|
UFL/COEL-95/009
PERFORMANCE OF THE P.E.P. REEF INSTALLATION
TWENTY MONTHS RESULTS
AUGUST 1993 TO MARCH 1995
by
Robert G. Dean
and
Renjie Chen
April, 1995
Prepared for:
Department of Environmental Protection,
and
Town of Palm Beach, Florida
UFL/COEL-95/009
PERFORMANCE OF THE P. E. P. REEF INSTALLATION
TWENTY MONTHS RESULTS
AUGUST 1993 TO MARCH 1995
April 1995
Prepared for;
Department of Environmental Protection
and
Town of Palm Beach
Prepared by:
Robert G. Dean and Renjie Chen
Department of Coastal and Oceanographic Engineering
University of Florida
Gainesville, Florida
TABLE OF CONTENTS
PAGE
LIST OF FIGURES ...................................................... iii
INTRODUCTION ................ ....................................... 1
RESULTS ..............................................................1
Bathym etric Changes ................................................. 1
Longshore Distribution of Volumetric Changes ............................. 1
Total Volume Changes ................ ............................... 5
POSSIBLE INTERPRETATION AND SUMMARY .............................. 5
REFERENCES ................ .......................................... 9
LIST OF FIGURES
FIGURE PAGE
1 Isolines of Elevation Change (ft) December 1994 to March 1995 .................. 2
2 Longshore Distribution of Volume Changes Landward of Reef. December 1994 to
March 1995 .......................................................... 3
3 Longshore Distribution of Volume Changes for 240 Feet Distance Seaward of Reef.
December 1994 to M arch 1995 ......................................... 4
4 Volumetric Changes in Six Zones. December 1994 to March 1995 ................. 6
5 Cumulative Volumetric Changes Landward of Reef Alignment Following
Installation ................................................. ......... 7
6 Cumulative Volumetric Changes Seaward (240 Feet) of Reef Alignment Following
Installation .. ........................................ ... ........... 8
PERFORMANCE OF THE P. E. P. REEF INSTALLATION
TWENTY MONTHS RESULTS
AUGUST 1993 TO MARCH 1995
INTRODUCTION
This report presents a preliminary and partial analysis of the March, 1995 survey data collected in
conjunction with the PEP Reef monitoring program at the Midtown Beach installation. In particular,
the analysis presented herein includes only the profile data concentrating on volume changes. The data
representing the elevations of the individual PEP Reef units has just been received. After receipt of
all data, the full results of this monitoring period will be incorporated in a later report.
RESULTS
The survey analysis results will be presented in the same format as in previous reports.
Bathymetric Changes
Figure 1 presents contours ofbathymetric changes in the vicinity of the PEP Reef for the intersurvey
period: December 1994 to March 1995. It is seen that landward of the Reef, there was some accretion
near the northern end of the Reef. However, as will be discussed later, the erosion south of the Reef
more than offset this accretion. On an average basis, the water depths landward of the Reef have
increased 2.9 feet since installation of the first 57 units in July 1992 and 2.3 feet since installation of
the full 330 units in August 1993.
Longshore Distribution of Volumetric Changes
The longshore distribution of volumetric changes landward and seaward of the Reef are shown in
Figures 2 and 3, respectively. Note the areas of accretion and erosion landward of the Reef as
discussed above.
f395old5 Apr. 16, 1995
250
, 200 '
150 -i : :
'100 -' o o
1 0
S50
Cd ,..
50 '
100 -"
-150 -
P.4.-200 "" ,"
-250
0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000
--- North Distance from monument 92F (ft)
Elevation Change (ft)
December 1994 to March 1995
(0.5 ft. contours)
Figure 1. Isolines of Elevation Change (ft) December 1994 to March 1995.
f395old2 Apr. 16, 1995
5 0 I I I I Ii i i I
-- Reef
4-( 40 ...... -- Dec.94-Mar.95
co 3 0 ..... ..... ....
< 20
Q) 10
S-10 -
0
a 2 0 -----.- ..... I ..... ..
S 3 0 ........... .. ...- -.... .I- ..................... ...................
Q ) 2 0 _- . . . ... . . .. .. .. .. . . . .. ..
-30 --------------------------------- : -
-50 I I I I
0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000
--- North Distance from monument 92F (ft)
Volume Change (yds3/lf)
Inner Region
Figure 2. Longshore Distribution of Volume Changes Landward of Reef. December 1994 to March 1995.
50
40
c 30
20
10
zj 0
*" -10
-20
S-30
S-40
-^n
f395old3 Apr. 16,1995
---------- -'--------------- .. Dec.94-Mar.95
............. .............................. ................................ ................................ ........ -- Dec.94-Mar.95
----- -- --- -- . . . . . ..... .... ... ...... . ...... .. .. .. ..... -- - -:-- - - - - - -
-t
SIReef -
0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000
---North Distance from monument 92F (ft)
Volume Change (yds3/lf)
Outer Region
Figure 3. Longshore Distribution of Volume Changes for 240 Feet Distance Seaward of Reef. December 1994 to March 1995.
Total Volume Changes
The volumetric changes in the six zones during the December 1994 to March 1995 intersurvey period
are shown in Figure 4. It is seen that the regions losing the greatest amount of material are those
landward of the Reef and the area to the south and landward of the Reef alignment. The area to the
south lost 23,900 cubic yards and the area directly landward of the Reef lost 19,200 cubic yards.
The history of volumetric changes in the six zones defined in earlier reports is shown in Figures 5 and
6, respectively. Of particular interest is that the zone immediately landward of the Reef has continued
to lose sediment.
POSSIBLE INTERPRETATION AND SUMMARY
The total volumetric losses landward of the PEP Reef have continued. Although there remain some
uncertainties regarding the loss mechanisms, a scenario consistent with the data and known
mechanisms is as follows.
As found in the laboratory tests for the Vero Beach installation (Dean et al., 1994), as documented
in coastal engineering literature (Longuet-Higgins, 1967; Diskin et al., 1970; Dalrymple and Dean,
1971; Gourlay, 1971; Dalrymple, 1978; Seelig and Walton, 1980) and as suggested from full scale
field tests in Japan (Funakoshi et al., 1994), one effect of a low submerged breakwater (reef) is the
pumping of water over the reef and, due to the presence of the reef over a portion of the water
column, some of this water is ponded behind the reef and a portion of the ponded water flows
longshore rather than returning to sea as undertow as it would if the reef were not present. This
longshore flow of water also transports sand in the longshore direction to the ends of the reef where
it is released and deposited as the current expands, reduces in magnitude and loses its sediment
transport capacity.
In the early months of the PEP Reef installation, the mechanism above is consistent with the
deposition of volumes of sediment north and south of the Reef which were approximately
commensurate with the volume eroded behind the Reef. Due to the predominant wave direction from
the north, this left a particularly large sand deposit near the south end of the Reef. The effects of the
Azum9a Apr. 16. 1995
December 1994 to March 1995
5,300 2,700
R'Ree
-19,200
-23,900
*- 240'
-3,000
-6,400
Figure 4. Volumetric Changes in Six Zones. December 1994 to March1995.
94A
95E
99B
101A
2000'
4000'
2000'
iL
--< 240'+/--
Landward of Reef Alignment
150000
50000
-50000
-150000
- -*.- 2000' N and S of Reef
---- within Reef confines zone 3)
- Net
---- 2000'N (zone 1)
*--*.- 2000' S (zone 5)
..... V---- --..... -V..
Figure 5. Cumulative Volumetric Changes Landward of Reef Alignment Following Installation.
Seaward of Reef Alignment
150000
50000
-50000
-150000
S--*.- 2000' N and S of Reef
--U-- within Reef confines (zone 4)
Net
--4-- 2000' N (zone 2)
S---V-- 2000' (zone 6)
Time ( months)
0 3 17 2,5 33
4/93 8/93 1 /93 3/94 7/9 11/94 12/94 0
4/93 8/93 12/93 3/94 7/94 11/9412/9403
Figure 6. Cumulative Volumetric Changes Seaward (240 Feet) of Reef Alignment Following Installation.
/95
Total Volume Changes
The volumetric changes in the six zones during the December 1994 to March 1995 intersurvey period
are shown in Figure 4. It is seen that the regions losing the greatest amount of material are those
landward of the Reef and the area to the south and landward of the Reef alignment. The area to the
south lost 23,900 cubic yards and the area directly landward of the Reef lost 19,200 cubic yards.
The history of volumetric changes in the six zones defined in earlier reports is shown in Figures 5 and
6, respectively. Of particular interest is that the zone immediately landward of the Reef has continued
to lose sediment.
POSSIBLE INTERPRETATION AND SUMMARY
The total volumetric losses landward of the PEP Reef have continued. Although there remain some
uncertainties regarding the loss mechanisms, a scenario consistent with the data and known
mechanisms is as follows.
As found in the laboratory tests for the Vero Beach installation (Dean et al., 1994), as documented
in coastal engineering literature (Longuet-Higgins, 1967; Diskin et al., 1970; Dalrymple and Dean,
1971; Gourlay, 1971; Dalrymple, 1978; Seelig and Walton, 1980) and as suggested from full scale
field tests in Japan (Funakoshi et al., 1994), one effect of a low submerged breakwater (reef) is the
pumping of water over the reef and, due to the presence of the reef over a portion of the water
column, some of this water is ponded behind the reef and a portion of the ponded water flows
longshore rather than returning to sea as undertow as it would if the reef were not present. This
longshore flow of water also transports sand in the longshore direction to the ends of the reef where
it is released and deposited as the current expands, reduces in magnitude and loses its sediment
transport capacity.
In the early months of the PEP Reef installation, the mechanism above is consistent with the
deposition of volumes of sediment north and south of the Reef which were approximately
commensurate with the volume eroded behind the Reef. Due to the predominant wave direction from
the north, this left a particularly large sand deposit near the south end of the Reef. The effects of the
waves on this deposit were twofold. One tendency was that of the waves to drive the sand behind the
Reef from where it had originated and the other tendency was to transport the sand to the south. The
tendency to drive the sand behind the breakwater was counterbalanced by the increased longshore
currents referenced above. The southerly transport tendency caused a slow diminution of the deposit
immediately south of the Reef and much of this removed sand was deposited farther south. The
removal of the deposit at the south end of the Reef caused the transport processes from behind the
Reef to be more efficient which offset to some degree the reduced tendency for sediment removal
from behind the Reef due to the greater water depths.
REFERENCES
Dalrymple, R. A. And R. G. Dean (1971) a Discussion of"Piling-Up Behind Low and Submerged
Breakwaters" Discussion in Journal of Waterways and Harbors Division, ASCE, Vol. 97,
WW2, pp.423-427.
Dalrymple, R. A. (1978) "Rip Currents and Their Causes", Proceedings, Sixteenth International
Conference on Coastal Engineering, American Society of Civil Engineers, pp. 1414-1427.
Dean, R. G., A. E. Browder, M. S. Goodrich and D.G. Donaldson (1994) "Model Tests of the
Proposed P.E. P Reef Installation at Vero Beach, Florida", University of Florida Department
of Coastal and Oceanographic Engineering, Report No. UFL/COEL-94/012.
Diskin, M. H., M. J. Vajda and I. Amir (1970)"Piling-Up Behind Low and Submerged Breakwaters"
Journal of Waterways and Harbors Division, ASCE, Vol. 96, WW2, pp. 359-372.
Funakoshi, H., T. Siozawa, T. Tadokoro, and S. Tsuda (1994) "Drifting Characteristics of Littoral
Sand Around Submerged Breakwater (Field Study on Niigata West Coast)", Proceedings,
International Conference on Hydro-Technical Engineering for Port and Harbor Construction,
Yokuska, Japan, pp. 1157-1178.
Gourlay, M. R. (1971) a Discussion of "Piling-Up Behind Low and Submerged Breakwaters"
Discussion in Journal of Waterways and Harbors Division, ASCE, Vol. 97, WW1, pp. 219-
222.
Longuet-Higgins, M.S. (1967) "On the Wave-Induced Difference in Mean Sea Level Between the
Two Sides of a Submerged Breakwater", Journal of Marine Research, Vol. 25, No. 2.
Seelig, W. N. And T. L. Walton (1980) "Estimation of Flow Through Offshore Breakwater Gaps
Generated by wave Overtopping" U. S. Army Corps of Engineers, Coastal Engineering Research
Center, Report No. CETA 80-8.
waves on this deposit were twofold. One tendency was that of the waves to drive the sand behind the
Reef from where it had originated and the other tendency was to transport the sand to the south. The
tendency to drive the sand behind the breakwater was counterbalanced by the increased longshore
currents referenced above. The southerly transport tendency caused a slow diminution of the deposit
immediately south of the Reef and much of this removed sand was deposited farther south. The
removal of the deposit at the south end of the Reef caused the transport processes from behind the
Reef to be more efficient which offset to some degree the reduced tendency for sediment removal
from behind the Reef due to the greater water depths.
REFERENCES
Dalrymple, R. A. And R. G. Dean (1971) a Discussion of"Piling-Up Behind Low and Submerged
Breakwaters" Discussion in Journal of Waterways and Harbors Division, ASCE, Vol. 97,
WW2, pp.423-427.
Dalrymple, R. A. (1978) "Rip Currents and Their Causes", Proceedings, Sixteenth International
Conference on Coastal Engineering, American Society of Civil Engineers, pp. 1414-1427.
Dean, R. G., A. E. Browder, M. S. Goodrich and D.G. Donaldson (1994) "Model Tests of the
Proposed P.E. P Reef Installation at Vero Beach, Florida", University of Florida Department
of Coastal and Oceanographic Engineering, Report No. UFL/COEL-94/012.
Diskin, M. H., M. J. Vajda and I. Amir (1970)"Piling-Up Behind Low and Submerged Breakwaters"
Journal of Waterways and Harbors Division, ASCE, Vol. 96, WW2, pp. 359-372.
Funakoshi, H., T. Siozawa, T. Tadokoro, and S. Tsuda (1994) "Drifting Characteristics of Littoral
Sand Around Submerged Breakwater (Field Study on Niigata West Coast)", Proceedings,
International Conference on Hydro-Technical Engineering for Port and Harbor Construction,
Yokuska, Japan, pp. 1157-1178.
Gourlay, M. R. (1971) a Discussion of "Piling-Up Behind Low and Submerged Breakwaters"
Discussion in Journal of Waterways and Harbors Division, ASCE, Vol. 97, WW1, pp. 219-
222.
Longuet-Higgins, M.S. (1967) "On the Wave-Induced Difference in Mean Sea Level Between the
Two Sides of a Submerged Breakwater", Journal of Marine Research, Vol. 25, No. 2.
|
RSS
HIDE
