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Review of dredging effects on adjacent park systems

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Title:
Review of dredging effects on adjacent park systems
Series Title:
UFLCOEL
Creator:
Dean, Robert G ( Robert George ), 1930-
Dolan, Robert
University of Florida -- Coastal and Oceanographic Engineering Dept
United States -- National Park Service
Place of Publication:
Gainesville Fla
Publisher:
Coastal & Oceanographic Engineering Dept., University of Florida
Publication Date:
Language:
English
Physical Description:
viii, 115 leaves : ill. ; 28 cm.

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Subjects / Keywords:
Dredging -- Environmental aspects -- Florida ( lcsh )
Beaches -- Florida ( lcsh )
Dredging spoil -- Environmental aspects -- Florida ( lcsh )
Coastal and Oceanographic Engineering thesis M.S
Coastal and Oceanographic Engineering -- Dissertations, Academic -- UF
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government publication (state, provincial, terriorial, dependent) ( marcgt )
bibliography ( marcgt )
technical report ( marcgt )
non-fiction ( marcgt )

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Bibliography:
Includes bibliographical references.
General Note:
"December, 1988."
Funding:
This publication is being made available as part of the report series written by the faculty, staff, and students of the Coastal and Oceanographic Program of the Department of Civil and Coastal Engineering.
Statement of Responsibility:
by Robert G. Dean with a contribution by Robert Dolan ; prepared for National Park Service.

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University of Florida
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University of Florida
Rights Management:
All rights reserved, Board of Trustees of the University of Florida
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22191054 ( OCLC )

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Full Text
UFL/COEL-88/015

REVIEW OF DREDGING EFFECTS ON ADJACENT PARK SYSTEMS
by
Robert G. Dean

with a contribution by: Robert Dolan
Prepared for: National Park Service 75 Spring Street, SW Atlanta, GA 30303

December, 1988




REPORT DOCUMENTATION PAGE
1. Report No. 2. 3. Recipient'a Accession No.
4.* Title &ad Subtitle 1 Report Date
REVIEW OF DREDGING EFFECTS ON ADJACENT PARK SYSTEMS December,, 1988
6.
7. Author(s) 8. Performing Organizatin Report No.
Robert G. Dean
with a contribution by: Robert Dolan UFL/COEL-88/015
9. Performing organization Name and Address 10. Project/Taak/Wort Unit No.
Coastal and Oceanographic Engineering Department
University of Florida 11. Contract or Grant No.
336 Weil Hall CA-500-7-8007
Gainesville, FL 32611 13. Type of Report
12. Sponsoring Organization Name and Address
National Park ServiceFia 75 Spring Street, SW
Atlanta, GA 30303 ______________14.
15. Supplementary Notes
16. Abstract
In today's environment, most park systems can be influenced by human
activities well outside the park boundaries. For coastal areas, dredging is known to have the potential of altering the natural beach system many kilometers downdrift of the activities. In some cases where previous dredging effects have
adversely impacted a park system, beach nourishment with clean sand can be a byproduct of a dredging project and can be beneficial to a park by reinstating the
natural sand flows.
This report is intended to assist park personnel in the Southeast Region to
better assess potential dredging impacts on the natural system and to present
methods of ameliorating adverse effects. The subject is introduced by four generic examples in which dredging can play a role in the quality and behavior of the natural system. The response of the beach system to natural forces and
to dredging activities is reviewed. Dredging techniques are discussed as well as their potential for beneficial and adverse effects. A literature review is presented on the biological effects of dredging. Three actual case studies are
reviewed in which dredging is being carried out adjacent to park systems in the Southeast Region. State and federal regulations governing dredging activities are summarized. An annotated bibliography includes contributions of dredging activities on nearshore ecology, beach stability and sand management practices.
17. originator's Key words 18. Availability Statement
Beaches
Beach erosion
Beach nourishment
Dredging
Intertidal effects
19 _. S. Security Classif. of the Report 20. U. S. Security Classif. of This Page 21. No. of Pages 22. Price Unclassified I Unclassified 1 123 11




UFL/COEL-88/015

REVIEW OF DREDGING EFFECTS
ON ADJACENT PARK SYSTEMS
December, 1988
Prepared For: National Park Service 75 Spring Street, SW
Atlanta, GA 30303
Prepared By: Robert G. Dean
Coastal and Oceanographic Engineering Department
University of Florida
336 Weil Hall
Gainesville, FL 32611
With A Contribution By: Robert Dolan University of Virginia
Charlottesville, VA 22903




TABLE OF CONTENTS

PART I
INTRODUCTION AND GENERAL TYPES OF DREDGING AND COASTAL
PROBLEMS ENCOUNTERED BY THE NATIONAL PARK SERVICE I
Introduction 2
Generic Problems 3
Generic Problem 1 Inlet Dredging 4
Problem 4
Discussion of Natural System 4
The Altered System 4
Physical Effects 4
Environmental Effects 4
Solution 5
Generic Problem 2 Channel Stabilization through Jetty
Construction 6
Problem 6
Discussion of Natural System 6
The Altered System 6
Physical Effects
Environmental Effects 7
Solution 7
Generic Problem 3 Coastal Armoring 8
Situation 8
Discussion of Natural System 8
The Altered System 8
Physical Effects 8
Environmental Effects 8
Solution 8
Generic Problem 4 Beach Nourishment Using Sand Dredged
from Offshore Dredging 10
Problem 10
Discussion of Natural System 10
The Altered System 10
Physical Effects 10
Environmental Effects 10
Solution 11
PART II
THE NATURAL BEACH SYSTEM
Geology of Barrier Islands 12
Introduction 13
Origin of Barrier Islands 13
Sea Level Rise and Barrier Islands 16
The Importance of Natural Processes 16




Beach Features and Processes 17
Longshore Sediment Transport 17
Cross-Shore Sediment Transport 19
Variation of Sand Size Across the Nearshore 22
Role of Inlets 24
PART III
THE DREDGING PROCESS 30
Introduction 31
Dredging Objectives 31
Dredging Equipment Methodologies 31
PART IV
ALTERED COASTAL SYSTEMS 38
A. GENERAL 39
Introduction 39
Modifications of Channel Entrances 39
Beach Nourishment Projects and.Their Evolution 41
Case (1) Project on a Long Uninterrupted Beach 41
Case (2) Placement Immediately Downdrift of a
Littoral Barrier 43
Profile Equilibration After Nourishment 43
Relative Benefits of Offshore Sand Placement at Various
Depths 43
Need for Profile Contouring 44
B. POTENTIAL DREDGING IMPACTS 45
Physical Effects 45
Dredging to Obtain Material 45
Dredging to Increase Navigation Channel Depths 47
Environmental Effects of Beach Nourishment Projects 47
Sediment Quality 47
Emerita Talpoida (Mole Crabs) 48
Donax (Coquina Clams) 49
Ocypode Quadrate (Ghost Crab) 50
A Case Study: Panama City, FL 50
Summary Regarding Intertidal Biological Effects of Beach
Nourishment 51
Sea Turtles 52
Consolidated Beach Sediments 53
Blocking of Turtle Crawls by Dredge Pipe
Miscellaneous Effects 53
Nest Relocation Programs 54
A Case Study: Jupiter Island, Florida 54
Summary Regarding Impact of Beach Renourishment on Sea
Turtle Nesting 56




PART V

CASE STUDIES AS EXAMPLES 57
CASE STUDY I PERDIDO KEY 58
Introduction
Background 60
Rationale for Selected Plan 60
Monitoring Plan 64
Physical Monitoring 64
Performance Related Monitoring Needs 64
Profile and Planform Evolution 64
Wave Measurements 64
Wind and Precipitation Measurements 64
Vegetation Response 65
Public Interest/Education Monitoring Needs 65
Management Monitoring Needs 65
Biological Monitoring 65
Benthic Community Studies 66
Vegetation Analysis 66
Beach Mouse Population 66
CASE STUDY II OREGON INLET 66
Introduction 66
Historic Inlet Behavior 66
Present Situation 68
The National Park System and State of North Carolina
Position on Oregon Inlet 68
CASE STUDY III CUMBERLAND SOUND 71
Introduction 71
Concerns of the National Park Service 71
Monitoring Program 71
Coastal Assessment Component 73
Cumberland Sound Physical Processes Component 73
Ecological Research 73
PART VI
LEGAL AND REGULATORY ASPECTS OF DREDGING 74
Introduction 75
THE FEDERAL PROGRAM 75
Rivers and Harbors Act of 1899 75
National Environmental Policy Act of 1969 (NEPA) 75
Federal Water Pollution Control Act Amendments of 1972 (FWPCA) 76
Marine Protection, Research and Sanctuaries Act of 1972 76
Coastal Zone Management Act of 1972 (CZMA) 76




THE STATE
The The The The The The

PROGRAMS North Carolina Program South Carolina Program Georgia Program Florida Program Alabama Program Mississippi Program

PART VII

AN INVENTORY OF NATIONAL PARK SERVICE UNITS IN THE SOUTHEAST REGION SUSCEPTIBLE TO EROSION AND EFFECTS OF DREDGING

PART VII

SUMMARY AND CONCLUSIONS
Summary
Conclusions REFERENCES
PART IX
ANNOTATED BIBLIOGRAPHY
Ecological Effects of Beach Nourishment
Physical Performance of Beach Nourishment Projects
Bypassing at Inlets
Effects of Inlets
General




LIST OF FIGURES

FIGURE PAGE
1. Generic Problem 1 -Inlet Dredging 4
2. Generic Problem 2 Jetty Construction 6
3. Generic Problem 3 Coastal Armoring 8
4. Generic Problem 4 Beach Nourishment 10
5. The Rise of Sea Level as Obtained from Carbon 14 Dates in Relatively Stable Areas (From Shepard, 1963). Break in Slope
Some 6400 Years Before Present (BP) May Have Provided Basis
for Barrier Island Stability 15
6. Waves Arriving Obliquely to Shoreline Cause Longshore Current and Longshore Sediment Transport Primarily Within Surf Zone 18
7. Estimates of Net Annual Longshore Sediment Transport Along Florida's East Coast 20
8. Normal and Storm Profiles on a Natural Shoreline 21
9. Variation of Median Sediment Size with Location Across Beach Profile. North Jupiter Island, FL 23
10. Relationship between Spring Range Tidal Prism and Minimum
Cross-Section, Compared with Maximum Inlet Velocity of
1 m/s. Modified from O'Brien (1931) 25
11. The Balance of Forces which Maintains the Ebb Tidal Shoal
Volume in Equilibrium 27
12. Relationship Between Equilibrium Volume of Sand Stored
in Ebb Tidal Shoal and Tidal Prism (Adapted From Walton
and Adams, 1976) 28
13. The "Sand Sharing System" Comprising the Inlet, the Ebb Tidal
Shoal and Adjacent Shorelines 29
14. The Clam Shell Dredge (From Bray, 1979) 32
15. Bucket Ladder Dredge (From Richardson, 1976) 32
16. Plan View of Operation of a Pipeline Dredge (From Bray,
1979) 33
17. Self-propelled Hopper Dredge with Trailing Dragarm (From
Richardson, 1976) 33




F IGURE PG

18. Plain Suction Dredge (From Richardson, 1976) 35
19. Cutter Suction Dredge (with Spuds) (From Richardson, 1976) 35
20. Split Hopper Barge (Self-propelled) (From Richardson, 1976) 37
21. Example of Evolution of Initially Rectangular Nourished Beach
Planform. Example for Project Length, Q,, of 6 kin, Effective
Wave Height, H, of 0.6 m and Initial Nourished Beach Width of
30 m 42
22. Effect of a Dredged Borrow Area on Wave Refraction and Wave
Energy Distribution along the Shoreline 46
23. Perdido Key and Entrance Channel to Pensacola Bay 59
24. Shoreline Change Rates for Escambia County, January 1974 to
October 1984. Based on Florida DNR Surveys. Note Shoreline
Change Rates Shown Have Been Smoothed by a Five Point Running
Average 61
25. Recommended Characteristics of Nourished Profile. Illustrated
for DNR Monument No. 48 63
26. Oregon Inlet 67
27. Cross-Section of Sloping Floating Breakwater Planned for
Deployment at Oregon Inlet to Provide Shelter for Sand Bypassing Dredge Operating in its Lee. From Inman and
Dolan (1987) 69
28. Location Map of Kings Bay Site Relative to Cumberland Island
National Seashore 72

PAGE




LIST OF TABLES

TABLE PAGE
1. SUMMARY OF SHORELINE RESPONSE TO NEW JERSEY STORM OF
NOVEMBER 6-7, 1953 (From Caldwell, 1959) 21
2. FIELD TESTS CARRIED OUT TO EVALUATE SHOREWARD SEDIMENT
TRANSPORT FROM OFFSHORE PLACEMENT 44
3. CHARACTERISTICS OF SEA TURTLE AND NESTING IN FLORIDA 52
4. HISTORY OF MAINTENANCE DREDGING PENSACOLA ENTRANCE CHANNEL
1885-1987 58
5. CHRONOLOGY OF PENSACOLA BAY ENTRANCE CHANNEL DIMENSIONS 62
6. UNITS WITHIN THE SOUTHEAST REGION SUBJECT TO SALT/BRACKISH
WATER RELATED EROSION AND ADVERSE EFFECTS OF DREDGING 81
6. (Continued) 82

viii




PART I
INTRODUCTION AND GENERAL TYPES OF DREDGING AND COASTAL PROBLEMS
ENCOUNTERED BY THE NATIONAL PARK SERVICE




PART I
INTRODUCTION AND GENERAL TYPES OF DREDGING AND COASTAL PROBLEMS ENCOUNTERED BY THE NATIONAL PARK SERVICE
Introduction
The coastal zone is ever-dynamic responding to the forces of waves, tides, currents and winds. Long periods of relative stability can be terminated by a
sudden storm causing both temporary and permanent changes much greater than those occurring over many years of mild weather. Even during periods when the beach is relatively stable, there may be a large unnoticed transport along the shore.
The coastal zone is a desirable region for habitation, recreation and industry. Some of these uses lead to desires to alter the natural system by various means. Such modifications could include channel deepening for
navigational purposes, dredging for beach nourishment, coastal armoring to stabilize an eroding shoreline, etc. Engineering interaction with the coastal zone usually causes effects which can be anticipated adequately only through a detailed and quantitative understanding of the natural processes. Although
understanding of these processes has developed considerably over the past few
decades, our information base is still inadequate and generally unanticipated effects of engineering interaction may occur. Some of these effects are slow
and large scale and may influence the shoreline for distances of many kilometers from their cause.
The National Park Service (NPS) as a manager of coastal lands including
barrier islands can be impacted by a variety of modifications by adjoining property owners. In some cases, the concern occurs on NPS property and the NPS may initiate a study seeking appropriate remedial measures. The present report
is directed to Park resource managers with the intent of providing a familiarization of the natural processes, the range of dredging related modifications that can occur and the potential areas of concern that should be voiced at the first
level of review by the resource managers. The following section presents several generic problems to illustrate with greater specificity the types of modifications, impacts and the significant factors.




Generic Problems
To some degree the overall purpose of this report is to develop an awareness for natural coastal processes and an ability to foresee the potential problems associated with alterations to the coastal system. Later sections of this report will discuss the processes in detail. To provide a preview of the types and range of problems addressed in this report four generic case studies
are presented. The format is a brief presentation for each problem in which the problem is introduced with two diagrams, a before and after, the dominant physical and environmental impacts and focus areas warranting attention by NPS personnel in their considerations of this type of generic problem.
A common conceptual thread in all coastal engineering problems is that of a sediment budget. That is, the natural system has adjusted 'to the current situation of sediment inflows and outflows. Any alteration of the sediment transport processes will tip the sediment budget out of balance and cause areas of erosion and possibly deposition.




Generic Problem 1 Inlet Dredging
Problem Channel deepening of a natural inlet is being considered. The sand dredged will be disposed of offshore.
The Natural System The Altered System
Figure 1. Generic Problem 1I Inlet Dredging.
Discussion of Natural System In the natural system, waves arriving at an angle to the shoreline cause a transport of sand along the shoreline. The
transport rate is Q. Upon reaching this inlet, the transport occurs over a broad flat sand body termed an ebb tidal shoal.
The Altered System Since the shallow depths over the ebb tidal shoal are not suitable for navigation, a channel is incised through the shoal by dredging, thus severing the natural transport pathway or "bridge". The natural response of the system is to rebuild the sand bridge through deposition in the channel. This will require periodic dredging to maintain the channel depth.
Physical Effects The ultimate physical effects that can be anticipated include erosion of the downdrift shoreline at a rate Q. In cases where transport occurs in both directions, both shorelines may erode.
Environmental Effects The erosion will degrade the natural characteristics of the beach and may destroy valuable habitat. Over long periods, the dunes




may be eroded away, along with associated vegetation, the barrier island will
be overtopped by storms causing impact to back barrier vegetation. Stable areas for turtle nesting may be affected.
Solution Sand dredged should be returned to the adjacent beaches in locations established through a comprehensive monitoring program. Large
quantities of sand placed at infrequent intervals may cause substantial fluctuations of the shoreline which could impact turtle nesting.




Generic Problem 2 Channel Stabilization through Jetty Construction
Problem Jetty construction is being considered to stabilize a natural or deepened navigational channel.
The Natural System The Altered System
Figure 2. Generic Problem 2 -Jetty construction.
Discussion of Natural System In the natural system, waves arriving at an angle to the shoreline cause a transport of sand along the shoreline. The
transport rate is Q. Upon reaching this inlet, the transport occurs over a broad flat sand body termed an ebb tidal shoal.
The Altered System Since the shallow depths over the ebb tidal shoal are not suitable for navigation and dredging without jetty construction may be considered as too temporary a solution, jetties are planned to: (1) maintain the channel alignment, (2) to limit sand deposition from adjacent areas, and (3) to jet the deposited sand seaward from the channel.
Physical Effects The updrift jetty will cause impoundment of the sand arriving at the jetty. Downdrift of the inlet, the waves have the same
transporting capacity and thus will cause erosion at the same rate as the sum
of the deposition on the updrift side, and accumulation of sand farther seaward.




Environmental Effects The erosion will degrade the natural characteristics of the beach and may destroy valuable habitat. Over long periods, the dunes may be eroded away, along with associated vegetation, the barrier island will be overtopped by storms causing impact to back barrier vegetation. Stable areas for turtle nesting may be affected.
Solution Provision should be made for bypassing of sand around the entrance. Ideally the sand transfer should be at fairly frequent intervals so as to minimize the shoreline fluctuations. A degree of flexibility should be provided for placement of sand at various locations downdraft of the entrance.
Beach surveys as part of a monitoring program would establish the optimal bypassing locations.




Generic Problem 3 Coastal Armoring
Situation A developed area updrift of a park is affected by a long-term erosional trend as is the park area. To stabilize the shoreline, the developed area is considering armoring the shoreline by construction of a seawall or other shore protection structure.
The Natural System The Altered System
Figure 3. Generic Problem 3 Coastal Armoring.
Discussion of Natural System Natural forces, assumed unknown, are causing a large scale erosional trend. This erosion is shared by both the developed area and Park area as indicated above.
The Altered System By armoring the developed area shoreline, and thus preventing erosion, this source of sand to the longshore transport system is eliminated, thus placing greater erosional pressure on the downdrift shoreline in the amount of the deficit imposed by the armoring.
Physical Effects Increased erosion rates of the downdrift shoreline.
Environmental Effects A more rapid rate of dune loss and the associated habitat. Generally a narrower dry sand beach and thus less favorable for successful turtle nesting.
Solution The developed area could compare the relative economic benefits of beach nourishment using high quality sand. If not feasible, an alternate




approach would be for the armored area to place annually sand volumes equivalent to the reduction in supply caused by the armoring.




Generic Problem 4 Beach Nourishment Using Sand Dredged from Offshore Dredging
Problem Stabilization of an eroding beach is being considered by beach nourishment. This comprises the removal of a large quantity of material from an offshore area (the "borrow" area) and placement by pipeline dredge on the beach. A coral reef is present near the borrow area.
The Natural System The Altered System
Figure 4. Generic Problem 4 Beach Nourishment.
Discussion of Natural System The natural system is experiencing a longterm mild erosional trend.
The Altered System The completed altered system will include an offshore deepened "borrow" area with the removed material placed on the shore.
Physical Effects Possible physical effects include local modification of the waves affecting the shoreline due to the deepened borrow area. Additionally, the longevity or "life" of the project may be a matter of concern as it relates to the length of time that the benefits will occur to the area and the associated frequency for maintenance renourishment.
Environmental Effects In most cases the primary environmental effects are related to the quality of sediment or damage to the reefs by improper handling of equipment such as anchors. In this case quality relates to the grain




size characteristics and color of the sediment. Ideally, the sediment should
be of about the same grain size characteristics as the sand originally occurring on the beach. An important characteristic relating to turbidity and sedimentation in both the borrow and placement areas is the percentage of fine sediments in the material dredged. Also too great a fine sediment content will cause a
partial cementation of the sediment placed on the beach and thus adversely affect turtle nesting.
Solution Ensure, through an extensive sediment coring program, that the
best quality sediment available is being used and that the sediment contains less than 5% silt and clay. Additionally, require adequate set-backs from the reef, state-of-the-art positioning equipment on the dredge and marking of the borrow area and reef perimeter with floating buoys for easy visual identification.




PART II
THE NATURAL BEACH SYSTEM




PART II
THE NATURAL BEACH SYSTEM
Geology of Barrier Islands
(Pages 13-16 Contributed by R. Dolan)
Introduction
The Atlantic and Gulf coastal plains that form the seaward perimeter of the S.E. Region are relatively flat lands that slope gently seaward to a wide submarine continental shelf. The shore zone, or interface between the land and sea portions of the coastal plains, consists of a series of barrier islands 3
to 30 km offshore. These islands are 2 to 5 km wide, 10 to 100 km long, and low in elevation. The highest topographic features are sand dunes usually 3 to 6 m above sea level. The lagoons or bays on the sound side of the islands are shallow and may have large tidal mud flats and marshes.
The storms that generate large waves are the principal agents of change on barrier islands. Winter extratropical storms produce waves of 5 to 10 m, with
storm surges of I to 2 m. Hurricanes (tropical storms), which occur less
frequently, also cause major landscape changes, especially in the vicinity of their landfall.
Extratropical and tropical storms, with their strong waves and storm surges, often drive water and beach sands completely across the barrier island. In
contrast, during periods between storms the beaches build seaward. Thus at times the barrier island shorelines move landward and at other times seaward, in response to varying energy conditions. In recent decades this movement has been mostly landward, at a rate of about 1.5 in/yr for the Atlantic coast, and somewhat less along the Gulf coast.
Origin of Barrier Islands
Barrier island formation and migration has been a subject of debate among earth scientists for many years. There is, however, evidence that most of the mid-Atlantic and Gulf coast barrier islands are migrating landward. Beats and tree stumps, remnants of forest stands on the back sides of the islands emerge on open ocean beaches, indicating barrier island migration or transgression.




Change along and across the barrier islands is usually a function of one or more of these factors: the amount of sediment within a coastal segment, the magnitude of natural processes (storms), and the stability of sea level. These
factors are also directly related to the geological origin of the barrier islands.
Sea level has oscillated several times during the past half-million years.
During the interglacial periods, continental ice melted, and the shorelines advanced inland across the continental shelves. During the glacial periods, as
water was withdrawn from the seas and stored in the form of glacial ice, the shorelines moved seaward across the continental shelves. This process involved great quantities of seawater, enough to move the ocean shoreline across roughly
150 km of the coastal plain and continental shelf. When the last period of glaciation, the Wisconsin, came to an end about 20,000 years ago, sea level was
approximately 120 m lower than it is today (Figure 5), and the shorelines of the Atlantic and Gulf coasts were 60 to 150 km seaward of their present positions.
With the change from glacial to interglacial, the sea started to rise and continued to rise for about 14,000 years, reaching within a few meters of the present about 6,000 to 7,000 years ago.
As the sea rose and the shoreline moved across the continental shelf, large masses of sand were moved with the migrating shore zone in the form of beach deposits. Sediment that had been deposited as deltas and floodplains within the coastal river systems was also reworked by wave action and moved along the shore. Once sea level became fairly stable, waves, currents, and winds worked together on the sand to form the beaches and barrier islands that rim the coast of the S.E. Region. As long as the inshore system contained surplus sediment, the beaches continued to build seaward until equilibrium was reached--in this
case the balance among storm and wave energy, sea level, and the amount of sediment in the transport system.
All the evidence suggests that this equilibrium was reached about 4,000 to 5,000 years ago. At that time the barrier islands were wider--some by as much as 2 km or more. As time passed, the complex landscape of the barrier islands evolved. In the narrow areas, inlets breached the islands and filled in to reform them. Long spits connected the more stable sections, such as the land
area near Cape Hatteras, where sequences of beach ridges developed, building long




0 C & . 0
0.08m/1 dOyrs+
100 25
'I.
LLJ Q50
wL 200 m
E
Clq
75
& Texas Shelf
300 + Holland
x Australia
o Southwest Louisiana
* Eastern Argentina
* West Louisiana Shelf 100
a Western Mexico
II I I
5 10 15 20
THOUSANDS OF YEARS BEFORE PRESENT
Figure '5. The Rise of Sea Level as Obtained from Carbon 14 Dates in Relatively Stable Areas (from Shepard, 1963). Break in Slope some 6400 Years
Before Present (BP) may have Provided Basis for Barrier Island Stability.




chains of Holocene barrier islands. Exceptions to this model are the more stable "sea islands" of Georgia (Cumberland), which differ significantly from Holocene barriers in that Holocene material is deposited on the seaward side of detached segments of the mainland Pleistocene terrace.
Sea Level Rise and Barrier Islands
Although Holocene sea level remained fairly stable following the initial rise during the post-Wisconsin, sea level has risen several meters in the past
2,000 years. This slow rise has resulted in the recession of shorelines and the enlargement of bays and sounds behind the barrier islands. Over the past 200 years, the rise has been rapid, totaling slightly more than 30 cm.
The rate of barrier island recession over the last 2,000 years undoubtedly
varied as the rate in the rise of sea level changed, as the supply of sand waned, and as the slope of the bottom of the inshore zone evolved in response to storms
and waves. Some of the eroded material has been lost into large offshore sediment sinks, such as Diamond Shoals off Cape Hatteras. Much of it, however,
has remained within the barrier island sediment budget and has contributed to spit growth, inlet filling, dune building, and storm-overwash deposits.
The Importance of Natural Processes
Within the coastal and marine parks of the S.E. Region, the National Park
Service has long recognized the importance of allowing natural processes to proceed in an uninterrupted manner. However, the NPS recognizes that some of
the coastal lands now administered as parks, recreation areas, and monuments were altered by engineering structures or sediment management practices decades before the areas were added to the NPS system. In addition, some of the bays, lagoons, and inlets that are now part of the NES lands have been and continue to be part of the vital coastal waterways. For these reasons, the NPS realizes that all of the barrier islands, inlets, and lagoons within their jurisdiction cannot be
managed as totally "natural" systems; however, it is important to recognize, when assessing the potential implications of a dredging project within park lands, that the natural processes are the processes that were responsible for the formation of the islands, and for the great natural beauty of these areas. These processes should not be interfered with unless absolutely essential.




Beach Features and Processes

Longshore Sediment Transport
Generally waves approach the coastline at an angle due to the relative location of the wave generating area. In many locations, for example, the East coast of Florida, the predominant wave direction is seasonal due to the dominance of various storm patterns and locations at differing times during the year.
When waves reach a sufficiently shallow depth, they break, thereby establishing the outer limit of the "surf zone", as shown in Figure 6. The
character of the water and sediment motions within the surf zone differ greatly from those seaward of the surf zone. Within the surf zone, the breaking waves exert a "force" on the water causing a movement of water along the shore called a "longshore current". These currents are apparent to the casual swimmer as he or'she is displaced along the shoreline. The magnitudes of longshore currents are generally small, on the order of 30 cm/second, but can range up to 150 cm/second. Due to wave breaking, the water inside the surf zone is much more turbulent and chaotic than that outside the surf zone. These two characteristics, the turbulent water motions and the relatively weak longshore current are responsible for the mobilization and transport of sediment in a longshore direction. As can be appreciated, the magnitudes of sand transported along the shoreline depend on the wave height and direction characteristics and can vary considerable from place to place and can even vary from year to year at a particular locality. Interference with the longshore sediment transport will cause areas of accretion and erosion.
Methods exist for the calculation of longshore sediment transport based on wave heights and directions; however, due to our imprecise understanding of transport processes and lack of quality wave data, results of such calculations should be considered as estimates only. Some of the best field estimates of longshore sediment transport are based on the rates of accumulation caused by the construction of long impermeable structures on the updrift sides of channel entrances. Still, such data must be interpreted carefully.
The notation generally adopted for the direction of longshore sediment transport is that positive transport is to the right as an observer faces




Figure 6. Waves Arriving Obliquely to Shoreline
Cause Longshore Current and Longshore
Sediment Transport Primarily Within
Surf Zone.

seaward. At most locations, both positive and negative transport occur during a year. The difference between the positive and negative annual transport is termed the "net" annual transport and is either positive or negative. In some applications, it is the "gross" transport which is the sum of the positive and negative components (irrespective of sign) that is of importance. An example
will serve to illustrate this convention. A published estimate (Walton and Dean, 1973) of positive and negative transport rates slightly south of Cumberland Island, GA is
Q+ = 37,000 m3 y
Q-= 3 70,000 m /yr




Thus the total annual southerly and northerly transport components are 370,000 m3/yr and 170,000 m3/yr, respectively. The "net" and "gross" components are
QNET = + 200,000 m 3/yr (Southerly)
NET (2)
QGROSS 370,000 + 170,000 = 540,000 m3/yr
In general, the net longshore sediment transport is southward along the East coast portion of the Southeast Region. Fairly detailed estimates exist for the East coast of Florida as shown in Figure 7.
Cross-Shore Sediment Transport
It is well-known that beaches change seasonally and with differing wave conditions. Although beach profile changes can occur due to longshore sediment transport, the focus here will be limited to cross-shore sediment transport.
Winter waves are usually higher and generally have shorter periods than those occurring during the summer months. The resulting summer and winter beach profiles differ substantially as idealized in Figure 8. The summer profile
tends to be steeper with a wider berm and the winter profile tends to be milder in slope and to have a narrower berm. Although the range in seasonal shoreline fluctuations is not known for many locations, it has been shown to be on the order of 30 m at Long Island, NY (Bokuniewicz et al., 1980), 80 m at Stinson Beach, CA (Johnson, 1971), and 10 m at Boca Raton, FL (Dewall and Richter, 1977). Additionally, in many locations, there is a bar present in the winter profile. At some locations, the bar is perennial.
The mechanics of cross-shore transport are not understood completely; however storm waves of greater heights and shorter periods cause offshore transport. Table 1 presents an example of shoreline changes that occurred in New Jersey due to a severe storm.
If the dunes are sufficiently high during a storm to prevent overtopping, transport may be limited to the offshore direction. However, if the storm tide level exceeds the dune elevation or if the dunes are breached, a process called "overwash" may occur. Overwash is the transport of water and sand over a normally subaerial feature usually due to storm-elevated water levels and increased wave heights. The sand deposit resulting from an overwash event is




tcSANTA K *_JACKSONI RADN
1/ SANTA K HOLMA .. ROSA / A NANDINA
o WALT 7, 460,OOOm 3/yr
M 0 W A L TDO NI HS O -uV
\ 'S'i 10 1 ~/~AITN JACKSONVILLE
A .B Q, I YDSO
BAY Ilk i, V'MDIO U BAKER(
--LIBERTY WAKULLA TA O 'e I BAKER GULF FRANKLIN R A.1 ST. AUGUSTINE
/ '~. A F RD ST.
>--" GIL-' RD I CLHRIS TJOHNSMA
CHRIST JOHNS MARINELAND
I ALACHUAj PUTN M(0
GJY Op LEVY ,
'" '--; AYTONA SMARION -I\ 400st\3 y
SVOLUSIt 400,000 m3/yr ', EW SMYRNA
CITUS> } LAKE r
-- SUMTER
HERNAND I I I I ORANGE
PAsco I I APE CANAVERAL
1OSSCEOLA
PASs IE A
P POLK IA 300,OOm 3/yr N 0 Dto
E -/ l rTNE
L.- --- 7------ RIVER ERO BEACH
^ MANATEE HARDEE I EE. ST. 200,OOOm 3/yr S H -'~s FT PIERCE
$4 I ----1HIGHLAN I LUCIE U \ -,DE SOTO: t -H \ 4L ,_ ,AKEI")IARTIN' \ 4 HAO TiA OKEECHO -AT JUPITER I.
SHAR LADE E 200,000m 3yr
1 PALM BEACH S LEE I HENRY I PALM BEACH
"_ EERFIELD
100,000m 3/yr
COLLIER BROWARD 100, m yr BAKERS HAULOVER
* -4 10,000m3/yr
O N RO DADE MIAMI
1;
ONROt
Figure 7. Estimates of Net Annual Longshore Sediment Transport Along
Florida's East Coast.




SUMMARY OF SHORELINE RESPONSE TO NEW JERSEY STORM OF NOVEMBER 6-7, 1953 (From Caldwell, 1959)
Contour Elevation Landward Retreat of Contours (m)
(m Above Mean Low Water) Average Maximum
0 20 34
1.5 19 27
3.0 30 55
4.5 16 37

Figure 8. Normal and Storm Profiles on a Natural Shoreline.
TABLE 1

Normal Profile




termed "washover" and may be up to 2 meters or more in thickness. As relative sea level rises, barrier islands maintain their elevation by washover deposits which occur in "plaques" or layers. Deposition by wind also plays a role in increasing the elevation of barrier islands. Significant overwash may not occur for several decades or more and with a single storm, the resulting deposits may achieve equilibration with increased sea level which has occurred since the previous significant overwash event.
Variation of Sand Size Across the Nearshore
If one were to collect and analyze sediment samples ranging from the dune to water depths of 10 m or so, it would be apparent that the "forces" in this region cause a sorting of the available sediment according to size. Although there would be a great deal of variability in sediment size from profile to profile, in general the sand in shallower waters is coarser than in deeper waters. There are a number of theories to explain the details of this sorting, the most intuitive being that the shallow water zone is an area of breaking waves and thus if fine sediment were introduced it would be repeatedly resuspended and could only be stable in the deeper water offshore where the near-bottom water velocities are much weaker. This is the same argument explaining why dust particles settle in the relatively quiet corners of rooms. Figure 9 presents an example from Martin County, FL of sand size variation from the dune crest out to a water depth of nearly 10 meters. It is seen that the size decreases from 0.4 mm to 0.1 mm in the deeper water. The past processes that are responsible for the present distribution of nearshore sediments are complex and it is possible to find nearshore deposits of coarse sediments although the decrease in size in the offshore direction is the general case and is relevant to the quality of nearshore material available for beach nourishment purposes.
In addition to the distribution of size discussed above, there is a general increase in the offshore direction of the range of sizes of a sediment sample. Due to the fairly intense turbulence in the nearshore zone and the resuspension mechanism discussed earlier, there is almost no silt/clay content present. However in depths exceeding 5-10 m, it is not unusual to find silt/clay percentages of 5-10% or greater.




Z" 0or
uJ
C
z
<> Wj
uJ E mac
2 Lu Oc
1-

0 200

600

1000

1400

1800

DISTANCE OFFSHORE (m)

200

600

1000

1400

1800

Figure 9. Variation of Median Sediment Size with Location Across
Beach Profile. North Jupiter Island. Florida.

0.4 0.3
0.2 0.1

I I I I I I I I I I

4 Dun -e 2
2 4 6 8 10

. III.I..ll011
- ; .

-




Role of Inlets
Inlets are channels connecting outer waters to interior lagoons or bays. Inlets are subjected to two competing forces. The rising and falling tides in the ocean cause water to flow into the bay (flood currents) and out of the bay (ebb currents). The volume of water entering an inlet during flood (inward) flow or leaving during ebb (seaward) flow is termed the "tidal prism", an important characteristic of the inlet bay system. Through refraction, waves tend to transport sand toward inlets and to cause closure. The tidal currents through the inlets scour excess sand from the channel maintaining it open. To understand how these two competing forces interact, consider the simple system discussed below. If an inlet were excavated wider than equilibrium, the scouring velocities would decrease, sand would enter the channel and deposit thereby decreasing the cross-sectional area with a corresponding increase in tidal currents which would decrease the tendency for sand deposition. Conversely, if sand were placed in an inlet in equilibrium conditions, thereby decreasing the flow area, the velocities would increase, scouring out the excess and returning the area to equilibrium. Thus the inlet cross-sectional area tends to be selfequilibrating. O'Brien (1931) found the surprisingly simple relationship shown
in Figure 10 between the equilibrium cross-section of an inlet and the total volumetric flow of water passing through an inlet during flood or ebb flow. The dashed line in Figure 10 represents a peak velocity through the inlet of 1 m/s.
Thus it appears that in a sandy material, under equilibrium conditions, the inlet adjusts itself such that the peak velocities in and out of the inlet are on the order of 1 m/s. As described previously, any change in cross-sectional area to alter this velocity will induce velocity changes to reestablish the equilibrium area.
With the above discussion of the flow in and out of inlets and the related scour of excess sediments, it is not surprising to find extensive sand deposits wayward and seaward of the inlet channel. These deposits are termed flood and
ebb tidal shoals signifying the currents causing their transport to these locations. These shoals are extremely important to the inlet stability; their roles will be reviewed below.
The flood tidal shoals represent deposits that are relatively static and grow to substantial volumes and, due to the usually moderate wave climate inside




0 No Jetty
z A One Jetty
E: 109 O Two Jetties _..
Cl,
Z- E ----- -. -m
0 Al
w Corresponds to
0 Vmax lm/s
- O'Brlen's Best Fit
_j to Data
1 -.. ................... ...................... ............ .
_6 1 itF I_ l ; I 11
10 102 103 104 10 5 10 6
MINIMUM CROSS-SECTIONAL
FLOW AREA (M2)

Figure 10.

Relationship between Spring Range Tidal Prism and Minimum Cross-Section, Compared with Maximum Inlet Velocity of 1m/s. Modified from O'Brien (1931).




the bays, may become vegetated and emerge as islands. As these features grow,
they reduce the hydraulic efficiency of the inlet and may contribute to slow downdraft migration of the inlet to a more hydraulically favorable location or
may contribute to inlet closure and formation of a new inlet at a more hydraulically conducive location.
The ebb tidal shoals are located in an area of much greater wave energy than the flood tidal shoals. Breaking waves tend to drive the sand toward shore and the ebb tidal currents induce seaward transport, Figure 11. Immediately after formation of an inlet, the wave effect is weak due to the greater depths in the
vicinity of eventual ebb shoal formation. With continuing deposition and local shoaling, the shoreward forces due to waves become more effective and ultimately an equilibrium is achieved when any additional sand transported to the shoal by the ebb tidal currents is driven back into the nearshore system by the waves, Figure 11. In areas where a net longshore sediment transport is present, the
ebb tidal shoal and its extensions to shore provide a "sand bridge" by which the net transport makes its way around the entrance. The shape of the ebb tidal shoal is indicative of the relative wave energy with shoals in high energy regions characterized by rather smooth and regular outer contours and those in low energy regions by irregular contours. Volumes contained in these ebb tidal
shoals can be enormous. Dean and Walton (1975) developed and applied a technique to establish the volume of sand in an ebb tidal shoal. It was found that the
Boca Grande Pass ebb tidal shoal on the West coast of Florida contained approximately 200 million cubic yards of sand. Later Walton and Adams (1976) calculated the ebb tidal shoal volumes for a large number of inlets and found
that the volumes correlated well with tidal prism and relative wave energy. Figure 12 presents these results where it is noted that in accordance with earlier discussions, the ebb shoal volumes decrease with increasing wave energy.
It is important to recognize that in the vicinity of an inlet, the ebb tidal shoal and the adjacent beaches form components of a system in equilibrium. If,
foursome reason sand is removed from one component of this system, all components will respond to reestablish equilibrium. These components have been termed appropriately a "sand sharing system" (Figure 13). We will see later the impact of removing sand from the ebb tidal shoal of this "sand sharing system".




Figure

(C)
(W)

Flood

Ebb Tidal Shoal

Bay

The Balance of Forces which Maintains the Ebb Tidal Shoal Volume In Equilibrium




1000
- I I I I I I I|l I I I i i~ Il i I I I l l -4S100- 0
S
10
L.U
1
1.5O -0n 5 I I l i li ll I I I I II11 ll I I 1 1 1111I
1 10 100 1000
TIDAL PRISM (m 3x 10-6 Figure 12. Relationship Between Equilibrium Volume of Sand Stored
in Ebb Tidal Shoal and Tidal Prism (Adapted From Walton
and Adams, 1976).




Inlet

Figure 13. The "Sand Sharing System" Comprising the Inlet, the Ebb
Tidal Shoal and Adjacent Shorelines.




PART III
THE DREDGING PROCESS




PART III
THE DREDGING PROCESS
Introduction
In this section we review the objectives of dredging, the equipment and methodologies used in dredging and some of the general effects of dredging that can adversely impact the environment.
Dredging Objectives
There are two general and fairly obvious reasons for dredging. First is the removal of quantities of material from an area in which it is regarded as an impediment to one or more particular activities. Examples are dredging of
a navigational channel or a marina. In this case, the placement of the material removed is usually of secondary interest to those carrying out the dredging and in the absence of other considerations, the material will be disposed of by the least costly method. The second reason for dredging is to obtain material for some use. In our context, beach nourishment is the more usual example and the quality of the material can be of prime concern. Regardless of the reason for dredging, removal and placement of large quantities of material will obviously cause physical and environmental perturbations in the dredging area and in the area where the material is placed.
Dredging Equipment Methodologies
The two general classes of dredges include mechanical dredges and hydraulic dredges. Mechanical dredges include clam shell dredges (Figure 14) and bucket dredges (Figure 15). Practically all large dredging projects are carried out
with hydraulic dredges; therefore, this discussion will be limited to this class.
Within the hydraulic dredge class, there are two general types of dredges, i.e. the pipeline dredge and the hopper dredge. Pipeline dredges move very slowly, excavating to a substantial additional depth before they leave an area, Figure 16. This material is transported as a water-sediment mix or "slurry" through a pipeline to the area desired. Hopper dredges load material into a hull while underway and transport the material as a bulk cargo, Figure 17. The
original hopper dredges were designed (as their name implies) to store the




Luffing Wire Hoist and Hold
Wires

Hoist and Hold

Winch

Aft Wire

Underwater Fairleads

Figure 14. The Clam Shell Dredge (From Bray, 1979).

Ladder
O

Discharge Chute
O

"- Bucket

Figure 15. Bucket Ladder Dredge (From Richardson, 1976).




Figure 16. Plan View of Operation of a Pipeline Dredge (From Bray, 1979)

HoppeAAr7,__

Figure 17.

Self-propelled Hopper Dredge with Trailing Dragarm (From Richardson, 1976).




dredged material in hoppers and upon reaching the disposal site, to discharge
the cargo through bottom dumping hopper doors. During the last two decades, due to the need for beach nourishment, a number of hopper dredges have been modified to include a capability to pump out the hulls and complete the delivery to the beach or nearshore area via a pipeline.
Pipeline dredges are rated by the size of their discharge lines (or pipes) and the rate of sand discharge varies substantially with pipe size. The
approximate range of pipe sizes is 15 cm to 120 cm with corresponding pumping rates from 50 cubic meters per hour to 3,000 cubic meters per hour. Thus the size of a project will dictate, to some degree, the size of the equipment. As
an example, a project requiring dredging of 1,000,000 cubic meters would usually result in contracting a dredge of 60 cm diameter, i.e. approximately 1,000 hrs of required pumping time.
The elements of a pipeline dredge include an intake pipe mounted on a "ladder", a dredge pump and a discharge line to the placement area. The sediment to be pumped can be mobilized by jets of water in which case the dredge is called a "suction head" dredge (Figure 18) or if sediment mobilization is caused by a rotating cutter head, the appellation "cutter head" dredge is used, Figure 19.
The ladder can be moved both horizontally and vertically to access more sediment while the dredge is in a f ixed location. The dredge pump is mounted on a barge and is a centrifugal type pump with hardened elements to resist wear caused by
the pumped sand. The discharge line connects to the outlet of the pump and this line, generally in segments of 10 m length or greater, transports the sand to
the point of delivery. If the discharge line is so long that the power supplied by the dredge pump will not transport the slurry at sufficiently high velocities, it may be necessary to install "booster" pumps periodically along the pipeline
with a booster pump every mile or so for smaller pipelines and booster pumps every two to three miles for the larger pipelines. Pumping over distances in excess of 20 km have been accomplished. It is necessary to maintain velocities
above the sediment settling values or else there is a risk of deposition occurring in the pipeline leading to its eventual plugging. Since settling
velocity increases with size of the sediment particles, the larger the size, the greater the required water velocity in the pipeline. Typical pipeline slurries




.Pumps, Motors, Etc.

Discharge Pipe

i Pipe

-"4- Jet Cutting Assist

Figure 18. Plain Suction Dredge (Swell-compensated)
(From Richardson, 1976).

Figure 19. Cutter Suction Dredge (With Spuds)
(From Richardson, 1976).




are on the order of 16% to 20% solids by volume with the remainder being water and pipeline velocities are on the order of 5 to 8 m/s.
The "side-casting" dredge is a variation of a suction dredge which discharges the sediment only a short distance (30 m to 100 m) to the side through a pipe-line supported above the water surface. The relocation of sediment by such short distances raises questions about its effectiveness, i.e. the length
of time before the sand will be redeposited in the area deepened by the dredging. Because of these concerns, most sidecasting is carried out only for emergency purposes.
Hopper dredges are essentially a ship hull configured as a bulk carrier. These dredges can have bottom doors which allow release of the material carried or more recent designs are termed "Split Hull", with large hinges fore and aft allowing the hull to split, dropping its cargo of material, Figure 20. Loading of hopper dredges occurs through two "drag heads" while the dredge is underway;
these drag heads are pulled along the bottom agitating and entraining the material into a pipe which carries the slurry up and into the hull. The hull functions as a settling basin with the sediment settling out and water and fine sediments returning over the side. Once the dredge is fully loaded, the drag heads are raised above the water and the material transported to the placement site.




Plan

1~

I % __L
\' 14rvw

Iz

0m

Front Elevation
Side Elevation
Figure 20. Split Hopper Barge (Self-propelled)
(From Richardson, 1976).




PART IV
ALTERED COASTAL SYSTEMS




PART IV
ALTERED COASTAL SYSTEMS
A. GENERAL
Introduction
Natural beach and inlet systems may be altered in several ways, including dredging and constructing channels at entrances, building structures along the shoreline and nourishing beaches. Each of these alterations and their potential impacts on the natural system will be described below.
Modifications of Channel Entrances
Modifications of natural channel entrances or construction of new entrances have been carried out primarily for purposes of navigation and secondarily to improve flushing and renewal of interior waters. Even those entrances that were constructed initially for water quality improvement have been modified later for navigational purposes. The reasons for navigational modifications include the aforementioned shallow and energetic ebb tidal shoal which under even moderate wave action may be treacherous or unsuitable for navigation. Even though some ebb shoals have relatively deep natural channels incised through them, these channels are generally circuitous and tend to migrate in an unpredictable manner, thus contributing to the navigation jeopardy. To improve these channels for navigation, many have been stabilized through construction of jetties which are usually long stone structures lining the channel and extending up to several kilometers into the sea. The term "jetty" derives from their intended function, i.e. to constrain the seaward flows causing excess sand to be jetted offshore by the ebb tidal currents. Jettied inlets can cause/institute changes to the downdrift shoreline by interfering with the longshore sediment transport and by modifying wave patterns. The greatest effect is the physical interference with the longshore sediment transport. If no sand is bypassed around the entrance, and if the jetties are impermeable, the updrift jetty will trap, on an annual basis, the net longshore sediment transport rate. Not surprisingly, the annual erosion on the downdrift beaches will occur at the same rate. If the jetties are leaky allowing sand to flow through them and transport reversals occur, the downdrift erosion can exceed the net longshore sediment transport. Also leaky




jetties can result in erosion of the updrift shoreline. If all of the downdrift transport passes through the updrift jetty, the updrift shoreline will erode at the rate of the updrift transport component. For the same scenario, the
downdrift shoreline will erode at the rate of the downdrift transport component.
From the preceding discussion, there is a clear need at modified entrances to attempt to reinstate the sediment transport that has been interrupted by the modifications. Unfortunately our "track record" in this regard has been much less than exemplary. In many cases sand removed by hopper dredges for channel maintenance has been transported offshore and deposited in water too deep to benefit the nearshore system. Data available for the East coast of Florida shows that within the last 5 decades or so, more than 50 million cubic meters of beach quality sand has been disposed of in excessive water depths. Today's market value of this sand is on the order of $250 million to $500 million. Sand
deposits as a result of channel modifications and construction should be regarded as a valuable natural resource and not as a material to be disposed of in the least costly manner. Returning to Florida East coast examples, it can be shown that this 50 million cubic meters is sufficient to advance the entire 600 km East coast shoreline seaward by 8 m. Dean (1988) has estimated that 80% of the erosion along Florida's East coast is due to poor sand management practices, which continue today albeit to a lesser degree.
In general, there are two approaches to maintaining longshore sediment transport. One approach is to allow the sediment to accumulate either updrift of the updrift jetty or in the channel and to bypass periodically, relatively large quantities of sand. Such bypassing could be carried out annually or biennially and could involve from hundreds of thousands of cubic meters to 2 million cubic meters in each bypassing event. This mode of bypassing is
accomplished by a rather large dredge brought to the area periodically or when needed. The alternative approach is a "dedicated" bypass facility which transfers sand with much greater frequency more or less as it becomes available. The downdrift consequences of these two modes of bypassing differ markedly. In the "batch mode" of bypassing, the downdrift shoreline will widen and narrow as the replenishment and erosional sand waves move downdrift. This variation in beach width may not be favorable for intertidal or nearshore fauna. Clearly in cases where nearshore rock or reef is present and considered a valuable habitat,




the covering and uncovering of these resources may cause adverse effects. By contrast, the more-or-less continuous bypassing mode tends to mimic the natural processes and thus minimizes any resulting disturbances.
Some modified inlets will continue to bypass small quantities of sand naturally whereas others will represent a complete obstruction. In many cases the distinguishing feature is whether or not and to what depth the channel is dredged. If the channel is not dredged, the presence of the jetties will alter the sand transport patterns usually resulting in an increase in volume of the
ebb tidal shoal and a deflection offshore and downdrift of the ebb shoal and associated "sand bridge" or sand bypassing bar. Thus, the bypassing efficiency by natural forces will be decreased markedly.
Beach Nourishment Projects and Their Evolution
Beach nourishment comprises the addition of relatively large quantities of
beach quality sand. Generally, the length of time that sand remains in the area placed is considered as a measure of the physical performance of a beach nourishment project. The discussion on performance will be presented for two
situations: (1) a project on a long uninterrupted beach, and (2) a project immediately downdrift of a littoral barrier.
Case (1) Project on a Long Uninterrupted Beach In this case the longevity of a beach nourishment project is defined as the length of time that a specified percentage of the added material remains in the area placed. The longevity can be shown to be proportional to the square of the length, 2,, of a project, inversely proportional to the breaking wave height H b, raised to the 5/2 power and related to the sediment size. The half life, t 50, of an initially
rectangular beach planform composed of medium sized sand can be shown to be
t 5= 0.17 -15/2 (1)
(H b)
in which t 5 represents the time in years required for 50% of the sand to be transported out of the region placed, 2, is the project length in kilometers and H b is the effective wave height in meters. Figure 21 presents an example of the evolution of an initially rectangular planform. Initially the sharp corners are




DISTANCE FROM ORIGINAL
SHORELINE (m)

-Original Nourished Beach Planform
-Planform After 3 Months
- 10 Months
- 7 Years
-30 Years
-130 Years
Pre-Nourished
%- rz-2 horelbkme

9 6 3 0 3 6 9

ALONGSHORE DISTANCE (km)

Figure 21.

Example of Evolution of Initially Rectangular Nourished Beach Planform. Example for Project Length, -, of 6 km, Effective Wave Height, H, of 0.6 m and initial Nourished Beach Width of 30 m.




rounded and changes occur rapidly. As the evolution progresses, the planform
anomaly begins to behave as a longer project and changes occur much more slowly.
En evaluating the performance of a beach nourishment project, it is important to note that if the sediment is of good quality, although eventually
the sediment will be transported out of the region placed, it will remain within the region of active nearshore sediment transport and will continue to provide benefits to those areas to which it is transported.
Case (2) Placement Immediately Downdrift of a Littoral Barrier This situation is fairly common due to the aforementioned adverse impact of inlets
modified or constructed for navigational purposes. As intuition would suggest, if the longshore sediment transport deficit is large, the life of the beach nourishment project will be short and in such cases, rather than considering the longevity of the project as a measure of its performance, it may be more appropriate to regard the nourishment as a "feeder beach" placed to reinstate the longshore sediment transport.
Profile Equilibration After Nourishment
In addition to planform evolution, the profile will change from that initially placed to one that approaches equilibrium with the incoming wave characteristics and sediment size. The quality or size of sand used in
nourishment governs the shape of the equilibrium beach profile. Sand of the same size characteristics as the original beach will have an equilibrium profile the same as the pre-nourished beach. Sand coarser or finer than the original will
have equilibrium profiles steeper or milder, respectively, than the original profiles.
Relative Benefits of Offshore Sand Placement at Various Depths
In some cases, it may be less expensive to place the sand in the nearshore
region than on the dry beach. Questions have arisen regarding the effectiveness of this approach. There have been several attempts to place substantial
quantities of sand in the nearshore region and to carry out monitoring to determine whether the sand was transported shoreward. The field test programs
and the experience with each is summarized in Table 2. As can be seen, only the




Location Water Depth Documented
(m) Movement
Toward Shore
Santa Barbara, CA 6 No
Long Beach, NJ 11 No
Atlantic City, NJ 4.5 8 No
New River Inlet, NC 2 4 Yes

TABLE 2

FIELD TESTS CARRIED OUT
TO EVALUATE SHOREWARD SEDIMENT TRANSPORT FROM OFFSHORE PLACEMENT

placement in water depths of 2-4 m was definitively concluded to be a success in terms of shoreward sediment transport.
Based on results such as summarized in Table 2, the state of Florida has considered that sediment placed in water depths greater than 4 m is relatively ineffective in nourishing the shoreline. There can be undesirable effects of
placing sand in the nearshore region. In particular, if the sand deposited offshore is not at a uniform elevation in the longshore direction, local sheltering can occur causing sand to accumulate on the shoreline behind those segments with the greatest elevations and erosion of adjacent areas. Thus if
sand is to be placed offshore, it should be placed in an underwater berm of nearly uniform elevation with a gradual decrease in elevation to the ambient profile at the ends of the berm.
Need for Profile Contouring
Sand placed in a beach nourishment project should be configured to allow
natural processes to complete the shaping to natural profile characteristics with the elements described previously. The underwater portion of the profile does
not present a problem as the waves will carry out the contouring. However, the




above water portion of the profile should be constructed at a sufficiently low elevation that the run-up and overtopping due to waves can complete and "finetune" the prof ile shaping. If the berm portion of the prof ile is placed too high for waves and run-up to play a role, the resulting profile will retain an artificial characteristic.
B. POTENTIAL DREDGING IMPACTS
Physical Effects
As described previously dredging is usually carried out to provide or remove sediment for some purpose, such as a beach nourishment project or to provide desired channel depths for improved navigation. Each of these two cases will be discussed below.
Dredging to Obtain Material In this case the area from which the material is removed (the "borrow" area) can be fairly extensive in size and on the order of 3-6 m deeper than the ambient bottom. This anomaly can cause less damping as the waves propagate toward shore, thereby causing slightly greater breaking wave heights. Probably of greater importance than the net increase in wave energy is the modified distribution of wave energy along the shoreline due to wave refraction. The wave rays which are everywhere perpendicular to the wave
crests will tend to diffuse or spread out over the deepened area thereby lessening the wave energy at some areas along the shoreline and increasing it at others. The areas of wave energy increase and decrease would depend on the wave direction as can be seen by reference to Figure 22. As there is no simple
"rule of thumb" to define the effect of such a bathymetric anomaly, wave refraction studies should be carried out for each case to establish the potential impact.
For purposes of later discussion, it will be of interest to comment on the
filling of the borrow depression. Although there is not a large data base relating to this matter, borrow areas are characterized by low wave energy and
thus tend to fill with finer sediment than that removed. In areas where the bottom is highly mobile and where concentrations of suspended sediment are small, a greater percentage of the filling material will be from the adjacent bottom.




Zone of Increased
Wave Energy
Zone of Reduced
Wave Energy
Zone of Increased
Wave Energy

'- Deepened
"Borrow" Area

Effect of a Dredged Borrow Area on Wave Refraction and Wave Energy Distribution along the Shoreline.

Figure 22.




Dredging to Increase Navigation Channel Depths Earlier sections of this report have discussed the "sand sharing" system composed of the ebb tidal shoal and the adjacent shorelines. A useful basis for consideration purposes is that' a given system in its natural condition is in equilibrium and that if changes are made to the system, it will respond to reestablish equilibrium. Thus when
sand is removed from an ebb tidal shoal, sand will flow toward the deepened area and a portion of this deficit will be felt at the updrift shoreline and a portion at the downdrift shoreline. If the longshore sediment transport were nearly
unidirectional, one can simplify considerations as follows. The longshore
sediment transport tends to rebuild the ebb tidal shoal which functions as a "sand bridge"' across which this transport occurs. With the sand bridge cut (shoal deepened), the longshore sediment transport will deposit in the cut to reestablish the bridge. The volume of material deposited appears as a deficit
to the downdrift shoreline and results in a volumetrically equal amount of erosion there.
The obvious appropriate approach to placement of beach quality sediment removed from navigation channels is, through surveys of the adjacent shorelines, to develop a basis for apportioning the high quality dredged sand on these shorelines.
Environmental Effects of Beach Nourishment Projects
Primary potential environmental effects of beach nourishment relate to: quality of sediment, impact of burial by the placed sediment and the more subtle effects above water such as altering the natural dune system. The actual impact of each of these is species dependent and to some extent locality dependent.
Sediment Quality In this section sediment quality will be considered on a relative basis and will be quantified in terms of grain size and color. As
an ideal measure of sediment quality, the grain size distribution of the material to be placed should match the native grain size distribution. As a more
realistic measure of good sediment quality, the general mean grain size of the
material to be placed should not be much smaller than that of the native material and the percentage of the silt and clay fraction (the fines) should be relatively small.




There has been considerable debate concerning the allowable percentage of
silt and clay and understandably in some project areas, the allowable limit will be less than in others. A biological study conducted after the Miami Beach, FL
nourishment project (1976-1981) concluded that silt and clay percentages greater than 10% could cause substantial damage to offshore coral reefs. (The silt and
clay portion of a sediment sample is that fraction with diameters less than 0.0625 mm). The Department of Environmental Regulation of the State of Florida
is currently attempting to quantify acceptable levels of silt and clay for placement on the beach. It appears that if a value is adopted, it will be less
than or equal to 10% with 5% being a value which has been discussed considerably. Turbidity concerns are both short-term and long-term. During placement, a small percentage of silt and clay will generate quite visible turbidity. In some
cases, this turbidity remains confined primarily within the active surf zone,
spreading out in the longshore direction. Apart from the surf zone, the initial turbidity is spread offshore over a wide region with generally low concentrations. If silt and clay concentrations are high, the turbidity considerations
are likewise high and can present potential problems to both sessile animals (those which cannot move) and motile animals (those which can move). Generally fish will move away from turbidity avoiding the potential effects.
Nelson (1985) has presented an excellent review of the effects of beach nourishment on the nearshore biota. The primary focus was on four common
nearshore organisms: (1) Emerita talpoida (mole crabs), (2) Donax (coquina clams), (3) Ocypode (ghost crabs), and (4) Sea Turtles.
Emerita Talpoida (Mole Crabs)
This organism is a filter feeder that burrows in the lower foreshore of the beach and can be very abundant, although the densities tend to be quite irregular. The highly energetic swash zone appears to be the preferred environment for E. Talpoida probably enhancing the food supply. Densities in
excess of 3,700 animals per square meter have been reported (Bowman, 1981). The animals tend to be in greatest abundances in Florida in December to January.
E. Talpoida, are very mobile and apparently have the capability to avoid being buried by beach nourishment by leaving an area. In a project in which
956,000 m3 sand was placed on Cape Hatteras beach, Hayden and Dolan (1974) found




no dead animals and they concluded that the affected areas recovered in less than two weeks. The sand used in this nourishment project was quite compatible with the native sand. A second project of similar quantity (904,000 m3) at Fort Macon, NC, was monitored by Reilly and Bellis (1978, 1983); however the sand was taken from dredged harbor sediments and was not compatible in size characteristics. Additionally the sediment was from a chemically reducing environment. Monitoring of this latter project indicated that the E. Talpoida populations were nonexistent in the project area during material placement but recolonized rapidly several months later during the spring recruitment period. A delay of one month during the recruitment period was evident. The summer after the commencement of nourishment (the preceding December), the animal densities were the same on the nourished and control beaches. However, there were significant differences in the size classes with the nourishment containing exclusively juveniles. The investigators concluded that the adult mole crabs in the vicinity of the nourished site were killed by turbidity and that the juvenile animals had repopulated the area from the adjacent beaches. Nelson (1985) has suggested that the liberated hydrogen sulfide in the nourished sediments may also have contributed to the mortality of adult animals.
In summary of the impact of beach nourishment on E. Talpoida, it is concluded that these animals are very mobile and are able to vacate an area unsuitable for their physiology. Moreover, with the return of favorable
conditions, they rapidly recolonize the area. If the material placed is
compatible with that originally present on the beach, effects are of quite short duration. If poor quality sediment is used, recovery is slower, but still relatively rapid, probably due to the high motility of these animals and the longshore currents on the beachface.
Donax (Coquina Clams)
This genus of bivalves has two species that have been reported to be present in the Southeast Region. The documented range of Donax Variabilis is from Virginia Beach, VA to Mississippi. Also Donax Texasianus has been found in the Florida panhandle.
Most Donax Variabilis migrate up and down the beach with the tide, presumably to be in the active swash zone where the high velocities ensure ample




quantities of moving water from which these filter feeders obtain nourishment. However some studies have reported populations that do not migrate with the tide. The life of Donax is generally 2-3 years with one or two spawning periods per year. Primary spawning occurs in February and in Florida a second spawning may occur in June. The peak seasonal abundance tends to occur in June and July. Maximum densities of Donax Texasianus in Panama City, FL was 2,050 animals/m2.
Few studies are available documenting the effects of beach nourishment on Donax. Reilly and Bellis (1978, 1983), reporting on the effects of nourishment on a North Carolina beach found that following a December nourishment event, Donax were not found in the nourished area until the following July. These were young believed to be transported in by the longshore currents and it was suggested that the adults were killed by burial in the offshore area.
Ocypode Quadrata (Ghost Crab)
These animals burrow in the dry beach although they lay their eggs in water. The older crabs tend to burrow higher on the beach than the young animals. Their diet varies from dead plant and animal material to live Donax and Emerita. Although seen frequently during the daytime, they are primarily nocturnal.
Only the studies of Reilly and Bellis (1978, 1983) have evaluated the effects of beach nourishment on ghost crab populations. Their limited data
indicated that the summer following nourishment, there was a 50% lower population. Their interpretation was that, since the material was placed below a level that would cause direct burial and since the crabs could probably burrow up through placed sand, it is likely that the reduced population was a result of emigration of the crabs due to a reduced food supply.
A Case Study: Panama City, FL
Saloman (1976), Culter and Mahadevan (1982) and Saloman, et al. (1982) have reported on extensive biological studies in conjunction with the 1976 nourishment of some 300,000 cubic meters placed along the beaches of Panama City.
Saloman (1976) conducted a pre-nourishment baseline study in 1974-1975 and documented the effects of Hurricane Eloise (September, 1975) on the biota. It




was found that there was no decline in the abundance of intertidal animals following the hurricane.
Culter and Mahadevan (1982) conducted studies in 1979-1980 to examine longterm effects of the 1976 nourishment. They concluded
"No long-term adverse environmental effects as a result of beach nourishment could be detected within the nearshore zone of the Panama City beaches. There were also no adverse or stressful conditions present at the
borrow sites."
Saloman, et al. (1982) carried out a study analyzing data collected between April 1976 and November 1977. The purpose of the study was to examine shortterm effects of offshore dredging on the benthic community. It was concluded
that there was an immediate decline in the benthic community; however, the populations recovered rapidly and were virtually at pre-construction levels within one year. It was noted that the borrow pits were relatively small and no more than 5 m of sand (vertically) was removed from each pit. The pits were located in water depths of 6 to 9 m. Initially the pits filled with material
finer than on the adjacent bottom; however, these differences tended to diminish with further filling.
Summary Regarding Intertidal Biological Effects of Beach Nourishment
Based on a comprehensive review of published information, Nelson (1985) has concluded that the intertidal beach organisms are well adapted to this high energy environment including significant erosion and accretion events and fluctuations in turbidity. During and immediately following storms, massive erosion and deposition occur over segments of beaches long in comparison to nourishment projects. Thus any adverse effects of beach nourishment carried out with compatible sand tend to be short-lived as the animals can either survive the event or are adapted to rapid lateral recolonization. Nelson notes that
although the available evidence indicates minimal and short-lived biological effects, the present level of understanding is such that biological monitoring




programs are necessary to further document the quantitative impacts of beach nourishment projects.
Sea Turtles
Sea turtles nest on the upper portions of the beach generally during the months of April through September. Table 3 presents the nesting characteristics and ranges of four species of sea turtles. The turtle nesting period coincides approximately with the period of lowest wave activity and thus from the standpoint of cost and least turbidity, the most desirable dredging period. Several potential adverse effects of beach nourishment projects on sea turtles are reviewed below.
TABLE 3
CHARACTERISTICS OF SEA TURTLES AND
NESTING IN FLORIDA*
Primary Nesting Nesting Density
Species Status Range Period (nests/km)
Loggerhead Threatened North Carolina April to I 600
(Caretta Caretta) to Florida August
Green Sea Turtle Endangered East Central May to I 20
(Chelonia mydas) (Florida) and Southeast September Florida Beaches
Leatherback Endangered Puerto Rico Late Too Small
(Dermochelys and Virgin February to to Be
coriacea) Islands (Some Late July Significant
in Florida)
Hawksbill Endangered Very Few Nests June to Too Small
(Eretmochelys in the U.S. October to Be
imbricata) Significant
*This table assembled from information provided by Dr. Earl Possardt, U.S. Fish and Wildlife Service.




Consolidated Beach Sediments Sediments dredged from an offshore borrow area may have silt and clay content in excess of normal beach sediments which can result in more consolidated beach material in the nesting area. Nelson and
Dickerson (1987) used a cone penetrometer to test 21 Florida natural and nourished beaches to determine the shearing resistance of the sediments. The cone penetrometer measures in approximate units of pounds per square inch. Of the 11 nourished beaches tested, it was concluded that 5 were sufficiently hard to reduce nesting. Nelson (1987) recommended tilling to a depth of 90 cm for
those nourished beaches with shearing resistances exceeding 500 pounds per square inch.
There do not seem to be well-established acceptable limits for the siltclay content, but an upper limit of 5 to 10% may be appropriate. Following
construction, waves will mobilize and transport the material back and forth across the profile with the finer and coarser sediments preferentially residing
in the offshore and onshore portions of the profile, respectively. Additionally, material transported to the project area by the longshore processes will intermix with the placed sands resulting in a more appropriate beach for turtle nesting. Thus projects that are initially poorly suited for nesting will improve as they mature.
Some studies have concluded that nourished beaches experience increased percentages of false crawls (Mann, 1977; Fletmeyer, 1980), whereas others show no significant difference. For those areas in which nesting appeared to be impacted, improvements were noted in subsequent years after dredging.
Blocking of Turtle Crawls by Dredge Pipe Dredge pipe oriented parallel to the beach may interfere with the attempts of female turtles to reach a nesting site. To reduce this potential problem the length of dredge pipe oriented so as to cause this problem should be kept to a minimum.
Miscellaneous Effects Additional potential impacts of beach nourishment to sea turtles include: (1) the disturbance represented by any related activities and lights on the beach, (2) compaction of the sediments by vehicles moving along the beach, and (3) tire depressions which can act as impediments to the return of hatchlings to the sea.




Nest Relocation Programs
If beach nourishment programs are carried out during turtle nesting season in a nesting area, it is essential to conduct a program of locating new nests each morning and relocate the eggs to a protected hatchery area. The hatchery
is essentially a fenced natural sand area which is protected from humans and other predators. Care is necessary in moving and placing the eggs to avoid a high mortality. Nelson, et al. (1987) have found the hatching success to be above 85% if natural sand is used in the hatchery area. This is only slightly less than in natural reference areas. Thus it can be concluded that although
further study is necessary, egg relocation to a carefully monitored hatchery area is effective in maintaining the survival rate of hatchlings.
A Case Study: Jupiter Island, Florida
Lund (1986) has reported on a comprehensive monitoring program on Jupiter Island to evaluate the impact of beach nourishment on sea turtle nesting. The program was carried out each summer from 1969 to 1983 and extended from Blowing Rocks to St. Lucie Inlet, a distance of approximately 23 kilometers. This
monitoring period encompassed major beach nourishments in 1973, 1977, 1978 and 1983, totalling 4.4 million cubic yards.
To compare the nourished and unnourished beach segments, the beach was segmented into "South", "North" and "Fill" regions, the latter region denoting a segment of some 8 km within which the nourishment occurred.
High erosion rates along the northern end of Jupiter Island are due to the interruption of the longshore sediment transport by St. Lucie Inlet which was cut in 1892. The long-term shoreline change rates vary from 9 in/year erosion
at the north end of the study area to a stable shoreline near the south end. The "South" and "Fill" regions are within the Town of Jupiter Island. Prior to the major nourishment projects which commenced in 1973, many shore protection
structures including seawalls, groins and revetments had been constructed to limit erosion of the upland (Aubrey and Dekimpe, 1988). Because of the erosional trend and the presence of the shore protection structures, the beach narrowed significantly reducing the beach area suitable for turtle nesting.
The beach material used in nourishment was substantially finer than the
sand naturally present on the beach. The silt-clay content was sufficiently high to result in a beach somewhat more compact and dense than optimum for nesting.




Lund's studies included documentation of the number of turtle nests per mile along the shoreline throughout the dominant nesting of loggerhead turtles which frequent this area. Significant findings of the study include:
(1) Prior to beach nourishment, the nesting activity in the central Fill
segment was considerably lower than in the other two segments. This was
interpreted as being due to the narrow beaches resulting from the
considerable armoring in the "Fill" segment.
(2) Following nourishment, the increase in nesting activity increased in all
three segments with the increase in the Fill segment being much greater than in the other two (125% increase vs. an average of 28% for the other two). However, the nesting density in the Fill segment always remained
below that in the North and South segments, and
(3) Adverse effects of nourishment included displacement from the site during
construction, difficulties in climbing up the steep erosional scarp that develops after nourishment, and inability to excavate egg chambers in the
highly compacted fill.
As an overall summary statement, Lund documented a net beneficial effect
of beach nourishment on sea turtle nesting at Jupiter Island. Some of the
concerns discussed in (3) above are being addressed through mechanical loosening and shaping of the beach nourishment.
Following Lund's report in 1986, additional studies have been carried out
during the Summer 1988 nesting season which followed the 1987 nourishment of 1.7 million cubic meters of sand in three segments. This fill material was loosened by tilling, thereby facilitating turtle nesting. It was found that the number of turtle nests in all three areas (North, South and Fill) increased dramatically (Bill Gahagan, Personal Communication) and that the density of nests was approximately equal in all three segments.




Summary Regarding Impact of Beach Renourishment on Sea Turtle Nesting
In summary, although much is not known regarding the detailed effects of beach nourishment on turtle nesting, research and field programs over the last decade have developed techniques effective in ameliorating the major potential adverse impacts. In fact, an effective program of nest relocation during beach
nourishment projects and, where necessary, tilling of the nourished beach appear to be effective in essentially mitigating adverse effects. Finally, in areas where beaches have narrowed due to a beach erosion trend and the presence of shore protection structures, the wider beaches resulting from beach nourishment can improve substantially nesting conditions and ultimately turtle populations.




PART V
CASE STUDIES AS EXAMPLES




PART V
CASE STUDIES AS EXAMPLES

CASE STUDY I PERDIDO KEY
Introduction
The Perdido Key Gulf Island National Seashore is located on the westernmost island in the Panhandle area of Florida. The eastern end of Perdido Key is bounded by the entrance to Pensacola Bay, Figure 23. This entrance is a
navigation channel which has been dredged to depths of 13 m, significantly exceeding the natural bar depth of approximately 6 m. Table 4 presents the available history of dredging over more than one century: from 1885 to 1987.
TABLE 4
HISTORY OF MAINTENANCE DREDGING
PENSACOLA ENTRANCE CHANNEL
1885-1987
Year Volume Dredged Type Dredge Disposal Area
(m3)
1885-1975 Unknown Hopper Gulf Disposal
1975 840,000 Hopper Gulf Disposal
1981 500,000 Hopper Gulf Disposal
1983 87,000 Hopper Gulf Disposal
1984 700,000 Hopper Gulf Disposal
1985 1,860,000 Pipeline Perdido Key
1987 150,000 Hopper Gulf Disposal
Recently Pensacola Bay was designated as a homeport for the aircraft carrier "Kittyhawk". This required an additional channel deepening with depths up to
14.6 m resulting in the attendant availability of more than 8 million cubic meters of high quality sand. The availability of this material represented both an opportunity and a dilemma for the National Park Service. The sections below




0 2 4 Miles

Pensacola

Figure 23.

Perdido Key and Entrance Channel to Pensacola Bay.

Entrance Channel

Gulf of Mexico




detail the background of the project and the rationale leading to the implemented plan.
Background
The net longshore sediment transport in the vicinity of Pensacola Bay Entrance is from east to west with an estimated magnitude of approximately 200,000 m3/year. In its natural condition, depths over the ebb tidal shoal were on the order of 6 m and formed a sand bridge from Santa Rosa Island to the downdrift Perdido Key. Deepening as documented in Table 5 severed this bridge
and the longshore sediment transport tended to deposit in the channel, reestablish the sand bridge and resume the natural bypassing process. Clearly as noted before for many cases, a shallow bar which is required for bypassing
is not compatible with safe navigation. Thus the material deposited must be removed from the channel by dredging as a periodic maintenance operation.
From the earlier discussion of natural and altered systems, it is clear that unless the dredged material is placed on the downdrift shorelines, it will represent a deficit and result in an erosional stress. As shown in Table 4, with the exception of the 1985 placement of approximately 1,860,000 in3 on Perdido Key, all placement has been at sea. As documented in Figure 24, this practice
of disposal at sea has taken a severe erosional toll on Perdido Key. This figure presents shoreline change data collected by the Florida Department of Natural
Resources showing that over the 10 year period represented by these data, an area extending over almost the entire Park limits was eroding at an average rate of approximately 1.3 rn/year. Using a standard rule of thumb, this is equivalent
to 100,000 m3/yr. Undoubtedly, the remainder of the deficit resulting from interruption of the net longshore sediment transport of 200,000 m3/yr occurs by erosion west of the western Park boundary. The nearest condominium to the west Park boundary is clearly in jeopardy due to the erosion and erosion is evident to substantial distances farther west.
Rationale for Selected Plan
In keeping with National Park Service policy to maintain, as near as possible, parks in their natural condition, an overriding factor in the considerations at Perdido Key was that the natural system had been impacted




+5.0
It

1 Mile

igure 24. Shoreline
Based on Smoothed

Change Rates for Escambla County, January 1974 Florida DNR Survey. Note Shoreline Change Rates by a Five Point Running Average.

SOctober 4.
Shown have been

FLORIDA DNR MONUMENT NUMBER

Approximate Western
SPark Boundary
West

I




TABLE 5
CHRONOLOGY OF PENSACOLA BAY ENTRANCE CHANNEL DIMENSIONS
Channel Dimensions Authorized
Year Depth (m) Width (m) or Actual
1881 7.3 24 Authorized
1885 6.9 24 Actual
1890 7.3 37 Actual
1896 9.1 91 Authorized
1902 9.1 152 Authorized
1935 9.8 152 Authorized
1959 11.3 244 Actual
Present 13.4 244 Authorized

significantly by over a century of dredging and interruption of the natural system.
The availability of large quantities of good quality sand was viewed as an opportunity to compensate for some of the adverse impacts to the natural system
that had occurred for more than a century. A decision was made to accept
approximately 4 million cubic meters of high quality beach sand with strict conditions on the placement and subsequent monitoring of the project.
Experience gained through the 1985 placement was utilized in developing requirements for the forthcoming project. Specifically, the 1985 material was
placed too high to allow normal waves to overtop the berm and contour the profile. Additionally, this prior project had left a relatively coarse shell residue on the berm and no vegetation program nor attempt to configure the sand to natural berm forms had been carried out. Recommendations for the planned project included placement over a length of approximately 6 km. The recommended profile is as shown in Figure 25.




20
a 10 Natural Berm Elevation 6 +ft
> +5ft
0 ++4ft
z
~~280tti-o \
0
Im 0
z
O \Recommended
-1 Nourishment Profile
> -10 DNR Profile
W Measured October 31,1984
-J
-20
0 300 600 900 1200 1500 1800
DISTANCE GULFWARD FROM DNR MONUMENT R-48 (ft)
Figure 25. Recommended Characteristics of Nourished Profile. Illustrated For DNR Monument No. 48




Monitoring Plan
The monitoring plan included both Physical and Biological components.
Physical Monitoring The physical monitoring program addressed three needs:
(1) Performance related, (2) Public information, and (3) Park management.
Performance Related Monitoring Needs
The primary performance related monitoring need is associated with the performance and evolution of the system, especially the sand flows and beneficial and adverse effects of the placement. Monitoring is particularly valuable to assist in understanding the natural system and to fine-tune later maintenance nourishment projects. Detailed needs are discussed below.
Profile and Planf orm Evolution Repeated profile surveys serve to document the three-dimensional changes in the nourishment volumes. Usually sand is placed on a profile that is steeper than the equilibrium profile. The equilibration process occurs as a result of storms which mobilize the sediment at greater and
greater depths. Associated with this equilibration process can be a substantial change in shoreline position that is not related to sand flow laterally along the beach. Documented volumetric changes along with an estimate of longshore
sediment transport at one location allow determination of the rates of sand flow as a function of alongshore distance. A sufficient number of profiles should
be measured to allow definition of anomalous features, such as the rhythmic platform. features that can be fairly accentuated at some locations; an example is Perdido Key.
Wave Measurements The wave characteristics relevant to sediment transport include: height (or energy), period and direction. Results obtained from a directional wave gage provide such data and allow much better interpretation of volumetric changes and profile adjustment. Available wave measurements also facilitate interpretation of storm effects including any documented difference between the effects to nourished and control areas.
Wind and Precipitation Measurements Following nourishment, generally
there will be a fairly broad expanse of dry sandy beach. Onshore winds blowing




across dry sand will tend to transport the fine fraction and deposit it as dunes. In addition to providing a better basis for understanding this process, these
measurements along with sediment samples will assist in interpreting armoring of the surface by the remaining larger particles, particularly shell fragments.
Vegetation Response In order to document vegetation response to nourishment and, where carried out, the effectiveness of vegetation establishment efforts, the monitoring should include a systematic plan for photographic documentation, yet retain sufficient flexibility to respond to unanticipated vegetation features of interest.
Public Interest/Education Monitoring Needs
It is anticipated that due to the substantial volume of sediment to be placed and the obvious resulting physical changes to the system, there will be
substantial public interest in any large beach nourishment project, including NPS rationale and justification for the placement, basis for need, etc., actual versus anticipated consequences and modification of NPS policy as the result of
experience obtained. An adequate monitoring program will ensure a basis to respond to this public interest consistent with NPS management policies and responsibilities.
Management Monitoring Needs
Consistent with NPS responsibilities to manage park systems in a nearnatural state and to understand the consequences of various management alternatives, it is essential to monitor perturbations to these systems in order to better understand the natural system and its capacity to adjust to anthropogenic perturbations. Knowledge gained will assist in providing guidance to future management decisions related to beach nourishment.
Biological Monitoring
The monitoring to establish the biological effects of the beach nourishment project includes three elements; each of these is described briefly below.




Benthic Community Studies Studies will be carried out to establish the effect of beach nourishment project on the benthic community. Sampling will be conducted along transects extending from the Gulf and Lagoon shores of Perdido Key.
Vegetation Analysis Natural and revegetation success will be documented by a combination of transects supplemented by color infrared aerial photography. The objective will be to quantify the revegetation with time as affected by various ground conditions including elevation, compactness, distance from shoreline, etc.
Beach Mouse Population Effects of the nourishment project on the beach mouse will be monitored through a series of population studies augmented by other relevant factors including food supply and predator populations. The mouse
population studies include marking and recapture studies along selected transects within the project area and at control transects outside the area. Predator
studies will include tracking using radio telemetry methods.
CASE STUDY II OREGON INLET
Introduction
Oregon Inlet is a natural inlet located approximately 63 km north of Cape Hatteras in the Cape Hatteras National Seashore. This inlet connects Pamlico Sound with the waters of the north Atlantic Ocean, Figure 26. In 1960, the
"Bonner Bridge" was constructed across Oregon Inlet thereby providing access via State Highway NC 12 from the north to Hatteras Island. Over historic times,
the inlet had migrated fairly rapidly toward the south. With the combined
effects of construction of the fixed bridge and increasing interest in establishing an all weather navigational channel, the stage was set for concerted efforts to stabilize the inlet through jetty construction.
Historic Inlet Behavior
The geometric characteristics of Oregon Inlet have varied considerably over historic times. Storms tend to widen the inlet, followed by narrowing during periods of milder weather. The inlet center migrated southward at an average




Bar
-

I I f I I
0 4000
Scale (ft)
Coast Guard Station

Figure 26. Oregon Inlet




rate of 20 rn/year during the period 1931-1988 (Task Force, 1988). The net southerly longshore transport is 0.5 to 1.0 million cubic meters per year (Inman and Dolan, 1989).
Present Situation
Since the bridge construction in 1960, the inlet has continued its relentless migration such that a spit has grown to the south under the northern part of the elevated bridge span. This migration has caused the channel to be
dangerously close to the southern bridge abutment, where protection has been provided by revetment construction.
The Corps attempts to maintain the inlet navigable through hopper and sidecast dredging. From September, 1983 to February, 1988, an average of 550,000 cubic meters annually has been dredged from the inlet with the material placed
south of the inlet in water depths exceeding 6 m. Due to this substantial depth, it is questionable whether this placement provides significant benefit to the downdrift (south) shoreline.
The Corps of Engineers (COE) has developed a plan to stabilize Oregon Inlet through the construction of two jetties with sand transfer accomplished by a floating pipeline dredge which would remove accumulated sand north of the north
jetty and transfer this sand to the northern portions of Pea Island. The dredge would operate during the summer months with protection against waves provided
by a "Sloping Floating Breakwater" (SFB), essentially a new and untried concept, see Figure 27. The COE plan was authorized in 1970 with an estimated construction cost of approximately $50 million. Since then the estimated cost has risen to in excess of $100 million with an annual maintenance and sand bypassing cost of approximately $7 to $8 million.
Present concern centers on three issues: (1) the erosional threat to the
bridge, especially near the south abutment, (2) the erosional threat to the Coast Guard station south of the inlet as shown in Figure 26, and (3) the unstable and hazardous channel.
The National Park System and State of North Carolina Position on Oregon Inlet
NPS policy is to allow natural systems to remain in as near a natural condition as possible. This is consistent with the State of North Carolina




- 160 Ft 15" Nystron
(Jacketed) \Chafe Chain
I1 Shot 3" Grade 3 114 Shot
,T-.= =..,- 2 3/4" Grade 3
8200 Lb Sinker
20,000 Lb Nav Moor
Figure 27. Cross Section of Sloping Floating Breakwater Planned for Deployment at Oregon Inlet to Provide Shelter for Sand Bypassing Dredge Operating in Its Lee. From Inman and Dolan (1987).




policy which essentially prohibits the construction of armoring in the coastal zone. NPS recognizes the three concerns noted above and also recognizes the uncertainties associated with the construction of a substantial jetty system and a sand transfer system on an unprecedented scale. NPS has sought alternatives
to the jetty plan on the grounds that: (1) it is contrary to NPS and State policy, and (2) the performance is uncertain and once constructed, the system is there essentially forever. Although not within NPS purview, it is not clear that the jetties are the most cost effective approach.
An approach has been sought by NPS that would be consistent with state and NPS policies and yet accomplish common objectives. A recommendation has been made for a two-year Demonstration Project to evaluate the effectiveness of a "dredge only" option. In this option, flexibility would be provided to place the sand where needed as indicated by beach monitoring. This option appears to have a number of advantages, including:
(1) If not effective, this option could be discontinued without any lasting
impact as would be the case with the jetty option.
(2) Much could be learned about the physical system through a concerted
monitoring program during the two year demonstration project. This
information would serve to guide alternate designs or fine tune the
"dredge-only" option.
(3) Through the flexibility of sand placement, the option could address
immediately areas threatened by erosion.
(4) Through a multi-year dredging contract, the latest'in dredging equipment
and technology could be brought to bear on the project, and the performance of the contractor could be assessed on a several year basis and changes
made, if desired.
(5) Although detailed cost estimates have not been carried out, it appears that
this method is competitive. In particular the interest on the initial investment of approximately $100 million plus the estimated annual jetty maintenance and operating costs of the sand bypassing facility of $7 to $8 million appear to be of the same magnitude as if not greater than the
annual cost of the dredging only option.




As of the time of writing this report (December, 1988), the U.S. Army Corps of Engineers is still maintaining a limited navigation capability through operation of the hopper dredge with the placement of dredged material in water depths exceeding 6 m.
CASE STUDY III CUMBERLAND ISLAND
Introduction
Cumberland Island National Seashore is the southernmost island along the Georgia coastline. The waterway along the southern end of Cumberland Island is St. Marys River; the outlet to this river is protected by two long navigational jetties. As shown in Figure 28, the community of Kings Bay, GA is on the mainland to the west of Cumberland Island and approximately 8 km north of the
south tip of Cumberland Island. Kings Bay has been designated as a homeport for the Ohio Class submarines.
Channel modifications necessary to accommodate these submarines include substantial deepening, widening and lengthening of the current navigational channel. The total initial construction dredging is in excess of ten million cubic meters. The EIS prepared in conjunction with the project predicted an
annual maintenance dredging requirement of 1.4 million cubic yards. Later more detailed estimates performed by the Coastal Engineering Research Center have yielded a substantially lower value, i.e. 788,000 cubic yards per year.
Concerns of the National Park Service
Due to the large quantities of dredging being considered, the NPS has concerns over the effects on inner and outer shorelines of Cumberland Island,
on the marsh ecosystem on the western side of Cumberland Island and on the biota in the interior waters. These concerns led to negotiations with the Navy which eventually culminated in a five-year comprehensive monitoring and evaluation program. This program is reviewed briefly below.
Monitoring Progra
Responsibilities for the monitoring program are shared by the Waterways Experiment Station (WES) of the U.S. Army Corps of Engineers and the National Park Service. The WES program includes a Coastal Assessment component and a




Scale (km)

OL
.St. Marys Entrance

Kings E
Site
10

0

Figure 28. Location Map of Kings Bay Site Relative to Cumberland
Island National Seashore.




Cumberland Sound Physical Processes component. The NPS is responsible for ecological studies, primarily in Cumberland Sound. Where practical, efforts have been made to structure all program elements such that they complement other studies being carried out for the Navy on this project.
Coastal Assessment Component
The purpose of this component is to develop an information base that will
allow interpretation of past shoreline changes along Cumberland Island and Amelia Island (immediately to the south of the St. Marys River Entrance). No attempt will be made to present the component details; however, waves and tides will be documented as the principal agents affecting the shoreline. The shoreline will be monitored through profiling and aerial photography and sediment samples will be taken. These results, when combined with those from a historical substudy will provide the basis for an extrapolation subcomponent, the purpose of which is to develop predictions of the impact of the project on the outer and inner shorelines.
Cumberland Sound Physical Processes Component
Measurements of tides, currents and salinities and dredging in interior waters will be combined with computational models to predict probable changes in the physical regime of the Cumberland Sound waters. Concerns of particular interest are the effect of channel deepening on tidal range, salinity, shoaling patterns and mean tide range inside the sound. The possible effect of rising
sea level combined with a dredging induced increase in mean water level may affect ability of the marshes to accrete and keep pace vertically.
Ecological Research
This component of the program is administered by the NPS and is not as structured as the other components. The plan is to pursue initially the study components of greatest concern and to allow the program direction to respond to results developed. Initial efforts are focused on the effect of the Kings Bay project on: marsh dynamics, bivalves, ground water, and manatees. In addition
a geographic information system is being developed/tailored to organize and make all data from this study readily available.




PART VI
LEGAL AND REGULATORY ASPECTS OF DREDGING




PART VI
LEGAL AND REGULATORY ASPECTS OF DREDGING
Introduction
Dredging in the waters of the United States is regulated by both federal and state agencies. Some of the material presented in this section is based on
the twenty-six (and still counting) review articles which Peter Graber has published in Shore and Beach. Articles referenced are included in the
bibliography.
THE FEDERAL PROGRAM
A brief review of the evolution of the history of the federal laws may be helpful.
Rivers and Harbors Act of 1899
The purpose of this statute was to prevent obstruction to navigation and placed responsibility on the U.S. Army Corps of Engineers for issuing permits. Although as noted above the concern of the original act was navigation, it was
broadened through litigation in 1970 and 1971 to require consideration of ecology and allowed denial of a permit if the proposed project would cause ecological damage.
National Environmental Policy Act of 1969 (NEPA)
This statute, administered by the Environmental Protection Agency, declares a national policy which will encourage productive and enjoyable harmony between man and his environment." This act formalized the change toward greater concern for the environment and states as a goal 11 ... a balance between population and resource use which will permit high standards of living and a wide sharing of life's amenities." The character of environmental impact statements required in "major Federal actions significantly affecting the quality of the human environment" are formalized to include, "(i) the environmental impact of
the proposed action, (ii) any adverse environmental effects which cannot be avoided should the proposal be implemented, (iii) alternatives to the proposed action,... .11




Federal Water Pollution Control Act Amendments of 1972 (FWPCA)
The purpose of this act also called the Clean Water Act is to "restore and maintain the chemical, physical and biological integrity of the Nation's waters". A system of permits is required to regulate the discharge of dredged or fill materials into navigable waters. The Corps of Engineers is the responsible agency to administer this program. Section 404 of this act provides for the states to assume responsibility for permitting dredge and fill activities and
establishes requirements which these state programs must satisfy including procedures to ensure compliance with the program.
Marine Protection, Research and Sanctuaries Act of 1972
This statute is also referred to as the Ocean Dumping Act and requires a
permit when any material is to be discharged into the territorial sea and contiguous zone of the United States. Regulatory responsibilities are shared by the U.S. Army Corps of Engineers for dredged material and the Environmental
Protection Agency for other materials. Criteria for permitting dumping are that the project should not 11 ... unreasonably degrade or endanger human health, welfare or amenities, or the marine environment, ecological systems, or economic potentialities."
Coastal Zone Management Act of 1972 (CZMA)
This act provides financial incentive to coastal states to develop and adopt approved coastal zone management programs. In 1976, the federal cost sharing of the program was increased from 66.6% to 80%. Requirement of the CZMA are that a state program must include a designation of the states' boundaries
of the coastal zone, an inventory of the areas of particular concern, broad guidelines on priority of uses in those areas, lists of permissible land and water uses, etc. All states within the Southeast Region have approved programs with the exception of Georgia.
Section 307 of the Coastal Zone Management Act of 1972 requires that federal agencies comply with federal ly-approved coastal zone management programs. This section, termed the "consistency provision", also requires that a state or local project which affects the coastal zone must be in accordance with the




state coastal zone management program. The consistency provision encompasses harbor development, improvement and maintenance and dredge and fill activities.
THE STATE PROGRAMS
The following paragraphs provide a brief summary of the dredging, filling and disposal regulatory responsibilities within the six coastal states located
in the Southeast Region of the National Park Service and which have coastal park units.
The North Carolina Progra
In September 1978, North Carolina received federal approval for their proposed Coastal Management Program. State environmental concern increased in
1969, and studies were carried out and legislation adopted to preserve the state's coastal resources. The Coastal Wetlands Act of 1971 and Coastal Area Management Act of 1974 provide regulatory functions. Dredging and filling of estuarine land are regulated under the Coastal Resources Commission.
The South Carolina Progra
South Carolina received federal approval for their proposed coastal zone management program in September, 1979. Under their program, a permit must be
obtained from the South Carolina regulatory body, the Coastal Council, to "fill, remove dredge, drain or erect any structure on or in any way alter any critical really.
The Georgia Program
The Georgia Coastal Marshlands Act of 1970 provided that "no person shall remove, fill, dredge or drain or otherwise alter any marshlands in the State within the estuarine area thereof without first obtaining a permit". This
regulatory program is administered by the Coastal Marshlands Protection Committee.
Georgia does not participate in the federal Coastal Zone Management Program; thus dredging and disposal outside the jurisdiction of the Marshlands Act is administered by the U.S. Army Corps of Engineers.




The Florida Program
Florida submitted its proposed Coastal Management Program to the U. S. Office of Coastal Zone Management in February 1981 and the program was approved
in August 1981. Permits for dredging and filling in sovereign lands are regulated by statute. This program is under the responsibility of the Department of Florida Environmental Regulation with participation by the Department of Natural Resources.
The Alabama Program
In 1976, Alabama established the Alabama Coastal Area Act which provides
the legal framework for the coastal zone program. The Coastal Area Board is the responsible agency. The Coastal Area Board is responsible for issuing dredge and dredge and fill material disposal permits.
The Mississippi Program
The Mississippi Coastal Wetlands Protection Law of 1973 formalizes public policy as "the preservation of the natural state of the coastal wetlands .... except where an alteration of specific wetlands would serve a higher public interest." The Bureau of Marine Resources under the Mississippi Department of Wildlife Conservation administers the program and is responsible for permitting activities in the wetlands including dredging and filling.




PART VII
AN INVENTORY OF NATIONAL PARK SERVICE UNITS IN THE SOUTHEAST REGION SUSCEPTIBLE TO EROSION
AND EFFECTS OF DREDGING




PART VII
AN INVENTORY OF NATIONAL PARK SERVICE UNITS
IN THE SOUTHEAST REGION SUSCEPTIBLE TO EROSION AND EFFECTS OF DREDGING
Within the Southeast Region of the National Park Service there are 19 units that are subject to erosion by salt or brackish waters. Of these, at least seven are considered to be mildly to highly susceptible to dredging effects.
Table 6 lists the NPS units in the SE region which fall within the classification above, i.e. either subject to erosion by salty or brackish water
or are possibly subject to adverse effects of dredging. An attempt has been made to rank the effects of dredging as Low (L), Medium (M), High (H) and extremely high (EH). This ranking is based on the proximity of planned or past dredging activities and the impact on the site.




TABLE 6

UNITS WITHIN THE SOUTHEAST REGION
SUBJECT TO SALT/BRACKISH WATER RELATED EROSION AND ADVERSE EFFECTS OF DREDGING

Susceptibility Erosion to Dredging
Units Concerns Effects Comments

Cape Hatteras National Seashore
(NC)

Cape Lookout National Seashore (NC)
Fort Raleigh National Historic Site (NC)
Fort Sumter National Monument (SC)
Fort Pulaski National Monument (GA)
Fort Frederica National Monument (GA)
Cumberland Island National Seashore (GA)
Fort Caroline National Monument (FL)
Fort Matanzas National Monument (FL)
Canaveral National Seashore (FL)

EH
(Cape Hatteras Light House)
L
7
M

H
M
L
M-H

Dredging Effects High in Vicinity of Oregon Inlet

Proximity to Channel Dredging
Could Induce Erosion
Proximity to Channel Dredging
Could Induce Erosion
Channel Deepening at Kings Bay. Both Inner
and Outer Shorelines
Dredging in St. Johns River Entrance
Possible Modifications to Matanzas Inlet Bridge
Coastal Armoring to North May Cause Some Erosional Stress

Key to Ranking: L = Low; M = Medium; H = High; EH = Extremely High




TABLE 6

UNITS WITHIN THE SOUTHEAST REGION SUBJECT TO SALT/BRACKISH WATER RELATED EROSION AND ADVERSE EFFECTS OF DREDGING (Cant inued)
Susceptibility
Erosion to Dredging
Unit Concerns Effects Comments
Biscayne National L L
Monument (FL)

Fort Jefferson National Monument (FL)
DeSoto National Monument (FL)
Gulf Islands National Monument (FL)
-Santa Rosa Island
-Perdido Key
Gulf Islands National Seashore (MS)
-Petit Bois Island
-Horn Island
-Ship Island
San Juan National Historic Site, Puerto Rico
Virgin Islands National Park (St. Johns Island)
Buck Island Reef National Monument (An Island Of f St. Croix)
Christiansted National

Proximity of Dredging in Pensacola Entrance Channel
Navigation Channel Dredging from Gul fpo rt
El Morro Castle is Founded on Cavernous Limestone and is Being Undermined

Key to Ranking: L = Low; M = Medium; H = High; EH = Extremely High




PART VIII
SUMMARY AND CONCLUSIONS




PART VIII
SUMMARY AND CONCLUSIONS
Summary
Dredging and other engineering alterations to the nearshore system have
the potential to cause physical and biological impacts to the natural beach, dune and sand-sharing system that are both extensive spatially and long lasting over time. The physical impacts generally occur due to the interference with the natural sand transport system. In cases where sand is removed from this system, the inevitable result is erosion only the distribution is unknown. In other cases where sand is trapped (perhaps by groins) or prevented from entering the
system (by coastal armoring), the total amount of sand in the system remains the same but is redistributed; thus there are localized areas of relative deposition or stability and erosion. The biological impacts are generally closely related to the quality of sand used in beach nourishment projects and the large magnitudes of alterations that can place the system out of balance to a degree
that the biota may not be able to adapt. Examples include the use of fine
sediment that could impact offshore reefs or result in a beach too compact for turtle nesting.
In particular instances where the natural system is out of balance due to
prior engineering actions, beach nourishment with high quality sand can be beneficial by restoring the natural balance in the physical and biologi-cal systems.
Conclusions
Within the general policy of the National Park Service to maintain systems in their natural condition, each situation should be considered on a case-bycase basis recognizing that systems may be impacted by prior engineering alterations and that some engineering activities such as sand by-passing and beach nourishment can exert a beneficial impact on both the (altered) physical and biological systems.
Where systems are in their natural state, the general policy of maintaining this natural state is appropriate and consistent with the NPS mandate as stewards




and managers of these systems for the use of and enjoyment by present and future generations.
If consideration is given to allowing substantial dredging or construction related activities which could affect NPS systems, it is essential that: (1) where appropriate, the best geological, biological and engineering expertise be used to analyze the potential impact of the activity and to identify the most beneficial approach, and (2) that a thorough biological and physical monitoring and analysis plan be implemented to document the impact and to improve general understanding of the complex coastal sediment processes and biological
interactions resulting from substantial alterations to the system. Only by this approach can NPS appropriately fulfill its responsibility to maintain the wellbeing of those systems for which it is charged against the increasing pressures for modifications which could alter these systems.




REFERENCES

Aubrey, D.M. and N.M. Dekimpe (1988) "Performance of Beach Nourishment at Jupiter
Island, Florida", Paper Presented at Beach Technology Conference,
Gainesville, FL, 20 pages.
Bokuniewicz, H.J., M. Zimmerman, M. Keyes, and B. McCabe (1980) "Seasonal Beach
Response at East Hampton, NY", Special Report 38, Marine Sciences Center,
State University of New York, Stony Brook, N.Y.
Bowman, M.L. (1981) "The Relationship of Emerita Talpoida to Beach Characteristics", M.S. Thesis, University of Virginia, Charlottesville, Virginia,
106 pp.
Culter, J.K. and S. Mahadevan (1982) "Long-Term Effects of Beach Nourishment on
the Benthic Fauna of Panama City Beach, Florida", Miscellaneous Report No. 82-2, U.S. Army Corps of Engineers, Coastal Engineering Research
Center, Fort Belvoir, VA.
Dean, R.G. (1977) "Equilibrium Beach Profiles: U.S. Atlantic and Gulf Coasts",
Ocean Engineering Technical Report No. 12, Department of Civil Engineering,
University of Delaware, Newark, DE.
Dean, R.G. (1983) "Principles of Beach Nourishment", in Handbook of Coastal
Processes and Erosion, CRC Press, p. 217-231.
Dean, R.G. and T.L. Walton (1975) "Sediment Transport Processes in the Vicinity
of Inlets with Special Reference to Sand Trapping", in Estuarine Research, Volume II, Geology and Engineering, Edited by L. Eugene Cronin, Academic
Press, New York, p. 129-150.
DeWall, A.E. and J.J. Richter (1977) "Beach Nearshore Processes in Southeastern
Florida", Proceedings, ASCE Specialty Conference: Coastal Sediments '77,
p. 425-443.
Gren, G.G. (1976) "Hydraulic Dredges, Including Boosters", Proceedings of the
ASCE Specialty Conference on Dredging and Its Environmental Effects,
Mobile, Alabama, p. 115-124.
Graber, P.F. (1981) "The Law of the Coast in a Clamshell: Part II", Shore and
Beach, Vol. 49, No. 1, Jan., p. 16-20.
Graber, P.F. (1981) "The Law of the Coast in a Clamshell: Part IV The Florida
Approach", Shore and Beach, Vol. 49, No. 3, July, p. 13-20.




Graber, P.F. (1983) "The Law of the Coast in a Clamshell: Part X The North
Carolina Approach", Shore and Beach, Vol. 51, No. 1, Jan., p. 18-23.
Graber, P.F. (1984) "The Law of the Coast in a Clamshell: Part XV The South
Carolina Approach", Shore and Beach, Vol. 52, No. 2, April, p. 18-25.
Graber, P.F. (1986) "The Law of the Coast in a Clamshell: Part XII The
Mississippi Approach", Shore and Beach, Vol. 54, No. 1, Jan., p. 3-7.
Graber, P.F. (1986) "The Law of the Coast in a Clamshell: Part XXII The Georgia
Approach", Shore and Beach, Vol. 54, No. 3, July, p. 3-7.
Graber, P.F. (1988) "The Law of the Coast in a Clamshell: Part XXV The Alabama
Approach", Shore and Beach, Vol. 56, No. 2, April, p. 12-16.
Hayden, B. and R. Dolan (1974) "Impact of Beach Nourishment on Distribution of
Emerita Talpoida, the Common Mole Crab", Journal Waterways, Harbors and
Coastal Engineering Division, ASCE, Vol. 100, WW2, p. 123-132.
Inman, D.L. and R. Dolan (1987) "Discussion of the U.S. Army Corps of Engineers
Proposed Manteo (Shallowbag) Bay Project: The Stabilization of Oregon Inlet, North Carolina," Draft Report Submitted to the National Park
Service, December.
Inman, D.L. and R. Dolan (1989) "The Outer Banks of North Carolina: Budget of
Sediment and Inlet Dynamics Along a Migrating Barrier System", Journal of
Coastal Research, Vol. 5, No. 2, p. 193-353.
Johnson, J.W. (1971) "The Significance of Seasonal Beach Changes in Tidal
Boundaries", Shore and Beach, April, p. 26-31.
Long, E.G. (1967) "Improvement of Coastal Inlets by Sidecast Dredging",
Proceedings, ASCE, Vol. 93, WW4, November, p. 185-200.
Lund, F. (1986) "Impacts of Beach Nourishment Programs Upon Marine Turtle Nesting
at Jupiter Island, Florida, 1969-1983", Report Submitted to the Town of
Jupiter Island.
Mohr, A.W. (1976) "Mechanical Dredges", Proceedings of the ASCE Specialty
Conference on Dredging and Its Environmental Effects, Mobile Alabama, p.
125-138.
Nelson, D.A. (Undated Working Draft) "The Use of Tilling to Soften Nourished
Beach Sand Consistency for Nesting Sea Turtles", U.S. Army Engineer
Waterways Experiment Station.




Nelson, D.A., K. Mauck and J. Fletemeyer (1987) "Physical Effects of Beach
Nourishment on Sea Turtle Nesting, Delray Beach, Florida", Technical Report EL-87-15, U.S. Army Waterways Experiment Station, Vicksburg, Mississippi. Nelson, D.A. and D.D. Dickerson (1988) "Hardness of Nourished and Natural Sea
Turtle Nesting Beaches on the East Coast of Florida", U.S. Army Engineer
Waterways Experiment Station (Manuscript).
Nelson, D.A. and C.H. Mayes (Undated Working Draft) "St. Lucie Inlet Dredged
Material Disposal Effects on the Firmness of Sand Used by Nesting Turtles",
U.S. Army Engineer Waterways Experiment Station.
Nelson, W.G. (1985) "Guideline for Beach Restoration, Part I: Biological
Guidelines", Report No. 76, Florida Sea Grant College.
O'Brien, M.P. (1931) "Estuary Tidal Prisms Related to Entrance Areas", Civil
Engineering, Vol. 1, No. 8, p. 738-739.
Pearce, W.B. (1976) "Analysis of Dredging Projects", Proceedings of the ASCE
Specialty Conference on Dredging and Its Environmental Effects, Mobile
Alabama, p. 139-162.
Rutgers University (Undated) "Measurements of Shoreline Positions Along Perdido
Key, 1985-1987".
Reilly, F.J. and V.J. Bellis (1978) "A Study of the Ecological Impact of Beach
Nourishment with Dredged Materials on the Intertidal Zone", Institute for Coastal and Marine Resources, East Carolina University, Technical Report
No. 4.
Reilly, F.J. and V.J. Bellis (1983) "The Ecological Impact of Beach Nourishment
with Dredged Materials on the Intertidal Zone at Bogue Banks, North Carolina", U.S. Army Corps of Engineers, Coastal Engineering Research
Center, Miscellaneous Report No. 83-3.
Saloman, C.H. (1976) "The Benthic Fauna and Sediments of the Nearshore Zone Off
Panama City, Florida", Miscellaneous Report No. 76-10, U.S. Army Corps of
Engineers, Coastal Engineering Research Center, Fort Belvoir, VA.
Saloman, C.H., S.P. Naughton and J.L. Taylor (1982) "Benthic Community Response
to Dredging Borrow Pits, Panama City Beach, Florida", Miscellaneous Report No. 82-3, U.S. Army Corps of Engineers, Coastal Engineering Research
Center, Fort Belvoir, VA.




Sanderson, W.H. (1976) "Sand Bypassing with Split-Hull Self-Propelled Barge
Currituck", Proceedings of the ASCE Specialty Conference on Dredging and
Its Environmental Effects, Mobile, Alabama, p. 163-172.
Schwartz, R.K. and F.R. Musalowski (1977) "Nearshore Disposal: Onshore Sediment
Transport", Proceedings, ASCE Specialty Conference on Coastal Sediments
'77, Charleston, SC, p. 85-101.
Thompson Engineering Testing, Inc. (1987) "Grain Size Distribution and Calcium
Carbonate Analyses of Sediment Samples", Contract N62467-85-C-0593,
Amendment/Modification No. P00009, Mobile Alabama.
U.S. Congress, 1948. House Document No. 6924, Santa Barbara, CA, Beach Erosion
Control Study, Letter from Chief of Engineers, Army, Submitting Report on Cooperative Study for Beach Erosion Control at Santa Barbara, CA, Dec. 22,
1948, p. 1-35.
U.S. Congress, 1950. House Document No. 15787, Atlantic City, NY Beach Erosion
Control Study, Letter from Chief of Engineers, Army, Submitting Report on
Cooperative Beach Erosion Control Study of Atlantic City, NJ, p. 1-55.
Walton, T.L. and R.G. Dean (1973) "Application of Littoral Drift Roses to Coastal
Engineering Problems", Proceedings, Conference on Engineering Dynamics in
the Surf Zone, Sydney, Australia, p. 221-227.
Walton, T.L. and W.D. Adams (1976) "Capacity of Outer Bars to Store Sand",
Fifteenth International Conference on Coastal Engineering, American Society
of Civil Engineers, Honolulu, HI, p. 1919-1937.




PART IX
ANNOTATED BIBLIOGRAPHY




Full Text

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REPORT DOCUMENTATION PAGE 1. Report No. 2. 3. Recipient Accerion No. 4. Title and Subtitle 3. Report Date REVIEW OF DREDGING EFFECTS ON ADJACENT PARK SYSTEMS December, 1988 6. 7. Author(s) 8. Performing Organiatioo Report No. Robert G. Dean with a contribution by: Robert Dolan UFL/COEL-88/015 9. Performiln Organization Name and Address 10. Project/Task/Work Unit No. Coastal and Oceanographic Engineering Department University of Florida 11. contract or crant No. 336 Weil Hall CA-500-7-8007 Gainesville, FL 32611 13. Type of Report 12. Sponsoring Organization Name and Addres National Park Service Final 75 Spring Street, SW Atlanta, GA 30303 14. 15. Supplementary Notes 16. Abstract In today's environment, most park systems can be influenced by human activities well outside the park boundaries. For coastal areas, dredging is known to have the potential of altering the natural beach system many kilometers downdrift of the activities. In some cases where previous dredging effects have adversely impacted a park system, beach nourishment with clean sand can be a byproduct of a dredging project and can be beneficial to a park by reinstating the natural sand flows. This report is intended to assist park personnel in the Southeast Region to better assess potential dredging impacts on the natural system and to present methods of ameliorating adverse effects. The subject is introduced by four generic examples in which dredging can play a role in the quality and behavior of the natural system. The response of the beach system to natural forces and to dredging activities is reviewed. Dredging techniques are discussed as well as their potential for beneficial and adverse effects. A literature review is presented on the biological effects of dredging. Three actual case studies are reviewed in which dredging is being carried out adjacent to park systems in the Southeast Region. State and federal regulations governing dredging activities are summarized. An annotated bibliography includes contributions of dredging activities on nearshore ecology, beach stability and sand management practices. 17. Originator's Key Words 18. Availability Statement Beaches Beach erosion Beach nourishment Dredging Intertidal effects 19. U. S. Security Classif. of the Report 20. U. S. Security Classif. of This Page 21. No. of Pages 22. Price Unclassified Unclassified 123



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PART II THE NATURAL BEACH SYSTEM



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i..-^I^l -_ ,..,., I... SAir Station 0 2 4 Miles / ..I | ..* .-'" *. S ."." Pensacola Figure 23. Perdido Key and Entrance Channel to Pensacola Bay. Scale .' .: y ., SSanta Rosa island c., .-9 a.3.-erdo, KeY \\ \Entrance Channel Gulf of Mexico



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PART II THE NATURAL BEACH SYSTEM Geology of Barrier Islands (Pages 13-16 Contributed by R. Dolan) Introduction The Atlantic and Gulf coastal plains that form the seaward perimeter of the S.E. Region are relatively flat lands that slope gently seaward to a wide submarine continental shelf. The shore zone, or interface between the land and sea portions of the coastal plains, consists of a series of barrier islands 3 to 30 km offshore. These islands are 2 to 5 km wide, 10 to 100 km long, and low in elevation. The highest topographic features are sand dunes usually 3 to 6 m above sea level. The lagoons or bays on the sound side of the islands are shallow and may have large tidal mud flats and marshes. The storms that generate large waves are the principal agents of change on barrier islands. Winter extratropical storms produce waves of 5 to 10 m, with storm surges of 1 to 2 m. Hurricanes (tropical storms), which occur less frequently, also cause major landscape changes, especially in the vicinity of their landfall. Extratropical and tropical storms, with their strong waves and storm surges, often drive water and beach sands completely across the barrier island. In contrast, during periods between storms the beaches build seaward. Thus at times the barrier island shorelines move landward and at other times seaward, in response to varying energy conditions. In recent decades this movement has been mostly landward, at a rate of about 1.5 m/yr for the Atlantic coast, and somewhat less along the Gulf coast. Origin of Barrier Islands Barrier island formation and migration has been a subject of debate among earth scientists for many years. There is, however, evidence that most of the mid-Atlantic and Gulf coast barrier islands are migrating landward. Peats and tree stumps, remnants of forest stands on the back sides of the islands emerge on open ocean beaches, indicating barrier island migration or transgression. 13



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Lund's studies included documentation of the number of turtle nests per mile along the shoreline throughout the dominant nesting of loggerhead turtles which frequent this area. Significant findings of the study include: (1) Prior to beach nourishment, the nesting activity in the central Fill segment was considerably lower than in the other two segments. This was interpreted as being due to the narrow beaches resulting from the considerable armoring in the "Fill" segment. (2) Following nourishment, the increase in nesting activity increased in all three segments with the increase in the Fill segment being much greater than in the other two (125% increase vs. an average of 28% for the other two). However, the nesting density in the Fill segment always remained below that in the North and South segments, and (3) Adverse effects of nourishment included displacement from the site during construction, difficulties in climbing up the steep erosional scarp that develops after nourishment, and inability to excavate egg chambers in the highly compacted fill. As an overall summary statement, Lund documented a net beneficial effect of beach nourishment on sea turtle nesting at Jupiter Island. Some of the concerns discussed in (3) above are being addressed through mechanical loosening and shaping of the beach nourishment. Following Lund's report in 1986, additional studies have been carried out during the Summer 1988 nesting season which followed the 1987 nourishment of 1.7 million cubic meters of sand in three segments. This fill material was loosened by tilling, thereby facilitating turtle nesting. It was found that the number of turtle nests in all three areas (North, South and Fill) increased dramatically (Bill Gahagan, Personal Communication) and that the density of nests was approximately equal in all three segments. 55



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Generic Problem 4 -Beach Nourishment Using Sand Dredged from Offshore Dredging Problem -Stabilization of an eroding beach is being considered by beach nourishment. This comprises the removal of a large quantity of material from an offshore area (the "borrow" area) and placement by pipeline dredge on the beach. A coral reef is present near the borrow area. The Natural System The Altered System Figure 4. Generic Problem 4 -Beach Nourishment. Discussion of Natural System -The natural system is experiencing a longterm mild erosional trend. The Altered System -The completed altered system will include an offshore deepened "borrow" area with the removed material placed on the shore. Physical Effects -Possible physical effects include local modification of the waves affecting the shoreline due to the deepened borrow area. Additionally, the longevity or "life" of the project may be a matter of concern as it relates to the length of time that the benefits will occur to the area and the associated frequency for maintenance renourishment. Environmental Effects -In most cases the primary environmental effects are related to the quality of sediment or damage to the reefs by improper handling of equipment such as anchors. In this case quality relates to the grain 10



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0 > x 6000 yrs BP -0 -i" +o 0.08m/1 dOyrs -t x 100 25 WLU 50 o LU 200 m E co Cl, S75 A Texas Shelf 300 + Holland x Australia o Southwest Louisiana Eastern Argentina West Louisiana Shelf100 a Western Mexico I I I I 5 10 15 20 THOUSANDS OF YEARS BEFORE PRESENT Figure 5. The Rise of Sea Level as Obtained from Carbon 14 Dates in Relatively Stable Areas (from Shepard, 1963). Break in Slope some 6400 Years Before Present (BP) may have Provided Basis for Barrier Island Stability. 15



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rounded and changes occur rapidly. As the evolution progresses, the planform anomaly begins to behave as a longer project and changes occur much more slowly. In evaluating the performance of a beach nourishment project, it is important to note that if the sediment is of good quality, although eventually the sediment will be transported out of the region placed, it will remain within the region of active nearshore sediment transport and will continue to provide benefits to those areas to which it is transported. Case (2) Placement Immediately Downdrift of a Littoral Barrier -This situation is fairly common due to the aforementioned adverse impact of inlets modified or constructed for navigational purposes. As intuition would suggest, if the longshore sediment transport deficit is large, the life of the beach nourishment project will be short and in such cases, rather than considering the longevity of the project as a measure of its performance, it may be more appropriate to regard the nourishment as a "feeder beach" placed to reinstate the longshore sediment transport. Profile Equilibration After Nourishment In addition to planform evolution, the profile will change from that initially placed to one that approaches equilibrium with the incoming wave characteristics and sediment size. The quality or size of sand used in nourishment governs the shape of the equilibrium beach profile. Sand of the same size characteristics as the original beach will have an equilibrium profile the same as the pre-nourished beach. Sand coarser or finer than the original will have equilibrium profiles steeper or milder, respectively, than the original profiles. Relative Benefits of Offshore Sand Placement at Various Depths In some cases, it may be less expensive to place the sand in the nearshore region than on the dry beach. Questions have arisen regarding the effectiveness of this approach. There have been several attempts to place substantial quantities of sand in the nearshore region and to carry out monitoring to determine whether the sand was transported shoreward. The field test programs and the experience with each is summarized in Table 2. As can be seen, only the 43



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Generic Problems To some degree the overall purpose of this report is to develop an awareness for natural coastal processes and an ability to foresee the potential problems associated with alterations to the coastal system. Later sections of this report will discuss the processes in detail. To provide a preview of the types and range of problems addressed in this report four generic case studies are presented. The format is a brief presentation for each problem in which the problem is introduced with two diagrams, a before and after, the dominant physical and environmental impacts and focus areas warranting attention by NPS personnel in their considerations of this type of generic problem. A common conceptual thread in all coastal engineering problems is that of a sediment budget. That is, the natural system has adjusted to the current situation of sediment inflows and outflows. Any alteration of the sediment transport processes will tip the sediment budget out of balance and cause areas of erosion and possibly deposition. 3



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FIGURE PAGE 18. Plain Suction Dredge (From Richardson, 1976) 35 19. Cutter Suction Dredge (with Spuds) (From Richardson, 1976) 35 20. Split Hopper Barge (Self-propelled) (From Richardson, 1976) 37 21. Example of Evolution of Initially Rectangular Nourished Beach Planform. Example for Project Length, Q, of 6 km, Effective Wave Height, H, of 0.6 m and Initial Nourished Beach Width of 30 m 42 22. Effect of a Dredged Borrow Area on Wave Refraction and Wave Energy Distribution along the Shoreline 46 23. Perdido Key and Entrance Channel to Pensacola Bay 59 24. Shoreline Change Rates for Escambia County, January 1974 to October 1984. Based on Florida DNR Surveys. Note Shoreline Change Rates Shown Have Been Smoothed by a Five Point Running Average 61 25. Recommended Characteristics of Nourished Profile. Illustrated for DNR Monument No. 48 63 26. Oregon Inlet 67 27. Cross-Section of Sloping Floating Breakwater Planned for Deployment at Oregon Inlet to Provide Shelter for Sand Bypassing Dredge Operating in its Lee. From Inman and Dolan (1987) 69 28. Location Map of Kings Bay Site Relative to Cumberland Island National Seashore 72 vii



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approach would be for the armored area to place annually sand volumes equivalent to the reduction in supply caused by the armoring. 9



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Role of Inlets Inlets are channels connecting outer waters to interior lagoons or bays. Inlets are subjected to two competing forces. The rising and falling tides in the ocean cause water to flow into the bay (flood currents) and out of the bay (ebb currents). The volume of water entering an inlet during flood (inward) flow or leaving during ebb (seaward) flow is termed the "tidal prism", an important characteristic of the inlet bay system. Through refraction, waves tend to transport sand toward inlets and to cause closure. The tidal currents through the inlets scour excess sand from the channel maintaining it open. To understand how these two competing forces interact, consider the simple system discussed below. If an inlet were excavated wider than equilibrium, the scouring velocities would decrease, sand would enter the channel and deposit thereby decreasing the cross-sectional area with a corresponding increase in tidal currents which would decrease the tendency for sand deposition. Conversely, if sand were placed in an inlet in equilibrium conditions, thereby decreasing the flow area, the velocities would increase, scouring out the excess and returning the area to equilibrium. Thus the inlet cross-sectional area tends to be selfequilibrating. O'Brien (1931) found the surprisingly simple relationship shown in Figure 10 between the equilibrium cross-section of an inlet and the total volumetric flow of water passing through an inlet during flood or ebb flow. The dashed line in Figure 10 represents a peak velocity through the inlet of 1 m/s. Thus it appears that in a sandy material, under equilibrium conditions, the inlet adjusts itself such that the peak velocities in and out of the inlet are on the order of 1 m/s. As described previously, any change in cross-sectional area to alter this velocity will induce velocity changes to reestablish the equilibrium area. With the above discussion of the flow in and out of inlets and the related scour of excess sediments, it is not surprising to find extensive sand deposits bayward and seaward of the inlet channel. These deposits are termed flood and ebb tidal shoals signifying the currents causing their transport to these locations. These shoals are extremely important to the inlet stability; their roles will be reviewed below. The flood tidal shoals represent deposits that are relatively static and grow to substantial volumes and, due to the usually moderate wave climate inside 24



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TABLE 5 CHRONOLOGY OF PENSACOLA BAY ENTRANCE CHANNEL DIMENSIONS Channel Dimensions Aut Authorized Year Depth (m) Width (m) or Actual 1881 7.3 24 Authorized 1885 6.9 24 Actual 1890 7.3 37 Actual 1896 9.1 91 Authorized 1902 9.1 152 Authorized 1935 9.8 152 Authorized 1959 11.3 244 Actual Present 13.4 244 Authorized significantly by over a century of dredging and interruption of the natural system. The availability of large quantities of good quality sand was viewed as an opportunity to compensate for some of the adverse impacts to the natural system that had occurred for more than a century. A decision was made to accept approximately 4 million cubic meters of high quality beach sand with strict conditions on the placement and subsequent monitoring of the project. Experience gained through the 1985 placement was utilized in developing requirements for the forthcoming project. Specifically, the 1985 material was placed too high to allow normal waves to overtop the berm and contour the profile. Additionally, this prior project had left a relatively coarse shell residue on the berm and no vegetation program nor attempt to configure the sand to natural berm forms had been carried out. Recommendations for the planned project included placement over a length of approximately 6 km. The recommended profile is as shown in Figure 25. 62



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chains of Holocene barrier islands. Exceptions to this model are the more stable "sea islands" of Georgia (Cumberland), which differ significantly from Holocene barriers in that Holocene material is deposited on the seaward side of detached segments of the mainland Pleistocene terrace. Sea Level Rise and Barrier Islands Although Holocene sea level remained fairly stable following the initial rise during the post-Wisconsin, sea level has risen several meters in the past 2,000 years. This slow rise has resulted in the recession of shorelines and the enlargement of bays and sounds behind the barrier islands. Over the past 200 years, the rise has been rapid, totaling slightly more than 30 cm. The rate of barrier island recession over the last 2,000 years undoubtedly varied as the rate in the rise of sea level changed, as the supply of sand waned, and as the slope of the bottom of the inshore zone evolved in response to storms and waves. Some of the eroded material has been lost into large offshore sediment sinks, such as Diamond Shoals off Cape Hatteras. Much of it, however, has remained within the barrier ipland sediment budget and has contributed to spit growth, inlet filling, dune building, and storm-overwash deposits. The Importance of Natural Processes Within the coastal and marine parks of the S.E. Region, the National Park Service has long recognized the importance of allowing natural processes to proceed in an uninterrupted manner. However, the NPS recognizes that some of the coastal lands now administered as parks, recreation areas, and monuments were altered by engineering structures or sediment management practices decades before the areas were added to the NPS system. In addition, some of the bays, lagoons, and inlets that are now part of the NPS lands have been and continue to be part of the vital coastal waterways. For these reasons, the NPS realizes that all of the barrier islands, inlets, and lagoons within their jurisdiction cannot be managed as totally "natural" systems; however, it is important to recognize, when assessing the potential implications of a dredging project within park lands, that the natural processes are the processes that were responsible for the formation of the islands, and for the great natural beauty of these areas. These processes should not be interfered with unless absolutely essential. 16



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PART IV ALTERED COASTAL SYSTEMS



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Benthic Community Studies -Studies will be carried out to establish the effect of beach nourishment project on the benthic community. Sampling will be conducted along transects extending from the Gulf and Lagoon shores of Perdido Key. Vegetation Analysis -Natural and revegetation success will be documented by a combination of transects supplemented by color infrared aerial photography. The objective will be to quantify the revegetation with time as affected by various ground conditions including elevation, compactness, distance from shoreline, etc. Beach Mouse Population -Effects of the nourishment project on the beach mouse will be monitored through a series of population studies augmented by other relevant factors including food supply and predator populations. The mouse population studies include marking and recapture studies along selected transects within the project area and at control transects outside the area. Predator studies will include tracking using radio telemetry methods. CASE STUDY II -OREGON INLET Introduction Oregon Inlet is a natural inlet located approximately 63 km north of Cape Hatteras in the Cape Hatteras National Seashore. This inlet connects Pamlico Sound with the waters of the north Atlantic Ocean, Figure 26. In 1960, the "Bonner Bridge" was constructed across Oregon Inlet thereby providing access via State Highway NC 12 from the north to Hatteras Island. Over historic times, the inlet had migrated fairly rapidly toward the south. With the combined effects of construction of the fixed bridge and increasing interest in establishing an all weather navigational channel, the stage was set for concerted efforts to stabilize the inlet through jetty construction. Historic Inlet Behavior The geometric characteristics of Oregon Inlet have varied considerably over historic times. Storms tend to widen the inlet, followed by narrowing during periods of milder weather. The inlet center migrated southward at an average 66



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may be eroded away, along with associated vegetation, the barrier island will be overtopped by storms causing impact to back barrier vegetation. Stable areas for turtle nesting may be affected. Solution -Sand dredged should be returned to the adjacent beaches in locations established through a comprehensive monitoring program. Large quantities of sand placed at infrequent intervals may cause substantial fluctuations of the shoreline which could impact turtle nesting. 5



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LIST OF FIGURES FIGURE PAGE 1. Generic Problem 1 -Inlet Dredging 4 2. Generic Problem 2 -Jetty Construction 6 3. Generic Problem 3 -Coastal Armoring 8 4. Generic Problem 4 -Beach Nourishment 10 5. The Rise of Sea Level as Obtained from Carbon 14 Dates in Relatively Stable Areas (From Shepard, 1963). Break in Slope Some 6400 Years Before Present (BP) May Have Provided Basis for Barrier Island Stability 15 6. Waves Arriving Obliquely to Shoreline Cause Longshore Current and Longshore Sediment Transport Primarily Within Surf Zone 18 7. Estimates of Net Annual Longshore Sediment Transport Along Florida's East Coast 20 8. Normal and Storm Profiles on a Natural Shoreline 21 9. Variation of Median Sediment Size with Location Across Beach Profile. North Jupiter Island, FL 23 10. Relationship between Spring Range Tidal Prism and Minimum Cross-Section, Compared with Maximum Inlet Velocity of 1 m/s. Modified from O'Brien (1931) 25 11. The Balance of Forces which Maintains the Ebb Tidal Shoal Volume in Equilibrium 27 12. Relationship Between Equilibrium Volume of Sand Stored in Ebb Tidal Shoal and Tidal Prism (Adapted From Walton and Adams, 1976) 28 13. The "Sand Sharing System" Comprising the Inlet, the Ebb Tidal Shoal and Adjacent Shorelines 29 14. The Clam Shell Dredge (From Bray, 1979) 32 15. Bucket Ladder Dredge (From Richardson, 1976) 32 16. Plan View of Operation of a Pipeline Dredge (From Bray, 1979) 33 17. Self-propelled Hopper Dredge with Trailing Dragarm (From Richardson, 1976) 33 vi



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Physical Performance of Beach Nourishment Projects Baumgardner, P.F. (1984) "Charlotte Harbor Beach Nourishment", Proceedings of the Conference Dredging '84, Dredging and Dredge Material Disposal, pp. 10241029. This project entailed the placement of 230,000 cubic meters of sand dredged in conjunction with channel maintenance on badly eroded beaches of Charlotte Harbor. The Corps of Engineers hopper dredge McFarland was used and was moored approximately 3 km offshore. One booster pump was required to achieve the sand placement. The operation worked 24 hours per day except for necessary delays for fueling. It is concluded that with disposal areas being moved offshore, costs may soon force the use of beach disposal areas in some areas. Beachler, K. and T.J. Campbell (1984) "Offshore-Dredging -Is It Still CostEffective for Beach Restoration?", Proceedings of the Conference Dredging '84, Dredging and Dredge Material Disposal, pp. 229-236. The various approaches to coping with beach erosion are reviewed to determine whether beach restoration using an offshore sand source is still the optimum approach. Cited are the increasing difficulty of permitting such a project and the rising costs from the earliest projects. Various sources of sand for southeast Florida including bay areas and the use of aragonite from the Bahamas is being considered. Only preliminary results were available at the time of the reporting; however, it was concluded that dredging from an offshore source was economically viable, that aragonite may become cost-competitive as the higher quality sources of sand become depleted and that inlet maintenance and bypassing should serve as an essential element of an overall beach management plan. Hobson, R.D. (1981) "Beach Nourishment Techniques, Report 3: Typical Beach Nourishment Projects Using Offshore Sand Deposits", Geotechnical Engineering Branch, U.S. Army Coastal Engineering Research Center, Fort Belvoir, VA, 117 pages. This report provides a summary and review for 20 Corps of Engineers beach nourishment projects. Useful data is provided including, where available, history and project description, location and bathymetry, loss rates, recession rates, grain size characteristics, presence of stabilization structures, etc. 104



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<0 -V (C) IetEbb. (W) Inlet Flood (WC) (C) S Bay Ebb Tidal Shoal Figure 11. The Balance of Forces which Maintains the Ebb Tidal Shoal Volume in Equilibrium. 27



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LIST OF TABLES TABLE PAGE 1. SUMMARY OF SHORELINE RESPONSE TO NEW JERSEY STORM OF NOVEMBER 6-7, 1953 (From Caldwell, 1959) 21 2. FIELD TESTS CARRIED OUT TO EVALUATE SHOREWARD SEDIMENT TRANSPORT FROM OFFSHORE PLACEMENT 44 3. CHARACTERISTICS OF SEA TURTLE AND NESTING IN FLORIDA 52 4. HISTORY OF MAINTENANCE DREDGING PENSACOLA ENTRANCE CHANNEL 1885-1987 58 5. CHRONOLOGY OF PENSACOLA BAY ENTRANCE CHANNEL DIMENSIONS 62 6. UNITS WITHIN THE SOUTHEAST REGION SUBJECT TO SALT/BRACKISH WATER RELATED EROSION AND ADVERSE EFFECTS OF DREDGING 81 6. (Continued) 82 viii



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PART I INTRODUCTION AND GENERAL TYPES OF DREDGING AND COASTAL PROBLEMS ENCOUNTERED BY THE NATIONAL PARK SERVICE



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1000I I ll ll I i I 111 _E m z zw 1000 E .LU 0Z Mildly Exposed Coasts m Moderately Exposed Coasts-~Highly Exposed Coasts LU 10.1 10 100 1000 TIDAL PRISM (m 3x 106) Figure 12. Relationship Between Equilibrium Volume of Sand Stored in Ebb Tidal Shoal and Tidal Prism (Adapted From Walton and Adams, 1976). 28



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PART V CASE STUDIES AS EXAMPLES CASE STUDY I -PERDIDO KEY Introduction The Perdido Key Gulf Island National Seashore is located on the westernmost island in the Panhandle area of Florida. The eastern end of Perdido Key is bounded by the entrance to Pensacola Bay, Figure 23. This entrance is a navigation channel which has been dredged to depths of 13 m, significantly exceeding the natural bar depth of approximately 6 m. Table 4 presents the available history of dredging over more than one century: from 1885 to 1987. TABLE 4 HISTORY OF MAINTENANCE DREDGING PENSACOLA ENTRANCE CHANNEL 1885-1987 Year Volume Dredged Type Dredge Disposal Area (m3) 1885-1975 Unknown Hopper Gulf Disposal 1975 840,000 Hopper Gulf Disposal 1981 500,000 Hopper Gulf Disposal 1983 87,000 Hopper Gulf Disposal 1984 700,000 Hopper Gulf Disposal 1985 1,860,000 Pipeline Perdido Key 1987 150,000 Hopper Gulf Disposal Recently Pensacola Bay was designated as a homeport for the aircraft carrier "Kittyhawk". This required an additional channel deepening with depths up to 14.6 m resulting in the attendant availability of more than 8 million cubic meters of high quality sand. The availability of this material represented both an opportunity and a dilemma for the National Park Service. The sections below 58



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are on the order of 16% to 20% solids by volume with the remainder being water and pipeline velocities are on the order of 5 to 8 m/s. The "side-casting" dredge is a variation of a suction dredge which discharges the sediment only a short distance (30 m to 100 m) to the side through a pipe-line supported above the water surface. The relocation of sediment by such short distances raises questions about its effectiveness, i.e. the length of time before the sand will be redeposited in the area deepened by the dredging. Because of these concerns, most sidecasting is carried out only for emergency purposes. Hopper dredges are essentially a ship hull configured as a bulk carrier. These dredges can have bottom doors which allow release of the material carried or more recent designs are termed "Split Hull", with large hinges fore and aft allowing the hull to split, dropping its cargo of material, Figure 20. Loading of hopper dredges occurs through two "drag heads" while the dredge is underway; these drag heads are pulled along the bottom agitating and entraining the material into a pipe which carries the slurry up and into the hull. The hull functions as a settling basin with the sediment settling out and water and fine sediments returning over the side. Once the dredge is fully loaded, the drag heads are raised above the water and the material transported to the placement site. 36



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Lazor, R.L., C.C. Calhoun, and T.R. Patin (1984) "The Corps' Environmental Effects of Dredging Programs", Proceedings of the Conference Dredging '84, Dredging and Dredged Material Disposal, pp. 100-106. The Dredged Materials Research Program (DMRP) was initiated in 1973 and completed in 1978 at an approximate cost of $33 million. The objectives, methods of investigation and findings of the program are reviewed. Three new programs are discussed to investigate: (1) The Long-Term Effects of Dredging Operations, (2) A Field Verification Program and (3) A Study of Dredging Contaminated Sediments. Marsh, G.A., P.R. Bowen, D.R. Deis, D.B. Turbeville and W.R. Courtenay (1980) "Ecological Evaluation of a Beach Nourishment Project at Hallandale (Broward County), Florida: Volume II -Evaluation of Benthic Communities Adjacent to a Restored Beach, Hallandale (Broward County), Florida", U.S. Army, Corps of Engineers, Coastal Engineering Research Center, Miscellaneous Report 80-1(11), 32 pages. In 1971, 205,000 cubic meters of sand was placed on the beaches of Hallandale, FL from borrow areas located seaward of a second offshore reef in water depths of approximately 12-14 meters. This study was carried out seven years after the nourishment event to evaluate possible effects on the benthic communities. Methodology included comparison of sampling results with a control transect extending offshore from Golden Beach, FL south of the nourished beach. The same sampling techniques were applied to the stations established along each of the two transects. The study concluded that no lasting effects on the benthic community are discernible. Although damaged or diseased coral heads were found along both transects, this condition was found to be similar to other areas in Broward County and could not be attributed to the nourishment project. Mauer, D., R. Biggs, W. Leathem, P. Kinner, W. Treasures, M. Otley, L. Watling, and V. Klemas (1974) "Effect of Spoil Disposal On Benthic Communities near the Mouth of Delaware Bay". This field study investigated the disposition and effects on the benthic communities, of placing 360,000 cubic meters of spoil in water depths of approximately 6-7 m immediately inside Delaware Bay. The study period commenced prior to the disposal and included surveys immediately after, and one, two and 93



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Pick Up/Marker Buoy Pick Up Buoy Quick Release Hook 160 Ft 15" Nystron Kevlar (Jacketed) Chafe Chain < hRelease Line 1 Shot 3" Grade 3 -1/4 Shot 2 3/4" -Grade 3 8200 Lb Sinker 20,000 Lb Nav Moor Figure 27. Cross -Section of Sloping Floating Breakwater Planned for Deployment at Oregon Inlet to Provide Shelter for Sand Bypassing Dredge Operating in Its Lee. From Inman and Dolan (1987).



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PART VIII SUMMARY AND CONCLUSIONS Summary Dredging and other engineering alterations to the nearshore system have the potential to cause physical and biological impacts to the natural beach, dune and sand-sharing system that are both extensive spatially and long lasting over time. The physical impacts generally occur due to the interference with the natural sand transport system. In cases where sand is removed from this system, the inevitable result is erosion -only the distribution is unknown. In other cases where sand is trapped (perhaps by groins) or prevented from entering the system (by coastal armoring), the total amount of sand in the system remains the same but is redistributed; thus there are localized areas of relative deposition or stability and erosion. The biological impacts are generally closely related to the quality of sand used in beach nourishment projects and the large magnitudes of alterations that can place the system out of balance to a degree that the biota may not be able to adapt. Examples include the use of fine sediment that could impact offshore reefs or result in a beach too compact for turtle nesting. In particular instances where the natural system is out of balance due to prior engineering actions, beach nourishment with high quality sand can be beneficial by restoring the natural balance in the physical and biological systems. Conclusions Within the general policy of the National Park Service to maintain systems in their natural condition, each situation should be considered on a case-bycase basis recognizing that systems may be impacted by prior engineering alterations and that some engineering activities such as sand by-passing and beach nourishment can exert a beneficial impact on both the (altered) physical and biological systems. Where systems are in their natural state, the general policy of maintaining this natural state is appropriate and consistent with the NPS mandate as stewards 84



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Reilly, F.J. and V.J. Bellis (1983) "The Ecological Impact of Beach Nourishment with Dredged Materials on the Intertidal Zone at Bogue Banks, North Carolina", U.S. Army, Corps of Engineers, Coastal Engineering Research Center, Miscellaneous Report No. 83-3, 74 pages. Field studies were conducted over the period January 1977 to August 1978 to evaluate the immediate effects and recovery rates of a nourished beach. The studies were carried out on the nourished beach at Fort Mason, NC and a comparable unnourished beach. Significant findings indicated that during nourishment, all organisms were buried since no increase in populations were found on the adjacent beaches. Emerita talpoida was found to recover rapidly; however the age of the population was primarily solely at the one-year class whereas at the control beach, the ages were more widely distributed. Although all other numerically important species showed signs of recovery, their populations remained lower than before nourishment. Saloman, C.H., S.P. Naughton and J.L. Taylor (1982) "Benthic Community Response to Dredging Borrow Pits, Panama City Beach, Florida" U.S. Army, Corps of Engineers, Coastal Engineering Research Center, Miscellaneous Report No. 82-3, 138 pages. In July and August, 1976, the Corps of Engineers pumped approximately 230,000 cubic meters of sand onto the beaches of Panama City, FL. The sand was taken from numerous borrow areas located 305 to 610 meters offshore in water depths of 6-9 meters. The dredge holes were initially 5 m below the ambient bottom. This study focusses on the environmental effects in the vicinity of the dredge areas and included documentation of the hydrography (temperature and salinity). The borrow areas were found to fill initially with material that was finer than on the adjacent bottom; however when the pits were nearly filled, the surface sediment characteristics approached those of the adjacent bottom. The bottom community in the vicinity of the borrow pit declined immediately following the dredging; however the recovery was virtually complete after one year. Measures of recovery included species richness, abundance of individuals, diversity and equitability indices and several statistical tests. It is concluded that the dredging has had no adverse long-term effects on bottom100



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UFL/COEL-88/015 REVIEW OF DREDGING EFFECTS ON ADJACENT PARK SYSTEMS December, 1988 Prepared For: National Park Service 75 Spring Street, SW Atlanta, GA 30303 Prepared By: Robert G. Dean Coastal and Oceanographic Engineering Department University of Florida 336 Weil Hall Gainesville, FL 32611 With A Contribution By: Robert Dolan University of Virginia Charlottesville, VA 22903



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and managers of these systems for the use of and enjoyment by present and future generations. If consideration is given to allowing substantial dredging or construction related activities which could affect NPS systems, it is essential that: (1) where appropriate, the best geological, biological and engineering expertise be used to analyze the potential impact of the activity and to identify the most beneficial approach, and (2) that a thorough biological and physical monitoring and analysis plan be implemented to document the impact and to improve general understanding of the complex coastal sediment processes and biological interactions resulting from substantial alterations to the system. Only by this approach can NPS appropriately fulfill its responsibility to maintain the wellbeing of those systems for which it is charged against the increasing pressures for modifications which could alter these systems. 85



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Graber, P.F. (1983) "The Law of the Coast in a Clamshell: Part X -The North Carolina Approach", Shore and Beach, Vol. 51, No. 1, Jan., p. 18-23. Graber, P.F. (1984) "The Law of the Coast in a Clamshell: Part XV -The South Carolina Approach", Shore and Beach, Vol. 52, No. 2, April, p. 18-25. Graber, P.F. (1986) "The Law of the Coast in a Clamshell: Part XII -The Mississippi Approach", Shore and Beach, Vol. 54, No. 1, Jan., p. 3-7. Graber, P.F. (1986) "The Law of the Coast in a Clamshell: Part XXII -The Georgia Approach", Shore and Beach, Vol. 54, No. 3, July, p. 3-7. Graber, P.F. (1988) "The Law of the Coast in a Clamshell: Part XXV -The Alabama Approach", Shore and Beach, Vol. 56, No. 2, April, p. 12-16. Hayden, B. and R. Dolan (1974) "Impact of Beach Nourishment on Distribution of Emerita Talpoida, the Common Mole Crab", Journal Waterways, Harbors and Coastal Engineering Division, ASCE, Vol. 100, WW2, p. 123-132. Inman, D.L. and R. Dolan (1987) "Discussion of the U.S. Army Corps of Engineers Proposed Manteo (Shallowbag) Bay Project: The Stabilization of Oregon Inlet, North Carolina," Draft Report Submitted to the National Park Service, December. Inman, D.L. and R. Dolan (1989) "The Outer Banks of North Carolina: Budget of Sediment and Inlet Dynamics Along a Migrating Barrier System", Journal of Coastal Research, Vol. 5, No. 2, p. 193-353. Johnson, J.W. (1971) "The Significance of Seasonal Beach Changes in Tidal Boundaries", Shore and Beach, April, p. 26-31. Long, E.G. (1967) "Improvement of Coastal Inlets by Sidecast Dredging", Proceedings, ASCE, Vol. 93, WW4, November, p. 185-200. Lund, F. (1986) "Impacts of Beach Nourishment Programs Upon Marine Turtle Nesting at Jupiter Island, Florida, 1969-1983", Report Submitted to the Town of Jupiter Island. Mohr, A.W. (1976) "Mechanical Dredges", Proceedings of the ASCE Specialty Conference on Dredging and Its Environmental Effects, Mobile Alabama, p. 125-138. Nelson, D.A. (Undated Working Draft) "The Use of Tilling to Soften Nourished Beach Sand Consistency for Nesting Sea Turtles", U.S. Army Engineer Waterways Experiment Station. 87



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state coastal zone management program. The consistency provision encompasses harbor development, improvement and maintenance and dredge and fill activities. THE STATE PROGRAMS The following paragraphs provide a brief summary of the dredging, filling and disposal regulatory responsibilities within the six coastal states located in the Southeast Region of the National Park Service and which have coastal park units. The North Carolina Program In September 1978, North Carolina received federal approval for their proposed Coastal Management Program. State environmental concern increased in 1969, and studies were carried out and legislation adopted to preserve the state's coastal resources. The Coastal Wetlands Act of 1971 and Coastal Area Management Act of 1974 provide regulatory functions. Dredging and filling of estuarine land are regulated under the Coastal Resources Commission. The South Carolina Program South Carolina received federal approval for their proposed coastal zone management program in September, 1979. Under their program, a permit must be obtained from the South Carolina regulatory body, the Coastal Council, to "fill, remove dredge, drain or erect any structure on or in any way alter any critical area". The Georgia Program The Georgia Coastal Marshlands Act of 1970 provided that "no person shall remove, fill, dredge or drain or otherwise alter any marshlands in the State within the estuarine area thereof without first obtaining a permit". This regulatory program is administered by the Coastal Marshlands Protection Committee. Georgia does not participate in the federal Coastal Zone Management Program; thus dredging and disposal outside the jurisdiction of the Marshlands Act is administered by the U.S. Army Corps of Engineers. 77



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Beach Features and Processes Longshore Sediment Transport Generally waves approach the coastline at an angle due to the relative location of the wave generating area. In many locations, for example, the East coast of Florida, the predominant wave direction is seasonal due to the dominance of various storm patterns and locations at differing times during the year. When waves reach a sufficiently shallow depth, they break, thereby establishing the outer limit of the "surf zone", as shown in Figure 6. The character of the water and sediment motions within the surf zone differ greatly from those seaward of the surf zone. Within the surf zone, the breaking waves exert a "force" on the water causing a movement of water along the shore called a "longshore current". These currents are apparent to the casual swimmer as he or she is displaced along the shoreline. The magnitudes of longshore currents are generally small, on the order of 30 cm/second, but can range up to 150 cm/second. Due to wave breaking, the water inside the surf zone is much more turbulent and chaotic than that outside the surf zone. These two characteristics, the turbulent water motions and the relatively weak longshore current are responsible for the mobilization and transport of sediment in a longshore direction. As can be appreciated, the magnitudes of sand transported along the shoreline depend on the wave height and direction characteristics and can vary considerable from place to place and can even vary from year to year at a particular locality. Interference with the longshore sediment transport will cause areas of accretion and erosion. Methods exist for the calculation of longshore sediment transport based on wave heights and directions; however, due to our imprecise understanding of transport processes and lack of quality wave data, results of such calculations should be considered as estimates only. Some of the best field estimates of longshore sediment transport are based on the rates of accumulation caused by the construction of long impermeable structures on the updrift sides of channel entrances. Still, such data must be interpreted carefully. The notation generally adopted for the direction of longshore sediment transport is that positive transport is to the right as an observer faces 17



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There has been considerable debate concerning the allowable percentage of silt and clay and understandably in some project areas, the allowable limit will be less than in others. A biological study conducted after the Miami Beach, FL nourishment project (1976-1981) concluded that silt and clay percentages greater than 10% could cause substantial damage to offshore coral reefs. (The silt and clay portion of a sediment sample is that fraction with diameters less than 0.0625 mm). The Department of Environmental Regulation of the State of Florida is currently attempting to quantify acceptable levels of silt and clay for placement on the beach. It appears that if a value is adopted, it will be less than or equal to 10% with 5% being a value which has been discussed considerably. Turbidity concerns are both short-term and long-term. During placement, a small percentage of silt and clay will generate quite visible turbidity. In some cases, this turbidity remains confined primarily within the active surf zone, spreading out in the longshore direction. Apart from the surf zone, the initial turbidity is spread offshore over a wide region with generally low concentrations. If silt and clay concentrations are high, the turbidity considerations are likewise high and can present potential problems to both sessile animals (those which cannot move) and motile animals (those which can move). Generally fish will move away from turbidity avoiding the potential effects. Nelson (1985) has presented an excellent review of the effects of beach nourishment on the nearshore biota. The primary focus was on four common nearshore organisms: (1) Emerita talpoida (mole crabs), (2) Donax (coquina clams), (3) Ocypode (ghost crabs), and (4) Sea Turtles. Emerita Talpoida (Mole Crabs) This organism is a filter feeder that burrows in the lower foreshore of the beach and can be very abundant, although the densities tend to be quite irregular. The highly energetic swash zone appears to be the preferred environment for E. Talpoida probably enhancing the food supply. Densities in excess of 3,700 animals per square meter have been reported (Bowman, 1981). The animals tend to be in greatest abundances in Florida in December to January. E. Talpoida are very mobile and apparently have the capability to avoid being buried by beach nourishment by leaving an area. In a project in which 956,000 m3 sand was placed on Cape Hatteras beach, Hayden and Dolan (1974) found 48



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PART IX ANNOTATED BIBLIOGRAPHY Ecological Effects of Beach Nourishment Courtenay, W.R., B.C. Hartig and G.R. Loisel (1980) "Ecological Evaluation of a Beach Nourishment Project at Hallandale (Broward County), Florida: Volume I Evaluation of Fish Populations Adjacent to Borrow Areas of Beach Nourishment Project", U.S. Army, Corps of Engineers, Coastal Engineering Research Center, Miscellaneous Report 80-1(I), 23 pages. A study of the fish populations was conducted within the surf zone and over the first and second reefs seven years following the Hallandale beach nourishment project (1971). A previous study conducted during and after dredging activities had noted extensive damage to offshore patch reefs. The present study assessed the status of fish populations in the borrow areas. It was found that no damage could be identified on the second reef off Hallandale. The first reef appears to have been affected through deposition of fine grained sediments. No attempt was made to quantify the degree of this damage. Additionally, it was found that the visibility over the inner reef appeared to have been affected by suspension of the fine fraction of the nourishment material. Culter, J.K. and S. Mahadevan (1982) "Long-Term Effects of Beach Nourishment on the Benthic Fauna of Panama City Beach, Florida", U.S. Army, Corps of Engineers, Coastal Engineering Research Center, Miscellaneous Report No. 82-2, 94 pages. This study was conducted over the period 1979-1980 to determine whether any long-term effects of the 1976 beach nourishment at Panama City, FL were discernible. Sampling included forty-seven stations on nine east-west transects and two borrow pit areas. No effects on temperature, salinity or grain size or carbon content characteristics were found to be attributable to the dredging. Although the biota parameters were found to differ from the baseline surveys the magnitude of these variations were such that it was concluded that they could be due to temporal fluctuations. It was concluded that no long-term adverse 91



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programs are necessary to further document the quantitative impacts of beach nourishment projects. Sea Turtles Sea turtles nest on the upper portions of the beach generally during the months of April through September. Table 3 presents the nesting characteristics and ranges of four species of sea turtles. The turtle nesting period coincides approximately with the period of lowest wave activity and thus from the standpoint of cost and least turbidity, the most desirable dredging period. Several potential adverse effects of beach nourishment projects on sea turtles are reviewed below. TABLE 3 CHARACTERISTICS OF SEA TURTLES AND NESTING IN FLORIDA* Primary Nesting Nesting Density Species Status Range Period (nests/km) Loggerhead Threatened North Carolina April to 1 -600 (Caretta Caretta) to Florida August Green Sea Turtle Endangered East Central May to 1 -20 (Chelonia mydas) (Florida) and Southeast September Florida Beaches Leatherback Endangered Puerto Rico Late Too Small (Dermochelys and Virgin February to to Be coriacea) Islands (Some Late July Significant in Florida) Hawksbill Endangered Very Few Nests June to Too Small (Eretmochelys in the U.S. October to Be imbricata) Significant *This table assembled from information provided by Dr. Earl Possardt, U.S. Fish and Wildlife Service. 52



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dredged material in hoppers and upon reaching the disposal site, to discharge the cargo through bottom dumping hopper doors. During the last two decades, due to the need for beach nourishment, a number of hopper dredges have been modified to include a capability to pump out the hulls and complete the delivery to the beach or nearshore area via a pipeline. Pipeline dredges are rated by the size of their discharge lines (or pipes) and the rate of sand discharge varies substantially with pipe size. The approximate range of pipe sizes is 15 cm to 120 cm with corresponding pumping rates from 50 cubic meters per hour to 3,000 cubic meters per hour. Thus the size of a project will dictate, to some degree, the size of the equipment. As an example, a project requiring dredging of 1,000,000 cubic meters would usually result in contracting a dredge of 60 cm diameter, i.e. approximately 1,000 hrs of required pumping time. The elements of a pipeline dredge include an intake pipe mounted on a "ladder", a dredge pump and a discharge line to the placement area. The sediment to be pumped can be mobilized by jets of water in which case the dredge is called a "suction head" dredge (Figure 18) or if sediment mobilization is caused by a rotating cutter head, the appellation "cutter head" dredge is used, Figure 19. The ladder can be moved both horizontally and vertically to access more sediment while the dredge is in a fixed location. The dredge pump is mounted on a barge and is a centrifugal type pump with hardened elements to resist wear caused by the pumped sand. The discharge line connects to the outlet of the pump and this line, generally in segments of 10 m length or greater, transports the sand to the point of delivery. If the discharge line is so long that the power supplied by the dredge pump will not transport the slurry at sufficiently high velocities, it may be necessary to install "booster" pumps periodically along the pipeline with a booster pump every mile or so for smaller pipelines and booster pumps every two to three miles for the larger pipelines. Pumping over distances in excess of 20 km have been accomplished. It is necessary to maintain velocities above the sediment settling values or else there is a risk of deposition occurring in the pipeline leading to its eventual plugging. Since settling velocity increases with size of the sediment particles, the larger the size, the greater the required water velocity in the pipeline. Typical pipeline slurries 34



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DISTANCE FROM ORIGINAL SHORELINE (m) .30 Original Nourished Beach Planform 7Planform After 3 Months 10 Months -20 -7 Years .. -30 Years S-10 130 Years 130------s .Pre-Nourished _..., / *_ : I\ -. --...horeline-9 6 3 0 3 6 9 12 ALONGSHORE DISTANCE (km) Figure 21. Example of Evolution of Initially Rectangular Nourished Beach Planform. Example for Project Length,, of 6 km, Effective Wave Height, H, of 0.6 m and Initial Nourished Beach Width of 30 m. 42



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PART IV ALTERED COASTAL SYSTEMS A. GENERAL Introduction Natural beach and inlet systems may be altered in several ways, including dredging and constructing channels at entrances, building structures along the shoreline and nourishing beaches. Each of these alterations and their potential impacts on the natural system will be described below. Modifications of Channel Entrances Modifications of natural channel entrances or construction of new entrances have been carried out primarily for purposes of navigation and secondarily to improve flushing and renewal of interior waters. Even those entrances that were constructed initially for water quality improvement have been modified later for navigational purposes. The reasons for navigational modifications include the aforementioned shallow and energetic ebb tidal shoal which under even moderate wave action may be treacherous or unsuitable for navigation. Even though some ebb shoals have relatively deep natural channels incised through them, these channels are generally circuitous and tend to migrate in an unpredictable manner, thus contributing to the navigation jeopardy. To improve these channels for navigation, many have been stabilized through construction of jetties which are usually long stone structures lining the channel and extending up to several kilometers into the sea. The term "jetty" derives from their intended function, i.e. to constrain the seaward flows causing excess sand to be jetted offshore by the ebb tidal currents. Jettied inlets can cause/institute changes to the downdrift shoreline by interfering with the longshore sediment transport and by modifying wave patterns. The greatest effect is the physical interference with the longshore sediment transport. If no sand is bypassed around the entrance, and if the jetties are impermeable, the updrift jetty will trap, on an annual basis, the net longshore sediment transport rate. Not surprisingly, the annual erosion on the downdrift beaches will occur at the same rate. If the jetties are leaky allowing sand to flow through them and transport reversals occur, the downdrift erosion can exceed the net longshore sediment transport. Also leaky 39



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Bypassing at Inlets Jones, C.P. and A.J. Mehta (1977) "A Comparative Review of Sand Transfer Systems at Florida's Tidal Entrances", Proceedings, ASCE Specialty Conference on Coastal Sediments '77, pp. 48-66. Sand bypassing at inlets modified for navigational purposes is essential to reinstate the natural longshore sand transport processes. This paper reviews the six types of sand transfer systems that have been used in Florida at eleven inlets. The categories of types of systems include: Hydraulic dredging from the inlet, navigational channel, shoal areas or sand trap; hydraulic dredging in the entrance vicinity from an impoundment basin adjacent to a weir jetty; fixed bypassing plants, movable bypassing plants; land-based transfer by dragline or truck; and jet-pump system. The historical quantities and costs at each of the entrances is reviewed and a sketch is presented showing the individual arrangements. The installations are ranked on the basis of: entrance characteristics, navigation; beach erosion and unit cost. The annual cost was found to be $1.09 per cubic yard. Richardson, T.W. (1977) "Systems of Bypassing of Sand at Coastal Inlets" Proceedings, ASCE Specialty Conference on Coastal Sediment '77, pp. 67-84. A planning framework is developed for the selection of bypassing system type and the system design. Factors affecting the system type and design include purpose, sand pickup location, discharge location, etc. Various types of bypassing systems and three actual installations are reviewed. Possible system types for bypassing include mobile systems such as a hopper dredge or pipeline dredging, pumping to the downdrift shoreline, jet pumps which in principle can operate unattended but in practice experience severe clogging problems, and fixed bypass systems. The particular systems reviewed are: Marina di Carrara, Italy, Santa Cruz, CA and Rudee Inlet, VA. A discussion is presented of possible future development. 108



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less than for nests in the natural sand. The nourishment project resulted in a decrease in the number of nests, an increase in the number of false crawls and a small decrease in the number of turtle emergences onto the beach. Finally the scarp which was higher in the project area was found to be a slight impediment to turtles approaching the beach for nesting. Nelson, D.A. and D.D. Dickerson (1988) "Hardness of Nourished and Natural Sea Nesting Beaches on the East Coast of Florida", U.S. Army Corps of Engineers Waterways Experiment Station (Unpublished Manuscript). A total of twenty-one natural and nourished beaches were selected for field study to examine the hardness properties as measured by a cone penetrometer. Results were available from five previously studied beaches yielding a total of twenty-six beaches. Of this total, five of the eleven nourished beaches were judged sufficiently hard to inhibit normal nesting. Three additional nourished beaches were sufficiently hard that their suitability for nesting was questionable. It was also found that the nourished beaches would intermix with natural sand with time thereby improving their nesting qualities. Beaches nourished with inlet sand were found to be quite suitable for nesting. Of the fifteen natural beaches only one was found to be of a hardness which could inhibit turtle nesting. Nelson, D.A. and C.H. Mayes (Undated Working Draft) "St. Lucie Inlet Dredged Material Disposal Effects on the Firmness of Sand Used by Nesting Turtles". The study area was located south of St. Lucie Inlet, FL where 300,000 cubic meters of sand was placed following inlet dredging in December 1984 and January 1985. Control areas were selected outside of the project area in Hobe Sound National Wildlife Refuge. A measure of shear resistance of the beaches was obtained using a cone penetrometer and measurements were taken in the project area before and after the dredge material placement. An increase of shear resistance was found in the project area after sand placement. The placed sands tended to be more poorly sorted with increased percentages of the coarse and fine fractions relative to the natural sands. Turtles were found to nest in sand with a wide range of shear resistances. 96



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Change along and across the barrier islands is usually a function of one or more of these factors: the amount of sediment within a coastal segment, the magnitude of natural processes (storms), and the stability of sea level. These factors are also directly related to the geological origin of the barrier islands. Sea level has oscillated several times during the past half-million years. During the interglacial periods, continental ice melted, and the shorelines advanced inland across the continental shelves. During the glacial periods, as water was withdrawn from the seas and stored in the form of glacial ice, the shorelines moved seaward across the continental shelves. This process involved great quantities of seawater, enough to move the ocean shoreline across roughly 150 km of the coastal plain and continental shelf. When the last period of glaciation, the Wisconsin, came to an end about 20,000 years ago, sea level was approximately 120 m lower than it is today (Figure 5), and the shorelines of the Atlantic and Gulf coasts were 60 to 150 km seaward of their present positions. With the change from glacial to interglacial, the sea started to rise and continued to rise for about 14,000 years, reaching within a few meters of the present about 6,000 to 7,000 years ago. As the sea rose and the shoreline moved across the continental shelf, large masses of sand were moved with the migrating shore zone in the form of beach deposits. Sediment that had been deposited as deltas and floodplains within the coastal river systems was also reworked by wave action and moved along the shore. Once sea level became fairly stable, waves, currents, and winds worked together on the sand to form the beaches and barrier islands that rim the coast of the S.E. Region. As long as the inshore system contained surplus sediment, the beaches continued to build seaward until equilibrium was reached--in this case the balance among storm and wave energy, sea level, and the amount of sediment in the transport system. All the evidence suggests that this equilibrium was reached about 4,000 to 5,000 years ago. At that time the barrier islands were wider--some by as much as 2 km or more. As time passed, the complex landscape of the barrier islands evolved. In the narrow areas, inlets breached the islands and filled in to reform them. Long spits connected the more stable sections, such as the land area near Cape Hatteras, where sequences of beach ridges developed, building long 14



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Normal Profile Storm Profile -. Figure 8. Normal and Storm Profiles on a Natural Shoreline. TABLE 1 SUMMARY OF SHORELINE RESPONSE TO NEW JERSEY STORM OF NOVEMBER 6-7, 1953 (From Caldwell, 1959) Contour Elevation Landward Retreat of Contours (m) (m Above Mean Low Water) Average Maximum 0 20 34 1.5 19 27 3.0 30 55 4.5 16 37 21



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PART III THE DREDGING PROCESS Introduction In this section we review the objectives of dredging, the equipment and methodologies used in dredging and some of the general effects of dredging that can adversely impact the environment. Dredging Objectives There are two general and fairly obvious reasons for dredging. First is the removal of quantities of material from an area in which it is regarded as an impediment to one or more particular activities. Examples are dredging of a navigational channel or a marina. In this case, the placement of the material removed is usually of secondary interest to those carrying out the dredging and in the absence of other considerations, the material will be disposed of by the least costly method. The second reason for dredging is to obtain material for some use. In our context, beach nourishment is the more usual example and the quality of the material can be of prime concern. Regardless of the reason for dredging, removal and placement of large quantities of material will obviously cause physical and environmental perturbations in the dredging area and in the area where the material is placed. Dredging Equipment Methodologies The two general classes of dredges include mechanical dredges and hydraulic dredges. Mechanical dredges include clam shell dredges (Figure 14) and bucket dredges (Figure 15). Practically all large dredging projects are carried out with hydraulic dredges; therefore, this discussion will be limited to this class. Within the hydraulic dredge class, there are two general types of dredges, i.e. the pipeline dredge and the hopper dredge. Pipeline dredges move very slowly, excavating to a substantial additional depth before they leave an area, Figure 16. This material is transported as a water-sediment mix or "slurry" through a pipeline to the area desired. Hopper dredges load material into a hull while underway and transport the material as a bulk cargo, Figure 17. The original hopper dredges were designed (as their name implies) to store the 31



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As of the time of writing this report (December, 1988), the U.S. Army Corps of Engineers is still maintaining a limited navigation capability through operation of the hopper dredge with the placement of dredged material in water depths exceeding 6 m. CASE STUDY III -CUMBERLAND ISLAND Introduction Cumberland Island National Seashore is the southernmost island along the Georgia coastline. The waterway along the southern end of Cumberland Island is St. Marys River; the outlet to this river is protected by two long navigational jetties. As shown in Figure 28, the community of Kings Bay, GA is on the mainland to the west of Cumberland Island and approximately 8 km north of the south tip of Cumberland Island. Kings Bay has been designated as a homeport for the Ohio Class submarines. Channel modifications necessary to accommodate these submarines include substantial deepening, widening and lengthening of the current navigational channel. The total initial construction dredging is in excess of ten million cubic meters. The EIS prepared in conjunction with the project predicted an annual maintenance dredging requirement of 1.4 million cubic yards. Later more detailed estimates performed by the Coastal Engineering Research Center have yielded a substantially lower value, i.e. 788,000 cubic yards per year. Concerns of the National Park Service Due to the large quantities of dredging being considered, the NPS has concerns over the effects on inner and outer shorelines of Cumberland Island, on the marsh ecosystem on the western side of Cumberland Island and on the biota in the interior waters. These concerns led to negotiations with the Navy which eventually culminated in a five-year comprehensive monitoring and evaluation program. This program is reviewed briefly below. Monitoring Program Responsibilities for the monitoring program are shared by the Waterways Experiment Station (WES) of the U.S. Army Corps of Engineers and the National Park Service. The WES program includes a Coastal Assessment component and a 71



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PART III THE DREDGING PROCESS



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size characteristics and color of the sediment. Ideally, the sediment should be of about the same grain size characteristics as the sand originally occurring on the beach. An important characteristic relating to turbidity and sedimentation in both the borrow and placement areas is the percentage of fine sediments in the material dredged. Also too great a fine sediment content will cause a partial cementation of the sediment placed on the beach and thus adversely affect turtle nesting. Solution -Ensure, through an extensive sediment coring program, that the best quality sediment available is being used and that the sediment contains less than 5% silt and clay. Additionally, require adequate set-backs from the reef, state-of-the-art positioning equipment on the dredge and marking of the borrow area and reef perimeter with floating buoys for easy visual identification. 11



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across dry sand will tend to transport the fine fraction and deposit it as dunes. In addition to providing a better basis for understanding this process, these measurements along with sediment samples will assist in interpreting armoring of the surface by the remaining larger particles, particularly shell fragments. Vegetation Response -In order to document vegetation response to nourishment and, where carried out, the effectiveness of vegetation establishment efforts, the monitoring should include a systematic plan for photographic documentation, yet retain sufficient flexibility to respond to unanticipated vegetation features of interest. Public Interest/Education Monitoring Needs It is anticipated that due to the substantial volume of sediment to be placed and the obvious resulting physical changes to the system, there will be substantial public interest in any large beach nourishment project, including NPS rationale and justification for the placement, basis for need, etc., actual versus anticipated consequences and modification of NPS policy as the result of experience obtained. An adequate monitoring program will ensure a basis to respond to this public interest consistent with NPS management policies and responsibilities. Management Monitoring Needs Consistent with NPS responsibilities to manage park systems in a nearnatural state and to understand the consequences of various management alternatives, it is essential to monitor perturbations to these systems in order to better understand the natural system and its capacity to adjust to anthropogenic perturbations. Knowledge gained will assist in providing guidance to future management decisions related to beach nourishment. Biological Monitoring The monitoring to establish the biological effects of the beach nourishment project includes three elements; each of these is described briefly below. 65



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20 Q 1 0 Natural Berm Elevation =6 +ft +5ft 5ft +4ft > \ 0 Im 0 z 0 \ Recommended -.Nourishment Profile -10 DNR Profile II Measured October 31,1984 W -20 0 300 600 900 1200 1500 1800 DISTANCE GULFWARD FROM DNR MONUMENT R-48 (ft) Figure 25. Recommended Characteristics of Nourished Profile. Illustrated For DNR Monument No. 48



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Selzak, W.F., J.D. Phillips, J.R. Allen and N.P. Psuty (1984) "Sediment Recycling For Beach Nourishment, Sandy Hook, NJ", Proceedings of the Conference Dredging '84, Dredging and Dredge Material Disposal, pp. 1072-1080. An area immediately to the north (downdrift) of a segment of hardened shoreline was suffering severe erosion at Sandy Hook, Gateway National Recreation Area. Based on a 1978 environmental assessment by the National Park Service, a decision was made to recycle sand back from dredging of Sandy Hook and Ambrose Channels to provide relief to the eroded area. The recycling was conducted in three phases involving a placement of 2.3 million cubic meters at a cost of $21 million and over a time span of 18 months. Surveys documented that at the end of the 18 month period, 42% of the material remained on the beach. Of the material lost, some 400,000 cubic meters could not be accounted for by estimates of longshore transport or aeolian transport. Stauble, D.K. and W.G. Nelson (1984) "Biological and Physical Monitoring of Beach Erosion Control Project: Indialantic/Melbourne Beach, Florida", Department of Oceanography and Ocean Engineering, Florida Institute of Technology, Melbourne, FL. Combined biological and physical monitoring was carried out to document the impacts and performance of the 1980-1981 beach nourishment project at Indialantic and Melbourne Beach, Florida. The project entailed placement by truck of 195,100 cubic meters along 3.4 km of beach. Project construction commenced in October 1980 and was completed in January 1981. Five sampling profiles were established, one on either side of the project as control and three profiles within the project limits. Beach profiles were surveyed out to depths of approximately 3 m and sediment and biological samples were collected along the profiles. Sampling was conducted before the project and quarterly, after placement. It was found that due to extratropical storms during the 1980-1981 winter season, the profiles adjusted rapidly. With the milder 1981 summer weather, the profiles tended to stabilize. Whereas, the control profiles exhibited considerable erosion and dune scarping, the dunes within the project area were not eroded. The biological monitoring results were found to show little difference either in number of individuals or number of species between the project and the 106



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Monitoring Plan The monitoring plan included both Physical and Biological components. Physical Monitoring -The physical monitoring program addressed three needs: (1) Performance related, (2) Public information, and (3) Park management. Performance Related Monitoring Needs The primary performance related monitoring need is associated with the performance and evolution of the system, especially the sand flows and beneficial and adverse effects of the placement. Monitoring is particularly valuable to assist in understanding the natural system and to fine-tune later maintenance nourishment projects. Detailed needs are discussed below. Profile and Planform Evolution -Repeated profile surveys serve to document the three-dimensional changes in the nourishment volumes. Usually sand is placed on a profile that is steeper than the equilibrium profile. The equilibration process occurs as a result of storms which mobilize the sediment at greater and greater depths. Associated with this equilibration process can be a substantial change in shoreline position that is not related to sand flow laterally along the beach. Documented volumetric changes along with an estimate of longshore sediment transport at one location allow determination of the rates of sand flow as a function of alongshore distance. A sufficient number of profiles should be measured to allow definition of anomalous features, such as the rhythmic planform features that can be fairly accentuated at some locations; an example is Perdido Key. Wave Measurements -The wave characteristics relevant to sediment transport include: height (or energy), period and direction. Results obtained from a directional wave gage provide such data and allow much better interpretation of volumetric changes and profile adjustment. Available wave measurements also facilitate interpretation of storm effects including any documented difference between the effects to nourished and control areas. Wind and Precipitation Measurements -Following nourishment, generally there will be a fairly broad expanse of dry sandy beach. Onshore winds blowing 64



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five months following the disposal. Dye and drogue studies were carried out to determine the current and flushing regime at this site. The benthic studies encompassed the dredge and disposal areas and control areas near the bay mouth. The primary disruption was found to be limited to the dredge areas, disposal areas and those areas to which the material had migrated. It was concluded that some recruitment of benthic invertebrate occurred within the five month study period. High ambient turbidity and energetic currents were listed as significant unique characteristics of the site. Naqvi, S.M. and E.J. Pullen (1982) "Effects of Beach Nourishment and Borrowing on Marine Organisms", U.S. Army, Corps of Engineers, Coastal Engineering Research Center, Miscellaneous Report No. 82-14, 43 pages. A literature review is presented of the biological effects in the nourished and borrow areas. The manner in which beach nourishment may effect the benthic environment includes direct burial, modification of beach interface and an increase in turbidity. The compatibility of the placed sand is important to the minimization of impact. The generally energetic and unstable nature of the beach system and the associated high motility of the resident fauna contribute to their survival and rapid recruitment. Motile animals, such as fish, can leave the area and are affected least, although their food supply may be affected. Hard corals are more susceptible to sedimentation than soft corals although studies have shown the ability of corals to recover from limited sedimentation damage. The quality of the sediment placed is important to turtle nesting. Fill with excessive fines will tend to become partially cemented and be less suitable for turtle nesting. Proper timing of nourishment to avoid nesting season (April to September) will lessen any impact to turtles. Assessments of recovery in the nourishment and borrow sites are made. Recommendations are presented relating to the use of various types of dredging equipment and positioning capabilities. Nelson, D.A. (Undated Working Draft) "The Use of Tilling to Soften Nourished Beach Sand Consistency for Nesting Sea Turtles", U.S. Army Waterways Experiment Station. An evaluation was conducted of the effectiveness of tilling a beach nourishment project. The test was conducted at Delray Beach, FL and effectiveness was based on reduction in shearing resistance as measured by a cone 94



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the covering and uncovering of these resources may cause adverse effects. By contrast, the more-or-less continuous bypassing mode tends to mimic the natural processes and thus minimizes any resulting disturbances. Some modified inlets will continue to bypass small quantities of sand naturally whereas others will represent a complete obstruction. In many cases the distinguishing feature is whether or not and to what depth the channel is dredged. If the channel is not dredged, the presence of the jetties will alter the sand transport patterns usually resulting in an increase in volume of the ebb tidal shoal and a deflection offshore and downdrift of the ebb shoal and associated "sand bridge" or sand bypassing bar. Thus, the bypassing efficiency by natural forces will be decreased markedly. Beach Nourishment Projects and Their Evolution Beach nourishment comprises the addition of relatively large quantities of beach quality sand. Generally, the length of time that sand remains in the area placed is considered as a measure of the physical performance of a beach nourishment project. The discussion on performance will be presented for two situations: (1) a project on a long uninterrupted beach, and (2) a project immediately downdrift of a littoral barrier. Case (1) Project on a Long Uninterrupted Beach -In this case the longevity of a beach nourishment project is defined as the length of time that a specified percentage of the added material remains in the area placed. The longevity can be shown to be proportional to the square of the length, 2, of a project, inversely proportional to the breaking wave height Hb, raised to the 5/2 power and related to the sediment size. The half life, t of an initially rectangular beach planform composed of medium sized sand can be shown to be t = 0.17 5/2 (1) (Hb) in which t5 represents the time in years required for 50% of the sand to be transported out of the region placed, is the project length in kilometers and Hb is the effective wave height in meters. Figure 21 presents an example of the evolution of an initially rectangular planform. Initially the sharp corners are 41



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Luffing Wire Hoist and Hold Wires Boom. 'A' Frame .,/ Grab Hoist and HoldTagine Drums Winch. Aft Wire Unit Luffing Drum ead Aft Wire n I HHad Wire PONTOON --q Side Wire -Underwater Fairleads -ide Wire Figure 14. The Clam Shell Dredge (From Bray, 1979). Ladder Discharge Chute Bucket Figure 15. Bucket Ladder Dredge (From Richardson, 1976). 32



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Effects of Inlets Morton, R.A. (1976) "Nearshore Changes at Jettied Inlets, Texas Coast", ASCE Specialty Conference on Coastal Sediments '77, pp. 267-286. A review is provided of the seven jettied inlets along the Texas coast. The geomorphic features and the erosional and accretional effects are presented. The inlets reviewed are: Sabine Pass, Galveston, Freeport, Matagorda, Aransas Pass, Mansfield, and Grazos-Santiago. The updrift accretion and downdrift erosion volumes ranged up to 21.5 million cubic meters and 36.6 cubic meters, respectively. Although it was found that accretional and erosional values were qualitatively in agreement with expectations, it was not generally possible to develop a sediment budget for each inlet. It was concluded that some of the more significant effects on coastal processes due to dredging and jetty construction are: (1) changes in refraction patterns, (2) deflection of longshore currents and tidal currents, (3) development of large-scale gyres or counter currents, (4) increased cross-sectional areas of channels, (5) altered shoreface slope, and (6) disruption of bar bypassing. Olsen, E.J. (1977) "A Study of the Effects of Inlet Stabilization at St. Marys Entrance, Florida", Proceedings, ASCE Specialty Conference on Coastal Sediments '77, pp. 311-329. Jetties were constructed on St. Marys River during the period 1881-1903. These jetties are quite low and permeable and allow a substantial amount of the flood flow to enter the channel over and through the jetties. However, during ebb flows when the tides are low, the seaward directed currents are confined primarily between the jetties. This has resulted in a strong seaward bias of the tidal currents. Additional effects of the jetty construction include wave sheltering, primarily of a portion of the downdrift shoreline (Amelia Island). A comparison of surveys conducted in 1870 and 1970, indicate major changes in the nearshore and offshore morphology have occurred. The greatest effect is the shifting of approximately 90 million cubic meters from the nearshore areas to seaward of the jetties. 109



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Richardson, T.W. (1976) "Beach Nourishment Techniques, Report 1: Dredging Systems For Beach Nourishment From Offshore Sources", Technical Report H-7613, Hydraulics Laboratory, U.s. Army Waterways Experiment Station, 83 pages. The concepts of and need for beach nourishment are presented. The various types of existing dredges and concepts in the testing/evaluation stages are discussed. Various methods of delivering sand to the nourishment areas are described including those providing direct placement on the beach and those requiring rehandling of the sand. A logical classification of dredging systems is proposed. Richardson, T.W. (1984) "Agitation Dredging: Lessons and Guidelines from Past Projects", U.S. Army Waterways Experiment Station Technical Report HL-84-6, 141 pages. Agitation dredging is the removal of material from an area of interest through mechanical or hydraulic destabilization of this material during periods when the currents will transport it away. There are several means of effecting agitation dredging, including: propwash, dragging of a rake or beam, and hopper dredge agitation. The primary advantages of agitation dredging include the relatively low cost. The primary disadvantage is that the material is really only redistributed and its presence in the immediate area may increase the rate of reshoaling. A second disadvantage occurs if the sediment being dredged contains toxic substances. The report concludes that the technique of agitation dredging may be underutilized in the United States and that it should be considered further for some applications. Schwartz, R.K. and F.R. Musialowski (1977) "Nearshore Disposal: Onshore Sediment Transport", ASCE Specialty Conference on Coastal Sediments '77, pp. 85-101. A field experiment was conducted in the vicinity of New River Inlet, NC, to determine whether sand placed in relatively shallow water would move under the action of natural forces into the active beach system. A total of 26,750 cubic meters of relatively coarse sand was dredged from New River Inlet and placed along a 215 m coastal downdrift reach between the 2 m and 4 m contours. The disposal established initial shoal areas with minimum depths of 0.6 m. The sand was considerably coarser than the native sand in the area. Observations, conducted over a 12 week period, documented the shoreward and longshore movement 114



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C|E 0.4 ZW 0.2 o0.1 u2 a SI II I II I I I 0 200 600 1000 1400 1800 DISTANCE OFFSHORE (m) u E_ 6 > Dune :--'. 2 u De 200 600 1000 1400 1800 ma S I-I I I I l 16 LUw 8 wo FFigure 9. Variation of Median Sediment Size with Location Across Beach Profile. North Jupiter Island. Florida.



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THE STATE PROGRAMS 77 The North Carolina Program 77 The South Carolina Program 77 The Georgia Program 77 The Florida Program 78 The Alabama Program 78 The Mississippi Program 78 PART VII AN INVENTORY OF NATIONAL PARK SERVICE UNITS IN THE SOUTHEAST REGION SUSCEPTIBLE TO EROSION AND EFFECTS OF DREDGING 79 PART VII SUMMARY AND CONCLUSIONS 82 Summary 83 Conclusions 83 REFERENCES 86 PART IX ANNOTATED BIBLIOGRAPHY 90 Ecological Effects of Beach Nourishment 91 Physical Performance of Beach Nourishment Projects 104 Bypassing at Inlets 108 Effects of Inlets 109 General 110 v



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Wave Crest Wave Ray Zone of Increased -Wave Energy Zone of Reduced Wave Energy Zone of -Increased --Deepened Wave Energy "Borrow" Area Figure 22. Effect of a Dredged Borrow Area on Wave Refraction and Wave Energy Distribution along the Shoreline. 46



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Consolidated Beach Sediments -Sediments dredged from an offshore borrow area may have silt and clay content in excess of normal beach sediments which can result in more consolidated beach material in the nesting area. Nelson and Dickerson (1987) used a cone penetrometer to test 21 Florida natural and nourished beaches to determine the shearing resistance of the sediments. The cone penetrometer measures in approximate units of pounds per square inch. Of the 11 nourished beaches tested, it was concluded that 5 were sufficiently hard to reduce nesting. Nelson (1987) recommended tilling to a depth of 90 cm for those nourished beaches with shearing resistances exceeding 500 pounds per square inch. There do not seem to be well-established acceptable limits for the siltclay content, but an upper limit of 5 to 10% may be appropriate. Following construction, waves will mobilize and transport the material back and forth across the profile with the finer and coarser sediments preferentially residing in the offshore and onshore portions of the profile, respectively. Additionally, material transported to the project area by the longshore processes will intermix with the placed sands resulting in a more appropriate beach for turtle nesting. Thus projects that are initially poorly suited for nesting will improve as they mature. Some studies have concluded that nourished beaches experience increased percentages of false crawls (Mann, 1977; Fletmeyer, 1980), whereas others show no significant difference. For those areas in which nesting appeared to be impacted, improvements were noted in subsequent years after dredging. Blocking of Turtle Crawls by Dredge Pipe -Dredge pipe oriented parallel to the beach may interfere with the attempts of female turtles to reach a nesting site. To reduce this potential problem the length of dredge pipe oriented so as to cause this problem should be kept to a minimum. Miscellaneous Effects -Additional potential impacts of beach nourishment to sea turtles include: (1) the disturbance represented by any related activities and lights on the beach, (2) compaction of the sediments by vehicles moving along the beach, and (3) tire depressions which can act as impediments to the return of hatchlings to the sea. 53



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policy which essentially prohibits the construction of armoring in the coastal zone. NPS recognizes the three concerns noted above and also recognizes the uncertainties associated with the construction of a substantial jetty system and a sand transfer system on an unprecedented scale. NPS has sought alternatives to the jetty plan on the grounds that: (1) it is contrary to NPS and State policy, and (2) the performance is uncertain and once constructed, the system is there essentially forever. Although not within NPS purview, it is not clear that the jetties are the most cost effective approach. An approach has been sought by NPS that would be consistent with state and NPS policies and yet accomplish common objectives. A recommendation has been made for a two-year Demonstration Project to evaluate the effectiveness of a "dredge only" option. In this option, flexibility would be provided to place the sand where needed as indicated by beach monitoring. This option appears to have a number of advantages, including: (1) If not effective, this option could be discontinued without any lasting impact as would be the case with the jetty option. (2) Much could be learned about the physical system through a concerted monitoring program during the two year demonstration project. This information would serve to guide alternate designs or fine tune the "dredge-only" option. (3) Through the flexibility of sand placement, the option could address immediately areas threatened by erosion. (4) Through a multi-year dredging contract, the latest in dredging equipment and technology could be brought to bear on the project, and the performance of the contractor could be assessed on a several year basis and changes made, if desired. (5) Although detailed cost estimates have not been carried out, it appears that this method is competitive. In particular the interest on the initial investment of approximately $100 million plus the estimated annual jetty maintenance and operating costs of the sand bypassing facility of $7 to $8 million appear to be of the same magnitude as if not greater than the annual cost of the dredging only option. 70



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Beach Features and Processes 17 Longshore Sediment Transport 17 Cross-Shore Sediment Transport 19 Variation of Sand Size Across the Nearshore 22 Role of Inlets 24 PART III THE DREDGING PROCESS 30 Introduction 31 Dredging Objectives 31 Dredging Equipment Methodologies 31 PART IV ALTERED COASTAL SYSTEMS 38 A. GENERAL 39 Introduction 39 Modifications of Channel Entrances 39 Beach Nourishment Projects and.Their Evolution 41 Case (1) Project on a Long Uninterrupted Beach 41 Case (2) Placement Immediately Downdrift of a Littoral Barrier 43 Profile Equilibration After Nourishment 43 Relative Benefits of Offshore Sand Placement at Various Depths 43 Need for Profile Contouring 44 B. POTENTIAL DREDGING IMPACTS 45 Physical Effects 45 Dredging to Obtain Material 45 Dredging to Increase Navigation Channel Depths 47 Environmental Effects of Beach Nourishment Projects 47 Sediment Quality 47 Emerita Talpoida (Mole Crabs) 48 Donax (Coquina Clams) 49 Ocypode Quadrate (Ghost Crab) 50 A Case Study: Panama City, FL 50 Summary Regarding Intertidal Biological Effects of Beach Nourishment 51 Sea Turtles 52 Consolidated Beach Sediments 53 Blocking of Turtle Crawls by Dredge Pipe Miscellaneous Effects 53 Nest Relocation Programs 54 A Case Study: Jupiter Island, Florida 54 Summary Regarding Impact of Beach Renourishment on Sea Turtle Nesting 56 iii



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termed "washover" and may be up to 2 meters or more in thickness. As relative sea level rises, barrier islands maintain their elevation by washover deposits which occur in "plaques" or layers. Deposition by wind also plays a role in increasing the elevation of barrier islands. Significant overwash may not occur for several decades or more and with a single storm, the resulting deposits may achieve equilibration with increased sea level which has occurred since the previous significant overwash event. Variation of Sand Size Across the Nearshore If one were to collect and analyze sediment samples ranging from the dune to water depths of 10 m or so, it would be apparent that the "forces" in this region cause a sorting of the available sediment according to size. Although there would be a great deal of variability in sediment size from profile to profile, in general the sand in shallower waters is coarser than in deeper waters. There are a number of theories to explain the details of this sorting, the most intuitive being that the shallow water zone is an area of breaking waves and thus if fine sediment were introduced it would be repeatedly resuspended and could only be stable in the deeper water offshore where the near-bottom water velocities are much weaker. This is the same argument explaining why dust particles settle in the relatively quiet corners of rooms. Figure 9 presents an example from Martin County, FL of sand size variation from the dune crest out to a water depth of nearly 10 meters. It is seen that the size decreases from 0.4 mm to 0.1 mm in the deeper water. The past processes that are responsible for the present distribution of nearshore sediments are complex and it is possible to find nearshore deposits of coarse sediments although the decrease in size in the offshore direction is the general case and is relevant to the quality of nearshore material available for beach nourishment purposes. In addition to the distribution of size discussed above, there is a general increase in the offshore direction of the range of sizes of a sediment sample. Due to the fairly intense turbulence in the nearshore zone and the resuspension mechanism discussed earlier, there is almost no silt/clay content present. However in depths exceeding 5-10 m, it is not unusual to find silt/clay percentages of 5-10% or greater. 22



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Cumberland Sound Physical Processes component. The NPS is responsible for ecological studies, primarily in Cumberland Sound. Where practical, efforts have been made to structure all program elements such that they complement other studies being carried out for the Navy on this project. Coastal Assessment Component The purpose of this component is to develop an information base that will allow interpretation of past shoreline changes along Cumberland Island and Amelia Island (immediately to the south of the St. Marys River Entrance). No attempt will be made to present the component details; however, waves and tides will be documented as the principal agents affecting the shoreline. The shoreline will be monitored through profiling and aerial photography and sediment samples will be taken. These results, when combined with those from a historical substudy will provide the basis for an extrapolation subcomponent, the purpose of which is to develop predictions of the impact of the project on the outer and inner shorelines. Cumberland Sound Physical Processes Component Measurements of tides, currents and salinities and dredging in interior waters will be combined with computational models to predict probable changes in the physical regime of the Cumberland Sound waters. Concerns of particular interest are the effect of channel deepening on tidal range, salinity, shoaling patterns and mean tide range inside the sound. The possible effect of rising sea level combined with a dredging induced increase in mean water level may affect ability of the marshes to accrete and keep pace vertically. Ecological Research This component of the program is administered by the NPS and is not as structured as the other components. The plan is to pursue initially the study components of greatest concern and to allow the program direction to respond to results developed. Initial efforts are focused on the effect of the Kings Bay project on: marsh dynamics, bivalves, ground water, and manatees. In addition a geographic information system is being developed/tailored to organize and make all data from this study readily available. 73



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Generic Problem 2 -Channel Stabilization through Jetty Construction Problem -Jetty construction is being considered to stabilize a natural or deepened navigational channel. The Natural System The Altered System Figure 2. Generic Problem 2 -Jetty Construction. Discussion of Natural System -In the natural system, waves arriving at an angle to the shoreline cause a transport of sand along the shoreline. The transport rate is Q. Upon reaching this inlet, the transport occurs over a broad flat sand body termed an ebb tidal shoal. The Altered System -Since the shallow depths over the ebb tidal shoal are not suitable for navigation and dredging without jetty construction may be considered as too temporary a solution, jetties are planned to: (1) maintain the channel alignment, (2) to limit sand deposition from adjacent areas, and (3) to jet the deposited sand seaward from the channel. Physical Effects -The updrift jetty will cause impoundment of the sand arriving at the jetty. Downdrift of the inlet, the waves have the same transporting capacity and thus will cause erosion at the same rate as the sum of the deposition on the updrift side, and accumulation of sand farther seaward. 6



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Sanderson, W.H. (1976) "Sand Bypassing with Split-Hull Self-Propelled Barge Currituck", Proceedings of the ASCE Specialty Conference on Dredging and Its Environmental Effects, Mobile, Alabama, p. 163-172. Schwartz, R.K. and F.R. Musalowski (1977) "Nearshore Disposal: Onshore Sediment Transport", Proceedings, ASCE Specialty Conference on Coastal Sediments '77, Charleston, SC, p. 85-101. Thompson Engineering Testing, Inc. (1987) "Grain Size Distribution and Calcium Carbonate Analyses of Sediment Samples", Contract N62467-85-C-0593, Amendment/Modification No. P00009, Mobile Alabama. U.S. Congress, 1948. House Document No. 6924, Santa Barbara, CA, Beach Erosion Control Study, Letter from Chief of Engineers, Army, Submitting Report on Cooperative Study for Beach Erosion Control at Santa Barbara, CA, Dec. 22, 1948, p. 1-35. U.S. Congress, 1950. House Document No. 15787, Atlantic City, NY Beach Erosion Control Study, Letter from Chief of Engineers, Army, Submitting Report on Cooperative Beach Erosion Control Study of Atlantic City, NJ, p. 1-55. Walton, T.L. and R.G. Dean (1973) "Application of Littoral Drift Roses to Coastal Engineering Problems", Proceedings, Conference on Engineering Dynamics in the Surf Zone, Sydney, Australia, p. 221-227. Walton, T.L. and W.D. Adams (1976) "Capacity of Outer Bars to Store Sand", Fifteenth International Conference on Coastal Engineering, American Society of Civil Engineers, Honolulu, HI, p. 1919-1937. 89



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deposited on the beach. Although the intent of this report appears to be to investigate cross-shore transport, the efforts quickly focus on longshore sediment transport perhaps in part because this is the more tractable transport component. A discussion of the general wave and current forces exerted on the bottom sediments is followed by a presentation of the various theories relating to cross-shore and longshore sediment transport. A calculation model is proposed encompassing boundary layer considerations and laboratory results of sediment motion initiation. As an example, the model is applied to Point Pedernales, CA where reasonable wave, profile and sediment characteristics are available. These calculations resulted in the longshore sediment seaward of the 12 ft contour; these results were compared with previously published estimates by Bowen and Inman. The predictions exceeded considerably the Bowen/Inman values. The model was found to predict sediment transport out to depths of 50 ft. The need for improved wave climate for use in such models was noted. Hands, E.B. and S.R. DeLoach (1984) "Offshore Mound Constructed of Dredged Material", Proceedings of the Conference on Dredging '84, Dredging and Dredge Material Disposal, pp. 1030-1039. An underwater mound was constructed in water depths of 10 to 11 m at the Dam Neck (VA) disposal areas using approximately 650,000 cubic meters of silt and fine sand. Interest in constructing the mound is that it could be used elsewhere to provide shoreline protection against high waves by inducing tripping of the waves or could serve to "perch" a nourished beach or stabilize a natural beach against offshore transport during storms. A variety of techniques was employed to document the characteristics and evolution of the placed material, including: grab samples, diving observations, reference rods, seismics and bottom cores. It was found that only limited dispersion of the material occurred during the first few months following placement. Hobson, R.D. (1977) "Sediment Handling and Beach Fill Design", ASCE Specialty Conference on Coastal Sediments '77, pp. 167-180. When material is dredged from an offshore borrow area and placed onshore, it is usually found to be finer and more poorly sorted than the native material on the beach. With such material characteristics, a portion of the fine fraction will be lost due to handling techniques resulting in less volume placed on the 112



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above water portion of the profile should be constructed at a sufficiently low elevation that the run-up and overtopping due to waves can complete and "finetune" the profile shaping. If the berm portion of the profile is placed too high for waves and run-up to play a role, the resulting profile will retain an artificial characteristic. B. POTENTIAL DREDGING IMPACTS Physical Effects As described previously dredging is usually carried out to provide or remove sediment for some purpose, such as a beach nourishment project or to provide desired channel depths for improved navigation. Each of these two cases will be discussed below. Dredging to Obtain Material -In this case the area from which the material is removed (the "borrow" area) can be fairly extensive in size and on the order of 3-6 m deeper than the ambient bottom. This anomaly can cause less damping as the waves propagate toward shore, thereby causing slightly greater breaking wave heights. Probably of greater importance than the net increase in wave energy is the modified distribution of wave energy along the shoreline due to wave refraction. The wave rays which are everywhere perpendicular to the wave crests will tend to diffuse or spread out over the deepened area thereby lessening the wave energy at some areas along the shoreline and increasing it at others. The areas of wave energy increase and decrease would depend on the wave direction as can be seen by reference to Figure 22. As there is no simple "rule of thumb" to define the effect of such a bathymetric anomaly, wave refraction studies should be carried out for each case to establish the potential impact. For purposes of later discussion, it will be of interest to comment on the filling of the borrow depression. Although there is not a large data base relating to this matter, borrow areas are characterized by low wave energy and thus tend to fill with finer sediment than that removed. In areas where the bottom is highly mobile and where concentrations of suspended sediment are small, a greater percentage of the filling material will be from the adjacent bottom. 45



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beach than excavated and a coarser and better sorted material on the beach. The concepts are quantified with two beach nourishment projects including Rockaway, NY, where a hopper dredge was used to dredge and transport the sand to a rehandling location where it was dumped. The final phase of the process was by a suction hydraulic dredge which completed the transfer to the beach. The total losses due to this process were 10%. The second case study was at New River Inlet, NC, where a split-hull hopper dredge was used to transport the sand from the inlet to the downdrift nearshore. In this case, the losses were 16%. Jin, Jau Scott (1976) "Stabilization of Dredged Materials", Ph.D. Dissertation, Department of Civil Engineering, Northwestern University, Evanston, IL, 289 pages. The primary objective of this study was to investigate various physical, physico-chemical and chemical stabilization methods to improve the settlement and strength characteristics of dredge disposal material. Emphasis is on chemical stabilization methods and the types and amounts of the more effective additives to improve flocculation. The effects of these additions on the water released from the dredge disposal was quantified. Both laboratory and field tests were conducted. Conclusions are presented summarizing the characteristics of each of the methods examined. McMahon, G.F. (1984) "Practicality of Advance Maintenance: Savannah Harbor", Proceedings of the Conference Dredging '84, Dredging and Dredge Material Disposal, pp. 212-218. Advance maintenance dredging is carried out with the intent of decreasing the frequency of required dredging. This can entail dredging deeper and/or wider than the channel project dimensions. An attempt is made to analyze data available to determine whether or not advance maintenance dredging is economically justified. It is concluded that even without recognizing such intangible benefits an improved vessel safety, the economics benefits justify this practice. 113



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N :". -..: Inlet Figure 13. The "Sand Sharing System" Comprising the Inlet, the Ebb Tidal Shoal and Adjacent Shorelines.



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Environmental Effects -The erosion will degrade the natural characteristics of the beach and may destroy valuable habitat. Over long periods, the dunes may be eroded away, along with associated vegetation, the barrier island will be overtopped by storms causing impact to back barrier vegetation. Stable areas for turtle nesting may be affected. Solution -Provision should be made for bypassing of sand around the entrance. Ideally the sand transfer should be at fairly frequent intervals so as to minimize the shoreline fluctuations. A degree of flexibility should be provided for placement of sand at various locations downdrift of the entrance. Beach surveys as part of a monitoring program would establish the optimal bypassing locations. 7



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the bays, may become vegetated and emerge as islands. As these features grow, they reduce the hydraulic efficiency of the inlet and may contribute to slow downdrift migration of the inlet to a more hydraulically favorable location or may contribute to inlet closure and formation of a new inlet at a more hydraulically conducive location. The ebb tidal shoals are located in an area of much greater wave energy than the flood tidal shoals. Breaking waves tend to drive the sand toward shore and the ebb tidal currents induce seaward transport, Figure 11. Immediately after formation of an inlet, the wave effect is weak due to the greater depths in the vicinity of eventual ebb shoal formation. With continuing deposition and local shoaling, the shoreward forces due to waves become more effective and ultimately an equilibrium is achieved when any additional sand transported to the shoal by the ebb tidal currents is driven back into the nearshore system by the waves, Figure 11. In areas where a net longshore sediment transport is present, the ebb tidal shoal and its extensions to shore provide a "sand bridge" by which the net transport makes its way around the entrance. The shape of the ebb tidal shoal is indicative of the relative wave energy with shoals in high energy regions characterized by rather smooth and regular outer contours and those in low energy regions by irregular contours. Volumes contained in these ebb tidal shoals can be enormous. Dean and Walton (1975) developed and applied a technique to establish the volume of sand in an ebb tidal shoal. It was found that the Boca Grande Pass ebb tidal shoal on the West coast of Florida contained approximately 200 million cubic yards of sand. Later Walton and Adams (1976) calculated the ebb tidal shoal volumes for a large number of inlets and found that the volumes correlated well with tidal prism and relative wave energy. Figure 12 presents these results where it is noted that in accordance with earlier discussions, the ebb shoal volumes decrease with increasing wave energy. It is important to recognize that in the vicinity of an inlet, the ebb tidal shoal and the adjacent beaches form components of a system in equilibrium. If, for some reason sand is removed from one component of this system, all components will respond to reestablish equilibrium. These components have been termed appropriately a "sand sharing system" (Figure 13). We will see later the impact of removing sand from the ebb tidal shoal of this "sand sharing system". 26



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Nelson, D.A., K. Mauck and J. Fletemeyer (1987) "Physical Effects of Beach Nourishment on Sea Turtle Nesting, Delray Beach, Florida", Technical Report EL-87-15, U.S. Army Waterways Experiment Station, Vicksburg, Mississippi. Nelson, D.A. and D.D. Dickerson (1988) "Hardness of Nourished and Natural Sea Turtle Nesting Beaches on the East Coast of Florida", U.S. Army Engineer Waterways Experiment Station (Manuscript). Nelson, D.A. and C.H. Mayes (Undated Working Draft) "St. Lucie Inlet Dredged Material Disposal Effects on the Firmness of Sand Used by Nesting Turtles", U.S. Army Engineer Waterways Experiment Station. Nelson, W.G. (1985) "Guideline for Beach Restoration, Part I: Biological Guidelines", Report No. 76, Florida Sea Grant College. O'Brien, M.P. (1931) "Estuary Tidal Prisms Related to Entrance Areas", Civil Engineering, Vol. 1, No. 8, p. 738-739. Pearce, W.B. (1976) "Analysis of Dredging Projects", Proceedings of the ASCE Specialty Conference on Dredging and Its Environmental Effects, Mobile Alabama, p. 139-162. Rutgers University (Undated) "Measurements of Shoreline Positions Along Perdido Key, 1985-1987". Reilly, F.J. and V.J. Bellis (1978) "A Study of the Ecological Impact of Beach Nourishment with Dredged Materials on the Intertidal Zone", Institute for Coastal and Marine Resources, East Carolina University, Technical Report No. 4. Reilly, F.J. and V.J. Bellis (1983) "The Ecological Impact of Beach Nourishment with Dredged Materials on the Intertidal Zone at Bogue Banks, North Carolina", U.S. Army Corps of Engineers, Coastal Engineering Research Center, Miscellaneous Report No. 83-3. Saloman, C.H. (1976) "The Benthic Fauna and Sediments of the Nearshore Zone Off Panama City, Florida", Miscellaneous Report No. 76-10, U.S. Army Corps of Engineers, Coastal Engineering Research Center, Fort Belvoir, VA. Saloman, C.H., S.P. Naughton and J.L. Taylor (1982) "Benthic Community Response to Dredging Borrow Pits, Panama City Beach, Florida", Miscellaneous Report No. 82-3, U.S. Army Corps of Engineers, Coastal Engineering Research Center, Fort Belvoir, VA. 88



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TABLE 6 UNITS WITHIN THE SOUTHEAST REGION SUBJECT TO SALT/BRACKISH WATER RELATED EROSION AND ADVERSE EFFECTS OF DREDGING (Continued) Susceptibility Erosion to Dredging Unit Concerns Effects Comments Biscayne National L L Monument (FL) Fort Jefferson National Monument (FL) DeSoto National Monument (FL) Gulf Islands National Monument (FL) *Santa Rosa Island H H Proximity of Dredging *Perdido Key EH EH in Pensacola Entrance Channel Gulf Islands National Seashore (MS) *Petit Bois Island M L *Horn Island M L *Ship Island H H Navigation Channel Dredging from Gulfport San Juan National H El Morro Castle is Historic Site, Founded on Cavernous Puerto Rico Limestone and is Being Undermined Virgin Islands National L Park (St. Johns Island) Buck Island Reef National L Monument (An Island Off St. Croix) Christiansted National L Key to Ranking: L = Low; M = Medium; H = High; EH = Extremely High 82



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UFL/COEL-88/015 REVIEW OF DREDGING EFFECTS ON ADJACENT PARK SYSTEMS by Robert G. Dean with a contribution by: Robert Dolan Prepared for: National Park Service 75 Spring Street, SW Atlanta, GA 30303 December, 1988



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by reducing the concentrations of suspended materials from the water column. With respect to marine and estuarine bivalves, most studies indicate that with the exception of individuals directly covered by the disposal, the mortality rate is low. However laboratory studies suggest that an increase in turbidity causes a reduction in normal development of larvae and eggs. Adult fishes are generally more sensitive to suspended solids than invertebrate. Most field studies have shown that similarities exist in affected and control areas. It is concluded that with the exception of coral or other communities especially sensitive to turbidity, the effects of dredging and disposal are usually localized and of short duration. Moreover, any such effects can be reduced through careful selection of and control in disposal sites and considerations of biological cycles. Turbeville, D.B. and G.A. Marsh (1982) "Benthic Fauna of an Offshore Borrow Area in Broward County, Florida", U.S. Army, Corps of Engineers, Coastal Engineering Research Center, Miscellaneous Report No. 82-1, 42 pages. These studies were carried out 5 years after the 1972 Broward County beach nourishment project in which 274,000 cubic meters was placed on the beach. The studies included quarterly samplings from June 1977 to March 1978 in the borrow area and at two control stations off Hillsboro Beach. The grain size within the borrow areas was slightly coarser than the control areas. It was found that the productivity and species diversities were generally higher in the borrow area than in the control areas. It was also determined that there had been some change in the types of fauna inhabiting the borrow areas, however this was not considered detrimental. It was concluded that there were no long-term impacts identifiable in the borrow areas. 103



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was found that there was no decline in the abundance of intertidal animals following the hurricane. Culter and Mahadevan (1982) conducted studies in 1979-1980 to examine longterm effects of the 1976 nourishment. They concluded "No long-term adverse environmental effects as a result of beach nourishment could be detected within the nearshore zone of the Panama City beaches. There were also no adverse or stressful conditions present at the borrow sites." Saloman, et al. (1982) carried out a study analyzing data collected between April 1976 and November 1977. The purpose of the study was to examine shortterm effects of offshore dredging on the benthic community. It was concluded that there was an immediate decline in the benthic community; however, the populations recovered rapidly and were virtually at pre-construction levels within one year. It was noted that the borrow pits were relatively small and no more than 5 m of sand (vertically) was removed from each pit. The pits were located in water depths of 6 to 9 m. Initially the pits filled with material finer than on the adjacent bottom; however, these differences tended to diminish with further filling. Summary Regarding Intertidal Biological Effects of Beach Nourishment Based on a comprehensive review of published information, Nelson (1985) has concluded that the intertidal beach organisms are well adapted to this high energy environment including significant erosion and accretion events and fluctuations in turbidity. During and immediately following storms, massive erosion and deposition occur over segments of beaches long in comparison to nourishment projects. Thus any adverse effects of beach nourishment carried out with compatible sand tend to be short-lived as the animals can either survive the event or are adapted to rapid lateral recolonization. Nelson notes that although the available evidence indicates minimal and short-lived biological effects, the present level of understanding is such that biological monitoring 51



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Dredged .Area Dredger -I Pipeline Sea -il S: Land Figure 16. Plan View of Operation of a Pipeline Dredge (From Bray, 1979) Hoppers Dragarm Draghead Figure 17. Self-propelled Hopper Dredge with Trailing Dragarm (From Richardson, 1976). 33



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Nester, R.T. and T.P. Poe (1982) "Effects of Beach Nourishment on the Nearshore Environment in Lake Huron at Lexington Harbor, Michigan", U.S. Army Corps of Engineers, Coastal Engineering Research Center, Miscellaneous Report No. 8213, 56 pages. In 1980, the Corps of Engineers placed 54,000 cubic meters of sand on the shoreline south of Lexington Harbor. The nourishment material was compatible with that originally on the beach. Biological data included bottom grab samples and seine catches. It was concluded that no adverse effects on the physical or biological system could be identified that were attributable to the beach nourishment project. O'Connor, J.M., D.A. Newmann and J.A. Stark (1977) "Sublethal Effects of Suspended Sediments on Estuarine Fish", U.S. Army, Corps of Engineers, Coastal Engineering Research Center, Technical Paper No. 77-3, 89 pages. A laboratory study was carried out to examine sublethal effects of suspended sediments on estuarine fish. Concentrations were in the same range as occur near dredging sites and dredge disposal sites. Sediments used were natural sediment from the Patuxent River Estuary, MD and commercially available Fuller's earth. Seven species of estuarine fish were subjected to the testing program, oxygen consumption and hematoxical changes were measured. Comparisons were made between fish in the water containing suspended sediment and in filtered Patuxent River water. The sublethal suspended sediments were found to cause stress as measured by the comparisons described above. Oliver, J.S. and P.N. Slattery (1976) "Effects of Dredging and Disposal on Some Benthos at Monterey Bay, California", U.S. Army, Corps of Engineers, Coastal Engineering Research Center, Technical Paper No. 76-15, 80 pages. Field studies were carried out to determine the initial impact and recovery characteristics of benthic animals to dredging and dredge disposal. The studies were carried out in Monterey Bay, CA. It was found that dredging or dredge disposal removed approximately 60% of the animals in the immediate area. After 1.5 years, the numbers of animals remained low; however, the species diversity index was higher than before the dredging activity. It was found that those organisms adapted to unstable bottoms were less affected by burial than others. 97



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quantities of moving water from which these filter feeders obtain nourishment. However some studies have reported populations that do not migrate with the tide. The life of Donax is generally 2-3 years with one or two spawning periods per year. Primary spawning occurs in February and in Florida a second spawning may occur in June. The peak seasonal abundance tends to occur in June and July. Maximum densities of Donax Texasianus in Panama City, FL was 2,050 animals/m2. Few studies are available documenting the effects of beach nourishment on Donax. Reilly and Bellis (1978, 1983), reporting on the effects of nourishment on a North Carolina beach found that following a December nourishment event, Donax were not found in the nourished area until the following July. These were young believed to be transported in by the longshore currents and it was suggested that the adults were killed by burial in the offshore area. Ocypode Quadrata (Ghost Crab) These animals burrow in the dry beach although they lay their eggs in water. The older crabs tend to burrow higher on the beach than the young animals. Their diet varies from dead plant and animal material to live Donax and Emerita. Although seen frequently during the daytime, they are primarily nocturnal. Only the studies of Reilly and Bellis (1978, 1983) have evaluated the effects of beach nourishment on ghost crab populations. Their limited data indicated that the summer following nourishment, there was a 50% lower population. Their interpretation was that, since the material was placed below a level that would cause direct burial and since the crabs could probably burrow up through placed sand, it is likely that the reduced population was a result of emigration of the crabs due to a reduced food supply. A Case Study: Panama City, FL Saloman (1976), Culter and Mahadevan (1982) and Saloman, et al. (1982) have reported on extensive biological studies in conjunction with the 1976 nourishment of some 300,000 cubic meters placed along the beaches of Panama City. Saloman (1976) conducted a pre-nourishment baseline study in 1974-1975 and documented the effects of Hurricane Eloise (September, 1975) on the biota. It 50



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Pumps, Motors, Etc. DischargeDischarge Pipe Pump Suction Pipe Ladder Jet Cutting Assist Figure 18. Plain Suction Dredge (Swell-compensated) (From Richardson, 1976). Pump, Motors, Etc. Discharge Pipe Suction Pipe Spuds Ladder Cutterhead Figure 19. Cutter Suction Dredge (With Spuds) (From Richardson, 1976).



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PART VI LEGAL AND REGULATORY ASPECTS OF DREDGING



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Stauble, D.K. and W.G. Nelson (1984) "Biological and Physical Monitoring of Beach Erosion Control Project: Indialantic/Melbourne Beach, Florida", Department of Oceanography and Ocean Engineering, Florida Institute of Technology, Melbourne, FL. Combined biological and physical monitoring was carried out to document the impacts and performance of the 1980-1981 beach nourishment project at Indialantic and Melbourne Beach, Florida. The project entailed placement by truck of 195,100 cubic meters along 3.4 km of beach. Project construction commenced in October 1980 and was completed in January 1981. Five sampling profiles were established, one on either side of the project as control and three profiles within the project limits. Beach profiles were surveyed out to depths of approximately 3 m and sediment and biological samples were collected along the profiles. Sampling was conducted before the project and quarterly after placement. It was found that due to extratropical storms during the 1980-1981 winter season, the profiles adjusted rapidly. With the milder 1981 summer weather, the profiles tended to stabilize. Although the control profiles exhibited considerable erosion and dune scarping, the dunes within the project area were not eroded. The biological monitoring results were found to show little difference either in number of individuals or number of species between the project and the control areas. Observed seasonal variability was much greater than differences between the control and project sites. It was concluded that the lack of adverse biological impact was due to the good match between the placed and native sands and possibly due to the tendency for the species Donax to migrate offshore during the winter which corresponded to project construction. Stern, E.M. and W.B. Stickle (1978) "Effects of Turbidity and Suspended Material in Aquatic Environments, Literature Review", Technical Report D-78-21 Dredged Material Research Program, prepared for Office Chief of Engineers, U.S. Army, Washington, D.C., 117 pages. Definitions, characteristics and various measures of turbidity are reviewed. The causes of turbidity can be natural or due to human activity such as dredging. Suspended material can have beneficial or detrimental effects depending on the organisms present. It is noted that many filter feeders can lessen turbidity 102



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REFERENCES Aubrey, D.M. and N.M. Dekimpe (1988) "Performance of Beach Nourishment at Jupiter Island, Florida", Paper Presented at Beach Technology Conference, Gainesville, FL, 20 pages. Bokuniewicz, H.J., M. Zimmerman, M. Keyes, and B. McCabe (1980) "Seasonal Beach Response at East Hampton, NY", Special Report 38, Marine Sciences Center, State University of New York, Stony Brook, N.Y. Bowman, M.L. (1981) "The Relationship of Emerita Talpoida to Beach Characteristics", M.S. Thesis, University of Virginia, Charlottesville, Virginia, 106 pp. Culter, J.K. and S. Mahadevan (1982) "Long-Term Effects of Beach Nourishment on the Benthic Fauna of Panama City Beach, Florida", Miscellaneous Report No. 82-2, U.S. Army Corps of Engineers, Coastal Engineering Research Center, Fort Belvoir, VA. Dean, R.G. (1977) "Equilibrium Beach Profiles: U.S. Atlantic and Gulf Coasts", Ocean Engineering Technical Report No. 12, Department of Civil Engineering, University of Delaware, Newark, DE. Dean, R.G. (1983) "Principles of Beach Nourishment", in Handbook of Coastal Processes and Erosion, CRC Press, p. 217-231. Dean, R.G. and T.L. Walton (1975) "Sediment Transport Processes in the Vicinity of Inlets with Special Reference to Sand Trapping", in Estuarine Research, Volume II, Geology and Engineering, Edited by L. Eugene Cronin, Academic Press, New York, p. 129-150. DeWall, A.E. and J.J. Richter (1977) "Beach Nearshore Processes in Southeastern Florida", Proceedings, ASCE Specialty Conference: Coastal Sediments '77, p. 425-443. Gren, G.G. (1976) "Hydraulic Dredges, Including Boosters", Proceedings of the ASCE Specialty Conference on Dredging and Its Environmental Effects, Mobile, Alabama, p. 115-124. Graber, P.F. (1981) "The Law of the Coast in a Clamshell: Part II", Shore and Beach, Vol. 49, No. 1, Jan., p. 16-20. Graber, P.F. (1981) "The Law of the Coast in a Clamshell: Part IV -The Florida Approach", Shore and Beach, Vol. 49, No. 3, July, p. 13-20. 86



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PART VI LEGAL AND REGULATORY ASPECTS OF DREDGING Introduction Dredging in the waters of the United States is regulated by both federal and state agencies. Some of the material presented in this section is based on the twenty-six (and still counting) review articles which Peter Graber has published in Shore and Beach. Articles referenced are included in the bibliography. THE FEDERAL PROGRAM A brief review of the evolution of the history of the federal laws may be helpful. Rivers and Harbors Act of 1899 The purpose of this statute was to prevent obstruction to navigation and placed responsibility on the U.S. Army Corps of Engineers for issuing permits. Although as noted above the concern of the original act was navigation, it was broadened through litigation in 1970 and 1971 to require consideration of ecology and allowed denial of a permit if the proposed project would cause ecological damage. National Environmental Policy Act of 1969 (NEPA) This statute, administered by the Environmental Protection Agency, declares "... a national policy which will encourage productive and enjoyable harmony between man and his environment." This act formalized the change toward greater concern for the environment and states as a goal "... a balance between population and resource use which will permit high standards of living and a wide sharing of life's amenities." The character of environmental impact statements required in "major Federal actions significantly affecting the quality of the human environment" are formalized to include, "(i) the environmental impact of the proposed action, (ii) any adverse environmental effects which cannot be avoided should the proposal be implemented, (iii) alternatives to the proposed action,... 75



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PART VII AN INVENTORY OF NATIONAL PARK SERVICE UNITS IN THE SOUTHEAST REGION SUSCEPTIBLE TO EROSION AND EFFECTS OF DREDGING Within the Southeast Region of the National Park Service there are 19 units that are subject to erosion by salt or brackish waters. Of these, at least seven are considered to be mildly to highly susceptible to dredging effects. Table 6 lists the NPS units in the SE region which fall within the classification above, i.e. either subject to erosion by salty or brackish water or are possibly subject to adverse effects of dredging. An attempt has been made to rank the effects of dredging as Low (L), Medium (M), High (H) and extremely high (EH). This ranking is based on the proximity of planned or past dredging activities and the impact on the site. 80



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PART IX ANNOTATED BIBLIOGRAPHY



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environmental effects could be detected either within the nearshore zone or in the vicinity of the borrow sites. Environmental Protection Agency/Corps of Engineers (1977) "Technical Committee on Criteria for Dredge and Fill Material -Ecological Evaluation of Proposed Discharge of Dredged Material into Ocean Waters", Environmental Effects Laboratory, U.S. Army Waterways Experiment Station, 127 pages. This is an implementation manual developed jointly by the U.S. Army Corps of Engineers and the Environmental Protection Agency to comply with Section 103 of Public Law 92-532. The report develops recommendations for general approaches, dredge material sample and preparation, analysis procedures and estimation of initial mixing. The manual is not intended to provide a rigid framework for approaching projects but rather guidelines for designing a program. Harris, M.E. and R.M. Miller (1981) "Environmental Impacts of Dredged Material Disposal", University of Dubuque, Dubuque, Iowa, 125 pages. An annotated literature survey is presented of 136 references related to environmental effects of dredged material disposal. In addition limited field monitoring was conducted at three dredge disposal sites. Sampling and analysis included influent and effluent water and analysis of plants for heavy metals. In most cases, there was little change in the heavy metal content as the effluent flowed from the inflow to the outflow of the disposal area. In general, the plants and seeds were found to contain concentrated amounts of heavy metals. Hurme, A.K., R.M. Yancey and E.J. Pullen (1979) "Sampling Macroinvertebrates on High-Energy Sand Beaches", U.S. Army, Corps of Engineers, Coastal Engineering Research Center, Technical Aid No. 79-3, 37 pages. This report provides a framework for developing an efficient plan for quantitative sampling high-energy sand beach macroinvertebrates. Sufficient detail is provided to allow effective organization of the field effort including materials and numbers and qualifications of personnel required. 92



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rate of 20 m/year during the period 1931-1988 (Task Force, 1988). The net southerly longshore transport is 0.5 to 1.0 million cubic meters per year (Inman and Dolan, 1989). Present Situation Since the bridge construction in 1960, the inlet has continued its relentless migration such that a spit has grown to the south under the northern part of the elevated bridge span. This migration has caused the channel to be dangerously close to the southern bridge abutment, where protection has been provided by revetment construction. The Corps attempts to maintain the inlet navigable through hopper and sidecast dredging. From September, 1983 to February, 1988, an average of 550,000 cubic meters annually has been dredged from the inlet with the material placed south of the inlet in water depths exceeding 6 m. Due to this substantial depth, it is questionable whether this placement provides significant benefit to the downdrift (south) shoreline. The Corps of Engineers (COE) has developed a plan to stabilize Oregon Inlet through the construction of two jetties with sand transfer accomplished by a floating pipeline dredge which would remove accumulated sand north of the north jetty and transfer this sand to the northern portions of Pea Island. The dredge would operate during the summer months with protection against waves provided by a "Sloping Floating Breakwater" (SFB), essentially a new and untried concept, see Figure 27. The COE plan was authorized in 1970 with an estimated construction cost of approximately $50 million. Since then the estimated cost has risen to in excess of $100 million with an annual maintenance and sand bypassing cost of approximately $7 to $8 million. Present concern centers on three issues: (1) the erosional threat to the bridge, especially near the south abutment, (2) the erosional threat to the Coast Guard station south of the inlet as shown in Figure 26, and (3) the unstable and hazardous channel. The National Park System and State of North Carolina Position on Oregon Inlet NPS policy is to allow natural systems to remain in as near a natural condition as possible. This is consistent with the State of North Carolina 68



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detail the background of the project and the rationale leading to the implemented plan. Background The net longshore sediment transport in the vicinity of Pensacola Bay Entrance is from east to west with an estimated magnitude of approximately 200,000 m3/year. In its natural condition, depths over the ebb tidal shoal were on the order of 6 m and formed a sand bridge from Santa Rosa Island to the downdrift Perdido Key. Deepening as documented in Table 5 severed this bridge and the longshore sediment transport tended to deposit in the channel, reestablish the sand bridge and resume the natural bypassing process. Clearly as noted before for many cases, a shallow bar which is required for bypassing is not compatible with safe navigation. Thus the material deposited must be removed from the channel by dredging as a periodic maintenance operation. From the earlier discussion of natural and altered systems, it is clear that unless the dredged material is placed on the downdrift shorelines, it will represent a deficit and result in an erosional stress. As shown in Table 4, with the exception of the 1985 placement of approximately 1,860,000 m3 on Perdido Key, all placement has been at sea. As documented in Figure 24, this practice of disposal at sea has taken a severe erosional toll on Perdido Key. This figure presents shoreline change data collected by the Florida Department of Natural Resources showing that over the 10 year period represented by these data, an area extending over almost the entire Park limits was eroding at an average rate of approximately 1.3 m/year. Using a standard rule of thumb, this is equivalent to 100,000 m3/yr. Undoubtedly, the remainder of the deficit resulting from interruption of the net longshore sediment transport of 200,000 m3/yr occurs by erosion west of the western Park boundary. The nearest condominium to the west Park boundary is clearly in jeopardy due to the erosion and erosion is evident to substantial distances farther west. Rationale for Selected Plan In keeping with National Park Service policy to maintain, as near as possible, parks in their natural condition, an overriding factor in the considerations at Perdido Key was that the natural system had been impacted 60



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General Boumar, A.H. (Editor) (1976) "Shell Dredging and Its Influence on Gulf Coast Environments", Gulf Publishing Company, Houston, TX, 454 pages. This book comprises twenty-four individual contributions each as a separate chapter. The book is organized in five sections. Section 1 reviews the magnitude and commercial value of shell dredging over the period 1912-1930 and 1960-1969 and also reviews the literature addressing the effects of shell dredging. Section 2 reviews the physical and geological characteristics of San Antonio Bay, TX including the bathymetry, weather, geology and circulation. Sections 3 and 4 examine the chemical and biological conditions respectively of San Antonio Bay. Section 5 provides information on shell dredging from each of the following states: Florida, Alabama, Mississippi, Louisiana and Texas. Included are the magnitudes and value of shell dredging and the associated regulatory programs of the individual states. Brahme, S.B. (1983) "Environmental Aspects of Suction Cutterheads", Ph.D. Dissertation, Ocean Engineering, Texas A and M University, College Station, TX, 166 pages. Scaled model studies were carried out to investigate the flow field, sediment entrainment and sediment concentration in the vicinity of a cutterhead intake. It was found that scale modeling approaches were quite effective in investigating these phenomena. Five model sediments were used including sand of three sizes, glass beads and coal. The studies suggested that silt curtains placed in front of the cutter can reduce turbidity substantially. Bray, R.N. (1979) "Dredging: A Handbook For Engineers", Edward Arnold, Limited, London, 176 pages. A comprehensive tutorial of all physical aspects of dredging equipment and techniques is presented. Only limited attention is directed to environmental effects. The suitability of each type of dredge for various sediment characteristics is reviewed. The factors affecting performance and selection of dredge type include: water depth, pumping distance, depth of cut, type of material and waves, winds and currents. The hydraulics of pipeline transport is addressed with respect to horsepower requirements and sediments of differing 110



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Plan Hopper Plan a" O Front Elevation Side Elevation Figure 20. Split Hopper Barge (Self-propelled) (From Richardson, 1976). 37



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penetrometer. Two types of equipment were evaluated. The first was a rootrake attached to a front-end loader and was capable of penetrating to approximately 20 to 55 cm. The second type of equipment was a single tined ripper which penetrated from 90 to 120 cm. It was found that both of the methods were effective in reducing significantly the shearing resistance. Measurements six months after the initial tilling showed some increase in shearing resistance; however, the resistance was still lower than in areas where tilling had not been carried out. It was recommended that in areas where the shear resistance exceeds 500 pounds per square inch, tilling be conducted prior to the nesting season. Approximate costs of tilling are presented. Nelson, D.A., K. Mauck, and J. Fletemeyer (1987) "Physical Effects of Beach Nourishment on Sea Turtle Nesting, Delray Beach, Florida", U.S. Army Waterways Experiment Station, Vicksburg, Mississippi. This report commences with the important observation that "A large percentage of all sea turtle nests in the United States are located in beaches that have been nourished or renourished". Field tests were conducted before and after the 1984 Delray Beach renourishment project which entailed the placement of 630,000 cubic meters of sand on the beach. A cone penetrometer was used to determine the shearing resistance at various depths in the vicinity of nests and false crawls before and after the 1984 project. The size and shape characteristics of the sand were also determined. In order to evaluate nest relocation effectiveness, the eggs in some nests were relocated to a fenced hatchery area. After an appropriate incubation period, the nests were excavated to determine a number of parameters including hatching success. Within the hatchery, three equally-sized areas were established. The material in each of these areas was different and included aragonite sand, nourishment sand and natural beach sand. Findings of the study included a significantly higher sediment shearing resistance in the project area following renourishment compared to prerenourishment conditions. A scarp formed in the nourished beach which was somewhat higher than in a control beach located south of the project. There was no significant difference in the hatching success for the three sand types in the nursery area; however, the success of the hatchery areas nests was slightly 95



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PART V CASE STUDIES AS EXAMPLES



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It was concluded that by timing of dredging so as to not coincide with the reproductive season, recovery could be enhanced. Parr, T., D. Diener, and S. Lacy (1978) "Effects of Beach Replenishment on the Nearshore Sand Fauna at Imperial Beach, California", U.S. Army, Corps of Engineers, Coastal Engineering Research Center, Miscellaneous Report No. 78-4, 125 pages. This study was carried out to identify any possible impacts on the nearshore sand fauna in response to a beach nourishment project of 765,000 cubic meters comprising material which was mostly finer than the native. It was found that measurable effects were short lived (5 weeks or less) and that the finer sediment resulted in an increase in the numbers of crustaceans. The finer sediments gradually moved overshore and there was a positive correlation between the finer sediments and the number of species and abundance. It was concluded that the overall abundance and diversity were not affected adversely by beach nourishment. It was believed that because the beach environment is energetic, the normally resident fauna must be able to cope with considerable stress; hence their capability to respond after beach nourishment. Peddicord, R.K. and V.A. McFarland (1978) "Effects of Suspended Dredged Material on Aquatic Animals", U.S. Army Waterways Experiment Station, Technical Report D-78-29, 115 pages. A laboratory study was conducted to investigate limits of tolerance of a variety of juvenile and laboratory fish and invertebrates to contaminated and uncontaminated concentrations of harbor sediments. Additionally, animal tissues were analyzed for concentrations of contaminants. It was found that the various species could tolerate high levels of uncontaminated concentrations longer than the same levels of contaminated concentrations. Most animals survived durations longer than are created during harbor dredging operation. Concentration levels that proved lethal were quite high and generally persist in nature only in the bottom fluid mud layer, if one is present. Tissue accumulation of contaminants was found to be present in less than 25% of those exposed. 98



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Federal Water Pollution Control Act Amendments of 1972 (FWPCA) The purpose of this act also called the Clean Water Act is to "restore and maintain the chemical, physical and biological integrity of the Nation's waters". A system of permits is required to regulate the discharge of dredged or fill materials into navigable waters. The Corps of Engineers is the responsible agency to administer this program. Section 404 of this act provides for the states to assume responsibility for permitting dredge and fill activities and establishes requirements which these state programs must satisfy including procedures to ensure compliance with the program. Marine Protection, Research and Sanctuaries Act of 1972 This statute is also referred to as the Ocean Dumping Act and requires a permit when any material is to be discharged into the territorial sea and contiguous zone of the United States. Regulatory responsibilities are shared by the U.S. Army Corps of Engineers for dredged material and the Environmental Protection Agency for other materials. Criteria for permitting dumping are that the project should not "... unreasonably degrade or endanger human health, welfare or amenities, or the marine environment, ecological systems, or economic potentialities." Coastal Zone Management Act of 1972 (CZMA) This act provides financial incentive to coastal states to develop and adopt approved coastal zone management programs. In 1976, the federal cost sharing of the program was increased from 66.6% to 80%. Requirement of the CZMA are that a state program must include a designation of the states' boundaries of the coastal zone, an inventory of the areas of particular concern, broad guidelines on priority of uses in those areas, lists of permissible land and water uses, etc. All states within the Southeast Region have approved programs with the exception of Georgia. Section 307 of the Coastal Zone Management Act of 1972 requires that federal agencies comply with federally-approved coastal zone management programs. This section, termed the "consistency provision", also requires that a state or local project which affects the coastal zone must be in accordance with the 76



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control areas. Observed seasonal variability was much greater than differences between the control and project sites. It was concluded that the lack of adverse biological impact was due to the good match between the placed and native sands and possible due to the tendency for the species Donax to migrate offshore during the winter which corresponded to project construction. 107



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Nest Relocation Programs If beach nourishment programs are carried out during turtle nesting season in a nesting area, it is essential to conduct a program of locating new nests each morning and relocate the eggs to a protected hatchery area. The hatchery is essentially a fenced natural sand area which is protected from humans and other predators. Care is necessary in moving and placing the eggs to avoid a high mortality. Nelson, et al. (1987) have found the hatching success to be above 85% if natural sand is used in the hatchery area. This is only slightly less than in natural reference areas. Thus it can be concluded that although further study is necessary, egg relocation to a carefully monitored hatchery area is effective in maintaining the survival rate of hatchlings. A Case Study: Jupiter Island, Florida Lund (1986) has reported on a comprehensive monitoring program on Jupiter Island to evaluate the impact of beach nourishment on sea turtle nesting. The program was carried out each summer from 1969 to 1983 and extended from Blowing Rocks to St. Lucie Inlet, a distance of approximately 23 kilometers. This monitoring period encompassed major beach nourishments in 1973, 1977, 1978 and 1983, totalling 4.4 million cubic yards. To compare the nourished and unnourished beach segments, the beach was segmented into "South", "North" and "Fill" regions, the latter region denoting a segment of some 8 km within which the nourishment occurred. High erosion rates along the northern end of Jupiter Island are due to the interruption of the longshore sediment transport by St. Lucie Inlet which was cut in 1892. The long-term shoreline change rates vary from 9 m/year erosion at the north end of the study area to a stable shoreline near the south end. The "South" and "Fill" regions are within the Town of Jupiter Island. Prior to the major nourishment projects which commenced in 1973, many shore protection structures including seawalls, groins and revetments had been constructed to limit erosion of the upland (Aubrey and Dekimpe, 1988). Because of the erosional trend and the presence of the shore protection structures, the beach narrowed significantly reducing the beach area suitable for turtle nesting. The beach material used in nourishment was substantially finer than the sand naturally present on the beach. The silt-clay content was sufficiently high to result in a beach somewhat more compact and dense than optimum for nesting. 54



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+. +5.0 S+5. Area of 1985 W -Approximate Western Nourishment t Park Boundary S -Mile ( -/to\ I Vigure 24. Shoreline Change Rates for Escambla County, January 1974 tob 4. Based on Florida DNR Survey. Note Shoreline Change Rates Shown have been Smoothed by a Five Point Running Average. u i ~ II I I \I ~ S30 40 50 60 FLORIDA DNR MONUMENT NUMBER



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(/`SAjN K HOALM ..t ROSA A I TJ N NANDINA A( L `A ,L ,--LT67 .,,s 460,000m 3/yr WALTHAMITON JACKSONVILLE .10 BAY g^ ',MADISONlL U BAKER( --LIBERTY WAKULLAT YLOR I BAKER GULF FRANKLIN ;RA' .ST. AUGUSTINE / e'. I DFAR'C ST. DI CHRIST JOHN MARINELAND DIXIE ALACHUA PUTN GL Op LEVY M ARION 'voLust 400, m3/yr YVOLU St oo m34yr EW SMYRNA S CITUS I LAKE SI-SUMTE'R HER"NAND" I IEN S I I ORANGE B R /PAsco OSSCEOL IAPE CANAVERAL S1-_--C \OSSCEOLA S POLK IA \ \ 300,000m 3/yr (N 0 \ ID El rTiN n IA L -/-------L-1 RIVER VERO BEACH ^ MANATEE HARDEE .I OK EEr \ST200,00 m 3/yr S % HAR-EE | \ HBEE ST. \\\ FT PIERCE S---HIGHLAN F LUCIERCE \" -DE SOTO --t--Hf \ _--_ ,-AKE I "MARTINH \-.R i OKEECHO --JUPITER I. HARLOTTLADES B 200,000m 31yr I PALM BEACH S LEE I HENDRY I PALM BEACH S_--/EERFIELD COLLIER BROWAR 100,000m 3yr SBAKERS HAULOVER *" 4 10,000m3/yr RO DADE MIAMI ONROt Figure 7. Estimates of Net Annual Longshore Sediment Transport Along Florida's East Coast. 20



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PART I INTRODUCTION AND GENERAL TYPES OF DREDGING AND COASTAL PROBLEMS ENCOUNTERED BY THE NATIONAL PARK SERVICE Introduction The coastal zone is ever-dynamic responding to the forces of waves, tides, currents and winds. Long periods of relative stability can be terminated by a sudden storm causing both temporary and permanent changes much greater than those occurring over many years of mild weather. Even during periods when the beach is relatively stable, there may be a large unnoticed transport along the shore. The coastal zone is a desirable region for habitation, recreation and industry. Some of these uses lead to desires to alter the natural system by various means. Such modifications could include channel deepening for navigational purposes, dredging for beach nourishment, coastal armoring to stabilize an eroding shoreline, etc. Engineering interaction with the coastal zone usually causes effects which can be anticipated adequately only through a detailed and quantitative understanding of the natural processes. Although understanding of these processes has developed considerably over the past few decades, our information base is still inadequate and generally unanticipated effects of engineering interaction may occur. Some of these effects are slow and large scale and may influence the shoreline for distances of many kilometers from their cause. The National Park Service (NPS) as a manager of coastal lands including barrier islands can be impacted by a variety of modifications by adjoining property owners. In some cases, the concern occurs on NPS property and the NPS may initiate a study seeking appropriate remedial measures. The present report is directed to Park resource managers with the intent of providing a familiarization of the natural processes, the range of dredging related modifications that can occur and the potential areas of concern that should be voiced at the first level of review by the resource managers. The following section presents several generic problems to illustrate with greater specificity the types of modifications, impacts and the significant factors. 2



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PART VII AN INVENTORY OF NATIONAL PARK SERVICE UNITS IN THE SOUTHEAST REGION SUSCEPTIBLE TO EROSION AND EFFECTS OF DREDGING



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Generic Problem 3 -Coastal Armoring Situation -A developed area updrift of a park is affected by a long-term erosional trend as is the park area. To stabilize the shoreline, the developed area is considering armoring the shoreline by construction of a seawall or other shore protection structure. The Natural System The Altered System Figure 3. Generic Problem 3 -Coastal Armoring. Discussion of Natural System -Natural forces, assumed unknown, are causing a large scale erosional trend. This erosion is shared by both the developed area and Park area as indicated above. The Altered System -By armoring the developed area shoreline, and thus preventing erosion, this source of sand to the longshore transport system is eliminated, thus placing greater erosional pressure on the downdrift shoreline in the amount of the deficit imposed by the armoring. Physical Effects -Increased erosion rates of the downdrift shoreline. Environmental Effects -A more rapid rate of dune loss and the associated habitat. Generally a narrower dry sand beach and thus less favorable for successful turtle nesting. Solution -The developed area could compare the relative economic benefits of beach nourishment using high quality sand. If not feasible, an alternate 8



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TABLE 6 UNITS WITHIN THE SOUTHEAST REGION SUBJECT TO SALT/BRACKISH WATER RELATED EROSION AND ADVERSE EFFECTS OF DREDGING Susceptibility Erosion to Dredging Units Concerns Effects Comments Cape Hatteras EH EH Dredging Effects National Seashore (Cape Hatteras High in Vicinity (NC) Light House) of Oregon Inlet Cape Lookout National L L Seashore (NC) Fort Raleigh National ? ? Historic Site (NC) Fort Sumter National M M Proximity to Monument (SC) Channel Dredging Could Induce Erosion Fort Pulaski National M M Proximity to Monument (GA) Channel Dredging Could Induce Erosion Fort Frederica National ? ? Monument (GA) Cumberland Island H H Channel Deepening at National Seashore (GA) Kings Bay. Both Inner and Outer Shorelines Fort Caroline National M M Dredging in St. Johns Monument (FL) River Entrance Fort Matanzas National L L Possible ModificaMonument (FL) tions to Matanzas Inlet Bridge Canaveral National M-H L Coastal Armoring to Seashore (FL) North May Cause Some Erosional Stress Key to Ranking: L = Low; M = Medium; H = High; EH = Extremely High 81



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Summary Regarding Impact of Beach Renourishment on Sea Turtle Nesting In summary, although much is not known regarding the detailed effects of beach nourishment on turtle nesting, research and field programs over the last decade have developed techniques effective in ameliorating the major potential adverse impacts. In fact, an effective program of nest relocation during beach nourishment projects and, where necessary, tilling of the nourished beach appear to be effective in essentially mitigating adverse effects. Finally, in areas where beaches have narrowed due to a beach erosion trend and the presence of shore protection structures, the wider beaches resulting from beach nourishment can improve substantially nesting conditions and ultimately turtle populations. 56



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N 0 4000 Scale (ft) Bar (Q / / / Figure 26. Oregon Inlet .. I J \ S:Coast Guard Station Figure 26. Oregon Inlet 67



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Thus the total annual southerly and northerly transport components are 370,000 m3/yr and 170,000 m3/yr, respectively. The "net" and "gross" components are QNET = + 200,000 m /yr (Southerly) (2) QGROSS = 370,000 + 170,000 = 540,000 m3/yr In general, the net longshore sediment transport is southward along the East coast portion of the Southeast Region. Fairly detailed estimates exist for the East coast of Florida as shown in Figure 7. Cross-Shore Sediment Transport It is well-known that beaches change seasonally and with differing wave conditions. Although beach profile changes can occur due to longshore sediment transport, the focus here will be limited to cross-shore sediment transport. Winter waves are usually higher and generally have shorter periods than those occurring during the summer months. The resulting summer and winter beach profiles differ substantially as idealized in Figure 8. The summer profile tends to be steeper with a wider berm and the winter profile tends to be milder in slope and to have a narrower berm. Although the range in seasonal shoreline fluctuations is not known for many locations, it has been shown to be on the order of 30 m at Long Island, NY (Bokuniewicz et al., 1980), 80 m at Stinson Beach, CA (Johnson, 1971), and 10 m at Boca Raton, FL (Dewall and Richter, 1977). Additionally, in many locations, there is a bar present in the winter profile. At some locations, the bar is perennial. The mechanics of cross-shore transport are not understood completely; however storm waves of greater heights and shorter periods cause offshore transport. Table 1 presents an example of shoreline changes that occurred in New Jersey due to a severe storm. If the dunes are sufficiently high during a storm to prevent overtopping, transport may be limited to the offshore direction. However, if the storm tide level exceeds the dune elevation or if the dunes are breached, a process called "overwash" may occur. Overwash is the transport of water and sand over a normally subaerial feature usually due to storm-elevated water levels and increased wave heights. The sand deposit resulting from an overwash event is 19



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fall velocity. Administrative/management elements of the project are examined including contracts, supervision and planning. Survey techniques to determine a basis for payment quantities are reviewed. The nature of the fill and its consolidation properties are examined as a function of the material characteristics and method of placement. Clark, G.R. (1983) "Survey of Portable Hydraulic Dredges", U.S. Army Waterways Experiment Station, Technical Report HL-83-4, 113 pages. This study summaries the numbers and characteristics of portable hydraulic dredges available in the United States. For each dredge model or series, the following are provided: geometric dimensions, pump type, pump horsepower, pump capacity, suction and discharge diameters, characteristics of cutterhead (if present), working capacity (depth, production and pumping distances), anchoring system and mode of transport. Durham, D.L., L.Z. Hales, and T.W. Richardson (1981) "Beach Nourishment Techniques, Report 4: Wave Climates for Selected U.S. Offshore Beach Nourishment Projects", Presented in Two Volumes: "Main Text" and "Appendixes A-K", Technical Report H-76-13, Hydraulics Laboratory, U.S. Army Engineer Waterways Experiments Station, 55 pages. Average wave climates are presented for 10 beach nourishment locations along the continental U.S. shoreline, including 5 East coast, 2 Gulf of Mexico and one West coast with two Great Lake sites. The data for nine of these sites were obtained from ship observation data and the tenth (in California) from wave hindcasts. The data include monthly summaries of wave height, period and direction. Additionally, monthly cumulative percentage wave height distributions are presented. Garcia, A.W. and F.C. Perry (1976) "Beach Nourishment Techniques, Report 2: A Means of Predicting Littoral Sediment Transport Seaward of the Breaker Zone", Technical Report H-76-13, Hydraulics Laboratory, U.S. Army Waterways Experiment Station, 60 pages. The purpose of this study is to provide methods of evaluating the effectiveness of offshore placement of sand for beach nourishment. Ideally sand placed offshore would be transported by natural forces and eventually be 111



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*CU • -'{ //i Kings Bay Site .. -4:.= St. Marys Entrance 0 10 20 .I I ...' Scale (km) Figure 28. Location Map of Kings Bay Site Relative to Cumberland Island National Seashore. 72



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dwelling invertebrate sediments, or water quality in the vicinity of the borrow pits. Spadoni, R.H. and T.J. Campbell (1981) "Environmental Monitoring for the Delray Beach Maintenance Nourishment Project", Arthur V. Strock and Associates, Inc., Delray Beach, Florida. The 1978 Beach nourishment program at Delray Beach, Florida comprised the placement of 700,000 cubic yards of beach fill along approximately 1.7 miles of shoreline. This report presents the result of a monitoring program to document any adverse environmental effects of this project. Of specific concern is a coral reef located 4,000 ft offshore and parallel to the general orientation of the shoreline. The borrow area was in excess of 6,000 ft long located inside the coral reef and at one location was within 400 ft of the reef. The major concern was the possibility of sedimentation due to the dredging operation damaging the reef. The monitoring program extended from November, 1977 to April, 1979, a period of 18 months. The dredging operations had been conducted from January 30, 1978 to May 25, 1978. Field techniques included: sedimentation rates as determined by collection in jars, repeated photographs of the reef in selected areas, collection and later analysis of water samples, and wave and current observations. Findings of this monitoring project included: (1) a strong correlation of sedimentation rate with wave height, (2) with one exception no increase in sedimentation rate over the reef area monitored during the dredging period as compared to the preand post-dredging period, (3) the turbidity of all water samples collected over the reef during dredging operations were less than 1.0 NTU. On one occasion during a storm prior to dredging the turbidity exceeded 1.0 NTU, (4) turbidity near the disposal area exceeded 50 JTU the State of Florida standards; however these high values of turbidity were localized, (5) the only reef damage was a one acre area and was due to an anchor inadvertently dropped on the reef during demobilization. Within one year after the damage, the coral reef has begun to repopulate with native benthic invertebrates. 101



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Pullen, E.J. and R.M. Yancey (1979) "Beach Nourishment: Its Effect on Coastal Ecology", Proceedings 23rd Annual Meeting of the Florida Shore and Beach Preservation Association, Florida Sea Grant Marine Advisory Program, p. 5164. The beach and nearshore environment is divided into three zones: beach, surf and offshore. These zone are defined and the animals inhabiting them described. The results of CERC's research in each of these three zones are presented. The three major physical effects of beach nourishment are: covering of existing beach sediments, modifications of the beach interface and increasing water turbidity. Nearshore benthic communities are well adapted to substantial changes due to the dynamic nature of this area; thus these communities recover well following a nourishment project. However, offshore communities, especially those requiring low turbidity are less able to adapt. Motile animals appeared to fare well by departing the area during undesirable conditions, such as high turbidity. Corals, especially the hard corals, are sensitive and care should be taken to avoid direct covering or deposition by suspended sediment. Prolonged periods of high turbidity are to be avoided. It was noted that in borrow areas of low transport activity, the borrow pits may tend to fill with fine sediments; thus where possible it is preferable to utilize sands from dynamic transport areas and/or to minimize cut depths. The importance of using high quality material was noted. A turtle egg relocation program should be developed if nourishment is carried out during the nesting season in an area frequented by nesting turtles. It is concluded that water quality changes related to beach nourishment are usually of short duration due to energetic mixing in the nearshore environment. Pullen, E.J., R.M. Yancey, P.L. Knutson and A.K. Hurme (1980) "An Annotated Bibliography of CERC Coastal Ecology Research", U.S. Army Corps of Engineers Coastal Engineering Research Center, Miscellaneous Report No. 80-5. A total of 61 references is listed with a brief review of the contents of each. Of the 61 references, 12 relate directly or indirectly to the subject of the present report. 99



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PART V CASE STUDIES AS EXAMPLES 57 CASE STUDY I -PERDIDO KEY 58 Introduction Background 60 Rationale for Selected Plan 60 Monitoring Plan 64 Physical Monitoring 64 Performance Related Monitoring Needs 64 Profile and Planform Evolution 64 Wave Measurements 64 Wind and Precipitation Measurements 64 Vegetation Response 65 Public Interest/Education Monitoring Needs 65 Management Monitoring Needs 65 Biological Monitoring 65 Benthic Community Studies 66 Vegetation Analysis 66 Beach Mouse Population 66 CASE STUDY II -OREGON INLET 66 Introduction 66 Historic Inlet Behavior 66 Present Situation 68 The National Park System and State of North Carolina Position on Oregon Inlet 68 CASE STUDY III -CUMBERLAND SOUND 71 Introduction 71 Concerns of the National Park Service 71 Monitoring Program 71 Coastal Assessment Component 73 Cumberland Sound Physical Processes Component 73 Ecological Research 73 PART VI LEGAL AND REGULATORY ASPECTS OF DREDGING 74 Introduction 75 THE FEDERAL PROGRAM 75 Rivers and Harbors Act of 1899 75 National Environmental Policy Act of 1969 (NEPA) 75 Federal Water Pollution Control Act Amendments of 1972 (FWPCA) 76 Marine Protection, Research and Sanctuaries Act of 1972 76 Coastal Zone Management Act of 1972 (CZMA) 76 iv



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PART VIII SUMMARY AND CONCLUSIONS



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Generic Problem I -Inlet Dredging Problem -Channel deepening of a natural inlet is being considered. The sand dredged will be disposed of offshore. The Natural System The Altered System Figure 1. Generic Problem 1 -Inlet Dredging. Discussion of Natural System -In the natural system, waves arriving at an angle to the shoreline cause a transport of sand along the shoreline. The transport rate is Q. Upon reaching this inlet, the transport occurs over a broad flat sand body termed an ebb tidal shoal. The Altered System -Since the shallow depths over the ebb tidal shoal are not suitable for navigation, a channel is incised through the shoal by dredging, thus severing the natural transport pathway or "bridge". The natural response of the system is to rebuild the sand bridge through deposition in the channel. This will require periodic dredging to maintain the channel depth. Physical Effects -The ultimate physical effects that can be anticipated include erosion of the downdrift shoreline at a rate Q. In cases where transport occurs in both directions, both shorelines may erode. Environmental Effects -The erosion will degrade the natural characteristics of the beach and may destroy valuable habitat. Over long periods, the dunes 4



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no dead animals and they concluded that the affected areas recovered in less than two weeks. The sand used in this nourishment project was quite compatible with the native sand. A second project of similar quantity (904,000 m3) at Fort Macon, NC, was monitored by Reilly and Bellis (1978, 1983); however the sand was taken from dredged harbor sediments and was not compatible in size characteristics. Additionally the sediment was from a chemically reducing environment. Monitoring of this latter project indicated that the E. Talpoida populations were nonexistent in the project area during material placement but recolonized rapidly several months later during the spring recruitment period. A delay of one month during the recruitment period was evident. The summer after the commencement of nourishment (the preceding December), the animal densities were the same on the nourished and control beaches. However, there were significant differences in the size classes with the nourishment containing exclusively juveniles. The investigators concluded that the adult mole crabs in the vicinity of the nourished site were killed by turbidity and that the juvenile animals had repopulated the area from the adjacent beaches. Nelson (1985) has suggested that the liberated hydrogen sulfide in the nourished sediments may also have contributed to the mortality of adult animals. In summary of the impact of beach nourishment on E. Talpoida, it is concluded that these animals are very mobile and are able to vacate an area unsuitable for their physiology. Moreover, with the return of favorable conditions, they rapidly recolonize the area. If the material placed is compatible with that originally present on the beach, effects are of quite short duration. If poor quality sediment is used, recovery is slower, but still relatively rapid, probably due to the high motility of these animals and the longshore currents on the beachface. Donax (Coquina Clams) This genus of bivalves has two species that have been reported to be present in the Southeast Region. The documented range of Donax Variabilis is from Virginia Beach, VA to Mississippi. Also Donax Texasianus has been found in the Florida panhandle. Most Donax Variabilis migrate up and down the beach with the tide, presumably to be in the active swash zone where the high velocities ensure ample 49



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jetties can result in erosion of the updrift shoreline. If all of the downdrift transport passes through the updrift jetty, the updrift shoreline will erode at the rate of the updrift transport component. For the same scenario, the downdrift shoreline will erode at the rate of the downdrift transport component. From the preceding discussion, there is a clear need at modified entrances to attempt to reinstate the sediment transport that has been interrupted by the modifications. Unfortunately our "track record" in this regard has been much less than exemplary. In many cases sand removed by hopper dredges for channel maintenance has been transported offshore and deposited in water too deep to benefit the nearshore system. Data available for the East coast of Florida shows that within the last 5 decades or so, more than 50 million cubic meters of beach quality sand has been disposed of in excessive water depths. Today's market value of this sand is on the order of $250 million to $500 million. Sand deposits as a result of channel modifications and construction should be regarded as a valuable natural resource and not as a material to be disposed of in the least costly manner. Returning to Florida East coast examples, it can be shown that this 50 million cubic meters is sufficient to advance the entire 600 km East coast shoreline seaward by 8 m. Dean (1988) has estimated that 80% of the erosion along Florida's East coast is due to poor sand management practices, which continue today albeit to a lesser degree. In general, there are two approaches to maintaining longshore sediment transport. One approach is to allow the sediment to accumulate either updrift of the updrift jetty or in the channel and to bypass periodically, relatively large quantities of sand. Such bypassing could be carried out annually or biennially and could involve from hundreds of thousands of cubic meters to 2 million cubic meters in each bypassing event. This mode of bypassing is accomplished by a rather large dredge brought to the area periodically or when needed. The alternative approach is a "dedicated" bypass facility which transfers sand with much greater frequency more or less as it becomes available. The downdrift consequences of these two modes of bypassing differ markedly. In the "batch mode" of bypassing, the downdrift shoreline will widen and narrow as the replenishment and erosional sand waves move downdrift. This variation in beach width may not be favorable for intertidal or nearshore fauna. Clearly in cases where nearshore rock or reef is present and considered a valuable habitat, 40



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TABLE OF CONTENTS PART I INTRODUCTION AND GENERAL TYPES OF DREDGING AND COASTAL PROBLEMS ENCOUNTERED BY THE NATIONAL PARK SERVICE 1 Introduction 2 Generic Problems 3 Generic Problem 1 -Inlet Dredging 4 Problem 4 Discussion of Natural System 4 The Altered System 4 Physical Effects 4 Environmental Effects 4 Solution 5 Generic Problem 2 -Channel Stabilization through Jetty Construction 6 Problem 6 Discussion of Natural System 6 The Altered System 6 Physical Effects Environmental Effects 7 Solution 7 Generic Problem 3 -Coastal Armoring 8 Situation 8 Discussion of Natural System 8 The Altered System 8 Physical Effects 8 Environmental Effects 8 Solution 8 Generic Problem 4 -Beach Nourishment Using Sand Dredged from Offshore Dredging 10 Problem 10 Discussion of Natural System 10 The Altered System 10 Physical Effects 10 Environmental Effects 10 Solution 11 PART II THE NATURAL BEACH SYSTEM Geology of Barrier Islands 12 Introduction 13 Origin of Barrier Islands 13 Sea Level Rise and Barrier Islands 16 The Importance of Natural Processes 16 ii



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Two predicted measures of sediment quality, presented for the projects, are the fill factor and the renourishment factor. Nersesian, G.K. (1977) "Beach Fill Design and Placement at Rockaway Beach, New York Using Offshore Ocean Borrow Sources", ASCE Specialty Conference on Coastal Sediments '77, pp. 228-247. Three separate contracts were let to place sand on Rockaway Beach, a popular recreational beach approximately 10 km in length. A total of 5.7 million cubic meters was obtained from two borrow areas and placed over a period of 3 years. The first contract utilized a 24 inch cutter head suction dredge in combination with four scow barges into which the dredge material was placed. The barges were towed approximately eight miles to the protected waters to a rehandling station in Jamaica Bay. The material was then pumped out of the barges across Rockaway Beach to the shoreline. The second project used the hopper dredge "Ezra Sensibar" which has a maximum capacity of 12,100 m3.The loaded dredge was towed to a location approximately 1,200 m offshore where a direct pumpout operation was carried out. The third phase was carried out in the same manner as the second phase. Project evaluation was still in progress at the time of finalization of the paper. Oertel, G.F., C.F. Chamberlain, M. Larsen and W. Schaaf (1977) "Monitoring the Tybee Beach Nourishment Project", ASCE Specialty Conference on Coastal Sediment '77, pp. 1049-1056. The evolution of the Tybee Island beach nourishment project (1975) is presented. Monitoring methods included staff and horizon leveling procedures and a special time lapse video camera mounted at a vantage point on a tower. The evolution was documented as a 40% decrease in the shoreline volume within 6 months with much of the sand loss migrating over and through a low permeable terminal structure built at the north end of the project. Wind transport was also identified as an effective agent in causing evolution of the project. 105



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FIgure 6. Waves Arriving Obliquely to Shoreline Cause Longshore Current and Longshore Sediment Transport Primarily Within Surf Zone. seaward. At most locations, both positive and negative transport occur during a year. The difference between the positive and negative annual transport is termed the "net" annual transport and is either positive or negative. In some applications, it is the "gross" transport which is the sum of the positive and negative components (irrespective of sign) that is of importance. An example will serve to illustrate this convention. A published estimate (Walton and Dean, 1973) of positive and negative transport rates slightly south of Cumberland Island, GA is 3 Q = 370,000 m /yr + 3 (1) 18 Figure 6. Waves Arriving Obliquely to Shoreline Cause Longshore Current and Longshore Sediment Transport Primarily Within Surf Zone. seaward. At most locations, both positive and negative transport occur during a year. The difference between the positive and negative annual transport is termed the "net" annual transport and is either positive or negative. In some applications, it is the "gross" transport which is the sum of the positive and negative components (irrespective of sign) that is of importance. An example will serve to illustrate this convention. A published estimate (Walton and Dean, 1973) of positive and negative transport rates slightly south of Cumberland Island, GA is Q+ = 370,000 m3/yr Q_ = -170,000 m3/yr 18



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10 -I I I I ". ..".1 1 1 II I II 0 No Jetty "z i One Jetty E 1o9 __ 0 Two Jetties .__ z E Oi08 wU Corresponds to 2.0 Vmax = m/s to Data ^• QV ^^,,.,^.,.,.,y. ................................ ........ 10 I 10 102 103 104 10 5 10 6 MINIMUM CROSS-SECTIONAL FLOW AREA (m2) Figure 10. Relationship between Spring Range Tidal Prism and Minimum Cross-Section, Compared with Maximum Inlet Velocity of 1m/s. Modified from O'Brien (1931). 25



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TABLE 2 FIELD TESTS CARRIED OUT TO EVALUATE SHOREWARD SEDIMENT TRANSPORT FROM OFFSHORE PLACEMENT Location Water Depth Documented (m) Movement Toward Shore Santa Barbara, CA 6 No Long Beach, NJ 11 No Atlantic City, NJ 4.5 -8 No New River Inlet, NC 2 -4 Yes placement in water depths of 2-4 m was definitively concluded to be a success in terms of shoreward sediment transport. Based on results such as summarized in Table 2, the state of Florida has considered that sediment placed in water depths greater than 4 m is relatively ineffective in nourishing the shoreline. There can be undesirable effects of placing sand in the nearshore region. In particular, if the sand deposited offshore is not at a uniform elevation in the longshore direction, local sheltering can occur causing sand to accumulate on the shoreline behind those segments with the greatest elevations and erosion of adjacent areas. Thus if sand is to be placed offshore, it should be placed in an underwater berm of nearly uniform elevation with a gradual decrease in elevation to the ambient profile at the ends of the berm. Need for Profile Contouring Sand placed in a beach nourishment project should be configured to allow natural processes to complete the shaping to natural profile characteristics with the elements described previously. The underwater portion of the profile does not present a problem as the waves will carry out the contouring. However, the 44



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of the placed material, usually during the more energetic wave conditions. The relative merits of this method of beach nourishment are discussed. U.S. Army Corps of Engineers (1967) "Hopper Dredge Improvement Program: Item X -Pumpout Facilities, Studies on Use of Hopper Dredges For Beach Nourishment", Philadelphia District, 59 pages. A description is presented of a field trial to evaluate the capability of hopper dredges to pump sand to the beach. Two hopper dredges were selected to carry out the evaluation. With the first test (Dredge: COMBER) a total of 2,000 cubic yards was pumped a distance of 6,600 ft to a dredge disposal area. For the second test, the dredge GOETHALS was converted to direct pumpout. The GOETHALS had a capacity of 5,600 cubic yards. The tests were conducted at Sea Girt, New Jersey and lasted a total of about two months. On an average working day, the dredge pumped approximately 30,000 cubic yards at a cost of $1.30 per cubic yard. Based on experience gained in the project, recommendations for improvement to the GOETHALS were developed. 115



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Dredging to Increase Navigation Channel Depths -Earlier sections of this report have discussed the "sand sharing" system composed of the ebb tidal shoal and the adjacent shorelines. A useful basis for consideration purposes is that' a given system in its natural condition is in equilibrium and that if changes are made to the system, it will respond to reestablish equilibrium. Thus when sand is removed from an ebb tidal shoal, sand will flow toward the deepened area and a portion of this deficit will be felt at the updrift shoreline and a portion at the downdrift shoreline. If the longshore sediment transport were nearly unidirectional, one can simplify considerations as follows. The longshore sediment transport tends to rebuild the ebb tidal shoal which functions as a "sand bridge" across which this transport occurs. With the sand bridge cut (shoal deepened), the longshore sediment transport will deposit in the cut to reestablish the bridge. The volume of material deposited appears as a deficit to the downdrift shoreline and results in a volumetrically equal amount of erosion there. The obvious appropriate approach to placement of beach quality sediment removed from navigation channels is, through surveys of the adjacent shorelines, to develop a basis for apportioning the high quality dredged sand on these shorelines. Environmental Effects of Beach Nourishment Projects Primary potential environmental effects of beach nourishment relate to: quality of sediment, impact of burial by the placed sediment and the more subtle effects above water such as altering the natural dune system. The actual impact of each of these is species dependent and to some extent locality dependent. Sediment Quality -In this section sediment quality will be considered on a relative basis and will be quantified in terms of grain size and color. As an ideal measure of sediment quality, the grain size distribution of the material to be placed should match the native grain size distribution. As a more realistic measure of good sediment quality, the general mean grain size of the material to be placed should not be much smaller than that of the native material and the percentage of the silt and clay fraction (the fines) should be relatively small. 47



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The Florida Program Florida submitted its proposed Coastal Management Program to the U.S. Office of Coastal Zone Management in February 1981 and the program was approved in August 1981. Permits for dredging and filling in sovereign lands are regulated by statute. This program is under the responsibility of the Department of Florida Environmental Regulation with participation by the Department of Natural Resources. The Alabama Program In 1976, Alabama established the Alabama Coastal Area Act which provides the legal framework for the coastal zone program. The Coastal Area Board is the responsible agency. The Coastal Area Board is responsible for issuing dredge and dredge and fill material disposal permits. The Mississippi Program The Mississippi Coastal Wetlands Protection Law of 1973 formalizes public policy as "the preservation of the natural state of the coastal wetlands..., except where an alteration of specific wetlands would serve a higher public interest." The Bureau of Marine Resources under the Mississippi Department of Wildlife Conservation administers the program and is responsible for permitting activities in the wetlands including dredging and filling. 78