• TABLE OF CONTENTS
HIDE
 Front Matter
 Report documentation page
 Title Page
 Acknowledgement
 Table of Contents
 List of Figures
 List of Tables
 Introduction
 Literature review
 Laboratory constraints and modeling...
 Laboratory experiments
 Laboratory ebb tidal shoal definition...
 Experimental results
 Comparisons with prototype...
 Evaluation of ebb tidal shoal...
 Summary and conclusions
 Appendix A: Cross-shore profiles...
 Appendix B: Cross-shore profiles...
 Appendix C: Bathymetry surveys...
 Appendix D: Bathymetry surveys...
 Appendix E: Changes in bathymetry...
 Appendix F: Accretion and erosion...
 Appendix G: Cross-shore profiles...
 Appendix H: Cross-shore profiles...
 Appendix I: Cross-shore profiles...
 References






Group Title: Technical report – University of Florida. Coastal and Oceanographic Engineering Program ; 117
Title: Impacts on the inlet-beach system of ebb tidal shoal mining
CITATION PAGE IMAGE ZOOMABLE
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00075469/00001
 Material Information
Title: Impacts on the inlet-beach system of ebb tidal shoal mining
Series Title: UFLCOEL-TR
Physical Description: vii, 102 leaves : ill. ; 28 cm.
Language: English
Creator: Trudnak, Michael E., 1973-
Wang, Hsiang
University of Florida -- Coastal and Oceanographic Engineering Dept
Coastal Engineering Research Center (U.S. Army Engineer Waterways Experiment Station)
Publisher: Coastal & Oceanographic Engineering Dept., University of Florida
Place of Publication: Gainesville Fla
Publication Date: 1997
 Subjects
Subject: Banks (Oceanography) -- Florida   ( lcsh )
Beach nourishment -- Florida   ( lcsh )
Inlets -- Florida   ( lcsh )
Shore protection -- Florida   ( lcsh )
Coastal and Oceanographic Engineering thesis, M.S   ( lcsh )
Dissertations, Academic -- Coastal and Oceanographic Engineering -- UF   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Bibliography: Includes bibliographical references (leaves 101-102).
Statement of Responsibility: by Michael E. Trudnak, Hsiang Wang.
General Note: Final report.
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.
 Record Information
Bibliographic ID: UF00075469
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved, Board of Trustees of the University of Florida
Resource Identifier: oclc - 40802470

Table of Contents
    Front Matter
        Front Matter 1
        Front Matter 2
    Report documentation page
        Unnumbered ( 3 )
    Title Page
        Title Page
    Acknowledgement
        Acknowledgement
    Table of Contents
        Table of Contents 1
        Table of Contents 2
    List of Figures
        List of Figures 1
        List of Figures 2
    List of Tables
        List of Tables
    Introduction
        Page 1
        Page 2
        Page 3
        Page 4
    Literature review
        Page 5
        Page 6
    Laboratory constraints and modeling laws
        Page 7
        Page 8
        Page 9
        Page 10
        Page 11
        Page 12
        Page 13
        Page 14
        Page 15
        Page 16
        Page 17
    Laboratory experiments
        Page 18
        Page 19
        Page 20
        Page 21
        Page 22
    Laboratory ebb tidal shoal definition and calculations
        Page 23
        Page 24
        Page 25
    Experimental results
        Page 26
        Page 27
        Page 28
        Page 29
        Page 30
        Page 31
        Page 32
        Page 33
        Page 34
        Page 35
        Page 36
        Page 37
        Page 38
    Comparisons with prototype data
        Page 39
        Page 40
        Page 41
        Page 42
        Page 43
        Page 44
        Page 45
        Page 46
        Page 47
        Page 48
        Page 49
        Page 50
        Page 51
        Page 52
        Page 53
    Evaluation of ebb tidal shoal mining
        Page 54
        Page 55
        Page 56
        Page 57
    Summary and conclusions
        Page 58
        Page 59
        Page 60
    Appendix A: Cross-shore profiles for EC1 after 3200 MIN
        Page 61
        Page 62
        Page 63
        Page 64
        Page 65
        Page 66
    Appendix B: Cross-shore profiles for EC2 after 3200 MIN
        Page 67
        Page 68
        Page 69
        Page 70
        Page 71
    Appendix C: Bathymetry surveys for EC1
        Page 72
        Page 73
        Page 74
        Page 75
        Page 76
    Appendix D: Bathymetry surveys for EC2
        Page 77
        Page 78
        Page 79
        Page 80
        Page 81
    Appendix E: Changes in bathymetry for EC1
        Page 82
        Page 83
        Page 84
        Page 85
    Appendix F: Accretion and erosion patterns for EC2
        Page 86
        Page 87
        Page 88
        Page 89
    Appendix G: Cross-shore profiles for Sebastian Inlet ebb tidal shoal
        Page 90
        Page 91
        Page 92
        Page 93
    Appendix H: Cross-shore profiles for Jupiter Inlet ebb tidal shoal
        Page 94
        Page 94(sic)
        Page 95
        Page 96
        Page 97
    Appendix I: Cross-shore profiles for Boca Raton Inlet ebb tidal shoal
        Page 98
        Page 99
        Page 100
        Page 101
    References
        Page 101(sic)
        Page 102
Full Text



UFL/COEL-TR/117


IMPACTS ON THE INLET-BEACH SYSTEM OF
EBB TIDAL SHOAL MINING


Final Report


by


Michael E. Trudnak
Hsiang Wang


December, 1997



Sponsored by

Coastal Engineering Research Center
U.S.A.E. Waterways Experiment Station
Engineering Application Unit (CEWES-CD-SE)
Contract No. DACW39-95-K-0084



COASTAL & OCEANOLORAPHC ENINEERIN DEPATME T
University of Florida Gainesville, Florida 32611








UFL/COEL-TR/117


IMPACTS ON THE INLET-BEACH SYSTEM OF
EBB TIDAL SHOAL MINING




Final Report



by


Michael E. Trudnak
Hsiang Wang


December, 1997



Sponsored by

Coastal Engineering Research Center
U.S.A.E. Waterways Experiment Station
Engineering Application Unit (CEWES-CD-SE)
Contract No. DACW39-95-K-0084





REPORT DOCUMENTATION PAGE
1. report lo. 2. 3. Recipient's AccesLioea o.


4. Title and Subtitle 5. Report Date
IMPACTS ON THE INLET-BEACH SYSTEM OF EBB TIDAL December, 1997
SHOAL MINING 6.
FINAL REPORT
7. Author(s) S. Performing Organisation Report No.
Michael E. Trudnak UFL/COEL-TR-117
Hsiang Wang
9. Performing Organitioa Name and Address 10. Project/Task/Work Unit No.
Department of Coastal and Oceanographic Engineering
University of Florida 11. contract or crant o.
336 Weil Hall, P.O. Box 116590 DACW39-95-K-0084
Gainesville, FL 32611-6590 13. T .p of port
12. Sponsoring Organization Name and Addres
Coastal Engineering Research Center Final Report
U.S.A.E. Waterways Experiment Station
Engineering Application Unit (CEWES-CD-SE)
Vicksburg, MS 39180-6199 14.
15. Supplemntary Notes



16. Abstract


The ebb tidal shoal is an attractive source of compatible sand for beach renourishment.
However, ebb shoal mining has not become common practice, for little is known about the effects
of removing the ebb tidal shoal. Physical movable bed modeling was performed in order to determine
the impacts on the inlet-beach system of removing a portion of the ebb-tidal shoal. The main focuses
were on the downdrift erosion and the regeneration process of the borrow area. Two models were
run, one with and one without removal of the ebb tidal shoal, using an idealized inlet of rectangular
cross-section representing a typical mid-sized Florida east coast inlet. The laboratory results showed
that utilizing ebb tidal shoal mining for downdrift nourishment is potentially feasible from the point
of view of renourishment and borrow area regeneration requirements. Methods were proposed to
evaluate the feasibility and potential of ebb shoal mining utilizing laboratory data. The laboratory ebb
tidal shoal characteristics were compared with the characteristics of three small to medium sized
Florida east coast inlets. The results demonstrate that ebb tidal shoals similar to those occurring in
nature can be duplicated in the laboratory and showed the potential of parameterizing ebb shoals, both
in the laboratory and in nature.



17. Origiator's Key Words 1. Availability Statement
Ebb-tidal shoal
Inlet
Inlet mining
Mobile bed
Sediment transport
19. U. S. Security Claseif. of the Report 20. U. S. Security Clasitf. of This Plag 21. No. of Pages 22. Price
Unclassified Unclassified 109









UFL/COEL-TR/117


IMPACTS ON THE INLET-BEACH SYSTEM OF

EBB TIDAL SHOAL MINING



FINAL REPORT



by



Michael E. Trudnak

Hsiang Wang


Sponsored by



Coastal Engineering Research Center

U.S.A.E. Waterways Experiment Station

Engineering Application Unit (CEWES-CD-SE)

Contract No. DACW39-95-K-0084


December, 1997









ACKNOWLEDGEMENTS


The authors gratefully acknowledge support of this study by the Coastal Engineering Research

Center, U.S.A.E. Waterways Experiment Station, Engineering Application Unit, Vicksburg, MS,

Contract Number DACW39-95-K-0084. Mr. Jack Davis is the project monitor. His assistance and

guidance throughout the project is sincerely acknowledged.
















TABLE OF CONTENTS


ACKNOWLEDGEMENTS .....................................................................................................

LIST O F FIG U RE S .................................................................................................................

LIST O F TA B LE S ....................................................................................................................



CHAPTERS

1 INTRODUCTION ..........................................................................................

2 LITERATURE REVIEW .............................................................................

3 LABORATORY CONSTRAINTS AND MODELING LAWS ......................

3.1 Considerations and Constraints ............................................
3.2 Scaling Laws ....................................................................

4 LABORATORY EXPERIMENTS .......................................... ................

4.1 Design of Initial Inlet-Beach Model ..........................................
4.2 Test Conditions .......................................................................
4.3 Design of Ebb Shoal Mining ................................... ................
4.4 Test Procedures .............................................................

5 LABORATORY EBB TIDAL SHOAL DEFINITION AND
CALCULATIONS ........................................................ ...............................

5.1 Defining the Ebb Tidal Shoal in the Laboratory .............................
5.2 Ebb Tidal Shoal Volume Calculations ...........................................

6 EXPERIMENTAL RESULTS .....................................................................

6.1 Ebb Tidal Shoal Growth ...................................................................
6.2 Beach Erosion ...........................................................................
6.3 Inlet Channel Shoaling ............................................. ................
6.4 Accumulation of Sand at Downdrift Boundary and Inside Inlet.....












7 COMPARISONS WITH PROTOTYPE DATA ..........................................

7.1 Volumetric comparisons ........................................ ................
7.2 Ebb Tidal Shoal Location ...................................... ...............
7.3 Geometric Shape ......................................................................

8 EVALUATION OF EBB TIDAL SHOAL MINING.........................................

9 SUMMARY AND CONCLUSIONS ................................... ..............


APPENDICES

A

B

C

D

E

F

G

H

I

REFERENCES


CROSS-SHORE PROFILES FOR EC ......................................... .............

CROSS-SHORE PROFILES FOR EC2 ........................................ ...........

BATHYMETRY SURVEY FOR EC ........................................... .............

BATHYMETRY SURVEY FOR EC2 ...................................... ..........

CHANGES IN BATHYMETRY FOR EC 1 ............................................

CHANGES IN BATHYMETRY FOR EC1 .....................................

CROSS-SHORE PROFILES FOR SEBASTIAN INLET .............................

CROSS-SHORE PROFILES FOR JUPITER INLET ..................................

CROSS-SHORE PROFILES FOR BOCA RATON INLET .........................

................................................................................. ........................................















LIST OF FIGURES


1. Tidal Prism-Ebb Shoal Volume Relationship for Florida's East Coast Inlets ....... ... 9
(after Marino, 1986).

2. Location Map of Nineteen Inlets Along Florida's East Coast ............................................ 10

3. Jonson's Flow Regime Chart. ................................................................... 13

4. Sediment Transport Modes Diagram (after Shibayama and Horikawa, 1980) ............. 13

5. Two Different Beach Profile Regions Scheme. ................................................................. 16

6. Schematic Setup for the Movable Bed Inlet Model. ........................................................ 19

7. Current M easurements at Sebastian Inlet. ........................................................................ 21

8. Changes in Bathymetry in EC1 after 3200 min. ................................................................ 24

9. Bathymetry Contours for EC1 after 0 min, 1600 min, and 3200 min ........................... 27

10. Bathymetry Contours for EC2 after 0 min, 1600 min, and 3200 min .......................... 28

11. Changes in Bathymetry for ECI after 800 min, 1600 min, and 3200 min. .................. 29

12. Changes in Bathymetry for EC2 after 800 min, 1600 min, and 3200 min. ................... 30

13. Volume of Ebb Tidal Shoal Versus Time for ECI and EC2 ............................................ 32

14. Rate of Ebb Tidal Shoal Growth Versus Time for EC 1 and EC2 ................................... 32

15. Volume of Downdrift Erosion Versus Time for EC and EC2 ................................... .. 33

16 Rate ofDowndrift Erosion Versus Time for EC1 and EC2 .......................................... 33

17. Volume of Accumulation at Downdrift Boundary Versus Time for EC 1 and EC2 .......... 36

18 Rate of Accumulation at Downdrift Boundary Versus Time for EC 1 and EC2 ........... 36

19. Volume of Accumulation Inside Inlet Versus Time for EC1 and EC2 ............................ 37















20. Rate of Accumulation Inside Inlet Versus Time for EC 1 and EC2 ................................. 37

21. Sebastian Inlet Bathymetry Surveyed in 1989. ............................................. ........... 40

22. EC Ebb Tidal Shoal Bathymetry After 3200 min. ........................................ .......... 40

23. Jupiter Inlet Bathymetry (after Coastal Planning & Engineering, 1989) .......................... 41

24. Boca Raton Inlet and Offshore Bathymetry Chart
(after Coastal Planning & Engineering, 1991). ............................................. ........... 42

25. Boca Raton Beach Topographic and Offshore Bathymetry Survey
(after Coastal Planning & Engineering, 1991). .............................................. ........... 43

26. Sebastian Inlet Ebb Tidal Shoal Above Uninfluenced Downdrift Profile ....................... 46

27. EC1 Ebb Tidal Shoal Above Initial Profile After 3200 min .......................................... 46

28. Jupiter Inlet Ebb Shoal Above Uninfluenced Downdrift Profile ....................................... 47

29. Boca Raton Inlet Ebb Tidal Shoal Above Uninfluenced Downdrift Profile ...................... 48

30. Baseline Definition for Determining the Radial Distance and Bearing Angle ................... 49

31. Geometric Shape of Sebastian Inlet Ebb Tidal Shoal. ................................... ......... 51

32. Geometric Shape of the Laboratory Inlet Ebb Tidal Shoal ...................................... 51

33. Geometric Shape of Jupiter Inlet Ebb Tidal Shoal. ..................................... ........... 52

34. Geometric Shape of Boca Raton Inlet Ebb Tidal Shoal. ................................... ......... 52

35. Idealized Ebb Tidal Shoals for Sebastian, Jupiter, Boca Raton,
and Laboratory Inlets. .................................................................................................. 53
















LIST OF TABLES


1. Entrances Where Ebb Delta Mining has been Performed ........................................... 3

2. Benefits, Adverse Impacts, and Monitoring at Entrances as Given in Table 1.................. 4

3. Summary of Fall Velocity Distorted Models. .................................................................. 15

4. M modified M modeling Law ....................................................................................................... 17

5. Inlet Model Experimental Conditions. ......................................................................... 20

6. Volume of Ebb Shoal and Rate of Ebb Shoal Growth for EC 1 and EC2 ......................... 34

7. Volume and Rate of Downdrift Erosion for EC1 and EC2 ............................................ 34

8. Volume and Rate of Accumulation at Downdrift Boundary for EC and EC2 ............... 38

9. Volume and Rate of Accumulation Inside Inlet for EC and EC2 ...................................... 38

10. Calculated Ebb Tidal Shoal Volumes and Locations for Sebastian, Jupiter,
Boca Raton, and Laboratory Inlets. ..................................................................................... 49

11. Geometrical Parameters for Sebastian, Jupiter, Boca Raton, and Laboratory Inlets ........... 50
















CHAPTER 1
INTRODUCTION


As offshore sand sources with reasonable reclaiming costs for beach renourishment

diminish, other methods of supplying sand must be utilized. In Florida, severe erosion occurs mainly

along the downdrift side of tidal inlets. Thus, mining an inlet's ebb tidal shoal is becoming an

attractive alternative for renourishing adjacent beaches. The ebb tidal shoal is created from the

combined deposition of sand eroded from adjacent beaches and the inlet channel together with

longshore sediment transport that is entrained by the ebb tidal currents. Because sand stored in the

ebb tidal shoal theoretically is deprived from the downdrift beach, it is only natural to return the sand

to the beach. In addition, owing to the more energetic flow environment over the ebb shoal, the

material stored there is usually of good quality compatible to the downdrift beach. However, such

practice is not prevalent as there is general reluctance to dredge the ebb tidal shoal. This is simply

because the formation of the ebb tidal shoal is a natural process and little is known about the impact

on the inlet-beach system due to such a man made disturbance. Mehta et al. (1996) studied the

limited cases along the east coast of the United States where a portion of the ebb tidal shoal has been

removed. Their results are summarized in Tables 1 and 2. It can be seen that presently the

knowledge on ebb shoal dynamics as well as the knowledge of its effects on adjacent shorelines is

poor and post-dredging monitoring has not been extensively performed.

An ebb tidal shoal is formed due to the accumulation of sediment outside the inlet entrance

under the combined influence of waves and currents. It can be expected to grow to a volume in

equilibrium with the prevailing tidal prism and wave climate (Walton and Adams, 1976). Once the












ebb shoal attains this equilibrium size, the shoal acts as a sand "bridge" to allow for natural

bypassing of sediment across the mouth of the inlet (Dean, 1988). Dredging a large portion of the

ebb tidal shoal can create a sediment sink, decrease natural bypassing, alter inlet hydrodynamics, and

expose previously sheltered parts of the downdrift shoreline to increased wave energy (Walther and

Douglas, 1993) resulting in more downdrift erosion. These potential detrimental effects have

aroused controversies concerning removal of the ebb tidal shoal as a sand source for downdrift

renourishment.

The goal of this study is to examine the effects on the inlet-beach system due to ebb tidal

shoal mining through physical models, focusing primarily on the effects on downdrift erosion and the

regeneration process of the ebb tidal shoal. Physical modeling is a useful tool to achieve these goals,

for the models can be executed at accelerated time scales and the results can be used to determine the

effects of ebb shoal removal including shoreline changes and ebb shoal borrow area response.

However, the reliability of the results could be severely affected by the physical size limitations in the

laboratory and techniques used to extrapolate the results to prototype scale. Therefore, in the design

of laboratory experiments of this kind one must first address the scaling problem and have a

reasonable understanding of the limitations and the validity of the test results.

The modeling laws used in this investigation for the inlet-beach model were determined in a

previous study by 2-D wave tank and 3-D wave basin experiments. The results were reported by

Wang et al. (1994). The feasibility and usefulness of physical models to study the ebb tidal shoal

evolution process and the corresponding shoreline changes for natural and improved inlets were

further demonstrated by Wang et al. (1995). The present study was performed with a more refined

scope to shed insight on ebb tidal shoal borrow area response and the effects on the inlet-beach

system due to dredging a portion of the ebb tidal shoal.


















Table 1: Entrances Where Ebb Delta Mining has been Performed (Mehta et al., 1996)


Entrance

John's Pass, FL

Longboat Pass, FL

New Pass, FL

Redfish Pass, FL


Boca Raton, FL

Jupiter FL

Nassau Sound, FL

Port Royal Sound, SC

Fripp, SC


Mining Site

Seaward side ofnorthem delta lobe

Seaward side of delta

Seaward side of delta

Center of delta from channel to seaward
extent of delta

Top of delta

Seaward side of delta

Outer, updrift and relict portion of delta

Seaward edge of delta

North delta of entrance


Year

1988

1993

1993

1981
1988

1985

1995

1994

1990

1974
1980


Volume (nm)

405,000

1,020,000

720,000

501,000
1,220,000

169,000

392,000

2,140,000

596,000

469,000
1,080,000


Placement Location

Updrift beach

Downdrift beach

Updrift beach

Downdrift beach


Downdrift beach

Downdrift beach

Updrift beach

Downdrift beach

Updrift beach


Method of Dredging

61 cm Cutterhead

Dustpan Dredge

Dustpan Dredge

53 cm Cutterhead


61 cm Cutterhead

76 cm Cutterhead

76 cm Cutterhead

76 cm Cutterhead

51-61 cm pipeline


Port Isidro, SC Landward edge of delta 1990 524,000 Beach eroded by entrance flood 76-84 cm pipeline
channel

Captain Sam's, SC Closed off migrating old entrance, creating a 1983 134,000 Operation meant to nourish Earthmovers and Bulldozers,
new entrance updrift ofthe old one (by tides and waves) downdrift beach 99,000 m' to close old channel

Hog. Sc Shore-attached delta 1990 288,000 Updrift beach hydraulic hoe at low tide

Townsend's, NJ Updrift entrance swash bar complex 1978 483,000 Updrift beach 76 or 91 cm Cutterhead
1983 626,000

Townsend's, NJ Downdrift entrance swash bar complex 1987 1,030,000 Surrounding beaches 76 or 91 cm Cutterhead

Great Egg, NJ Undetermined portion of delta 1992 to 1994 4,900,000 Downdrift beach Dustpan or Hopper dredges

Absecon, NJ Spit attached to north jetty 1986 76,500 Downdrift beach 76 or 91 cm Cutterhead




















Table 2: Benefits, Adverse Impacts, and Monitoring at Entrances as Given in Table 1 (Mehta et al., 1996)


Entrance Benefits Adverse Impacts Monitoring

John's Pass, FL Beach was restored; reduced shoaling in entrance channel due to Increased beach erosion in the vicinity due to reduced sand Borrow area shoaled at the rate of 24,000 m' from 1988 to 1992
sand trapping in borrow area bypassing

Longboat Pass/ Calculated wave refraction patterns showed a reduction of sediment None were predicted to occur, no impacts were monitored Between Dec. '91 and Dec. '92 Longboat Pass borrow area volume
New Pass, FL "trapped" by deltas and a more even spreading of wave energy to increased by 150,000 m'; however, between Dec. '92 and April'93
the south of each entrance (due to March 13-14 storm) borrow area volume decreased by
41,000 m'

Redfish Pass, FL Erosion protection for downdrift shoreline; accretion to the north of No specific studies were performed Approximately 80,000 m' of fine-grained material was carried into
the entrance and south of the project the borrow area within 18 months after 1981 project; between 1989
and 1991 35,000 m' filled both (1981 and 1988) borrow area

Boca Raton, FL Beach Erosion contained, improved navigation conditions over delta Feeder beach within 600 m of entrance eroded critically, beach Beach I km south ofentrance grew by an average of 12m; the
and maintenance of water quality in Lake Boca Raton nourishment project planned for 1995 using delta sediment entire ebb delta including borrow area exceeded pre-project volumes

Jupiter, FL Erosion protection for downdrift shoreline None were predicted to occur, including focusing of wave energy on Pre- and post-project surveys of fill area to be canied out
jetties, changing of littoral pattern or increased salinity in
Loxahatchee River

Nassau Sound, FL Refraction analysis for borrow area showed a reduction of wave None were predicted to occur No monitoring of the relict delta region
energy on shoreline and an increase of energy in the sound,
resulting in decreased sediment transport

Port Royal Sound, SC Mitigated chronic erosion problem with a predicted 8 year project None were predicted to occur No monitoring of delta
life

Fripp, SC Temporary Beach Nourishment No studies were performed; no impacts were monitored Rapid recovery of borrow area, approximately 153,000 m'
accumulated in delta since 1980

Port Isidro, SC Dredging the ebb delta moved the channel 125 m offshore, None were predicted to occur, no impacts were monitored Sediment filled the borrow area, and the channel slowly migrated
removing the source of scour and renourishing the beach landward towards the equilibrium position

Captain Sam's, SC Relict delta "pushed" ashore by wave action nourished the beach at None were predicted to occur, no impacts were monitored Entrance began migrating south at its previous rate
the rate of 130,000 m'/yr between Mar. '83 to May'85; totally
1,150,000 m' by 1993

Hog, SC Emergency nourishment for heavily armored sections of shoreline Delta filled with sediment at the expense of deltas further offshore Position of Hog Inet channel did not shift toward Myrtle Beach
following Hurricane Hugo and the downdrift shoreline; 7,000 m' ofremedial nourishment shoreline; six months after the project, 95 % of the dry beach was
became necessary to guard downdrift shoreline recovered due to nourishment and seasonal effects

Townsend's, NJ Beach Renourishment Mining redirected the ebb channel northward through the delta, Critical beach erosion along the Avalon shoreline, and growth of a
resulting in changed channel hydraulics large spit in the interior of the entrance where the channel once
occurred

Townsend's, NJ Emergency Renourishment, redirection of channel No studies were done; no impacts were monitored Monitoring to verify channel position

Great Egg, NJ Beach Renourishment No studies were performed Monitoring of delta system planned

Abecon. NJ Beach Renourishment No studies were performed 43% of fill remained in 1991, some sediment was washed offshore;
no monitoring ofdelta















CHAPTER 2
LITERATURE REVIEW


Although the ebb tidal shoal is an appealing source of high quality sand compatible for

renourishment of the downdrift beach, the physical and ecological impacts to the natural system of

removing this sand must be assessed. Likewise, the feasibility of modeling the ebb tidal shoal must

be considered. However, information on the above topics is scarce. Laboratory experiments

performed recently by Wang et al. (1994, 1995) at the University of Florida have shed some light on

modeling the ebb tidal shoal in the laboratory, and other researchers have investigated various

aspects of ebb tidal shoal mining. A brief review of those works most relevant to the present study is

presented in this chapter.

Wang et al. (1995) studied the ebb tidal shoal evolution process in the laboratory under

storm wave conditions with a natural inlet and an improved inlet with porous and impervious jetties.

The ebb shoal evolution process was documented for all cases, and a prediction of the sediment flux

patterns was attempted using a new empirical eigen function approach. Results indicated that ebb

tidal shoals similar to those found in nature can be established in the laboratory.

Wang et al. (1994) investigated the modeling laws to be used in laboratory beach modeling.

Several different modeling laws were tested and compared using two-dimensional wave tank models

and a three-dimensional wave basin model. A modified modeling law was derived based on the work

of Wang (1990) and proved to be the most accurate. This modeling law was adopted by Wang et al.

(1995) and in the present study.










6

Sill (1981) and Hayter (1988) investigated ebb tidal shoal dynamics in the laboratory using a

small scale movable-bed inlet model. The models mixed prototype-scale sand and tidal period with

laboratory-scale geometry and waves. The small scale yielded highly distorted model conditions. The

questions on modeling laws and the morphological time scale on ebb tidal shoal evolution could not

be addressed. The results showed that the volume and shape of the laboratory ebb tidal shoal

resembled those occurring in nature.

Mehta, Dombrowski, and Devine (1996) addressed research needs for developing site

selection criteria for ebb shoal mining and examined the role of waves in ebb tidal shoal growth. A

review of ebb shoal mining undertaken at several tidal inlets showed that the choice of mining

location and the method of mining have been specific to those inlets, and it is unclear whether general

guidelines for determining the site and volume of mining can be developed. An analytic method was

used to show that the rate of ebb shoal growth for a newly opened tidal inlet depends on a parameter,

B, representing the ratio of wave power to tidal power. Observations suggested that an ebb shoal

may never reach a true equilibrium size. However, a quasi-equilibrium volume may be predicted

given the B value characteristic of a particular tidal inlet representing the long term wave and tidal

conditions of that inlet.

Walther and Douglas (1993) studied the ebb shoal borrow area recovery rate. A transport

ratio method was developed to quantify the trapping rates and sediment transport rates over a mined

ebb shoal. Values calculated with this method were reasonably accurate compared to measured data

from Boca Raton Inlet, Redfish Pass, and John's Pass in Florida. The results demonstrated that a

shallower cut will decrease the bypassing rate less initially, however, a deep cut will result in

approximately the same bypassing rate over a longer period of time.















CHAPTER 3
LABORATORY CONSTRAINTS AND MODELING LAWS


In conducting laboratory experiments, the constraints must be acknowledged and considered

to determine the range of experimental parameters. There are three basic kinds of physical properties

one needs to address: the geometrical parameters, the sediment properties, and the natural forces. The

geometrical parameters include such quantities as bathymetries, shoreline configurations, and inlet

geometries. The most relevant sediment properties are grain sizes, specific gravity, and others such

as shapes and porosity as well as the dynamic properties such as the rate and direction of sediment

supplies from the boundaries. The important natural forces to be modeled include ocean waves, tidal

currents, and water level changes. Ocean waves are a vital force in mobilizing bottom sediment and

producing longshore and cross-shore sediment transport. Tidal current is a primary force in shaping

the ebb tidal shoal due to its sediment transport capacity and its strong interactions with nearshore

waves and bathymetric features. The water level defines the boundary affected by the dynamic forces

and modifies the nearshore current and wave conditions. It is evident that the inlet ebb tidal shoal

evolution process is extremely complicated owing to the large number of physical parameters

involved. In laboratory modeling one must first simplify the process to be tested. This is done by

imposing constraints through modeling laws. The methodologies are discussed in this chapter.



3.1 Considerations and Constraints

The inlet model is located in the wave basin in the University of Florida's Coastal and

Oceanographic Engineering Department laboratory. The basin is approximately 25 m wide, 30 m









8

long, and 1 m deep and is equipped with a snake-type wave-maker consisting of 88 independent

paddles each 24 cm wide. Waves of varying angles of incidence can be produced by adjusting the

phase of each individual paddle. Because of the basin's lateral constraints, angles greater than 15

degrees are unsuitable. Depending on the water depth, which is limited to 75 cm, wave heights

ranging from 1 to 15 cm and periods from 0.9 to 1.9 seconds can be produced without difficulty.

The physical dimensions of the wave basin and the scaling laws required limit the size of the

ebb tidal shoal that can be accurately simulated in the laboratory. The basic model scale, defined as

the prototype to model ratio of horizontal scale, must be large enough to accurately reproduce the ebb

tidal shoal volumes found in nature. Thus, data on ebb tidal shoal characteristics found in nature

must be known.

Inlet characteristics in nature vary widely as do the ebb tidal shoal shapes and volumes.

Walton and Adams (1976) and Marino and Mehta (1986) compiled ebb shoal volumes for 15 inlets

along the east coast of Florida and proposed different empirical relationships between the ebb tidal

shoal volume and tidal prism. The results of Marino and Mehta (1986) and the location of the tidal

inlets are shown in Figures 1 and 2 respectively. The ebb tidal shoal volumes generally decrease from

north to south in these samples. The volumes of the four northernmost ebb tidal shoals are similar

and significantly greater than those in the southern and middle coastline. The majority of ebb tidal

shoal volumes in the southern and middle coastline range from 0.1 to 10 million cubic meters which

is considered to be small to moderate in size. These inlets can generally be characterized as mixed

energy type in which both waves and currents change inlet morphology in time scales of engineering

interest from days to decades. Matanzas Inlet and Nassau Sound are the only natural inlets while the

rest have been improved with jetties.

The laboratory inlet model was chosen to represent the inlets in the latter group, for the

group includes more than two thirds of Florida's east coast inlets and the ebb shoal volumes are










9

within the constraints imposed by the basin dimensions and modeling laws. The ebb tidal shoal

volumes associated with the smaller inlets in this group can be simulated in the laboratory wave

basin with a horizontal scale of 40 to 80, and a horizontal scale of 100 can accommodate the mid-

sized inlets. The model inlet design is based on an idealized inlet configuration with the general

hydraulic characteristics of this group. The range of tidal current strength and inlet cross-sectional

area can be estimated from Figure 1 which plots tidal prism versus ebb tidal shoal volume.




100 1 1 1 1 I I I
o _- V s 5.59 x 10-p1" (Marino, 1986)
S---V 6.08 10 p23 (Walton and Adam, 1976)



10- /0
x St Augustine
X Ft. George
5 Nassau St. Johns
Lake Worth x Sound
S/St. x Ft.Plerce
Baers Hiaulover x Lucle Ponce do Leon
1 In x Mantanzas -





0.1 05 1.0 5 10 50 100 500 1000
EBB SHOAL VOLUME, V (x 10 S3 )


Figure 1: Tidal Prism-Ebb Shoal Volume Relationship for Florida's East Coast Inlets
(after Marino and Mehta, 1986).


The selection of experimental wave conditions is also limited due to the laboratory

restrictions and time limitations. In nature, wave conditions are random in magnitude, period, and

direction. Wang et al. (1995) devised a simple plan to select the experimental wave conditions by

examining the effects of waves on the sediment transport and associated bathymetry changes. They











10

assumed that along a coast waves can be separated into two groups: those from a dominant wave

direction and the rest lumped into non-dominant direction. Four categories of waves were then

analyzed including waves from the dominant wind direction causing beach erosion, waves from the

dominant wind direction causing beach accretion, waves from the non-dominant wind direction

causing beach erosion, and waves from the non-dominant wind direction causing beach accretion.

Along the east coast of Florida, the dominant wind is from the northwest, and the non-dominant wind

direction is from the southeast. For Florida's mid east coastal region, it is estimated that 75% of the

time waves are from the dominant direction, and 25% of the time waves are either from the non-

dominant direction or negligibly small in magnitude (Wang et al., 1992).





I Z': St Mary$
I Nassau Sound
S. Fl. F Ge-orge
S. -SLt. Johns
.* StL Augustine


once do Lion
00
Port Canaveral
Sbastlan
041 Pierce
o/ SL Lucie

Co I k'- L Worth
L .....South Lake Worth


Figure 2: Location Map of Nineteen Inlets Along Florida's East Coast.


-A .-'










11

Based on laboratory experiments and field observations, the sediment transport rate and

associated bathymetry changes are governed by extreme waves from either the dominant or non-

dominant direction. Thus, the effects of storm waves from the dominant weather direction were tested

first by Wang et al. (1995). However, a major constraint in movable-bed physical modeling is the

compatibility of the flow regime and modes of sediment transport between field and laboratory

scales. During a storm wave event under natural conditions, sediment transport is governed by the

suspended load and the flow is mainly turbulent. Therefore, these modes must be preserved in the

laboratory.

Laboratory flow conditions are determined using Jonsson's (1966) flow regime chart shown

in Figure 3 as a guideline. The flow regime consists of three different flow zones and three transition

zones. The flow condition is determined by two parameters: a roughness parameter

a,/k,

and Reynolds number


R Ubam
a V



where a, and ub are the amplitudes of the fluid particle displacement and velocity respectively, v is

the kinematic viscosity, and k, is the roughness length generally considered to be on the order of the

sand grain size.

Sediment transport conditions are classified using a diagram proposed by Shibayama and

Horikawa (1980) shown in Figure 4. The diagram consists of two parameters: the relative fall

velocity


UIW











and the Shields parameter


fu
m2sgd


where Wis the fall velocity, ub is the bottom flow velocity, f, is the bottom friction coefficient, s is

the sediment specific gravity, d is the particle size, and g is the gravitational constant.

To preserve turbulent flow and suspended sediment transport in the laboratory model while

maintaining horizontal scales in the range of 40 to 100, there exists some flexibility in selecting the

combinations of sediment material and vertical geometrical scale. Different materials have been

proposed and used in movable-bed model experiments, however, the most common one is natural

quartz sand because it closely resembles the natural beach material and is easier to obtain at low cost.

To use natural sand as bottom material, however, vertical geometrical scale distortion appears to be

necessary. The degree of distortion is addressed in the following section in Scaling Laws.

The final constraint considered in physical modeling is the time scale. In prototype, the ebb

tidal shoal evolution and regeneration are of long-term morphological process taking years or

decades. These processes need to be accelerated with a different time scale in the laboratory model.

Based on Froude number consideration, the time scale can be shown to be inversely proportional to

the square root of the vertical scale. However, this time scale is not sufficient to describe the ebb

shoal process, for one year prototype time would require nearly two months model run time in a

laboratory with an undistorted model of vertical scales ranging from 40 to 100. However, as

mentioned previously, the sediment transport rate and the associated bathymetric changes in the

nearshore environment are dominated by storm events. Hence, the experiments can be conducted

under storm wave conditions in order to accelerate the processes. The results of Sebastian Inlet

movable-bed model testing conducted by Wang et al. (1992) support this reasoning.























1o'





10'





10
102
ia


0 No movement
1 Bed load(BL)
2 Bed Load-Suspendd load
Internndlete (BSI)
3 Suspended load(SL)
4 Sheetflow(SF)



2 2 2
0 1



I L-|
No movement jBL' SI


Transilon


4 SF


10li
10


*2


.0I


10"
Shields Parameter


Figure 4: Sediment Transport Modes Diagram (after Shibayama and Horikawa, 1980).


id 10o 1id 1
Re,Reynolds Number

Figure 3: Jonsson's Flow Regime Chart.


I I










14

In the experiments of Wang et al. (1992), bathymetry changes were examined for a six-day

NE storm wave attack with a wave height of 1.8 meters and a wave period of 8 seconds in prototype

equivalents, followed by an eight-day ENE swell condition with a wave height of 0.6 meters and a

wave period of 16 seconds. The horizontal length scale, vertical length scale, hydrodynamic time

scale, and morphological time scale used in the testing were Nx=60, N8=41, N=9.5, and Nt=6.3

respectively. The experimental results indicated that the six-day storm waves produced a prototype

equivalent sediment transport of 1700 m3/day at the downdrift side boundary as opposed to 370

m3/day in the following eight-day swell period. A marked ebb shoal topographic change (contour

increment of 25 cm in prototype equivalent) occurred only during the six-day storm event. This trend

was also observed for the net sediment loss into the inlet. The commonly accepted sediment transport

formulas also support this condition. It is evident that the impacts from the swell conditions were

insignificant, therefore, all the present model experiments are conducted under storm wave conditions

in order to accelerate the processes governing the morphological change of the nearshore

environment.



3.2 Scaling Laws.

As mentioned in the previous section, under storm conditions the nearshore flow is mainly

turbulent and sediment transport is dominated by suspended load. The modeling law must have the

flexibility to accommodate these conditions in the laboratory, therefore, a distorted vertical scale may

be necessary in order to fulfill the requirements using quartz sand as the bottom material. The

modeling law selected was derived by Wang et al. (1994). It was originally developed for studying

morphological changes in a plane beach model and was later applied to an inlet model (Wang et al.

1995) for describing the generation of the ebb tidal shoal. A brief review of the modeling law

derivation is presented here.









15

The work of Wang et al. (1994) entailed two-dimensional wave tank and three-dimensional

wave basin modeling on beach profile response carried out at different geometric scales. Four

different modeling laws proposed by Le Mehaute (1970), Vellinga (1982), Hughes (1983), and

Wang et al. (1990), as shown in Table 3, were evaluated at horizontal scales of 20, 30, and 40 with

vertical distortions specified by the modeling laws. A parallel set of experiments with undistorted

scales proved to be unsuccessful. The results were compared with data from a prototype scale

experiment performed in the German Large Wave Tank (GWK) test (Dette and Uliczka, 1986). The

comparison of wave tank results with GWK data was presented separately (Wang et al., 1994).



Table 3: Summary of Fall Velocity Distorted Model Laws.

Author Geometric Hydrodynamic Morphological
_Distortion Time Scale Time Scale
Le Mehaute (1970) Na=(N)Vo)2/3 NT="N, Nt =N6


Vellinga (1982) N=NO44O8 N=N, N,7N


Hughes (1983) N, =(NAx)2/3 NT=NxN, Nt=N N


Wang et al. (1994) N=(N,)0.4N,. NT=N/, Nm N

N= prototype to model scale ratio
W = fall velocity scale
S = sediment specific gravity scale
X = horizontal length scale
8 = vertical length scale
H = wave height scale
T= hydrodynamic time scale


Since the intent of Wang et al. (1995) was to extend the beach profile modeling laws to also

cover the offshore shoal region, the model evaluation criteria were extended to include that region.













Dune Region Bar Region
------^^*^^*K -- *1 --- --- -


SWL
-I
-- -\ --------------------------




-- Initial Profile
Storm Profile




Figure 5: Two Different Beach Profile Regions Scheme.



tank stopped at the offshore bar which includes a portion of the ebb tidal shoal. The evaluation of

the modeling laws was carried out in two different beach profile regions: the dune region (shore

region) and bar region (offshore region) as shown in Figure 5. The modeling laws were evaluated

based on five criteria including dune erosion volume, nearshore profile, bar volume, bar crest

location, and geometrical location. The results from the two-dimensional wave tank tests indicated

the following:

For dune erosion, all four existing modeling laws were reasonably adequate to predict the

final erosion volume but over predict the erosion rate before reaching the final experimental

stage.

Wang's and Vellinga's modeling laws performed better for nearshore profile.

All the modeling laws predicted the main bar location closer to the shoreline than the

prototype data.

One probable cause for the latter is that all existing models treated wave height scale the same as the

vertical scale. However in the nearshore zone it is known that wave breaking is affected by water

depth as well as local beach slope. Waves tend to break earlier (at a larger water depth) on a gentle









17

slope than on a steeper slope. A general breaking criterion incorporating slope effect can be given as


Hb=y(m)hb


where H, and hb are the wave height and water depth at breaking, respectively, and y is the breaking

index here expressed as a function of slope, m. In general the value of y increases with increasing

beach slope. In other words, when the slope becomes exaggerated in a distorted model, the wave

height scale should also be enhanced accordingly in order to preserve the surf zone width. Therefore,

if the wave height is simply scaled according to the vertical scale, the surf zone width in the model

when scaled up to prototype will be narrower than that found in nature. Hence, the breaking bar

location from the model prediction will also be closer to shore than bars occurring in nature. To solve

this problem, a modified modeling law was proposed with wave height scaling enhanced as follows:

Na




where N, and N, are the vertical and horizontal scale ratios, respectively. The quantity in the

parenthesis can also be viewed as the breaking index scale (Wang et al., 1994). Accordingly, the new

set of equations that were established for the modified modeling law are shown in Table 4. This

modified modeling law was found to adequately scale both nearshore and offshore regions in the 2-D

wave tank tests and proved effective in 3-D tests.

Table 4: Modified Modeling Law.

Geometric Wave Height Hydrodynamic Morphological
Distortion Distortion Time Scale Time Scale


N =(NNw 0.N8 NT=Nx N,=Nx NtfN















CHAPTER 4
DESIGN OF EXPERIMENTS


4.1 Design of Initial Inlet-Beach Model

The laboratory model design considered the constraints and modeling laws addressed in the

previous chapter. The model design is shown schematically in Figure 6. Tidal currents were

generated by recirculating water through the channels as depicted. The flow discharge is controlled

by the weir boxes located on either side of the basin. Water is supplied from the upper basin weir

boxes (flood flow weirs) to create the flood current and from the lower basin weir box (ebb flow

weir) to create the ebb current. The test section is bounded on the sides by semi-perforated wave

guides formed by concrete blocks to allow flows in and out of the test section. The downdrift wave

guide has an opening in the nearshore zone to allow the longshore sediment transport to deposit in

the catch channel. For this inlet model configuration, the wave generator is located about 27 m from

the shoreline based on an average water depth of 0.35 m.

An idealized inlet of rectangular cross-section was constructed cutting through a plane beach

made of natural beach sand with Ds0=0.19mm. The plane beach consists of a flat back shore.segment

and a mild-sloped offshore profile which extends to about 6 meters offshore before merging with the

flat concrete basin floor. The beach profile approximates an equilibrium shape h =AxO' where h is the

water depth and x is the offshore distance from the shoreline. The overall length of the beach from

the updrift end to the downdrift end is approximately 19 meters. The inlet is a straight rectangular

channel with impervious jetties defining an inlet channel with a uniform width and depth of 1.2 m

and 0.2 m respectively. The updrift and downdrift jetties are parallel and of equal length extending










19

0.7 meters seaward of the initial shoreline. The jetty height is about 10 cm above the flood tide water

elevation, and the jetty width is about 20 cm. The inlet is located offset from the center towards the

updrift end creating an updrift beach length of 4.5 m and a downdrift beach length of 12 m.

Sand is supplied to the test section using a curved feeder beach at the updrift end, therefore,

the sand supply to the downdrift is purely wave-induced transport. This design allows for uniform

sediment supply, yet the feeder beach has to be replenished from time to time during the intervals of

conducting beach surveys.





MOVERBLE-BED INLET MODEL


0 2 4 6 8 10
SCALE IN METERS


Figure 6: Schematic Setup for the Movable-Bed Inlet Model.










20

4.2 Test Conditions

Two models were run to study the effects of ebb shoal removal on the inlet-beach system.

The test conditions and run times are given in Table 5. The models have the same inlet configuration

and differ only in the initial bathymetry. The first model, EC1, is the case without ebb shoal removal,

and the second model, EC2, is the case where the ebb shoal was partially removed. The wave maker

at the offshore boundary generated storm condition waves of 7 cm height and 1 sec period and an

approach angle of 7.5 degrees.

The tidal currents are simulated by alternating the ebb and flood cycles every 40 minutes.

This time interval roughly corresponds to a semi-diurnal tidal period at 1:80 geometric scale ratio

based on Froude criterion. The tidal current condition can be simulated with equal flood-ebb



Table 5: Inlet Model Experimental Conditions.

Case Mean Incident Wave Conditions Beaches Slope Ebb Test
Water Tidal Time
Depth Wave Wave Wave Foreshore Offshore Shoal (min)
Period Height Angle Mining

EC1 35 cm 1 sec 7 cm 7.50 1:2.9 1:14.5 No 3200

EC2 35 cm Isec 7 cm 7.50 1:2.9 1:14.5 Yes 3200


discharge, equal flood-ebb current strength, or unequal discharges or current strengths at the inlet

throat. Equal discharge, which usually results in stronger ebb current, was adopted for the laboratory

models based on field measurements at Sebastian Inlet (Wang et al., 1991) and other inlets. In the

present study, the cross-sectional averaged flood and ebb currents in the inlet were 0.12 m/sec and

0.14 m/sec, respectively. The discharge was kept constant at 0.04 m3/sec within each ebb and flood

period. The ebb and flood currents were simulated alternatively in step-wise fashion, instead of

sinusoidal or other types, based on current measurements from Sebastian Inlet, shown in Figure 7.






















SI I
0 1
I i I .
>1 I







-0.5 \.


10 10.5 11 11.5 12
January,1990


Figure 7: Current Measurements at Sebastian Inlet.



It is evident that the current variations within each ebb or flood cycle can be reasonably

approximated by uniform step function.

The significant effect of water level on beach erosion must also be considered. In the present

study, no attempt was made to simulate storm surges, however, the periodical water level change due

to tidal cycles was included. The water level is higher for flood tides as water is pulled towards the

inlet, whereas water jets away from the inlet during ebb tides. The simulated tidal range is 3 cm in the

experiment with an inlet water depth of 0.2 m for the flood tide and 0.17m for the ebb tide.










22

4.3 Design of Ebb Shoal Mining

The testing procedures and conditions were identical for EC 1 and EC2 with the exception of
i
the initial model bathymetry. The initial bathymetry for EC1 was described in section 4.1. The initial

bathymetry for EC2 was obtained by modifying the final (after 3200 min) bathymetry of EC1 by

mining the ebb shoal and renourishing the downdrift beach. The ebb tidal shoal mining was designed

so that sand would only be removed from the seaward side of the ebb tidal shoal which has been

common practice in actual ebb shoal mining cases. The ebb tidal shoal was dredged to a depth of -40

cm in the model. This sand was used in all for renourishing the downdrift beach in the preparation of

the initial topography for EC2. The volume of sand mined from the ebb tidal shoal was not sufficient

to complete the renourishment of the downdrift beach, thus, additional sand from outside the model

was required.



4.4 Test Procedures

The laboratory experiments were conducted according to the following procedures:

(1) Prepare model initial bathymetry.

(2) Survey initial profiles at the 20 cross-sections..

(3) Adjust water level and discharge to specified design values. Start experiment with ebb cycle

first.

(4) Start wave generator with pre-calibrated settings. The experiment is interrupted at intervals of

40 min. for the change of tidal conditions between ebb and flood cycles.

(5) Conduct bottom profile surveys at selected time intervals at 40 min, 80 min, 120 min, 160

min, 480 min, 800 min, 1120 min, 1600 min, and 3200 min.

(6) Measure sand accumulated outside the downdrift boundary and inside the inlet.
















CHAPTER 5
LABORATORY EBB TIDAL SHOAL DEFINITION AND CALCULATIONS


5.1 Defining the Ebb Shoal in the Laboratory.

The goal of this study is to determine the impact on the inlet-beach system due to ebb tidal

shoal mining. The main focuses are on the downdrift shoreline erosion and the regeneration process

of the ebb tidal shoal after removal. In order to examine the ebb shoal characteristics of EC1 and

EC2, it is necessary to first clearly define the ebb tidal shoal in the laboratory.

The ebb tidal shoal is defined as the accumulation of sediment above a specified reference

contour in the region under the influence of the ebb tidal current. In reality, specifying the reference

contour can be subjective. The reference contour is usually chosen as the updrift or downdrift

shoreline not affected by the tidal inlet. Large discrepancies in volume calculations can exist in nature

when the updrift and downdrift shorelines are notably offset and when the bathymetry is significantly

complicated by bottom undulations (Mehta et al., 1996). In the laboratory, the task is considerably

easier by simply using the initial bathymetry of the respective model tests.

A more difficult task is the determination of the region of influence of the ebb tidal current.

Often the ebb tidal shoal will merge with the channel shoals and the offshore bars as they grow. In

the present study, the ebb tidal shoal and channel shoals were separated by defining the channel

shoals as the accumulation of sediment in the inlet channel within the confines of the jetties. Since

the experiments were conducted mainly under storm wave conditions, offshore bars induced by

breaking waves were present. These offshore bars would eventually merge with the ebb tidal shoal.

To separate them is not always easy. In the model, the breaking wave bar is defined by a minimum










24

accumulation of 4 cm and a maximum accumulation of approximately 8 cm. However, the points of

+8 cm accumulation of the bar are far enough updrift and downdrift of the inlet to assume that they

are not part of the ebb shoal. Thus, the location of the ebb tidal shoal boundary was chosen to

exclude the updrift and downdrift portions of the bar and include the accumulation of sediment above

the +4 cm isoline within the vicinity of the inlet. The downdrift limit was chosen as the survey line

#15 (approximately 3.5 meters downdrift of the inlet). This line is far enough downdrift from the

jetty yet not too close to the physical limit of the model. The updrift limit of the ebb tidal shoal is

defined by a shore perpendicular line drawn from the tip of the updrift jetty. By inspecting the

contour plot for EC1 after 3200 min shown in Figure 8, one sees that there is no significant

accumulation of sediment outside the defined boundaries.


Contour Changes in EC1 After 3200 min

I 1-- Ebb Shoal Boundary
E5- 4

04-

3 ............

02l ~ ~. ~" "1 --1

I I f__fil_, Ii
0 2 4 6 8 10 12 14 16
longshore distance (m)


Figure 8: Changes in Bathymetry in EC1 after 3200 min.



5.2 Ebb Tidal Shoal Volume Calculations

After defining the reference contour and the horizontal limits, the ebb shoal volumes can be

calculated. Each of the survey lines contained 80 equally spaced data points. By viewing the cross-









25

shore profiles for each survey with respect to the initial bathymetry profile, the amount of

accumulation at each survey line is evident (as is the amount of erosion). The volumes were

calculated after every survey by first calculating the area of accumulation for each survey line within

the region of influence. The areas were calculated by summing the product of the differential height

at each data point and the data point spacing. The areas of every two adjacent survey lines were then

averaged and multiplied by the longshore distance between the two survey lines to obtain the

estimated volume between those two survey lines. The total volume of the ebb tidal shoal is the

summation of these partial volumes throughout the region of influence. Appendix A and Appendix B

contain cross-shore profiles at every survey line after 3200 min for EC1 and EC2 respectively.















CHAPTER 6
EXPERIMENTAL RESULTS


Experiments EC1 and EC2 were designed to determine the impact on the inlet-beach system

due to ebb tidal shoal mining. Both experiments were run for a total of 3200 min (40 complete tidal

cycles) under the test conditions specified in section 4.2. In prototype scale, this time is equivalent to

20 days of storm wave conditions. The experiments were terminated at this time due to the downdrift

erosion being too severe to continue. In both cases, the downdrift shoreline retreated close to the

model's onshore boundary. Bathymetry surveys were conducted at 0 min, 40 min, 80 min, 120 min,

160 min, 480 min, 800 min, 1120 min, 1600 min, and 3200 min in order to monitor downdrift beach

erosion, regeneration of the ebb shoal, and inlet shoaling. Figure 9 and Figure 10 illustrate, as

examples, the results of bathymetry surveys at 0 min, 1600 min, and 3200 min for EC1 and EC2

respectively. Appendix C and Appendix D contain the complete set of results from the bathymetry

surveys for EC 1 and EC2. The longshore sediment transport and net upchannel sediment transport

inside the inlet were estimated by collecting sand outside the downdrift boundary and inside the inlet

at the survey times specified above.

The impacts on shoreline erosion, ebb shoal establishment, and inlet channel shoaling can be

quantified by comparing the changes in bathymetry between the surveys. Figure 11 and Figure 12

show the changes in bathymetries at 800 min, 1600 min, and 3200 min with respect to initial

condition (0 minute) for EC 1 and EC2 respectively. The complete set of bathymetry changes with

respect to the initial surveys for EC 1 and EC2 are given in Appendix E and Appendix F.





























1I


0 2 4


6

3


0 2 4 6
Iongshor


0 min
. ... 1i-40 ,

-30

.20






8 10 12 14 16

600 min



-30
I -40 p -







-10


8 10 12 14 16

200 min

S- 430










8 10 12 14 16
e distance (m)


Figure 9: Bathymetry Contours for ECI after 0 min, 1600 min, and 3200 min.
































1


3:


0 2 4 6
Iongshor


0 min

-40



------- --
-20





8 10 12 14 16

600 min

-40










8 10 12 14 16

200 min

-40










8 10 12 14 16
re distance (m)


Figure 10: Bathymetry Contours for EC2 after 0 min, 1600 min, and 3200 min.












800 min


0 2 4


-4

~Vfc~~--~--=--
6 I I1 1I I
6 8 10 12 14 1


E5


54
3
0















a2
0)

4




5




6






o2
0)


0 2 4


6 8


10 12 14 16


3200 min


0 2 4 6 8 10
longshore distance (m)


12 14 16


Figure 11: Bathymetry Changes for EC1 after 800 min, 1600 min, and 3200 min.


1600 min


~-4
-< -- ..- --.. -

._ ,- -* -... _-- =













800 min


5 I I


co



0 2 j = = -0 --- t--1-- -"-->--
I) I










44

1-
r -------
0 2 4 6 8 10 12 14 16

1600 min
6I


6 -4------ --- --









0 2 4 6 8 10 12 14 16


6

E5


.a


52
0o
i1


3200 min






9
--

-4

--16 ----..
--_ -4
-16 ----
T"" ae a


0 2 4 6 8 10
longshore distance (m)


12 14 16


Figure 12: Bathymetry Changes for EC2 after 80 0 min, 1600 min, and 3200 min.









31

6.1 Ebb Tidal Shoal Growth

The degree of ebb tidal shoal growth can be quantified using the changes in bathymetry

generated from the surveys. Using the definition of the ebb shoal and ebb shoal boundaries discussed

in section 5.1, the volume of the ebb shoal can be calculated. Figure 13 compares the calculated ebb

tidal shoal volume versus elapsed time for EC1 and EC2, and Figure 14 illustrates the rate of ebb

shoal growth in both experiments. In the first 800 min, the ebb tidal shoal in EC2 accumulated less

volume than the shoal in ECI implying a slower rate of growth in EC2. However, from 800 min to

3200 min, the ebb shoal growth approaches a steady rate at approximately 0.017 m3/hr in both

experiments. The volumetric changes fluctuate greatly in the first 160 min reflecting the effects of

individual ebb and flood tidal cycles during this initial period. These results are also presented in

tabular form in Table 6. As can be seen during the initial stage, the ebb tidal shoal grows during ebb

cycle but diminishes during flood cycle, although the net effect is the accumulation of sediment in the

form of ebb tidal shoal.



6.2 Beach Erosion

Downdrift beach erosion is defined as the volume of sediment eroded from the beach

between the downdrift jetty and the downdrift model boundary. Using the same method described in

section 6.1 for calculating the ebb tidal shoal, the volume of sand eroded between survey lines 9-20

can be calculated. The calculated volumes of downdrift beach erosion and the rates of erosion are

included in Table 7. These results are illustrated graphically in Figure 15 and Figure 16 which show

the accumulated downdrift erosion versus elapsed time and the rate of downdrift beach erosion

respectively for both EC1 and EC2. Extensive downdrift beach erosion occurred in the first 160 min

of the two experiments, with a greater erosion rate in EC2 than in EC1. After 160 min, the downdrift

beach was eroded at about an equal rate in EC1 and EC2. From 480 min to 3200 min, the downdrift




































0 500 1000 1500 2000 2500 3000 3500
elapsed time (min)

Figure 13: Volume of Ebb Tidal Shoal Versus Time for EC1 and EC2.


0 500 1000 1500 2000 2500 3000 3500
elapsed time (min)

Figure 14: Rate of Ebb Tidal Shoal Growth Versus Time for ECI and EC2.











































0 500 1000 1500 2000 2500 3000 3500
elapsed time (min)


Figure 15: Volume of Downdrift Erosion Versus Time for ECI and EC2.


0.25

C
| 0.2
UJ

S0.15
a:


Figure 16: Rate of Downdrift Erosion Versus Time for EC1 and EC2.












Table 6: Volume of Ebb Shoal and Rate of Ebb Shoal Growth for EC1 and EC2.

EC1 EC2
Elapsed Time
(min) Volume of Ebb Rate of Ebb Volume of Ebb Rate of Ebb
Shoal Shoal Growth Shoal Shoal Growth
(ms) (m3/hr) (m') (m3/hr)
40 0.0948 0.1422 0.0402 0.0603

80 0.0805 -0.0214 0.0805 0.0604

120 0.1033 0.0342 0.0855 0.0075

160 0.1078 0.0068 0.0880 0.0037

480 0.2667 0.0298 0.1999 0.0210

800 0.3917 0.0234 0.2783 0.0147

1120 0.4743 0.0155 0.3053 0.0051

1600 0.6006 0.0158 0.4321 0.0158

3200 0.9399 0.0127 0.8589 0.0160


Table 7: Volume and Rate of Downdrift Erosion for EC1 and EC2.

ECI EC2
Elapsed Time
(min) Volume of Rate of Erosion Volume of Rate of Erosion
Erosion (m3) (m3/hr) Erosion (m3) (m3/hr)

40 0.2521 0.3782 0.1819 0.2729

80 0.3139 0.0927 0.4351 0.3798

120 0.4359 0.1830 0.5006 0.0983

160 0.4988 0.0944 0.6395 0.2083

480 0.8748 0.0705 1.1037 0.0870

800 1.1513 0.0518 1.3552 0.0472
1120 1.3755 0.0420 1.5282 0.0324

1600 1.7336 0.0448 1.9671 0.0549

3200 2.3164 0.0219 2.7105 0.0279









35

erosion continued but at a decreasing rate from approximately 0.08 m3/hr at 480 min to 0.025 m'/hr

after 3200 min in both experiments. Neither EC 1 nor EC2 appeared to have reached an equilibrated

state at 3200 min.



6.3 Inlet Channel Shoaling

The inlet channel shoaling is defined as the accretion of sediment in the inlet within the

confines of the jetties. The inlet channel shoaling, which occurred mainly in the inlet channel near the

updrift jetty, was noticeable in both EC1 and EC2. This inlet channel shoaling was more severe in

EC2 than in EC1. The total sand volumes of inlet channel shoaling evaluated at 3200 min. in EC1

and EC2 were 0.022 and 0.115 m3, respectively.



6.4 Accumulation of Sand Outside Downdrift Boundary and Inside Inlet

Sediment transport across the downdrift boundary and sand carried into the inlet by the

combined currents and waves were determined by the amount of sand collected outside the downdrift

boundary and inside the inlet in EC1 and EC2. Tables 8 and 9 contain the volume of sand

accumulation and rate of accumulation at the downdrift boundary and inside the inlet, respectively,

for ECI and EC2. These results are expressed graphically in Figures 17 and 18 which show the

accumulated volume and rate of sand accumulation versus time at the downdrift boundary and

Figures 19 and 20 which illustrate the same parameters for inside the inlet. It is apparent that the

longshore sediment transport at the downdrift boundary was significant in both EC1 and EC2, with

more transport in EC2 than in EC1. The rate of sand accumulation outside the downdrift boundary

generally decreased with time for both EC1 and EC2. Inside the inlet, there was not a significant

amount of sand accumulated in EC2 compared to a much greater amount in EC1. The rate of sand

accumulation inside the inlet decreased with time for EC 1 and increased, though not significantly, for

EC2.





































0 500 1000 1500 2000 2500 3000 3500
elapsed time (min)

Figure 17: Volume of Accumulation at Downdrift Boundary Versus Time for EC1 and EC2.


1500 2000
elapsed time (min)


Figure 18: Rate of Accumulation at Downdrift Boundary Versus Time for EC1 and EC2.


















U.16


0.14 ---"


0.12 -
/
/
0.1 /


0.08 /
/
0.06 / __ EC1

/ EC2
0.04


0.02


0 'i'


0 500 1000 1500 2000 2500 3000 3500
elapsed time (min)


Figure 19: Volume of Accumulation Inside Inlet Versus Time for EC1 and EC2.


035



).03



025



1.02 __ EC1

EC2
015 I



.01 -



)05 /

0 ~~
0 I


0 500 1000 1500 2000 2500 3000 3500
elapsed time (min)


Figure 20: Rate of Accumulation Inside Inlet Versus Time for EC1 and EC2.


o
0

E
ZB


0.


-0.







(o
E
S0.


S0


I


0.0












Table 8: Volume and Rate of Sand Accumulation at Downdrift Boundary for EC 1 and EC2.

EC1 EC2
Elapsed Time
(min) Volume of Rate of Volume of Rate of
Accumulation Accumulation Accumulation Accumulation
(m3) (m3/hr) (m3) (m3/hr)
40 0.030 0.045 0.060 0.090

80 0.060 0.045 0.105 0.068

120 0.080 0.030 0.145 0.060

160 0.105 0.037 0.185 0.060

480 0.255 0.028 0.475 0.054

800 0.380 0.023 0.655 0.034

1120 0.505 0.023 0.855 0.038

1600 0.650 0.018 1.135 0.035

3200 0.810 0.006 1.167 0.0012


Table 9: Volume and Rate of Sand Accumulation Inside Inlet for EC1 and EC2.

EC1 EC2
Elapsed Time
(min) Volume of Rate of Volume of Rate of
Accumulation Accumulation Accumulation Accumulation
(m3) (m3/hr) (m3) (m3/hr)
40 0.020 0.030 0.0 0.0

80 0.024 0.006 0.0 0.0

120 0.032 0.012 0.0 0.0

160 0.036 0.006 0.0 0.0

480 0.056 0.004 0.001 0.0002

800 0.096 0.008 0.004 0.0006

1120 0.116 0.004 0.009 0.0009

1600 0.136 0.003 0.014 0.0006

3200 0.156 0.0008 0.039 0.0009
















CHAPTER 7
COMPARISONS WITH PROTOTYPE DATA


In the previous chapters it was shown that an ebb tidal shoal can be successfully created in a

laboratory setting. In this chapter, an attempt is made to compare the laboratory results with field

data. Three small to medium sized inlets along the east coast of Florida were chosen for the analysis

which include Sebastian Inlet (Wang et al., 1992), Jupiter Inlet (Coastal Planning & Engineering,

1989), and Boca Raton Inlet (Coastal Planning & Engineering, 1991). These three east-coast Florida

inlets were chosen based on their relatively recent bathymetry surveys that indicated distinct ebb tidal

shoals. Figures 21-25 illustrate the bathymetries for these three inlets. The laboratory data from EC1

were used here for comparisons because it represents the ebb tidal shoal formation starting from an

initial condition of a plane beach form.

As discussed previously, the characteristics of ebb tidal shoals can vary widely and there are

no clear-cut criteria on which to base this comparison. Several simple indices were chosen for the

present effort which include the volume, location, base dimensions and geometrical shape of the ebb

tidal shoal. These comparisons should at least show whether on a semi-quantitative basis the

laboratory results can portray that occurring in nature.



7.1 Volumetric Comparisons

The volumes of the ebb tidal shoals for the three inlets mentioned above were calculated via

the same method used for the laboratory models in order to maintain consistency. From the

hydrographic survey maps, profiles were first constructed across the contour plots perpendicular to



















200


c150
a



CO
(D


0 50 100 150 200 250 300 350 400
Longshore Distance (m)


Figure 21: Sebastian Inlet Bathymetry Surveyed in 1989




EC1 Bathymetry After 3200 min


3 4 5 6 7
longshore distance (m)



Figure 22: ECI Bathymetry After 3200 min..
































,I-



//




I~ -
*-:-.-)
;~r~Lcfl
,ai ~WP~~tf M~ UYOU O EL ~ .9k .t~k'( ,4



.-- 9 !
Figuc 23Jupier nictBatbmetr (aLer *Coata Planning &C1 Engincrng,199)
















I .1 .


BOCA RATON INLET- .
AND
.OFFSHORE SHOAL BATHYMETRIC CHART -.
APRIL 18. 1990'





"... en.., .... 4_____ -,__ ".p ..' c '. ... ,.
-""-, .... ..... ...." '- --- .. -



-* ----; --. .... ----,--.,. -.- -- "----- --* ..





-"...,....... .
--*-
"*S " ","I, U .w LI 11 __


"- .. ,,. :-.L_...-,,.- "- --1, .






I -.4 !--I


SMIET 1--

Figure 24: Boca Raton Inlet Ebb Shoal Bathymetry (after Coastal Planning & Engineering, 1991).


















BOCA HATON BEACH


TOPOGRAPHIC ANO OFFSHORE
OCTOBER. 21.1990
I ,


BATHYMETRIC SURVEY


1 I f a


SCA0 i 400flc
(CutM In rE


N-


C asa i nos..
sast ..,


Figure 25: Boca Raton Inlet Bathymetry (after Coastal Planning & Engineering, 1991).


I


I









44

the downdrift shoreline. The configurations of ebb tidal shoal were then established by plotting these

contours in reference to the updrift and downdrift shoreline profiles uninfluenced by the inlets.

Appendix G-I contain the profiles for Sebastian Inlet, Jupiter Inlet, and Boca Raton Inlet

respectively.

Large discrepancies occurred between the volume calculations obtained using the updrift

and downdrift uninfluenced profiles as reference contours for both Jupiter and Boca Raton Inlets.

This was due to the significant offset of the updrift and downdrift shorelines. The downdrift

uninfluenced profile was selected here as the reference contour. For Jupiter Inlet, a volume of

315,000 m3 was calculated using the uninfluenced downdrift profile which compares favorably with

the 300,000 m3 volume calculated by Marino and Mehta (1996). A volume of 440,000 m3 was

calculated using the uninfluenced downdrift profile for Boca Raton Inlet ebb tidal shoal which is

much less than the 800,000 m3 obtained by Marino and Mehta (1996). For Sebastian Inlet, a volume

of lx106 m3 was calculated using the uninfluenced downdrift profile. This volume agrees with the

volume calculated by Wang et al. (1992) where the updrift profile was used as a reference.

The laboratory experiments were of generic nature with no designated scale to represent any

specific inlet in nature. As noted earlier, the results are likely to be valid only if the horizontal scale is

in between 40 to 100. Volumes were computed based on two horizontal scales of 60 and 100. The

equivalent prototype volumes of EC for a scale of 60 and 100 were computed to be 89,500 m3 and

374,200 m3, respectively. These values are seen to be generally smaller than that of the three

prototype inlets but are of the same order of magnitude. However, the time scale in the experiment

reflected only between twenty to thirty days of storm wave conditions, depending upon whether the

horizontal scale is 60 or 100. It was estimated by Wang et al. (1994) that along the east coast of

Florida the net longshore sediment transport produced by twenty storm days from the dominant wave

direction is approximately equivalent to the annual longshore transport rate. With this duration the









45

ebb tidal shoal has not yet reached its equilibrium condition, hence, the corresponding ebb tidal shoal

volume is also likely to be smaller than its potential capacity. It is, however, difficult to estimate the

volume that the ebb shoal could actually achieve should the experiment be continued until

equilibrium is reached. Thus, given that the ebb tidal shoal did not reach an equilibrium size in the

experiment, the laboratory ebb shoal volume seems reasonably representative of ebb tidal shoals

associated with small inlets found in nature.



7.2 Ebb Tidal Shoal Location

Contours of the ebb tidal shoal were constructed using the accumulation of sediment above

the reference contours discussed above for each inlet. The location of the ebb tidal shoal with respect

to the inlet entrance can be approximated from these contours which are shown in Figures 26-29 for

Sebastian Inlet, Jupiter Inlet, and Boca Raton Inlet respectively. The locations discussed here are

determined by a radial distance and a bearing angle. The origin of the baseline is set at the mid point

between the tips of the two jetties and the orientation of the baseline is determined as parallel to the

updrift jetty near the entrance. This definition is shown in Figure 30. The radial distance is measured

from the center of the ebb tidal shoal defined by the point of maximum accumulation. The bearing

angle is defined as positive in the clockwise direction. Table 10 contains the calculated volumes and

locations for Sebastian Inlet, Jupiter Inlet, Boca Raton Inlet, and EC1.

It can be seen that the radial distance to the ebb tidal shoal at Sebastian Inlet, Boca Raton

Inlet, and EC 1 are in the same order but is considerably longer at Jupiter Inlet. The bearing of the

laboratory ebb tidal shoal is much smaller than that of the three prototype inlets. This indicates the

ebb tidal shoals of the three prototype inlets are located further downdrift from the inlet than the ebb

tidal shoal in the model. One could speculate that a young ebb tidal shoal probably will form closer

to the inlet but gradually moves downdrift when it becomes more mature.














1989 Sebastian Inlet Ebb Shoal Above Downdrift Reference Contour


100 150 200 250 300
Longshore Distance (m)


Figure 26: Sebastian Inlet Ebb Tidal Shoal.


EC1 Ebb Tidal Shoal After 3200 min


3 4 5 6 7
longshore distance (m)

Figure 27: EC1 Ebb Tidal Shoal After 3200 min.













Jupiter Inlet Ebb Shoal Above Downdrift Profile


800



700



600

E
a)
c 500
CO



- 400



300



200



100


0..5
-S
-^- ^ s--


200


300 400
Longshore Distance (m)


Figure 28: Jupiter Inlet Ebb Tidal Shoal Above Uninfluenced Downdrift Profile.


900


N
4..
-0 z-
-~4-
---N^ ^-O


100


500


600















ioal Contours Above Downdrift Profile


350



300


E
a,
O 250



o
200
| 200


- -


100


0 50 100 150 200 250 300
Longshore Distance (m)

Figure 29: Boca Raton Inlet Ebb Tidal Shoal Above Uninfluenced Downdrift Profile.


Boca Raton Inlet


*- - --1














6-

5.5





8 Siradial distance

0 3.5 -









3 4 5 6 7
longshore distance (m)


Figure 30: Baseline Definition for Determining the Radial Distance and Bearing Angle.



Table 10: Calculated Ebb Tidal Shoal Volumes and Locations for Sebastian, Jupiter,
Boca Raton, and Laboratory Inlets

Inlet Ebb Tidal Shoal Radial Distance to Bearing Angle to
Volume Ebb Tidal Shoal (m) Ebb Tidal Shoal (m)
(m')
Sebastian 1,000,000 160 32
Jupiter 315,000 615 27
Boca Raton 440,000 180 40

EC1 (1:60) 89,500 155 8

EC1 (1:100) 374,200 310 8









50

7.3 Geometrical shape

The geometrical shapes of the four cases are shown in Figures 31-34. It can be seen that with

reference to a natural beach profile, the shapes of the ebb tidal shoal for all four cases are similar and

can be roughly described as cone shaped. The shape of the base varies from near circular (EC1 and

Sebastian Inlet) to elliptical (Jupiter Inlet and Boca Raton Inlet). For the elliptical shaped base, the

major axis is approximately parallel to the shoreline. The geometrical parameters including the major

and minor axes, the vertex height, and aspect ratios are given in Table 11. The three dimensional

plots of these four idealized ebb tidal shoal are shown in Figure 35.



Table 11: Geometrical Parameters for Sebastian, Jupiter, Boca Raton, and Laboratory Inlets

Inlet Major Axis Minor Axis Height Minor / h / Minor

(m) (m) (m) Major
Sebastian 95 95 4 1 0.04

Jupiter 340 175 2 0.51 0.01

Boca Raton 200 95 2.5 0.48 0.026

EC1 (1:60) 78 78 3.2 1 0.04

EC1 (1:100) 130 130 4.8 1 0.037


































0 50 100 150 200 250 300 350 400
Longshore Distance (m)

Figure 31: Geometric Shape of Sebastian Inlet Ebb Tidal Shoal.




6-

5.5


5 4







3--4
2.5- jJ J

2--

1.5 *^- B

3 4 5 6 7
longshore distance (m)

Figure 32: Geometric Shape of the Laboratory Inlet Ebb Tidal Shoal.


































0 100 200 300 400 500 600
Longshore Distance (m)

Figure 33: Geometric Shape of Jupiter Inlet Ebb Tidal Shoal.


0 50 100 150 200 250 300
Longshore Distance (m)


Figure 34: Geometric Shape of Boca Raton Inlet Ebb Tidal Shoal.














3-D View (Exagerated vertical scale)


Sebastian Inlet








Jupiter Inlet








Boca Raton Inlet








Laboratory Inlet


Figure 35: Idealized Ebb Tidal Shoals for Sebastian, Jupiter, Boca Raton, and Laboratory Inlets.


Plan View















CHAPTER 8
EVALUATION OF EBB TIDAL SHOAL MINING


In this chapter the subject of applying the experimental results to assess the potential of ebb

tidal shoal mining is addressed. The question of whether ebb shoal mining is viable for downdrift

beach nourishment has to be evaluated in terms of feasibility and benefit under a set of economical

and environmental constraints. Here we illustrate how the laboratory results can be applied to address

some of these questions excluding the environmental constraints.

The question of economic feasibility is based mainly on the requirement of renourishment

frequency. The period of renourishment can be computed by equating the mined volume from the ebb

shoal to the cumulative volume of erosion in the nourished downdrift region. The time required to

reach this cumulative volume (or a fraction/multiple of it) is the required period of renourishment.

This cumulative volume can be computed in two different ways; one is an absolute volume and the

other is a relative volume. The absolute volume is the cumulative downdrift erosional volume

measured with respect to the fixed initial condition. This volume can be read directly from the

ordinate in Figure 15 for different elapsed time and is defined as Ta. As an example, the mined

volume from the ebb shoal in the laboratory is approximately equal to 2.1 m3. This volume was

placed on the downdrift beach segment. From Figure 15, for a cumulative volume of 2.1 m3, the

corresponding elapsed time can be obtained from the EC2 curve as equal to 2,100 min. This is the

time period in which the nourished quantity of 2.1 m3 placed on the downdrift side from mining has

been eroded away.









55

The relative volume, on the other hand, is computed with respect to the no-mining condition.

Since the downdrift beach is also erosional under the no-mining condition (a background erosion so

to speak), this volume is clearly different from the absolute volume. This volume also depends upon

the timing of ebb shoal mining. If the mining takes place when the ebb shoal is at a young stage the

background erosion is higher than that at a mature stage. This relative volume is more relevant in

terms of economic evaluation as it is measured with respect to the existing condition. The present

experiment was carried out in sequence, therefore, the erosion rate at the end of EC1 (at 3200 min)

should apply. From Table 7, this rate is obtained as 0.0219 m3/hr, or 3.67x 10- m3/min. The

following equation then approximates the background erosion:


V = 3.67x10 -4t


where V. is the volume of the background erosion in m3 based on the no-mining case and t is time in

minutes. Similarly the post nourishment cumulative downdrift erosion volume is given by


Vm= 1.9+4.7x10-4(t-1500) for t>1500


where V, is in m3 and t is in min. Thus, relative to the no-mining case, the return period for a net

volume loss of 2.1 m3 becomes,

2.1= V V


which yields T, = 8800 min and is defined as the relative renourishment period.

Based upon the present experiments, there is a significant difference in magnitude between

T, and T,. If one assumes here that a 3200 min laboratory test time is equivalent to one year

prototype, then the prototype absolute renourishment period is equal to 8 months whereas the relative

renourishment period is equal to 2 years and 9 months. The absolute renourishment period is clearly









56

unrealistically low. One of the major factors that influenced this low value is the laboratory test

condition using storm waves throughout. This storm wave test condition caused rather drastic beach

profile adjustment during the initial period in the form of an offshore bar. This contributed to the

bulk of the beach erosion. Since the test contained no recovery process the volume stored in the

offshore bar though still in the limits of the nourished beach segment is not accounted for.

Another way of estimating the renourishment period is by comparing the volume lost

downdrift of the nourished region with the volume of the mined quantity. In this way, sediment

retained in the offshore bar is not counted as a loss but preserved in the system. Using the same

approach as the first method, the volume lost downdrift can be estimated by


Vd= 1.0+.x104(t-1,400) for t> 1,400


where Vd is the volume lost downdrift in m3 and t is time in min. The renourishment period can be

calculated by equating the mined volume to this downdrift volume and solving for t. The

renouishment period, Td, so computed is equal to 12,400 min, or approximately equivalent to 4

years in prototype. This method appears to be more reasonable for defining the renourishment period

The next question to be addressed is whether it is feasible for repeated ebb tidal shoal

minings. This depends on whether the ebb tidal shoal can be regenerated within the required

renourishment period. Again using the same approach given above, the ebb shoal regenerating

volume can be calculated based on the following empirical relationship which is derived from Figures

13 and 14, or values given in Table 6:


V, = 0.31+2.64x10-4(t-1,200) for t > 1,200


where V, is the volume of ebb shoal regeneration in m3 and t in minutes. For V, to regenerate to 2.1

m3, the required time period is T, = 7,980 min., or 2 years 6 months prototype equivalent.










57



It should be remarked here that material presented in this section is more for illustrating the

methodology rather than provide quantitative prediction for an actual inlet. Although the values as

presented appear to be reasonable, there is no field evidence to support them.















CHAPTER 9
SUMMARY AND CONCLUSIONS


The present study aimed at determining the impacts on the inlet-beach system due to partial

mining of ebb tidal shoals through laboratory experiments. The experiments consisted of studying a

generic inlet with main focuses on downdrift beach erosion and ebb shoal borrow area regeneration.

The effect on downdrift erosion is of obvious importance as the goal of ebb shoal mining is to use the

mined sand to renourish and protect the downdrift beach. Mining the ebb tidal shoal would not be

worthwhile if the erosion rate increased dramatically, thus quickly negating the benefits of the

renourishment. The regeneration process is of interest to determine whether the borrow area will

reattain its post-dredging configuration and at what rate. This is important in order to assess whether

or not or how often the ebb tidal shoal can be mined repeatedly. In the present study, these effects

were analyzed based on the removal of a seaward portion of the ebb tidal shoal. The major findings

from the experiments are as follows:

1. Ebb shoal mining increased the volume of downdrift erosion. This increase is

mainly due to the increase of erosion rate in the early stage right after mining the ebb shoal.

However, the rate of erosion soon becomes closer to but still slightly larger than the rate of erosion in

the natural case.

2. In the regeneration process, the mined ebb shoal initially grew at a slower rate than

the natural case. However, the rate of growth soon equaled and slightly exceeded the rate of growth

compared with the natural case.

3. Inlet channel shoaling increased due to ebb tidal shoal removal.










59

4. Downdrift longshore transport volume as well as transport rate also increased due to

ebb tidal shoal removal. However, the rate of downdrift transport gradually decreased and became

less than that of the natural case as time progressed.

The laboratory ebb tidal shoal characteristics were compared with the characteristics of three

small to medium sized Florida east coast inlets. The similarities among them were discussed. These

results combined with those by Wang et al. (1995) who studied the evolution process of the ebb tidal

shoal in similar laboratory conditions as the present study demonstrate that ebb tidal shoals similar to

those occurring in nature can be duplicated in the laboratory. The results presented here also showed

the potential of parameterizing ebb shoals, both in the laboratory and in nature.

Methods were proposed to evaluate the feasibility and potential of ebb shoal mining utilizing

laboratory data. The methods address two issues: the renourishment intervals based on downdrift

erosion and the ebb shoal regeneration intervals to meet the required volume. These methods were

applied to the present model study.

In summary, the present study demonstrated the feasibility and effectiveness of simulating

the inlet-ebb tidal shoal processes in the laboratory. Partial success was also achieved in determining

the effects on the inlet-beach system due to mining the ebb tidal shoal. The laboratory results showed

that utilizing ebb tidal shoal mining for downdrift nourishment is potentially feasible from the point

of view of renourishment and regeneration requirements. However, the study is only exploratory; any

quantitative extrapolation for field application at this stage is not recommended. Clearly, more

comprehensive work is necessary on the subject. As mentioned earlier, the laboratory test conditions

did not realistically represent the environmental conditions in nature for long term predictions. The

parameters tested were also very limited as only one set of geometry was tested with a limited time

duration and under one set of wave-current combinations.









60

In the present study, the seaward portion of the ebb shoal was removed, however, there are

many aspects that can be analyzed for future studies of ebb shoal mining. One suggestion is to

analyze in more detail the effects due to various borrow area locations such as a seaward portion

(present study), landward portion, top of ebb shoal, center of ebb shoal, or the sides of the ebb shoal.

Another suggestion is to determine the effects due to the percentage of the ebb shoal volume mined

and whether a cutoff percentage exists below which adverse impacts on downdrift erosion are

minimal. The effects on channel hydraulics and channel shoaling are also important in ebb shoal

mining.

One critical area where more study is badly needed is physical modeling. In the present

study, the modeling laws proposed by Wang et al. (1994) were adopted. They are basically the

extension of modeling laws for beach profile evolution process. Although they were evaluated by

Wang et al. (1995) for the application to 3-D inlet experiments and the present study appeared to

yield reasonable results based on them, the modeling laws are restrictive and strictly speaking should

apply only to the downdrift profile development. Refinement is needed to address the temporal scales

of shoal evolution and channel shoaling. Similarly, restrictions were imposed by using unrealistic test

conditions, of which the most serious one is the absence of beach recovery process. Hence, much

work remains to be done to understand ebb tidal shoal dynamics and improve movable bed physical

modeling of the ebb tidal shoal.















APPENDIX A
CROSS-SHORE PROFILES FOR EC1 AFTER 3200 MIN


Appendix A shows cross-shore profiles for EC1 after 3200 min at every survey line

compared to the initial bathymetry of EC1.













EC1 Profiles 1-5
0.5,


0-


-0.5 '
0 1 2 3 4 5 6 7


0.5


0


-0.5

0.5


0


-0.5

0.5


0


-0.5


0 1 2 3 4 5 6 7








0 1 2 3 4 5 6 7








0 1 2 3 4 5 6 7


-r


3 4
offshore distance (m)


-I


FI C I I I


Figure Al. Cross-shore Profiles for EC 1 after 3200 min for Survey Lines 1-5
(Dashed Line Represents Initial Profile).





62


-n


. 0
0













63





EC1 Profiles 1-5
0.5







-0.5 ,--,
0 1 2 3 4 5 6

0.5,,,,



0-



-0.5
0 1 2 3 4 5 6
n c;--- --------------- --


-A


0 1 2 3 4 5 6
S---


.
0


3 4
offshore distance (m)


Figure Al. Cross-shore Profiles for EC1 after 3200 min for Survey Lines 1-5
(Dashed Line Represents Initial Profile).


-n


s


L ------ -----


--e
5


p


I I I I t I







64




EC1 Profiles 6-10


0 1 2 3 4 5 6 7
0
E
.0

--0.5

0 1 2 3 4 5 6 7
0


.0

| -0.5
0 1 2 3 4 5 6 7
0.5 ,-,





-0.5
0 1 2 3 4 5 6 7
0.5 1 I -Ii-I


0 1 2 3 4 5 6
offshore distance (m)



Figure A2. Cross-shore Profiles for EC1 after 3200 min for Survey Lines 6-10.
(Dashed Line Represents Initial Profile).





















EC1 Profiles 11-15
;.


0 1 2 3 4 5 6
S0-


S0


. 0


U.0

0~ ---- ------ ------------






-0.5 '
0 1 2 3 4 5 6 7

0.5








_n g IIIIII


3 4
offshore distance (m)


0


Figure A3. Cross-shore Profiles for EC1 after 3200 min for Survey Lines 11-15.
(Dashed Line Represents Initial Profile).


-n


I I


-I


-n


-n


i I


-I


I i i 1


I I 1 II I I


SI I


--


--
----












66





EC1 Profiles 16-20


0


0..3 4


3 4
offshore distance (m)


Figure A4. Cross-shore Profiles for EC1 after 3200 min for Survey Lines 16-20.
(Dashed Line Represents Initial Profile).


3-


rL


0


-0.i


51 1 .


)I I I I I I -


I


-0.!=















APPENDIX B
CROSS-SHORE PROFILES FOR EC2 AFTER 3200 MIN


Appendix B shows cross-shore profiles for EC2 after 3200 min at every survey line

compared to the initial bathymetry of EC2.












68





EC2 Profiles 1-5


-A
0 1 2 3 4 5 6
n -


0
n r


-0.5'
C


1 2 3 4 5 6


0-



-0.5
0 1 2 3 4 5 6 7

0.5



0-



-0.5
0 1 2 3 4 5 6 7
offshore distance (m)


Figure B1. Cross-shore Profiles for EC2 after 3200 min for Survey Lines 1-5
(Dashed Line Represents Initial EC2 Profile).


-
- I I I


SI I I I


I I I I ------I


B E I I m Ill I I


r'


_n


',


*.


-.n


)









69



EC2 Profiles 6-10


0 1 2 3 4 5 6 7


S 1 2 3 4 5 6 7

-I




3 1 2 3 4 5 6 7


S1 2 3 4 5 6 7
) 1 2 3 4 5 6 7




1 2 3 4 5 6 7
0 1 2 3 4 5 6 7


3 4
offshore distance (m)


Figure B2. Cross-shore Profiles for EC2 after 3200 min for Survey Lines 6-10
(Dashed Line Represents Initial EC2 Profile).


0
._o

1-0.5


0




Z -0.5


0.5


0


-0.5


I I i I I


-0.5
0


I















EC2 Profiles 11-15
0.5

0

-0.5 i 4 5 6
0 1 2 3 4 5 6


-n


-n i


0


-I


S0 1 2 3 4 5 6 7
0.5



0
-0.5 7--
0 1 2 3 4 5 6 7


3 4
offshore distance (m)


Figure B3. Cross-shore Profiles for EC2 after 3200 min for Survey Lines 11-15
(Dashed Line Represents Initial EC2 Profile).


0 -

5;


* I


[ I I
-I- 7


-0.5


0


Ik 1 .. I.111 1... 11 11 1. I .. I .I I . I I ,.,. ., .... 1.1,,1













71




EC2 Profiles 16-20
c;.


-n0


-n


'I


0


-I


0


-0.5'
C


U.0 I


0- L


-0.5 I
0 1 2 3 4 5 6


:ii

.1 -

_______________
0 3 4


3 4
offshore distance (m)


Figure B4. Cross-shore Profiles for EC2 after 3200 min for Survey Lines 16-20
(Dashed Line Represents Initial EC2 Profile).


1 2 3 4 5 6


.0


SI I I I


SI


)


-0.

















APPENDIX C
BATHYMETRY SURVEYS FOR EC


Appendix C shows the results from each bathymetry survey in EC 1 after every time interval.

















0 min

E,5 -- -








0 2 4 6 8 10 12 14 16
40 min
6-
E5-
-30
c 4
3 -





1ihi
62









0 2 4 6 8 10 12 14 16
80 min


0 2 4 6 8 10 12 14 16
longshore distance (m)


Figure Cl: Bathymetry Contours for ECI after 0 min, 40 min, and 80 min.













74



120 min











0 2 4 6 8 10 12 14 16
160 min
6













52
-30

4
-20
3 --

o0



0 2 4 6 8 10 12 14 16
480 min
6:- -40 -




13
24 --



02
~1








0 2 4 6 8 10 12 14 16
longshore distance (m)


Figure C2: Bathymetry Contours for EC1 after 120 min, 160 min, and 480 min.
















800 min
6 -40
E 5
-30



353
02
4 1- -

0 2 4 6 8 10 12 14 16
1120 min
6-

0-30
. 6= J ."40 -





---- ---il-I..J------- ---- -------i----



0 2 4 6 8 10 12 14 16
1600 min


0 2 4 6 8 10 12 14 16
longshore distance (m)


Figure C3: Bathymetry Contours for EC1 after 800 min, 1120 min, and 1600 min.

















3200 min


0 2 4 6 8 10 12 14 16
longshore distance (m)


Figure C4: Bathymetry Contours for EC1 after 3200 min.


















APPENDIX D
BATHYMETRY SURVEYS FOR EC2


Appendix D shows the results from each bathymetry survey in EC2 after every time interval
















0 min


0 2 4 6 8 10 12 14 16
40 min


0 2 4 6 8 10 12 14 16
80 min


0 2 4 6 8 10 12 14 16
longshore distance (m)


Figure Dl: Bathymetry Contours for EC2 after 0 min, 40 min, and 80 min.
















120 min
I -40







or
2-

0 2 4 6 8 10 12 14 16
160 min
6-40






5- '



0 2 4 6 8 10 12 14 16














Iongshore distance (m)
480Figure D2: Bathymetry Contours for EC2 after 120 inn, 160 mi, and 480 mi
,-40









2 4 6 8 10 12 14 16

longshore distance (m)



Figure D2: Bathymetry Contours for EC2 after 120 min, 160 min, and 480 min.


















800 min








2 I



0 2 4 6 8 10 12 14 16

1120 min

-40


U)
c4




U)

0 2 4 6 8 10 12 14 16

1600 min
6-
-40
E5


3

62



0 2 4 6 8 10 12 14 16
longshore distance (m)


Figure D3: Bathymetry Contours for EC2 after 800 min, 1120 min, and 1600 min.
















3200 min

S-40



3
02-



0 2 4 6 8 10 12 14 16
longshore distance (m)


Figure D4: Bathymetry Contours for EC2 after 3200 min.

















APPENDIX E
CHANGES IN BATHYMETRY FOR EC 1


Appendix E illustrates the changes in bathymetry with respect to the initial bathymetry for

EC1 after all the surveys.

















40 min


6
E5
a)
4




0
52
ol


0 2 4 6 8 10 12 14 16

80 min
6

E5-

04


: 4q 2


0 2 4 6 8 10 12 14
0 2 4 6 8 10 12 14 16


120 min


E,5
0)
04

-3

02


0 2 4 6 8 10
longshore distance (m)


12 14 16


Figure El: Changes in bathymetry for EClafter 40 min, 80 min, and 120 min.













84




160 min


4 =. 4


4 I4 I 4



0 2 4 6 8 10 12 14 16

480 min





4
4
4

4
44
[ 1 ,7 ,0


Ei
I1
C'
cc















53
I-






(





o






2o







03
(




O


4

__ILIII I I
0 2 4 6 8 10 12 14 1
longshore distance (m)


Figure E2: Changes in bathymetry for EC1 after 160 min, 480 min, and 800 min.


0 2 4 6 8 10 12 14 16

800 min


>

I



t


5

4

3
2

1





6


1

3
3


6
5



3














1120 min



4

3 o


a -- L- L-

0 2 4 6 8 10 12 14 16
1600 min



8II I -4


L I-1. -i'---'- ---- ----


0 2 4 6 8 10 12 14 16
3200 min


( 12




___ ILi 1

0 2 4 6 8 10 12 14 16
longshore distance (m)


Figure E3: Changes in bathymetry for ECI after 1120 min, 1600 min, and 3200 min.


















APPENDIX F
ACCRETION AND EROSION PATTERNS FOR EC2


Appendix F illustrates the accretion and erosion patterns with respect to the initial

bathymetry for EC2 after all the surveys.



















6


4,



o2
0)
.W
=53


87



40 min


0 2 4 6 8 10 12 14 16

80 min
6I
5 I
I I


3- 44
2- 24 -- 6 8 1


10 2 4 6 8 10 12 14 16
0 2 4 6 8 10 12 14 16


120 min


0 2 4 6 8 10
longshore distance (m)


12 14 16


Figure DI: Changes in Bathymetry for EC2 after 40 min, 80 min, and 120 min.















160 min


E 5 I
I -I
s -4


3 34 4

-2

0 2 4 6 8 10 12 14 16
480 min
6 -* '
l5 I I
|.- 3- -^
4 -
3-




0 2 4 6 8 10 12 14 16
800 min


0 2 4 6 8 10 12 14 16
longshore distance (m)


Figure D2: Changes in Bathymetry for EC2 after 160 min, 480 min, and 800 min.













89




1120 min


0 2 4 6 8 10 12 14 16

1600 min


0 2 4 6 8 10 12 14 16


3200 min







-4
l---l
i 5.T2 -
+-:.;- 'i -


0 2 4 6 8 10
longshore distance (m)


12 14 16


Figure D3: Changes in Bathymetry for EC2 after 1120 min, 1600 min, and 3200 min.


E5
,--
0
t: 4
03

2
02
-r
I)



















APPENDIX G
CROSS-SHORE PROFILES FOR SEBASTIAN INLET EBB TIDAL SHOAL


Appendix G shows cross-shore profiles for Sebastian Inlet ebb tidal shoal based on a 1989

survey by Wang, et al. (1992). The profiles in this appendix include every other survey line between

the downdrift jetty and the downdrift limit. The profile of the updrift-most and the downdrift-most

survey lines are included for comparison.




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