Citation
Evaluation study and comparison of erosion models and effects of seawalls for coastal construction control line

Material Information

Title:
Evaluation study and comparison of erosion models and effects of seawalls for coastal construction control line interim report #4
Series Title:
UFLCOEL-94020
Creator:
Lin, Li-Hwa
Zheng, Jie
Dean, Robert G ( Robert George ), 1930-
University of Florida -- Coastal and Oceanographic Engineering Dept
Florida -- Dept. of Environmental Protection
Place of Publication:
Gainesville Fla
Publisher:
Coastal & Oceanographic Engineering Dept., University of Florida
Publication Date:
Language:
English
Physical Description:
iii, 34 leaves : ill. ; 28 cm.

Subjects

Subjects / Keywords:
Storm surges -- Mathematical models ( lcsh )
Coastal engineering -- Mathematical models ( lcsh )
Sea-walls -- Models ( lcsh )
Genre:
bibliography ( marcgt )
non-fiction ( marcgt )

Notes

Bibliography:
Includes bibliographical references (leaf 34).
General Note:
"June 20, 1994."
Funding:
This publication is being made available as part of the report series written by the faculty, staff, and students of the Coastal and Oceanographic Program of the Department of Civil and Coastal Engineering.
Statement of Responsibility:
by Lihwa Lin, Jie Zheng, Robert G. Dean ; prepared for Department of Environmental Protection, State of Florida.

Record Information

Source Institution:
University of Florida
Holding Location:
University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
33143056 ( OCLC )

Full Text
UFL/COEL-94/020

EVALUATION STUDY AND COMPARISON OF EROSION MODELS AND EFFECTS OF SEAWALLS FOR COASTAL CONSTRUCTION CONTROL LINE
Interim Report #4
by
Lihwa Lin Jie Zheng and
Robert G. Dean
June 20, 1994
Prepared for: Department of Environmental Protection State of Florida




Evaluation Study and Comparison of Erosion Models and Effects of Seawalls for Coastal Construction Control Line
Interim Report #4 by
Lihwa Lin Jie Zheng Robert G. Dean

June 20, 1994 Prepared for: Department of Environmental Protection State of Florida




PREFACE
This is the fourth in a series of reports presenting experimental results from the physical modeling of beach erosion in the vicinity of a seawall for a DEP Coastal Construction Control Line (CCCL) study. The beach and the associated seawall are modelled after a DNR profile at Range Number R-192 in Highland Beach, Palm Beach County, Florida. In this report, the effects of the model beach profile responses with and without seawall, and with the seawall failure during the peak surge level interval of the modelled storm surge were investigated.




Contents

1 Scope of this Report 1
2 Experimental Conditions 1
2.1 Laboratory Facility . . . . . . . . . . . . . . . . . . . . 1
2.2 Scaling . . . . . . . . . . . . . . . . . . . . . . . 3
2.3 Initial Beach Profile and Seawall Configuration . . . . . . . . . . . . 5
2.4 Storm Surge . . . . . . . . . . . . . . . . . . . . . . 5
2.5 Sediment Size . . . . . . . . . . . . . . . . . . . . . 7
2.6 Wave Conditions . . . . . . . . . . . . . . . . . . . . 7
2.7 Seawall Failure Conditions . . . . . . . . . . . . . . . . . . 7
2.8 Survey of Model Beach Profile . . . . . . . . . . . . . . . . 8
3 Comparison of Experimental Results 8
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . 8
3.2 Effect with Seawall versus No Seawall . . . . . . . . . . . . . . 9
3.3 Effect of Complete Seawall Failure . . . . . . . . . . . . . . . 17
3.4 Effect of Partial Seawall Failure . . . . . . . . . . . . . . . . 17
3.5 Effect of Regular Waves versus Random Waves . . . . . . . . . . . . 24




4 Summary

5 References 34
List of Tables
1 Summary of experimental cases and test parameters ...................... 2
2 Experiments compared in the present and previous reports . . . . . . . . . 2
3 Summary of the varied and fixed parameters in B3, B4, N1, N2, F1, F2, F3, and F4. 9
List of Figures
1 Schematic diagram of wave tank facility . .. . . . . . . . . . . . . . 4
2 Initial profile and Seawall #1, modelled after DNR profile R-192 . . . . . . . 6
3 Continuous and stepped simulation of storm surge #2 . . . . . . . . . . 6
4 Model beach profiles and elevation differences from initial profile Experiment B3 . . 11 5 Model beach profiles and elevation differences from initial profile Experiment B4 . . 12 6 Model beach profiles and elevation differences from initial profile Experiment N1. 13 7 Model beach profiles and elevation differences from initial profile Experiment N2. 14 8 Elevation differences from initial profile comparison between B3 and Nl . . . . . 15
9 Elevation differences from initial profile comparison between B4 and N2 . . . . . 16
10 Model beach profiles and elevation differences from initial profile Experiment F1 . . 18 11 Model beach profiles and elevation differences from initial profile Experiment F2 . . 19 ii




12 Elevation differences from initial profile comparison between B3 and Fl . . . . . 20
13 Elevation differences from initial profile comparison between B4 and F2 . . . . . 21
14 Model beach profiles and elevation differences from initial profile Experiment F3 . . 22 15 Model beach profiles and elevation differences from initial profile Experiment F4. . . 23 16 Elevation dIfferences from initial profile comparison between B3 and F3 . . . . . 25
17 Elevation differences from initial profile comparison between B4 and F4 . . . . . 26
18 Elevation differences from initial profile comparison between B3 and B4 . . . . . 28
19 Elevation differences from initial profile comparison between N1 and N2 . . . . . 29
20 Elevation differences from initial profile comparison between F1 and F2 . . . . . 30
21 Elevation differences from initial profile comparison between F3 and F4 . . . . . 31




Evaluation Study and Comparison of Erosion Models and Effects of Seawalls for Coastal Construction control Line Interim Report #4 Physical Model Result
1, Scope of this Report
This is the fourth in a series of reports presenting results from wave tank experiments performed at the University of Florida Coastal and Oceanographic Engineering Laboratory as part of the physical modeling component of a DEP Coastal Construction Control Line (CCCL) study. The modeling examines the effects of seawalls on adjacent beaches under controlled forcing conditions. The beach profile used in the experiments is modelled after DNR Range Number R-192 located in Highland Beach, Palm Beach County of Florida.
This project is sponsored by the Beaches and Shores Center at Florida State University. The technical monitor of the project is Dr. T. Y. Chiu.
A total of 27 experiments has been completed to date. Table 1 summarizes the experimental cases and parameters for the individual tests in the modeling study. These experiments were designed to serve as sensitivity tests for individual experimental parameters. Table 2 provides a summary of the various parameter values for comparison of experimental results presented in this and previous reports.
In the previous reports, the effect of varying sand size tests (A2, Bi), the effect of regular versus random waves (C-series), the effect of different storm surge configurations (Al, A2, B2, B39), and the effects of lowering the initial model beach profile and lowering the wave energy level (B-series) were investigated. In this report, the effects of various seawall failure conditions (F-series) versus the case of a normal seawall without failure and the cases with no seawall (N-series) were examined.
2 Experimental Conditions
2.1 Laboratory Facility
The laboratory experiments were conducted in the air-sea tank at the University of Florida Coastal and Oceanographic Engineering Laboratory. The tank section used for the experiments is 37 m




Table 1: Summary of experimental cases and test parameters.
water level condition seawall condition sediment wave characteristics water
stepwise varying const. plan, vertical; median wave type deepwater wave volume
exp. storm surge level model elevation diameter regul random wind wave height period overID# model peak level cm] [cm] cm [mm waves waves waves cm s topping
14.4 16.8 14.4 21.12122.34119.9 0.18 0.09 16 115 1. 1 seawall
#1 1 #2 #3 1 #4 #5 #1 #2 #3 #1 #2 #1 #2 #3 #1 #2 #2 measured
Al X X X X X X
A2 X X X X X X
A3 X X X X X X X
A4 X X X X X X X X
B1 X X X X X X
B2 X X X X X X
B3 X X X X X X
B4 X X X X X X
B5 X X X X X X X
B6 X X X X X X X
B7 X X X X X X
B8 X X X X X X
B9 X X X X X X
C3 X X X X X X X
C4 X X X X X X X
CS X X X X X X X
C6 X X X X X X X
S3 X X X X X X
T3 X X X X X X
R3 X X X X X X X
R4 X X X X X X X
N1 X X X X X
N2 X X X X X
Fl X X X X X X
F2* X X X X X X
F3* X X X X X X
F4* X X X X X X
* For Fl, F2, F3, and F4, seawall failed during the surge peak level.
Table 2: Experiments compared in the present and previous reports.
Interim Varied Experimental Parameters Experiments
Report [model units] compared
#1 sediment size: 0.18mm vs. 0.09mm A2 B1
(median diameter)
wave period: 1.65s vs. 1.3s C3 C4
#2 (for time-invariant SWL) 05 C6
wave type: regular vs. random 3 C
04 C6
storm surge: peak level at 14.4cm vs. 16.8 cm Al A2
#3 (for time-varying SWL) B2 B9
wave type: regular vs. random B6 B7
B9 B8
initial profile: original vs. lowered profile B6 B9*
B7 B8*
wave energy: H**=15cm vs. 16cm B5 B7
(random waves)
seawall status: (i) regular seawall vs. no seawall B3 N1
#4 B4 N2
(present) (ii) regular seawall vs. seawall failure B3 F1
(seawall failed during the peak level B4 F2
of storm surge) B3 F3
B4 F4
wave type: regular vs. random B3 B4
N1 N2
F1 F2
F3 F4
* both the initial profile and SWL of B8 and B9 were lowered in comparisons.
** H, denotes the deepwater significant wave height.




long, 0.9 m wide, and 1.2 m high (Figure 1). The tank is equipped with a hydraulic powered wavemaker capable of generating regular and irregular waves. The wavemnaker is controlled by a Wavetek Model 110 computer system. The wavemaker and a powered fan used to generate wind waves axe located at one end of the tank. A wave energy absorbing basin is located at the far end of the wave tank where the model beach is located.
Above the wave tank there is an electrically powered trolley capable of moving over the entire length of the wave tank. This trolley is used in measuring the model beach profiles in the following way. Along the entire length of the model beach, a grid is marked on the top of the wave tank wall. The trolley is equipped with a graduated vertical rod which can be raised or lowered manually. After stopping the cart at predetermined increments along the grid, model beach elevations are measured by lowering the graduated rod so that it just rests on the sand and an elevation is read from the graduated survey rod. Horizontal distances are adjusted with zero datum at the seawall location. Elevations are referenced to the DNR vertical datum of NGVD. The model beach profile surveys were conducted at various time levels for each experiment depending on the objectives and time allotted (Thompson, et al., 1993).
Two capacitance type wave gauges were installed in the tank for monitoring waves Gage 1 is located 18.3 mn (457.5 m prototype) seaward of the seawall and Gage 2 is located 5.3 m (132.5 m prototype) seaward of the seawall.
The volume of water overtopping the seawall was measured during some experiments by collecting the water in a movable catch pan located immediately landward of the seawall. Measurement of this overtopping volume requires the experiment to be performed twice. Since the profile response behind the seawall is also of interest, the same experiment needs to be performed once for each measurement.
2.2 Scaling
A model to prototype length scale ratio of 1:25 and time scale ratio of 1:5 are used in all experiments. This means that, for instance, a distance of 1 m in the model corresponds to a distance of 25 m in the prototype or actual case being modelled. Similarly, a one second time duration in the model corresponds to 5 seconds in the prototype. Dimensions in this report are given primarily in model units.




red
n -3.0
I I H -1.5
II,,0

\
Wave Gauge

Sand / Wave Bed Gauge
CROSS-SECTION

36.6

'
Location of Seawall

m 1< 5.8 m---*

Wave Screens

Caage for Wave Location of Carriage forWave Seawall N

|oH ro Power Drain Valves Unit

Wave Tank Wave
Gauge Divider Gauge

Bulkhead

PLAN VIEW

Figure 1: Schematic diagram of wave tank facility.

Powe
Fa

Wavemaker

- 3.4m .




2.3 Initial Beach Profile and Seawall Configuration

The initial beach profile used in the experiments is modelled after an actual beach profile in Highland Beach in Palm Beach County of Florida. The profile coincides with DNR Range Number R-192. A modelled initial profile is presented in Figure 2.
Three simple vertical seawalls were used in the Highland Beach model experiments. Since these seawalls varied only in seawall height, they were constructed out of the same piece of 2.54 cm thick plywood which was placed at three different elevations to create the three model seawalls. The seawall location along the profile was fixed for all the experiments listed in Table 1 which involve seawalls. Here, Seawall 1 is modelled after the actual seawall located at R-192 which has a model elevation of 21.12 cm 05.28 m prototype). The Seawall 2, at 22.34 cm (5.59 rn prototype), is 1.22 cm (model) higher than Seawall 1 and Seawall 3, at 19.9 cm (4.98 m prototype ) is 1.22 cm (model) lower.
2.4 Storm Surge
Four time-varying severe surge conditions are modelled in the experiments listed in Table 1. They are referred to as Storm Surges 1, 2, 3, and 4. These severe surge conditions are numerically determined combined total storm tides which have been established for various portions of Palm Beach County (Dean, et al., 1992). These total storm tides include storm induced surge, astronomical tide, and dynamic wave set-up which occurs primarily in the inner surf zone (landward of wave breaking). The storm tides are physically modelled in the wave tank by raising the water level in a stepwise fashion. Figure 3 presents a schematic of the continuous storm surge profile of the prototype and the stepped simulation (Storm surge 2) which was applied in the Highland Beach physical model experiment.
In contrast to the time-varying water level of the aforementioned storm surges, Storm Surge 5 is a, time-invariant water level which is modelled by fixing the surge water level (SWL) at 14.4 cm (3.6 m prototype). This time-invariant water level is the predicted peak value for Highland Beach in Palm Beach County. A constant storm surge of 14.4 cm was used in the Series C experiments.




-0.5 0.0 0.5 1.0 1.5 2.0
model distance from seawall [meters]

2.5 3.0 3.5 4.0

Figure 2: Initial profile and Seawall #1, modelled after DNR profile R-192.

Figure 3: Continuous and stepped simulation of storm surge #2.

0.25

0.20 0.15
0.10 .20.05 0.00 '150.05

-0.10
-1.0

..seawall #2 elevation 0.223m initial profilE
NOVD

=-----

I ____ 0 minutes elapsed I

4.5 18
4.0 Storm Surge2 Stage 3 16
3.5 14
30 12
2.5 10
2. 2p Stage2 -- s -2
S1.5 6 Z3
/ .~~~Stage 4
/Stage 1
8-.0.5 rttp Dtrm surge -stepwise model surge
-1.0 -4
0 3 6 9 12 15 18 21 24 27 30 33 36 39 42 45 prototype time [hours ]




2.5 Sediment Size

Median diameters of the two sediment sizes used in the experiments are 0.18 mm for sand in the A-series experiments and 0.09 mm for all other experiments (B,C,N, and F-series). These model diameters correspond to prototype values of 0.65 mm and 0.21 mm, respectively, according to the similitude of sediment fall velocity- The smaller size sand is scaled in accordance with the natural sediment in the Highland Beach area.
2.6 Wave Conditions
Both regular and random waves are modelled in the wave tank experiments listed in Table 1. The regular waves are modelled with a deepwater wave height of 0.16 m for all the experiments completed thus far. This model wave height corresponds to a prototype value of 4 m. In A4, the regular wave height was slightly higher than 0.16 m since the experiment includes the effects of wind.
The random waves are modelled by a Pierson-Moskowitz spectrum with a deepwater significant wave height of 0.16 m (4 m prototype) for all the random wave experiments except in B5 where a significant wave of 0.15 m (3.75 m prototype) was used.
Two different wave periods are modelled in the regular wave experiments Wave Period 1 is 1.65 seconds in the model (8.25 seconds prototype) and wave period 2 is 1.3 seconds in the model (6.5 seconds prototype). The modal wave period of 1.65 seconds (8.25 seconds prototype) has been used in all the experiments except in 04 and C6 where a modal wave period of 1.3 seconds (6.5 seconds prototype) was utilized.
2.7 Seawall Failure Conditions
Experiments Fl, F2, F3, and F4 were conducted to determine the effects of seawall failure on the model beach profile adjacent to the seawall. Cases Fl (regular waves) and F2 (random waves) represent total seawall failure during the time of maximum storm surge interval. Cases F3 (regular waves) and F4 (random waves) represent failure of the upper half of the seawall above zero NGVD at the time of maximum storm surge.




2.8 Survey of Model Beach Profile

The technique for surveying the model beach profile was described in Section 2.1. The survey interval is 5cm (1.25m prototype) in the area from the landward end of the profile to 5.3m seaward of seawall, and the interval is 10cm thereof to the seaward end of the profile.
The surveys of model beach profile generally include the initial profile, the final profile, and the intermediate profiles corresponding to four different stages of the modelled time-varying storm surge. Of these four different SWL stages, two are those right before and after the main escalation of storm surge modelled, while the third and the last are those at the end of the peak SWL and at the end of the descending period of the peak surge, respectively. Figure 3 shows these four different surge stages as Stages #1, #2, #3, and #4, upon the simulated storm surge #2.
3 Comparison of Experimental Results
3.1 Introduction
Experiments B3, B4, Ni, N2, Fl, F2, F3, and F4 are chosen for comparisons in the present report to evaluate the effect of seawall failure to model beach responses during the peak SWL interval. Experiments B3, B4 correspond to the cases of a normal seawall without failure, and Ni, N2 correspond to the cases with no seawall present in the model, whereas Fl, F2, F3, F4 correspond to the cases with various degrees of seawall failure. All of these experiments were compared under the same conditions of initial profile #1, storm surge #2, and sand #2 of Table 1.
The varied parameters of these experiments are: (i) Seawall #1 is fixed in B3 and B4; no seawall if; present in Ni and N2, (ii) Seawall #1 is fixed in F1, F2, F3, and F4, up to the mid point of the maximum surge interval at which time the seawall is lowered to appropriate elevation to simulate the desired condition of seawall failure. In F1 (regular waves) and F2 (random waves), the seawall was lowered to an elevation of 0 cm. NGVD to simulate complete seawall failure. In F3 (regular waves) and F4 (random waves), the seawall was lowered to the elevation of 10.56cm (2.64m prototype) NGVD to simulate a half failed seawall.
Experiments B3, Ni, F1, and F3 are all performed based on regular waves with the deepwater height and period maintained at 16cm and 1.65 seconds, respectively, while B4, N2, F2, and F4 are




Table 3: Summary of the varied and fixed parameters in B3, B4, N1, N2, Fl, F2, F3, and F4.
varied parameters fixed parameters
exp. seawall height [model units) wave type storm surge #2 sediment #2
I.D.# before midway after midway regular* random** (model peak: (median size:
of peak SWL of peak SWL waves waves 14.4cm) 0.09mm)
B3 21.12cm 21.12cm X X X
(seawall #1) (seawall #1) X X
B4 21.12cm 21.12cm X X X
(seawall #1) (seawall #1) X X
N1 X X X
(no seawall) (no seawall) X X
N2 X X
(no seawall) (no seawall) X X X
F1 21.12cm 0cm X X X
(seawall #1) X X
F2 21.12cm Ocm X X
(seawall #1) X X X
F3 21.12cm 10.56cm X X X
(seawall #1) X X
F4 21.12cm 10.56cm X X
(seawall #1) X X X
* regular waves with the deepwater height and period fixed at 16cm and 1.65s.
** random waves with the deepwater significant height and modal period fixed at 16cm and 1.65s.
performed based on random waves with the deepwater significant height and modal period equal to 16cm
and 1.65 seconds, respectively. A summary of the varied and fixed parameters of these experiments is
presented in Table 3.
In this report, the model beach profiles surveyed at the four different surge water level (SWL)
stages, as described in Section 2.7, are selected for the comparisons of experimental results. The four
different SWL stages are also shown in Figure 3 as Stages #1, #2, #3, and #4, which correspond to
model times of 3.0, 3.6, 4.2, and 4.8 hours, respectively. In order to denote clearly the four SWL stages,
they are referred in the following sections as the pre-escalation of SWL, escalation of SWL, peak SWL,
and descending SWL, respectively.
3.2 Effect with Seawall versus No Seawall
The experimental results from B3, B4, N1, and N2 are chosen for comparison of the effects with
and without a seawall present in the model. In B3 (regular waves) and B4 (random waves), Seawall #1 is
fixed in the model. In N1 (regular waves) and N2 (random waves), no seawall was present in the model.
All of these four experiments were performed based on initial profile #1 and storm surge #2.




Figures 4 to 7 show the individual beach profiles measured at the four aforementioned SWL stages as the pre-escalation of SWL, escalation of SWL, peak SWL, and descending SWL, for B3, B4, Ni, and N2, respectively. The differences of these profiles from the initial profile are also plotted in these figures. In B3 and B4, the experiments with a seawall present in the model, the erosion was seen to be mild in the area seaward of seawall between im and 2.5m (25m and 62.5m prototype), in the pre-escalation of SWL stage, in which the SWL has not reached the seawall. This erosion continued in B3 and B4 in the stage of escalation of SWL when the SWL reached the seawall. During stages of the peak SWL and descending SWL, large erosion was observed in B3 and B4 in the area from the seawall to about 2m (50m prototype) seaward of the seawall. In the peak SWL stage, the erosion was the most severe with somewhat deeper scour at the seawall toe in B3 than in B4. During the descending SWL period, the large erosion in B3 and B4 became uniformly distributed in front of the seawall. Landward of the seawall, the erosion was very slight in both B3 and B4 experiments.
In Ni and N2, in which the seawall was not present in the model, similar erosion patterns between these two experiments were observed. Seaward of the horizontal datum at Omn, the model beach profile erosion was generally small. Landward of this horizontal datum, however, erosion was found to be substantial during the peak SWL stage in the area between the horizontal distances of Om and -1m (Om and -25m prototype).
Figures 8 and 9 compare the profile differences from the initial between B3 and Ni, both were performed under regular waves, and those between B4 and N2, under random waves, respectively, for the four selected SWL stages. These comparisons show that the presence of Seawall #1 in B3 and B4 does provides good protection to the profile behind the seawall. However, the seawall also induces significant erosion in the area from the seawall to about 2m (50m prototype) seaward of the seawall with deep scour at the seawall toe during the peak SWL stage. On the other hand, if the seawall is not present in the model, very different erosion patterns resulted as shown in the Ni and N2 experiments. Without a seawall present in the model, erosion was insignificant seaward of the horizontal datum of Omn. However, heavy erosion has occurred landward of the horizontal datum of Om.
A small accretion of sediment was observed in Experiments B3, B4, Ni, and N2, regardless of whether or not a seawall was present in the model. This accretion occurred in the nearshore area between the horizontal distances of 2m and 3.5m (50m to 87.5m prototype).




0.3 0.2 S0.2 0.1 0.1 0.0 0.0
--0.0
0.3
S0.2 0.2 0.1 0.1 0.0 0.0
-.0.0
-0.1
0.3
0.2 0.2 0.1 0.1 0.0 0.0

-1.0

-0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
model distance from seawall [m]

Figure 4: Model beach profiles and elevation differences from initial profile Experiment B3.

Experiment B3
0
5 seawall #1 Storm Surge #2
. elevation 0.211m Pre-escalation of SWL
0 3.0 hours elapsed (model)
5
0
5 -SWL: 0.036m
0 N GVD
NGVD ----------------05 -'
- model beach profile difference from initial 10 1 1 1
-1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
0
5 seawall #1 Storm Surge #2
,- elevation 0.211m SWL escalation
0 3.6 hours elapsed (model)
5 SWL: 0.12m
0
0 NGVD .----..... ---------50

0.
0.
0.1 2 0.0
0.0
0
S-0.
-0.

-0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

-1.0
0
0
5
0
5 0
5
0 -

30
5 seawall #1 Storm Surge #2
_-- elevation 0.211m Descending SWL
0 4.8 hours elapsed(model)
5
0
5 SWL: 0.048m
0 NGY1 -----------------05 / --- ... "
10 I I I I i I




Experiment B4
0.30
-0.25 seawall #1 Storm Surge #2
- -elevation 0.211m Pre-escalation of SWL
0.20 3.0 hours elapsed (model)
0.15
. 0.10
S0.05- SWL: 0.036m
0.00 NGVD _------ -------0.05- model beach profile ---- difference from initial
-- 0I I
-1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
0.30
0.25 seawall #1 Storm Surge #2
A--elevation 0.211m SWL escalation
0.20 3.6 hours elapsed (model)
o 0.15
0.15 SWL: 0.12m
> 0.10
0
) 0.05
0.00 NGVD -------.----60.050
-0.10
-1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
0.30
-0.25 seawall #1 Storm Surge #2
_--elevation 0.211m Peak SWL
0.20 4.2 hours elapsed (model)
o. 0.15
SWL: 0.144m > 0.10
0)
0.05
N~~o GVD ---- I-.-- 0 .0 0 - --. .- -.. . --.. . . .. . . .
0
~-0.05 -

0.3
0.2 0.2 0.1 0.1
0.0 0.0
--0.
-.0.

-1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2
model distance from seawall [m]

.5 3.0 3.5 4.0

Figure 5: Model beach profiles and elevation differences from initial profile Experiment B4.

-1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.(
0
5 seawall #1 Stormr Surge #2
- elevation 0.211m Descending SWL
0 4.8 hours elapsed(model)
5
0
5 -SWL: 0.048m
0 NGVD ------ -----)05
10




0.3
S0.2 0.2 S0.1
S0.1 0.0 0.0
0
-0.o
-0.1
0.3
0.2 0.2 .2 0.1 > 0.1 0.0 S0.0
0
-0.2
-0.1
0.3
0.2 0.2 o 0.1 > 0.1 S0.0 0.0
0
-0.2
-0.1
0.3
0.2 0.2 .0 0.1 > 0.1 0.0 0.0
0
-0.1

0
5
0
5
0
5
0
0
5
0
5
0
5
0
IC

-1.0
5

-1.0
-t

-1.0

-0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
model distance from seawall [m]

Figure 6: Model beach profiles and elevation differences from initial profile Experiment N1.

Experiment N1
0
5 -Storm Surge #2 Pre-escalation of SWL
0 3.0 hours elapsed (model)
5
0
5 SWL: 0.036m
0 NGVD ,- ------5
0- model beach profile ---- difference from initial
0_iIII I 1
-1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.C
0
5 Storm Surge #2
5SWL escalation
0 3.6 hours elapsed (model)
5 -SWL: 0.12m
0
5
NGVD .-_ -.... .95
0
5 _________ -- -- --------

-0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

Storm Surge #2
Descending SWL
- 4.8 hours elapsed(model)
.SYL: 0.048m NGVD --. --.-5- --0 _ __ __II I I




Experiment N2
0
5 Storm Surge #2
Pre-escalation of SWL 0 3.0 hours elapsed (model)
5
0
5 SWL: 0.036m
m hfNGVDom
05
-- model beach profile --- difference from initial
I0I I

-1.0
0.30
0.25
0.20 0.15 0.10 0.05 0.00
-0.05

0.5 1.0 1.5 2.0 2.5 model distance from seawall [im]

Figure 7: Model beach profiles and elevation differences from initial profile Experiment N2.

0.3
0.2 0.2 0.1 0.1 0.0 0.0
-0.0

1.0 1.5 2.0 2.5 3.0 3.5 4.0

0.30 0.25
0.20 0 0.15 > 0.10 0.05 e 0.00
0
-0.05
-0.10

-0.5 0.0 0.5




Comparison Between B3 and N1

0.30

Storm Surge #2

0
1

-UI
-1.0
0.30
S0.25 S0.20 S0.15 0.10 S0.05
- 0.00
-0.05-0.10
0~ -

.15U
-1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
.30
.25 Storm Surge #2
Peak SWL
.20 4.2 hours elapsed (model)
.15 seawall
.10 location
.05
0.00 .NG -I. ..
0.10
0-1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
.30
.25 Storm Surge #2
Descending SWL
.20 4.8 hours elapsed(model)
.15 seawall
.10 -location .05
0. NGYL---0.05-
0.10
0.15r- i"

-1.0

-0.5 0.0 0.5 1.U 1.0 2.U 2
model distance from seawall [m]

.5 O.U O.5

Figure 8: Elevation differences from initial profile comparison between B3 and N1.

0.25 Storm Surge #2
SWL escalation
0.20 3.0 hours elapsed (model)
0.15 seawall
0.10 location
0.05
-0.00 NGVD --0.05
-0.10 experiment B3 --- experiment NI
- experiment B3 ---- experiment N1

-0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
Storm Surge #2 SWL escalation
3.6 hours elapsed (model) seawall location
NGVD ..

I I I I I

0
0
0
0
0
0
0 0
0
0
0
-c
0
0
(
S-(




0
0

0
0
0
0
2.. -(
0
-c
0
0
.--0
0 w.0
0
2 -.(;
0 -0
0
0
0
0
0 0
,- 0
0
o
0
0
0

-1.0

-0.5 0.0

0.5 1.0 1.5 2.0 model distance from seawall [rr

2.5 3.0 3.5 4.0

Figure 9: Elevation differences from initial profile comparison between B4 and N2.
16

Comparison Between B4 and N2 .30
.25 Storm Surge #2
SWL escalation
.20 3.0 hours elapsed (model)
i.15 seawall
.10 /location
.05
0. 0 NGVD -- -- -- .. .. .. .. .. .
0.00
0.105
0.10 experiment B4 .... experiment N ,
0.15, 1.
-1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
.30
.25 Storm Surge #2
SWL escalation
.20 3.6 hours elapsed (model)
.15 seawall
.10 /location
.05
0.00 JQVD 1: . . ._ ,. .. . _. .
0.05
0.10
0. 15 ',,,
-1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
.30
.25 Storm Surge #2
Peak SWL
.20 4.2 hours elapsed (model)
.15 seawall
.10 /location
.05
*0 NGVD ---...-- .. -0.05 V
0.10
).15[',,,
-1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
.30
.25 Storm Surge #2
Descending SWL
.20 4.8 hours elapsed(model)
.15 seawall
.10 location
.05
).00 NGVD -----... . . . _---------).05
0.10
I __CU I__II I III




3.3 Effect of Complete Seawall Failure

The effect of complete seawall failure occurred during the peak surge level is discussed in this subsection. The effect is demonstrated by comparing the experimental results from F1 (regular waves) and F2 (random waves) with those from B3 (regular waves) and B4 (random waves). The varied and fixed parameters for F1, F2, B3, B4 experiments are shown in Table 3.
Figures 10 and 11 show the model beach profiles and the differences of profiles from the initial for F1 and F2, respectively, at the four SWL stages. From these figures, it is seen that in the stages of pre-escalation and escalation of SWL, before the seawall failure, the model beach profile behind the seawall was not affected by the combined forces of waves and storm surge, whereas in the peak SWL stage, after the seawall failure, the profile landward of the failed seawall was severely eroded.
Figures 12 and 13 show the comparisons of the profile differences from the initial between B3 and Fl (regular waves), and those between B4 and F2 (random waves), respectively, at the four different SWL stages. In the stages of pre-escalation and escalation of SWL, similar erosion patterns were observed in the nearshore region between B3 and Fl. This is because the experiments B3 and Fl are practically identical in these two stages before the seawall failure. The erosion observed was overall insignificant. Similar model beach profile responses were also observed in B4 and F2 during these two SWL stages.
In the peak SWL stage, erosion was severe in B3 and B4 in the area from the seawall to a seaward distance of 2m. (50m. in prototype). In F1 and F2, however, severe erosion occurred in the area behind the seawall. This erosion was greatest immediately landward of the seawall extending to a distance of
-1m. (-25m. prototype). Erosion in the descending SWL stage is quite small.
Accretion of sediment was seen in the nearshore area between 2m. and 3.5m. (50m. to 87.5m. in prototype) seaward of seawall in B3, B4, Fl, and F2, regardless of whether or not the seawall failed.
3.4 Effect of Partial Seawall Failure
This subsection investigates the effect of a partial seawall failure during the peak storm surge interval, based on the experimental results obtained from F3 (regular waves) and F4 (random waves). Figures 14 and 15 show the surveyed profiles and the corresponding differences of profiles from the initial for F3 and F4, respectively, at the four different SWL stages. In the stages of pre-escalation and escalation




Experiment F1

0.25 Storm Surge #2
Peak SWL
0.20 4.2 hours elapsed (model)
0.15
0.10 SWL: 0.144m
0.10 0.05
- - --NG V D
-0.10
--0.15

I I I I I I 1 1
-0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
model distance from seawall [m]

-1.0
0.30 0.25 0.20 S0.15 0.10
0.05
_n an

-0.05-
-0.10
--0.15
-1.0

Figure 10: Model beach profiles and elevation differences from initial profile Experiment Fl.
18

.4
-4,
4)

0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

Ir

Storm Surge #2 Descending SWL
4.8 hours elapsed(model)

SWL: 0.048m

NGVD

--------

.. I
~-~.~2

,

0.30

-0.5 0.0

---------------------------




Experiment F2



0.30
0.25 0.20 0.15 0.10
0.05

NGVD

seawall #1
- elevation 0.211m

Storm Surge #2
Pre-escalation of SWL 3.0 hours elapsed (model)

0.30
0.25 0.20 0.15 0.10 0.05
-0.00 NGVD
-0.05
-0.10
-0.15
-1.0 -0.5
0.30 0.25 0.20 0.15 0.10 0.05
-0.00 NGVD
-0.05
-0.10
-0.15
-1.0 -0.5

------ ----- -- model beach profile difference from initialI
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.
0.0 0.5 1'.0 1.5 2'.0 2'.5 3.0 3.5 4.,

seawall #1
,- elevation 0.211m

Storm Surge #2
SWL escalation
3.6 hours elapsed (model)

SWL: 0.12m
!I I I I I
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0-------0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

Storm Surge #2
Peak SWL
4.2 hours elapsed (model)
SWL: 0.144m

0.00 ------
--0.05 -"
-0.10
-0.15 I I
-1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.

model distance from seawall [m]

Figure 11: Model beach profiles and elevation differences from initial profile Experiment F2.

SWL: 0.036m

"

---- ---- --




0.3
S0.2 0.2 S0.1
0
0.1 0.0 0.
--0.0
-0.1
-0.1
0.3
0.2 0.2 S0.1 0.1 0.0 S- 0.0
.-.0.0
-0.1
-0.1
0.3

0.25 0.20 0.15 0.10
0.05
-0.00
-0.05
-0.10

Comparison Between B3 and F1
0
5 Storm Surge #2
SWL escalation
0 3.0 hours elapsed (model)
5 seawall
0 location
5
00 NGVD .,---. .. -<--I0
0 [- experiment B3 experiment F1
5 I I I.
-1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
0
5 Storm Surge #2
SWL escalation
0 3.6 hours elapsed (model)
5 seawall
0 location
5
NGVD
0
5 I
0
-1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
0

1.U -U.5 U.U

.D 3.0

.5 '.U

model distance from seawall [m]

Figure 12: Elevation differences from initial profile comparison between B3 and Fl.

Storm Surge #2
Peak SWL
4.2 hours elapsed (model)

seawall location

--I

-U.
0.3 0.2 0.2 0.1 0.1
0.0
-0.
-0.
- ID.
-0.1

15
-1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
0
5 Storm Surge #2
Descending SWL
0 4.8 hours elapsed(model)
5 seawall
0 location
5
0 0 N G- -.. -05
10 --. .
5

I

J I I i I i




0.30 0.25
0.20 0.15 0.10 0.05
--0.0
--0.0
--0.2
-0.15
0.30 0.25 0.20 0.15
0.10 0.05

Comparison Between B4 and F2
Storm Surge #2 SWL escalation
3.0 hours elapsed (model) seawall
location
0 NGVD 5
0- experiment B4 .... experiment F
-1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3 0 35 401

0.30
0.25
0.20[

U.0 I seawall
0.10 !location
0.05
-.0.00o ; GvD --- -- - .. . . ... . . ----------...
-0.05 11 V . ..
-.0.10
-.D.I 5 I I I n I I I

0.5 1.0 1.5 2.0 2.5 model distance from seawall [m]

-1.0
0.30
- 0.25
0.20 o 0.15 0.10
0.05
-0.00
.- 0.05
-0 00
-0.05-n In[

Figure 13: Elevation differences from initial profile comparison between B4 and F2.

0
0

Storm Surge #2
Peak SWL
4.2 hours elapsed (model)

-0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

)




Experiment F3

seawall #1
-elevation 0.211m

Storm Surge #2
Pre-escalation of SWL 3.0 hours elapsed (model)

0.30 0.25
0.20 0.15 0.10 0.05
-0.00

I ___

- model beach profile ---. difference from initial

-0.
-0.
-0.
0.
0.
0.
0.
0.
0.
0.
-0.
-0.
-0.
0.
0.
0.
0.
0.
0.
0.
-0.
-0.
-0.
0.
0.
0.
0.
0.
0.1
-0.
-0.
-0.
"-0.

SWL: 0.036m

NGVD

0510-

- 1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
30
25 seawall #1 Storm Surge #2
25 ----elevation 0.211m SWL escalation
20 3.6 hours elapsed (model)
15 SWL: 0.12m
10
05
00 NGVD _.-.. -- ...... --05
10
15
-1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
30
25 Storm Surge #2
Peak SWL
20 seawall 4.2 hours elapsed (model)
15 /elevation 0.101m
15
SWL: 0.144m
10
NGVD - - - - - - - - -
00 "--%05- "
10
15'
-1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
30
25 Storm Surge #2
Descending SWL
20 ./ seawall 4.8 hours elapsed(model)
15 elevation 0.101m
10
)5 SWL: 0.048m
05 NGVD --- ---.-- --------------------------10
15
-1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
model distance from seawall [m]

Figure 14: Model beach profiles and elevation differences from initial profile Experiment F3.
22




Experiment F4

---- difference from initial

NGVD

seawall elevation 0.lOlm

Storm Surge #2 Descending SWL
4.8 hours elapsed(model)

SWL: 0.048m

U.ULI ... ........
- .-- - - - - - - -. . _0.05j0.101
0.15 ,

-1.0 -0.5

0.5 1.0 1.5 2.0 2.5 3.0 model distance from seawall [m]

Figure 15: Model beach profiles and elevation differences from initial profile Experiment F4.
23

0.30 0.25
0.20 0.15 0.10 0.05

3.5 4.0

I




of SWL, before seawall failure, the model beach profile behind the seawall was not affected by the forcing of waves and storm surge, whereas in the peak SWL stages, after the seawall failure, the profile landward of the failed seawall was eroded significantly. A small accretion of sediment was observed in F4 (random wave experiment), in the area from the seawall to about 0.5m (12.5m prototype) seaward of the seawall.
Figures 16 and 17 compare the profile differences from the initial between B3 and F3 (regular waves) and those between B4 and F4 (random waves), respectively, for the four different SWL stages. In the stages of pre-escalation and escalation of SWL, model beach profile responses were similar in B3 and F3. This is expected since in these two SWL stages, before the seawall failure, the experiments B3 and Y3 are essentially identical. The model behaviors were also similar between B4 and F4 in these two SWL stages. Beach erosion was overall insignificant in these two SWL stages.
In Figures 16 and 17, severe erosion was observed during the peak SWL stage. In B3 and B4, the severe erosion occurred in the area from the seawall to a seaward distance of 2m (50m in prototype). In F3 and F4, however, severe erosion occurred immediately behind the seawall and continued landward with diminishing order to a landward distance of -1m (-25m prototype).
A small accretion pattern was seen in B3, B4, F3, and F4, in the nearshore area between 2m and
3.5m (50m and 87.5m prototype) seaward of seawall.
3.5 Effect of Regular Waves versus Random Waves
The effect of regular waves versus random waves in the wave tank beach model experiments is investigated based on the comparison of experiments among B3, B4, Ni, N2, F1, F2, F3, and F4. Specifically, the experiment B3 (regular waves) is compared to B4 (random waves); Ni (regular waves) to N2 (random waves); F1 (regular waves) to F2 (random waves), and F3 (regular waves) to F4 (random waves). Wave type is the only experimental parameter that differs between the two experiments in each comparison. However, B3 and B4 used Seawall #1 throughout the model experiments whereas in Ni and N2 no seawall was present in the models. In Experiments F1, F2, F3, and F4, Seawall #1 was placed in the model from the beginning of the experiment to the mid point of the time during peak SWL period. The seawall was changed to a lower elevation at the mid point of the time during peak SWL period to simulate various seawall failure conditions.




0.30 0.25
0.20 0.15 0.10
0.05

Comparison Between B3 and F3
Storm Surge #2 SWL escalation
3.0 hours elapsed (model)

--I
--I
--I
0
0
0
0
0
0
--I
--I
--I

-1.0

-0.5 0.0 0.5 1.0 1.5 2.0 2.5
model distance from seawall [im]

3.0 3.5

Figure 16: Elevation differences from initial profile comparison between B3 and F3.

seawall location

NGVD

0.05
0.10 experiment B3 .... experiment F3
0.15_ 1 1
-1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
0.30
9.25 Storm Surge #2
SWL escalation
.20 3.6 hours elapsed (model)
0.15 seawall
.10 /location
0.05
NGVD
0.00 . . . .
0.05
0.10
-.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
0.30
).25 Storm Surge #2
Peak SWL
).20 4.2 hours elapsed (model)
.15 seawall
).10 location
).05
0.00 ---- ---- ---- ---0.05 P
0.10
0.15 ,I
-1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
).30
.25 Storm Surge #2
Descending SWL
).20 4.8 hours elapsed(model)
).15 seawall
O.10 /location
).05
o~oo -----------------------.
0.05
0.10
0.15r 1 I I I

0




Comparison Between B4 and F4

0.30 0.25 0.20 0.15 0.10 0.05
--0.00
-0.05
--0.10-

--0 .15 I I I I
-1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
0.30
0.25 Storm Surge #2
SWL escalation
0.20 3.6 hours elapsed (model)
0.15 seawall
0.10 location
0.05
--0 00 NGVD -z-- ... .

--0.05
-0.10

-1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
0.30
0.25 Storm Surge #2
Peak SWL
0.20 4.2 hours elapsed (model)
).15 seawall
).10 location
).05
0.00 NGV rI -------------------- ---- -----0.05
0.10
0.15
-1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
0.30
0.25 Storm Surge #2
Descending SWL
0.20 4.8 hours elapsed(model)
).15 seawall
.10 location
0.05
0. NGVD - ... ..
0.05
0.10
0 1 5 1 1 l

-0.5 0.0

0.5 1.0 1.5 2.0 2.5
model distance from seawall [m]

Figure 17: Elevation differences from initial profile comparison between B4 and F4.
26

seawall location
- experiment B4

Storm Surge #2
SWL escalation
3.0 hours elapsed (model)

NGVD

---- experiment F4

0

0
0
0

"1
J

-1.0

3.0 3.5




Figures 18 to 21 present the comparisons of the profile differences from the initial between B3 and B4, N1 and N2, F1 and F2, and F3 and F4, respectively, at the four SWL stages described in Section 2.7. In Figure 18, which compares B3 and B4, mild erosion was seen in the area from the seawall to about 2m. (50m. prototype) seaward of the seawall. The erosion was the greatest at the seawall toe in B3 and B4 in the peak SWL stage. The erosion was generally more severe with deep scour at the seawall toe in B3 than in B4. The reason that the erosion is more vigorous in B3 (regular waves) than in B4 (random waves) is due to the fact that the wave energy level is slightly higher in B3 than in B4, which results more wave reflection and, consequently, greater erosion in front of the seawall in B3. Landward of the seawall, erosion is noticeably small in both B3 and B4.
In Figure 19, which compares Nl and N2, in which no seawall is present, major erosion occurred in. the upper beach profile area between the landward distances of 0m. and -1m. (-25m. prototype). Erosion was significant in the upper beach profile in the stage of escalation of SWL. This erosion increased in the peak SWL stage. An interesting result is that although the wave energy content is greater in N1 (regular waves) than in N2 (random waves), the erosion in the upper beach profile appears to be less severe in N1 than in N2. Erosion is insignificant seaward of this erosive area in N1 and N2.
In Figure 20, which compares F1 and F2, the erosion was negligibly small behind the seawall in the stages of pre-escalation and escalation of SWL. However, erosion was extensive in the area from the seawall to a landward distance of -1m. (-25m. prototype) after the seawall failure during the peak SWL interval. This erosion worsened slightly at the descending SWL stage. The erosion was overall more severe in F1 than in F2. Similar model behaviors were also seen in the comparison of F3 and F4, as shown in Figure 21. Overall, generally small differences occurred between these experiments conducted with regular and random waves with the significant wave heights equal to those of the regular wave tests.
4 Summary
In the present report, the model beach profile behavior in Experiments B3, B4, N1, N2, F1, F2, F3, and F4, were examined to investigate the following effects: (1) model behavior with and without a seawall, (2) complete seawall failure during the peak SWL interval, (3) partial seawall failure during the peak SWL interval, and (4) regular waves versus random waves. These experiments were compared based on the same initial profile #1, storm surge #2, and sediment #2. The varied and fixed parameters used in these experiments were presented in Table 3. Comparisons of model beach profile responses were




Comparison Between B3 and B4

0.30 0.25 0.20 0.15 0.10 0.05
-0.00
-0.05
-0.10

Storm Surge #2
SWL escalation
3.0 hours elapsed (model)

seawall #1 location

I- experiment B3

---- experiment B4

-I0.15 1 I I I I I I
1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.{
0.30
0.25 Storm Surge #2
SWL escalation
0.20 3.6 hours elapsed (model)
0.15 seawall #1
0.10 location
0.05
-0.00 NGVD-0.05
-0.10
-0 1 I I i I

Storm Surge #2 Peak SWL
4.2 hours elapsed (model)
seawall #1 location

NGY-11 -----__ _ _ _ _ I I l l
1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
- Storm Surge #2
Descending SWL
4.8 hours elapsed(model)
seawall #1 location
____ __I I I l l

I1.U

-U.model distance from seawall [ .]
model distance from seawall [m]

Figure 18: Elevation differences from initial profile comparison between B3 and B4.

NGVD

-0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

0.30 0.25 0.20 S0.15
0
0.10
0.05 S-0.00
*- -0.05
0
-0.10
-0.15
0.30 0.25
0.20 S0.15
0
0.10
2 0.05 S-0.00
-0.05
0
-0.10
-0.15

. .
-1.0

3.U 3.5




0.30 S0.25 0.20 0.15 0.10 0.05 S--0.00
--0.05
0
--0.10

Comparison Between N1 and N2
Storm Surge #2 SWL escalation
3.0 hours elapsed (model)

0
0
M
73
0
0
V
.8
V
a
6

-1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2
model distance from seawall [m]

Figure 19: Elevation differences from initial profile comparison between N1 and N2.

SNGVD ..
I- -

- experiment N1 ---- experiment NE

-1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
0.30
0.25 Storm Surge #2
SWL escalation
0.20 3.6 hours elapsed (model)
0.15 0.10 0.05
0.00 I-VD..
--0.05 ----0.10
0.15
-1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
0.30
0.25 Storm Surge #2
Peak SWL
0.20 4.2 hours elapsed (model)
0.15 0.10 0.05
.00.NGVD -----0.00 V --------- -- -------
-0.05
--0.10
--0.150
-1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
0.30
0.25 Storm Surge #2
Descending SWL
0.20 4.8 hours elapsed(model)
0.15 0.10 0.05
--0.00 NGVD ----
--0.05
--0.10
-0 15r

I I

..

.9

.5 3.0 3.5 4.0




0.30 0.25 0.20 0.15 0.10 0.05 -

Comparison Between F1 and F2
Storm Surge #2 SWL escalation
3.0 hours elapsed (model) seawall #1
location
NGVD --------------- .----

0
0
0 0
o
0 V)

(
0 0.,


0
0

0

-0.5 0.0

0.5 1.0 1.5 2.0
model distance from seawall [ix

2.5 3.0 3.5 4.0

Figure 20: Elevation differences from initial profile comparison between F1 and F2.

-0.05
0.10
0- experiment FI ---- experiment FZ
-0.151 I II
-1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
0.30
0.25 Storm Surge #2
SWL escalation
0.20 3.6 hours elapsed (model)
0.15 seawall #1
0.10 location
0.05
-0.00 NGVD -- --0.05
0.10
0.15 I
-1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
0.30
0.25 Storm Surge #2
Peak SWL
0.20 4.2 hours elapsed (model)
0.15
0.10
0.05
0 .0 0 N G D'-.. .. . --..--. - .. . .
.0.05
0.10
0.15 n ,
-1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
0.30
0.25 Storm Surge #2
Descending SWL
0.20 4.8 hours elapsed(model)
0.15
0.10
0.05
0.00 NGVD ------
0.05
0.10-

. -1.0




Comparison Between F3 and F4

0.30

0.25 Storm Surge #2
SWL escalation
0.20 3.0 hours elapsed (model)
0.15 seawall #1
0.10 location
0.05
-0_O NGVD ; --.

--0.05
--0.10

0
5 -Storm Surge #2 Peak SWL
0 4.2 hours elapsed (model)
5 seawall
0 -location
NGVD r --05
10
15 I i I I
-1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
30
25 Storm Surge #2
Descending SWL
20 4.8 hours elapsed(model)
15 seawall
10 location
05 -r
00 NGVD i --- - ..-05
10
I I i I I I II

-1.0

-0.5 0.0 0.5 1.0 1.5 2.0 2
model distance from seawall [m]

.5 3.0 3.5 4.0

Figure 21: Elevation differences from initial profile comparison between F3 and F4.

- experiment F3 ---- experiment F4
l I I ii

3.0 3.5

1.0 1.5

0.3
0.1
0.2 0.1 0.1 0.0
-0.
0.
0.
-0.
0.
0.
0.
0.
0.
0.
-0.
-0.
-0.

0 15, 1

t

----|




carried out for four different SWL stages, which are the pre-escalation of SWL, escalation of SWL, peak SWL, and descending SWL stages, respectively, as described in Section 2.7.
The effect of a normal seawall versus no seawall case is evaluated by comparing the experimental results between B3 and Ni (regular wave experiments), and between B4 and N2 (random wave experiments). When a seawall is present in the model, as in the cases of B3 and B4, it is seen to provide sufficient protection to the model beach profile behind the seawall. However, it also induces significant erosion in the area in front of the seawall with deep scour at the seawall toe, particularly in the peak SWL stage. This significant erosion is casued by the large reflection of waves at the seawall. On the other hand, when no seawall is present in the model, as in the cases of Ni and N2, the erosion can be significant in the area landward of the mean sea level. Seaward of this erosive area, erosion is quite small. In fact, limited accretion of sediment occurred in the nearshore area between the seaward distances of 2mn and 3.5m (50m to 87.5m prototype). This accretion pattern was also observed in the Experiments B3 and B4.
The effect of the complete seawall failure during the peak SWL stage is investigated by comparing the experimental results from F1 and B3 (regular waves) experiments, and from F2 and B4 (random waves) experiments. Both F1 and F2 utilized Seawall #1 in the model prior to the peak SWL stage at which time seawall failure was simulated. The seawall was lowered to the elevation of 0 NGVD to simulate a completely failure midway through the peak SWL stage. The model beach profile erosion was insignificant in the stages of pre-escalation and escalation of SWL, before the failure. However, landward of the seawall the model beach profile was extremely significant in the peak SWL stage, after the seawall failure. Accretion of sediment was seen in B3, B4, Fl, and F4, in the nearshore area between the horizontal distances of 2m and 3.5m (50m to 87.5m prototype), regardless of whether or not the seawall failed. Subsequent to seawall failure, erosion occurred with surprising rapidity.
The effect due to a partially failed seawall, which occurred midway through the peak surge level, was simulated in Experimental results F3 and F4. Again, Seawall #1 was used in F3 and F4 prior to the mid peak SWL interval and was lowered to half height at 10.56cm (2.64m prototype) NGVD halfway through the peak SWL interval to simulate a partially failed seawall. At the stages of pre-escalation and escalation of SWL, before the failure, the model beach profile behind the seawall was not affected in the model. However, in the peak SWL stage after the seawall failure, the model beach profile landward of the partially failed seawall was heavily and rapidly eroded, limited accretion of sediment was observed in F4 (random waves) experiment in the area from the seawall to about 0.5m (12.5m prototype) seaward of the




seawall. A general trend of accretion pattern in F3 and F4 in the nearshore area between the horizontal distances of 2m and 3.5m (50m to 87.5m prototype) was also observed.
The effect of regular versus random waves in the model was investigated by comparing B3 (regular waves) and B4 (random waves); Ni (regular waves) and N2 (random waves); F1 (regular waves) and F2 (random waves); F3 (regular waves) and F4 (random waves). Comparison of B3 and B4 shows similar erosion and accretion patterns with the erosion occurred in the area from the seawall to about 2m (50m prototype) seaward of the seawall. The erosion was overall more severe with deeper scour at the seawall toe in B3 than in B4. The larger erosion in B3 in front of the seawall is caused by more reflection of waves at the seawall in B3 than in B4.
Comparison of Ni and N2, in which no seawall is present in the model, shows similar erosion and accretion patterns with major erosion in the upper beach profile area between the horizontal distances of Om and -1m (-25m prototype). Although wave energy content level is greater in Ni (regular waves) than in N2 (random waves), the upper beach profile erosion appears to be less severe in Ni than in N2. Erosion is insignificant seaward of this erosive area.
Comparison of Fi and F2 shows little erosion behind the seawall in the stages of pre-escalation and escalation of SWL. However, erosion was extensive in the area landward of the seawall after the seawall failure at midway of the peak SWL stage. This erosion was somewhat more severe in Fi (regular waves) than in F2 (random waves). Similar model beach profile behaviors were also seen in the comparison of F3 and F4, the partial seawall failure experiments. Overall, the differences due to the testing with regular or irregular waves was small.
Acknowledgements
The authors would like to thank Mr. M. Goodrich and Mr. P. Miselis, both graduate students in the Coastal and Oceanographic engineering Department, University of Florida, for their assistance in preparing and conducting laboratory experiments.




5 References

[1] Dean, R.G., Chiu, T.Y., and Wang, S.Y., 1992. Combined total storm tide frequency analysis for Palm Beach County, Florida, Division of Beaches and Shores, Department of Natural Resources, State of Florida, 58pp.
[2] Thompson, L.L., Lin, L., and Dean, R.G., 1993. Evaluation study and comparison of erosion models and effects of seawalls for the CCCL, Physical Modelling Program Report- Interim Reports 1 and 2. Coastal and Oceanographic Engineering Department, University of Florida. UFL/COEL-94/003.
[3] Thompson, L.L., Lin, L., and Dean, R.G., 1993. Evaluation study and comparison of erosion models and effects of seawalls for the CCCL, Physical Modelling Program Report- Interim Report 3. Coastal and Oceanographic Engineering Department, University of Florida. UFL/COEL-94/005.