyzed wave
statistics may be available if instrumented buoys, offshore structures, and piers
are located near the study site. Published data, which are geographically
spotty, include statistics from wave gages, wave hindcasting, and visual obser-
vations from shipboard or the littoral zone. The titles of several important
publications and addresses for agencies that collect wave data are listed in
Chu, Lund, and Camfield (1987).
Chapter 2 Secondary Sources of Coastal Information
11
12
Wave hindcasting is a technique widely used for estimating wave statistics
by analysis of weather maps using techniques developed from theoretical
considerations and empirical data (Shore Protection Manual 1984). The
coastal scientist can use published hindcast data or may, at times, choose to
compute original estimates in a study of the geologic history of coasts. Over
the last several decades since wave hindcasting came into common use, many
improvements have been made in the technique, and reliable information on
wave climate in given areas can be obtained. Appendix B is a list of the
USACE Wave Information Studies reports, which cover the Atlantic, Pacific,
Gulf of Mexico, and Great Lakes coasts. Advantages of hindcasting include
the long-term database associated with weather maps and the comparatively
economic means of obtaining useful information. Disadvantages involve the
transformation of waves into shallow water, especially in areas of complex
bathymetry or near rivers.
Visual wave observations from ships at sea and from shore stations along
the coasts of the United States are also published in several references.
Although observations are less accurate than measured data, experienced
persons can achieve reasonably accurate results and the great amount of
observations available makes visual wave observation a valuable resource.
Offshore, shipboard wave observations have been compiled by the U.S. Navy
Oceanographic Research and Development Activity, now the Naval Research
Laboratory (NRL), in the form of sea and swell charts and data summaries
such as the Summary of Shipboard Meteorological Observations (SSMO).
While geographic coverage by these sources is extensive, the greatest amount
of observations come from shipping lanes and other areas frequented by ship
traffic.
At the shore, a program sponsored by HQUSACE for data collection is the
LEO program (Schneider 1981; Sherlock and Szuwalski 1987). The program,
initiated in 1966, makes use of volunteer observers who make daily reports on
conditions at specific sites along the coasts of the United States. Data from
over 200 observation sites are available from CERC (Figure 5). As shown,
LEO data not only include wave parameters, but also information on winds,
currents, and some morphologic features. LEO is best applied to a specific
site, and does not provide direct information on deepwater statistics. The
biggest disadvantage is the subjective nature of the wave height estimates.
LEO data should only be used as an indicator of long-term trends, not as a
database of absolute values.
Water Level Data
Water level information is important for analysis of geologic history over
modern process, historic, and geologic time scales (Figure 6). Over modern
process time scales, water level changes at the coast include tides, which
occur diurnally or semidiurnally, setup and setdown associated with storm
Chapter 2 Secondary Sources of Coastal Information
LITTORAL ENVIRONMENT OBSERVATIONS
RECORD ALL DATA CAREFULLY AND LEGIBLY
Record time
using the 24
hour system
WAVE PERIOD BREAKER HEIGHT
Record the time in seconds for Record the best estimate of the
eleven (I!) wove crests to pass a average wave height to the nearest
stationary point. If calm record O. tenth of a foot.
WAVE ANGLE AT BREAKER 22 23 24 WAVE TYPE
Record to the nearest degree the 0-Calm 3 - Surging
direction the waves are coming from 1 -— Spilling 4- Spill / Plunge
using the protractor on the reverse side. O if calm. 2 — Plunging
WIND SPEED Belisy WIND DIRECTION — Direction the wind
is coming from.
Record wind speed to the nearest 1-N 3-E 5-S 7-W O-Calm
mph. If calm record O. 2-NE 4-SE 6-SW 8-NW
FORESHORE SLOPE WIDTH OF SURF ZONE 3I_32_33_34
Record foreshore slope to the Estimate in feet the distance from
nearest degree. shore to breakers, if calm record 0.
LONGSHORE CURRENT OYE 36 37 38
Estimate distance in feet from
shoreline to point of dye injection.
CURRENT SPEED 43 44 45 CURRENT DIRECTION
Measure in feet the distance the dye O No longshore movement
patch is observed to move during a one (1) +1 Dye moves toward right
minute period ; If no longshore movement record O. - 1 Dye moves toward left
RIP CURRENTS 49 50 5i 52
If rip currents are present, indicate spacing ( feet). If spacing is irregular
estimate average spacing. If norips record 0.
BEACH CUSPS 5455 56
If cusps are present, indicate spacing (feet). If spacing is irregular
estimate average spacing. If no cusps record O.
PLEASE PRINT:
SITE NAME OBSERVER
Please Check The Form For Completeness
REMARKS:
CERC 113-7 ve Fi “ :
eRe! B 2 Make any additional remarks, computations or sketches on the reverse side of this form.
Figure 5. Littoral Environmental Observation (LEO) forms used by the
volunteer observers participating in the LEO program (from
Schneider 1981)
Chapter 2 Secondary Sources of Coastal Information
13
Milliman and
Emery 1968
Proposed
Sea Level
Curve: U.S.
East Coast
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Figure 6. Late Quaternary sea level curves inferred from radiocarbon dated samples along
the U.S. coastlines. Modified from Dillon and Oldale (1978)
surges, and seasonal changes in sea level, all on the order of centimeters to
meters. Short-term variations, particularly those associated with storms, are
important in increasing the effective wave base, allowing erosion to take place
further inland.
Over historic time scales, significant water level changes may occur.
Because of the complexity of this topic, it is necessary to introduce the con-
cepts of relative and absolute sea level.
A relative change in water level is, by definition, a change in the elevation
of the sea surface relative to some local land surface. The land, the sea, or
both may have moved in absolute terms with respect to the earth’s gravita-
tional center. It is exceptionally difficult to determine absolute sea level
changes because tide stations are located on land masses that have themselves
moved vertically. For example, if both land and sea are rising at the same
rate, a gage will indicate that relative sea level has been stable. Other clues,
such as beach ridges or exposed beach terraces, also merely reflect relative
sea level changes.
14
Chapter 2 Secondary Sources of Coastal Information
Eustatic sea level change is caused by change in the relative volumes of
the world’s ocean basins and the total amount of ocean water. It can be
measured by recording the movement in sea-surface elevation relative to some
universally adopted reference frame. This is an exceptionally difficult
problem because it is essential that eustatic measurements be obtained from
the use of a reference frame that is sensitive only to ocean water and ocean
basin volumes. Sahagian and Holland (1991) have recently used the
extensive, undeformed Russian platform to generate a Mesozoic-Cenozoic
eustatic sea level curve.
Changes in water level include:
a. Slow absolute secular sea and land level changes (time spans of thou-
sands or millions of years). These have been caused by glacioeustatic,
tectonic, climatologic, and oceanographic factors (to be discussed in
more detail in Chapter 5). Sea level was about 100 to 130 m lower
during the last glacial epoch (Figure 6), about 15,000 years before
present. Ancient shorelines and deltas can be found at such depths
along the edge of the continental shelf. Other changes of this magni-
tude have been recorded during other geological epochs (Payton
1977).
b. Short-term sea level changes caused by seasonal oceanographic
factors. These may be due to movements of ocean currents, runoff,
melting ice, and regional atmospheric variations. Figures 7 and 8 plot
monthly mean water levels from Juneau and Galveston, showing how
sea level, averaged over decades, is higher during certain months. The
1985 Juneau curve (Figure 7), however, shows that during any one
year, the average trend may not be followed.
c. Land level changes. These may be slow, occurring over centuries,
(for example, the compaction and dewatering of sediments in deltas)
or may be abrupt, the result of volcanic activity or earthquakes. A
notable example of rapid change was caused by the Great Alaskan
Earthquake of 1964, when shoreline elevations ranged from 10 m
uplift to 2 m downdrop (Hicks 1972; Hicks, Debaugh, and Hickman
1983). Vertical crustal displacements may be reflected in sea level
curves from localized areas. Figure 9 shows how the mean sea level
at Juneau is falling because of isostatic rebound of the land. In
Galveston (Figure 10), a rapid rise is recorded because the land is
subsiding (causing the tide gage to subside, too).
Variations in sea level, both long-term (geologic scale) and historic, do not
have a direct effect on most shorelines in the same manner that waves or
storm surges do. But storms have more devastating effects on a shore over
time if relative sea level in the area is rising. Data on water levels can be
important in predicting erosion or accretion and changes in shoreline response
(Wells and Coleman 1981; Hands 1980).
Chapter 2 Secondary Sources of Coastal Information
15
JUNEAU, ALASKA; STA 9452210
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Figure 7. Monthly water level changes at Juneau, AK. High water
typically occurs during October-December. Data from Lyles,
Hickman, and Debaugh (1988)
GALVESTON (PIER 21) TEXAS; STA 8771450
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Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Figure 8. Monthly water level changes at Galveston, TX. High water
occurs twice per year: April and September - November. Data
from Lyles, Hickman, and Debaugh (1988)
Chapter 2 Secondary Sources of Coastal Information
JUNEAU, ALASKA; STA 9452210
Elevation (m) above original datum
3.9
1900 1910 1920 1930 1940 1950 1960 1970 1980 1990
Figure 9. 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)
GALVESTON (PIER 21) TEXAS; STA 8771450
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Figure 10. 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. Data from Lyles,
Hickman, and Debaugh (1988)
Chapter 2 Secondary Sources of Coastal Information
17
18
Many sources of water level and current data are available. The National
Ocean Survey of the National Oceanic and Atmospheric Administration is
responsible for monitoring sea level variations at 115 station locations nation-
wide (Hicks 1972). Coastal Corps of Engineers District offices collect tidal
elevation data at additional locations. Daily readings are published in reports
that are titled "Stages and Discharges of the (location of District office)
District." Predicted water levels and tidal current information for each day
can be obtained from the annual "Tide Tables: High and Low Water
Predictions" and "Tidal Current Tables" published by the National Ocean
Service (NOS). A convenient way to obtain daily tides is a personal computer
(PC) program called TIDEMASTER.! Background information concerning
tidal datums and tide stations can be found in NOS publications titled "Index
of Tide Stations: United States of America and Miscellaneous Other Stations,"
and "National Ocean Service Products and Services Handbook."
An important consideration for evaluating water-level information or for
constructing and examining shoreline change maps is the level and type of
datum used. Because water levels are not constant over space and over time,
datums must be established from which depth and elevation changes can be
referenced. Common water level datums include mean lower low water
(mllw), mean low water (mlw), mean sea level (msl), mean tide level (mtl),
mean high water (mhw), and mean higher high water (mhhw) (Figure 11 and
Table 1). Of these, msl is most often used and is computed as the arithmetic
means of hourly water elevations observed over a specific 19-year cycle.
Some areas of the United States have established regional datums, based on
combinations of other datums, or based on local measurements of water level
over different periods. Often these water level datums are cited in reference
to fixed surfaces for land surveys; namely, the National Geodetic Vertical
Datum (NGVD) developed in 1929, and the North American Datum of 1983
(NAD 83). Specific definitions of the various datums and the relationship
between major water-level datums and geodetic datums are listed in references
from the NOS and HQUSACE (1989). Note that the land benchmarks, which
represent the various datums, can move because of the factors described
earlier. Therefore, datums must be corrected and updated periodically.
Low water reference datums used on the Great Lakes and their connecting
waterways are currently based on the International Great Lakes Datum (IGLD)
1985. This datum, which was established and revised under the auspices of
the Coordinating Committee on Great Lakes Basic Hydraulic and Hydrologic
Data, was implemented in January 1992, and replaces IGLD 1955. The main
difference between IGLD 1955 and IGLD 1985 is corrections in the elevations
assigned to water levels (Table 2). This is a result of benchmark elevation
changes due to adjustments for crustal movements, more accurate measure-
ment of elevation differences, a new reference zero point location, and an
: Commercially available from Zephyr Services, 1900 Murray Ave., Pittsburgh, PA 15217.
Other similar programs exist, some of which are updated quarterly or yearly.
Chapter 2 Secondary Sources of Coastal Information
LD rtareinrae ||| MAP DN
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Figure 11. Typical tide curve for Oregon coast. Based on 6 years of observations in
Yaquina Bay. By definition, milw is zero
expanded geodetic network. The reference zero point of IGLD 1985 is
located at Rimouski, Quebec (Figure 12). The new 1985 datum establishes a
set of elevations consistent with one another for surveys taken within the time
span 1982 - 1988. IGLD 1985 is referred to the North American Vertical
Datum (NAVD) 1988. Note that the IGLD’s are not parallel to NGVD 29 or
NAVD 1988 because the Great Lakes datums are dynamic or geopotential
heights and are designed to best represent the hydraulic structure of the lakes
and connecting waterways (Great Lakes Commission 1986, HQUSACE 1991).
Geologic and Sediment Data
It is often important in studies of the geologic and geomorphic history of
coasts to evaluate existing geologic and sediment data. This type of informa-
tion is dispersed among numerous agencies and sources and includes a variety
of materials such as geologic maps, soil surveys, highway borings, and pro-
cess data such as the concentrations and fluxes of suspended sediment from
nearby rivers. Differences in geology and soil type may provide clues toward
understanding erosion and accretion patterns. Geologic and sedimentologic
19
Chapter 2 Secondary Sources of Coastal Information
Table 1
Tidal Datums and Definitions, Yaquina Bay, Oregon
Datum and Definition
Extreme high tide. The highest projected tide that can occur. It is the sum of the
highest predicted tide and the highest recorded storm surge. Such an event would be
expected to have a very long recurrence interval. In some locations, the effect of a
rain-induced freshet must also be taken into consideration. The extreme high tide level
is used for the design of harbor structures.
Highest measured tide. The highest tide actually observed on the tide staff.
Highest predicted tide. Highest tide predicted by the Tide Tables.
Mean higher high water. The average height of the higher high tides observed over a
specific time interval. The intervals are related to the moon’s many cycles, which
range from 28 days to 18.6 years. The time length chosen depends upon the refine-
ment required. The datum plane of mhhw is used on NOS charts to reference rocks
awash and navigational clearances.
Mean high water. The average of all observed high tides. The average is of both the
higher high and of the lower high tide recorded each day over a specific time period.
The datum of mhw is the boundary between upland and the tideland. It is used on
navigational charts to reference topographic features.
Mean tide level. Also called half-tide level. A level midway between mhw and mlw.
The difference between mean tide level and local mean and sea level reflects the
asymmetry between local high and low tides.
Local mean sea level. The average height of the water surface for all stages of the
tide at a particular observation point. The level is usually determined from hourly
height readings.
Mean sea level. A datum based upon observations taken over a number of years at
various tide stations along the west coast of the United States and Canada. It is offi-
cially known as the Sea Leve/ Datum of 1929, 1947 adj. The msl is the reference for
elevations on USGS quadrangles. The difference between msl and local msl reflects
numerous factors ranging from the location of the tide staff within an estuary to global
weather patterns.
Mean low water. The average of all observed low tides. The average is of both the
lower low and of the higher low tides recorded each day over a specific time period.
The datum of mlw is the boundary line between tideland and submerged land.
Mean lower low water. The average height of the lower low tides observed over a
specific time interval. The datum plane is used on Pacific coast nautical charts to
reference soundings.
Lowest predicted tide. The lowest tide predicted by the Tide Tables.
Lowest measured tide. The lowest tide actually observed on the tide staff.
Extreme low tide. The lowest estimated tide that can occur. Used by navigational and
harbor interests.
Chapter 2 Secondary Sources of Coastal Information
Table 2
Low Water (chart) Datum for IGLD 1955 and IGLD 1985
Low Water Datum in Meters
International Great Lakes Datum 1985 Lake St. Lawrence (72.5) _
at Long Sault Dam, Ontario
Lake St. Francis (46.2)
at Summerstown, Ontario
St. Marys River Tee Lake St. Louis (20.4)
akes St. Clair River f at Pointe Claire, Quebec
Lake . Niagara
Su erior: ‘ Lake Erie Falls Montreal Harbour (5.6)
(183.2) (173.5) at Jetty Number 1
Lake
Ontario
(74.2) Gulf of
St. Lawrence
Detroit q
ster
Lake— |
St. Clair d
(174.4)
- 4 St. Lawrence River
Niagara River-
J Rimouski, Quebec
IGLD 1985 Reference
Zero Point
380 56] 242] 124 145 84 |53
Distance (Km.)
Figure 12. The reference zero point for IGLD 1985 at Rimouski, Quebec is shown in its
vertical and horizontal relationship to the Great Lakes-St. Lawrence River
System. Low- water datums for the lakes are shown in meters
21
Chapter 2 Secondary Sources of Coastal Information
data are often useful for characterizing significant environmental processes and
responses, such as the effects of severe storms on coastlines.
Information from secondary sources may be pertinent to studies from mod-
ern to paleoenvironmental time scales. Although some geologic data can be
compiled from secondary sources, generally it is necessary to conduct original
data collection programs using field instruments and observations. This must
be followed up by laboratory and office analyses and interpretation. Published
data are available from agencies such as the USGS, the U.S. Soil Conserva-
tion Service, the American Geological Institute, and CERC. Additional
sources of geologic and sedimentologic data in the United States are listed in
Chu, Lund, and Camfield (1987).
Sources of Aerial Photography
Historic and recent aerial photographs provide invaluable data for the inter-
pretation of geologic and geomorphic history. The photographs can be
obtained from Federal and state government agencies such as the USGS, the
U.S. Department of Agriculture, the EROS Data Center, and others listed in
Appendices C and D. Stereographic pairs with overlap of 60 percent are
often available, allowing very detailed information to be obtained using photo-
grammetric techniques. Temporal coverage for the United States is available
from the 1930’s to present for most locations. The types of analysis and
interpretation that can be performed depend in part on the scale of the
photographs, the resolution, and the percentage of cloud cover. The effects of
major events can be documented by aerial photography because the photo-
graphic equipment and airplane can be rapidly mobilized. By such means, the
capability exists for extensive coverage in a short time and for surveillance of
areas that are not readily accessible from the ground.
For modern process studies, a series of aerial photographs provides signifi-
cant data for examining a variety of problems. Information pertinent to
environmental mapping and classification such as the nature of coastal
landforms and materials, the presence of engineering structures, the effects of
recent storms, the locations of rip currents, the character of wave shoaling,
and the growth of spits and other coastal features can be examined on aerial
photographs. For the assessment of some morphologic features, photogram-
metric techniques may be helpful. If possible, it is generally considered pref-
erable to arrange flights or obtain photography acquired during low tide, so
that nearshore features will be exposed or partly visible through the water.
For studies over historical time scales, multiple time series of aerial photo-
graphs are required. Historical photography and maps are an integral com-
ponent of shoreline change assessments. Water level and, therefore, shoreline
locations show great variation according to when aerial photographic missions
were flown. Therefore, the coastal scientist should account for such
Chapter 2 Secondary Sources of Coastal Information
variations as potential sources of error in making or interpreting shoreline
change maps. Chapter 5 contains a more detailed discussion of aerial
photograph analysis.
Satellite Remotely Sensed Data
Satellite data are available from U.S. agencies, the French Systeme Pour
l’Observation de la Terre (SPOT) satellite data network, and from Soviet
coverage!. In most instances, the data can be purchased either as photo-
graphic copy or as digital data tapes for use in computer applications.
Imagery and digital data may assist in understanding large-scale phenomena,
especially processes that are indicators of geologic conditions and surface
dynamics. Agencies that collect and distribute satellite data are listed in
Appendix C.
Satellite data are especially useful for assessing large-scale changes in the
coastal zone. In the vicinity of deltas, estuaries, and other sediment-laden
locations, the determination of spatial patterns of suspended sediment concen-
tration can be facilitated with remote sensing (Figure 13). In shallow-water
depths of non-turbid water bodies, some features of the offshore bottom, in-
cluding the crests of submarine bars and shoals, can be imaged. On a rela-
tively crude level, satellites may assist in monitoring tidal changes,
particularly where the land-sea boundary changes several hundreds of meters.
The spatial extent of tidal flows may also be determined using thermal infra-
red data, which can be helpful in distinguishing temperature differences of ebb
and flood flows and freshwater discharges in estuaries (Figure 14). In deeper
waters, satellites can also provide data on ocean currents and circulation
(Barrick, Evans, and Weber 1977). Aircraft-mounted radar data also show
considerable promise in the analysis of sea state.
The Landsat satellite program was developed by the National Aeronautics
and Space Administration with the cooperation of the U.S. Department of the
Interior. When it began in 1972, it was primarily designed as an experimental
system to test the feasibility of collecting earth resources data from unmanned
satellites. Landsat satellites have used a variety of sensors with different
wavelength sensitivity characteristics, ranging from the visible (green) to the
thermal infrared with a maximum wavelength of 12 micrometers (um). Fig-
ure 15 shows bandwidths and spatial resolution of various satellite sensors.
Of the five Landsat satellites, only Landsat-4 and Landsat-5 are currently in
orbit. Both are equipped with the MSS (multispectral scanner), which has a
resolution of 82 m in four visible and near-infrared bands, and the thematic
mapper, which has a resolution of 30 m in six visible and near- and
Russian Sojuzkarta satellite photography data are available from Spot Image Corporation
(Appendix C). Almaz synthetic aperture radar data are available from Hughes STX
Corporation.
Chapter 2 Secondary Sources of Coastal Information
23
Figure 13. SPOT satellite image, Atchafalaya Bay, LA. Suspended sediment from runoff is
clearly visible. Data processed by the Earthscan Laboratory, School of
Geosciences, Louisiana State University, Baton Rouge, LA
mid-infrared bands and a resolution of 120 m in one thermal infrared band
(10.4-12.5 py).
SPOT is a commercial satellite program. The first satellite, which was
sponsored primarily by the French government, was launched in 1986. The
SPOT-1 satellite has two identical sensors known as HRV (high-resolution-
visible) imaging systems. Each HRV can function in a 10-m resolution
panchromatic mode with one wide visible band, or a 20-m-resolution multi-
spectral (visible and near infrared) mode with three bands (Figure 13).
24
Chapter 2 Secondary Sources of Coastal Information
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25
Chapter 2 Secondary Sources of Coastal Information
Landsat NOAA :
Multispectral Thermatic — Panchromatic S.P.0.T. Advanced Very High
Scanner (MSS) Mapper (TM) Band on High Resolution Resolution Radiometer (AVHRR)
Londsote 1,2,3,4,5 Landsats 4,5,6 Landsat 6 Visible (HRV) NOAA 6,8,10 NOAA 7,9,11
Panchromatic
*<*) Band’ 3 36
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Landsat Image Area
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Figure 15. Spectral resolution and approximate spatial resolution of sensors on LANDSAT,
SPOT, and NOAA satellites (from Earth Observation Satellite Company literature
and Huh and Leibowitz (1986))
Several generations of satellites have flown in the NOAA series. The most
recent ones contain the Advanced Very High Resolution Radiometer
(AVHRR). This provides increased aerial coverage but at much coarser reso-
lution than the Landsat or SPOT satellites. Figure 14 is an example of an
AVHRR Channel 4 image of the northeast Gulf of Mexico. More information
on the wide variety of satellites can be found in textbooks on remote sensing
(i.e. Colwell 1983; Lillesand and Kiefer 1987; Richards 1986; Sabins 1987;
Siegal and Gillespie 1980; Stewart 1985).
Aircraft-mounted scanners, including thermal sensors and radar and micro-
wave systems may also have applications in coastal studies. LIDAR (light
26
Chapter 2 Secondary Sources of Coastal Information
detection and ranging), SLAR (side-looking airborne radar), SAR (synthetic
aperture radar), SIR (shuttle imaging radar), and passive microwave systems
have applications including mapping of bottom contours of coastal waters.
Some of these systems, such as LIDAR, are capable of accurate profiling of
water depths by using transmission and reflection from a pulsed coherent laser
light beneath an aircraft. In operation, a strongly reflected return is recorded
from the water surface, followed closely by a weaker return from the bottom
of the water body.
Topographic and Bathymetric Data
Topographic and bathymetric maps are available from the USGS, many
Corps of Engineer District Offices, and the USCGS. USGS topographic maps
are generally revised every 20 to 30 years; sometimes more often in areas
determined to be of high priority. Nevertheless, the maps may be outdated
for some studies because of the ephemeral nature of many coastlines. The
USGS quadrangles are the 7.5 minute series (scale 1:24,000) and the 15 min-
ute series (scale 1:62,500). The resolution of these maps is typically inade-
quate to provide details of surface features, but may be sufficient for
examining large landforms and pronounced changes, particularly over long
periods.
Hydrographic survey data are available from the NOS and its predecessor,
the USCGS. Archives of all past surveys of these agencies are available from
NOS, a division within NOAA. Much of this data can be obtained in the
form of preliminary plots that are of larger scale and contain more soundings
and bottom notations than the published charts made from them.
Bathymetric survey maps are sometimes out of date because geomorphic
changes in many submarine areas occur rapidly. On some navigation charts,
the bathymetry may be more than 50 years old and the marked depths may be
quite different from actual depths. The greatest changes can be areas of
strong current activity, of strong storm activity, of submarine mass
movement, and of dredging near ship channels. The user must also be aware
of changes in the datum used in different maps.
Shoreline Change Maps
Shoreline changes may be interpreted from navigation maps, topographic
maps, aerial photographs, and property records. In some areas, maps show-
ing shoreline changes and land loss may have been produced by state and
Federal agencies, universities, or engineering firms. However, the user
should be aware of potential sources of error that may not have been ade-
quately corrected when these maps were prepared.
Chapter 2 Secondary Sources of Coastal Information
27
28
Shoreline and coastal change maps that are constructed from historic maps
and photographs are subject to numerous sources of error. For example,
maps may not have common datums, may have different scales, may have
variable accuracy due to age or loss of accuracy in publication procedures,
and may be based on different projections, which in turn cause geometric
distortions. Ideally, shoreline change maps constructed from aerial photo-
graphs should be corrected for distortions caused by pitch, tilt, and yaw of the
aircraft. Difficulties in identifying common points over time, problems in
rectifying scale, and distortions near margins and corners are common.
Additional problems include the unavailability of photographs of the desired
vintage, scale, clarity, or resolution. Haze, fog, and cloud cover may obscure
ground features. Finally, the water level at the time that the photographs
were taken can greatly influence the position of the shorelines.
Chapter 2 Secondary Sources of Coastal Information
3 Field Data Collection and
Observation
In order to apply appropriate technologies to a field study, the coastal
scientist should know something about the nature of the problem and the
expected outcome. For example, if a community is being threatened by
erosion, measurements of processes, topography, and bathymetry may be in
order to determine storm-induced and long-term erosion trends. Also, studies
of historical data may be required to determine the rates and spatial variability
of shoreline change over time. Studies involving stratigraphy may be
required, especially if finding local sources of borrow material for beach
nourishment is necessary. Design of a research study must include thorough
planning of objectives and sampling strategies, given temporal, logistical, and
budgetary constraints. Much time and effort can be wasted during a field
study if the research objectives are not well-defined and the sampling plan is
inappropriate.
Secondary sources of coastal data often cannot satisfy all of the specific
purposes or objectives of a study whose purpose is to assess the geologic and
geomorphic history of coasts. However, it is likely that secondary sources
can provide useful supplemental information. In addition, these sources can
be helpful in designing a field data collection program.
If a field collection program is to be undertaken, the type of data to be
acquired depends upon study objectives, parameters required, area to be
studied, funding available, refinement of data (resolution) and site conditions.
Thorough background work should be conducted and secondary sources
consulted before the field visit. While in the field, either for reconnaissance
or detailed sampling, relevant data and information should be meticulously
recorded in water-resistant field books. Details can also be recorded on a tape
recorder. Photographs serve as valuable records of field conditions, sampling
equipment, and procedures. Increasingly, video recorders are being used
during field reconnaissance.
The type of work conducted in the field may fall into several categories.
It may range from a simple visual site inspection to a detailed collection of
process measurements, sediment samples, stratigraphic samples, topographic
and bathymetric data, and geophysical data. Studies may include exploring
Chapter 3 Field Data Collection and Observation
29
30
the acting forces, rates of activity, interactions of forces and sediments, and
variations in activity over time. If the field work will involve extensive data
collection, a preliminary site visit is highly recommended in order to help
determine sampling considerations and to develop a sampling plan.
Spatial and temporal aspects of site inspection are important considerations.
The spatial dimensions of the sampling plan should have adequate longshore
and cross-shore extent, and an adequate grid or sample spacing with which to
meet study objectives. Temporal considerations include the frequency of
sampling and the duration over which samples will be collected. Sampling
frequency and duration are most important in modern process studies, such as
monitoring the topographic and bathymetric changes associated with storms.
Studies of paleoenvironmental or geologic time scales usually do not require
repetitive visits, but thorough spatial sampling is critical.
Information collected from the field observation and measurements can be
used in analysis and numerical models. A conceptual model is often
formulated while the initial observations are being conducted. The conceptual
model is in essence a perception or understanding of the situation. The
perception may be validated by the application of empirical relationships.
Further verification of the observed field relationships is obtained by the
application of physical or mathematical laws. The quantifying of parameters
and the use of these parameters in testing the physical or mathematical
relationships may support or negate the interpretation. Additional
observations may be required to test a wider variety of conditions, and
conceptual models may need to be revised depending on the results of the
study.
Site Inspection and Local Resources
A general site inspection can provide insights toward identifying significant
research problems at a study area, in verifying and enhancing data from aerial
photographs and remote sensing sources, and in developing sampling
strategies for more rigorous types of field work. Even for a brief site visit,
thorough preparation is strongly recommended. Preparation should include
reviewing the pertinent geologic, oceanographic, and engineering literature,
compiling maps and photographs, and understanding the scope of the problem
or situation. If one individual cannot achieve all these objectives, it is
necessary that a team conduct the preliminary project planning. The field
inspection should include observations by all members if at all possible.
The duration of the field examination must be sufficient to assess the major
objectives of the study. Local residents, existing data records, and field moni-
toring equipment may need to be used. A site inspection should include
observation of marine forces and processes, assessment of geomorphic
indicators, visits to neighboring sites, and interviews with residents and other
- Chapter 3 Field Data Collection and Observation
local or knowledgeable individuals. Questions to be asked might include
what, why, when, where, and how come? Why does this section of the shore
look as it does? How do humans influence the local environment? Is the
problem geologic (natural) or man-made? Do catastrophic events, such as
hurricanes, appear to have much impact on the region? A checklist of data to
be collected at a site visit for a coastal erosion study is presented in
Appendix F.
Photographs and Time Sequences
Photography is often an important tool for initial reconnaissance work as
well as for more detailed assessments of the study area. One special
application of cameras involves the use of time-lapse or time-interval
photography. Time-lapse and time-interval photography may be helpful in
studies of geomorphic variability to observe shoreline conditions, sand
transport (Cook and Gorsline 1972), and wave characteristics. If the camera
is set to record short-term processes, relatively frequent photographs are
typically obtained. If historic ground photographs are available, additional
pictures can be acquired from the same perspective. Changes in an area over
time, applicable to both short- and long-term studies, can also be recorded
with video photography. It is important that the following pertinent
photographic information be recorded in a field log:
@ Date.
© Time.
® Camera location.
@ Direction of each photograph.
@ Prominent landmarks, if any.
Wave Measurements and Observations
It is often relevant in studies of historic and process time scales to obtain
data regarding wave conditions at the site. Instrumented wave gages typically
provide the most accurate wave data. Unfortunately, wave gages are
expensive to purchase, deploy, maintain, and analyze. Often, they are
operated for a short term to validate data collected by visual observation or
hindcasting methods. Multiple gages, set across the shore zone in shallow and
deep water, can be used to determine the accuracy of wave transformation
calculations for a specific locale.
Chapter 3 Field Data Collection and Observation
Sil
32
Types of wave gages
Wave gages can be separated into two general groups: directional and
non-directional. In general, directional gages and gage arrays are more
expensive to build, deploy, and maintain than non-directional gages.
Nevertheless, for some applications, directional instruments are vital because
the directional distribution of wave energy is an important parameter in many
applications, such as sediment transport analysis and calculation of wave
transformation. Wave gages can be installed in buoys, placed directly on the
sea or lake bottom, or mounted on existing structures, such as piers, jetties, or
offshore platforms.
Of the non-directional wave gages, buoy-mounted systems such as the
Datawell Waverider are the most expensive to purchase initially but are
accurate and relatively easy to deploy and maintain. Data are usually
transmitted by radio between the buoy and an onshore receiver and recorder.
Bottom-mounted pressure gages measure water level changes by sensing
pressure variations with the passage of each wave. The gages are either self-
recording or are connected to onshore recording devices with cables. Bottom-
mounted gages must be maintained by divers, unless the mount can be
retrieved by hoisting from a workboat. Internal-recording gages usually need
more frequent maintenance because the data tapes must be changed or the
internal memory downloaded. Advantages and disadvantages of self-contained
and cable-telemetered gages are listed in Table 3. Structure-mounted wave
gages are the most economical and most accessible of the non-directional
gages, although their placement is confined to locations where structures exist.
The recording devices and transmitters can be safely mounted above water
level on the structure.
Directional wave gages are also mounted in buoys or on the sea floor
(Figure 16). Arrays of non-directional gages can be used for directional wave
analyses. Directional buoy-type wave gages are often designed to collect
other parameters such as meteorology. The buoys are relatively easy to
deploy, but they cost more initially and continuing maintenance is required.
Placement of wave gages
The siting of wave gages along the coast depends on the goals of the
monitoring project, funds and time available, environmental hazards, and
availability of previously collected data. The user must usually compromise
between collecting large amounts of data for a short, intensive experiment,
and maintaining the gages at sea for a longer period in order to try to observe
seasonal changes. There are no firm guidelines for placing gages at a site,
and each project is unique. A priori knowledge of the site or practical
considerations may dictate gage placement. Table 4 summarizes some sug-
gested practices based on budget and study goals. Suggestions on data
sampling intervals are discussed in Chapter 5.
Chapter 3 Field Data Collection and Observation
Table 3
Self-Contained and Cable-Telemetry Wave Gages; Advantages and
Disadvantages
. Self-contained gages
. Advantages
. Deployment is often simple because compact instrument can be handled by a small dive
team.
. Gage can be easily attached to piles, structural members, or tripods.
. Field equipment can be carried by airplane to remote sites.
. Gage wil! continue to function in severe storms as long as the mount survives.
. Disadvantages
. Gage must be periodically recovered to retrieve data or replace data tapes.
. Data collection time is limited by the capacity of the internal memory or data tapes.
Researcher must compromise between sampling density and length of time the gage can
be. gathering data between scheduled maintenance visits.
. Battery capacity may limit the deployment time.
. If bad weather forces delay of scheduled maintenance, gage may reach the limit of its
storage capacity. This will result in unsampled intervals.
. While under water, gage’s performance cannot be monitored. If it fails electronically or
leaks, data are usually lost forever.
. Gage may be struck by anchors or fishing vessels. The resulting damage or total loss may
not be detected until the next maintenance visit.
. Notes
. Data compression techniques and advances in low-energy memory have dramatically
increased the storage capacity of underwater instruments. Some can remain onsite as
long as 12 months.
. If a gage floods, data from electronic memory systems are usually irretrievably lost. On
the other hand, a wet data tape can sometimes be saved by flushing with fresh water and
carefully drying.
. Onboard data processing can extend deployment times by reducing the need to store raw
data.
. Data transmission by cable.
. Advantages
. Data can be continuously monitored. If a failure is detected (by human analysts or error-
checking computer programs), a repair team can be sent to the site immediately.
. Because of the ability to monitor the gage’s performance, infrequent inspection visits may
be adequate to maintain systems.
. Frequency and density of sampling are only limited by the storage capacity of the shore-
based computers.
. Gage can be reprogrammed in situ to change sampling program.
. Electrical energy is supplied from shore.
. Disadvantages
. Cable to shore is vulnerable to damage from anchors or fishing vessels.
. Shore station may be damaged in severe storms, resulting in loss of valuable storm data.
. Shore station and data cable are vulnerable to vandalism.
. Backup power supply necessary in case of blackouts.
. Installation of cable can be difficult, especially in harbors and across rough surf zones.
. Installation often requires a major field effort, with vehicles on beach and one or two
boats. Heavy cable must be carried to the site.
. Cable eventually deteriorates in the field and must be replaced.
. Cable may have to be removed after experiment has ended.
Ouhwn—- DO Uf
. Notes
- 0 on
. Some cable-based gages have internal memory and batteries so that they can continue to
collect data even if cable is severed.
. Ability to constantly monitor gage’s performance is a major advantage in conducting field
experiments.
to
Chapter 3 Field Data Collection and Observation
Figure 16. Bottom-mounted Sea Data/™ 635-12 directional wave gage mounted in tripod
using railroad wheels as corner weights
Seismic wave gage
Wave estimates based on microseismic measurements are an alternative
means to obtain wave data in high-energy environments. Microseisms are very
small ground motions that can be detected by seismographs within a few
kilometres of the coast. It is generally accepted that microseisms are caused
by ocean waves and that the amplitudes and periods of the motions correspond
to the regional wave climate. Comparisons of seismic wave gages in Oregon
with in situ gages have been favorable (Howell and Rhee 1990; Thompson,
Howell, and Smith 1985). The seismic system has inherent limitations, but
deficiencies in wave period estimates can probably be solved with more
sophisticated processing. Use of a seismometer for wave purposes is a long-
term commitment, requiring time to calibrate and compare the data. The
advantage of a seismograph is that it can be placed on land in a protected
building.
34
Chapter 3 Field Data Collection and Observation
Table 4
Wave Gage Placement for Coastal Project Monitoring
High-budget project (major harbor; highly populated area)
A. Recommended placement:
One (or more) wave gage(s) close to shore near the most critical features being moni-
tored (example, near an inlet). Although nearshore, gages should be in intermediate
or deep water based on expected most common wave period. Depth can be calcu-
lated from formulas in the Shore Protection Manual (1984).
In addition, one wave gage in deep water.
Schedule:
Minimum: 1 year. Monitor winter/summer wave patterns.
Optimum: 5 years or at least long enough to determine if there are noticeable
changes in climatology over time. Try to include one El Nifio season during coverage.
Notes:
Concurrent physical or numerical modeling: Placement of gages must be coordinated
with modellers if field data will be used as input or calibration for models.
Pre-existing wave data: may indicate that gages should be placed in particular
locations. Alternative, may want to place gages in the identical locations as the
previous deployment in order to make the new data as compatible as possible with
the older data. Long, continuous datasets are extremely valuable!
Complicated topography: If there is a complicated local topography near the critical
project site (example: ebb tidal shoal at an inlet), it may be better to place the
nearshore gage a few kilometres away where the isobaths are more parallel to the
shoreline.
Hazardous conditions: If there is a danger of gages being damaged by anchors or
fishing boats, the gages must be protected, mounted on structures (if available), or
deployed in a location that appears to be the least hazardous.
ll. Medium-budget project
A. Recommended placement:
One wave gage close to shore near project site.
Obtain data from nearest NOAA National Data Buoy Center (NDBC) buoy for
deepwater climatology.
Schedule: minimum 1-year deployment; longer if possible
Notes: same as IC above. Compatibility with existing data sets is very valuable.
Low-budget, short-term project
Recommended placement: gage close to project site.
Schedule: if 1-year deployment is not possible, try to monitor the season when the
highest waves are expected (usually winter, although this may not be true in areas
where ice pack occurs).
Notes: same as IC above. It is critical to use any and all data from the vicinity,
anything to provide additional information on the wave climatology of the region.
Water Level Measurements and Observations
To collect continuous water level data for site-specific, modern process
Studies, tide gages must be deployed near the project site. Three types of
instruments are commonly used to measure water level:
Chapter 3 Field Data Collection and Observation
36
@ Pressure transducer gages. These instruments are usually mounted on
the seafloor or attached to structures. They record hydrostatic pressure,
which is converted to water level during data processing. A major
advantage of these gages is that they are underwater and somewhat
inaccessable to vandals. In addition, those like the Sea Data
Temperature Depth Recorder are compact and easy to deploy.
© Stilling-well, float gages. These instruments, which have been in use
since the 1930’s, consist of a float that is attached to a stylus assembly.
A clockwork or electric motor advances chart paper past the stylus,
producing a continuous water level record. The float is within a stilling
well, which dampens waves and boat wakes. The main disadvantage of
these gages is that they must be protected from vandals. They are
usually used in estuaries and inland waterways where piles or bridges
are available for mounting the well and recording box. Figure 17 is an
example of tide data from Choctawhatchee Bay, Florida.
@ Staff gages. Water levels are either recorded manually by an observer
or calculated from electric resistance measurements. The resistance
staff gages require frequent maintenance because of corrosion and
biological fouling. The manual ones are difficult to use at night and
during storms, when it is hazardous for the observer to be at the site.
Typically, water level measurements recorded by gages are related to an
established datum, such as mean sea level. This requires that the gage eleva-
tions be accurately measured using surveying methods. The maximum water
level elevations during extreme events can also be determined by examining
water marks on structures or other elevated features.
Water level information over paleoenvironmental time scales has been
investigated by researchers using stratigraphic coring, seismic techniques, and
radiometric dating. The reconstruction of ancient sea levels is one of the
powerful tools used in seismic stratigraphy (Payton 1977; Sheriff 1980).
Current Measurements and Observations
Need for coastal current data
Currents, both shore-normal and shore-parallel, play a significant role in
shaping the geology of coasts. 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 pre-
dicting beach profile change, while knowledge of longshore (shore-parallel)
currents and associated transport can be used in predicting beach planview
Chapter 3 Field Data Collection and Observation
Beacon 49, near Fourmile Point
Beacon 4, near Shalimar
Fort Walton, Santa Rosa Sound
Beacon 1, SW Choctawhatchee Bay
~~
E
—
Cc
is)
=
oO
>
oO
oO
oO
~
E
Destin Coast Guard Station
Old Pass Lagoon
5 Oy ahh Ry IG. sire Ie eS) By rey
(NGVD = 0.0) April 1987
Figure 17. Tidal elevations from seven stations in Choctawhatchee Bay and vicinity,
Florida. The overall envelope of the curves is similar, but individual peaks are
shifted in phase from station to station. Original tide records courtesy of U.S.
Army Engineer (USAE) District, Mobile
Chapter 3 Field Data Collection and Observation
<i7/
38
changes. Cell circulation, the combined effect of both types of currents, may
explain or assist in identifying regularly spaced features along many coasts.
The longshore migration of such cells may also cause accompanying landform
migration.
An example of the interaction of topography and hydrodynamic forces is
provided by rip currents. Rip currents extend perpendicular from the shore-
line through the surf zone and serve as a conduit for water to escape from a
zone of elevated water. The spacing of rip currents may be controlled by
edge waves or other wave height variations along the surf zone (Bowen 1969;
Bowen and Inman 1969; Tang and Dalrymple 1989). However, such wave
height variations may not necessarily be the only cause of rip currents.
Irregular nearshore topography, manifested by shoreline protuberances, may
produce nearshore circulation cells (Sonu 1972). Rip currents are important
geologically because they have been shown to carry significant amounts of
sand offshore (Davidson-Arnott and Greenwood 1976; Sonu 1972). Rip
currents can be located by observers at the shore and from aerial photographs.
Their positions can also be identified indirectly by side-scan sonar when their
characteristic rip-scoured channels are imaged on the seafloor (Morang and
McMaster 1980).
The configuration of the shoreline can provide information regarding
littoral currents. Shoreline protuberances, especially in the vicinity of
structures, headlands and barriers, and tidal inlets are useful indicators of the
prevailing longshore littoral drift (Komar 1976). Such indicators cannot
generally be used for quantitative estimates of the sediment transport rate.
Usually, transport rate must be calculated from: (a) direct evidence, such as
sand impoundment in front of structures; (b) physical measurements of
currents and sediment size and type; and (c) the use of longshore transport
formulas, provided that local waves can be measured or hindcast.
General techniques of current measurement
The observation of hydraulic phenomena can be accomplished by two
general approaches. One of these, Lagrangian, follows the motion of an
element of matter in its spatial and temporal evolution. The other, Eulerian,
defines the motion of the water at a fixed point and determines its temporal
evolution. Lagrangian current-measuring devices are often used in sediment
transport studies, in pollution monitoring, and for tracking ice drift. Eulerian,
or fixed, current measurements are important for determining the variations in
flow over time at a fixed location. Recently developed instruments combine
aspects of both approaches.
Four general classes of current-measuring technology are presently in use
(Appell and Curtin 1990):
@ Radar and Lagrangian methods.
@ Spatially integrating methods.
Chapter 3 Field Data Collection and Observation
@ Point source and related technology.
@ Acoustic Doppler Current Profilers (ADCP) and related technology.
The large number of instruments and methods used to measure currents under-
scores that detection and analysis of fluid motion in the oceans is an exceed-
ingly complex process. The difficulty arises from the large continuous scales
of motion in the water. As stated by McCullough (1980), "There is no single
velocity in the water, but many, which are characterized by their temporal and
spatial spectra. Implicit then in the concept of a fluid ’velocity’ is knowledge
of the temporal and spatial averaging processes used in measuring it.
Imprecise, or worse, inappropriate modes of averaging in time and/or space
now represent the most prominent source of error in near-surface flow
measurements." McCullough’s comments were addressed to the measurement
of currents in the ocean. In shallow water, particularly in the surf zone,
additional difficulties are created by turbulence and air entrainment caused by
breaking waves, by suspension of large concentrations of sediment, and by the
physical violence of the environment. Trustworthy current measurement
under these conditions becomes a daunting task.
Lagrangian
Dye, drogues, ship drift, bottles, temperature structures, oil slicks, radio-
active materials, paper, wood chips, ice, trees, flora, and fauna have all been
used to study the surface motion of the oceans (McCullough 1980). Some of
these techniques, along with the use of mid-depth drogues and seabed drifters,
have been widely used in coastal studies. A disadvantage of all drifters is that
they are only quasi-Lagrangian sensors because, regardless of their design or
mass, they cannot exactly follow the movement of the water (Vachon 1980).
Nevertheless, they are particularly effective at revealing surface flow patterns
if they are photographed or video recorded on a time-lapse basis. Simple
drifter experiments can also be helpful in developing a sampling strategy for
more sophisticated subsequent field investigations. Floats, bottom drifters,
drogues, and dye are used especially in the littoral zone where fixed current
meters are adversely affected by turbulence.
High-frequency (HF) radar surface-current mapping systems have been
tested since the 1970’s. The advantage of using the upper high radar frequen-
cies is that these frequencies accurately assess horizontal currents in a mean
water depth of only 1 m (total layer thickness about 2 m). Hence, HF radar
accurately senses horizontal currents in the uppermost layers of the oceans,
where other instruments such as moored current meters and ADCP’s become
inoperable (Barrick, Lipa, and Lilleboe 1990). Nevertheless, HF radar has
had limited success in the oceanography community because of the difficulty
in proving measurement accuracy and because of relatively high system costs
(Appell and Curtin 1990).
Large-scale coastal circulation can be observed in satellite images, as seen
in Figures 13 and 14.
Chapter 3 Field Data Collection and Observation
39
40
Spatially integrating methods
To date, experiments in spatially averaging velocity by observing induced
electrical fields have been conducted by towing electrodes from ships or by
sending voltages in abandoned underwater telephone cables. Some of these
experiments have been for the purpose of measuring barotropic flow in the
North Pacific (Chave, Luther, and Filloux 1990; Spain 1990 - these two pa-
pers provide a substantial summary of the mathematics and methods). This
author (Morang) is unaware of whether these techniques have been tested in
shallow water or in restricted waterways such as channels. At this time,
therefore, spatially integrating methods appear to have no immediate applica-
tion to coastal engineering studies.
Point source (Eulerian) and related technology
In channels, bays, and offshore, direct measurements of the velocity and
direction of current flow can be made by instruments deployed on the bottom
or at various levels in the water column. Two general classes of current
meters are available: mechanical (impeller-type) and electronic. Several types
of electronic current meters are in common use, including electromagnetic,
inclinometer, and acoustic travel-time (Fredette et al. 1990, McCullough
1980, Pinkel 1980).
Impeller current meters measure currents by means of a propeller device
that is rotated by the current flow. They serve as approximate velocity
component sensors because they are primarily sensitive to the flow component
in a direction parallel to their axle. Various types of propeller designs have
been used to measure currents, but experience and theoretical studies have
shown that ducted propellers are more satisfactory in measuring upper ocean
currents than rotor/vane meters (Davis and Weller 1980). Impeller/propeller
meters are considered to be the most reliable in the surf zone (Teleki,
Musialowski, and Prins 1976), as well as the least expensive. One model, the
Endeco 174, has been widely used by CERC for many years throughout the
country. Impeller gages are subject to snarling, biofouling, and bearing
failures, but are more easily repaired in the field and are more easily cali-
brated than other types (Fredette et al. 1990).
Electronic current meters have many features in common, although they
operate on different principles. Their greatest common advantages are rapid
response and self-contained design with no external moving parts. They 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 influence on the quality of data acquired than
does the type of meter used (Fredette et al. 1990). The InterOcean Systems
S4 electromagnetic meter has been successfully used recently by CERC at
field experiments.
Chapter 3 Field Data Collection and Observation
Acoustic Doppler Current Profilers (ADCP)
These profilers operate on the principle of Doppler shift in the backscat-
tered acoustic energy caused by moving particles suspended in the water.
Assuming that the particles have the same velocity as the ambient water, the
Doppler shift is proportional to the velocity components of the water within
the path of the instrument’s acoustic pulse (Bos 1990). The backscattered
acoustic signal is divided into parts corresponding to specific depth cells, often
termed "bins." The bins can be various sizes, depending upon the depth of
water in which the instrument has been deployed, the frequency of the signal
pulse, the time that each bin is sampled, and the acceptable accuracy of the
estimated current velocity. Much excitement has been generated by ADCP’s,
both among scientists working in shallow water and in the deep ocean (a
comprehensive bibliography is listed in Gordon et al. 1990). A great
advantage of using ADCP’s in shallow water is that they provide profiles of
the velocities in the entire water column, providing more comprehensive
views of water motions than that from strings of multiple point source meters.
ADCP data are inherently noisy, and signal processing and averaging are
critical to the successful performance of the gages (Trump 1990).
Indirect estimates of currents
Indirect estimates of current speed and direction can be made from the
orientation, size, and shape of bed forms, particularly in shallow water. Sedi-
mentary structures on the seafloor are caused by the hydrodynamic drag of
moving water acting on sediment particles. The form and shape of bottom
structures reflect the effects of and interaction among tidal currents, waves,
riverine flow, and longshore currents. These complex interactions especially
affect bed forms in tidal channels and other restricted waterways. Bed forms
reflect flow velocity, but are generally independent of depth (Clifton and
Dingler 1984; Boothroyd 1985). Their shape varies in response to increasing
flow strength (Hayes and Kana 1976). Bed form orientation and associated
slipfaces also provide clues to flow direction (Morang and McMaster 1980;
Wright, Sonu, and Kielhorn 1972). Widespread use of side-scan sonar has
made this type of research possible in bays, inlets, and offshore.
Grab Sampling and Samplers
Seafloor sediments in coastal areas can show great spatial and temporal
variation. The surface sediments may provide information about the energy of
the environment as well as the long-term processes and movement of
materials, such as sediment transport pathways, sources, and sinks. Bed
surface sediments are typically collected with grab samplers and then analyzed
using standard laboratory procedures. These tests are described briefly in this
Chapter 3 Field Data Collection and Observation
41
42
report and in greater detail in other sources (Fredette et al. 1990; Buller and
McManus 1979).
There are a variety of grab type samplers of different sizes and design that
are used for collecting surface sediment samples. Most consist of a set of
opposing, articulated scoop-shaped jaws that are lowered to the bottom in an
open position and are then closed by various trip mechanisms to retrieve a
sample. Many grab samplers are small enough to be deployed and retrieved
by hand; others require some type of lifting gear.
A simple and inexpensive dredge sampler can be made of a section of pipe
that is closed at one end. It is dragged a short distance across the bottom to
collect a sample. Unlike grab samples, the dredged samples are not represen-
tative of a single point and may have lost finer material during recovery.
However, dredge samplers are useful in areas where shells or gravel that
prevent complete closure of the jaws are present.
Although obtaining surficial samples is helpful for assessing recent
processes, it is typically of limited value in stratigraphic study. Generally, the
expense of running track lines in coastal waters for the sole purpose of sam-
pling surficial sediments is not economically justified unless particularly
inexpensive boats can be used. Occasionally, grab and dredge samples can be
taken during geophysical surveys, but the sampling operations require the
vessel to stop at each station, thus losing survey time and creating interrupted
data coverage. Precise offshore positioning now allows grab samples to be
collected at specific locations along the boat’s track after the survey has been
run and the data examined.
Stratigraphic Sampling
Sediments and sedimentary rock sequences are a record of the history of
the earth and its changing environments, including sea-level changes,
paleoclimates, ocean circulation, atmospheric and ocean geochemical changes,
and the history of the earth’s magnetic field. On a global scale, the greatest
influences on the coastal zone are sea level fluctuations and plate tectonics.
By analyzing stratigraphic data, the age relations of the rock strata, rock form
and distribution, lithologies, fossil record, biopaleogeography, and episodes of
erosion and deposition at a coastal site can be determined. Erosion removes
part of the physical record, resulting in unconformities. Often, evidence of
erosion can be interpreted using physical evidence or dating techniques.
Sediment deposits located across a zone that ranges from the maximum
water level elevation to the depth of the wave base are largely indicative of
recent processes. Within this zone in unconsolidated sediments, simple recon-
naissance field techniques are available for collecting data. The techniques
often use ordinary construction equipment or hand tools. Smaller efforts
Chapter 3 Field Data Collection and Observation
require shovels, hand augers, posthole diggers, or similar hand-operated
devices. Larger scale efforts may involve trenches, pits, or other large open-
ings created for visual inspection, sample collection, and photography
(Figure 18). Often, undisturbed chunk or block samples and disturbed jar or
bag samples are hand carved from these excavations and taken back to the
laboratory.
Rates and patterns of sedimentation can be determined using marker
horizons. Marker horizons may occur in relation to natural events and
unintentional human activities or they may be directly emplaced for the
express purpose of determining rates and patterns of sedimentation. Recently,
several studies have estimated rates of sedimentation in marshes by spreading
feldspar markers and later measuring the thicknesses of materials deposited on
the feldspar with cryogenic coring devices.
The petrology and mineralogy of rock samples can be used to identify the
source of the sediment. This can indicate if river flow has changed or if
coastal currents have changed directions.
Direct sampling of subbottom materials is often essential for stratigraphic
studies that extend beyond historic time scales. Table 5 lists details on a num-
ber of subaqueous sediment sampling systems that do not require drill rigs.
One system listed in Table 5, the vibracorer, is commonly used by geologists
to obtain samples in the marine and coastal environments. Vibratory corers
consist of three main components: a frame, coring tube or barrel, and a drive
head with a vibrator (Figure 19). The frame consists of a quadrapod or tripod
arrangement, with legs connected to a vertical beam. The beam supports and
guides the core barrel and vibrator and allows the corer to be free-standing on
the land surface or seafloor. The core may be up to 3 or 4 m long, which is
adequate for borrow site investigations and many other coastal studies. Heavy
duty, longer corers are available.
While common vibratory corers are capable of penetrating 5 m or more of
unconsolidated sediment, actual performance depends on the nature of the
subbottom material. Under unfavorable conditions very little sediment may be
recovered. Limited recovery occurs for several reasons, chief among these
being lack of penetration of the core barrel. In general, stiff clays, gravel,
and hard-packed fine to very fine sands are usually most difficult to penetrate.
Compaction and loss of material during recovery can also cause a discrepancy
between penetration and recovery. In comparison with rotary soil-boring
operations, vibratory coring setup, deployment, operations, and recovery are
quite rapid. Usually a 3-m core can be obtained in a matter of minutes.
Longer cores require a crane or some other means of hoisting the equipment,
a procedure that consumes more time but is still comparatively rapid. Success
with vibracoring depends on some knowledge of soil type beforehand.
Cores can be invaluable because they allow a direct, detailed examination
of the layering and sequences of the subsurface sediment in the study area.
The sequences provide information regarding the history of the depositional
43
Chapter 3 Field Data Collection and Observation
Figure 18. Trench excavated in the edge of a sand dune, eastern Alabama near
Alabama/Florida state line
environment and the physical processes during the time of sedimentation.
Depending upon the information required, the types of analysis that can be
performed on the core include grain size, sedimentary structures, identification
of shells and minerals, organic content, microfaunal identification (pollen
counts), X-ray radiographs, radiometric dating, and engineering tests. If only
information regarding recent processes is necessary, then a box corer, which
samples up to 0.6-m depths, can provide sufficient sediment. Because of its
greater width, a box corer can recover undisturbed sediment from immediately
below the seafloor, allowing the examination of microstructure and
lamination. These structures are usually destroyed by traditional vibratory or
rotary coring.
44
Chapter 3 Field Data Collection and Observation
able 5
Subaqueous Soil Sampling Without Drill Rigs and Casing
Petersen dredge
Harpoon-type
gravity corer
Free-fall gravity
corer
Piston gravity
corer (Ewing
gravity corer)
Piggott explo-
sive coring tube
operated piston
Vibracorer
Application
Large, relatively
intact "grab"
samples of
seafloor.
Cores 1.5- to 6-in.
dia. in soft to firm
soils.
Cores 1.5- to 6-in.
dia. in soft to firm
soils.
2.5-in. sample in
soft to firm soils.
Cores of soft to
hard bottom
sediments.
Good-quality
samples in soft
clays.
High-quality sam-
ples in soft to firm
sediments. Dia.
3-1/2 in.
Large, intact slice
of seafloor.
(Adapted from Hunt (1984))
Chapter 3 Field Data Collection and Observation
Description
Clam-shell type grab
weighing about 1000 Ib
with capacity about
0.4 ft?
Vaned weight connected
to coring tube dropped
directly from boat. Tube
contains liners and core
retainer.
Device suspended on wire
rope over vessel side at
height above seafloor
about 15 ft and then
released.
Similar to free-fall corer
except that coring tube
contains a piston that
remains stationary on the
seafloor during sampling.
Similar to gravity corer.
Drive weight serves as gun
barrel and coring tube as
projectile. When tube
meets resistance of sea
floor, weighted gun barrel
slides over trigger
mechanism to fire a
cartridge. The exploding
gas drives tube into bot-
tom sediments.
Similar to the Osterberg
piston sampler, except
that the piston on the
sampling tube is activated
by gas pressure.
Apparatus is set on sea
floor. Air pressure from
the vessel activates an air-
powered mechanical vibra-
tor to cause penetration of
the tube, which contains a
plastic liner to retain the
core.
Weighted box with closure
of bottom for benthic bio-
logical sampling.
Penetration depth
To about 4 in.
To about 30 ft.
Soft soils to
about 17 ft.
Firm soils to
about 10 ft.
Standard core
barrel 10 ft;
additional 10-ft
sections can be
added.
Cores to 1-7/8 in.
and to 10-ft
lengths have been
recovered in stiff
to hard materials.
About 35 ft.
Lengths of 20 to
40 ft. Rate of
penetration varies
with material
strength. Samples
a 20-ft core in
soft soils in
2 min.
To about 1 ft.
Comments
Effective in water
depths to 200 ft. More
with additional weight.
Maximum water depth
depends only on
weight. Undisturbed
(UD) sampling possible
with short, large-
diameter barrels.
As above for harpoon
type.
Can obtain high-quality
UD samples.
Has been used
successfully in
20,000 ft of water.
Maximum water depth
about 200 ft.
Central part of sample
is undisturbed.
45
Cable Attached
To Winch
Vibrator
Gasoline
Engine
Power
Source
Securing
Clamps
Figure 19. Front view of lightweight vibracorer mounted on a barge
If it is necessary to obtain deep cores, or if there are cemented or very
hard sediments in the subsurface, rotary coring is necessary. Truck- or skid-
mounted drilling rigs can be conveniently used on beaches or on barges in
lagoons and shallow water. Offshore, rotary drilling becomes more complex
and expensive, usually requiring jack-up drilling barges or four-point anchored
drill ships (Figure 20). An experienced drilling crew can sample 100 m of the
subsurface in about 24 hr. Information on drilling and sampling practice is
presented in HQUSACE (1972) and Hunt (1984).
Sediment Movement and Surface Forms
Of great importance in investigations of geologic history is tracing sedi-
ment movement. This includes identifying the locations of sediment sources
and sinks, quantifying sediment transport rates, and discovering the pathways.
Sediment transportation is influenced by grain properties such as size, shape,
and density, with grain size being most important. Differential transport of
46
Chapter 3 Field Data Collection and Observation
coarse and fine, angular and rounded, and light and heavy grains leads to
grading. Field visits to a locality are often repeated to assess temporal
cvariability of these phenomena. Simultaneous measurement of energy
processes such as current and waves is often required for understanding the
rates and mechanisms of movement.
Measurement of sediment movement
The measurement of suspended and bed-load sediment movement in the
surf zone is an exceedingly difficult process. There are a variety of sampling
devices available for measuring suspended and bed-load transport in the field
(Dugdale 1981; Seymour 1989), but these devices have not performed
properly under some conditions or have been expensive and difficult to use.
For these reasons, new sampling procedures are being developed and tested at
CERC and other laboratories. Point measurements of sediment movement can
be performed by two general procedures:
@ Direct sampling and weighing of a quantity of material.
@ Detection of the fluid flow by electro-optical or acoustic instruments
deployed in the water.
Two general methods are available to directly sample the sediment in
suspension and in bed load. First, water can be collected in hand-held bottles
or can be remotely sucked into containers with siphons or pump apparatus.
The samples are then dried and weighed. The second method is to trap a
representative quantity of the sediment with a mesh or screen trap through
which the water is allowed to flow for a fixed time. A fundamental problem
shared by both methods is the question of whether the samples are truly
representative of the sediment in transport. For example, how close to the
seabed must the orifice be to sample bed load? If it is high enough to avoid
moving bed forms, will it miss some of the bed load? Streamer traps made
from mesh are inexpensive to build but difficult to use. The mesh must be
small enough to trap most of the sediment but must allow water to flow
freely. Kraus (1987) deployed streamers at Duck, NC, from stainless steel
wire frames (Figure 21). Kraus and Dean (1987) obtained the distribution of
longshore sand transport using sediment traps. A fundamental limitation of
traps is that they can usually only be used in mild conditions. In winter and
during storms it is too hazardous for the field technicians to maintain the
equipment. Perversely, it is under these harsher conditions when the greatest
sediment movement occurs. Another fundamental problem is relating the
instantaneous measured suspended and bed-load transport to long-term sedi-
ment movement. Because of the extreme difficulty of conducting research in
the surf zone, answers to these questions remain elusive.
47
Chapter 3 Field Data Collection and Observation
48
Figure 20. Rotary drilling operations under way in the estuary of the
Guayacan River, Ecuador. In this area, layers of cemented
coquina were very difficult to penetrate
Chapter 3 Field Data Collection and Observation
Current Flow
Legs Inserted
Into Seafloor
Figure 21. Side view of steel frame and polyester mesh sediment trap used at Duck, NC,
by Kraus (1987) during CERC’s DUCK-85 field experiments
Electronic instruments are being developed to detect or estimate sediment
transport. They have some advantages over direct sampling procedures.
These include the ability to measure the temporal variations of suspended or
bed-load sediment and the ability to be used in cold water or in harsh
conditions. (Note, however, that in severe storms, essentially no man-made
devices have survived in the surf zone.) Their disadvantages include the
difficulty of calibrating the sensors and testing their use with different types of
sand and under different temperatures. In addition, many of these instruments
are expensive and not yet commonly available. Sternberg (1989) and
Seymour (1989) discuss ongoing research to develop and test new instruments
for use in sediment transport studies in estuarine and coastal areas. Acoustic
doppler current profilers are being tested and calibrated at CERC to determine
49
Chapter 3 Field Data Collection and Observation
50
if they can be used to measure suspended sediment concentrations in the water
column.
Sediment movement, both bed load or total load, can also be measured
with the use of natural and artificial tracers (Dugdale 1981). Heavy minerals
are an example of a natural tracer which has been used in studies of sediment
movement (Komar et al. 1989; McMaster 1960). Natural sand can also be
labelled using radioactive isotopes and fluorescent coatings (Teleki 1966).
Radioactive tracers are not used any more because of health and safety con-
cerns. When fluorescent dyes are used, different colors can be used simulta-
neously on different size fractions to differentiate between successive experi-
ments at one locality (Ingle 1966). Artificial grains, which have the same
density and hydraulic response of natural grains, can also be used in tracer
studies. Aluminum cobble has been used by Nicholls and Webber (1987) on
rocky beaches in England. The aluminum rocks were located on the beaches
using metal detectors.
As with other phenomena, the experimental design for tracer studies may
be Eulerian or Lagrangian. For the time integration or Eulerian method, the
tracer grains are injected at a constant rate over a given interval of time. For
space integration or the Lagrangian method, the tracers are released over an
area at the same time. The choice of the method depends upon the nature of
the problem. Field experiments must be designed carefully to isolate the
parameter of interest that is to be measured or traced. For example, if the
purpose of the study is to assess bed load transport, then care must be taken
not to introduce tracers into the suspended load in the water column.
Bed forms
Introduction. When sediment is moved by flowing water, the individual
grains are usually organized into morphological elements called bed forms.
These occur in a baffling variety of shapes and scales. Some bed forms are
stable only between certain values of flow strength. Often, small bed forms
(ripples) are found superimposed on larger forms (dunes), suggesting that the
flow field may vary dramatically over time. Bed forms may move in the
same direction as the current flow, may move against the current (antidunes),
or may not move at all except under specific circumstances. The study of bed
form shape and size is of great value because it can assist in making quan-
titative estimates of the strength of currents in modern and ancient sediments
(Harms 1969; Jopling 1966). This introduction to a complex subject is by
necessity greatly condensed. For details on interpretation of surface structures
and sediment laminae, readers are referred to textbooks on sedimentology
such as Allen (1968; 1985), Komar (1976), Leeder (1982), Lewis (1984), and
Reineck and Singh (1980).
Chapter 3 Field Data Collection and Observation
In nature, bed forms are found in three environments of greatly differing
characteristics:
@ Rivers - unidirectional and channelized; large variety of grain sizes.
@ Sandy coastal bays - semi-channelized, unsteady, reversing (tidal) flows.
@ Continental shelves - deep, unchannelized; dominated by geostrophic
flows, storms, tidal currents, wave-generated currents.
Because of the diverse natural settings and the differing disciplines of
researchers who have studied sedimentology, the classification and nomencla-
ture of bed forms has been confusing and contradictory. The following classi-
fication scheme, proposed by the Society for Sedimentary Geology (SEPM)
Bedforms and Bedding Structures Research Group in 1987 (Ashley 1990) is
suitable for all subaqueous bed forms:
a. Ripples. These are small bed forms with crest-to-crest spacing less than
about 0.6 m and height less than about 0.03 m. It is generally agreed
that ripples occur as assemblages of individuals similar in shape and
scale. On the basis of crestline trace, Allen (1968) distinguished five
basic patterns of ripples: straight, sinuous, catenary, linguoid, and
lunate (Figure 22). The straight and sinuous forms may be symmetrical
in cross section if subject to primarily oscillatory motion (waves) or
may be asymmetrical if influenced by unidirectional flow (rivers or tidal
currents). Ripples form a population distinct from larger-scale dunes,
although the two forms share a similar geometry. The division between
the two populations is caused by the interaction of ripple morphology
and bed shear stress. At low shear stresses, ripples are formed. As
shear stress increases above a certain threshold (which varies with grain
size, fluid density, and other properties) a "jump" in behavior occurs,
resulting in the appearance of the larger dunes (Allen 1968).
b. Dunes. Dunes are flow-transverse bed forms with spacings from under
1 m to over 1,000 m that develop on a sediment bed under unidirec-
tional currents. These large bed forms are ubiquitous in sandy environ-
ments where water depths are greater than about 1 m, sand size coarser
than 0.15 mm (very fine sand), and current velocities greater than about
0.4 m/sec. In nature, these flow-transverse forms exist as a continuum
of sizes without natural breaks or groupings (Ashley 1990). For this
reason, "dune" replaces terms such as megaripple or sand wave, which
were defined on the basis of arbitrary or perceived size distributions.
For descriptive purposes, dunes can be subdivided as small (0.6 - 5 m),
medium (5 - 10 m), large (10 - 100 m), and very large (> 100 m). In
addition, the variation in pattern across the flow must be specified. If
the flow pattern is relatively unchanged perpendicular to its overall
direction and there are no eddies or vortices, the resulting bed form will
Chapter 3 Field Data Collection and Observation
51
STRAIGHT STRAIGHT TRANSVERSE SINUOUS
TRANSVERSE SWEPT IN PHASE
TRANSVERSE SINUOUS TRANSVERSE CATENARY TRAVERSE CATENARY CATENARY
OUT OF PHASE IN PHASE OUT OF PHASE
LINGUOID CUSPATE
CCC
CURRENT \: TW arene
F
LOW (h)
Figure 22. Plan view of basic ripple types (modified from Allen 1968)
be straight crested and can be termed two-dimensional (Figure 23a). If
the flow structure varies significantly across the predominant direction
and vortices capable of scouring the bed are present, a three-
dimensional bed form is produced (Figure 23b).
c. Plane beds. A plane bed is a horizontal bed without elevations or
depressions larger than the maximum size of the exposed sediment.
The resistance to flow is small, resulting from grain roughness, which
is a function of grain size. Plane beds occur under two hydraulic
conditions:
@ The transition zone between the region of no movement and the
initiation of dunes (Figure 24).
e The transition zone between ripples and antidunes, at mean flow
velocities between about 1 and 2 m/sec (Figure 24).
d. Antidunes. Antidunes are bed forms that are in phase with water sur-
face gravity waves. They resemble regular dunes, but their height and
wavelength depend on the scale of the flow system and characteristics of
the fluid and bed material (Reineck and Singh 1980). Trains of
antidunes gradually build up from a plane bed as water velocity
increases. As the antidunes increase in size, the water surface changes
52
Chapter 3 Field Data Collection and Observation
Mean Flow Direction
2 — Dimensional, Straight—Crested Dunes
Mean Flow Direction
3 — Dimensional, Lunate Dunes
Figure 23. Two- and three-dimensional bed forms (adapted from Reineck and Singh (1980))
DS
Chapter 3 Field Data Collection and Observation
Fr=1.0
Fr=Mean Velocity
Froude Number
Fr=0.84
No Movement
”
SS
£
>
Oo
2
o
>
>
&
x
iS
iS]
o
=
Ripples
Mean Flow Depth
0.25-0.40 m
Median Sediment Size, mm
Figure 24. Velocity-grain size relationships for subaqueous bed forms (from Ashley (1990))
from planar to wave-like. The water waves may grow until they are unstable
and break. As the sediment antidunes grow, they may migrate upstream or
downstream, or may remain stationary (the name "antidune" is based on early
observations of upstream migration).
e. Velocity - grain size relationships. Figure 24, from Ashley (1990) illus-
trates the zones where ripples, dunes, planar beds, and antidunes are
found. This figure is very similar to Figure 11.4 in Graf's (1984)
hydraulics text, although Graf uses different axis units.
Use of subsurface structure to estimate flow regime. Several useful
indices of foreset laminae, which may assist in making qualitative estimates of
the strength of currents in modern and ancient sediments, are given by Jopling
(1966). These include: (1) maximum angle of dip of foreset laminae (at low
velocities the angle may exceed the static angle of repose, whereas at high
velocities the angle is less than the static angle); (2) character of contact
between foreset and bottomset (the contact changes from angular to tangential
to sigmoidal with increasing velocity); (3) laminae frequency measured at
right angles to bedding (there are more laminae per unit area with increasing
velocity); (4) sharpness or textural contrast between adjacent laminae (at
54
Chapter 3 Field Data Collection and Observation
higher velocities laminae become less distinct); and (5) occurrence of regres-
sive ripples (regressive ripples indicate relatively higher velocities).
Measurements of bed forms can be accomplished on exposed sand banks at
low water using surveying techniques or large-scale aerial photographs.
Dimensionless parameters of ripples and other bed forms can indicate deposi-
tional environment (Tanner 1967). The 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 as well as 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 bed forms can also be estimated for a given
flow depth by the velocity-depth sequence of bed forms (Boothroyd 1985).
Navigation and Positioning Equipment
Accurate positioning is essential for most geological monitoring studies.
Several types of positioning and navigation systems are available for coastal
studies, with the most common being Loran-C and Global Positioning Systems
(GPS). Other technologies, such as short-range microwave and optical
systems, are also in common use (Fredette et al. 1990).
Loran-C computes microsecond time differences using pulsed low-
frequency radio waves between networks and receivers. The differences are
then computed as lines of position. The receivers can be used up to about
2,000 km from the networks with reasonable accuracy. The absolute accuracy
of Loran-C varies from 180 to 450 m, while the repeatable accuracy varies
from 15 to 90 m.
GPS is a Satellite navigation system developed by the U.S. Department of
Defense. An array of satellites collectively provides precise, continuous,
worldwide, all-weather, three-dimensional navigation and position for land,
sea, and air applications. Use of GPS for hydrographic surveying is
expanding, and procedures and equipment are improving rapidly.
Navigation (positioning) error standards have been established for USACE
hydrographic surveys. Three general classes of surveys have been defined
(HQUSACE 1991):
@ Class 1 - Contract payment surveys
@ Class 2 - Project condition surveys
®@ Class 3 - Reconnaissance surveys
Although the requirements of geologic site surveys may not be the same as
those of USACE hydrographic surveys, the accuracy standards are useful
criteria when specifying quality control requirements in contractual
55
Chapter 3 Field Data Collection and Observation
56
documents. The frequency of calibration is the major distinguishing factor
between the classes of survey, and directly affects the accuracy and adequacy
of the final results. With the increasing use of GIS for analysis and manipu-
lation of data, high standards of accuracy are imperative. Calibrations are
time-consuming and reduce actual data collection time. Nevertheless, this
must be countered with the economic impact that low quality data may be
useless or may even lead to erroneous conclusions (leading, in turn, to incor-
rectly designed projects and possible litigation).
The maximum allowable tolerances for each class of survey are shown in
Table 6.
able 6
Maximum Allowable Errors for Hydrographic Surveys
Survey Classification
1 2 3
ype of Error Contract Payment | Project Condition |Reconnaissance
Resultant Two-Dimensional One-
Sigma RMS Positional Error Not to
Exceed
Resultant Vertical Depth
Measurement One-Sigma Standard (+ 0.5 ft)
Error Not to Exceed
(From HQUSACE (1991))
Table 7 depicts positioning systems that are considered suitable for each
class of survey. The table presumes that the typical project is located within
40 km (25 miles) of a coastline or shoreline reference point. Surveys further
offshore should conform to the standards in the NOAA Hydrographic Manual
(National Oceanic and Atmospheric Administration 1976). Planning and suc-
cessful implementation of offshore surveys are sophisticated activities and
should be carried out by personnel or contractors with considerable experience
and a successful record in achieving the accuracies specified for the particular
surveys.
Geophysical Techniques
Geophysical survey techniques, involving the use of sound waves and high
quality positioning systems on ocean vessels, are widely used for gathering
subsurface geological and geotechnical data in terrestrial and subaqueous
coastal environments. Geophysical procedures provide indirect subsurface
data as opposed to the direct methods such as coring and trenching. The use
of geophysical methods can assist in locating and correlating geologic materi-
als and features by determining acoustic transparency, diffraction patterns,
configuration and continuity of reflectors, and apparent bedding patterns.
Chapter 3 Field Data Collection and Observation
able 7
Allowable Horizontal Positioning System Criteria
Estimated Allowable for
Positional Survey Class
Accuracy
ag Line (Static Measurements
rom Bank)
< 457 m (1500 ft) from baseline
> 457 m (1500 ft) but < 914 m (3000 ft)
> 914 m (3000 ft) from baseline
22
oe)
ag Line (Dynamic)
< 305 m (1000 ft) from baseline
> 305 m (1000 ft) but < 610 m (2000 ft) 3 to 6
> 610 m (2000 ft) from baseline 6 to 50+
<
t)
o
pete Geol
(Microwave or UHF) 1to 4
Low-Frequency EPS (Loran)
Satellite Positioning:
Doppler 100 to 300
STARFIX 5
NAVSTAR GPS:**
Absolute Point
Positioning (No SA) 15
Absolute Point
Positioning (w/SA) 50 to 100
Differential
Pseudo Ranging 2to5
Differential
Kinematic (future) 0.1 to 1.0
* Electronic Positioning System
** Global Positioning System
(From HQUSACE (1991))
Chapter 3 Field Data Collection and Observation
57
58
Inferences can often be made using these measures of stratigraphic and litho-
logic characteristics and important discontinuities.
Fathometers or depth sounders, side-scan sonar, and subbottom profilers
are three major types of equipment used to collect geophysical data in marine
exploration programs. All three systems use electrically powered acoustic
devices that function by propagating acoustic pulses in the water and measur-
ing the lapsed time between pulse initiation and the arrival of return signals
reflected from various features on or beneath the bottom. These systems are
used to obtain information on seafloor geomorphology, bottom features such
as ripple marks and rock outcrops, and the underlying rock and sediment
units. Acoustic depth sounders are used for conducting bathymetric surveys.
Side-scan sonar provides an image of the aerial distribution of sediment and
surface bed forms and larger features such as shoals and channels. It can thus
be helpful in mapping directions of sediment motion. Subbottom profilers are
used to examine the near-surface stratigraphy of features below the seafloor.
A single geophysical method rarely provides enough information about
subsurface conditions to be used without actual sediment samples or additional
data from other geophysical methods. Each geophysical technique typically
responds to several different physical characteristics of earth materials, and
correlation of data from several methods has been found to provide the most
meaningful results. All geophysical methods rely heavily on experienced
operators and analysts.
Bathymetric surveys are required for many studies of geology and geo-
morphology in coastal waters. Echo sounders are most often used to measure
water depths offshore. Errors in acoustic depth determination are caused by
several factors:
®@ Velocity of sound in water. The velocity in near-surface water is about
1500 m/sec but varies with water density, which is a function of
temperature, depth, and salinity. For high-precision surveys, the
acoustic velocity should be measured onsite.
@ Boat-specific corrections. As the survey progresses, the vessel’s draft
changes as fuel and water are used. Depth checks should be performed
several times per day to calibrate the echo sounders.
@ Survey vessel location with respect to known datums. An echo sounder
on a boat simply measures the depth of the water as the boat moves
over the seafloor. However, the boat is a platform that moves
vertically, depending on oceanographic conditions such as tides and
surges. To obtain water depths that are referenced to a known datum,
echo sounder data must be adjusted in one of two ways. First, tides can
be measured at a nearby station and the echo sounder data adjusted
accordingly. Second, the vertical position of the boat can be constantly
surveyed with respect to a known land datum and these results added to
Chapter 3 Field Data Collection and Observation
the water depths. For a class | survey, either method of data correction
requires meticulous attention to quality control.
@ Waves. As the survey boat pitches up and down, the seafloor is
recorded as a wave surface. To obtain the true seafloor for the highest
quality surveys, transducers and receivers are now installed on heave-
compensating mounts. These allow the boat to move vertically while
the instruments remain fixed. The most common means of removing
the wave signal is by processing the data after the survey. Both
methods are effective, although some contractors claim one method is
superior to the other.
Even with the best efforts at equipment calibration and data processing, the
maximum practicable achievable accuracy for nearshore depth surveys is about
+ 0.15 m (HQUSACE 1991). The evaluation of these errors in volumetric
calculations is discussed in Chapter 5. Survey lines are typically run parallel
to one another, with spacing depending on the survey’s purpose and the scale
of the features to be examined.
In geophysical surveys, the distance between the sound source and reflector
is computed as velocity of sound in that medium (rock, sediment, or water)
divided by one half of the two-way travel time. This measurement is con-
verted to an equivalent depth and recorded digitally or on a strip chart. A
recent development that is valuable in bottom sediment interpretation is a
signal processing unit that can be interfaced with an echo sounder and used to
indicate the seafloor sediments in terms of Wentworth or other general classi-
fication schemes. This is accomplished by measuring two independent
variables, roughness and hardness, from the acoustic signal and interpreting
these data in terms of sediment type.
The principles of subbottom seismic profiling are fundamentally the same
as those of acoustic depth sounding. Subbottom seismic devices employ a
lower frequency, higher power signal to penetrate the seafloor (Figure 25).
The transmission of the waves through earth materials depends upon the earth
material properties, such as density and composition. The signal is reflected
from interfaces between sediment layers of different acoustical impedance
(Sheriff 1980). Coarse sand and gravel, glacial till, and highly organic
sediments are often difficult to penetrate with conventional subbottom
profilers, resulting in poor records with data gaps. Digital signal processing
of multi-channel data can sometimes provide useful data despite poor signal
penetration. Spacing and grid dimensions again depend upon the nature of the
investigation and the desired resolution.
Acoustic characteristics are usually related to lithology so that seismic
reflection profiles can be considered roughly analogous to a geological cross
section of the subbottom material. However, because of subtle changes in
acoustic impedance, reflections can appear on the record where there are
minor differences in the lithology of underlying and overlying material. Also,
significant lithologic differences may go unrecorded due to similarity of
Chapter 3 Field Data Collection and Observation
59
Hydrophone
Source
Water
Surface
Bottom
Horizon
Horizon
aay
RRR ESS
SSS SS
ROR REEL SELES Horizon
Figure 25. Principles of obtaining subbottom seismic data
acoustic impedance between bounding units, minimal thickness of the units, or
masking by gas (Sheriff 1980). Because of this, seismic stratigraphy should
always be considered tentative until supported by direct lithologic evidence
from core samples.
The two most important parameters of a subbottom seismic reflection
system are its vertical resolution, or the ability to differentiate closely spaced
reflectors, and penetration. As the dominant frequency of the output signal
increases, the resolution becomes finer. Unfortunately raising the frequency
of the acoustic pulses increases attenuation of the signal and consequently
decreases the effective penetration. Thus, it is a common practice to use two
seismic reflection systems simultaneously during a survey; one having high
resolution capabilities and the other capable of greater penetration.
Side-scan sonar is used to distinguish topography of the seafloor. Acoustic
signals from a source towed below the water surface are directed at a low
angle to either or both sides of a track line, in contrast with the downward-
directed Fathometer and seismic reflection signals (Figure 26). The resulting
image of the bottom is similar to a continuous aerial photograph. Detailed
information such as spacing and orientation of bed forms and broad differ-
ences of seafloor sediments, as well as features such as rock outcrops,
boulders, bed forms, and man-made objects, can be distinguished on side-
scan. It is generally recommended that bathymetry be run in conjunction with
side-scan to aid in identifying objects with subtle vertical relief. The side-scan
60
Chapter 3 Field Data Collection and Observation
Chapter 3 Field Data Collection and Observation
\\
ae
Figure 26. Side-scan sonar in operation
system is Sensitive to vessel motion and is most suitable for use during calm
conditions.
Commonly available side-scan sonar equipment, at a frequency of
100 kHz, is capable of surveying the seafloor to over 500 m to either side of
the vessel track line; thus, a total swath of 1 km or more can be covered at
each pass. To provide higher resolution output at close range, some systems
are capable of dual operation using both 500-kHz and 100-kHz frequency
signals. The data are simultaneously recorded on separate channels of a four-
channel recorder. Digital side-scan sonar systems are available that perform
signal processing to correct for both slant range to seafloor targets and survey
vessel speed. The resulting records show true x-y location of seafloor objects,
analagous to maps or aerial photographs. The digital data can be recorded on
magnetic media, allowing additional signal processing or reproduction at a
later date.
Ground-penetrating radar (GPR) is a relatively new technique for subsur-
face exploration. In contrast to the acoustic systems described above, GPR is
used subaerially. The radio portion of the electromagnetic spectrum is emitted
from the source and reflected back to the sensors. The transparency of geo-
logic materials varies. Sands and limestones are typically reasonably
61
62
transparent. The use of GPR in marine environments is limited because salt
water is non-transparent to electromagnetic radiation in the radio frequencies.
Morphologic and Bathymetric Profiles
Periodic topographic and nearshore bathymetric surveys constitute the most
direct and accurate means of assessing geologic and geomorphic changes over
modern time scales. Time series data, such as repeated beach profiles, allow
the assessment of erosion and accretion in the littoral zone. The preferred
surveying technique involves collecting a series of shore-normal profile lines.
These must extend landward of the zone that can be inundated by storms,
usually behind the frontal dunes.
Permanent or semi-permanent benchmarks are required for reoccupying
profile sites over successive months or years. On rapidly transgressing coasts,
these benchmarks should be located at the landward end of the profile line in
order to minimize their likelihood of being damaged in storms. The locations
of survey monuments must be carefully documented and referenced to other
survey markers or control points. The ability to accurately reestablish a
survey monument is very important because it ensures that profile data col-
lected over many years will be comparable (Hemsley 1981). Locations that
might experience dune burial should be avoided, and care should also be taken
to reduce the visibility of benchmarks to minimize damage by vandals.
Both the frequency of the sampling and the overall duration of the study
must be considered when planning a beach profiling study. Morphologic
changes of beaches can occur over varying time scales, and if long-term
studies are to be conducted, the dynamic nature of the beach should be taken
into account. Often, it is financially or logistically impractical to conduct
frequent, repeated surveys for a sufficient length of time to obtain reliable and
comprehensive information on long-term processes at the study area.
Nonetheless, resurveying of profile lines over a period of more than one year
can be of substantial help in understanding the prevailing seasonal changes.
Resurveying of control profile lines at selected time intervals can reveal sea-
sonal patterns. In addition, special surveys can be made after significant
storms and events to determine their effects and measure the rate of recovery
of the local beach system. At a minimum, summer and winter profiles are
recommended. Unfortunately, there are no definitive guidelines for the timing
and spacing of profile lines. Table 8 outlines a suggested survey schedule for
monitoring beach fill projects. In summary, observation over a period of time
is recommended in order to document the range of variability of morphology
and bathymetry.
Some issues concerning the spatial aspects of study include the spacing of
profiles, longshore dimensions, and cross-shore dimensions. Profile lines
should be spaced at close enough intervals to show any significant changes in
Chapter 3 Field Data Collection and Observation
Collect within fill area and at control locations in
ummer and winter months to characterize seasonal
profile envelope (beach & offshore).
Collect all profiles immediately after fill placement at
leach site (beach & offshore) to document fill volume.
Collect control profiles immediately after project is
icompleted.
Four quarterly survey trips collecting all beach and
offshore profiles out to depth of closure. Begin series
during the quarter following the post-fill survey.
Continue year 1 schedule to time of renourishment (usually 4-6 years). If project is a single
nourishment, taper surveys in subsequent years:
6- and 12-month survey of all beach and offshore
profiles
6- and 12-month survey of all beach and offshore
profiles.
12-month survey of beach and offshore profiles.
If project is renourished, repeat survey schedule from post-fill immediately after each
renourishment to document new fill quantity and behavior.
Project-specific morphology and process requirements may modify this scheme.
Monitoring fill after major storms is highly desirable to assess fill behavior and storm
protection ability. Include both profile and sediment sampling. Conduct less than one
week after storm conditions abate to document the beach and offshore response.
(From CERC (1991))
lateral continuity. In a cross-shore direction, the uppermost and lowermost
limits of the profiles should be located where change is unlikely to occur, and
should adequately cover the most active zones such as the shore and upper
shoreface. The preferred closure depth is at the toe of the shoreface, although
a selected depth contour where variability becomes minimal is acceptable.
Historical shorelines are an important component of where these uppermost
and lowermost limits are located, particularly along rapidly changing
coastlines. For example, shore and dune deposits formed during earlier stages
of development that are now distant from the modern shoreline are likely to
be affected by marine or lacustrine processes only during large storms.
Large-scale aerial photographs or maps of these interior areas are usually ade-
quate for examining these more stable features. Appropriate longshore dimen-
sions of the survey grid depend upon the nature of the problem. Profile lines
should be connected with a shore-parallel survey to determine positions and
elevations of each profile relative to one another.
63
Chapter 3 Field Data Collection and Observation
64
Onshore portions of profiles are surveyed using standard land survey tech-
niques and equipment. Equipment commonly used in surveys includes
transits, levels, or theodolites, which are used for siting survey rods. Detailed
information concerning the techniques and equipment available for surveying
can be found in several surveying textbooks (i.e. Brinker and Wolf 1984).
Surveys are preferably conducted during low tide, when the profile line can
be extended as far seaward as possible. Extending profile lines offshore
beyond wading depths requires boats or amphibious vehicles. Amphibious
vehicles are better suited to this task because they can traverse the sea-land
boundary and maintain the continuity of profile lines. Although acoustic echo
sounders can be used for continuous profiling seaward of the breaker zone,
the signals are usually disrupted by breaking waves, and boats suitable for
offshore use cannot approach the shore close enough to connect directly with a
land profile. High-precision electronic navigation is recommended if the sur-
veys extend offshore more than a few hundred meters.
During calm weather conditions, sea sleds have been successfully used to
obtain shoreface profiles close to shore. A sea sled consists of a long, upright
stadia rod mounted vertically on a base frame with sled-like runners
(Clausner, Birkemeier, and Clark 1986) or a sled-mounted mast with a prism
for use by a total station survey system (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
the sea sled does not float, elevations are not subject to wave or tide
variations, thus providing a more accurate comparison between repeated
surveys. At present, it is not possible to obtain bottom samples with a sea
sled; these must be obtained from a boat or amphibious vehicle working in
conjunction with the sled. Sleds are currently limited to use within 4 km of
the coast and water depths of 12 m, less than the height of the sled masts.
A helicopter bathymetric surveying system has been in use at the USAE
District, Portland, since the 1960’s. The big advantage of this procedure is
that land-accuracy surveys can be conducted offshore in high waves and near-
structure conditions under which a boat could not perform. A helicopter is
fitted with a weighted, calibrated cable and prisms. A total-station survey
system is set up onshore to measure the location of the cable. Soundings are
commonly taken at 8-m intervals along profile lines up to 2,500 m offshore.
Operations are limited by poor visibility or winds over 15-20 m/sec
(30-40 knots).
The Coastal Research Amphibious Buggy (CRAB), a unique self-propelled
vehicle, was developed by the U.S. Army Corps of Engineers for making
continuous onshore-offshore profiles and obtaining concurrent bottom samples.
The CRAB consists of a structural tower mounted on wheels and is self-
propelled by hydraulic motors. It can traverse under its own power across
both the beach and shoreface to a depth of about 9 m. It has been widely
used at the CERC Field Research Facility at Duck, NC. Both the CRAB and
Chapter 3 Field Data Collection and Observation
sea sled are important tools for characterizing submarine bars and the overall
morphology of offshore profiles.
Prototype Monitoring
Prototype testing and monitoring bring together multiple means of
investigating and measuring the processes and responses of a coastal site.
Prototype studies often involve physical experiments, conducted under ideal or
well-monitored conditions in the field. The purpose of many prototype studies
is to test and evaluate theoretical formulae or conceptual asssumptions. Proto-
type studies, in other instances, are conducted to assess the status and varia-
tions of environmental conditions at a site and to develop information for
guidance in the construction of structures.
Chapter 3 Field Data Collection and Observation
65
66
4 Laboratory Techniques and
Approaches
Laboratory Observation and Experiment
The characteristics of samples obtained in the field can be further analyzed
in the laboratory. Some properties that are commonly examined include:
(a) sediment properties, such as grain size, shape, and density, mineralogy,
and heavy mineral type and content; (b) stratigraphic properties, which can be
characterized using core description, preservation, and analysis techniques;
and (c) geochronological history, obtained from radiometric dating and a
variety of relative dating approaches. In order to achieve maximum benefits
from laboratory analyses, the coastal scientist should be cognizant of the
limitations and variance of the precision and accuracy of each test and
procedure.
Laboratory Analysis of Sediment
Sediments are solid fragmental materials that originate from the weathering
of rocks and are transported and deposited by water, air, or ice. Coasts that
are comprised of sediment, in contrast to rock, are highly dynamic and are
likely to have a complex geologic history. Analyses of the sediment
characteristics, such as particle size, mineralogy, and heavy mineral content
can reveal information about sources of materials, depositional environment,
littoral processes, and the nature of coastal landforms. This knowledge of
sediment characteristics, in turn, may be useful for predicting sediment
movement during storms, the nature of seafloor features, and the geologic
history of the area of investigation.
Sediments can be classified into size range classes. Ranked from largest to
smallest, these include boulders, cobbles, gravel, sand, silt, and clay
(Table 9). The particle size is often expressed as D, or the diameter in
millimeters, and sometimes includes a subscript, such as Dg,, to indicate the
diameter corresponding to the listed percentile. As an alternative, grain size
is often expressed in phi (¢) units, where ¢ = -log, D (Hobson 1979). This
Chapter 4 Laboratory Techniques and Approaches
4096.00
1024.00 Boulder
256.00
128.00
107.64
90.51
76.00
64.00
58.82
45.26
Coarse Gravel 38.00
32.00
26.91
22.63
19.00
16.00
13.45
11.31
Fine Gravel SES
8.00
6.73
5.66
4.76
4.00
3.36
Coarse Sand 2.85 d Granule
2.35
2.00
1.68
1.41 A Very Coarse
1.19
Medium Sand 1.00
0.84
0.71
0.59
0.50
0.42
0.35
0.30
0.25
0.210
Fine Sand 0.177
0.149
0.125
0.105
0.088 Very Fine
0.074
0.0625
0.053
0.044
0.037
0.031
0.0156
0.0078
0.0039
0.0020
0.00098
0.00049
0.00024
0.00012
0.00006
67
Chapter 4 Laboratory Techniques and Approaches
68
procedure assists in normalizing the grain size distribution and allows compu-
tation of other size statistics based on the normal distribution.
Grain-size analysis involves a series of procedures to determine what
proportion of material in a given sample is in each grain size class. An
important aspect of the laboratory analysis program, which must be designed
into the field sampling scheme, is to obtain sufficient sediment to adequately
determine the sediment population characteristics (Table 10). The requirement
for obtaining adequate amounts of each sample underscores the importance of
some prior knowledge of the field conditions or of conducting a preliminary
field reconnaissance before undertaking a rigorous field sampling program.
Large samples should be divided using a sample splitter to prevent clogging of
sieves. Particle aggregates, especially those in the silt-clay range which show
cohesive properties, should be separated and dispersed by gentle grinding and
use of a chemical dispersant (sodium hexametaphospate) before analysis.
Table 10
Minimum Weight of Sample Required Given Maximum Particle Size
in Population
Maximum Particle Size Minimum Weight of Sample, g
8,000
2,400
nt Cecilia ido pee inlbe oyesa a |
eee ee a ie
iy ee a a co |
Se os ee
Laboratory techniques used to estimate sediment diameter depend in part
on the grain size. Pebbles and coarser sediments can be directly measured
with calipers or by coarse sieves. The grain-size distribution of sand is deter-
mined directly by sieve analysis, sedimentation tubes, or Coulter counter. For
silt and clay-sized material, grain-size distribution is determined indirectly by
hydrometer or pipette analysis, or the use of a Coulter counter. The size
distribution of mixed sediments is determined by using a combination of sieve
and hydrometer or pipette analyses. Practical procedures for conducting
laboratory tests on sediment samples are covered by Folk (1980) and Lewis
(1984). Laboratory manuals more oriented towards engineering applications
include American Society for Testing and Materials (1964), Bowles (1986),
and HQUSACE (1970). Although they describe some tests specific to
geotechnical engineering practice, many procedures, such as grain size
analyses, are universal.
Coastal sediments reflect the relative importance of various source areas,
and thus differences in the relative importance of the process mechanisms in
Chapter 4 Laboratory Techniques and Approaches
sediment supply. Some sources of coastal sediments include river basins that
empty into the coastal zone, nearshore cliffs and uplands that are denuded by
waves, wind, transported material mass wasting, and slope wash, and sedi-
ments transported by longshore currents.
Because gravel and larger particles require more energy to be transported,
they are typically found close to their source. In contrast, silt and clay, once
entrained, may be transported long distances. The size fraction distribution is
determined by the composition of the source rocks and weathering conditions.
The mineralogy of sediments, especially clays, shows varying mineralogy
controlled by source rocks and weathering conditions. Resistant minerals,
such as quartz and feldspars, comprise most coastal deposits. However, as
tracers, the least common minerals are generally the best indicators of source.
Heavy minerals can provide information regarding source and process and
other aspects of geomorphic variability in the coastal zone (Brenninkmeyer
1978; Judge 1970; McMaster 1960; Neiheisel 1962). Pronounced seasonal
variations in heavy minerals may 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 trans-
ported from the beach foreshore to deeper water during the winter and back
again during the summer (Inman 1953; Nordstrom and Inman 1975).
Analysis of size and texture can also be used to distinguish among sedi-
ments that may have come from the same original source area. As an
example, Mason and Folk (1958) used size analysis to differentiate dune,
beach, and eolian sediments on Mustang Island, Texas.
A variety of techniques are used to identify the mineralogy of coastal
sediments. Mineralogy of coarse sediments and rocks is typically assessed
using laboratory microscopes. Clay mineralogy is usually assessed with X-ray
diffraction methods or electron microscopy. Heavy minerals are separated
from light minerals using bromoform (specific gravity of 2.87) after crushing,
washing, and sieving. In unconsolidated sediments, heavy mineral samples
are examined under a microscope to determine approximations or percentages
of mineral types.
Core Description and Analysis
Core description is widely used to characterize the features and deposi-
tional environments of sediments. After being collected in the field, core
barrels are sealed to retain moisture. In the laboratory, they are cut in half
lengthwise. One side of the core is used for description and the other for
radiography, peels, and subsampling for grain size analysis, palynology, and
organic materials. Cores may also be cut into smaller working sections
depending upon the length of the working surface, such as a table, where the
examination or tests will be conducted. They may also be cut further into
Chapter 4 Laboratory Techniques and Approaches
69
70
lengths of about | or 2 m so that a long core can be laid into a rack that will
allow photography of the entire sequence.
A sample core description sheet is shown in Figure 27. Important char-
acteristics of the sedimentary sequence that need to be described include grain
size variations, sedimentary structures and directions, and occurrences of
cyclic bedding such as varves. Evidence of plant roots and features such as
color changes, mottling, discontinuities, and other variations in physical char-
acteristics may be indicators of key changes. Roots and rooting, for example,
often correspond to marshes in coastal sequences. Fossils and pollen in strati-
graphic sequences are indicative of paleoenvironmental characteristics and
changes. Techniques for analysis and interpretation of such evidence can be
found in Faegri and Iverson (1975), and Kapp (1969).
Variations in grain size in cores can yield much information about the sedi-
mentary environments and thus the geologic history of the region. Coarser
fractions settle first, followed by silts and clays. This separation is a function
of particle settling velocities, which vary depending upon particle size,
density, shape, and the nature of the transport media. Changes in the environ-
ment of deposition can result in the clay fraction being separated from granu-
lar material both spatially and temporally. For example, clay deposits are
usually deposited further from shore than granular material and usually appear
on top of granular material.
X-ray radiography is an imaging method that amplifies contrasts in grain
size, mineralogical composition, packing density, water content, diagenetic
products, sedimentary structures, and geochemical inclusions in cores that
otherwise appear homogeneous (Roberts 1981). Being able to distinguish
these features may assist in understanding the sequence of geomorphic changes
that occurred at that site. For example, the scale and direction of bed forms
can be used to estimate paleocurrents. Marker horizons are related to a date
or a significant event. Peat indicates stability and growth at or near sea level.
Radiography is based on the differential transmission of X-ray radiation
through a sample onto sensitized X-ray photographic film. Variations in tex-
ture as well as chemical composition throughout the sediment result in differ-
ential attenuation of the incident X-ray radiation before it reaches the
underlying film. Samples of uniform thickness of about 1 cm that are cut
longitudinally with a wire knife provide the best results in radiography
(Roberts 1981).
The occurrence of paleosols in cores may also provide important informa-
tion toward assessing the geologic history of coasts. In terrestrial coastal
environments, there may be prolonged periods of minimal sedimentation dur-
ing which soil development may occur, followed by periods of relatively rapid
sedimentation without soil development!. This scenario is characteristic of
1 The term "soil" in this context refers to unconsolidated surficial sediment which supports
plant life. This is a more restrictive definition than the one typically used in engineering texts,
which refer to soil as any unconsolidated material, even if barren of plant life.
Chapter 4 Laboratory Techniques and Approaches
LITHOLOGIC LOG
Vibracore 44
J
a
g 3 =
a a g a
3 F Z g
3 3 Sule a
Figure 27. Sample form for core description of sedimentary environments (courtesy of Dr.
Harry Roberts, Louisiana State University). Description of sediment size,
sedimentary structures, and other geologic characteristics of the cores, as well
as laboratory tests, assist in interpreting the depositional environment
va
Chapter 4 Laboratory Techniques and Approaches
72
recent sea level changes during the Quaternary. As alternative scenarios, such
cycles could occur in a semi-protected salt marsh subject to sedimentation dur-
ing a severe storm or in a soil that subsided as a result of rapid burial by
other sediments. As with modern soils, horizon color and horizon
assemblages based on color permit an initial identification. Important
paleosols, which may reflect only limited pedogenesis, are represented only by
thin, dark, organic horizons. Less apparent chemical and physical changes in
sediments that were exposed to atmospheric and meteorological processes may
also occur. Soils that are uniform over a wide area can sometimes be used as
approximate marker horizons and thus are valuable for relative dating
purposes. In some circumstances, soils may also contain enough organic
material to be suitable for radiocarbon dating.
Differing degrees of soil development and weathering characteristics may
also be helpful in correlating and determining relative ages of a series of
marine terraces. Characteristics such as soil color, the thickness and color of
clay skins, iron content, and the content of other basic elements and residual
chemical elements in soils are some potential indicators of relative age. A
variety of chemical analyses can be performed on field samples in the labora-
tory to determine soil chemistry, and the micromorphological characteristics
of the soils can be assessed to determine soil development.
Geochronology
Geochronology is the study of time in relationship to the history of the
earth. Geochronology encompasses a variety of radiometric and non-
radiometric techniques, which collectively can date materials whose ages
extend from near-present through the Pleistocene and earlier. Radiometric
techniques vary in precision, in time range, in the types of materials that can
be analyzed, and the type of information that results are capable of providing.
Non-radiometric techniques that may be useful in coastal areas include
archives, archeology, dendrochronology, thermoluminescence dating, mag-
netostratigraphy or paleomagnetic dating, paleoecology, the use of weathering
and coating indices for relative age dating, and varve chronology. A detailed
geochronology can provide information on the sequence of events and age of
surfaces, and can assist in estimating missing (erosion or non-deposition)
events. To be useful, it is important that the sample have a direct bearing
upon a geomorphological problem and that the stratigraphic relationship of the
sample to the site is well established. Use of multiple techniques typically
provides the best results for assessing the geologic history of coasts.
Radiometric Dating and Isotopes
Radiometric dating techniques have been applied mostly since 1950. Many
natural elements are a mixture of several isotopes, which have the same
chemical properties and atomic numbers, but different numbers of neutrons
and, hence, different atomic masses. Radiometric methods of dating are based
Chapter 4 Laboratory Techniques and Approaches
on radioactive decay of unstable isotopes. The duration of time leading to the
state where half the original concentration remains is known as the half-life.
In general, the useful dating range of individual isotopic methods is about
10 times their half-life. The radiometric isotopes Carbon-14, Potassium-
Argon-40, Caesium-137, Lead-210, and Thorium-230 are the most commonly
used in standard geologic investigations (Faure 1977; Friedlander, Kennedy,
and Miller 1955).
Radiocarbon (Carbon-14 or !4C) dating is perhaps the most widely used
technique for assessing the age of Holocene and late Pleistocene organic
materials. Once an organism or plant dies, its radiocarbon ('4C) content is no
longer replenished and begins to decrease exponentially, achieving a half-life
after some 5,730 years. Substances that are often examined with 14C dating
include wood, charcoal, peat, shells, bones, aqueous carbonates, rope, and
soil organics. Recent developments using mass spectrometers allow detection
of absolute amounts of '4C content in samples as small as 5 mg. To be
comparable, radiocarbon dates are adjusted to a zero age at AD 1950.
Analytical error factors are given as one or two standard deviations about the
mean. Other errors, associated with sample contamination, changes in atmo-
spheric or oceanic 14C content, and fractionation, are more difficult to
estimate. Absolute dates of samples less than 150 years old or greater than
50,000 years old are currently considered to be ambiguous.
Potassium-argon dating (Potassium-Argon-40 or K:Ar) can be applied to a
wide range of intrusive and extrusive igneous rocks that contain suitable
minerals. In addition to constraints on rock type, it is necessary for the
sample to be unaltered by weathering or other geological processes that may
allow diffusion of radiogenic argon from the sample. The occurrence of such
rocks along coasts is generally restricted to regions adjacent to plate bound-
aries and regions of active tectonics. Potassium-argon dating of Holocene
deposits is generally imprecise, with errors of + 15 to 30 percent. Only
certain minerals, particularly those with a high K and low atmospheric Ar
content, are suitable for extending the K:Ar dates into the late Pleistocene.
For these reasons, potassium-argon dating has limited applications in studies
of the geologic history of coasts.
Fission-track dating was developed as a complementary technique to
potassium-argon (K:Ar) dating. Most applications to Quaternary deposits
have involved dating airfall volcanic ash or glass deposits, a field known as
tephrochronology. This material usually has wide distribution and geologi-
cally speaking has infinitely narrow depositional time duration. However, it is
often absent or quickly removed in many coastal settings. If present, the
rapid deposition and large aerial extent of ash makes it an excellent tool for
correlation of rock strata and can provide radiometric age dates. A listing of
some of the important volcanic ash layers in North America, which include
very recent to Pleistocene dates, can be found in Sarna-Wojcicki, Champion,
and Davis (1983).
73
Chapter 4 Laboratory Techniques and Approaches
74
Cesium-137 (!37Cs) is an artificial isotope, primarily produced during the
atmospheric testing of nuclear weapons. These tests began in the 1940’s,
peaked in the early 1960s, and have declined since the advent of nuclear test
ban treaties (Wise 1980). !37Cs is strongly absorbed onto sediment or soil
and has been used in studies of soil erosion and sediment accumulation in
wetlands, lakes, and floodplains. The timing of very recent events (post-
1954) and human impacts on coastal ecosystems can be improved using such
techniques.
Lead-210 (7!°Pb) is an unstable, naturally occurring isotope with a half-life
of just over 22 years and a dating range of 100 to 200 years (Oldfield and
Appleby 1984; Wise 1980). It forms as part of a decay chain from
Radium-226 which escapes into the atmosphere as the inert gas Radon-222.
The excess or unsupported 2710p returns to the earth as rainfall or dry fallout,
and can be separated from that produced by in situ decay. Applications in
coastal environments are limited but show good potential. This technique
would be of greatest value in low-energy environments and would allow
documentation of the timing of recent events and human impacts on coastal
ecosystems.
Thorium-230/Uranium-234 @?°Th/?*4U), a useful dating technique which
complements other methods, is applicable for dating coral sediments. The
technique involves comparing the relative amounts of the radioactive isotope
of thorium, 72°Th, with that of uranium, 724U. Thorium-230 increases in
coral carbonate from zero at the death of the organism to an equilibrium with
Uranium-234 at 0.5 million years, allowing samples as old as middle
Pleistocene to be dated.
Non-Radiometric Methods of Dating and Relative Dating
Archival and archeological documentation can assist in understanding the
geologic history of coasts. Historical and social documents may contain
detailed descriptions of timing of major storms, of ice movements, of shore-
line changes, and of other catastrophic events. Historical records are most
useful if they correspond to a particular date or specified range of time, as do
newspaper reports. Archeological evidence can provide important clues for
assessing Holocene environmental changes. Pottery, stone tools, coins, and
other artifacts can be assigned ages and thus may be of assistance in dating
surface and subsurface deposits. If discovered in a stratigraphic sequence,
cultural artifacts provide a minimum age for deposits beneath and maximum
age for deposits above. Archeological evidence, such as buried middens,
inland ports, or submerged buildings, may also indicate shoreline changes and
sometimes can be used to estimate rates of deposition in coastal areas. For
example, the Holocene Mississippi River deltaic chronology was revised using
artifacts as indicators of the age of the deltaic surfaces (McIntire 1958).
Thermoluminescence (TL), a technique that is commonly practiced in
archeology for dating pottery, has been extended for use in geological studies.
Chapter 4 Laboratory Techniques and Approaches
It has been used for dating a variety of Pleistocene sediments, including loess.
For geological purposes, TL needs further refinement because most results to
date are considered in error, generally being too young. It does, however,
generally provide a good estimate of stratigraphic order. Thermoluminescence
dating has the best potential where clay-fired artifacts are present and has
promise for dating a variety of deposits of Quaternary age.
Magnetostratigraphy or paleomagnetic dating is a geochronologic technique
that is used in conjunction with correlations of regional radiometric dates and
paleomagnetic characteristics. Because the earth’s magnetic field changes
constantly, the magnetic characteristics of rock and sediments can be used to
determine an age for materials. The most dramatic changes are reversals, in
which the earth’s polarity switches from the north to the south pole. The
reversals are relatively infrequent occurrences, with the last one being
700,000 years ago. Less dramatic secular variations of the geomagnetic field,
however, can also be important in helping to provide a time scale useful for
dating over hundreds or thousands of years by linking magnetic properties
with time scales established by radiometric techniques. The combination of
declination (the angle between true and magnetic north), inclination (the dip of
the earth’s magnetic field), and the magnetic intensity produce a characteristic
paleomagnetic signature for a particular location and time. The magnetic
alignments can be incorporated and preserved in baked materials, in sediment
particles that settle out in standing water, and in cooled magma. The tech-
nique is most suited to lake sediments containing homogeneous particle sizes
and organics. This technique can be used in places where the magneto-
stratigraphy has been linked with radiometric dates and can be extended to
over 200 million years before present.
Dendrochronology or tree ring dating can provide precise data regarding
minimum age of a geomorphic surface. It can also provide proxy data con-
cerning environmental stresses, including climatic conditions such as cold
temperatures and droughts. In some parts of the world, overlapping sets of
rings on trees have been used to construct a comprehensive environmental
history of the region.
Lichenometry is the study of the establishment and development of lichen
to determine a relative chronology (Worsley 1981). Although used most
extensively for studies of glacier fluctuations, this technique also has applica-
tion in shoreline dating. The method involves the measurement of thallus
size, with increasing diameter representing increasing age. It is valid from
about 10 years to a few centuries before present. This measurement is often
conducted in the field with a ruler or with calipers. Field techniques differ,
although normally the largest diameters are measured. Although there has
been a lack of critical assessment of the technique, the majority of research
shows that the technique gives reasonable dates when applied to a variety of
environments.
Paleoecology is the study of fossil organisms in order to reconstruct past
environments. Pollen analysis, or palynology, is the single most important
75
Chapter 4 Laboratory Techniques and Approaches
76
branch of paleoecology for the late Pleistocene and Holocene. Uses of
paleoecological tools include: (a) the establishment of relative chronologies
and indirect dating by means of correlation with other dated sequences;
(b) characterization of depositional environments at or near the sampling site
since certain species and combinations of species are adapted to certain
conditions; (c) reconstruction of the paleoenvironmental and paleoclimatic
conditions; (d) establishment of human-induced transformations of the vegeta-
tion and land use regime (Oldfield 1981).
The use of weathering and coating indices for relative age dating in
geomorphology is rapidly increasing. Using laboratory microscopes, samples
are calibrated with those of known age and similar chemistry for each geo-
graphic area. One such method, obsidian hydration dating, is based on the
reaction of the surface of obsidian with water from the air or soil, which
produces a rind whose thickness increases with time (Pierce, Obradovich, and
Friedman 1976). Rock varnish-cation ratio dating is used primarily in deserts,
where rocks develop a coating (Dorn 1983). One study used dated graffiti to
determine the rates of erosion and weathering in sandstone cliffs (Emery
1941).
Varve chronology may be useful in quiescent or low energy basins where
thin laminae of clay and silt are deposited. In glaciated coastal areas, the thin
layers or varves are usually annual deposits. The sequences of successive
graded layers can be discerned visually. Color variations occur because
usually the winter season deposits have a higher organic material content.
The result is alternating light-colored, gray-brown sediment layers and dark-
colored organic layers.! Varve chronology rarely extends beyond about
7,000 years.
A major limitation of varve chronology is the fact that in the marine
environment, annual varves are usually only preserved in anoxic basins, where
a lack of oxygen causes a dearth of bottom-dwelling animals. Otherwise,
mollusks, worms, fish, and crustaceans thoroughly rework the seafloor. This
reworking, known as bioturbation, thoroughly destroys near-surface
microstructure in most of the shallow-water portions of the world’s oceans.
Examples of anoxic basins include portions of the Black Sea and Saanich inlet
in British Columbia. The latter receives an annual input of clays from the
Fraser River. Yearly variations in the discharge of the Fraser River’s spring
freshet cause changes in the varve thicknesses.
Physical Models
The use of physical models can be invaluable in understanding how
geomorphic variability occurs in coastal areas. Physical modelling provides
! In freshwater lakes, varves are caused by clay-silt deposition cycles. The silt settles out in
spring and summer, and the clay in fall and winter.
Chapter 4 Laboratory Techniques and Approaches
an opportunity for reducing the complexity of natural systems, for scaling
down dimensions, and for accelerating change over time so that detailed
interactions can be identified. Physical models can be applied in studies of
hydrodynamics, sediments, and structures. In studies of coastal processes and
responses, the wave tank is both the simplest and the most utilized physical
model.
Physical models are typically either two- or three-dimensional. A wave
tank is considered to be a two-dimensional model because changes over length
and over depth can be examined. Where variations over width are also
investigated, the model is considered to be three-dimensional. A three-
dimensional model or basin may have a variety of types of bottoms, including
beds that are fixed, fixed with tracers, or moveable. Physical models require
precise scaling and calibration, and much design and construction expertise
must be devoted to their initial construction. Once set up, however, they
allow for direct measurement of process elements, repeated experiments over
a variety of conditions, and the study and isolation of variables that are
difficult to assess in the field.
Some examples of physical model experiments (conducted principally in
wave tanks) that helped elucidate geomorphologic variability of coasts include
studies of littoral drift blockage by jetties (Seabergh and McCoy 1982),
breaker type classification (Galvin 1968), experiments 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).
Large-scale physical models of harbors, rivers, and estuaries have been
built and tested at WES in order to examine the effects of jetties, weirs, chan-
nel relocations, and harbor construction on hydrodynamics and shoreline
changes in these complex systems. Measurements made by gages at prototype
(i.e. field) sites have sometimes been used to help calibrate the physical
models. In turn, the results of tests run in the physical models have identified
locations where gages needed to be placed in the field to measure unusual
conditions. An example is provided by the Los Angeles/Long Beach Harbor
model (Figure 28). In operation since the early 1970’s, it has been used to
predict the effects of harbor construction on hydrodynamics and water quality.
As part of this project, wave gages were deployed in the two harbors at
selected sites. Figure 29 is an example of wave data from Long Beach
Harbor. Although the two gage stations were only a few hundred meters
apart, the instrument at sta 2 occasionally measured unusually high energy
compared to sta 1. The cause of these energy events is unknown but is
hypothesized to be related to long-period harbor oscillations.
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Chapter 4 Laboratory Techniques and Approaches
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78
Chapter 4 Laboratory Techniques and Approaches
LONG BEACH STATION 1
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Figure 29. Comparison of wave gage pressure measurements recorded at Long Beach sta 1
and 2. Although the two stations were only a few hundred meters apart,
unusual energy events were recorded at sta 2 which did not appear at sta 1.
The abrupt shifts in the curve at each 2-hr interval represent changes in tide
height. Each 2,048-point record is 34.13 min long and each new wave burst is
recorded at a 2-hr interval
79
Chapter 4 Laboratory Techniques and Approaches
80
5 Analysis and Interpretation of
Coastal Data
All geologic and engineering project data, whether obtained from
secondary sources, field prototype collection, laboratory analyses, or physical
models, must be analyzed and interpreted to ultimately be useful in studies of
the geologic and geomorphic history of coasts. The analysis procedures
depend upon the type of data collected. Some analyses require subjectivity or
interpolation, such as constructing geologic cross sections or making seismic
interpretations. Others are highly objective involving computer probabilistic
models. A coastal scientist or engineer should be aware of the assumptions
and errors involved, and should attempt to provide sufficient information so
that his analyses can be replicated and the interpretation supported.
Computers play an important role in analysis and interpretation of data
from various sources. Statistical techniques are applied to a variety of data,
including: (a) spectral analysis of wave characteristics; (b) wave refraction
analysis; (c) time series analysis of water level data; (d) Fourier analysis of
current data; (e) moment measures of grain size; (f) eigenvectors of shoreline
change; and (g) the use of fractals in shoreline geometry. Computers are also
used for numerous types of calculations, such as volumetric changes in beach
profiles, as well as two-and three-dimensional plotting of these changes. If
numerous types of spatial data exist for a location, they may be entered into a
GIS so that important questions can be addressed involving spatial changes.
Computer software and hardware are also used for analysis, classification, and
interpretation of digital remotely sensed data from satellites and aircraft.
The following sections will briefly outline some concepts and procedures
pertinent to analyses of coastal data. The reader is referred to specialized
texts for detailed descriptions of the underlying mathematics and data
processing methods.
Chapter 5 Analysis and Interpretation of Coastal Data
Wave Records
Importance of wave measurements
The measurement and analysis of wave data are of paramount importance
to the understanding of coastal processes. The following quote from the
Shore Protection Manual (1984) underscores reasons for obtaining wave
parameters from the coastal zone:
Waves are the major factor in determining the geometry and compo-
sition of beaches and significantly influence the planning and design
of harbors, waterways, shore protection measures, coastal structures,
and other coastal works. Surface waves generally derive their
energy from the winds. A significant amount of this wave energy is
finally dissipated in the nearshore region and on the beaches.
Waves provide an important energy source for forming beaches;
sorting bottom sediments on the shoreface; transporting bottom
materials onshore, offshore, and alongshore; and for causing many
of the forces to which coastal structures are subjected. An adequate
understanding of the fundamental physical processes in surface wave
generation and propagation must precede any attempt to understand
complex water motion in the nearshore areas of large bodies of
water. Consequently, an understanding of the mechanics of wave
motion is essential in the planning and design of coastal works.
To an observer on the shore or on a boat, the sea surface usually appears
as a chaotic jumble of waves of various heights and periods, moving in many
different directions. Wave gages measure and record the changing elevation
of the water surface. Unfortunately, these data, when simply plotted against
time, reflect the complexities of the sea’s surface and provide little initial
information about the characteristics of the individual waves that were present
at the time the record was being made (Figure 30). Once the water elevation
data are acquired, further processing is necessary in order to obtain wave
statistics that can be used by coastal scientists or engineers to infer which
wave forces have influenced their study area.
Wave data analysis typically consists of a series of steps:
Data transfer from gage to computer.
Conversion of data from voltage readings to engineering units.
Initial quality control inspection.
Spectral analysis.
Additional quality control (if necessary).
Summary statistics in table and plot form.
Plots of individual wave bursts or special processing.
Chapter 5 Analysis and Interpretation of Coastal Data
81
CONTINUOUS
J PRESSURE RECORD
yo SAMPLES COLLECTED BY WAVE GAGE
w
c
2
no
2)
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c
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NO SAMPLES OR NO SAMPLES
2,048
SAMPLES
2 HR OR 4 HA, ETC 2 HR OR 4 HA, ETC
Figure 30. Example of continuous wave pressure record and wave burst sampling of
pressure data
It is beyond the scope of this report to discuss details of the above procedures.
This section will summarize some aspects of data collection, quality control,
analysis, and terminology. Because of the complexity of the subject, the
reader is referred to Bendat and Piersol (1986), Horikawa (1988), the Shore
Protection Manual (1984), and Weaver (1983) for additional references.
Data collection planning
A continuous time series of raw pressure values plotted with time along the
X-axis is shown in Figure 30. Because it is impractical and too expensive to
collect data continuously throughout the day, discrete time series or "bursts"
are collected at predetermined intervals (often every 2, 4, or 6 hr; Figure 30).
Wave bursts typically consist of 1,024 or 2,048 consecutive pressure, U-
velocity, and V-velocity! samples. At a sampling frequency of 1 Hz, these
produce time series of 17.07 min and 34.13 min, respectively. Clearly, it
would be desirable to acquire wave bursts frequently, but the sheer amount of
data would soon overwhelm an analyst’s ability to organize, interpret, and
store the records. A researcher who plans a data acquisition program must
balance the need to collect data frequently versus the need to maintain gages
in the field for an extended period. There is a temptation to assume that as
long as the gages are at sea, they should be programmed to collect absolutely
as much data as possible. However, data management, analysis, and
1 Orthogonal horizontal water velocity measurements.
82
Chapter 5 Analysis and Interpretation of Coastal Data
archiving can cost at least as much as the deployment and maintenance of the
gages. It is essential that these analysis costs be factored into the project
budget. Typical sampling schemes used at CERC projects are listed in
Table 11.
able 11
ave Data Sampling Intervals, Typical CERC Projects
SE ee ee |
Quality control of wave data
One aspect of wave analysis, which is absolutely critical to the validity of
the overall results, is the quality control procedures used to ensure that the
raw data collected by the gages are truly representative of the wave climate at
the site. Wave gages are subject to mechanical and electrical failures. The
pressure sensors may be plugged or may be covered with growths while
underwater. Nevertheless, even while malfunctioning, gages may continue to
collect data which, on cursory examination, may appear to be reasonable. As
an example, Figure 31 shows pressure records from two instruments mounted
on the same tripod off the mouth of Mobile Bay, Alabama. The upper record
in the figure is from a gage with a plugged pressure orifice. The curve
reflects the overall change in water level caused by the tide, but high-
frequency fluctuations caused by the passing of waves have been severely
damped. The damping is more obvious when a single wave burst of 1,024
points is plotted (Figure 32). Without the record from the second gage,
would an analyst have been able to conclude that the first instrument was not
performing properly? This type of determination can be especially
problematic in a low-energy environment like the Gulf of Mexico, where calm
weather can occur for long periods.
Another difficult condition to diagnose occurs when the wave energy
fluctuates rapidly. Many computerized analysis procedures contain user-
specified thresholds to reject records that contain too many noise spikes.
Occasionally, however, violent increases in energy do occur over a short time,
and it is important that the analysis procedures do not reject these records. As
an example, one of two gages in Long Beach Harbor (the lower curve in
Figure 29) may have malfunctioned and written many noise spikes on the
tape. In reality, the gage recorded unusual energy events within the harbor.
Another example, from Burns Harbor, Indiana, is shown in Figure 33. When
wave height was plotted against time, numerous spikes appeared. In this case,
the rapid increase in energy was genuine, and the spikey appearance was
caused by the plotting of many weeks of data on one plot. An examination
of the individual pressure records (Figure 34) reveals how rapidly the energy
Chapter 5 Analysis and Interpretation of Coastal Data
83
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Figure 31.
POUNDS/SQUARE INCH
Pressure data collected by two gages mounted on a tripod off Mobile Bay,
Alabama. The upper record is from a gage with a plugged pressure orifice. The
abrupt increase in pressures near day 43 was caused when a fishing boat struck
and overturned the tripod
Figure 32.
84
512
SECONDS
Example of a single wave burst of 1,024 pressure points from the same gages
that produced the records in Figure 31. The data from the plugged gage (the
upper curve) are not only reduced in amplitude but also shifted in phase. It is
essentially impossible to correct the plugged data and recreate even an
approximation of the original
Chapter 5 Analysis and Interpretation of Coastal Data
INDIANA
MARCH - JUNE 1988
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CALENDAR DATE
MARCH - JUNE 1988
Figure 33. Analyzed wave data from Burns Harbor, Indiana. Spikey appearance is caused
by plotting almost 3 months of data on one plot
increased in only a few hours (a characteristic of Great Lakes storms). This
example demonstrates that the method of displaying wave statistics can have a
major influence on the way the data are perceived by an analyst. Additional
examples and quality control procedures for validating wave data are discussed
in Morang (1990).
Analysis procedures and terminology
Wave data analysis can be broadly subdivided into non-directional and
directional procedures. Although the latter are considerably more complex,
the importance of delineating wave direction in coastal areas is usually great
enough to justify the extra cost and complexity of trying to obtain directional
85
Chapter 5 Analysis and Interpretation of Coastal Data
x
g
E
3
g
=
2
Figure 34. Pressure data from Burns Harbor, Indiana, April 6, 1988. This plot shows how
dramatically the energy can increase in only a few hours
wave spectra. The types of wave statistics needed vary depending on the
application. For example, a geologist might want to know what the average
wave period, height, and peak direction are along a stretch of the shoreline.
This information could then be used to estimate wave refraction and longshore
drift. An engineer who is building a structure along the shore would be
interested in the height, period, and approach direction of storm waves. He
would use these values to calculate stone size for his structure. Table 12 lists
common statistical wave parameters.
Table 12 is intended to underscore that wave analyses are complex proce-
dures and should be undertaken by coastal researchers with knowledge of
wave mechanics and oceanography. In addition, researchers are urged to be
cautious of wave statistics from secondary sources and to be aware of how
terms have been defined and statistics calculated. For example, the term
"significant wave height" is defined as the average height of the highest one-
third of the waves in a record (Shore Protection Manual 1984). How long
should this record be? Are the waves measured in the time domain by
counting the wave upcrossings or downcrossings? The two methods may not
produce the same value of H,. Might it not be better to estimate significant
wave height by performing spectral analysis of a wave time series in the
frequency domain and equating H, = H,,,? This is the procedure commonly
used in experiments where large amounts of data are processed. The latter
86
Chapter 5 Analysis and Interpretation of Coastal Data
Table 12
Sea State Parameters
ie ee eee
Amplitude
[| Wave length measured in the direcvon of wave propagation _[m |
[PST ye PNET ay
ct | orsctoniotiwave prevaqatoniad inca niavsctonalapscvall 00 0 den
[laf | Bete trequency inorementindeeret Fourier analveie Me
ARH eae cco in aidnades With ues dht waved and
General Parameters
Spectral peak frequency 1/7,
H,
2
Significant wave height defined as the highest one-third of the wave m
heights calculated as H4/3 gowncrossing’ °° 11/3, upcrossing
Minima i os eis |
Time Domain Analysis Functions
Zero-downcrossing significant wave height. Average of the highest
one-third zero-downcrossing wave heights
Higa _[Pero-uperossing significant wave Reight dd
Frequency Domain Analysis Parameters
Spectral peak frequency. This frequency may be estimated by different
methods, such as: (1) Frequency at which S,(f) is a maximum;
(2) Fitting a theoretical spectral model to the spectral estimates
Estimate of significant wave height, 4Vmo
S(f)
i
rant
m
nth moment of spectral density
Spectral density
Spectral peak period 1/F, aes
Directional Parameters and Functions
a(f,O) Directional spreading function deg
S(f,8) Directional spectral density (m2/Hz)/
Wave direction. This is the commonly used wave-direction parameter,
representing the angle between true north and the direction from which
the waves are coming. Clockwise is positive in this definition
Direction of wave propagation describing the direction of k. Counter-
clockwise is positive
(Adapted from IAHR Working Group on Wave Generation and Analysis
(1989))
Chapter 5 Analysis and Interpretation of Coastal Data
87
88
equivalency is usually considered valid in deep and intermediate water but
may not be satisfactory in shallow water (Horikawa 1988).
Directional wave statistics are also subject to misinterpretations depending
upon the computation method. At sea, very rarely do the waves come from
only one direction. More typically, swell, generated by distant storms, may
approach from one or more directions, while the local wind waves may have a
totally different orientation. Researchers need to distinguish how the wave
energy is distributed with respect to both direction and period (i.e., the
directional spectral density, S8)). The directional distribution of wave
energy is often computed by a method developed by Longuet-Higgins,
Cartwright, and Smith (1963) for use with floating buoys in deep water.
Other distribution functions have been proposed and used by various
researchers since the 1970’s (Horikawa 1988). Although the various methods
do not produce the same directional wave statistics under some circumstances,
it is not possible to state that one method is superior to another.
The user of environmental data must be aware of the convention used to
report directions. Table 13 lists the definitions used at CERC; other
institutions may not conform to, these standards.
able 13
Reporting Conventions for Directional Environmental Measurements
five, so talcanennenl tne ena paee
FROM WHICH wind is blowing North wind blows from O deg
Waves 0. WlFROM WHICH waves come West waves come from 270 deg
Unidirectional {TO WHICH currents are flowing East current flowing to 90 deg
currents
Some oceanographic instruments are sold with software that performs semi-
automatic processing of the data, often in the field on PC computers. In some
instruments, the raw data are discarded and only the Fourier coefficients saved
and recorded. The user of these instruments is urged to obtain as much
information as possible on the mathematical algorithms used by the gage’s
manufacturer. If these procedures are not the same as those used to analyze
other data sets from the area, the summary statistics may not be directly
comparable. Even more serious, this author (Morang) has encountered
commercial processing software that was seriously flawed with respect to the
calculation of directional spectra. In one field experiment, because the
original raw data had not been archived in the gage, the data could not be
reprocessed or the errors corrected. As a result, the multi-month gage
deployment was rendered useless.
Chapter 5 Analysis and Interpretation of Coastal Data
In summary, it is vital that the user of wave data be aware of how wave
statistics have been calculated and thoroughly understand the limitations and
strengths of the computational methods that were employed.
Display of wave data and statistics
In order to manage the tremendous amount of data that are typically
acquired in a field experiment, perform quality control, and interpret the
results, wave data should be analyzed as soon as possible. In addition, there
is often an urgent need to examine the raw data to ascertain whether the gages
can be redeployed or must be repaired.
Figures 30 and 32 are examples of pressure plotted against time. The
value of this form of display for quality control purposes has been
demonstrated, but these plots are of limited value in revealing information
about the overall nature of the wave climate in the study area.
In order to review the data from an extended deployment, the summary
Statistics must be tabulated or plotted. Figure 35 is an example of tabulated
directional wave data from a Florida project site. These same data are
graphically displayed in Figure 36. The upper plot shows H,,,, wave height,
the center peak period, and the lower peak direction. Although other statistics
could have been plotted on the same page, there is a danger of making a
display too confusing. The advantage of the tabulation is that values from
individual wave bursts can be examined. The disadvantage is that it is
difficult to detect overall trends, especially if the records extend over many
months. As data collection and processing procedures improve, and as more
and more data are acquired at field projects, it will be increasingly difficult to
display the results in a useful and flexible format that does not overwhelm the
end user but yet also does not oversimplify the situation.
Applications of wave data
One important use of wave climate data in coastal engineering is in the
construction of wave refraction diagrams. These demonstrate how nearshore
bathymetry influences the direction of waves approaching the shoreline. This
information can be used to estimate mass transport and longshore transport of
sediment, which, in turn, can be used to predict morphologic changes under
both natural and structurally influenced coasts. Wave refraction analyses can
also be used for hypothetical scenarios, such as predicting the effects on
incident waves of dredging an offshore shoal or dumping dredged materials
offshore.
Chapter 5 Analysis and Interpretation of Coastal Data
89
EAST PASS, DESTIN, FLORIDA ANALYSIS SUMMARY
635-9 GAGE 05 YUV Version 3.5
APRIL - ¢UNE 1989 20-dAN- 90
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Figure 35. Example of tabular summary of wave data from offshore Fort Walton Beach,
Florida
90
Chapter 5 Analysis and Interpretation of Coastal Data
EAST PASS, DESTIN, FLORIDA
30°23'25" N; 86° 35°38" W
Wave Height, Hyp. m
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Figure 36. Plots of wave height, peak period, and peak direction from offshore Fort Walton
Beach, Florida
91
Chapter 5 Analysis and Interpretation of Coastal Data
92
Water Level Records
Marine (oceanic) coastlines
Changes in water levels along coastlines have profound influence on the
geology, the natural ecology, and human habitation in these regions. Predict-
ing and understanding these changes can guide coastal planners in developing
rational plans for coastal development and in the design, construction, and
operation of coastal structures and waterways. Sea level along open coasts
varies in response to many natural processes on various temporal scales.
Short-term factors are outlined in Table 14.
able 14
Short-Term Sea-Level Changes Along Open Coastlines
* Periodic sea-level changes
Astronomical tides (diurnal and semidiurnal)
Long-period tides
The Chandler effect - changes in the rotation of the earth
* Meteorological and oceanographic contributions
Atmospheric pressure
The effects of winds - storm surges
The contribution of water density (temperature and salinity)
The effects of currents (meanders in western boundary currents)
Evaporation and precipitation
Ocean surface topography - ocean surface topography changes caused by density
variations and climatic/current variations
El Nino/ southern oscillation
* Seasonal variations
Seasonal cycles (Atlantic, Pacific, Indian Oceans)
Seasonal variation in slope of the water surface
Seasonal water balance of the world’s oceans
River runoff/floods - influential in inland seas
* Seiches
*Tsunamis - Earthquakes and mean sea level
Tsunamis - Short-term, catastrophic water level changes
Earthquakes - Changes in land levels
(Adapted from Emery and Aubrey (1991) and Lisitzin (1974))
Sea level changes over historical and geologic time scales are the subject of
active research in the scientific community and the petroleum industry. The
study of these changes has been hampered by the poor worldwide distribution
of tide gages, as most gages were (and still are) distributed along the coasts of
industrial nations in the Northern Hemisphere. Many of the geomorphic fea-
tures with which we are familiar on contemporary coasts are the byproducts of
the eustatic rise in sea level caused by Holocene climatic warming and melting
of glaciers and ice sheets. The Holocene rise in sea level is well documented.
Using the existing distribution of gages, it is not possible to assess if the rise
is continuing because, while many gages record a recent rise in relative sea
level (rsl), an equal number record a fall (Emery and Aubrey 1991).
Chapter 5 Analysis and Interpretation of Coastal Data
The rsl has fluctuated throughout geologic time as the volume of ocean
water has fluctuated, the shape of the ocean basins has changed, and
continental masses have broken apart and reformed. Table 15 lists some of
the factors contributing to long-term (geologic time scale) factors that have
caused changes in rs]. Readers interested in details of this fascinating subject
are referred to Emery and Aubrey’s (1991) excellent book. This volume and
Gorman (1991) contain extensive bibliographies of the subject. Detailed
analyses of United States tide curves are documented in Hicks, Debaugh, and
Hickman (1983).
able 15
Long-Term Causes of Changes in Relative Sea Level
* Changes in ocean water volume
Waxing and waning of glaciers and Arctic ice cap
Juvenile water from volcanic eruptions
Thermal effects - volcanism, hot spots, aesthenospheric bumps
Plate tectonics and seafloor spreading
Changes in spreading rates (affect the hypsometric curve - average depths of the ocean
basins)
Changes in areas of ocean and land
Changes in direction of plate motions
Deep-ocean sedimentation
Isostacy (isostatic adjustment of the earth’s crust)
Glacio-isostacy - waxing and waning of glaciers
Hydro-isostacy - changing water load on crust below ocean basins
Sediment-isostacy - depositional-erosional cycles cause varying sediment load
Glacial surges and melting
Departures from the geoid (level surface of equal gravitational potential)
Shifts in the hydrosphere, aesthenosphere, core-mantle interface
Shifts in the rate of the earth’s rotation, tilt of the spin axis, and precession of the equinox
External gravitational changes
Geological faulting
Vertical and horizontal movement of large pieces of the crust in response to fault motions
* Sediment compaction and subsidence
Reduction of volume of poorly packed sediments into more dense matrix - common in river
deltas (Mississippi, Nile, Niger)
Draining of low-lying areas
Compaction under earthquake-induced vibration
Compaction as a result of loss of interstitial fluids - oil drilling and withdrawal of
groundwater for urban development
(Adapted from Emery and Aubrey (1991))
Tide gage records may be analyzed for spatial interpolation and for
assessing temporal variations such as surges, tides, seasonal changes, and
long-term trends. Discrepancies between the predicted tide at one site and the
actual tide measured only a short distance away may be considerable. A
method for adjusting between predicted tides at a station and those at a nearby
study area using only limited field measurements is discussed by Glen (1979).
Other analysis methods are discussed in HQUSACE (1989) and the Shore
Protection Manual (1984).
Chapter 5 Analysis and Interpretation of Coastal Data
93
94
For engineering projects, assessments of short-term water level changes
range from simple plotting of the data to more sophisticated mathematical
analyses. In some cases, some of the components which drive water level
changes can be isolated. To assess longer (multi-year) trends, it is important
to dampen or separate the effects of yearly variability so that the nature of the
secular trends becomes more pronounced. Least-squares regression methods
are typically inadequate because the secular trends often show pronounced
nonlinearity (Hicks 1972). It may also be important to examine long-term
periodic effects in a long data record such as the 18.6-year nodal period,
which Wells and Coleman (1981) concluded was important for mud flat
stabilization in Surinam.
West Coast of North America
The west coast of North America experiences extreme and complicated
water level variations. Short-term fluctuations are related to oceanographic
conditions like the El Nifio-Southern Oscillation. This phenomenon occurs
periodically when equatorial trade winds in the southern Pacific diminish,
causing a seiching effect, which travels eastward as a wave of warm water.
This raises water levels all along the U.S. west coast. Normally the effect is
only a few centimetres, but during the 1982-83 event, sea level was elevated
35 cm at Newport, OR (Komar 1992). Seasonal winter storms along the
Pacific Northwest can combine with elevated water levels to produce tides
over 3.6 m. During the 1983 winter storms, water levels were up to 60 cm
over the predicted level. Tectonic instability along the U.S. west coast affects
long-term water level changes. Parts of the coast are rising and falling at
different rates. Studies in Oregon have shown that the state’s northern coast is
falling while the southern part is rising relative to sea level (Komar 1992).
Along Alaska, some areas of the coast are rising nearly 1 cm/year.
Great Lakes of North America
On the Great Lakes of North America (Lakes Superior, Huron, Michigan,
Erie, and Ontario), astronomic tides have relatively little influence on water
levels. Short-term level fluctuations are primarily caused by local atmospheric
pressure changes and by winds. This is demonstrated in Figure 34, where the
first three wave bursts are shifted vertically from each other. In addition,
even during the recording of each 1,024-point burst (17.07 min long), the
mean water level changed.
Long-term changes of water levels in the Great Lakes are caused by
regional hydrographic conditions such as precipitation, runoff, temperature
and evapotranspiration, snowmelt, and ice cover (Great Lakes Commission
1986). These factors in turn are affected by global climate variations. Crustal
movements also influence levels. For example, the eastern end of Lake
Superior is rebounding at a rate about 10 in./century faster than the western
end, resulting in higher water at the west end at Duluth. Aquatic plant life
Chapter 5 Analysis and Interpretation of Coastal Data
and man-made control structures are additional factors that influence the
exceedingly complex cycles of water level changes in the Great Lakes. As a
result, the concept of mean water level is not applicable to these inland Great
Lakes, and attempts to predict lake levels have not been entirely successful
(Walton 1990).
Historic water levels have been used by Hands (1979, 1980) to examine
the changes in rates of shore retreat in Lake Michigan and to predict
beach/nearshore profile adjustments to rising water levels. Additional
research is being sponsored by the International Joint Commission to model
how changing water levels affect erosion of various bluff stratigraphies and
the nearshore profile.
Current Records
Current data are often critical for evaluating longshore and cross-shore
sediment transport and for evaluating hydraulic processes in inlets and other
restricted waterways. Currents, which are generated by a variety of
mechanisms, vary greatly spatially and temporally in both magnitude and
direction. Four general classes of unidirectional flow affect coastal
environments and produce geologic changes. These include:
@ Nearshore wave-induced currents, including longshore and rip currents.
@ Flow in tidal channels and inlets, which typically changes direction
diurnally or semidiurnally, depending on the type of tide along the
adjacent coast.
@ River discharge.
@ Oceanic currents, which flow along continental land masses.
This section will briefly discuss the first two of these topics and present
data examples. The third and fourth are beyond the scope of this report, and
the reader is referred to outside references for additional information.
Nearshore wave-induced currents
In theory, one of the main purposes for measuring nearshore, wave-
induced currents is to estimate longshore transport of sediments. At the
present level of technology and mathematical knowledge of the physics of
sediment transport, the direct long-term measurement of longshore currents by
gages is impractical. Two main reasons account for this situation. First, as
discussed earlier in this report, deployment, use, and maintenance of instru-
ments in the nearshore and the surf zone are difficult and costly. Second, the
mechanics of sediment transport are still little understood, and no one mathe-
matical procedure is yet accepted as the definitive method to calculate sedi-
ment transport, even when currents, grain size, topography, and other
Chapter 5 Analysis and Interpretation of Coastal Data
95
96
parameters are known. An additional consideration is how to monitor the
variation of current flow across and along the surf zone. Because of the
extreme difficulty of obtaining data from the surf zone, neither the cross-shore
variations of currents nor the temporal changes in longshore currents are well
known.
Longshore (or littoral) drift is defined as: "Material (such as shingle,
gravel, sand, or shell fragments) that is moved along the shore by a littoral
current" (Bates and Jackson 1984). Net longshore drift refers to the differ-
ence between the volume of material moving in one direction along the coast
and that moving in the opposite direction (Bascom 1964). Along most coasts,
longshore currents change directions throughout the year. In some areas,
changes occur in cycles of a few days, while in others the cycles may be
seasonal. Therefore, one difficulty in determining net drift is defining a
pertinent time frame. Net drift averaged over years or decades may conceal
the fact that significant amounts of material may also flow in the opposite
direction.
Because net longshore currents may vary greatly from year to year along a
stretch of coastline, it would be desirable to deploy current meters at a site for
several years in order to obtain the greatest amount of data possible.
Unfortunately, the cost of a multi-year deployment could be prohibitive. Even
a long deployment might not detect patterns which vary on decade-long scales,
such as the climatic changes associated with El Nifo. At a minimum, near-
shore currents should be monitored at a field site for at least a year in order to
assess the changes associated with the passing seasons. Coastal scientists must
be aware of the limitations of field current data and recognize that long-term
changes in circulation patterns may remain undetected despite the best field
monitoring efforts.
Figure 37 is an example of current data from offshore Fort Walton Beach,
Florida. The current directions and velocities were calculated from wave
orbital velocities measured by a wave gage in the 10-m water depth, 400 m
offshore. Because the gage was outside of the surf zone, the currents reflect
the combined influence of tides, winds, waves, and possibly offshore influ-
ences like the Gulf of Mexico Loop Current (Morang 1992). Nevertheless,
the isobaths in this area are parallel to the shore and the directions of the
nearshore currents are likely to be the same as those of the longshore currents
within the surf zone.
Flow in tidal channels and inlets
An inlet is "a small, narrow opening in a shoreline, through which water
penetrates into the land" (Bates and Jackson 1984). Inlets range in size from
short, narrow breaches in barrier islands to wide entrances of major estuaries
like Chesapeake Bay. Many geologic and engineering studies concern flow
through tidal inlets in sand-dominated barriers, particularly when the inlets
serve as navigation channels connecting harbors to the open sea.
Chapter 5 Analysis and Interpretation of Coastal Data
EAST PASS, DESTIN, FLORIDA
30° 23’25”" N; 86 35'38” W
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Figure 37. Coastal currents measured off Fort Walton Beach, Florida Panhandle. Note that
the currents flow east or west for periods of days at a time
97
Chapter 5 Analysis and Interpretation of Coastal Data
98
Inlets exchange water between the sea and the bay during each tidal cycle.
Therefore, currents in tidal inlets are typically unidirectional, changing
direction diurnally or semidiurnally, depending upon the tides along the
adjacent open coast. Flow through the inlets can be complicated by the
hydrodynamics of the inland bay, especially if there are other openings to the
sea.
Various numerical and conceptual models have been developed to describe
flow through inlets and allow researchers to predict the effects of changing
inlet dimensions, lengths, and orientations (Aubrey and Weishar 1988;
Escoffier 1977; Seelig, Harris, and Herchenroder 1977; Shore Protection
Manual 1984). Most models, however, benefit from or require calibration
with physical measurements made within the inlet and the general vicinity.
The required field measurements are usually either tidal elevations from the
open sea and within the adjacent bay or actual current velocities from within
the inlet’s throat.
Display of tidal elevation data is relatively straightforward, usually
consisting of date or time on the x-axis and elevation on the y-axis. Examples
of tidal elevations from a bay and an inlet in the Florida Panhandle are
presented in Figure 17. Although the overall envelope of the curves is
similar, each one is unique with respect to the heights of the peaks and the
time lags. The curves could be superimposed to allow direct comparison, but,
at least at this 1-month-long time scale, the result would be too complicated to
be useful.
Display of current meter measurements is more difficult because of the
large quantity of data usually collected. An added difficulty is posed by the
changing currents within an inlet, which require a three-dimensional repre-
sentation of the flow, which varies with time. Current measurements from
East Pass, Florida, collected during three field experiments in the mid-1980’s,
are presented as examples. Currents were measured with manual Price-type
AA meters deployed from boats and with tethered Endeco 174 current meters.
The manual measurements were made hourly for 24 hr in order to observe a
complete tidal cycle. The measurements were made across the inlet at
four stations, each one consisting of a near-surface, a mid-depth, and a near-
bottom observation (Figure 38). Therefore, 12 direction and velocity data
values were obtained at each hour (Figure 39). One way to graphically
display these values is to plot the velocities on a plan view of the physical
setting, as shown in Figure 38. This type of image clearly shows the direc-
tions and relative magnitudes of the currents. In this example, the data reveal
that the currents flow in opposite directions in the opposite halves of the inlet.
The disadvantage of the plan view is that it is an instantaneous snapshot of the
currents, and the viewer cannot follow the changes in current directions and
magnitudes over time unless the figure is redrawn for each time increment.
Temporal changes of the currents can be shown on dual plots of magnitude
and direction (Figure 40). Unfortunately, to avoid complexity, it is not
reasonable to plot the data from all 12 measurement locations on a single
page. Therefore, measurements from the same depth are plotted together, as
Chapter 5 Analysis and Interpretation of Coastal Data
DESTIN
LEGEND
CURRENT METER
LOCATION
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MIDDEPTH
BOTTOM
VELOCITY SCALES
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EAST PASS
OCT 26, 19835
02:10 CST
Figure 38. Current measurement stations in East Pass Inlet, Destin, Florida, during October,
1983. Measurements were made hourly from small boats. At 02:10 CST, cur-
rents were flowing to the northwest along the west side of the inlet and to the
southeast along the center and east sides of the inlet. Station 2 was in the
mixing zone
99
Chapter 5 Analysis and Interpretation of Coastal Data
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Figure 39. Example of hand-written field notes listing times and data values of East Pass
current measurements. The data are presented efficiently but are difficult to
visualize
100
Chapter 5 Analysis and Interpretation of Coastal Data
CURRENT DIRECTION (DEG)
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Figure 40. Time series plots of current speed (bottom) and direction (top)
101
Chapter 5 Analysis and Interpretation of Coastal Data
in Figure 40, or all measurements from one site can be plotted together (top,
middle, and bottom).
In summary, current data can be displayed in the form of instantaneous
snapshots of the current vectors or as time series curves of individual stations.
Many plots are usually needed to display the data collected from even short
field projects. It may be advantageous to present these plots in a data appen-
dix rather than within the text of a report.
Error analysis of current data
Error analysis of current records can be broadly divided into two
categories. The first concerns calibrations of the actual current sensing
instruments. A user needs to know how closely the numbers reported by a
particular instrument represent the water motions that it is purported to be
measuring. This information is important for both evaluation of existing data
sets and for planning of new field experiments, where some instruments may
be more suitable than others.
The second broad question pertains to whether the measurements that have
been gathered adequately represent the flow field in the inlet or channel that is
being examined. This second problem is exceedingly difficult to evaluate
because it raises the fundamental questions of "How much data do I need";
and, “Can I afford to collect the data that will really answer my questions?"
The user is typically tempted to respond that he wants just as much data as
possible, but this may prove to be counterproductive. For example, if the
currents in an inlet are being measured to determine variations in the tidal
prism over time, will a dense gridwork of sampling stations in an inlet
provide more useful data? Or might the excess data reveal unnecessary details
about turbulence and mixing in the inlet? These are intrinsically interesting
questions, but may not be germane to the engineering problems that must be
addressed. Although the dense grid pattern of data can be used to evaluate
overall flow, the collection, analysis, and management of the excess data can
be costly and time-consuming. The money used on management of this data
might be better spent extending a simpler sampling program for a longer
period at the site.
Possibly a statistical approach could be used to plan the placement of
instruments in an inlet. In order to plan the optimum deployment of current
meters in the 1973 North Atlantic Mid Ocean Dynamics Experiment
(MODE-73), Bretherton, Davis, and Fandry (1976) applied the Gauss-Markov
theorem to minimize the expected interpolation error between instruments and
map the expected error. These errors depended upon the statistics of the field
array and not upon the measurements themselves. Wunsch (1978) and
Wunsch and Minster (1982) used inverse theory to determine the circulation
of the Atlantic Ocean by modeling the conservation of various properties and
then comparing the resulting models to the flow field actually measured by
instruments. They concluded that there were serious shortcomings to the
102
Chapter 5 Analysis and Interpretation of Coastal Data
oceanic data set and that, despite the efforts that had gone into North Atlantic
hydrography over the last 100 years, the true general circulation was still
unknown. Applying inverse theory to model instrument deployment in
shallow water and to estimate, before the actual deployment, what types and
magnitudes of errors can be expected, promises to be a fruitful line of
research. The results may show that fewer instruments will suffice, providing
a significant cost savings. On the other hand, the results may reveal that flow
in inlets continues to be an under-determined problem and that past instrument
practices have been inadequate to define the flow field.
Analysis of error from various types of current sensors has been the
subject of extensive study in the last 30 years. Numerous types of error can
occur, both during field deployment of the instrument and during data
processing. These can result from instrument calibration, clock time errors,
and data recording and playback. In addition, the user is cautioned that each
of the many types and brands of current meters is capable of recording
accurately only a segment of the spectrum of water motions because of the
influence of the mooring assembly, type of velocity sensor used, and record-
ing scheme of the instrument (Halpern 1980). Halpern’s (1980) paper lists
many references that discuss tests of moored current meters.
Manufacturers of current meters publish accuracy standards in their
literature. These standards may be optimistic, especially under the adverse
conditions encountered in many coastal settings. In addition, the type of
mooring used for the instrument affects the quality of the measured data
(Halpern 1978). For these reasons, the user of existing data is urged to obtain
as much information as possible regarding the specifics of the deployment and
the type of mooring in order to try to assess the accuracy of the results.
Ultimately, successful use of current gages is critically dependent upon the
planning of the experiment and upon the care and skill of the technicians who
maintain and deploy the instruments.
River discharge
River outflow has a major effect on some coastlines, particularly where
massive deltas have formed (e.g. Mississippi, Nile, Niger, Ganges, Mekong,
Indus, Irriwadi Deltas). Even if a study area is not located on a delta, coastal
researchers must be aware of the potential impact of rivers on coastal
processes, especially if the study region is affected by freshwater runoff at
certain seasons or if longshore currents carry river-derived sediment along the
‘shore.
The physics of unidirectional flow in rivers has been extensively studied
for more than a century. It is beyond the scope of this report to discuss the
mechanics and procedures of current measurement in rivers, and the reader is
referred to texts on hydraulic engineering for methods and additional details.
An introduction to riverine hydraulics is provided in Linsley and Kohler
(1982). Calculation of river discharge is reviewed in HQUSACE (1959,
103
Chapter 5 Analysis and Interpretation of Coastal Data
1987). Graf (1984), Middleton and Southard (1984), and Vanoni (1975)
review general concepts of sediment transport and fluid-particle interactions in
rivers, and 15 excellent papers on hydraulic processes and primary sedi-
mentary structures are reprinted in Middleton (1977). Deltaic and estuarine
sedimentation and structures are reviewed in Boggs (1987), Nichols and Biggs
(1985), and Wright (1985).
River discharge data are available for many coastal rivers. A cursory
examination of the annual hydrograph will reveal the seasonal extremes.
Because of the episodic nature of coastal flooding, annual disharge figures
may be misleading. A useful parameter to estimate river influence on the
coast is the hydrographic ratio (Hp), which compares tidal prism volume with
fluvial discharge volume (Peterson et al. 1984).
Oceanic currents
Major oceanic currents intrude onto some continental shelves with enough
bottom velocity to transport sandy sediments. The currents operate most
effectively on the outer shelf, where they may transport significant volumes of
fine-grained sediments but presumably contribute little if any new sediment
(Boggs 1987). Along most coastlines, ocean currents have little direct effect
on shoreline sedimentation or erosion. Even off southeast Florida, where the
continental shelf is narrow, the western edge of the Gulf Stream flows at least
1/2 km offshore. However, in some locations where currents approach the
coastal zone, sediment discharged from rivers is transported and dispersed
along the adjacent coastline. This process may arrest the seaward prograda-
tion of the delta front while causing extensive accumulations of riverine-
derived clastics downdrift of the river mouth (Wright 1985). The most
prominent example of this phenomenon is the Amazon River mouth, where
the Guiana current carries Amazon sediments hundreds of kilometres to the
northwest (Wright 1985). The same current also disperses sediment from the
Rio Orinoco.
In shallow carbonate environments, reefs thrive where currents supply
clean, fresh ocean water. Reefs stabilize the bottom, provide habitat for
marine life, produce carbonate sediments, and sometimes protect the adjoining
shore from direct wave attack (i.e, the Great Barrier Reef of Australia). In
the United States, live reefs are found in the Gulf of Mexico off Texas and
west Florida and in the Atlantic off Florida. Coral islands are found in the
Pacific in the United States Trust Territories. For geologic or engineering
studies in these environments, there may be occasional need to monitor
currents. Procedures of deepwater current measurement are presented in
Appell and Curtin (1990) and McCullough (1980).
In summary, the effect of tide or wave-induced currents is likely to be
much more important to most coastal processes than ocean currents.
Measurement of ocean currents may occasionally be necessary for geologic
studies in deltaic or carbonate environments.
104
Chapter 5 Analysis and Interpretation of Coastal Data
Maps and Photographs
Introduction
Maps and aerial photographs can provide a wealth of useful information
for the interpretation of geologic coastal processes and evolution. Maps and
photographs can reveal details on:
@ Long-term and short-term advance or retreat of the shore.
@ Longshore movement of sediments.
@ The impact of storms, including breaches of barrier islands, overwash,
and changes in inlets, vegetation, and dunes.
@ Problems of siltation of tidal inlets, river mouths, estuaries, and
harbors.
@ Human impacts caused by construction or dredging.
© Compliance with permits.
@ Biological condition of wetlands and estuaries.
For example, the geometry of the coastline in the vicinity of headlands, inlets
and streams, and man-made structures is one key to assessing the dispersal of
the products of coastal erosion and sediments supplied by rivers (Figure 41).
Large sets of historical aerial photographs and maps have been used to
interpret regional geomorphic changes of coastal South Carolina (Anders,
Reed, and Meisburger 1990), northern New Jersey (Gorman, Reed, and
Stauble 1993), and the Kings Bay area of Georgia and Florida (Kraus and
Gorman 1993) (Figure 42). Using detailed historic data, Dolan and Hayden
(1983) were able to conclude that shore processes and landforms assume
systematic, as opposed to random, patterns both along and across the coast.
They found that large storms caused severe erosion in the same locations as
previous storms of lower intensity. Long-term erosion rates have been
examined even over large areas, although the quality and distribution of
historic maps is spotty (Dolan, Hayden, and May 1983). May and Britsch
(1987) examined the effects of natural and human-induced wetland losses in
the Mississippi Delta.
Historical shoreline change mapping
The use of maps and aerial photographs to determine historical changes in
shoreline position is increasing rapidly. Analyzing existing maps does not
require extensive field time or expensive equipment, and therefore often
provides valuable information at an economical price. This section
summarizes the interpretation of water line on photographs and maps and
corrections needed to convert historic maps to contemporary projections and
coordinate systems.
105
Chapter 5 Analysis and Interpretation of Coastal Data
Headland Tidal Inlet or Stream
D
Beach Ridge Headlands Jetties
Seawall Breakwater Offshore Breakwater
Figure 41. 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 offshore breakwaters (E-I) generally
show accumulation of sediment on the updrift side, and reduced sediment
supply on the downdrift side
Many possible datums can be used to monitor historical changes of the
shoreline. In many situations, the high water line (HWL) has been found to
be the best indicator of the land-water interface (Crowell, Leatherman, and
Buckley 1991). The HWL is easily recognizable in the field and can usually
be approximated from aerial photographs by a change in color or shade of the
beach sand. The datum printed on the NOS T-sheets is listed as "Mean High
Water." Fortunately, the early NOS topographers approximated HWL during
their survey procedures. Therefore, direct comparisons between historical
T-sheets and modern aerial photographs are possible. In order to calculate the
genuine long-term shoreline change, seasonal beach width variations and other
106
Chapter 5 Analysis and Interpretation of Coastal Data
TRANSECT 2 Shoreline Position
St. Marys Entrance
\t
\\l
\
Island | LEGEND
1857 Se ae
Aug. - Nov. 1924 ——-——-— =a
Dec. 1933
Mar. 1957
Oct. 1973 (Cumberland) ———
Apr. 1974 (Amelia) --————-
Oct. 1991 oe
Engineering structures ==
TRANSECT 4
ATLANTIC
OCEAN
Fernandina
Beach
Amelia Island
Kilometers
Universal Transverse Mercator
Zone 17 NAD 83
Figure 42. Changes in shoreline position near St. Marys entrance, Florida-Georgia (from
Kraus and Gorman 1993)
107
Chapter 5 Analysis and Interpretation of Coastal Data
short-term changes should be filtered out of the record. The best approach is
to use only maps and aerial images from the same season, preferably
summertime.
A crucial problem underlying the analysis of all historical maps is that they
must be corrected to reflect a common datum and brought to a common scale,
projection, and coordinate system before data from successive maps can be
compared (Anders and Byrnes 1991). Maps made before 1927 have an
obsolete latitude-longitude coordinate system-(U.S. datum or North American
(NA) datum) that must be updated to the current standard of NAD 1927 or the
more recent NAD 1983. To align maps to a specific coordinate system, a
number of stable and permanent points or features must be identified for
which accurate and current geographic coordinates are known. These
locations, called primary control points, are used by computer mapping
programs to calculate the transformations necessary to change the map’s
projection and scale. The most suitable control points are triangulation
stations whose current coordinates are available from the National Geodetic
Survey.
Maps that were originally printed on paper have been subjected to varying
amounts of shrinkage. The problem is particularly difficult to correct if the
shrinkage along the paper’s grain is different than across the grain. Maps with
this problem have to be rectified or discarded. In addition, tears, creases, and
folds in the paper maps must be corrected.
Aerial photographs, which are not map projections, must be corrected by
optical or computerized methods before shore positions compiled from the
photos can be directly compared with those plotted on maps. The distortion
correction procedures are involved because photos do not contain defined
control points like latitude-longitude marks or triangulation stations. On many
images, however, secondary control points can be obtained by matching prom-
inent features such as the corners of buildings or road intersections with their
mapped counterparts (Crowell, Leatherman, and Buckley 1991). Types of
distortion which must be corrected include:
@ Tilt. Almost all vertical aerial photographs are tilted with 1 deg being
common and 3 deg not unusual (Lillesand and Kiefer 1987). The scale
across tilted air photos is non-orthogonal, resulting in gross displace-
ment of features depending upon the degree of tilt.
@ Variable scale. Planes are unable to fly at a constant altitude.
Therefore, each photograph in a series varies in scale. A zoom transfer
scope can be used to remove scale differences between photos.
@ Relief displacement. Surfaces which rise above the average land eleva-
tion are displaced outward from the photo isocenter. Fortunately, most
U.S. coastal areas, especially the Atlantic and Gulf barriers, are rela-
tively flat and distortion caused by relief displacement is minimal.
108
Chapter 5 Analysis and Interpretation of Coastal Data
However, when digitizing cliffed shorelines, control points at about the
same elevation as the feature being digitized must be selected.
@ Radial lens distortion. With older aerial lenses, distortion varied as a
function of distance from the photo isocenter. It is impossible to cor-
rect for these distortions without knowing the make and model of the
lens used for the exposures (Crowell, Leatherman, and Buckley 1991).
If overlapping images are available, digitizing the centers, where distor-
tion is least, can minimize the problems.
Fortunately, most errors and inaccuracies from photographic distortion and
planimetric conversion can be quantified. Past shoreline mapping exercises
have shown that if care is taken in all stages of filtering original data
sources, digitizing data, and performing distortion corrections, the resulting
maps meet, and often exceed, National Map Accuracy Standards (Crowell,
Leatherman, and Buckley 1991).
Topographic and Bathymetric Data
Introduction
The analysis and examination of topographic and bathymetric data are
fundamental in many studies of coastal engineering and geology. When
assembling bathymetric surveys from a coastal area, a researcher is often
confronted with an immense amount of data that must be sorted, checked for
errors, redisplayed at a common scale, and compared year by year or survey
by survey in order to detect whether changes in bottom configuration have
occurred. This section will discuss three general aspects of geographic data
analysis:
@ Processing of bathymetric data using mapping software.
@ Applications and display of the processed results.
@ Error analyses.
Bathymetric data processing - data preparation and input
Most historical bathymetric data sets consist of paper maps with printed or
hand-written depth notations (Figure 43). Occasionally, these data are
available on magnetic media from agencies like NOAA, but often a reseacher
must first digitize the maps in order to be able to perform computer-based
processing and plotting. If only a very limited region is being examined, it
may be more expedient to contour the charts by hand. The disadvantage of
hand-contouring is that it is a subjective procedure. Therefore, one person
should be responsible for all the contouring in order to minimize variations
109
Chapter 5 Analysis and Interpretation of Coastal Data
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Figure 43. Example of a hand-annotated hydrographic map from a Florida project site. The
depths have been corrected for tide and are referenced to mlw. (Map courtesy
of USAE District, Mobile)
caused by different drawing styles or methods of smoothing topographic
variations.
In order to be able to manipulate three-dimensional (X, Y, and Z) data,
display and plot it at different scales, and compare different data sets, it is
necessary to use one of the commercial mapping programs such as Radian
Corporation’s Contour Plotting System 3 (CPS-3) or Golden Software’s
Surfer. These are comprehensive packages of file manipulation, mapping
algorithms, contouring, and two- and three-dimensional display. Their use
requires considerable training, but they are powerful analysis tools.
The raw data used by mapping programs consist of data in X-Y-Z form.
As described in the previous section, if the data are derived from old maps,
they must first be corrected to a common datum, map projection, and coor-
dinate system. For small files, visual examination of the data may be worth-
while in order to inspect for obviously incorrect values. Because it is
laborious to review thousands of data points, simple programs can be written
to check the raw data. For example, if all the depths in an area are expected
to be between +5.0 and -40.0 ft, the program can tag depths that are outside
110
Chapter 5 Analysis and Interpretation of Coastal Data
this range. The analyst can then determine if questionable points are errone-
ous Or represent genuine but unexpected topography. The X and Y points
should typically represent Cartesian coordinates, which is the case if the origi-
nal maps were based on State Plane coordinates. X and Y points that are
latitude and longitude must be converted by the program.
Gridding operations
Gridding is a mathematical process in which a continuous surface is
computed from a set of randomly distributed X, Y, and Z data!. The result
of the gridding operation is a data structure (usually a surface) called a grid.
Note that the grid is an artificial structure. It is based on the original data
(and hopefully is an accurate representation of the topography which was
surveyed in the field), but the grid points are not identical with the original
survey points (Figures 44 and 45). Because the grid represents the surface
that is being modeled, the accuracy of the grid directly affects the quality of
any output based on it or on comparisons with other grids generated from
other data sets. Computing a grid is necessary before operations such as
contouring, volume calculation, profile generation, or volume comparison can
be performed. The advantage of a grid is that it allows the program to
manipulate the surface at any scale or orientation. For example, profiles can
be generated across a channel even if the original survey lines were not run in
these locations. In addition, profiles from subsequent surveys can be directly
compared, even if the survey track lines were very different.
Several steps must be considered as part of the grid generation. These
include:
Selecting a gridding algorithm.
Identifying the input data.
Specifying the limits of the grid coverage.
Specifying gridding parameters.
Specifying gridding constraints.
Computing the grid.
The choice of a gridding algorithm can have a major effect on the ultimate
appearance of the grid. Software companies have proprietary algorithms
which they claim are universally superior. Often, however, the type or distri-
bution of data determines which procedure to use, and some trial and error is
necessary at the beginning of a project. Because a computed grid is an artifi-
cial structure, often it is a subjective evaluation whether one grid is “better”
than another. For subaerial topography, an oblique aerial photograph can be
compared with a computer-generated three-dimensional drawing oriented at
the same azimuth and angle. But for a subaqueous seafloor, other than
1 Material in this section has been condensed from course notes provided by Radian Corpora-
tion during a CPS-3 training seminar presented at CERC in November 1989.
Chapter 5 Analysis and Interpretation of Coastal Data
503000
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506000
EAST PASS, FLORIDA
505000
ris} i990
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1363000 1364000 1365000 1566000 1367000 1368000
Figure 44. Digitally collected hydrographic data from a Florida project site. The track lines
are obvious, as is the fact that the soundings are not uniformly distributed
throughout the survey area. (Data courtesy of USAE District, Mobile)
comparing a gridded surface with a hand-contoured chart, how can a
researcher really state that one surface does not look right while another does?
The fundamental challenge of a gridding algorithm is to estimate depth
values in regions of sparse data. The procedure must attempt to create a
surface that follows the trend of the terrain as demonstrated in the areas where
data do exist. In effect, this is similar to the trend-estimating that a human
performs when he contours bathymetric data by hand. The other challenge
occurs in complex, densely sampled terrains. The algorithm must fit the
surface Over many points, but genuine topographic relief must not be
12
Chapter 5 Analysis and Interpretation of Coastal Data
S09000
508000
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SO6000
505000
15635000 13564000 1365000 1566000 1367000 1368000
Figure 45. Surface grid computed by CPS-3 based on the data shown in Figure 44. The
nodes are uniformly spaced compared with the locations of the original
soundings. A grid does not necessarily have to be square, although this is
common
smoothed away! Along a rocky coast, for example, high pinnacles may
indeed project above the surrounding seafloor.
The gridding algorithms in CPS-3 include:
Convergent (multi-snap).
Least squares with smoothing.
Moving average.
Trend.
Polynomial.
flelkS
Chapter 5 Analysis and Interpretation of Coastal Data
The convergent procedure often works well for bathymetric data. It uses
multiple data points as controls for calculating the values at nearby nodes.
The values are blended with a distance-weighting technique such that close
points have more influence over the node than distant points. Several itera-
tions are made, with the first being crude and including many points, and the
final being confined to the closest points. The least-squares method produces
a plane that fits across several points near the node. Once the plane has been
calculated, the Z-value at the node is easily computed. The reader must con-
sult software manuals to learn the intricacies of how these and other algo-
rithms have been implemented.
Another important parameter that must be chosen is the gridding
increment. This is partly determined by the algorithm chosen and also by the
data spacing. For example, if survey lines are far apart, there is little purpose
in specifying closely spaced nodes because of the low confidence that can be
assigned to the nodes located far from soundings. In contrast, when the
original data are closely spaced, large X- and Y-increments result in an
artificially smoothed surface because too many data points influence each
node. Some programs, such as CPS-3, can automatically calculate increments
that produce good results for a wide variety of survey patterns.
Applications and display of gridded data
Contouring of an area is one of the most common applications of mapping
software (Figure 46). Not only is this faster than hand-contouring, but the
results are uniform in style across the area and precision (i.e. repeatability) is
vastly superior.
The power of mapping programs is best demonstrated when analyzing
different surveys. If at all possible, the different data sets should be gridded
with the same algorithms and parameters in order that the results be as
comparable as possible. Difficulty arises if earlier surveys contain data much
sparser than later surveys. Under these circumstances, it is probably best if
the optimum grid is chosen for each data set; the grid produced for the
densely sampled survey should not be compromised just to maintain uni-
formity with an earlier survey. A simple application is to plot a suitable
contour to demonstrate the growth over time of a feature like a shoal
(Figure 47). Computation of volumetric changes over time is another applica-
tion (Figure 48). This can graphically demonstrate how shoals develop or
channels migrate.
Volumetric data can be used to estimate growth rates of features like
shoals. As an example, using all 18 of the 1,000-ft squares shown in
Figure 47, the overall change in volume of the East Pass ebb-tidal shoal
between 1967 and 1990 was only 19 percent (Figure 49). Although the shoal
had clearly grown to the southwest, the minor overall increase in volume
suggests that considerable sand may have eroded from the inner portions of
the shoal. In contrast, when plotting the change in volume of nine selected
Chapter 5 Analysis and Interpretation of Coastal Data
510000
SO9000
508000
O
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506000
EAST PASS»
FEB 1990
505000
1363000 1364000 1365000 1366000 1367000 1368000
Figure 46. Contoured bathymetry of the same area shown in Figures 44 and 45
squares, the growth over time was 600 percent. This underscores how criti-
cally numerical values such as growth rates depend upon the boundaries of the
areas used in the calculations. The user of secondary data beware!
Error analysis of gridded bathymetry
A crucial question is how much confidence can a researcher place on
growth rates which are based on bathymetric or topographic data?
Unfortunately, in the past, many researchers ignored or conveniently over-
looked the possibility that error bars may have been greater than calculated
trends, particularly if volumetric computations were based on data of question-
able quality.
Chapter 5 Analysis and Interpretation of Coastal Data
EAST PASS, DESTIN, FLORIDA
1363000 1364000 1365000 1366000 1367000 1368000
EAST PASS, DESTIN, FLORIDA
EBB—TIDAL SHOAL GROWTH
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Figure 47. Overall growth of an ebb-tidal shoal over 24 years is shown by the advance of
the 15-ft isobath. This isobath was chosen because it represented
approximately the mid-depth of the bar front. The 1,000-ft squares are
polygons used for volumetric computations
116
Chapter 5 Analysis and Interpretation of Coastal Data
510000
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Figure 48. Isopach map showing overall changes in bottom configuration between 1967 and 1990
at East Pass, Florida. Red contours (2-ft interval) represent erosion, while green (1-ft
interval) represent deposition. The migration of the channel thalweg to the east is
obvious, as is the growth of scour holes at the jetties. Map computed by subtracting
June 1967 surface from February 1990 surface. (Original bathymetric data courtesy of
Mobile District)
17
Chapter 5 Analysis and Interpretation of Coastal Data
Bide 2a
ne
Polygons 4-9, 11-13 iy
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(Millions)
pe ye
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Jan-67 Jan-71 Jan-75 Jan-79 Jan-83 Jan-87 Jan-91
Figure 49. Growth of the ebb-tidal shoal at East Pass, FL. Areas used in the computations
are shown in Figure 47. Growth rates are dramatically different depending upon
which polygons are included in the volumetric computations
This section outlines a basic procedure that can be used to calculate
volumetric errors, provided that estimates of vertical (AZ) accuracy are
available. If AZ values are unavailable for the specific surveys, standard
errors of + 0.5, + 1.0, or + 1.5 ft, based on the class of the survey, can be
used (Table 6). For coastal surveys close to shore, this method assumes that
errors in positioning (AX and AY) are random and have an insignificant effect
on the volumes compared with possible systematic errors in water depth
measurements, tide correction, and data reduction. For older historic surveys,
positioning error may be important, requiring a much more complicated analy-
sis procedure. Positioning accuracy of hydrographic surveys is discussed in
HQUSACE (1991) and NOAA (1976).
The error in volumetric difference between surveys can be estimated by
determining how much the average depth in each polygon changes from one
survey to another and then calculating an average depth change over all
polygons. Maximum likely error (MLE) is:
2 x AZ
AZ(ave)
118
Chapter 5 Analysis and Interpretation of Coastal Data
For example, if AZ = 0.15 m and AZ(ave) = 0.94 m, then MLE is:
= 0.32 = 32 percent
Note that this is for a Class 1 survey; many offshore surveys are not
conducted under such tight specifications. If AZ = 0.46 m, then MLE for the
above example = 97 percent. Under these circumstances, it becomes mean-
ingless to say that an area has changed in volume by a certain amount plus or
minus 97 percent.
The size of the polygons used in the calculation of AZ(ave) can influence
the MLE. A particular polygon that covers a large area may average AZ of
only 0.3 or 0.6 m, but water depths from spot to spot within the polygon may
vary considerably more. Therefore, by using smaller polygons, AZ will
typically be greater and MLE correspondingly less. However, the use of
smaller polygons must be balanced against the fact that positioning errors (AX
and AY) become correspondingly more significant.
More research is needed to quantify errors associated with the various
types of offshore surveys and to identify how these errors are passed through
computed quantities. They must not be neglected when analyzing geologic
data, particularly if management or policy decisions will be based on
perceived trends.
Sources of error in beach and nearshore surveys
Repetitive surveys of beach and nearshore profiles are commonly used to
compute volume changes along the shoreline. Several sources of random
error must be considered:
@ Survey scheduling. If there is a time lag between the onshore and
offshore surveys, the profiles may not join vertically because of genuine
sediment changes (assuming that the mismatch is not due to incorrect
tide, wave, datum, or other survey corrections).
@ Seasonal changes. The profile may change seasonally because of storm
or fair weather patterns. These temporary changes may mask long-term
trends.
@ Yearly variations. From year to year, the profile may change because
of varying global climate or oceanographic conditions. Again, the long-
term trend may be masked.
© Variations in regional sediment input. Unusual sediment inputs, such as
a flood on a nearby river, may mask the overall trend.
A more fundamental limitation in using widely spaced profiles is that major
morphological features between the survey lines are not included in the
Chapter 5 Analysis and Interpretation of Coastal Data
119
volumetric computations. On land, the lines can usually be adjusted to
accomodate unusual features. However, a major limitation of hydrographic
surveys is that the operators cannot see significant morphological changes
beforehand. For example, sand waves parallel to the survey track line or rock
pinnacles may not be recorded, yet these features may represent a significant
volume of material. In effect, these features are smoothed out of the data set.
Saville and Caldwell (1953) estimated that spacing errors were much more
important than measurement errors. They provided some figures and formu-
las for estimating these errors, although their work may need to be updated.
Coastal Data Interpretation with Numerical Models
Introduction
The use of numerical models in assessing changes in coastal geomorph-
ology is rapidly increasing in sophistication. Models are designed to numeri-
cally simulate hydrodynamic processes or simulate sediment response on
beaches, offshore, and in inlets. Specific types include models of wave
refraction and longshore transport, beach profile response, coastal flooding,
and shoreline change and storm-induced beach erosion (Birkemeier et al.
1987; Komar 1983; Kraus 1990). The judicious use of prototype data and
models can greatly assist the understanding of coastal processes and landforms
at a study site. Because models should be tested and calibrated, field data
collection or mathematical simulations of waves, tides, and winds at a project
site are usually required.
The advantage of tools like numerical models is that they can simulate
phenomena only rarely observed, can generate complex and long-duration
changes, and can incorporate judgements and measurements from many
sources. The use of numerical models is a highly specialized skill, requiring
training, an understanding of the underlying mathematics, and empirical ("real
world") experience of coastal processes. This section summarizes types of
models and introduces some of their strengths and limitations.
Types of models’
Coastal experience / empirical models. This represents the process by
which an understanding or intuitive feeling of coastal processes and
geomorphology is adapted and extrapolated from a researcher’s experience to
a specific project. Prediction through coastal experience without the support
of objective quantitative tools has many limitations, including severe subjectiv-
ity and a lack of criteria to use for optimizing projects. Complete reliance on
coastal experience places the full responsibility for project decisions on the
I Material in this section has been summarized from Kraus (1989).
120
Chapter 5 Analysis and Interpretation of Coastal Data
judgment of the researcher without recourse to testing the "model" with alter-
nate tools. An empirical model is often necessary before choosing a numeri-
cal model.
Beach change numerical models. Figure 50 summarizes the time ranges
and spatial coverage of numerical models used by CERC. Summaries of the
capabilities of the models follow:
TIME RANGE
HOURS MONTHS
(ONE STORM) (SEASON)
PROFILE CHANGE MODELS
3-D MODELS MULTI-CONTOUR
LINE MODELS
SEVERAL HUNDRED
METERS
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BEACH CHANGE PREDICTION MODELS
CLASSIFICATION BY SPATIAL AND TEMPORAL SCALES
Figure 50. Classification of beach change models (Kraus 1989)
@ Analytical models of shoreline change. These are closed-form mathe-
matical solutions of simplified differential equations for shoreline
change derived under assumptions of steady wave conditions, idealized
initial shoreline and structure positions, and simple boundary conditions.
Because of the many simplifications needed to obtain closed-form
solutions, these models are too crude to use for design.
121
Chapter 5 Analysis and Interpretation of Coastal Data
@ Profile change/beach erosion models. These are used to calculate sand
loss on the upper profile caused by storm surge and waves. The models
are one-dimensional, assuming that longshore currents are constant.
Extra work needs to be done to extend their use to simulate major
morphological features such as bars and berms.
@ Shoreline change models. These models generalize spatial and
temporal changes of shorelines analytically in response to a wide
range of beach, wave, coastal structure, initial and boundary
conditions. These conditions can vary with time. Because the profile
shape is assumed to remain constant, onshore and offshore movement of
any contour can be used to represent beach change. These models are
sometimes referred to as "one-contour line" or "one-line" models. The
representative contour line is usually taken to be the shoreline (which is
conveniently measured or available from a variety of sources). The
GENESIS model has been extensively used at CERC (Hansen and
Kraus 1989).
@ Multi-contour line / schematic three-dimensional (3-D) models. These
models describe the response of the bottom to waves and currents,
which can vary both cross- and alongshore. The fundamental
assumption of constant shoreline profile, necessary for the shoreline
change models, is relaxed. 3-D beach change models have not yet
reached wide application. They have been limited by their complexity
and their large requirements for computer resources and user expertise.
In addition, they are still limited by the ability to predict sediment
transport processes and wave climates.
Calibration and verification. Model calibration is the procedure of repro-
ducing with a model the changes in the shoreline position that were measured
over a certain time interval. Verification refers to the application of the
model to reproduce beach changes over a time interval different than the one
used for the model’s calibration. Successful verification means that the
model’s predictions are independent of the calibration interval. However, if
empirical coefficients or boundary conditions change (for example, by the
construction of an entrance channel which interrupts sand transport) the verifi-
cation is no longer valid. Therefore, a modeler must be aware of any changes
in the physical conditions at the study site that could affect the validity of his
model.
Unfortunately, in practice, data sets are usually insufficient to perform
rigorous calibration and verification of a model. Wave gage data are typically
missing, and historical shoreline change maps are usually spotty or unsuitable.
In situations where data are lacking, coastal experience must be relied upon to
provide reasonable input parameters. This underscores that considerable
subjectivity is part of the modeling procedure, even if the model itself may be
mathematically rigorous.
122
Chapter 5 Analysis and Interpretation of Coastal Data
Sensitivity testing. This refers to the process of examining changes in the
output of a model resulting from intentional changes in the input. If large
changes are caused by minor changes in the input, the overall results will
depend greatly upon the quality of the verification. Unfortunately, for many
practical applications, there is some degree of doubt in the verification
(Hansen and Kraus 1989). If a model is oversensitive to small changes in
input values, the range of predictions will be too broad and will in essence
provide no information.
In summary, numerical models are a valuable complement to prototype
data collection and physical (scale) models of coastal processes. However,
useful numerical models require empirical input during the calibration and
may be based on incomplete data sets. Therefore, the reader is urged to be
cautious of the output of any model and to be aware of the results of the
verification and sensitivity tests.
123
Chapter 5 Analysis and Interpretation of Coastal Data
6 Summary and Conclusions
A wide variety of techniques and technologies are available for data
collection, analysis, and interpretation of the geologic and geomorphic history
of coasts. One means of acquiring coastal data is through field data collection
and observation. This data may be numerical or non-numerical, and may be
analyzed further in the laboratory and office depending upon the type of data
collected. Laboratory studies are used to analyze geological properties of data
collected in the field, such as grain size or mineralogy, or to collect data
through physical model experiments, such as in wave tanks. Office studies
are part of most investigations, in that they involve the analysis and/or the
interpretation of data collected in the field and laboratory, from primary and
secondary sources. These include analysis of historic maps and photographs,
as well as application of techniques and numerical simulation of field,
laboratory, and office data. Typically, the best overall understanding of
environmental processes and the geologic history of coasts is acquired through
a combination of techniques and lines of inquiry. A suggested flowchart for
conducting studies of coastal geology is illustrated in Figure 51.
The techniques and technologies for the study of the geologic and
geomorphic history of coasts are applicable over a variety of time scales.
Three principal time scales that are important in assessing the geologic and
geomorphic changes of coasts include the following: 1) modern studies,
which are based largely on field data or laboratory and office experiments of
environmental processes; 2) historic studies, which are based largely on
information from maps, photography, archives, and other sources; and,
3) paleoenvironmental studies, which are based largely on stratigraphy and
associated geological and paleoenvironmental principles. In actuality,
however, these general time scale approaches overlap. Further, within each
of the categories, certain time scales may be of particular importance for
influencing coastal changes.
Before initiating detailed field, laboratory, or office study, it is recom-
mended that a thorough literature review and investigation of secondary data
sources be conducted. Existing sources of data are numerous, including
information on processes such as waves, water levels, and currents,
information on geomorphology such as geologic, topographic, and shoreline
change maps, as well as information that has been previously interpreted in
the literature or has yet to be interpreted, such as aerial photography and
124
Chapter 6 Summary and Conclusions
INFORMATION
COLLECTION
1, GEOLOGIC DATA
Reports: geology and
groundwater, USACE
Technical literature:
journals, dissertations
Maps: geologic, shoreline
change
Soils/rock surveys: USGS
2. TERRAIN/BATHYMETRY
Topographic: USGS
Bathymetric: NOAA, USACE
Imagery: SPOT, LANDSAT,
AVHRR, NASA, SOYUZ
Photographs: Controlled
aerial, NASA U2
3, ENVIRONMENTAL:
Meteorology
Wave: WIS hindcasts or
gage if avail.
Tide: NOAA or USACE
Stream gaging: USGS
4. ENGINEERING:
Boring logs: USACE and local
Project reports: USACE
and local
PRELIMI-
NARY
SITE VISIT
Assess existing
data
SITE VISIT
Aerial
overflight
Limited data
collection
Seek local
archives
lf more
data
needed
FIELD DATA
COLLECTION
OCEANOGRAPHIC
Wave gages
Current meters
Drifters, dye
Salinity, temperature
METEOROLOGY
TOPOGRAPHIC/
BATHYMETRIC
Beach profiles
Hydrographic surveys
Sidescan sonar
LIDAR
REMOTE SENSING
Aerial photography
Satellite images
GEOLOGIC
Trenches
Core borings
Surface samples
Rock boring
Sub bottom profiling
Sediment traps
If existing data sufficient
Figure 51. Flowchart for studies of coastal geology
ANALYSIS
Currents
Spectral analysis
of waves
Circulation/mixing
Suspended sediment
Shoreline changes
Volumetric
changes
Shoal growth
Erosion/deposition
Longshore drift
Channel migration
Sand wave
migration
Sediment properties
Atterburg limits/
shear strength
Heavy minerals
Tracers (forams,
oolites)
Dating (C14, K-Ar)
PRODUCTS
GEOLOGICAL MODELS
Inlet migration
Shoreline retreat/
advance
Sediment budgets
Geologic maps
PHYSICAL MODELS
Shoreline configurations
Harbor circulation
Effects of structures
Dredging modifications
NUMERICAL MODELS
Shoreline configurations
Effects of structures
Predict future changes
ENGINEERING
CONCLUSIONS
Channel location
Structure design
Harbor design
Dredging practice
Dredged material disposal
Residential construction
scanner images. If such a search is not conducted, assessment of geologic
history is likely to be less reliable and more difficult.
Many recent developments and techniques are used in the analysis of
coastal data sets. The evaluation of geologic and geomorphic history is
largely dependent upon the availability and quality of research equipment,
techniques, and facilities. New techniques are constantly being introduced,
and it is important that the coastal geologist and engineer stay abreast of new
techniques and methods, such as remote sensing and geophysical methods,
computer software and hardware developments, and new laboratory methods.
In addition to keeping up with recent developments, the coastal scientist or
engineer has the serious responsibility for making accurate interpretations of
the geologic and geomorphic history of coasts. It is vital that the important
research problem and objectives be clearly defined, that important variables be
incorporated in the study, and that the inherent limits and errors of the
research techniques and technologies be recognized, including problems and
assumptions involved in data collection and analysis. To some extent, the
coastal scientist or engineer can make some adjustments for various sources of
error. However, because of the geologic and geomorphic variability of
125
Chapter 6 Summary and Conclusions
coasts, extreme caution should be taken in extrapolating the final interpreta-
tions and conclusions regarding geologic history, particularly from data
covering a short time period or a small area. For these reasons, the assess-
ment of geologic and geomorphic history of coasts is an exceptionally chal-
lenging endeavor.
126
Chapter 6 Summary and Conclusions
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Appendix A
Glossary
ANOXIC Refers to ocean basins which contain little or no dissolved oxygen
and hence little or no benthic marine life. These conditions arise in basins
or fjords where physical circulation of seawater is limited.
BACK BARRIER Pertaining to the lagoon-marsh-tidal creek complex in the
lee of a coastal barrier island, barrier spit, or bay mouth barrier
(Figure 2).
BARRIERS, COASTAL Elongate, shore parallel, usually sandy features that
front coasts in many places and are separated from the mainland by bodies
of water of various sizes, and/or salt marshes, lagoons, mud or sand flats,
and tidal creeks (Figures 2 and 3).
BED FORMS Deviations from a flat bed generated by stream flow on the
bed of an alluvial channel.
BIOTURBATION The disturbance of sediment bedding by the activities of
burrowing organisms.
BOTTOMSET (bed) One of the horizontal or gently inclined sediment layers
deposited in front of the advancing forest beds of a delta.
CLOSURE DEPTH The depth beyond which sediments are not normally
affected by waves.
COASTAL PLAIN A relatively low plain of subdued topography underlain
by horizontal or gently sloping sedimentary strata extending inland of a
coastline.
CONTINENTAL SHELF The submerged zone bordering a coast from the
toe of the shoreface to the depth where there is a marked steepening of
slope.
DELTAIC Pertaining to river deltas.
Appendix A Al
A2
DOWNDRIFT The direction in which littoral drift is moving.
DENDROCHRONOLOGY The examination and correlation of growth rings
of trees with the purpose of dating events in the recent past.
EL NINO Warm equatorial water which flows southward along the coast of
Peru during February and March of certain years. It is caused by
poleward motions of air, which cause coastal downwelling, leading to the
reversal in the normal north-flowing cold coastal currents. El Nino can
cause great reduction in the fisheries and severe economic hardships.
ESTUARY A widened tidal mouth at a river valley where fresh water comes
into contact with sea water, resulting in mixing and a complex biological
and chemical environment.
EUSTATIC SEA LEVEL CHANGE Change in the relative volume of the
world’s ocean basins and the total amount of ocean water. It must be
measured by recording the movement in sea surface elevation relative to a
stable, undeformed, universally adopted reference frame.
FLUVIAL Pertaining to streams; e.g. fluvial sediments.
FORESET (bed) Inclined layers of a cross-bedded unit, specifically on the
frontal slope of a delta or the lee of a dune.
HALF-LIFE The time required for half of the atoms of a radioactive element
to disintegrate into atoms of another element.
HEAVY MINERAL Mineral species with a specific gravity greater than a
heavy liquid such as bromoform used to separate heavies from lighter
minerals. Usually with a specific gravity of around 2.9 or higher.
HOLOCENE An epoch of the Quaternary period from the end of the
Pleistocene (approximately 8,000 years ago) to the present. Often used as
a synonym for recent.
INLET A connecting passage between two bodies of water (Figure 2).
INTERTIDAL Between high and low water.
JETTY A shore-perpendicular structure built to stabilize an inlet and prevent
the inlet channel from filling with sediment.
LAGOON Open water between a coastal barrier and the mainland. Also
water bodies behind coral reefs and enclosed by atolls (Figure 2).
LAMINAE (or lamina) The thinnest recognizable layers in a sediment or
sedimentary rock.
Appendix A
LICHENOMETRY The study of lichens, complex thallophytic plants
consisting of algae and fungus growing in symbiotic association, to
determine relative ages of sedimentary structures.
LITHOLOGY The general character of a rock or sediment.
LITTORAL DRIFT The movement of sediment alongshore. Also the mate-
rial being moved alongshore.
MARSH A permanently or periodically submerged low-lying area that is
vegetated.
MUD FLAT A level area of fine silt along a shore alternately covered or
uncovered by the tide or covered by shallow water.
NATURAL TRACER A component of a sediment deposit that is unique to a
particular source and can be used to identify the source and transport
routes to a place of deposition.
OVERWASH A process in which waves penetrate inland of the beach.
Particularly common on low barriers.
PALEOECOLOGY The study of the relationship between ancient organisms
and their environment.
PALEOSOLS A buried (possibly ancient) soil.
PALYNOLOGY The study of pollen and spores in ancient sediments.
PEAT Unconsolidated deposit of semicarbonized plant remains in a water-
saturated environment such as a bog. Peat is considered to be an early
stage in the development of coal.
PEDOGENESIS Soil formation.
PITCH Angle between the horizontal and any linear feature.
PLEISTOCENE An epoch of the Quaternary period before the Holocene. It
began 2 to 3 million years ago and lasted until the start of the Holocene
epoch about 8,000 years ago.
REEF Ridgelike or moundlike structure built by sedentary calcareous
organisms, especially corals.
RELATIVE SEA LEVEL Elevation of the sea surface relative to a nearby
land surface.
Appendix A
A3
A4
SEDIMENT Solid fragmented material (sand, gravel, silt, etc.) transported
by wind, water, or ice or chemically precipitated from solution or secreted
by organisms.
SEISMOGRAPH An instrument that records elastic waves in the ground
produced by earthquakes, explosions, landslides, or ocean waves.
SELECTIVE SORTING A process occurring during sediment transport that
tends to separate particles according to their size, density, and shape.
SHOREFACE A seaward-sloping ramp, seaward of the low water line that
leads to the inner continental shelf and is characteristically steeper than the
shelf floor (Figure A-1).
SHORELINE The line of demarcation between a shore and the water. May
fluctuate periodically due to tide or winds.
SOIL Unconsolidated sediments which contain nutrients, organic matter,
etc., and serve as a medium for the growth of land plants.
SPIT An elongated, usually sandy, feature aligned parallel to the coast that
terminates in open water (Figure 2).
STRAND PLAIN A prograded shore built seawards by waves and currents
(Figure 3).
SUBTIDAL Below the low water datum; thus, permanently submerged.
TEPHRA Clastic materials ejected from a volcano and transported through
the air.
TEPHROCHRONOLOGY The collection, description, and dating of tephra.
THERMOLUMINESCENCE The property displayed by many minerals of
emitting light when heated.
TIDAL CREEK A creek draining back-barrier areas with a current
generated by the rise and fall of the tide.
TIDAL SHOALS Shoals that accumulate near inlets due to the transport of
sediments by tidal currents associated with the inlet (Figure 2).
TILT Sideways inclination of an aircraft or spaceship.
UPDRIFT The direction along a coast from which littoral drift material is
moving.
VARVE A sedimentary lamina or set of laminae deposited in a body of still
water in a year’s time.
Appendix A
WASHOVER Sediment deposited inland of a beach by overwash processes
(Figure 2).
WEATHERING Destructive process by which atmospheric or biologic
agents change rocks, causing physical disintegration and chemical
decomposition.
YAW Refers to an aircraft’s or spaceship’s turning by angular motion about
a vertical axis.
Appendix A
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Appendix B
List of Wave Information
Studies (WIS) Reports
Atlantic, Pacific, and Gulf of Mexico Reports
Corson, W.D., Resio, D. T., and Vincent, C. L. 1980 July). "Wave Infor-
mation Study of U.S. Coastlines; Surface Pressure Field Reconstruction for
Wave Hindcasting Purposes," TR HL-80-11, WIS Report 1.
Corson, W. D., Resio, D. T., Brooks, R. M., Ebersole, B. A., Jensen,
R. E., Ragsdale, D. S., and Tracy, B. A. 1981 (January). "Atlantic Coast
Hindcast, Deepwater Significant Wave Information," WIS Report 2.
Corson, W. D., and Resio, D. T. 1981 (May). "Comparisons of Hindcast
and Measured Deepwater Significant Wave Heights," WIS Report 3.
Resio, D. T., Vincent, C. L., and Corson, W. D. 1982 (May). "Objective
Specification of Atlantic Ocean Windfields from Historical Data," WIS
Report 4.
Resio, D. T. 1982 (March). "The Estimation of Wind-Wave Generation in a
Discrete Spectral Model," WIS Report 5.
Corson, W. D., Resio, D. T., Brooks, R. M., Ebersole, B. A., Jensen,
R. E., Ragsdale, D. S., and Tracy, B. A. 1982 (March). "Atlantic Coast
Hindcast Phase II, Significant Wave Information," WIS Report 6.
Ebersole, B. A. 1982 (April). "Atlantic Coast Water-Level Climate," WIS
Report 7.
Jensen, R. E. 1983 (September). "Methodology for the Calculation of a
Shallow Water Wave Climate," WIS Report 8.
Jensen, R. E. 1983 (January). "Atlantic Coast Hindcast, Shallow-Water
Significant Wave Information," WIS Report 9.
Appendix B
B1
B2
Ragsdale, D. S. 1983 (August). "Sea-State Engineering Analysis System:
Users Manual," WIS Report 10.
Tracy, B. A. 1982 (May). "Theory and Calculation of the Nonlinear Energy
Transfer Between Sea Waves in Deep Water," WIS Report 11.
Resio, D. T., and Tracy, B. A. 1983 (January). "A Numerical Model for
Wind-Wave Prediction in Deep Water," WIS Report 12.
Brooks, R. M., and Corson, W. D. 1984 (September). "Summary of
Archived Atlantic Coast Wave Information Study, Pressure, Wind, Wave, and
Water Level Data," WIS Report 13.
Corson, W. D., Abel, C. E., Brooks, R. M., Farrar, P. D., Groves, B. J.,
Jensen, R. E., Payne, J. B., Ragsdale, D. S., and Tracy, B. A. 1986
(March). "Pacific Coast Hindcast, Deepwater Wave Information," WIS
Report 14.
Corson, W. D., and Tracy, B. A. 1985 (May). “Atlantic Coast Hindcast,
Phase II Wave Information: Additional Extremal Estimates," WIS Report 15.
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 (May). "Pacific
Coast Hindcast Phase II Wave Information," WIS Report 16.
Jensen, R. E., Hubertz, J. M., and Payne, J. B. 1989 (March). "Pacific
Coast Hindcast, Phase III North Wave Information," WIS Report 17.
Hubertz, J. M., and Brooks, R. M. 1989 (March). "Gulf of Mexico
Hindcast Wave Information," WIS Report 18.
Able, C. E., Tracy, B. A., Vincent, C. L., and Jensen, R. E. 1989 (April).
“Hurricane Hindcast Methodology and Wave Statistics for Atlantic and Gulf
Hurricanes from 1956-1975," WIS Report 19.
Jensen, R. E., Hubertz, J. M., Thompson, E. F., Reinhard, R. D., Groves,
B., Brown, W. A., Payne, J. B., Brooks, R. M., and McAneny, D. S.
"Southern California Hindcast Wave Information," in preparation, WIS
Report 20.
Tracy, B. A., and Hubertz, J. M. 1990 (November). "“Hindcast Hurricane
Swell for the Coast of Southern California," WIS Report 21.
Hubertz, J. M., and Brooks, R. M. "Verification of the Gulf of Mexico
Hindcast Wave Information," in preparation, WIS Report 28.
Appendix B
Great Lakes Reports
Resio, D. T., and Vincent, C. L. 1976 (January). "Design Wave
Information for the Great Lakes; Report 1: Lake Erie," TR H-76-1.
Resio, D. T., and Vincent, C. L. 1976 (March). "Design Wave Information
for the Great Lakes; Report 2: Lake Ontario," TR H-76-1.
Resio, D. T., and Vincent, C. L. 1976 (June). “Estimation of Winds Over
the Great Lakes," MP H-76-12.
Resio, D. T., and Vincent, C. L. 1976 (November). "Design Wave Infor-
mation for the Great Lakes; Report 3: Lake Michigan," TR H-76-1.
Resio, D. T., and Vincent, C. L. 1977 (March). "Seasonal Variations in
Great Lakes Design Wave Heights: Lake Erie," MP H-76-21.
Resio, D. T., and Vincent, C. L. 1977 (August). "A Numerical Hindcast
Model for Wave Spectra on Water Bodies with Irregular Shoreline Geometry:
Report 1, Test of Nondimensional Growth Rates," MP H-77-9.
Resio, D. T., and Vincent, C. L. 1977 (September). "Design Wave Infor-
mation for the Great Lakes; Report 4: Lake Huron," TR H-76-1.
Resio, D. T., and Vincent, C. L. 1978 (June). “Design Wave Information
for the Great Lakes; Report 5: Lake Superior," TR H-76-1.
Resio, D. T., and Vincent, C. L. 1978 (December). “A Numerical Hindcast
Model for Wave Spectra on Water Bodies with Irregular Shoreline
Geometry," Report 2, MP H-77-9.
Driver, D. B., Reinhard, R. D., and Hubertz, J. M. 1991 (October).
"Hindcast Wave Information for the Great Lakes: Lake Erie," WIS
Report 22.
Hubertz, J. M., Driver, D. B., and Reinhard, R. D. 1991 (October).
"Hindcast Wave Information for the Great Lakes: Lake Michigan," WIS
Report 24.
Reinhard, R. D., Driver, D. B., and Hubertz, J. M. 1991 (December).
"Hindcast Wave Information for the Great Lakes: Lake Ontario," WIS
Report 25.
Reinhard, R. D., Driver, D. B., and Hubertz, J. M. 1991 (December).
"Hindcast Wave Information for the Great Lakes: Lake Huron," WIS
Report 26.
Appendix B
B3
B4
Driver, D. B., Reinhard, R. D., and Hubertz, J. M. 1992 (January).
"Hindcast Wave Information for the Great Lakes: Lake Superior," WIS
Report 23.
General User’s Information
Hubertz, J. M. 1992 (June). “User’s Guide to the Wave Information Studies
(WIS) Wave Model, Version 2.0," WIS Report 27.
NOTE:
All reports listed above were published by and are available from the
U.S. Army Engineer Waterways Experiment Station, Coastal Engineering
Research Center, 3909 Halls Ferry Road, Vicksburg, MS 39180-6199.
Appendix B
Appendix C
List of Selected Sources for
Aerial Photography and Other
Remote Sensing Data
Agricultural Stabilization and Conservation Service (ASCS)
Aerial Photography Field Office
2222 West 2300 South
P.O. Box 30010
Salt Lake City, UT 84130
(801)524-5856
Soil Conservation Service (SCS)
Cartographic Division
P.O. Box 269
101 Catalpa Drive
Lapalta, MD 20646
(301)870-3555
Bonneville Power Administration (BPA)
Photogrammetry Unit
905 NE 11th Ave
Rt. EFBK
Portland, OR 97208
(503)230-4643
Bureau of Land Management (BLM)
Service Center
Denver Federal Center, Building 50
P.O. Box 25047
Denver, CO 80225-0047
(303)236-6452
Appendix C
C1
CZ
Defense Intelligence Agency (DIA)
Clarenton Square Building
3033 Wilson Blvd
Arlington, VA 22201
(703)284-1124
Susquehanna River Basin Commission (SRBC)
1721 N. Front Street
Harrisburg, PA 17102
(717)638-0422
National Ocean Survey (NOS)
Coastal Mapping Division, C-3415
Rockville, MD 20852
(301)713-0610
U.S. Forest Service (USFS)
Division of Engineering
Washington, DC 20250
(202)205-1400
USFS Regional Offices:
Regional Forester
U.S. Forest Service
Federal Building
P.O. Box 7669
Missoula, MT 59807
(406)326-3511
Regional Forester
U.S. Forest Service
11177 W 8th Ave
Box 25127
Lakewood, CO 80225
(303)236-9427
Regional Forester
U.S. Forest Service
324 25th St.
Ogden, UT 84401
(801)625-5605
Appendix C
Regional Forester
U.S. Forest Service
Printing and Reproduction Section, Room 548
630 Sansome Street
San Francisco, CA 94111
(415)705-2870
Regional Forester
U.S. Forest Service
333 SW First
Portland, OR 97204-3304
Regional Forester
U.S. Forest Service
1720 Peachtree Road, NW
Atlanta, GA 30367
(404)347-4177
Regional Forester
U.S. Forest Service
310 W. Wisconsin Avenue
Milwaukee, WI 53203
(414)297-3693
Regional Forester
U.S. Forest Service
P.O. Box 21628
Juneau, AK 99802-1628
(907)586-8863
U.S. Bureau of Reclamation (USBR)
Engineering and Research Center
P.O. Box 25007
Denver, CO 80225
(303)236-8098)
USBR Regional Offices:
Pacific Northwest Region
Federal Building
550 W. Fort Street, Box 043
Boise, ID 83724-0043
(208)334-1938
Appendix C
C3
C4
Mid-Pacific Region
Federal Office Building
2800 Cottage Way
Sacramento, CA 95825
(916)978-5135
Lower Colorado Region
P.O. Box 61470
Boulder City, NE 89006-1470
(702)293-8411
Upper Colorado Region
P.O. Box 11568
Salt Lake City, UT 84147
(801)542-5592
Great Plains
P.O. Box 36900
Billings, MT 59107-6900
(406)657-6214
U.S. Geological Survey (USGS)
Mid-Continent Mapping Center
Map and Field Data Section
1400 Independence Rd
Rolla, MO 65401
(314)341-0800
U.S. Geological Survey (USGS)
Rocky Mountain Mapping Center
Map and Field Data Section
Federal Center, Building 25
Denver, CO 80225
(303)236-5825
U.S. Geological Survey (USGS)
Western Mapping Center
Map and Field Data Section
345 Middlefield Road
Menlo Park, CA 94025
(415)329-4254
U.S. Geological Survey (USGS)
Eastern Mapping Center
Mapping and Field Data Section
536 National Center
Reston, VA 22092
(703)648-6002
Appendix C
U.S. Geological Survey (USGS)
Earth Resources Observation Systems
(EROS) Data Center
10th and Dakota Avenue
Sioux Falls, SD 57198
(605)594-7123
U.S. Geological Survey (USGS)
EROS Applications Assistance Facility
Stennis Space Center, Bldg 101
Bay St. Louis, MS 39529
(601)688-3541
EOSAT Corporation (Landsat images and digital products)
4300 Forbes Boulevard
Lanham, MD 20706
(301)552-0537 FAX: (301)552-0507
Hughes STX Satellite Mapping Technologies
(Almaz-1 Synthetic Aperture Radar Satellite Data)
4400 Forbes Boulevard
Lanham, MD 20706-4392
(301)794-5330 FAX: (301)306-0963
SPOT Image Corporation (SPOT images and digital products)
1897 Preston White Drive
Reston, VA 22091-4368
(703)620-2200 FAX: (703)648-1813
NOAA/National Environmental Satellite, Data & Information Service
(NOAA meteorological satellite images and digital products)
World Weather Building, Room 100
Washington, DC 20233
(202) 377-2985
Appendix C
C5
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Fatard Comite, Gull hing 2S) ane
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Appendix D
Addresses of Government
Agencies Producing Maps
FEDERAL GOVERNMENT
Defense Mapping Topographic Center
4600 Sangamore Rd
Bethesda, MD 20816-5003
(301)227-2050
Federal Communications Commission
Office of Public Information
1919 M Street NW
Washington, DC 20554
(202)632-7106
Federal Railroad Administration
Office of Public Affairs, ROA-30
400 Seventh Street NW
Washington, DC 20590
(202)366-0881
International Boundary Commission
United States and Canada
1250 23rd St. NW, Suite 3405
Washington, DC 20037
(202)736-9100
International Boundary and Water Commission
United States and Mexico, United States Section
Commons Bldg. C, Suite 310
4171 North Mesa
El Paso, TX 79902-1422
(915)534-6700
Appendix D
D2
Interstate Commerce Commission
Office of Public Information
12th St. & Constitution Ave. NW
Washington, DC 20423
(202)927-7119
Library of Congress
Geography and Map Division
James Madison Memorial
101 Independence Ave, SE
Washington, DC 20540
(202)707-8530
Tennessee Valley Authority
Mapping Services Branch
111 Haney Building
Chattanooga, TN 37402-2801
(615)751-6277
U.S. Army Engineer District, Chicago
111 N. Canal Street, Suite 600
Chicago, IL 60606-7206
(312)353-6400
U.S. Army Engineer District, Louisville
Post Office Box 59
Louisville, KY 40201-0059
(502)582-5639
U.S. Army Engineer District, Nashville
Post Office Box 1070
Nashville, TN 37202-1070
(615)736-7161
U.S. Army Engineer District, Omaha
215 North 17th Street
Omaha, NE 68102
(402)221-3917
U.S. Army Engineer District, Vicksburg
2101 N. Frontage Road
Post Office Box 60
Vicksburg, MS 39181-0060
(601)634-5000
Appendix D
U.S. Bureau of the Census
Subscriber Service Section (Pubs)
Administrative Service Division
Washington, DC 20233
(301)763-4051
U.S. Bureau of Indian Affairs
Office of Public Information
1849 Sea Street, NW
Washington, DC 20240-2620
(202)208-3711
U.S. Bureau of Land Management
Office of Public Affairs
1849 Sea Street, NW, RM 5600 MIB
Washington, DC 20240-9998
(202)208-3435
U.S. Geological Survey
Branch of Distribution
Box 25286, Federal Center
Denver, CO 80225
(303)236-7477
U.S. National Archives and Records Service
Cartographic Archives Division (NNSC)
Washington, DC 20408
(703)756-6700
U.S. National Climatic Center
Federal Building
Asheville, NC 28801
(704)259-0682
U.S. National Ocean Survey
Coastal Ocean Program
1100 Wayne Ave
Silverspring, MD 20910
(301)427-2089
U.S. National Park Service
Office of Public Inquiries, Room 3045
P.O. Box 37127
Washington, DC 20013-7127
(202)208-4621
Appendix D
D4
U.S. National Weather Service
1325 EW Highway
Silver Spring, MD 20910
(301)713-0689
U.S. Soil Conservation Service
Information Division
Post Office Box 2890
Washington, DC 20013
State Highway Departments
State Capitals
Appendix D
Appendix E
List of Journals That Contain
Articles Pertaining to the
Geologic and Geomorphic
History of Coasts
American Association of Petroleum Geologists Bulletin
American Journal of Science
Annals of the Association of American Geographers
Arctic and Alpine Research
Australian Journal of Science
Bulletin of the Association of Engineering Geologists
Bulletin of the International Association of Scientific Hydrology
Canadian Journal of Earth Sciences
Catena
Climatic Change
Continental Shelf Research
Earth Science Reviews
Earth Surface Processes and Landforms
Ecology
Environmental Conservation
Environmental Geology and Water Sciences
Environmental Management
EOS
Geografiska Annaler
Geographia Polonia
Geographical Journal
Geographical Review
Geography
Geo Journal
Geological Society of America Bulletin
Geology
Geomorphology
Geophysical Research Letters
The Holocene
Appendix E EI
E2
Hydrological Sciences
Journal of Applied Meteorology
Journal of Climatology
Journal of Coastal Engineering
Journal of Coastal Research
Journal of Fluid Mechanics
Journal of Geophysical Research
Journal of Geology
Journal of the Hydraulics Division, ASCE
Journal of Hydrology
Journal of Marine Research
Journal of Meteorology
Journal of Ocean and Shoreline Management
Journal of Physical Oceanography
Journal of Quaternary Science
Journal of River Management
Journal of Sedimentary Petrology
Journal of Soil and Water Conservation
Journal of Soil Science
Journal of Waterway, Port, Coastal and Ocean Engineering, ASCE
Marine Geology
Nature
Paleoclimatology, Paleoecology, and Paleography
Photogrammetric Engineering and Remote Sensing
Physical Geography
Proceedings of the Institute of Civil Engineers
Professional Geographer
Progress in Physical Geography
Quaternaria
Quaternary Research
Quaternary Science Reviews
Remote Sensing of the Environment
Science
Scientific American
Sedimentary Geology
Sedimentology
Shore and Beach
Soil Science Society of America Proceedings
Southeastern Geology
Stochastic Hydrology and Hydraulics
Transactions of the American Geophysical Union
Transactions of the Gulf Coast Assoc. of Geological Societies
Transactions of the Institute of British Geographers
Water Resources Bulletin
Water Resources Research
Zeitschrift fur Geomorphologie
Appendix E
Appendix F
Field Reconnaissance for
Coastal Erosion Study, Site
Visit Checklist
Surveys - Profiles
a. Profiles obtained using bank level & tape
b. Two typical beach profiles - extending from low tide line to at least
30 m beyond the toe of bluff or extreme high water mark
c. Reference location of profiles to local survey monuments or prominent
feature
d. Date & time of tide line measurement
e. Identify location of extreme high water line
jf. Approximate dimensions of erosion area
g. Photographs of beach where profiles are located
Sediments/Geology
a. Visual classification of eroding beach and bank
sediments
(1) Sandy beach - photos within 1 ft
(2) Gravel beach - photos within 2 ft
b. Occurrence of permafrost, ice lenses, or other frozen
ground features in the project area
d. Location of bedrock, gravel, sand, etc.
Appendix F FA
F2
e. Structure and lithologies of bedrock
Ff. Mineralogic/lithologic composition of beach material
g. Geomorphic features - bedrock and sediment types
Wave Climate - Erosion Description (local records & sources)
a. Erosion Rate
b. Time of year erosion occurs
c. Direction and magnitude of significant storms
d. Height, frequency, and period of storm-generated waves
e. Photographs of the eroding area
f. Possible erosion causes
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
Wave action
Tidal action
Storm surge
Upland drainage
Sloughing of bluff material
Ice action
Thermal degradation in permafrost areas
Uses by people, such as boat wakes and upland traffic (foot or
vehicle)
Real Estate Concerns
a. Brief description and photographs of threatened representative structures
b. Estimate value of land, structures, and utilities which are considered
threatened
c. Identify potential land available for relocation
d. Estimate value of land needed for relocation
Appendix F
REPORT DOCUMENTATION PAGE ee a
for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, |
Da Staining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this
Sollection of information, including suggestions for reducing this burden. to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson
Davis Highway, Suite 1204, Arlington, VA 22202-4302, and to the Office of Management and Budget, Paperwork Reduction Project (0704-0188), Washington, DC 20503.
1. AGENCY USE ONLY (Leave blank) | 2. REPORT DATE 3. REPORT TYPE AND DATES COVERED —
4. TITLE AND SUBTITLE ae [S. FUNDING NUMBERS
Technologies for Assessing the:Geologic and Geomorphic
History of Coasts
6. AUTHOR(S)
See reverse.
WU 32538
8. PERFORMING ORGANIZATION
REPORT NUMBER
7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)
See reverse. Technical Report
CERC-93-5
10. SPONSORING / MONITORING
AGENCY REPORT NUMBER
9. SPONSORING/ MONITORING AGENCY NAME(S) AND ADDRESS(ES)
Department of the Army
U.S. 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 geologic and geomorphic history of coastal areas can be assessed using a four-part process:
© Thorough examination of technical literature and existing data from various archives.
© Field data collection and observation.
© Laboratory examination of samples collected in the field.
© Office interpretation of all project data, both newly collected and historic.
It is vital that existing sources of data be evaluated before field studies are undertaken to prevent duplicating
efforts and to guide the optimum sampling scheme. Field studies must be designed to answer basic questions
about the study area:
© What physical processes affect the region?
© Does the underlying geology have a major influence?
© How has man modified or damaged the local environment?
© How much data can we afford to collect?
14. SUBJECT TERMS
Coastal geology Geomorphology
Coastal studies Oceanographic instruments
Geologic data
17. SECURITY CLASSIFICATION | 18. SECURITY CLASSIFICATION
OF REPORT OF THIS PAGE
UNCLASSIFIED UNCLASSIFIEI
= Standard Form 298 (Rev. 2-89)
a oe Prescribed by ANSI Std. 239-18
298-102
15. NUMBER OF PAGES
174
16. PRICE CODE
20. LIMITATION OF ABSTRACT
. SECURITY CLASSIFICATION
OF ABSTRACT
6. AUTHORS (Continued).
Andrew Morang
Joann Mossa
Robert Larson
7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES).
USAE Waterways Experiment Station
Coastal Engineering Research Center
3909 Halls Ferry Road
Vicksburg, MS 39180-6199
Department of Geography
University of Florida
Gainesville, FL 32611
USAE Waterways Experiment Station
Geotechnical Laboratory
3909 Halls Ferry Road
Vicksburg, MS 39180-6199
13. ABSTRACT (Continued).
@ Do we have the knowledge, ability, managerial skill, or money to properly analyze the data we want to
collect at the project site?
@ Is it more important to conduct a long-term sampling program or a shorter, more intensive program?
Coastal scientists must be aware of how historic data were collected, and what assumptions and procedures
were used by the original field technicians and analysts. The quality of historic data may vary from excellent to
worse than useless.
The use of instruments in the coastal zone is far from straightforward; incorrect use of instruments may lead
to erroneous results because the wrong parameters may be monitored. Coastal engineers are urged to consult
specialists in the field to help plan and conduct field studies. The analysis of contemporary coastal data is
difficult and also requires the skills of specialists with experience in the particular types of instruments and
methods that have been used.
Destroy this report when no longer needed. Do not retum it to the originator.
DEPARTMENT OF THE ARMY
WATERWAYS EXPERIMENT STATION, CORPS OF ENGINEERS SPECIAL
9909 HALLS FERRY ROAD
VICKSBURG, MISSISSIPPI 39180-6199 FOURTH CLASS
U.S. FOSTAGE FALD
VICKSBURG, 45
Ofoetel euenee FERHIT NO. 85
ee7/Lie2/ 1
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