• TABLE OF CONTENTS
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 Title Page
 Report documentation page
 Preface
 Table of Contents
 List of Figures
 List of Tables
 Introduction
 Model characteristics
 Experiments
 Experimental results
 Summary
 References
 Appendices
 Appendix A: Contour maps of bathymetry...
 Appendix B: Comparisons of downdrift...






Group Title: Sebastian Inlet physical model studies
Title: Part II Movable bed method
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Permanent Link: http://ufdc.ufl.edu/UF00078559/00002
 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
Physical Description: Serial
Language: English
Creator: Wang, Hsiang
Publisher: Coastal and Oceanographic Engineering Department, University of Florida
Publication Date: 1991
 Subjects
Subject: Sebastian Inlet (Fla)
Spatial Coverage: North America -- United States of America -- Florida -- Sebastian Inlet (Fla)
 Record Information
Bibliographic ID: UF00078559
Volume ID: VID00002
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved, Board of Trustees of the University of Florida

Table of Contents
    Title Page
        Title Page
    Report documentation page
        Unnumbered ( 2 )
    Preface
        Preface
    Table of Contents
        Page i
    List of Figures
        Page ii
        Page iii
    List of Tables
        Page iv
    Introduction
        Page 1
        Page 2
        Page 3
        Page 4
        Page 5
    Model characteristics
        Page 6
        Page 7
        Page 8
        Page 5
        Page 9
    Experiments
        Page 10
        Page 11
        Page 12
        Page 9
        Page 13
    Experimental results
        Page 14
        Page 15
        Page 16
        Page 13
        Page 17
        Page 18
        Page 19
        Page 20
        Page 21
        Page 22
        Page 23
        Page 24
        Page 25
        Page 26
        Page 27
        Page 28
        Page 29
        Page 30
        Page 31
        Page 32
        Page 33
        Page 34
        Page 35
        Page 36
        Page 37
        Page 38
    Summary
        Page 39
        Page 40
        Page 41
        Page 42
        Page 43
        Page 38
    References
        Page 43
    Appendices
        Page 44
    Appendix A: Contour maps of bathymetry changes
        Page 45
        Page 46
        Page 47
        Page 48
        Page 49
        Page 50
        Page 51
        Page 52
        Page 53
        Page 54
    Appendix B: Comparisons of downdrift profiles for S1 and S2
        Page 55
        Page 56
        Page 57
        Page 58
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.


I







REPORT DOCUMENTATION PAGE
1. Report No. 2. 3. IRcipiet's Accession No.


4. Title and Subtitle S. Report Date
SEBASTIAN INLET PHYSICAL MODEL STUDIES October 9. 1991

Part II -- Movable Bed Model, Interim Report 6

7. Author(s) 8. Performing Organization Report No.
Hsiang Wang, Lihwa Lin, Husui Zhong, Gang Miao UFL/COEL-91/014

9. Performing Organiation Nam and Address 10. Project/Task/Uork Unit No.
Coastal and Oceanographic Engineering Department
University of Florida 11. Contract orGrant No.
336 Weil Hall
Gainesville, FL 32611 13. Te of Reprt
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 1_"
15. 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: S1 -- 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 Key words 18. Availability Statment
Erosion
Shoreline recession
Structural alternative
Volume loss

19. U. S. Security Classtf. of the Report 20. U. S. Security Classif. of This Page 21. No. of Pages 22. 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 Com-
mission 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 show-
ing 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 S . .

after 6-day storm for S . .

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 quasi-
equilibrium 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


I








Sebastian Inlet Physical Model Studies
Part II Movable Bed Model



1 Introduction


1.1 Authorization

This study and report were authorized by the Sebastian Inlet District Commis-
sion 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 Cor-
poration was the technical monitor representing the Sebastian Inlet District.

On May 23, 1919, the original legislation establishing the Sebastian Inlet Dis-
trict (District) was passed by the State of Florida. In 1927 the Florida Legislature
passed Chapter 12259, Laws of Florida, which amend the original governing legis-
lation 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 sum-
marized in this report.








1.3 Background


Sebastian Inlet is located at the Brevard/Indian River County line approx-
imately 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 opera-
tions 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 A1A 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 Man-
agement Plan" study for the Sebastian Inlet District Commission (5). In which,





















' VOLUSIA
S B~u<

I

iI


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



















ATLANTIC OCEAN


OLD JETTIES (1924)
r JETTY EXTENSION(1955)
S5 czzzzzzzz RIPRAP (1959,1972)
0 500'
Sc---le in Fert r JETTY EXTENSIONS(1970)
Figure 2: Jetty configuration and shoreline changes since 1881.

various engineering alternatives for maintenance and improvement of inlet naviga-
tion 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 fixed-
bed 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 re-
sults 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 al-
ternatives. 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:

6 = W2/5 4/5 (1)
NT = A/ v (2)
N,= V4 (3)

where A is the horizontal length scale, 8 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:



am Ub am
Ra = (Reynold number), a
v Ks









7b Ub
(m = (Shield's parameter), (4)
(Ps pw)gDso W
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 ap-
proximation can be applied to compute Ub and am:

H rg HT g
Ub = -HJ- am = (5)
2 h 2 2x h'
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 Do0=0.17mm was used as the bed material
whereas the beach sand in Sebastian Inlet has a D5o=0.35mm. The corresponding
fall velocities to the two grain sizes at 100C or 500F 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 A1A bridge











































Figure 3: Classification of flow regime.


0 No movement
I Bed load (BL)
2 Bed load-Suspended load intefnndiate iBSI Transition 4
3 Suspended load (SL)4 4
4 Sheet flow (SF) .
O Field data 4
OHonkawa stal. (1982) 3 3
3 3

,. 3 .-.rn a

< f 2 SL(Suspe,



,2 2 BSI

o@ el5
o2 BL-

No movement BL BSI


(Sheet flow)
9 SF(Sheet flow)


ended load)


I I I I I I III


I I I I II I


0.02 0.04 0.06 0.08 0.1 0.2 0.4 0.6 0.81.0
Shields parameter w,,


Figure 4: Classification of sediment transport motion.


I 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
laminarr 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)

m 0.375 1.73
Ub/W 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/K, 190 5300
(rough turbulence flow)

m 0.5 3.45
Ub/W 23.0 49.0


(sheet flow)


Ra
am/K


Cm
UbIW


H
T

R,
am/Ks








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:

6 = W2/5 4/5 (1)
NT = A/ v (2)
N,= V4 (3)

where A is the horizontal length scale, 8 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:



am Ub am
Ra = (Reynold number), a
v Ks








(Figure 5). The model was constructed by placing a layer of natural fine sand,
Ds0 = 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 mon-
itor 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 S1, 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 WAVE MAKER


FLU
FLOOD FLOW
SHEIR


FLOOD FLOW
GATE ,





EBB FLOW
WEIRA


OFFSHORE HAVE STATION i

PROFILING LINES .-


III IIIIIIIIII.IIIII ii IIJ-II'. I I'IIII
I I Li- i IIIlII I.IHlII III I
I I I I l 1 Ii l1 1 11 111 I 1 111111 II
I I I I I I I I 1 I I I 1 1-1,11 H 1 141 1


1 1 11IIIIIII I ill ll I -IIIIII I I1 I
I I IIII II JIIIf I I I1111 1 f I III I'. -
I I II IIIIL I I II I I I I I. I T

I -- 11' ll II I I i.III: I i .I..

Si I i I 1iT- I III 1 I 1I
I I I I IIII I II fl l III I 11 III I III I
liii111111 f~i~iI~iiiii iii


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
GATE -


EBB FLOW
- 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 S1 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 structural configurations are shown in Figure 6.

The input wave conditions include storm(high), normal(moderate) and swell-
dominated(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 (shore-
line 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 semi-
diurnal 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.













S30

-30'


S2


-30`--


S3


-30-


Figure 6: Six alternative structural configurations.








(Figure 5). The model was constructed by placing a layer of natural fine sand,
Ds0 = 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 mon-
itor 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 S1, 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.








The survey of bottom profiles generally includes the pre-storm profiles, follow-
ing 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 S1
structures. For the SO (Sl) 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.

Establishment of the specified current and water level conditions following
the same procedures as the fixed-bed model experiments.

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.

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
(S1)
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
Iwagaki and Noda,1963 a
= Saville, 1957
Rector, 1954 a

a-a
I


i i 'a






0.001 0. 010 I10
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, 27rH/gT2,
and the non-dimensional sediment fall velocity, irW/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


JH JU Jl J2 J3


JA JS J6


8J J9 00 Ji2Jl4 Jl6 0


J22 J24 J26 J27 J28 J29 J30


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


5FT


5FT


- I. I I -* I T I i


" '"""~-~-- - ---


I








The survey of bottom profiles generally includes the pre-storm profiles, follow-
ing 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 S1
structures. For the SO (Sl) 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.

Establishment of the specified current and water level conditions following
the same procedures as the fixed-bed model experiments.

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.

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








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 pos-
itive 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 S1 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, S1, 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 bathymetry 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
5FT


Figure 9: Initial profiles prepared in the model.













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


5
5FT

5


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
















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


5
INCHES
5FT


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













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


5
5FT

5


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














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


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
















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


5
INCHES
SFT


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
















STRUCTURE:Si
.t PRE- (NE) STORM
J22 -- 8-DAY RECOVERY
20
18
J16

J12
10


5
INCHES
5FT



S>


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















122 STRUCTURE: S2
> 2 PRE- (NE) STORM
Xo -- 2-DAY (NE) STORM


5
INCHES
5FT


S


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















STRUCTURE:S2
PRE- (NE) STORM
-- 6-DRY (NE)STORM
8


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
















!2 STRUCTURE: S2
-- PRE- (NE) STORM
-- 8-DAY RECOVERY
J16
JI4
J12
10
8
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 re-
cedes under all tested structure cases. Relatively speaking, the recession is most
pronounced immediately downdrift from the south jetty and becomes smaller to-
wards 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 shore-
line 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 bathymet-
ric 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 configu-
rations. 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 S1 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:


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
S-- EROSION
--- EROSION
\J211


5FT


>


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-OAY(NE) STORM
J 2 ........... POST 8-DAY RECOVERY



-0. 5

0.5


0 J13


-0.5 -
0.5






0.5
I-


-0
S0.5


0 ..J15


ua
-0.5
0-






-J-0.5
U:
0.5
z










0 Ji8
-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


-----POST 6-DAY (NE)STORM
0 20 ...........POST 8-DAY RECOVERY
0 J20


-0.5

0.5


J22




0.5





S0.5 -

0.5 -

I-
J26
co



-j -0.5
Li



0 -- ^J28
-0.5
I-







0.5
0.5



0J30


-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.

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 (DAY)
5 10 15
e 25

Si E3
u. 4 e eS
S R E 20S
3 20
S2 -
X
ID / >

re s r s15
2. :-


LL 0a
a:: I/ I--.-
C)
z -
Co E SO ia-
eDl a.

STORM RECOVERY --- S2
0 0
0 10 20 30 q0 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 re-
cover 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 equilib-
rium profile. Natural forces tend to maintain and t intinrestore 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)0-8 (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 estab-
lish 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 unac-
counted 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:
= xdV// dV, y=JydV/ dV, (7)
and the spreading of the volume is expressed by a Rrms (root-mean-square radius)
value defined as
Rrms = {1[(x ) + (y )2]dV/ 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 struc-
ture (Sl), and south jetty extension of 150 ft to the S1 configuration (S2). The










































Figure 25: Contours of ebbshoal volume above the reference plane of quasi-
equilibrium 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 Rrms 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 a 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 x 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)0-8, 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:


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 detri-
mental 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. Sed-
iment 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.

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, Uni-
versity 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 Engi-
neering 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 Com-
prehensive 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.








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 estab-
lish 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 unac-
counted 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:
= xdV// dV, y=JydV/ dV, (7)
and the spreading of the volume is expressed by a Rrms (root-mean-square radius)
value defined as
Rrms = {1[(x ) + (y )2]dV/ 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 struc-
ture (Sl), and south jetty extension of 150 ft to the S1 configuration (S2). The








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, Uni-
versity 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 Engi-
neering 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 Com-
prehensive 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 1-3: 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 S1.




















































Figure 1-5: Contour map of bathymetry changes after 6-day storm for Sl.























































Figure 1-6: 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 1-8: Contour map of bathymetry changes after 6-day storm for S2.























































Figure 1-9: Contour map of bathymetry changes after 6-day storm and 8-day
recovery for S2.















B Comparisons of Downdrift Profiles for SlandS2








MEASURED PROFILES


STRUCTUREs SL
INITIAL PROFILE
-----POST 2-DAY INE) 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 II-1: Comparisons of surveyed profiles from J12 to J27 for S1.




56


J16







J20







_-J22


"=l








MEASURED PROFILES
0.5 STRUCTURE: S2
S- INITIAL PROFILE
-- POST 2-DAY (NE)STORM
-----POST 6-DAY(NE)STORM
0 Jl2 ...........--POST 8-DRTY RECOVERY


-0.5




0 J1 3
0.5



0.5






-0.5 -
0.5










j 0 Jl


-0.5
(,









z

-- 0 J16

-j
-0.5

0.5

0 J8

-0.5



0 10 20 30

SEAWARD .DISTANCE (FT)






Figure 1-2: Comparisons of surveyed profiles from J12 to J18 for S2.




57








MEASURED PROFILES STRUCTURE
0.5STRUCTURE 52
--------INITIL PROFILE
-----POST 2-DAYF(NE)STORM
Y-----POST 6-OAY(NE)STORM
0 J20 -........POST 8-DAY RECOVERY


-0.5




0 J22


-0.5
0.5


0 223







0 "-J24
I- =






- -0.5
- 0.5
z

c 0 J26



0.5



0 J27


-0.5

0 10 20 30

SEAWARD .DISTANCE (FT)





Figure 1-3: Comparisons of surveyed profiles from J20 to J27 for S2.




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