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Impacts on the inlet-beach system of ebb tidal shoal mining

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Title:
Impacts on the inlet-beach system of ebb tidal shoal mining
Series Title:
UFLCOEL-97003
Creator:
Trudnak, Michael E., 1973-
University of Florida -- Coastal and Oceanographic Engineering Dept
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Gainesville Fla
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Coastal & Oceanographic Engineering Dept., University of Florida
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English
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viii, 103 leaves : ill. ; 28 cm.

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Subjects / Keywords:
Banks (Oceanography) -- Florida ( lcsh )
Beach nourishment -- Florida ( lcsh )
Inlets -- Florida ( lcsh )
Shore protection -- Florida ( lcsh )
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bibliography ( marcgt )
non-fiction ( marcgt )

Notes

Thesis:
Thesis (M.S.)--University of Florida, 1997.
Bibliography:
Includes bibliographical references (leaves 101-102).
Statement of Responsibility:
by Michael E. Trudnak.

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Full Text
UFL/COEL-97/003

IMPACTS ON THE INLET-BEACH SYSTEM OF EBB TIDAL SHOAL MINING by
Michael E. Trudnak Thesis

1997




IMPACTS ON THE INLET-BEACH SYSTEM
OF EBB TIDAL SHOAL MINING
By
MICHAEL E. TRUDNAK
A THESIS PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
MASTER OF SCIENCE
UNIVERSITY OF FLORIDA

1997




ACKNOWLEDGEMENTS

I would like to express my sincere appreciation and gratitude to my advisor and supervisory committee chairman, Professor Hsiang Wang, for his continuous support and guidance throughout my study at the University of Florida. My thanks also extend to Dr. Robert G. Dean and Dr. Robert J. Thieke for serving as members on my supervisory committee. Special thanks go to Dr. Lihwa Lin who gave me helpful advice and suggestions.

ii




TABLE OF CONTENTS
A CKN O W LED G EM EN TS ...........................................................................................................
LIST O F FIG U RES .................................................................................................................
LIST OF TA BLES .................................................................................................................
A BSTRA CT .....................................................................................................................................
CHAPTERS
1 INTRO DU CTIO N ................................................................................................
2 LITERA TURE REV IEW .....................................................................................
3 LABORATORY CONSTRAINTS AND MODELING LAWS ........................
3.1 Considerations and Constraints ........................................................
3.2 Scaling Law s .....................................................................................
4 LABO RA TO R Y EXPERIM EN TS ......................................................................
4.1 D esign of Initial Inlet-Beach M odel ................................................
4.2 Test Conditions ...............................................................................
4.3 Design of Ebb Shoal M ining ............................................................
4.4 Test Procedures ................................................................................
5 LABORATORY EBB TIDAL SHOAL DEFINITION AND
CA LCU LATION S ...............................................................................................
5.1 Defining the Ebb Tidal Shoal in the Laboratory ...............................
5.2 Ebb Tidal Shoal V olum e Calculations .............................................
6 EX PERIM EN TAL RESU LTS .............................................................................
6.1 Ebb Tidal Shoal G rowth ...................................................................
6.2 Beach Erosion ...................................................................................
6.3 Inlet Channel Shoaling ......................................................................
6.4 Accumulation of Sand at Dowvndrift Boundary and Inside Inlet .....

iii

ii
v
vii viii
1
5
7
7
14 18 18
20 22 22
23 23
24 26 31
31 35
35




7 COMPARISONS WITH PROTOTYPE DATA ................................................ 39
7.1 Volumetric comparisons .................................................................. 39
7.2 Ebb Tidal Shoal Location ............................................................... 45
7.3 Geom etric Shape ............................................................................. 50
8 EVALUATION OF EBB TIDAL SHOAL MINING.................... 54
9 SUMMARY AND CONCLUSIONS ................................................................ 58
APPENDICES
A CROSS-SHORE PROFILES FOR ECI ............................................................. 61
B CROSS-SHORE PROFILES FOR EC2 ............................................................. 66
C BATHYMETRY SURVEY FOR ECL ................................................................ 71
D BATHYMETRY SURVEY FOR EC2 ............................................................... 76
E CHANGES IN BATHYMETRY FOR ECI ....................................................... 81
F CHANGES IN BATHYMETRY FOR ECI ....................................................... 85
G CROSS-SHORE PROFILES FOR SEBASTIAN INLET ............... 89
H CROSS-SHORE PROFILES FOR JUPITER INLET ................. 93
I CROSS-SHORE PROFILES FOR BOCA RATON INLET .............. 97
R EFER EN CES .............................................................................................................................. 10 1
BIOGRAPHICAL SKETCH ......................................................................................................... 103

iv




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 Regim e 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 EC 1 after 3200 min. ................................................................ 24
9. Bathymetry Contours for ECL 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 ECL 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 I and EC2. .................. 32
15. Volume of Downdrift Erosion Versus Time for EC I and EC2. ...................................... 33
16 Rate of Downdrift Erosion Versus Time for EC 1 and EC2. ........................................... 33
17. Volume of Accumulation at Downdrift Boundary Versus Time for EC I and EC2. .......... 36
18 Rate of Accumulation at Dowmdrift Boundary Versus Time for EC I and EC2. ............... 36
19. Volume of Accumulation Inside Inlet Versus Time for EC I and EC2. ............................. 37

V




20. Rate of Accumulation Inside Inlet Versus Time for EC 1 and EC2. .................. 37
21. Sebastian Inlet Bathymetry Surveyed in 1989. ................................................................... 40
22. EC 1 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. ECL 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 Deternining 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

vi




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 I. ................ 4
3. Summary of Fall Velocity Distorted Models. ........................................................................ 15
4. M odified M odeling Law ...................................................................................................... 17
5. Inlet Model Experimental Conditions. ................................................................................. 20
6. Volume of Ebb Shoal and Rate of Ebb Shoal Growth for EC I and EC2. ........................... 34
7. Volume and Rate of Downdrift Erosion for ECI and EC2. ................................................... 34
8. Volume and Rate of Accumulation at Downdrift Boundary for EC 1 and EC2. ................... 38
9. Volume and Rate of Accumulation Inside Inlet for EC 1 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

Vii




Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science IMPACT ON THE INLET-BEACH SYSTEM OF EBB TIDAL SHOAL MINING
By
Michael E. Trudnak
May 1997
Chairperson: Hsiang Wang
Major Department: Department of Coastal and Oceanographic Engineering
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 crosssection 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.

viii




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

I




2
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 (Mehlta et al., 1996)

Mining Site
Seaward side of northcm 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

Yeta 1988 1993 1993
1981 1988 1985

1995
1994

Volume (tt')
405,000
1.020.000 720,000 501,000
1.220,000 169,000 392,000
2,140,000

Pon Royal So nd. SC Seaward edge ofdelta 1990 596.000 Downdrtil beach 76 cm Cuurchc&a Fiipp. SC North delta of entrance 1974 469,000 Updeif beach 51-61 cm pipche 1980 1,080,000
Pon lbidro, SC Landward edge of delta 1990 524,000 Beach eroded by entrance flood 76-84 cm pipeline channel
Captain Sain's. SC Closed off migrating old entrance, creating a 1983 134,000 Operation meant to nourish Earthmovers and BuIldozers new entrance updrift of the old one (by tides and waves) dowdrift beach 99,000 m' to close old channel I log, Sc Shore-attached delta 1990 288,000 Updrifl beach hydraulic hoc at low tide Towsend's, NJ Updrif entrance swash bar complex 1978 483,000 Updrif beach 76 or 91 cm CuttrhcaJ 1983 626,000
Townsend's. NJ DowndriA entrance awash bar complex 1987 1.030,000 Surrounding beaches 76 or 91 cm Cutcrhead (heat Jg, NJ Undeternined portion ofdchla 1992 to 1994 4,900.000 Downdjift beach Dustpan or I opper dredges Absecon, NJ Spit attached to north jetty 1986 76.500 Downdrift beach 76 or 91 cm Cutterhead

Placement Location Updrift beach
Downdrift beach Uprift beach
Downdrift beach

Dosndrift beach Downdrift beach

Method of Dredging
61 cm Cutterhead Dustpan Dredge Dustpan Dredge 53 cm Cutcrhead

61 cm Cutterhead 76 cm Cutcrhead

Entrance
John's Pass, FL longboat Pass. Fl. New Pass, Fl, Redlish Pass, F-L

Boca Raton. L, Jupiter FL Nassau Sound, FL.t

L.J




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

lIL -i lts
be-h -a teetered, reduced shoaluig in entrance cluuml due to sand tuappng ir borrow area

Adverse Iinpascts Increased beach crosion ii, ie Viciniy doe to reduced send bypassing

ioaiaro string
Bonuw area shoaWe .1 the rate uf 2-4000 il' holoa 19Mgto 1992

t ongboat Pa/ Calculated wave reflection patterns showed a reduction ofsedinent None were predicted to occur; no impacts were monitored Between Dec. '91 and Dec. '92 Longboal Pass bonow area vousine New Puss, FL "trapped" by dehas and a more even spreading of wave energy to increased by 150,000 mi however, between Dec '92 and April '93 the south ofeach entrance (due to Maci 13-14 stone) bonow area volince decreased by 41,000m'
R1edhi Piak. FI. Erosion protection for downdiit shorcneu; accretion to the north of No specific studies were performed Approxaiately 10.000 i' uffiae-giainied material was caned ito the cillaice and south of the project die borrow area within 18 months after 19i project; between 1989 aid 1991 35.000 m' filed both (1981 and t9Mf) bonow awe
B.oc Reruoi, 11. beach Eision contained, improved navigation conditions over delta Feeder beach within 600 in of renrance eroded critcally, beach bac I kin south of erouance grew by an average of i Ill, die and minitennce of water quality in Lake Boca Raton nourinihent project planurd for 1995 using dto sediment entire ebb delta iituding bonow arca exceeded pie-project voiimes Jupe, I I. Erosion pictection for dowildilt stioreilie None were predicted to occur, including focusing of wve energy Oni Pie- and post-project surveys of fill area to be camed out jetties, changing of littoral pattern or increased salinity in
Loxahatchce River
Nassau S.-n, FL Reflaction analysis for borrow area showed a reduction of wave None were predicted to occur No monitorng of tie relict delta region energy on Atorelime and &it increase ofenergy in the sound,
rusultiig in decreased sdhnerit ransport
P~li Royal Souid, SC ttitigated cluunic cosion problem with a predicted 8 year project None were predicted to occur No Moninoring of delta life
I rlpp, SC Timpway Beach Noiislunent No studies were performed; no inipacts were monitored Rapid recovery of bonow area, approximately 153.000 ni' accunnulatd in delta since 1980
Polt Lideo, SC Diedging the ebti dclia moved die channel 125 m offshore, None were predicted to occrr; no impacts were monitored Sedriurent filled the borrow area, and the channel slowly grated removig the source of scour aid reriourishing die beach Landward towards the equitbriwn position Captain Sar's, SC Rcct delta "pushed" ashore by wave action nourished the beach at None were predicted to occur, no iupacts were monitored Entrance began migrating south st its previous rate the rate of 130,000 u'/yr between Mar. 83 to May '85, totally
1. 150.000 i' by 1993
IJog, SC Emekrlgncy iwiailuncrt for heavily arnoied sections ofhorelae Dia filled witi seiduent at die expense otlutis fwitier olhuiore Pusiuoun aflog idri cluhanel did not als taud 1iyre liach fultewlwn liricane lugo and the downdiftaiortie. 7.000 m' of reiadial liourisluaii shorlin; six mond after the project, 95 of the dry beach was became necssstry to guard dadrin shorcicre recovered due to noawiuhnent aid seasonal efccts Twnisends, NJ Beach iRoutisluneit Mining redirected the ebb channel northward through die delta, Cntical 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 charnl once occurred
Towvneud's. NJ Emergency Rerourishment, redirection of channel No studies were done; no impicts were monitored hitottring to very channel position
Great Egg, NJ beach Renouwisuent No studies were performed iloautoring of delta system planned A becon. NJ Beach Renourishment No studies were performed 43% of fill remained in 1991, soma sesinast waa washed offahoas; no monitoring of dela

FillriltaC Juli's Pas, 1-.




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.

5




6
Sill (1981) and Havter (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 I 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

7




8
long, and I 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 I 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 I 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 wNith 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 midsized 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 I which plots tidal prism versus ebb tidal shoal volume.
100
50 &9X 1.a4 p (Marino, 19S)
- -. a 6.08 x10 3pZ (Walton and Adams, 1976) E St. Marys r2f SL arys V 10
x St. Augustine
X FL George
. / Nassau S. Johns Lake Worth x / Sound I'/.-xSt. F- pierce
Baker Houover x Luca Poncs de Leon
1.0 Sebastan x Uatanzas
-j a.5 B oca Rao x
Jupit.
Ju X X South Lake Worth : X Pt. Canaveral
0.1 1 1 1 I I I I
0.1 0.5 1.0 5 10 50 100 5001000 EBB SHOAL VOLUME, V (x 10 6m2 )
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 bathymetrv 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 nondominant direction or negligibly small in magnitude (Wang et al., 1992).
Nassau Soundve
FL ~ unn Courg
00
0~r / Ls.ana
obastm R
L~aar Pie ovu
St L~...odenmn u

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




S1I
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 nondominant 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 ua
R = bai,
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

uVW




12

and the Shields parameter
'" 2sgd
where W is the fall velocity, u. 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.




13

9

idi

10 10
Re,Reynolds Number

Figure 3: Jonsson's Flow Regime Chart.

o No movemEnt trunajUan

a No movement I Bad lowd(BOL
2 Sed Load-Susponded bad IntgennedIata (3 SI) I Suspended load(S)
4 Sheatfiow(SF)
! 1-2 2
0
I L
No movement SL SS

2

as,

SL.

10*'
Shields Parameter

10,

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

Turb
Than. Won Ti~i Laminar
Transitbn Rough turbuls

10,

E

11

101

10
10

10

nt

id

rinfisilon
3-4




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 N,=60, N5=4 1, N-r=9.5, and N.=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) A=(N, N=. A=IN.
Vellinga (1982) N 04 078 ?T NrN. N=IN,
Hughes (1983) NV=(N)V N=N //NV N=N /NN
Wang et al. (1994) Na=(NV.) .4AN08 Nr=NI/N5 N =fN6
N = prototype to model scale ratio
W = fall velocity scale
S = sediment specific gravity scale
X = horizontal length scale
5 = vertical length scale
H = wave height scale
T= hvdrodynamic 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.




16

Dune Region Bar Region
- 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)h,
where H, and h, 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
NH=(-- a
Nt
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
iV =(N NfN 1V N=4fY N11=4N,




CHAPTER 4
DESIGN OF EXPERIMENTS
4.1 Desien 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 D50=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=Ax" 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

is




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.

-Z

MOVERBLE-BED INLET MOCEL

WAVE MAKER FLOOD FLOW FL WDFEIR EBB FLOW WEIR
GATE
WAVE
GUIDE
SURVEY LINES
FLOOD FLQW
GATE
EBB FLOW
WEIR
0 2 4 6 8

EBB FLOW
SGATE
NO TAP ANNEL

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, EC 1, 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 I 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 ECL 35 cm I sec 7 cm 7.50 1:2.9 1:14.5 No 3200 EC2 35 cm Isec 7 cm 7.5' 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 rn/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.




21

0.5
5.-.-. field data
-model simulation
E
0
-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 the initial model bathymetry. The initial bathymetry for EC 1 was described in section 4.1. The initial bathymetry for EC2 was obtained by modifying the final (after 3200 min) bathymetry of ECI 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 mini, 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 Definin2 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 EC 1 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

23




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 EC 1 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 6
- Ebb Shoal Boundary
I5 -4
4 4
5 ~-16 -0 +-------- -0 2 4 6 8 10 12 14 16 longshore distance (m)
Figure 8: Changes in Bathymetry in EC 1 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 EC 1 and EC2 respectively.




CHAPTER 6
EXPERIMENTAL RESULTS
Experiments EC I 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 ECI 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 I I 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 ECI and EC2 are given in Appendix E and Appendix F.

26




27

0 min

0 2 4

6 8 10 12 14 16

1600 min
-~~~~~ -- ......40
10

0 2 4

6 8 10 12 14 16

3200 min

0 (D
4 3
52
0

0 2 4 6 8 10 longshore distance (m)

12 14 16

Figure 9: Bathymetrv Contours for EC I after 0 nuin 1600 min, and 3200 min.

6
4 a3
0

-30
-20

6
3
52
0

-3




28

0 min
-40
- 20

0 2 4 6 8 10 12 14 16 1600 min

uc4
a
3 "2
0

0 2 4 6 8 10 12 14 1E 3200 min
0 2 4 8 10 2 1441

0 2 4 6 8 10 12 14 16 longshore distance (m)
Figure 10: Bathvmetrv Contours for EC2 after 0 min, 1600 min, and 3200 min.

6 F5
8
a4
13

82
0

,-4
..~ .........;... .....
-U




29

E 5
24
3
o1

E
C
0
(
z

-- -- -- --16 -- -___L- + .Z-t

0

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

Figure 11: Bathvmetry Changes for EC 1 after 800 min, 1600 min, and 3200 min.

800 min 6
5
4-4
3
2 ---8
0 2 4 6 8 10 12 14 1 1600 min
6
5
4- 4
-8--8 ---0 2 4 6 8 10 12 14 1E 3200 min

E
C
0
-C
0




30
800 min
6
5
4
3 4 2
- _--- -- -~ --- --- -1
0 2 4 6 8 10 12 14 1E 1600 min

6
TLKT

0 2 4

6 8 10 12 14 16

3200 min

2 4

6 8 10 12 14 16 longshore distance (m)

Figure 12: Bathvmetry Changes for EC2 after 80 0 min. 1600 min- and 3200 min.

E (D
c
(D I
0 In
0

1 4
U
(D I-

-4
8-~-

E5
c 4
3
S2
0
0~

6

- 16
-L- - -- -




31
6. 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 EC 1 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 EC I 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 0.0 17 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 ECI 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 EC 1. After 160 miin, the downdrift beach was eroded at about an equal rate in EC I and EC2. From 480 min to 3200 min, the downdrift




32

0.9
0.8
0.7
i0.6
0
CO, 20.5
00.4
E
0
> 0.3
0.2 EC2
0 500 1000 1500 2000 2500 3000 35 elapsed time (min)
Figure 13: Volume of Ebb Tidal Shoal Versus Time for ECI and EC2.

u--It,

0.14 0.12 0.1 0.08
0.06
0.04
0.02
0
-0.02

00

500 1000 1500 2000
elapsed time (min)

2500 3000 3500

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

EC1 EC2
I I

. 0




33

3

.3
>1

ECI EC2
0- 0 00 10 00 20 00 30

0 500 1000 1500 2000 2500 3000 35O0 elapsed time (min)
Figure 15: Volume of Downdrift Erosion Versus Time for ECL and EC2.

0.35 0.3 0.25
.20.2
2
0
2 0.15
0.1i o.05

0 500 1000 1500 2000 2500 elapsed time (min)

3000 3500

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

ECI EC2
-1
-i

[]_ 1 a

0.5|




34

Table 6: Volume of Ebb Shoal and Rate of Ebb Shoal Growth for ECL and EC2.
ECI EC2
Elapsed Time
(mn) Volume of Ebb Rate of Ebb Volume of Ebb Rate of Ebb
Shoal Shoal Growth Shoal Shoal Growth
(m') (m3/hr) (mi) (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 EC 1 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 I 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 EC I and EC2. This inlet channel shoaling was more severe in EC2 than in EC 1. The total sand volumes of inlet channel shoaling evaluated at 3200 min. in EC 1 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 ECI 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 ECL 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 EC 1 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 EC I 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 I and increased, though not significantly, for EC2.




36

1.2
1 S .8 -0.6
> 0.4
ECI
0.2 -- EC2
0
0 500 1000 1500 2000 2500 3000 3500
elapsed time (min) Figure 17: Volume of Accumulation at Downdrift Boundary Versus Time for ECI and EC2.
0.09
0.08
0.07
ECI
C
- 0.06
E
2o.04E
20.030.02
0.01 .
0
0 500 1000 1500 2000 2500 3000 3500
elapsed time (min) Figure 18: Rate of Accumulation at Downdrift Boundarv Versus Time for EC I and EC2.




37

0.16
0.14
0.12
E0.1
U 0.08
E
-0 0.060.04 0.02

/
/

/
/

/
ECi

/
/

EC2

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

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

0.03h

i

-I
-I

- 4
-.

- ECI
- EC2

, \

0 500 1000 1500 2000 2500 3000 3500

0 500 1000 1500 2000 2500 3000 3WOO elapsed time (min)
Figure 20: Rate of Accumulation Inside Inlet Versus Time for ECI and EC2.

0

'0.025
0.02
E
80.015 T 0.01
0.005

0.035




38

Table 8: Volume and Rate of Sand Accumulation at Downdrift Boundary for ECI and EC2.
ECI EC2
Elapsed Time
(min) Volume of Rate of Volume of Rate of
Accumulation Accumulation Accumulation Accumulation
(m) (m'/hr) (m') (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 EC 1 and EC2.
ECI EC2
Elapsed Time
(min) Volume of Rate of Volume of Rate of
Accumulation Accumulation Accumulation Accumulation
(m) (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, 199 1). These three east-coast Florida inlets were chosen based on their relatively recent bathymetry survevs that indicated distinct ebb tidal shoals. Figures 21-25 illustrate the bathymetries for these three inlets. The laboratory data from ECL 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 39




40

1989 Sebastian Inlet Bathymetry Survey9 10
7
2
4-

0 50 100 150 200 250 300 350 400
Longshore Distance (m)
Figure 21: Sebastian Inlet Bathymetry Surveyed in 1989

ECI Bathymetry After 3200 min
-35
-20 3
-15
5
,25
3 4 5 6 7
longshore distance (m)
Figure 22: EC I Bathymetry After 3200 min..

250
200 C 150 0100
50

6

4
3?.5
c
2.5

2 1.5

5.5




- ---- --I,
--- --
; w S
"-s -

--- N

S.
k 8. 484 *88V44 San, 4,. 8544.

Figure 23: Jupitcr Inlct Bathymcry (afler Coastal Planning & Engincering, 1989).

42
a~

1




BOCA RATON INLET
OFFSHORE SHOAL BATHYMETRIC CHART
APRIL 18. 1990 --- ---.* .-..S .. ...... ,n*.. ..... ... --*-l ------ 1
* w 6.r n 3 --.51--
- *.N -*** ,--
Jilli
Figure 24: Boca Raton Inlet Ebb Shoal Bathymectry (aftcr Coastal Planning & Engineering, 1991).




- - ---*-- -- M- e 8,
- .
-----------0661'*C I 390130
L3A~inS ZDIM3WAM4I1g 380I140 OtJY :flldVMDodlol HOV3g NJOMY 3G




44
the downdrift shoreline. The configurations of ebb tidal shoal were then established by plotting these contours in reference to the updrift and dondrift shoreline profiles uninfluenced by the inlets. Appendix G-1 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 in3 obtained by Marino and Mehta (1996). For Sebastian Inlet, a volume of 1x0 i3 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 ECI 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 EC 1.
It can be seen that the radial distance to the ebb tidal shoal at Sebastian Inlet, Boca Raton Inlet, and EC I 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 Lhe inlet but gradually moves downdrift when it becomes more mature.




46

1989 Sebastian Inlet Ebb Shoal Above Downdrift Reference Contour
250
200
E 2
0
a 150
50
C
o
0
505
0 0
0 50 100 150 200 250 300 350 400 Longshore Distance (m)
Figure 26: Sebastian Inlet Ebb Tidal Shoal.
EC1 Ebb Tidal Shoal After 3200 min 6
5.5
5
' 4.5 1
a
C 4
3.5 8
0
3
2.5
2
1.5
3 4 5 6 7
longshore distance (M)

Figure 27: ECI Ebb Tidal Shoal After 3200 min.




47

Jupiter Inlet Ebb Shoal Above Downdrift Profile 900 0.5
800
0.
700
1.5
600
C500
- 4- 4 00
200-N- -~ -+100 ---5
0
300S
200
0 100 200 300 400 500 600 Longshore Distance (m)

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




48

Boca Raton Inlet Ebb hoal Contours Above Downdrift Profile
450-
400 1.5 .
3. 2
350
300
E
Q1 O250
0
0 50 100 150 200 250 300 Longshore Distance (in)
Figure 29: Boca Raton Inlet Ebb Tidal Shoal Above Uninfluenced Downdrift Profile.




49

6

5.5

-4.5
E
(1)
4
3.5
3
0
2.5
2
1.5

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 (in) Ebb Tidal Shoal (m) (m 3)
Sebastian 1,000,000 160 32 Jupiter 315,000 615 27 Boca Raton 440,000 180 40 EC1 (1:60) 89,500 155 8 ECI (1:100) 374200 310 8

6 16
6 12
-radial distance bearing angl
--

5




50
7.3 Geometrical shape
The geometrical shapes of the four cases are shown in Figures 3 1-34. 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 (EC I 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 I1. The three dimensional plots of these four idealized ebb tidal shoal are shown in Figure 35.
Table I1: Geometrical Parameters for Sebastian, Jupiter, Boca Raton, and Laboratory Inlets
Inlet Major Axis Minor Axis Height Minor / h /Minor
(in) (in) (in) 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 ECI (1:60) 78 78 3.2 1 0.04 EC1 (1:100) 130 130 4.8 1 0.037




51
250
3
0100
3:
2+0 50 0
0
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
E4.5-4
3.5
0
.5
2
3 4 5 6 7 longshore distance (m) Figure 32: Geometric Shape of the Laboraton- Inlet Ebb Tidal Shoal.




52


- .- -1~ \ s- ~
-
S. -

0 100 200 300 400
Longshore Distance (m)

500 600

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

0 50 100 150 200 Longshore Distance (m)

250 300

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

\de\
450 01, 0

300* 250
200

.5 S

50
O
3 0 25
200

-+E

2
3
-5
0.5




53

Plan View

Sebastian Inlet Jupiter Inlet Boca Raton Inlet Laboratory Inlet

3-D View (Exagerated vertical scale)

0

.--

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




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 T.. 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 m, 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.

54




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 EC 1 (at 3200 min) should apply. From Table 7, this rate is obtained as 0.0219 m3/hr, or 3.67x 10' in/min. The following equation then approximates the background erosion: V =3.67x10 -4t
where V. is the volume of the background erosion in in3 based on the no-mining case and t is time in minutes. Similarly the post nourishment cumulative downdrift erosion volume is given by V,, =1.9+4.7x10-4(t-1500) for t>1500
where V., is in in3 and t is in min. Thus, relative to the no-mining case, the return period for a net volume loss of 2.1 in3 becomes,
2.1=V -V
m 9
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 +1.xI0 -4(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-l,200) for t > 1,200
where V, is the volume of ebb shoal regeneration in in3 and t in minutes. For V to regenerate to 2.1 in3, 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 dowindrift 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.

58




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 EC I AFTER 3200 MIN
Appendix A shows cross-shore profiles for EC 1 after 3200 min at every survey line compared to the initial bathymetry of EC1.




EC1 Profiles 1-5
5

0

C
0
C
0

1

0

1

2

2

3

3

4

4

5

5

6

6

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

.
.0

1

2

3

4

5

6

1

2

3 4
offshore distance (m)

5

6

7

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

62

A

7

0

.0

0.
*0.
0.

.5
0 .51

C
0
cc
0
0
C
(a
0
0

7

7

_n

0

-

5

0

0.5

0




63
EC1 Profiles 1-5

1

1

2

2

3

3

4

4

5 6

5

6

.5
0 .5
0 1 2 3 4 5 6 7
5
51
0 1 2 3 4 5 6 7
5
0 --

1

2

3

4

offshore distance (m)

5 6

7

Figure A 1. Cross-shore Profiles for ECI after 3200 min for Survev Lines 1-5
(Dashed Line Represents Initial Profile).

O0.

0

-0.5
0

E
0 cc
(a

0.51

0

7

0

0

7

C
0
C
0
C
0
Ca

0.
0.

-A

0

-

-

-0




E
.2
0
-0.
-0.
C Z~ -0.~

0

1

0

2

2

1

3

4

3 4
offshore distance (m)

5 6

5

7

6

7

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

64
EC1 Profiles 6-10
0
5
0 1 2 3 4 5 6 7
0
5
0 2 3 4 5 6 7
0
5 -r
S12 3 4 5 6 7
5
0 --

0.

C
0 0u

*1

C .D
W

0

-0.5

0

0.




65

EC1 Profiles 11-15

3

C

a
0
C

0
C
E
0
E
a
0
W

4

4

3 4
offshore distance (m)

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

0.5
0
-0.51
0
0.5 r

1

0

I I - -

6

7

3

0

0

0 1 2 3 4 5 6 '.5
0
.5
0 1 2 3 4 5 67
.5 TIII
0 -

'I

2

2

2

5

5

5

0
.0

1

0.

0

6

7

-0.5

0

6

7

51

7

-

1




66

EC1 Profiles 16-20

C
0 CD
0
0
0
C
0
Q
C
0
W
0
(D
Q

1

2

3 4
offshore distance (m)

5

6

7

Figure A4. Cross-shore Profiles for ECI after 3200 nuin for Suney Lines 16-20.
(Dashed Line Represents Initial Profile).

C

C
0

0
0

-a

0

U.0
0 -
0.51
0 1 2 3 4 5 6 7
15 1 1
0
0.51 - --- ---
0 1 2 3 4 5 6 7 ).5
0
.5
0 1 2 3 4 5 6 7 .5
0
.51
0 1 2 3 4 5 6 7 .5
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.

67




68
EC2 Profiles 1-5
0.51

1

E
a
C ca
(a a)

0 CO
0

1

2

2

2

2

2

1I

1

3

3

3

3

4

4

4

4

3 4
offshore distance (m)

5

5

5

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

0

-I

.05
0

5

6

7

0

0.

5
0 -

40

0

0

1

5 6

7

0

0*

6

7

0.5
0

-n

5 0.

.
0

6

6

7

7

5

5

-

0

.5

-

0.




C
0
-0
0

0

1

0

1

2

2

3

3

4

4

6

5

5

6

7

7

offshore distance (m)

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

69
EC2 Profiles 6-10
0
.5
0 1 2 3 4 5 6
0
0 1 2 3 4 5 6
0
.5 -
0 1 2 3 4 5 6 7 .5 I
0-

F
0
0 CU

7

-0.5

7

Ec
-Q

0

0.5




70

0

-0.5

EC2 Profiles 11-15
-

2

1

2

3

4

0
.51
0 1 2 3 4 5 6
.511111 I
0 II

2

0
C
0
75
C CD
C
0
cc CD

3

3

4

4

2 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

0
CD
75

0

5

6

7

-0
0

-n

0.

0

2

1

0

5

6

I -I- I
~
N
N

7

.1

n.
0

0.5

0

-0.5

1

1

6

7

I I I
7 N -~

2

5

5

6

7

j




71

EC2 Profiles 16-20
T

1

C Ci
C
0
C
0
0
0
E
a
0
0

2

2

2

3

3

3

4

4

4

5 6

5

5

6

7

7

6

7

0-
0.5
0 1 2 3 4 5 6 7
n05 *

0

2

3 4
offshore distance (m)

5

6

7

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

0

*0.
0.

0

--

0

0

I'

1

0

o
I -

0.5'
0

1

5

r.

0.

1

0.51

.

n -,;




APPENDIX C
BATHYMETRY SURVEYS FOR EC I
Appendix C shows the results from each bathymetry survey in EC 1 after every time interval.

72




73
0 min
-30-

0 2 4 6 8 10 12 14 16 40 min

16

0 2 4 6 8 10 12 14 80 min

6
E5
4
1
0 z,

0 2 4

6 8 10 longshore distance (m)

12 14 16

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

6
c 4 03
52
0

-5
c4
3
52
z

-3
-'l. ..... .........................
-... -.... ...... ..
..... -.

- -0
-2
-i-




74
120 min 6
$5 -3
CO -20 32 02
0 2 4 6 8 10 12 14 16 160 min
6
E5
CO
0 2 4 6 8 10 12 14 16 480 min

-40
--

0 2 4 6 8 10 longshore distance (m)

12 14 16

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

E
3
c4 CU
.3
(D t.)

----------- i- --- --- -




75

800 min

6 E5
c4
3
02
0

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

6
EU
0
d 2 0C

0 2 4 6 8

1600 min

0 2 4 6 8 10 longshore distance (m)

10 12 14 16

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

-30
C-7
r

E
(D
S3 02
0

12 14 16

-30
-10
---- ----------




76

3200 min

0 2 4 6 8 10 longshore distance (m)

12 14 16

Figure C4: Bathymetry Contours for EC 1 after 3200 min.

0
5 (D
4 U)

--




APPENDIX D
BATHYMETRY SURVEYS FOR EC2 Appendix D shows the results from each bathymetry survey in EC2 after every time interval

77




78

0 min
-40.
45
3- 20
2

0 2 4 6 8 10 12 14 16 40 min
6
-- -40
E5
-3
02
0 2 4 6 8 10 12 14 16 80 min

24
U

0 2 4 6 8 10 longshore distance (m)

12 14 16

Figure D 1: Bathymetry Contours for EC2 after 0 min, 40 min. and 80 min.

(D
0
0

-2 -
--




79
120 min
-40
* --- --

0 2 4 6 8 10 12 14 1E 160 min
-40
-2
- -2 0 ..... .

0 2 4 6 8 10 12 14 16 480 min

-40
- -- -- -

0 2 4 6 8 10 12 14 16 longshore distance (m)
Figure D2: Bathymetrv Contours for EC2 after 120 min, 160 mmi. and 480 min.

E
0
04
-5 3
CD
52

5 o4
3
521
0U

E5
Oc4
3 02
(U




80
800 min
-4

0 2 4 6 8 10 12 14 16 1120 min

0 2 4 6 8 10 12 14 16 1600 min

O 4
03
0
62
0 1

0 2 4 6 8 10 longshore distance (m)

12 14 16

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

6
S4
3 62
0

U
c 4 S3
0

-40

-20
-.............. -




81
3200 min

6
0

0 2 4 6 8 10 longshore distance (m)

12 14 16

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 EClafter all the surveys.

82




83

40 min 6
E5
oI 4 -.4
84
53 4 02'
0
0 2 4 6 8 10 12 14 16 80 min
6 I
5
(D
i2-- 44 --..
3
2
0 2 4 6 8 10 12 14 16 120 min 6
(D
4- 4
0o- 2 4 --

0 2 4 6 8 10
longshore distance (m)

12 14 16

Figure E1: Changes in bathymetry for EC lafter 40 mn, 80 min, and 120 mn.




84
160 min

02
1)
0

0 2 4 6 8 10 12 14 16 480 min
6
r=
o84 4
0 4
04
2 2 8
-1---~~
0 2 4 6 8 10 12 14 16

800 min
-
-F

0 2 4 6 8 10 longshore distance (m)

12 14 16

Figure E2: Changes in bathymetry for EC I after 160 min, 480 min, and 800 min.

4

- -

6 E5 C4 .3
52
0




85
1120 min
4 4
3
2 ----
0 2 4 6 8 10 12 14 1E 1600 min 6
5
- -
4
3
2 -4
0 2 4 6 8 10 12 14 16 3200 min

0 2 4 6 8 10 longshore distance (m)

12 14 16

Figure E3: Changes in bathvmetrv for ECI after 1120 min, 1600 mil. and 3200 mi.

0
0
0

0
0

E
24 (3
0

-12 1
-16
-..12




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.

86




87

40 min 6
5 I
I -8
4
3
- -4 o
0 2 4 6 8 10 12 14 1 80 min

6

0 2 4 6 8 10 12 14 16 120 min
6
4
3- 4
1u
02- 4 05

0 2 4 6 8 10 longshore distance (m)

12 14 16

Figure D1: Changes in Bathymetiv for EC2 after 40 min, 80 miin, and 120 min.

E co
0
0

03
C 153
02
0

- 6
--p
- 4-----

4l




88
160 min
L
-_ 4
-
Ii1 I

0 2 4 6 8 10 12 14 16 480 min

-
- - I-- 4 -- *
.4~_

0 2 4 6 8 10 12 14 16 800 min
E5
C04
. 4 4 '03
(D. -4
02 4 ~ o 1-

0 2 4 6 8 10 longshore distance (m)

12 14 16

Figure D2: Changes in Bathymetry for EC2 after 160 min. 480 min. and 800 min.

6
(5
oc4
- 3
(D
52
0 1

6

I.

5
(D
S4
3
(D
52
0




89
1120 min 6
5
4 3- 4
2
0 2 4 6 8 10 12 14 16 1600 min

-
- -

0 2 4 6 8 10 12 14 16 3200 min

--4
-
- -4- -
~ -2
.3i

0 2 4 6 a 10 12 14 16 longshore distance (m)
Figure D3: Changes in Bathymetry for EC2 after 1120 min. 1600 minl, and 3200 nun.

(D
C
(D
0

5
r- 4
-3
0 2
0p

g
E5
04
3
62
0p

- I

4
-

-




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.

90




91
Sebastian Inlet Profiles

10

10

10

10

15

15

15

15

seaward distance (m)

Figure GL: Cross-shore Profile for Sebastian Inlet Survey Lines 20, 22, 24 and 26.

0

0
c
-0
CD

-5
-10

0

5

20

E 0 0 -5
D
iD 10

25

1
0

5

20

E .0
0)

25

15'
0

5

5d

S 0
=-5 C
0
-5 10

-1.

20

25

0

5

0 0
-# 26 '

20

25

1

N

I

I

0 o 0 0 :ebb shoal
-~~~~b sh oo_ owdifl 0oo updrift
o0 0 # 20 0 0 '

o o 0
-# 22 'D

5( 01

0 o 0
- o o0
-0
-# 24 0ooS- -,

-10