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Title: Shoreline response and sediment transport in the vicinity of Lake Worth entrance on Palm Beach Island
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Permanent Link: http://ufdc.ufl.edu/UF00089494/00001
 Material Information
Title: Shoreline response and sediment transport in the vicinity of Lake Worth entrance on Palm Beach Island
Physical Description: Book
Creator: Dean, Robert G.
Publisher: Department of Coastal and Oceanographic Engineering, University of Florida
Publication Date: 1995
 Subjects
Subject: Coastal Engineering
Spatial Coverage: North America -- United States of America -- Florida
 Notes
Funding: This publication is being made available as part of the report series written by the faculty, staff, and students of the Coastal and Oceanographic Program of the Department of Civil and Coastal Engineering.
 Record Information
Bibliographic ID: UF00089494
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.

Table of Contents
    Cover
        Cover
    Title Page
        Page i
    Table of Contents
        Page ii
    List of Figures
        Page iii
    Shoreline response and sediment transport in the vicinity of Lake Worth entrance on Palml Beach Island
        Page 1
        Page 2
        Page 3
        Page 4
        Page 5
        Page 6
Full Text



UFL/COEL-95/024


SHORELINE RESPONSE AND SEDIMENT TRANSPORT
IN THE VICINITY OF LAKE WORTH ENTRANCE ON
PALM BEACH ISLAND

DECEMBER 1993 TO JUNE 1995



By



Robert G. Dean
and
Renjie Chen


November 1995




Prepared for:

Town of Palm Beach








UFL/COEL-95/024


SHORELINE RESPONSE AND SEDIMENT TRANSPORT IN THE VICINITY OF
LAKE WORTH ENTRANCE ON PALM BEACH ISLAND

DECEMBER 1993 TO JUNE 1995






November 1995







Prepared for:

Town of Palm Beach







Prepared by:

Robert G. Dean
and
Renjie Chen




Coastal and Oceanographic Engineering Department
University of Florida
Gainesville, Florida 32611








TABLE OF CONTENTS


LIST OF FIGURES ................... ................................... iii

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

DESCRIPTION OF AVAILABLE DATA ........................................ 1

ANALYSIS AND INTERPRETATION OF RESULTS .............................. 1

December 1993 to March 1994 ......................................... 4

March 1994 to November 1994 ...................................... ... 4

November 1994 to December 1994 ..................................... 4

December 1994 to M arch 1995 ...................................... ... 4

March 1995 to June 1995 .................. ........................... 4

December 1993 to June 1995 .......................................... 6

DISCUSSION ................... ...........................................6

SUMMARY AND CONCLUSION ............ ................................. 6

REFERENCE ............ ............................................ 6








LIST OF FIGURES


FIGURE PAGE

1 Survey Plan Immediately South of Lake Worth Entrance ........................ 2

2 Placement Distribution of 1993-1994 Beach Nourishment ....................... 3

3 Placement Distribution of 1994-1995 Beach Nourishment ....................... 3

4 Longshore Distribution of Longshore Sediment Transport, Various Intersurvey
Intervals ....................................................... 5







SHORELINE RESPONSE AND SEDIMENT TRANSPORT IN THE VICINITY OF
LAKE WORTH ENTRANCE ON PALM BEACH ISLAND



INTRODUCTION

This report interprets shoreline changes and sediment placement volumes in the vicinity of the
north end of Palm Beach Island in terms of sediment transport in the general region placed and
transported toward the south.


DESCRIPTION OF AVAILABLE DATA

The dates for the survey data available for the analysis presented in this report are: December
1993, March 1994, November 1994, December 1994, March 1995 and June 1995. In addition to the
surveys, there were two nourishments which occurred from December 1993 to March 1994 and
November 1994 to February 1995. The volumes placed during these two periods were 169,700
cu.yds. and 196,620 cu.yds., respectively. The approximate distributions of the material placed were
provided by the U.S. Army Corps of Engineers.

The survey plan comprises 24 profiles commencing 200 ft. south of the Lake Worth Entrance
south jetty as shown in Figure 1. The placements during the 1993-1994 and 1994-1995 beach
nourishments are presented in Figures 2 and 3, respectively.


ANALYSIS AND INTERPRETATION OF RESULTS

The volumes placed in the two nourishment periods and the profile changes from the various
surveys were interpreted to determine sediment transport and redistribution toward the south in the
following manner. The continuity equation can be expressed as

S+ =S(x) (1)
ax at

in which x is the distance south from the south jetty at Lake Worth Entrance, t is time, Q is the net
longshore sediment transport, S is the average rate of nourishment placement per unit beach length
and V is the sediment volume per unit length at a particular location along the beach. Integrating this
equation from the south jetty where the longshore sediment transport is considered to be zero to the
limits of the surveyed area yields

Q(x) = at + f S(x)dx (2)
Jo At (2)'











Profile Number


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Distance South of South Jetty (ft)


Figure 1. Survey Plan Immediately South of Lake Worth Entrance


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1993-1994 Nourishment 169,700 yd3


0 1000 2000 3000 4000 5000 6000 7000
Distance South of South Jetty (ft)
Figure 2. Placement Distribution of 1993-1994 Beach Nourishment


1994-1995 Nourishment 196,620 yd3


0 1000 2000 3000 4000 5000
Distance South of South Jetty (ft)


6000 7000


Figure 3. Placement Distribution of 1994-1995 Beach Nourishment









The transports associated with the various surveys are shown in Figure 4. These results interpreted
in terms of net annual longshore sediment transport are discussed below for the various intersurvey
periods.


December 1993 to March 1994

It is seen that the transport during this period increased fairly uniformly from the south jetty
to the end of the survey area. The net transport rate during this period was directed to the south at
a rate of approximately 400,000 cu.yds. per year. It is noted that this is a Winter period and also this
high rate may be explained partially by the fact that the nourished material may have created an
anomaly or "bulge" in the shoreline which tended to induce transport to the south.


March 1994 to November 1994

During this period, the transport over the 7,000 ft. monitored shoreline was actually directed
to the north at a rate of 54,000 cu.yds. per year. This period encompasses the entire Summer of 1994
during which northerly transport would be anticipated and also portions of the Winter seasons both
preceding and following the Summer of 1994. Although the effects are somewhat surprising, when
combined with the previous period, the net longshore sediment transport encompassing both
intersurvey periods is still to the south.


November 1994 to December 1994

This is an extremely short period. Additionally, some material from this second nourishment
effort was placed during this period complicating its interpretation. However, if strictly interpreted,
it would yield a very large longshore sediment transport rate to the south on the order of 450,000
cu.yds. per year; however in interpreting the figure, it should be noted that this rate is for an
extremely short period.


December 1994 to March 1995

During this four month period, the net longshore sediment transport was quite small,
amounting to an equivalent rate of approximately only 50,000 cu.yds. directed to the south.


March 1995 to June 1995

This three month period extends up to the most recent monitoring period and is equivalent
to 150,000 cu.yds. per year directed to the south.








500000



400000



300000


1000 2000 3000 4000 5000 6000


Distance from R76 (feet)


Figure 4. Longshore Distribution of Longshore Sediment Transport, Various Intersurvey Intervals


7000


Nourishment periods:12/93-03/94 and 11/94-02/95
| . . . . . . . . . . . . . . . . . . . . .

---- 12/93-03/94 .................. .................................. ................. ........
03/94-11/94
.. .11/94-12/94 .... ............................... ........ ..... ............
.-.*- 12/94-03/95
.--.:................ ---------- ................. : ................... :.................
03/95-06/95

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............... .. ... ................ ,.. .. .......... ..... ............ ...
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December 1993 to June 1995


This period encompasses all surveys for the entire 18 month period monitored. The total net
longshore sediment transport to the south is 156,000 cu.yds. which equates to 104,000 cu.yds. per
year.

On the basis of the results presented earlier, two results are evident: (1) the material placed
immediately south of the jetty does provide nourishment to the beaches to the south, and (2) the net
longshore sediment transport to the south is on the order of 100,000 cu.yds. per year.


DISCUSSION

There are some uncertainties associated with the results presented above that merit discussion.
First, the time period of 18 months, although significant, is relatively short and could have represented
a period during which the southerly net longshore sediment transport was not representative. It is
believed, based on calculations using wave data and wave direction, that there can be substantial
variabilities in longshore sediment transport including years when the net sediment transport direction
is even opposite to the average direction. A second possibility for uncertainty would be if some of
the sediments placed were carried back into the inlet. However, it is believed that the material placed
from maintenance dredging of the inlet was of such a size that it was not easily suspended and carried
back into the inlet. If sediments were transported back to the inlet, the effect on the calculated
longshore sediment transport would be to reduce the values below the approximate 100,000 cu.yds.
described above. This is because the volumetric reductions would be into the inlet rather than to the
south as concluded here.


SUMMARY AND CONCLUSION

Based on the results provided herein, the predominantly northeast waves and the material
placed during the Winters of 1993-94 and 1994-95 have resulted in sediment transport to the south
over the 7,000 ft. distance monitored. These values are approximately 100,000 cu.yds. per year and
compare reasonably well with an estimate (Dean, 1995) of 132,000 cu.yds. per year based on volumes
of material placed and associated shoreline changes occurring over a 44 year period.


REFERENCE

Dean, R.G. (1995) "Historical Shoreline Changes in the Vicinity of the PEP Reef Installation and
Reef Effects, Palm Beach, Florida", UFL/COEL-95/008, Coastal and Oceanographic Engineering
Department, University of Florida, Gainesville, Florida, 17 pages.




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