Citation
Part II Movable bed method

Material Information

Title:
Part II Movable bed method
Series Title:
Sebastian Inlet physical model studies
Alternate Title:
UFL/COEL (University of Florida. Coastal and Oceanographic Engineering Laboratory) ; 91/041
Creator:
Wang, Hsiang
Place of Publication:
Gainesville
Publisher:
Coastal and Oceanographic Engineering Department, University of Florida
Publication Date:
Language:
English

Subjects

Subjects / Keywords:
Sebastian Inlet (Fla)
Genre:
serial ( sobekcm )
Spatial Coverage:
North America -- United States of America -- Florida -- Sebastian Inlet (Fla)

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Source Institution:
University of Florida
Holding Location:
University of Florida
Rights Management:
All rights reserved, Board of Trustees of the University of Florida

Full Text
UFL/COEL-91/014

Sebastian Inlet Physical Model Studies Part II Movable Bed Model, Interim Report
by
Hsiang Wang Lihwa Lin Husui Zhong Gang Miao

October, 1991
Submitted to: Sebastian Inlet District Commission Sebastian Inlet, Florida.




REPORT DOCUMENTATION PAGE
ii3. Recipient' Accession No.
4. Title and Subtitle 5. Report Date
SEBASTIAN INLET PHYSICAL MODEL STUDIES October 9, 1991
Part II -- Movable Bed Model, Interim Report 6.
7. Author(s) S. Performing Organization Report No.
Hsiang Wang, Lihwa Lin, Husui Zhong, Gang Miao UFL/COEL-91/014
9. Performing Organization am and Address 10. Project/Tak/UWork Unit No.
coastal and Oceanographic Engineering Department University of Florida 11. Contract or Grant No.
336 Weil Hall
Gainesville, FL 32611 13. Tp ofeprt
12. Sponsoring Organization Nam and Address
Sebastian Inlet District Commission Interim
Sebastian Inlet Tax District Office
134 Fifth Avenue
Suite 103, Indialantic, FL 32903-3164 F415. Supplementary Notes
16. Abstract
A movable bed model study was conducted to investigate several structural alternatives for inlet navigation improvement and sand transfer schemes at the Sebastian Inlet. The model has a vertical to horizontal scale distortion of 2 to 3. A horizontal scale of 1 to 60 was selected to cover approximately 2,500 ft of shoreline. The vertical scale is 1 to.40. Natural beach sand of finer grain than the native sand at Sebastian Inlet was used to fulfill the scale requirement.
This report summarizes preliminary results from testing the existing inlet, SO, and two jetty-extension configurations: Sl -- extension of 250 ft of north jetty, and S2 -- south jetty extension of 150 ft to Sl. Both structures Sl and S2 appear to promote more downdrift beach erosion than SO under NE storm. However, the downdrift shoreline recession and sand volume loss are modest for all three structures.
The ebb tidal shoal is substantial with a total volume over 1.3 million cubic yards. Sediment movement is active in the top layer which grows slightly and moves southward. However, as a whole, the shoal is stable relative to both storm and recovery duration.
The experiment is now still in progress testing other structural configurations, including further extension of south jetty and removal of ebb tidal shoal, etc., and the results will be presented in another report.
17. Originator's Kay Words 18. Availability Statement
Erosion
Shoreline recession
Structural alternative
Volume loss
19. U. S. Security Classif. of the Report 20. U. S. Security Classif. of This Page 21. No. of Pages 122. Price
Unclassified Unclassified 64




PREFACE

This report summarizes results of the experiments of the existing inlet and two jetty structural alternatives to the Sebastian Inlet from the movable bed model. It is intended to find solutions for improvement of boating safety and protection of beaches adjacent to the inlet. The movable bed model experiment is now still in progress testing other structural configurations, including extension of south jetty and removal of ebb tidal shoal, etc., and the results will be presented in another report.
The research in this report was authorized by the Sebastian Inlet District Commission of September 15, 1989. The University of Florida was notified to proceed on November 14, 1989. The study and report were prepared by the Department of Coastal and Oceanographic Engineering, University of Florida. Coastal Technology Corporation was the technical monitor representing the Sebastian Inlet District.
Special appreciation is due to Mr. Michael Walther of Coastal Tech. for his continuous technical assistance. Other personnel at Coastal Tech. and Inlet District Office including Dr. Paul Lin, Ms. Kathy FitzPatrick and Mr. Raymond K. LeRoux also provided their support at various stages of the experiment. Appreciation is also due to Mr. T. Kim and Mr. J. Lee, both graduate assistants in the Coastal Engineering Department, University of Florida, for their participation in laboratory and field experiments.




Contents
1 Introduction 1
1.1 Authorization. .. .. .. .. ... ... .... ... ... ... ....1
1.2 Purpose. .. .. .. ... ... ... ... ... ... ... ... ....1
1.3 Background. .. .. .. ... ... ... ... ... ... ... .....2
1.4 Scope. .. .. .. ... ... ... .... ... ... ... ... ....4
2 Model Characteristics 5
2.1 Modeling Laws and Model Scales. .. .. .. ... ... ... .....5
2.2 Model Construction. .. .. .. .. ... ... ... ... ... .....6
3 Experiments 9
3.1 Test Program. .. .. .. ... ... ... ... ... ... ... ....9
3.2 Test Procedures. .. .. .. .. ... ... ... ... ... ... ...13
4 Experimental Results 13
4.1 General Observations. .. .. .. .. ... ... ... ... ... ...15
4.2 Shoreline Response .. .. .. .. ... ... ... ... ... ... ..28
4.3 Bathymetric Changes and Erosional Patterns. .. .. .. .. ... ..29
4.4 Ebb Shoal Movement. .. .. .. .. ... ... ... ... ... ...38
5 Summary 38
References 43
A Contour Maps of Bathymetry Changes 45
B Comparisons of Downdrift Profiles for S1 and S2 55




List of Figures

1 Location of Sebastian Inlet, FL., and the watershed of Indian River
Lagoon .........................................
2 Jetty configuration and shoreline changes since 1881 ...........
3 Classification of flow regime ............................
4 Classification of sediment transport motion .................
5 Schematic map of the movable bed model; short-dashed lines showing locations for monitoring the bottom profiles ..............
6 Six alternative structural configurations ....................
7 criterion of normal and storm profiles ....................
8 Locations and labels of bottom profiles surveyed in the model ... 9 Initial profiles prepared in the model ......................
10 Profile and shoreline changes after 2-day storm for SO ..........

Profile and shoreline changes Profile and shoreline changes for SO ..............
Profile and shoreline changes Profile and shoreline changes Profile and shoreline changes for S1 ..............
Profile and shoreline changes Profile and shoreline changes

after 6-day storm for SO ..........
after 6-day storm and 8-day recovery
after 2-day storm for S1 ..........
after 6-day storm for S1 ..........
after 6-day storm and 8-day recovery
after 2-day storm for S2 ..........
after 6-day storm for S2 ..........

18 Profile and shoreline changes after 6-day storm and 8-day recovery
for S2 ..........................................




19 Region of accretion and erosion with patterns of sediment motion
during flood ....... ............................... 31
20 Region of accretion and erosion with patterns of sediment motion
during ebb ....... ................................ 32
21 Erosion pattern after 6-day storm for SO structure ............. 33
22 Comparisons of surveyed profiles from J12 to J18 for SO ....... ..34 23 Comparisons of surveyed profiles from J20 to J30 for SO ....... ..35 24 Plot of downdrift nearshore volume losses versus time .......... 37 25 Contours of ebbshoal volume above the reference plane of quasiequilibrium form ................................... 39
26 Orthographic plots of ebbshoal above the reference quasi-equilibrium
plane ........ ................................... 40




List of Tables
1 Comparison of flow regime and mode of sediment motion . . . 8
2 Testing program and experimental conditions . . . . . . 14
3 Averaged downdrift shoreline changes*(ft) . . . . . . . 28
4 Cumulative downdrift volume loss*(ft3) . . . . . . . 36
5 Summary of ebbshoal statistics and downdrift nearshore erosion. . 41




Sebastian Inlet Physical Model Studies Part 11 Movable Bed Model
1 Introduction
1.1 Authorization
This study and report were authorized by the Sebastian Inlet District Commission of September 15, 1989. On November 14, 1989, the "University of Florida" was notified to proceed. This report was prepared by the Department of Coastal and Oceanographic Engineering, University of Florida. Coastal Technology Corporation was the technical monitor representing the Sebastian Inlet District.
On May 23, 1919, the original legislation establishing the Sebastian Inlet District (District) was passed by the State of Florida. In 1927 the Florida Legislature passed Chapter 12259, Laws of Florida, which amend the original governing legislation of the District. Chapter 12259 prescribes that "It shall be the duty of said Board of Commissioners of Sebastian Inlet District to construct, improve, widen or deepen, and maintain an inlet between the Indian River and the Atlantic Ocean..."
(1).
1.2 Purpose
The main objective of the study aims to find solutions improving the inlet navigation as well as beach preservation at the Sebastian Inlet through physical model experiments. The study was concentrated in testing the hydrodynamic and littoral sediment drift properties for the existing inlet and several other structure configurations, including modification of the jetties and excavation of the ebb shoal.
Two physical models were conducted in the study: a fixed bed model for the hydrodynamic study and a movable bed models for the littoral sand process study. The results of the fixed-bed model study were summarized in the Part I report. The results of the movable-bed model study for the existing inlet and two other alternative structural configurations, which modify the existing jetties, were summarized in this report.




Sebastian Inlet is located at the Brevard/Indian River County line approximately 45 miles south of Port Canaveral entrance and 23 miles north of Fort Pierce Inlet. It is a man-made cut connecting the Atlantic Ocean to the Indian River Lagoon (Figure 1). Its coordinates are as follows:
Latitude Longitude
270 51' 35" N 800 26' 45" W
The First attempt to cut a man-made inlet in the Sebastian area was made in 1886 (2). In the ensuing 60 years or so, the inlet closed, re-opened and shifted a number of times. The present configuration was maintained after a major dredging operation in 1947-48 to open a new channel. Since 1948, a series of dredging operations and jetty improvements have kept the inlet open in this existing configuration
(3). In 1962, a channel of 11 ft deep was excavated. In 1965, the AlA bridge across the inlet was completed (State Project Number 88070-3501) and navigation guides were installed in the open section under the bridge which forms a natural throat of the inlet.
East of the bridge the dredged channel width was 200 ft and west of the bridge the width was 150 ft. In 1970, the north and south jetties were extended to their present configuration as shown in Figure 2, based on the results of a model study by the Department of Coastal and Oceanographic Engineering, University of Florida
(4). The present south jetty is a sand-tight rubble mound structure. The north jetty, on the other hand, is of composite nature; the original section completed before 1955 is rubble mound but the extension in 1970 with total length of 452 ft is a pier structure supported by concrete pilings. The rubble mound base only extends to the mean sea level.
The channel has a rocky bottom of marine origin. The cross section in the vicinity of the throat is about one-half that which would result in a stable inlet with sandy bottom. In other words, the tidal prism is about twice the value corresponding to the cross section. This has resulted in rather strong currents through the inlet, over 8 ft/sec during both flood and ebb. So far, the channel remains open with minimal maintenance dredging. Shoals were, however, gradually forming on both sides along the banks of the inlet. The navigation channel becomes narrower as a consequence. The ebb shoal from the south is also slowly encroaching into the inlet creating a cross shoal near the mouth. This shoal enhances the incoming waves and causes them to break. These combined effects have created a hazardous condition for small craft in the vicinity of the inlet entrance.
In 1987, Coastal Technology Corporation carried out a "Comprehensive Management Plan" study for the Sebastian Inlet District Commission (5). In which,

1.3 Background




\~\~ L~i/\
'-' VOLUSIA
* ~
I?
I

Figure 1: Location of Sebastian Inlet, FL., and the watershed of Indian River Lagoon.




ArLANRiC OCEAN

OLD JETTIES (1924)
JETTY EXTENSION(1955)
0 cl i 00 Feetzzzc RIPRAP (1959,1972)
I ~JETTY EXTENSIONS (1970) Figure 2: Jetty configuration and shoreline changes since 1881.
various engineering alternatives for maintenance and improvement of inlet navigation and beach preservation were presented. The present study is to evaluate these alternatives through physical model experiments.
1.4 Scope
The general purpose of this study is to conduct physical model investigation for inlet navigation improvement and sand transfer schemes; the former is a fixedbed model study and the latter a movable-bed model study. The fixed-bed model experiments were completed in November, 1990, and the results were summarized in the Part I Report. The movable bed model, to which the experiments are now still in progress, has been tested for the existing inlet structure and two modified jetty configurations subject to the northeaster storm waves. The preliminary results from these experiments were given in this Part II report. The final results for the completed movable-bed model experiment will be given later in the Part III report.
The movable bed model was conducted in the three dimensional wave basin at the Coastal and Oceanographic Engineering Laboratory, University of Florida. This model study includes testing the existing inlet and five other structure alternatives. Through the model study, the relative importance of the littoral sand




drift, onshore and offshore sand transport, entrapment of sand by the inlet and ebb shoal system, etc., from different structure alternatives were then evaluated. The information is useful for preparing the budget of littoral sediment transport in the inlet. And it is important to the evaluation of different structure alternatives in capable of improving the beach preservation under the environment of strong wave action and tidal currents.
2 Model Characteristics
The movable bed model was constructed at the Coastal and Oceanographic Engineering Laboratory, University of Florida, for the purpose testing the littoral and ebbshoal sand drift processes at the Sebastian Inlet due to different alternative structural configurations.
2.1 Modeling Laws and Model Scales
The movable bed modeling laws utilized here were developed by Wang et.al.(6). The basic hypotheses are that both wave forms and the trajectories of fallen sand particle motion caused by waves should be preserved in the modeling. Based upon this hypothesis, the following modeling laws were derived:
8= W/A45(1) NT = A/ vF8 (2)
Nt = v46 (3)
where A is the horizontal length scale, 85 is the vertical length scale, W is the fall velocity scale, NT is the fluid motion time scale, and Nt is the morphological time scale. All the scales are defined as the ratios of prototype to model.
It was also stipulated by Wang et.al that the flow regime and the mode of sediment motion should be the same between the prototype and the model. They suggested that the flow should be turbulent and the mode of sediment motion should be dominated by suspended load in order to be consistent with the fall trajectory hypothesis. These conditions are established with the aid of the two graphs shown in Figures 3 and 4, which define the flow regime and the mode of sediment motion according to the following four parameters:
Ra-amUb (Reynold number), am
LI




Tb Ub
(P )D (Shield's parameter), w (4)
C(PS pw)gDh0
where am is the largest water particle displacement on bed;
Ub is the largest water particle velocity at viscous boundary layer;
K, is the roughness of bed surface;
Tb is the bed shear stress due to wave motion.
Since sediment motion is most active in nearshore region, shallow water approximation can be applied to compute Ub and am:
Ub = r, am h (5)
where h is the water depth, H is the wave height, and T is the wave period.
Since the modeling laws are based on suspended sediment mode, they seem to be more applicable to storm conditions as opposed to mild wave environment. In the model, natural fine sand with D50=0.17mm was used as the bed material whereas the beach sand in Sebastian Inlet has a D50=0.35mm. The corresponding fall velocities to the two grain sizes at 10'C or 50OF are 0.6inch/sec and 1.8inch/sec, respectively. Thus, W=3 in Eq.(1). A horizontal length scale of A = 60 was selected, which permits to model the desired prototype range without encountering significant scale effect. The proper vertical length scale was then calculated from Eq.(1), which yielded 6 = 41. This vertical scale was rounded off to 40 in the model. That is, the movable bed model constructed is, accordingly, scaled with a horizontal to vertical distortion of 3:2. The fluid motion time scale and the morphological time scale were computed from Eqs.(2) and (3), which gave NT = 9.5 and Nt = 6.324.
As examples, the flow regime and the mode of sediment motion at the model scale were computed for Hprototype=l.5, 3, and 6 ft, and Tprotot pe=8 sec. The corresponding flow type and mode of sediment transport can be then determined from Figures 3 and 4. The results from the computation are summarized in Table 1. It is seen that the model may not properly simulate the flow and sediment motion for Hprototype=1.5 ft.
2.2 Model Construction
The movable bed model was conducted in the three dimensional wave basin at the Coastal and Oceanographic Engineering Laboratory, University of Florida. It models the study area approximately 2,000 ft of shoreline on either side of the inlet entrance, landward of the 30 ft offshore depth contour to the AlA bridge




Figure 3: Classification of flow regime.

0 No movement I Bed load (BL)
2 Bed load-Suspended load ntemediate iBSI) Transition 4
3 Suspended load (SL)4 4
4 Sheet flow (SF) / ,
O Field data 4j
OHonkawa stal. (1982) 3
3 3
, 2'!. 3 "Q.-l.r []
I 1 2 2
24
22
222 BSI
I
o BLNo movement BL BSI
No movement: BL BSI

9]
SF(Sheet flow)

nded load)

I I I I I I I

I I I ,I I I I

0.02 0.04 0.06 0.08 0.1 0.2 0.4 0.6 0.81.0
Shields parameter E,
Figure 4: Classification of sediment transport motion.

? f




Table 1: Comparison of flow regime and mode of sediment motion.

parameter model prototype
H 0.45 inch 1.5 ft
T 0.84 sec 8 sec
D50 0.17 mm 0.35 mm
W 0.6 inch/sec 1.8 inch/sec

3.1x103 1.2x106
91 2700
(laminar flow) (rough turbulent)
0.208 1.35
11.7 25.0
(suspended load) (sheet flow)

parameter model prototype

0.9 inch 3.0 ft
0.84 sec 8 sec
6.7x103 2.3X106
130 3750

(smooth turbulence flow)
0.375 1.73
UbIW 15.0 34.6
(suspended load) (sheet flow) parameter model prototype
H 1.8 inch 6.0 ft
T 0.84 sec 8 sec
Ra 1.2x104 4.7x106
am/Ks 190 5300
(rough turbulence flow)
0.5 3.45
UbIW 23.0 49.0

(sheet flow)

Ra am/K
Om UbIW

H T
R am / I.




(Figure 5). The m odel was constructed by placing a layer of natural fine sand,
D0= 0.17mm., over the existing fixed-bed physical model. The sand layer is generally thick, at least 2 inches in thickness to insure movable bed characteristics, in the beach and ebbshoal area, and becomes thinner in the offshore, region. The bed was then molded by sections using templates to the scaled-down prototype topography of 1989 survey (provided by Coastal Tech. Corp.). Since the Inlet bottom is bed rocks; it was simulated with small pebbles to attain the proper roughness. The general north-to-south transport of sediment is also simulated in the model where a sufficiently large amount of source sand was placed just inside the north beach boundary before an experiment. Therefore, the original shoreline in model is seen curving toward the sea near the north boundary. The model setup is shown in Figure 5.
3 Experiments
The existing inlet configuration and six other structure alternatives were tested in the movable bed model. In each case, a combination of current/wave conditions were tested. The survey program was also established in the experiments to monitor the sediment drift in the model from different structure alternatives.
3.1 Test Program
The test program is designed to examine the following:
*The effects of jetty alternations on shorelines and nearshore topography.
*The effects of ebb tidal shoal removal (partial and total) on shorelines and
nearshore topography.
* The effects of jetties to nearshore environment.
Three structure alternatives tested in the fixed bed model are selected here for the movable bed model experiment. They are identified as 51, S2, and S5 structures whereas the existing jetty configuration is designated as SO structure. The S1 structure is the same as the Type 1 structure referred in the fixed-bed model study which extends the existing north jetty by 250 ft with a radius of approximately 900 ft. The S2 structure is similar to the S1 structure but with the addition of a hooked south jetty extension of 150 ft. The S5 structure is the same as the Type 5 structure tested in the fixed bed model which is the SO structure plus the partial removal of ebb shoal.




SEBRSTIRN INLET MOVEABLE BED MODEL

SNAKE-TTPE HAVE MAKER
FU
FLO00O FLOW WHEIR

FLOOD FLOM
GATE ,
EBB FLOW
WEIR

OFFSHORE AVE STATION
PROFILING LINES .
II I I LI.J.1.+ '1 I fit F1 1 1 114 1 I it
I I I I I I I I I I i J I I I I-.LI I I 4I1 1
II II IIIIIIIII IIIII II I IIt-I'.I I II'1 I II I LJIl- II Iioi 'IIII I IIIIIi1, III I I I I I Il IIIII I ~I 1 11 1 I I 1 1 11 1 I I III I
I I I I 1 1 1 1 1 161 1 1 1 1 1 1 61 1 1 1 1 1 1 1 1 I 1 11 1-IIIII IIIj i -J i I III III I Ill '1. I I I I I I I III I h 1 111 1 I I l i l III I I I I I 1- 11li Ill I IIII I I l 1 I I II I T I I I Iil I l J- I I I I III l I i I 1, I I IIIIII I iffl IIII I IIII l I III I

SEDIMENT
TRAP PLATE

SCALE FEET

Figure 5: Schematic map of the movable bed model; short-dashed lines showing locations for monitoring the bottom profiles.

EBB FLOW
GRTE

EBB FLOW S GATE

INENT P CHANNEL




Three more structure alternatives are also to be tested, which are identified as the S3, S4, and S6 structures. The S3 structure is the similar to SO but with south jetty extended towards SE by 150 ft. The S4 structure is similar to S5 but with more sand removed from the ebb shoal nearly a 100% removal of ebb shoal. The S6 structure is similar to S4 but with both north and south jetties removed. The seven tested structures are summarized here:
SO Existing jetty configuration.
S1 North jetty extended 250 ft with a radius of approximately 900 ft.
S2 Si plus south jetty extended by 150 ft.
S3 SO plus south jetty extended by 150 ft.
S4 Existing jetty with removal of ebb shoal.
S5 Existing jetty with partial removal of ebb shoal.
S6 S4 plus removal of north and south jetties.
The six tested alternative structuiral configurations are shown in Figure 6.
The input wave conditions include storm(high), normal(moderate) and swelldominated(recovery) waves. They are defined in the model experiments as:
1. 6 Days Storm waves(high), H=6 ft) T=8 sec;
2. 20 Days Normal waves (moderate), H=2 ft, T=6 sec;
3. 8 Days Swell-dominated(recovery), H=2 ft, T=16 sec.
The tested wave directions are from NE (100 left to shoreline normal), E (shoreline normal) and SE (100 right to shoreline normal). The test durations vary from 6 to 20 days prototype equivalent depending whether the test is intended for storm erosion (6 days) or moderate erosion (20 days) or swell-dominated recovery (8 days). Within each test period, the maximum flood and ebb currents for semidiurnal tides (which consist approximately of two high, two low tides in a day) are generated alternately based on the scaled time durations. The corresponding current strength is 6.6 ft/sec for flood and 5.0 ft/sec for ebb.
The survey program of the model experiment includes monitoring 34 bottom profiles six profiles are located at the inlet with the spacings and ranges shown in Figure 5. Along each line, the survey intervals are 3 inches (15 ft prototype equivalent) from shoreline to the 10 ft contour line and one foot (60 ft prototype equivalent) beyond the 10 ft contour line.




Si
-301

S2

S3
-30-

Figure 6: Six alternative structural configurations.




The survey of bottom profiles generally includes the pre-storm profiles, following by one intermediate survey of the 2-day storm profiles, the post-storm and post-recovery profiles. Due to rapid change of topography in the case of storm erosion, several more intermediate surveys were also conducted to the SO and Si structures. For the SO (Si) structure, intermediate surveys of the 1/4, 1/2, 1, and 2-day (1/4, 1/2, 1, 2, 3, and 4-day) storm profiles were added in the experiments.
Table 2 summarizes the test program as described. In this report, only the preliminary results from those tests highlighted in Table 2 are presented.
3.2 Test Procedures
The model experiment is conducted according to the following procedures:
*Preparation of initial bathymetry.
*Survey of initial profiles.
e Establishment of the specified current and water level conditions following
the same procedures as the fixed-bed model experiments.
e Generation of waves in model to start the experiment for the scaled duration.
For instance, a 6-day storm wave test is equivalent to a total 22.8 hours run time in the model consisting of 12 complete semi-diurnal tidal cycles (one
complete tidal cycle consists of one high and one low tides).
@ Survey of bottom profiles at designated tidal cycles, say, at 1, 2, 4 or other
integer number of tidal cycles and, of course, the post-storm or post-recovery
profiles.
* collections of sand transported to the downdrift boundary and those into the
inlet.
e Reshape of the bottom to the initial bathymetry and repeat test for the
next condition. For recovery tests, the initial condition is the post-storm
condition.
4 Experimental Results
The experiment carried out so far consists of three structural configurations, SO, S1 and S2. Each structural configuration was tested subject to NE storm waves for a duration equivalent to six days in prototype, then to E swell-dominated waves




Table 2: Testing program and experimental conditions.

Wave NEt E NE SE
Condition Storm Recovery Normal Storm
Testing H=6' T=8s H=2' T=16s H=2' T=6s H=6' T=8s
structure* D=6 days D=8 days D=30 days D=6 days
(SO)
Existing 6-day run+ 6-day run+ 20-day run+ 6-day run+
structure 3 surveys 1 survey 1 survey 3 surveys
($1)
Extension of same same
N jetty
(S2)
Extension of same same same
N/S jetties
(S3)
Extension of same same same
S jetty
(S4)
Ebb shoal same same same same
removal
(S5)
Partial ebb same same
shoal removal
(S6)
Removal same same
of N/S jetties
North jetty is extended by 250 ft in Structures S1 and S2; South jetty by 150 ft in Structures S2 and S3; Ebb shoal is removed from SO in structures S4, S5 and S6. t Wave directions (from).




LEGEND
INVESTIGATOR SYMBOL
Normal Profile Storm Profile
-wagaki and Noda,1963 a
= Saville, 1957 A
Recor, 1954 a
1,3 06
- I
A a/
I lo/ iA I o.r l
0.00 0. 010 0-I0
W
gT
Figure 7: criterion of normal and storm profiles.
intended for beach recovery for eight days prototype equivalent. The state of erosive or accretive beach against the tested wave conditions is determined by the established criterion delineated in Figure 7 using the wave steepness, 21rH/gT2, and the non-dimensional sediment fall velocity, 7rW/gT as the parameters. If the plotting position of the test condition falls in the region above the diagonal line, the condition should be accretional (or normal profile); if the plotting position falls below the line it is erosional (or storm profile). It is seen that the tested storm condition falls inside the zone of erosive profile and the recovery condition falls in the zone of normal profile.
4.1 General Observations
Surveys were performed for the SO structure along the 34 profile lines as shown in Figure 8. They were numbered from the north boundary at JA (in the present case the updrift boundary) to the south boundary at J30 (the downdrift boundary). The spacing between any two adjacent profiles is generally small, ranging from 1.5 ft to 3.5 ft. The surveys for the S1 and S2 structural configurations, however, included only 26 (J3 to J27) and 30 (JA to J27) profiles, respectively, as they were selected in the earlier stage of the experiment. More survey lines were added in the latter experiments to provide better spatial resolutions. The most northern four profiles (JA to J2) and the most southern four profiles (J28 to J30) are judged to be in the regions influenced by the model boundaries. Therefore, they are excluded in




STRUCTURE:SO

JA JU Jl J2 J3

JA JS J6

J8J JI JI2JlI4 J16 J18 J2O

J22 J24 J26 J27 J28 J29 J30

Figure 8: Locations and labels of bottom profiles surveyed in the model.

5FT
5FT

SI. g L I I I l l l I i -

I




most of the analyses. Along each profile, bottom was surveyed at a regular interval of 1 ft in the offshore region and 0.25 ft in the nearshore region.
The north jetty is located in the model at J6 and the south jetty is at J12. The shoreline south of the inlet is as about twice long as the shoreline north of the inlet. The initial profile lines surveyed for the SO structural configuration is shown in Figure 9. Ideally, these initial profiles should be the same for all other structural configurations. In practice, they vary somewhat because of the remolding process. All the surveyed data collected are digitized and stored in the VAX-8350 computer and the reduced data are available in 3.5" floppy diskettes at the Department of Coastal and Oceanographic Engineering, University of Florida.
Based upon the results of the profile survey, the changes of topography and shoreline in the model can be shown by plotting the difference between the survey at a later time level and the initial profiles. Figures 10, 11, and 12, respectively, show the profile changes and shoreline positions in SO case after two and six days of storm waves and, then, after eight days of recovery process. In here, the positive change of profile elevation indicates accretion and negative change indicates erosion. The shoreline is defined in the model as corresponding to the elevation of 0 NGVD in the prototype. Similar plots are given for Si case in Figures 13 to 15, and for S2 case in Figures 16 to 18. These figures provide a visual assessment where erosion and accretion occurred. These data were also presented in Appendix I as the contour maps of bathymetry changes between surveys. The quantities of net sediment loss or gain can be determined from these maps.
As expected the overall sand transport direction is from north to south due to the NE waves. The downdrift shoreline erosion is strong along the downdrift beach south of the jetty in all three (SO, Si, and S2) cases. The shoreline on the north side is overall rather stable although it fluctuates from stage to stage for different test conditions.
The bathymetry changes, on the other hand, are noticeable on both sides of the inlet in the shallow water region where water depth is smaller than 9 inches in model (or 30 ft prototype equivalent). On the north (updrift) side near the inlet, the sediment transport is found to follow the path from nearshore to offshore and then to south with most of the sand being transported seaward the north jetty and a small amount through the partially submerged jetty under storm conditions. This southward sand bypassing is seen weaker in the S1 and S2 cases than the SO case as the north jetty in these two cases is longer and tends to block the passage of the sediment. However, this weaker southward transport could be a transient phenomenon. As the bathlymetry becomes gradually adjusted to the new jetty configuration, the southward transport could also be gradually restored to the existing condition.




STRUCTURE: SO PRE- (NE) STORM

20
INCHES SFT
5

Figure 9: Initial profiles prepared in the model.




STRUCTURE: SO
- PRE- (NE) STORM
-- 2-DRY (NE) STORM

5
INCHES SFT

Figure 10: Profile and shoreline changes after 2-day storm for SO.




STRUCTURE:SO
-PRE- (NE) STORM
--6-DRY (NE) STORM

5
INCHES 5FT
5P

Figure 11: Profile and shoreline changes after 6-day storm for SO.




STRUCTURE:SO
- PRE- (NE) STORM
-- 8-OAT RECOVERY

5
INCHES
5FT

Figure 12: Profile and shoreline changes after 6-day storm and 8-day recovery for SO.




STRUCTURE:SI
- PRE-(NE) STORM
-- 2-DATY (NE) STORM

Figure 13: Profile and shoreline changes after 2-day storm for Sl.




STRUCTURE: Si
- PRE- (NE) STORM
-- 6-DAY (NE) STORM

5
INCHES SFT

Figure 14: Profile and shoreline changes after 6-day storm for S1.




STRUCTURE:S .tu PRE- (NE) STORM
J22 -- 8-DAY RECOVERY
J20O
J18
- J16
Ji2
J10

5
INCHES
5FT
S>

Figure 15: Profile and shoreline changes after 6-day storm and 8-day recovery for S1.




122 STRUCTURE: S2
>J2 PRE- (NE) STORM
o -- 2-DAYT (NE) STORM

5
INCHES SFT

Figure 16: Profile and shoreline changes after 2-day storm for S2.




STRUCTURE:S2
- PRE-(NE) STORM
-- 6-DAY (NE)STORM

Figure 17: Profile and shoreline changes after 6-day storm for S2.




2 STRUCTURE: S2
2- PRE- (NE) STORM
-- 8-DAY RECOVERY
J16
Ji4
3
12
10 18
6

Figure 18: Profile and shoreline changes after 6-day storm and 8-day recovery for S2.




Table 3: Averaged downdrift shoreline changes*(ft).

Structure Type: SO
Case Tested Section Included in Computation
J12-21 J12-22 J12-23 J12-24 J12-25 J12-26 J12-27 2-Day Storm -0.33 -0.35 -0.31 -0.22 -0.16 -0.13 -0.12
6-Day Storm -0.40 -0.39 -0.29 -0.19 -0.13 -0.11 -0.13
8-Day Recovery -0.48 -0.52 -0.57 -0.61 -0.64 -0.59 -0.4
Structure Type: S1
Case Tested Section Included in Computation
J12-21 J12-22 J12-23 J12-24 J12-25 J12-26 J12-27 2-Day Storm -0.41 -0.39 -0.39 -0.36 -0.33 -0.31 -0.22
6-Day Storm -0.49 -0.44 -0.45 -0.45 -0.43 -0.41 -0.31
8-Day Recovery -0.47 -0.46 -0.46 -0.42 -0.36 -0.29 -0.23
Structure Type: S2
Case Tested Section Included in Computation
J12-21 J12-22 J12-23 J12-24 J12-25 J12-26 J12-27 2-Day Storm -0.20 -0.18 -0.16 -0.18 -0.18 -0.17 -0.14
6-Day Storm -0.57 -0.53 -0.43 -0.44 -0.48 -0.45 -0.41
8-Day Recovery -0.64 -0.67 -0.67 -0.67 -0.69 -0.63 -0.52
, Negative values indicate shoreline recession.
4.2 Shoreline Response
From the experiments, the northshore was seen rather stable for all three tested structural cases. However, the shore just south of the inlet always experienced strong erosion with uneven changes of the shoreline. Therefore, shoreline response was only examined here for the southshore. Based on the surveyed profile data, the analysis of shoreline response was performed by averaging the shoreline changes with respect to the initial shoreline between the profile adjacent to the south jetty (J12) and a profile further south (from J21 to J27). The results of the analysis are presented in Table 3.
These results show that under storm condition, the downdrift shoreline recedes under all tested structure cases. Relatively speaking, the recession is most pronounced immediately downdrift from the south jetty and becomes smaller towards further south. Beyond J27, the shoreline actually shows mild advances in most cases. It appears that under the storm condition (at the 6-day duration) the extension of north jetty adversely affects the shoreline by more than doubling the amount of averaged recession in the range J12-27. This is most likely due to




stronger currents through the shallow nearshore zone in the range J12-27 caused by lengthening of the north jetty.
The effect of lengthening the south jetty is, on the other hand, not as evident. It might provide some short term benefit in the immediate vicinity of the south jetty by preventing local beach sand being sucked into the inlet (see 2-day storm change). For longer storm duration (here the 6-day results), the south jetty extension as proposed in S2 does not seem to have any beneficial effects. This issue will be addressed later.
As to the absolute magnitudes of the shoreline retreats found in the model, they are quite modest comparing with some of the open coast erosions experienced along the Florida coast under comparable storm strength. For instance, the most severe shoreline recession occurred in the model is in the immediate south of the south jetty and is in the order of 0.4 ft in the first two days. This amount is equal to 25 ft/day when scaled to prototype. This recession rate reduces rapidly as the storm advances. After 6-day storm, the additional shoreline retreat is less than 0.15 ft (or 9 ft in prototype). This was due to the fact that in the earlier erosional stage, offshore bars were formed which retard the shore erosion. The overall modest shoreline recession is most likely due to the protection offered by the jetties and the ebb tidal shoal.
One of the unexpected results is from the recovery tests. The downdrift shoreline does not appear to respond to recovery waves. The shoreline either remains not responsive (S2) or continues to recede (SO and Sl) at a moderate rate. One possibility is simply that the present laboratory model is only suitable for storm wave condition (see Section 2.1). The other explanation which is based upon the interpretation of the experimental results will be presented later after examining the profile response and volumetric changes.
4.3 Bathymetric Changes and Erosional Patterns
During any single tidal cycle under storm condition, the most visible bathymetric changes occur in the nearshore zone on the south side of the inlet including the region near the tip of the south jetty. In the early stage of the storm, beach face is being eroded by wave action and sand is carried out towards offshore forming offshore bars. Meanwhile, the ebb tidal shoal also experienced vigorous sediment motion due to wave breaking and the sediment is carried into the nearshore zone. Therefore, sand is being transferred to the nearshore zone from both beach face and ebb tidal shoal. During the flood, this sand is coming into the inlet with currents through marginal flood channels and around the tip of the south jetty creating strong erosion zone in the vicinity of the inlet. During the ebb, the sand in the nearshore zone south of the inlet is also coming towards the inlet and then




back to the ebb tidal shoal region following a clockwise gyro on the downdrift side. Figures 19 and 20 show the regions of accretion and erosion with patterns of sediment motion based on sand tracer study during a single flood and ebb cycles, respectively. These patterns of sediment motion are in close agreement with the current patterns measured in the fixed-bed model.
The effect of cumulative changes of bathymetry due to different structural configurations over a number of tidal cycles can be shown in patched erosion and accretion patterns. Figure 21, for instance, shows erosional pattern for SO structure after 6-day storm condition. These patterns vary for different structural configurations. However, the integrated effect over the downdrift nearshore zone is clearly erosional for all the tested structural configurations.
For recovery runs, no bottom survey was made after a single flood or ebb. The integrated effect appears to be accretional in the nearshore zone. However, like the storm runs, the accretion does not extend to the beach face and in certain cases beach continues to erode and feed sand into the nearshore zone.
The sediment movement in the ebbshoal region is found only active in the upper layer. Visually, the ebbshoal appears to be slowly moving towards south. The pattern of ebbshoal change, however, is not all that clear and not necessarily consistent from run to run. A more detailed assessment is presented later.
Another area appears to have consistent bathymetric changes is in the vicinity of the tip of the north jetty where erosion prevails. However, the erosion is not severe in any cases.
As far as the inlet channel change is concerned, it varies from case to case in response to the jetty changes. In all three structural configurations, accretion is visible inside the jetties, particularly near the inlet entrance. For Si and S2, new channels were quickly formed south of the existing channel while the existing channel was being filled in steadily.
To examine the erosional and accretional patterns in further detail, the profile lines surveyed at different time stages are plotted against each others. Figures 22 and 23, for instance, show the comparisons of the 12 profile sections located south of the inlet for SO. Here, at each location 4 profiles representing the initial, the 2-day post storm, the 6-day post storm and the 8-day post-recovery profile are plotted against each other. Also plotted in these figures is the quasi-equilibrium profile (thick line), which represents the beach in an equilibrium form away from inlet. Similar plots for S1 and S2 are presented in Appendix II. Based upon these plots, the following properties can be examined:
9 The profile response.




STRUCTURE: SO
- ACCRETION
--- EROSION

5FT 5>

Figure 19: Region of accretion and erosion with patterns of sediment motion during flood.




STRUCTURE: SO
- ACCRETION 6-,,2 --- EROSION
--EROSION

5FT S>

Figure 20: Region of accretion and erosion with patterns of sediment motion during ebb.




Figure 21: Erosion pattern after 6-day storm for SO structure.
33




MEASURED PROFILES STRUCTURE: SO
0.5 INITIAL PROFILE
-----POST 2-DAY (NE) STORM
- ---POST 6-DAY(NE)STORM J12 ........... POST 8-DARY RECOVERY
-0. 5
0.5
0 Jl3
-0. 5
0.5
- 0 J 11
0.5
S0.5
0.5
0 J6.
j -0.5
I
-J-0.5
U
0.5
z
I I I 1
Lii
0 s
-0.5
0 10 20 30
SEAWARD DISTANCE (FT)
Figure 22: Comparisons of surveyed profiles from J12 to J18 for SO.




MEASURED PROFILES STRUCTURE: SO
0.5 INITIAL PROFILE
-----POST 2-0AY (NE) STORM
---J-POST 6-DAY (NE)STORM 020 ........... POST 8-DAY RECOVERY
0J2
-0.5
0.5
0 J22
0.5
0.5
1
S-0.5
"- 0.5
0 .... J2
,
-0.5
0 J30
-0. 5
-.
0 I I
-0.5
0 10 20 30
SEAWARD DISTANCE (FT)
Figure 23: Comparisons of surveyed profiles from J20 to J30 for SO.




Table 4: Cumulative downdrift volume loss*(ft3).

Structure Type: SO
Case Tested Section Included in Computation
J12-21 J12-22 J12-23 J12-24 J12-25 J12-26 J12-27 2-Day Storm -0.88 -0.98 -1.08 -1.16 -1.23 -1.28 -1.39
6-Day Storm -1.22 -1.32 -1.43 -1.54 -1.68 -1.81 -2.08
8-Day Recovery -2.60 -2.94 -3.22 -3.48 -3.70 -3.85 -4.22
Structure Type: S1
Case Tested Section Included in Computation
J12-21 J12-22 J12-23 J12-24 J12-25 J12-26 J12-27 2-Day Storm -1.42 -1.52 -1.71 -1.91 -2.11 -2.15 -2.20
6-Day Storm -2.17 -2.44 -2.84 -3.37 -3.73 -3.88 -3.96
8-Day Recovery -3.14 -3.51 -3.94 -4.36 -4.58 -4.68 -4.75
Structure Type: S2
Case Tested Section Included in Computation
J12-21 J12-22 J12-23 J12-24 J12-25 J12-26 J12-27 2-Day Storm -0.83 -0.94 -1.08 -1.21 -1.33 -1.44 -1.64
6-Day Storm -1.66 -1.85 -2.09 -2.34 -2.61 -2.82 -3.21
8-Day Recovery -1.92 -2.16 -2.43 -2.67 -2.87 -3.10 -3.60
Volume loss computed up to a nearshore depth of -2.0 inches; Negative values indicate erosion.
* The volume change in the downdrift nearshore zone.
e The change of ebbshoal.
The cumulative volume loss in the downdrift nearshore zone with reference to the initial condition was computed to a depth of -2.0 inches in the model (or -6.7 ft. in prototype, approximately the mean breaking depth under storm condition). The range selected in the computation was between J12 to J27 which is judged as the downdrift zone directly influenced by the jetty structure. The computed results are tabulated in Table 4. A loss of 2.0 ft3 (roughly 6-day storm duration for SO structure) is equivalent to 10,700 yd3 in prototype, or in average about 32 yd3 per ft per day. Both S1 and S2 structures appear to adversely affect the volume losses under 6-day storm condition by an increase of 50 to 100 percent. In the recovery runs, the volume changes are generally small in all cases.
Figure 24 plots the downdrift nearshore volume losses as a function of model run time. Clearly, the rate of the volume loss decreases as storm advances. Under the storm condition, SO is seen to yield the smallest volume loss while S1 yields the




PROTOTYPE TIME (DAT)
5 10 15
5 II
0 25
Si E
/ 0 20 "
S2
-j AX
I_ j
1:2L 10 uJ
a::: I.ZC
z IE 5
C E- mSO caSTORM RECOVERY S2
0 10
0 10 20 30 q10 50 60
MODEL RUN TIME(HOUR)
Figure 24: Plot of downdrift nearshore volume losses versus time.
largest loss. After 8-day recovery test, S2 is seen to give the smallest loss among the three structural cases.
It is shown in the last section that the downdrift beach does not seem to recover under recovery runs. One explanation of this behavior is given here. From the profile plots shown in Figures 22 and 23, it is evident that the downdrift beach profiles are significantly different from an open coast profile which under normal condition tends to assume a monotonically concaved shape known as the equilibrium profile. Natural forces tend to maintain and restore beaches in equilibrium form. If the updrift or downdrift beach away from the inlet is assumed in a state of quasi-equilibrium representative of this region, then this profile can be used as a template to gauge the abnormality of the downdrift beach near inlet. The quasi-equilibrium profile shown in Figures 22 and 23 is expressed by
d = -0.042 (y 6)08 (6)
where d is the water depth in ft and y is the normal shore distance in ft relative to the baseline aligned with Highway AlA in the model. It is seen in Figures 22 and 23 that there is -a substantial sand deficit in the nearshore zone if the profiles were to be restored to equilibrium. Therefore, there is a natural tendency for the nearshore zone to draw sand both from the beach and from the ebbshoal. It was also shown earlier that in this zone tidal currents, both ebb and flood, constantly carries sand away. Consequently, the nearshore zone behaves like a ditch which deprives the beach even from normal recovery. This indeed is a detrimental effect.




4.4 Ebb Shoal Movement

The ebbshoal changes were determined by three parameters: the volume change, the movement of the centroid of the volume and the spreading of the volume. In the volumetric change computation, the quasi-equilibrium profile is used to establish a reference plane. The ebbshoal volume was then computed as the volume above this datum. Since the offshore boundary and the downdrift boundary are restricted by the survey limits the volume computation can only be carried out to these boundary limits. Figure 25, for instance, shows contours of the elevation differences for the 1989 survey. Figure 26 displays the orthographic views from two viewing angles. All the volume above the reference plane contributes to the ebbshoal. Clearly not all the ebbshoal volume can be accounted for. The unaccounted volume was estimated to be about 10 percent of the total from this 1989 survey. This would put the total volume of the ebb shoal around 1.3 million cubic yards.
Figures 25 and 26 reveal two very interesting aspects. First, the shape of the ebbshoal with respect to the reference plane appears to be very symmetrical even though it is crescent-shaped in the prototype appearance. Second, the sand deficit in the downdrift nearshore zone and the ditch effect discussed previously are clearly demonstrated.
The centroid location of the ebbshoal volume is established by the following equations:
T= xdVI JydV/J dV,(7
and the spreading of the volume is expressed by a Rrms (root-mean-square radius) value defined as
Rrmns {JV(x 0 + (y y)2]dV/ V dy]1/2. (8)
The results for SO, S1 and S2 configurations for the ebbshoal statistics and, also, the downdrift nearshore erosion information are summarized in Table 5. It is noticed that the ebb shoal as a whole is very stable. The top layer of the ebb shoal, mainly above the 12 ft contour, is still active and is growing slightly while moving slowly towards south.
5 Summary
In this report, only partial test results from the laboratory movable bed model are reported. The tests included three jetty structural configurations: the existing jetty configuration (SO), north jetty extension of 250 ft to the existing jetty structure (S1), and south jetty extension of 150 ft to the S1 configuration (S2). The




Figure 25: Contours of ebbshoal volume above the reference plane of quasiequilibrium form.




SOUTH JETTY
Figure 26: Orthographic plots of ebbshoal above the reference quasi-equilibrium plane.
40




Table 5: Summary of ebbshoal statistics and downdrift nearshore erosion.
Structure Type: SO
Ebbshoal Statistics* South Beach Erosiont
Case Surveyed Y y Rrm3 Vol. Average Change Cumulative
(ft) (ft) (ft) (ft3) of Shoreline(ft) Vol. Loss(ft3) Pre-(NE)Storm 38.1 29.7 7.6 69.9 -
2-Day Storm 38.3 29.6 7.4 69.9 -0.12 -1.39
6-Day Storm 38.3 29.4 7.5 69.6 -0.13 -2.08
8-Day Recovery 38.4 29.2 7.7 70.2 -0.40 -4.22
Structure Type: S1
Ebbshoal Statistics* South Beach Erosiont
Case Surveyed Y y Rrms Vol. Average Change Cumulative
(ft) (ft) (ft) (ft3) of Shoreline(ft) Vol. Loss(ft3) Pre-(NE)Storm 37.7 29.6 7.7 68.3 - -
2-Day Storm 37.7 29.6 7.6 67.5 -0.22 -2.20
6-Day Storm 37.9 29.6 7.6 69.9 -0.31 -3.96
8-Day Recovery 38.0 29.4 7.7 70.1 -0.23 -4.75
Structure Type: S2
Ebbshoal Statistics* South Beach Erosiont
Case Surveyed Y y Rrms Vol. Average Change Cumulative
(ft) (ft) (ft) (ft3) of Shoreline(ft) Vol. Loss(ft3) Pre-(NE)Storm 37.8 29.6 7.8 68.3 - -
2-Day Storm 38.0 29.6 7.7 67.5 -0.14 -1.64
6-Day Storm 38.3 29.6 7.6 69.9 -0.41 -3.21
8-Day Recovery 38.4 29.6 7.7 70.1 -0.52 -3.60
* Statistics based on volume above a reference plane, d = -0.042(y 61)0.s, where d is water depth in ft; 7 and y are referenced to J3 on the baseline (x axis) aligned with the Highway A1A.
t Volume loss computed up to a nearshore depth of -2.0 inches in model between Profiles J12 (south jetty) and J27.




test conditions conducted so far consisted of 6-day (prototype equivalent) storm waves from NE followed by 8-day recovery waves from E.
The findings which are of preliminary nature are summarized here:
9 In terms of shoreline movement, the updrift shoreline north of north jetty
is relatively stable for all structure configurations under both storm and recovery wave conditions. The downdrift shoreline, immediately south of south jetty (to profile J27, or 1500 ft prototype equivalent) suffers erosion under both storm and recovery waves. Both structures S1 and S2 appear to promote more erosion by almost doubling the averaged shoreline recession compared with the SO structural configuration. The absolute magnitudes of the recession are, however, modest being less than 12 ft in the early stage
(2-day duration) of the storm and decreasing further as storm advances.
* The most visible bathymetric changes occur in the nearshore zone on the
south side of the jetty, where active sediment movement is due to two major factors: it is a zone of deficit which attracts sand from beach face and from ebbshoal and it is a zone of active transport due to nearshore current. The magnitudes of the volume losses in the nearshore zone (from shoreline to mean breaking point) under storm condition are also modest, averaging 3 to 6 yd3 per ft per day in the early stage of the storm and decrease further
thereon.
Since both shoreline recession and sand volume loss are modest, certainly no worse than open coast beaches under storm wave attack, one of the detrimental effects of inlet appear to be the inability of post storm recovery.
* The ebbshoal is substantial with a total volume over 1.3 million yd3. Sediment movement is active in the top layer which grows slightly and moves southward. However, as a whole, the shoal is stable relative to both storm
and recovery duration.
* Another area appears to be active is in outer region of the north jetty where
most the sand bypassing occurs. It is erosional under storm condition on both side of the jetty and accretional under recovery condition outside the jetty. However, the rate of accretion or erosion does not appear sufficient as
a potential bypassing site.
9 The channel between the jetties appears to be accretional as extended from
the ebb shoal under both storm and recovery conditions. For S1 and S2 structural configurations, new ebb channels just outside the jetty develop
rapidly while the existing ebb channel is being filled in.
* The south jetty appears to be ineffective whether in the existing configuration
(SO) or in the new configuration (S2).




Test is now still in progress as scheduled. In view of the ineffectiveness of the south jetty more alternative configuration will be investigated. The aim of the test remains unchanged at improving the navigation condition while on the same time seeking optimum scheme for downdrift erosion mitigation.
References
[1] Law of Florida, Chapter 12259.
[2] Mehta, A.J., Wm.D. Adams, and C.P. Jones, 1976. "Sebastian Inlet Glossary
of Inlets, Report #3," Coastal and Oceanographic Engineering Laboratory, University of Florida. UFL/COEL-76-011.
[3] Wang, H., L. Lin, H. Zhong, and G. Miao, 1991. "Sebastian Inlet Physical
Model Studies: Part I Fixed Bed Model," Coastal and Oceanographic Engineering Department, University of Florida. UFL/COEL-91-001.
[4] Engineering and Inductrial Experiment Station, 1965. "Coastal Engineering
Hydraulic Model Study of Sebastian Inlet, Florida," Coastal and Oceanographic
Engineering Laboratory, University of Florida. UFL/COEL-65-006.
[5] Coastal Technology Corporation, Florida, 1988. "Sebastian Inlet District Comprehensive Management Plan".
[6] Wang, H., T. Toue, and H.H. Dette, 1990. "Movable Bed Modeling Criteria
for Beach Profile Response," Proc. 22nd Coastal Engineering Conf., Deft, The
Netherlands, pp.2566-2579.




APPENDICES




A Contour Maps of Bathymetry Changes




5FT
5FT

Figure I-1: Contour map of bathymetry changes after 2-day storm for SO.
46




Figure 1-2: Contour map of bathymetry changes after 6-day storm for SO.
47




Figure I-3: Contour map of bathymetry changes after 6-day storm and 8-day recovery for SO.




Figure 1-4: Contour map of bathymetry changes after 2-day storm for Si.




Figure I-5: Contour map of bathymetry changes after 6-day storm for Sl.




Figure I-6: Contour map of bathymetry changes after 6-day storm and 8-day recovery for Sl.
51




Figure 1-7: Contour map of bathymetry changes after 2-day storm for S2.




Figure I-8: Contour map of bathymetry changes after 6-day storm for S2.




Figure I-9: Contour map of bathymetry changes after 6-day storm and 8-day recovery for S2.




B Comparisons of Downdrift Profiles for SlandS2




MEASURED PROFILES

STRUCTURE: St
INITIAL PROFILE
-----POST 2-DAY(NE) STORM
- - -----POST 6-DAY (NE) STORM ........... POST 8-DAT RECOVERY

0.5
0
-0.5
0.5
0
-0.5
0.5
0
-0.5
0.5
0
-0.5
0.5
0
-0.5
0.5
0
-0.5

0 10 20 30
SEAWARD .DISTANCE (FT)
Figure H-1: Comparisons of surveyed profiles from J12 to J27 for S1.
56

J20
J22
---1..,.--. -.=_ ... - .-.

"=l




MEASURED PROFILES STRUCTURE:S2
0.5 STRUCTURE: S2
INITIAL PROFIT LE
POST 2-DAY (NE) STORM
-POST 6-DAY(NE)STORM 0 J12 ...****....-POST 8-DAY RECOVERY
0
-0.5
0.5
0
-0.5
0.5
-- -0.5
* 0.5 I
0 Jl
-0.5
-- 0 J16
._j
0,5
0.5
--0.5
0 J18
-0.5
0 10 20 30
SEAWARD DISTANCE (FT)
Figure II-2: Comparisons of surveyed profiles from J12 to J18 for S2.
57




MEASURED PROFILES STRUCTURE:S2
0.5STRUCTURE 2
0.5 "
--- INITIAL PROFILE
-----POST 2-DAY(NE)STORM POST 6-0AY(NE)STORM 0 J20 ..**.**.-*POST 8-DAY RECOVERY
-0.5
0.5
0 J22
-0.5
0.5
0 J23
0-- 0
-- -o.S
0.5
S-0.5
- 0.5
0J2
-0.5
. =I .I ,,.I .
0.5
0""
-0.5
0 10 20 30
SEAWARD .DISTANCE (FT)
Figure II-3: Comparisons of surveyed profiles from J20 to J27 for S2.