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CECW-EH-W Department of the Army EM 1110-2-1204
U.S. Army Corps of Engineers
Engineer Manual Washington, DC 20314-1000 10 July 1989
1110-2-1204
Engineering and Design
ENVIRONMENTAL ENGINEERING FOR
COASTAL SHORE PROTECTION
Distribution Restriction Statement
Approved for public release; distribution is
unlimited.
EM 1110-2-1204
10 July 89
US Army Corps
of Engineers
ENGINEERING AND DESIGN
Environmental Engineering
for Coastal Protection
ENGINEER MANUAL
DEPARTMENT OF THE ARMY EM 1110-2-1204
US Army Corps of Engineers
CECW-EH Washington, DC 20314-1000
Engineer Manual
No. 1110-2-1204 10 July 1989
Engineering and Design
ENVIRONMENTAL ENGINEERING FOR COASTAL SHORE PROTECTION
1. Purpose. The purpose of this manual is to provide guidance in
enviromental engineering for coastal shore protection projects.
2. Applicability. This manual applies to all field operating activities
that have responsibility for environmental impact studies related to
coastal shore protection projects.
3. Discussion. This manual summarizes research and field experience
gained in the area of environmental engineering for coastal shore
protection. It addresses both natural and human induced changes in the
coastal zone; the structural and nonstructural measures that coastal
engineers employ against these changes; and the desirable and adverse
impacts of the measures. This manual is intended to be compatible and
used in conjunction with other OCE engineering manuals and the coastal
Engineering Research Center's "Shore Protection Manual." As new
information becomes available the manual will be periodically revised.
FOR THE COMMANDER:
DEPARTMENT OF THE ARMY EM 1110-2-1204
US Army Corps of Engineers
CECW-EH Washington, DC 20314-1000
Engineer Manual
No. 1110-2-1204 10 July 1989
Engineering and Design
ENVIRONMENTAL ENGINEERING FOR COASTAL SHORE PROTECTION
Table of Contents
Subject Paragraph Page
CHAPTER 1. INTRODUCTION
Purpose l-l l-l
Applicability l-2 l-l
Scope l-3 l-l
References l-4 l-l
Appendices l-5 l-2
Glossary l-6 l-3
CHAPTER 2. OVERVIEW OF COASTAL SHORE PROTECTION PROJECTS
Classification 2-l 2-l
Alternatives 2-2 2-l
Considerations 2-3 2-l
CHAPTER 3. ENVIRONMENTAL RESOURCES
Environmental Requirements 3-l 3-l
Environmental Resource Categories 3-2 3-4
Physical 3-3 3-4
Water Quality 3-4 3-5
Biological 3-5 3-6
Recreational 3-6 3-8
Aesthetic 3-7 3-9
Cultural 3-8 3-11
CHAPTER 4. PROTECTIVE BEACHES AND DUNES
Protective Beaches 4-l 4-l
Dunes 4-2 4-15
CHAPTER 5. HUMAN-MADE STRUCTURES
Bulkheads, Seawalls, and Revetments 5-l 5-l
Jetties and Breakwaters 5-2 5-9
Groins 5-3 5-25
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Subject Paragraph Page
CHAPTER 6. NONSTRUCTURAL ALTERNATIVES
Salt Marshes 6-1 6-l
Seagrasses 6-2 6-7
CHAPTER 7. ENVIRONMENTAL MONITORING
Monitoring Programs 7-1 7-l
Data Collection 7-2 7-3
Habitat Assessment 7-3 7-16
Data Analysis, Interpretation, and Presentation 7-4 7-23
CHAPTER 8. MITIGATION DECISION ANALYSIS
Policy 8-1 8-l
Definitions 8-2 8-l
Key Concepts for Mitigation 8-3 8-2
Examples 8-4 8-3
APPENDIX A BIBLIOGRAPHY A-l
APPENDIX B MODELS B-l
APPENDIX C ENVIRONMENTAL PROTECTION STATUTES AND OTHER
ENVIRONMENTAL REQUIREMENTS C-l
APPENDIX D ESTUARINE/MARINE SPECIES PROFILES D-l
GLOSSARY GLOSSARY-l
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LIST OF TABLES
Table Page
2-l Classification of Coastal Engineerinq Solutions 2-2
2-2 Classification of Coastal Engineering Considerations 2-3
3-l Recreational Activities and Facilities 3-10
5-l Environmental Design Considerations for Revetments,
Seawalls, and Bulkheads 5-10
7-l Sediment Sampling Equipment 7-9
7-2 An Example of a BRAT Data Tabulation 7-22
B-l Froude Criteria Scaling Relationships for physical
Coastal Models B-16
LIST OF FIGURES
Figure Page
4-l Visual definition of terms describing a typical
beach profile 4-2
4-2 Beach nourishment operation, Mayport, Florida
(courtesy of US Army Engineer District, Jacksonville) 4-3
4-3 Schematic diagram of storm wave attack on beach
and dune 4-4
4-4 Reef fauna near outer edge of second reef off
Golden Beach, Florida (Courtenay et al. 1980) 4-10
4-5 Nesting sea turtle 4-11
4-6 Recreational use of Delray Beach, Florida 4-12
4-7 Dunes under wave attack, Cape Cod, Massachusetts
(courtesy of Stephen P. Leatherman) 4-20
4-8 Dunes erosion during severe storm, Cape Cod,
Massachusetts ((courtesy of Stephen P. Leatherman) 4-20
4-9 Dissipative surf conditions during storm, Outer Banks,
North Carolina 4-22
4-10 Vegetation landward (left on photo) of artificially
stabilized dune, Padre Island, Texas (courtesy
of Bill E. Dahl) 4-25
4-11 Salt marshes landward of barrier island system,
Murrels Inlet, South Carolina 4-26
4-12 Linear shaped, planted dune system, Outer Banks,
North Carolina (courtesy of R. P. Savage) 4-28
5-l Steel sheet pile bulkhead 5-2
5-2 Concrete curved-face seawall 5-4
5-3 Quarrystone revetment 5-5
5-4 Concrete combination stepped- and curved-face
seawall with public access points 5-8
5-5 Quadripod and rubble-mound breakwater 5-13
5-6 Sand bypassing, Murrells Inlet, South Carolina 5-14
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LIST OF FIGURES (Continued)
Figure Page
5-7 Erosion and accretion patterns in association
with detached and attached breakwaters 5-18
5-8 Breakwater protecting recreational harbor,
Santa Barbara, California 5-23
5-9 Rubble-mound groin 5-27
5-10 General shoreline changes associated with single
or multiple groins 5-29
5-11 Irregular beach formed by cellular steel
sheet-pile groin 5-32
6-1 Oldest reported salt marsh planting in the
United States 6-2
6-2 Aesthetic comparison of nonstructural (salt marsh
planting) and structural (revetment) measures 6-8
6-3 Cost comparison of alternative erosion control
measures (after Knutson and Woodhouse 1983) 6-9
6-4 Typical seagrass and generalized method of making
transplant unit 6-11
6-5 Sediment capture in seagrass meadow 6-12
7-1 Three possible distribution patterns 7-5
7-2 Cumulative means calculated for a random and a
cluster distribution 7-6
7-3 Core sampling of sandy-bottom stations 7-11
7-4 Diver using transect line in the surf 7-12
7-5 Quadrat sampling of epibiota at reef stations 7-12
7-6 Example of a mechanistic Habitat Suitability
Index model 7-17
7-7 Suitability index curve for substrate type for
juvenile Atlantic croakers Habitat Suitability
Index model (Diaz and Onuf 1985) 7-18
7-8 Benthic resources assessment technique (BRAT) 7-20
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CHAPTER 1
INTRODUCTION
l-l. Purpose. This manual provides guidance for incorporating
environmental considerations into the engineering, design, construction,
operation, and maintenance of coastal shore protection projects.
l-2. Applicability. The manual is applicable to all Corps field
operating activities having civil works responsibilities in the area of
coastal shore protection.
l-3. Scope. Selection of the best environmental and engineering solution
to a specific coastal problem reguires a systematic and thorough study
because of the complexity of coastal projects and the diversity of coastal
environments. The prerequisites to such a study are a clear definition of
the problem and cause of the problem and then a comprehensive review of
potential solutions (alternatives). This manual addresses both natural
and human-induced changes in the coastal zone; the structural and
nonstructural measures that coastal engineers employ against these
changes; and the beneficial and adverse impacts of these measures.
Immediate and long-term impacts in the project area, as well as adjacent
environments, are summarized. In addition, this manual emphasizes
potential steps for obtaining desirable results and reducing adverse
impacts. The manual focuses primarily on shore protection, i.e., coastal
projects designed to stabilize the shore against erosion related
principally to current and wave action: however, the material is also
applicable to harbor and navigation channel improvements. The manual
applies to both the Great Lakes and the coastal marine systems. It
identifies the principal environmental factors that should be considered
in design and construction and provides techniques for attaining
environmental quality objectives. Proper techniques for collection,
analysis, and interpretation of environmental data to use in planning and
engineering are outlined. This manual is intended to be compatible and
used in conjunction with other OCE engineering manuals and the Coastal
Engineering Research Center's "Shore Protection Manual" (US Army Engineer
Waterways Experiment Station 1984). As new information becomes available,
this manual will be periodically revised.
l-4. References. The Corps references listed below provide guidance to
field personnel concerned with planning, design, construction, operation,
and maintenance of coastal shore protection projects.
a. ER 200-2-2, Procedures for Implementing NEPA.
b. ER 1105-2-10, Planning Programs.
C. ER 1105-2-20, Projects Purpose Planning Guidance.
d. ER 1105-2-35, Public Involvement and Coordination.
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EM 1110-2-1204
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e. ER 1105-2-50, Environmental Resources.
f. ER 1110-2-400, Design of Recreation Sites, Areas, and Facilities.
g. ER 1110-2-1403, Hydraulic and Hydrologic Studies by Corps Seperate
Field Operating Activities and others.
h. ER 1110-2-8102, Model Testing at Waterways Experiment Station.
i. ER 1110-2-1404, Deep-Draft Navigation Project Design.
j. ER 1130-2-307, Dredging Policies and Practices.
k. ER 1165-2-130, Federal Participation in Shore, Hurricane, Tide,
and Lake Flood Protection.
l. EM 1110-l-400, Recreation Planning and Design Criteria.
m. EM 1110-2-1202, Environmental Engineering for Deep-Draft
Navigation.
n. EM 1110-2-1614, Design of Coastal Revetments, Seawall, and
Bulkheads.
0. EM 1110-2-2502, Retaining Walls.
p. EM 1110-2-2904, Design of Breakwaters and Jetties.
q. EM 1110-2-2906, Design of Pile Structures and Foundations.
r. EM 1110-2-3300, Beach Erosion Control and Shore Protection
Studies.
s. EM 1110-2-5025, Dredging and Dredge Material Disposal.
t. EM 1110-2-5026, Dredged Material Beneficial Uses.
u. EP 1165-2-1, Digest of Water Resources Policies and Authorities.
l-5. Appendices.
a. Bibliography. Bibliographical. references are indicated throughout
the text by last names of authors listed alphabetically in Appendix A. The
WES reports referenced are available on loan from the Technical Information
Center, US Army Corps of Engineer, Waterways Experiment Station, PO Box
631, Vicksburg, Mississippi 39180-0631.
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b. Models. Appendix B contains information on both numerical and
physical models available for environmental studies. The capability of
each model is briefly discussed and its source is identified.
c. Regulations. Federal regulations related to implementing coastal
shore protection projects are listed in Appendix C. All projects will
also need to achieve compliance (most likely through the local sponsor)
with state or territorial, county, and other local government statutes.
d. Species Profiles. A list of published and unpublished
estuarine/marine species profiles is provided (Appendix D). The profiles
give brief but conprehensive sketches of the biological characteristics
and environmental and habitat requirement of coastal fish and
invertebrates.
l-6. Glossary. Definitions of key terms frequently used are provided at
the end of this manual.
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CHAPTER 2
OVERVIEW OF COASTAL SHORE PROTECTION PROJECTS
2-1. Classification. Coastal shore protection projects are classified into
four general categories in the "Shore Protection Manual:"
a. Shoreline stabilization.
b. Backshore protection (from waves and surge).
C. Inlet stabilization.
d. Harbor protection.
A coastal problem may fall into one or more categories.
2-2. Alternatives. Once the project is identified, various alternatives are
available to the coastal engineer. These alternatives involve the placement
or removal of sediment, rock, wood, or other material to create new struc-
tures, to modify existing structures, or to physically alter the shore in some
manner. In this manual, potential alternatives have been grouped into three
categories: protective beaches, dunes, and levees; man-made structures; and
nonstructural alternatives (Table 2-l). While this manual primarily addresses
these three action alternatives, information presented will also be useful in
evaluating passive solutions such as coastal zoning and land-use management.
Dredging, a potential solution to inlet stabilization problems, and envi-
ronmental considerations for this activity are addressed in EM 1110-2-1202
(see para l-4). Mitigation policy for Federal projects is summarized in
ER 1105-2-50. Chapter 8 of this manual provides an additional discussion of
mitigation.
2-3. Considerations.
a. Table 2-2 lists the factors that must be considered in analyzing each
project category and its associated considerations. Hydraulic considerations
include wind-generated waves, swells, currents, tides, storm surge or wind
setup, and the basic bathymetry of the area. Sedimentation considerations
include the littoral material and processes (i.e., direction of movement, net
and gross rates of transport, and sediment classification and characteris-
tics), and changes in shore alignment. Control structure considerations
include the selection of the protective works by evaluating type, use, effec-
tiveness, economics, and environmental impact. Navigation considerations
include the design craft or vessel data, traffic lanes, channel depth, width,
length, and alignment. In selecting the shape, size, and location of shore
protection works, the objective should be not only to design an engineering
work that will accomplish the desired results most economically, but also to
consider effects on adjacent areas. An economic evaluation includes the main-
tenance and replacement costs, along with the interest on and the amortization
of the first costs. If any plan considered would potentially increase the
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TABLE 2-1
Classification of Coastal Engineering Solutions
Problems to Address Solutions
Shore Stabilization Beach & Dune
Beach nourishment
Sand bypassing
Structures
Bulkheads
Revetments
Seawalls
Detached breakwaters
Groins
Nonstructural
Marsh plants
Seagrasses
Backshore Protection Beach & Dune
Protective beach
Dune stabilization
Structures
Bulkheads
Revetments
Seawalls
Inlet Stabilization Structures
Jetties
Dredging
Harbor Protection Structures
Breakwaters
Jetties
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TABLE 2-2
Classification of Coastal Engineering Considerations
CONSIDERATIONS
PROJECT
impact of a project to a larger coastal stretch or prevent an extension of the
impacts, the economic effect of each such consequence should be evaluated. A
convenient measurement for comparing various plans on an economic basis is the
average annual cost over the evaluation period and the average annual benefit
captured by each plan.
b. Effects on adjacent land areas are considered to the extent of pro-
viding the required protection with the least amount of disturbance to current
and future land use, ecological factors, and aesthetics of the area. The
form, texture, and source of material should be considered in the design, as
well as how the material is used. Proper consideration must be given to the
legal and social consequences where shore protection measures may result in
significant effects on physical or ecological aspects of the environment.
c. Coordination between the design and environmental elements should
begin early in the planning process to assure that environmental concerns,
opportunities, and features are adequately considered.
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CHAPTER 3 10 Jul 89
ENVIRONMENTAL RESOURCES
3-l. Environmental Requirements.
a. General. As noted in Table 2-2, the "Environment" is a
consideration in each coastal shore protection project category. The
environmental effects of all project alternatives must, by law as well as
normal engineering considerations, be evaluated. Opportunities for
incorporating environmental considerations and enhancements in coastal
shore protection projects should be investigated.
b. Policies. The planning, design, construction, and operation and
maintenance activities of coastal shore protection projects must be
consistent with national environmental policies. Those policies require
that such activities be done to the extent practicable in such a manner as
to be in harmony with the human and natural environment, and to preserve
historical and archaeological resources. Corps project development is
documented by a series of studies, each being more specific than the
previous study. The series of reports produced for a project varies by
Corps District and Division and through time due to scientific judgment,
the unique conditions specific to each project, and changing regulations.
In general, an initial evaluation (or reconnaissance) report and a
feasibility (or survey) report are prepared prior to congressional project
authorization. Refer to ER 1105-2-10, for a description of this planning
process. Environmental studies are included along with engineering,
economic, and other types of analysis (ER 1105-2-50).
C. Statutes and Regulations. Complying with Federal statutes,
executive orders and memoranda, and Corps regulations requires careful
study of existing environmental conditions and those expected to occur in
the future with and without shore protection. Principal environmental
statutes/regulations that are applicable to Corps coastal shore protection
projects arelisted in Appendix C.
d. Environmental Studies. During each stage of project planning,
design and construction, major environmental concerns and corresponding
information needs should be identified. Forecasting of information needs
is necessary in order to schedule sufficient time for field data
collection, physical or numerical modeling if needed, and other needs.
Scheduling of field studies should allow for administrative time related
to contract preparation, contractor selection, report and NEPA document
preparation, review of findings, and coordination or consultation with
concerned Federal agencies and the interested public.
(1) Checklist of studies. The following checklist consists of some
of the environmental factors that should be considered for coastal shore
protection projects. Environmental factors selected for study will depend
upon the type project being considered. This checklist is not all
inclusive and not all factors are appropriate for all projects.
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(a) Determine the bounds of the project areas.
(b) Characterize existing environmental (physical, ecological,
cultural, economic conditions at a project site.
(c) Be aware of other planned construction activities likely to be
associated with the Federal project and evaluate their cumulative impacts.
(d) Evaluate project effects on long-shore sedimentation processes,
circulation patterns, currents, and wave action.
(e) Evaluate project effects on water quality, including
characterization and testing of sediments as required in Section 103 of
the Ocean Dumping Act (PL 92-532) or Section 404 of the Clean Water Act
(PL 92-500) evaluations.
(f) Evaluate the no action alternative and nonstructural solutions.
(g) Evaluate project effects on erosion and deposition.
(h) Evaluate all reasonable and practicable construction alternatives
(construction equipment, timing, etc.).
(i) Evaluate effects of the final array of alternative plans on
significant biological, aesthetic, cultural and recreational resources.
(j) Describe relationships of each plan to the requirements of
environmental laws, executive orders, Federal permits and state and local
land use plans and laws.
(k) Include feasibledesigns, operational procedures, and appropriate
mitigation measures to reduce or avoid adverse environmental impacts in
the preferred plan and alternatives evaluated.
(l) Coordinate with other agencies, the public, and private groups.
(m) Plan and design an environmental monitoring program as needed.
(2) Critical issues. Time and money constraints will generally
dictate the level and scope of investigation and data collection for all
environmental areas of interest. Therefore, the most significant
environmental issues identified by the public and resource agencies during
scoping should be investigated. It is essential that the issues
investigated fully account for all significant effects of a project and
that a realistic balance be achieved between the study requirements and
funds available. The addition of factors determined at a later date will
increase the time, cost, and expertise required for the study.
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Chapters 4, 5, and 6 of this manual identify major environmental
considerations associated with alternative shore protection solutions.
Criteria for determining significant issues include statutory
requirements, executive orders, agency regulations and guidelines, and
other institutional standards of regional and local interest. (see
Appendix C).
(3) Environmental monitoring. The Council on Environmental Quality
regulations at 40 CFR 1505.3 state that agencies may provide for
monitoring to assure that their decisions are carried out and should do so
in important cases and upon request, make available to the public the
results of relevant monitoring. The 40 CFR 1505.2 also states that a
monitoring and enforcement program shall be adopted and summarized where
applicable. The term "environmental monitoring" as defined in ER 200-2-2
is that oversight activity necessary to ensure that the decision,
including required mitigation measures, is implemented. Environmental
monitoring as discussed in Chapter 7 of this manual refers to the overall
process of data collection, management, analysis and interpretation of
short and long term changes over the life of the project and analysis are
discussed in Chapter 7 of this manual.
(4) Each study must have well-defined, detailed objectives prior to
field data collection. The study design should include a rationale for
hypotheses to be tested, the variables to be monitored, techniques and
equipment to be used, sample station locations and frequencies, and data
storage and analysis. Monitoring may extend beyond water quality and
ecological studies and include monitoring noise, emission from equipment
engines, cultural resources, archeological resources, etc., if deemed
appropriate.
(a) Environmental studies during early stages of project formulation
should emphasize identification of resources, development of an evaluation
framework, and collection of readily available information for all
potential alternatives. Resources likely to be impacted should be
investigated, and additional data needs should be identified.
(b) Detailed analysis of a project occurs after evaluations narrow
the range of specific alternatives to the most feasible (usually three or
four) which have been selected for study. Beneficial and adverse
environmental effects of each alternative should be quantified where
possible or qualified in adequate detail so they can be included with the
economic and technical analysis to compare and select the plan that
maximizes NED benefits. Although a preferred alternative can be
identified at this stage, formal selection of an alternative for
construction must await the completion and agency review of the
Environmental Impact Statement or Environmental Assessments. In this way
the Corps, the public, and outside agencies have the benefit of a full
evaluation of all feasible alternatives and a comparison of them by the
lead agency. Post-construction monitoring, if authorized, should also be
done to verify the impact predictions made during without project
analysis. Where monitoring reveals the presence of unexpected impacts,
measures should be considered to minimize the impacts.
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3-2. Environmental Resource Categories. The remainder of this chapter
summarizes the environmental resource categories that should be considered
in evaluating the coastal shore protection alternatives. The six
categories are physical, water quality, biological, recreational,
aesthetic, and cultural.
3-3. Physical.
a. General. The physical modifications of the environment from
coastal shore protection projects can result in both desirable and
undesirable impacts. Many adverse impacts can be avoided by evaluating
alternatives for siting and design. Consideration of physical impacts
must occur during both the design stage and impact assessment stage.
b. Physical Design Considerations. Structural and, to a lesser
extent, nonstructural measures have the potential of altering the
hydrodynamic regime (circulation) and the hydraulic and wave energy
conditions of the project area. Furthermore, construction frequently
alters the shoreline configuration and/or bathymetry at the project site
and occasionally up or down coast, by modifying the littoral transport
system. In many instances these modifications are the objective of the
design process. The purpose of a shoreline breakwater project is to
reduce wave energy entering a harbor, marina, or other facilities. Groin
projects and jetty construction result in modification of the littoral
transport regime. If the project is not properly designed, adverse
physical impacts, such as changes in shoreline configuration (shore
erosion) or changes in bathymetry (navigation channel infilling), my
occur. These impacts should be identified during the impact assessment
stage and, if necessary, the project redesigned or relocated to minimize
unwanted effects, such as excessive maintenance dredging and beach
nourishment.
c. Physical Impact Assessment. Physical impacts can occur on both a
short-term and long-term basis. Short-term impacts are generally
construction related (i.e., short sections of a beach may be temporarily
restricted during the fill and grading operations). During a beach
nourishment project or dune construction, sands can become compacted
altering transport phenomena. Physical effects from construction of
breakwaters, jetties, groins, piers, or other nearshore structures stem
from rock placement, jetting or driving piles, dredging to a solid bed or
required depth, and other on site construction activities. Following the
completion of these activities, impacts usually diminish rapidly (Naqvi
and Pullen 1982, Van Dolah et al. 1984). Long-term impacts may be more
important and more difficult to predict. Several tools will help in
assessing potential adverse impacts: interviews with long-time residents,
review of old aerial photos, on site monitoring, case studies of similar
projects numerical models, and physical models. Using any or all of
these tools, an evaluation of potential changes in circulation patterns,
flushing conditions, and sediment transport phenomena should be
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completed. Other studies of physical factors may be warranted on a
case-by-case basis.
3-4. Water Qualitv.
a. General. Unlike physical impacts, water quality impacts involve
changes in the water column's characteristics rather than changes in
shoreline configuration or local bathymetry. Again the impacts are
manifested on both a short-term and long-term basis.
b. Water Quality Design Considerations. The construction process is
often responsible for increases in local turbidity levels, changes in
salinity, releases of toxicants or biostimulants from fill materials,
introduction of petroleum products, and/or the reduction of dissolved
oxygen levels. These impacts can be minimized by modifying or selecting
specific construction practices, carefully selecting fill materials, and
in some instances by construction scheduling. These impacts are
short-lived, and ambient water quality conditions will rapidly return
unless long-term changes in the hydrodynamics and hydraulics have
occurred. It is these long-tern impacts that must be identified during
the design process. In addition to the general impacts of the selected
alternatives (whether structural or nonstructural), the proposed design
specifications of any selected alternative also have the potential for
affecting water quality. For example, the design of an off-shore
breakwater (length, height, water depth, spacing) will greatly influence
its impact on circulation and flushing and thus its impact on water
quality.
c. Water Quality Impact Assessment. The long-term impact on water
quality of nonstructural alternatives, i.e., planting beach grasses for
dune stabilization, marsh grasses for bank stabilization, and seagrasses
for bottom sediment stabilization, is generally negligible, whereas
structural alternatives have a range of potential impacts. The range is a
function of the location, size, and type of structure. In general, groins
have the least potential for water quality impacts. Because groins change
local patterns of water circulation, some changes in specific water
quality parameters may occur, but these impacts are minimal for most groin
projects. The water quality effects of bulkheads and seawalls are similar
in that both will reduce erosion of the backshore and decrease local
levels of suspended solids. Revetments, similarly to bulkheads and
seawalls, may promote erosion of the foreshore and increase levels of
suspended solids but to lesser extent. On the other hand, these
structures may reduce overall levels of suspended solids by preventing
erosion of uplands and backshore materials. Jetties and breakwaters have
the greatest potential impact on circulation and flushing. The placement
of jetties my not only alter circulation patterns and flushing
conditions, as well as erosion and deposition patterns, but may also alter
both river outflow and tidal conditions. These impacts may be of
consequence well into the estuary and may have widespread effects, such as
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changing salinity and circulation patterns. Breakwaters, by definition,
are wave energy barriers designed to protect landforms or harbor-
behind them. These off-shore structures also often influence circulation
and flushing action in their lee. If the breakwater is constructed to
form a semienclosed basin for use as a harbor or marina, the flushing
conditions of the project area may be dramatically altered. Assessment
and evaluation of water quality impacts must begin in the planning stage
and continue at least through the design stage. Postconstruction
monitoring may also be recommended to provide feedback for future
projects.
d. Other Contaminants. Activities involving sediments or other
construction materials known to contain chemical toxins should be
conducted with special precautions to avoid unnecessary chemical release
into the water body. Of particular concern would be potential
introduction of chemical agents either during preparation, application, or
cleanup of construction equipment. Chemical cleaning agents may also
contain toxic compounds. Little is known about the potential affects of
these compounds on aquatic organisms even in trace amounts. Howev


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