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Perdido Key Beach Nourishment Project : Gulf Islands National Seashore

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Title:
Perdido Key Beach Nourishment Project : Gulf Islands National Seashore
Series Title:
Perdido Key Beach Nourishment Project : Gulf Islands National Seashore
Creator:
Browder, Albert E.
Place of Publication:
Gainesville, Fla.
Publisher:
Coastal & Oceanographic Engineering Dept. of Civil & Coastal Engineering, University of Florida
Language:
English

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University of Florida
Holding Location:
University of Florida
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All applicable rights reserved by the source institution and holding location.

Full Text
UFL/COEL-97/014

PERDIDO KEY BEACH NOURISHMENT PROJECT: GULF ISLANDS NATIONAL SEASHORE 1997 Performance Monitoring Report

by
Albert E. Browder and
Robert G. Dean
August, 1997

Submitted to: Gulf Islands National Seashore National Park Service

Coastal & Oceanographic Engineering Department
433 Weil Hall P.O. Box 116590 Gainesville, Florida 32611-6590

UNIVERSITY OF FLORIDA




Perdido Key Beach Nourishment Project:
Gulf Islands National Seashore
1997 Performance Monitoring Report
Albert E. Browder
Robert G. Dean
Coastal & Oceanographic Engineering Department University of Florida
Gainesville, FL
August, 1997
EXECUTIVE SUMMARY
The performance of the beach nourishment project along the eastern 7.5 kmn of Perdido Key, FL, has been monitored on an annual or biennial basis since project construction began in November, 1989. This report presents the results of the most recent monitoring survey, conducted in January and July of 1997. The construction of the project included the placement of 4.1 million m3 o sand directly on the shoreline between 1989 and 1990, and the additional placement of another 3 million m3 of sand in an offshore berm roughly 600 m from the shoreline in approximately 6 mn water depth between 1990 and 1991.
Conclusions and observations from the latest monitoring efforts include:
+ As of January, 1997, approximately 56% of the original volume placed in the
beach nourishment remains within the original construction limits. In terms of planform area, the project has retained roughly 43% of its originally placed planform. area. It is noted that the natural and expected profile equilibration of the project is primarily responsible for the greater reduction
in planform area.
* The latest monitoring survey data suggest that of the 44% of the volume
eroded from the project area, approximately 25% of that volume (over 1 million in) eroded during the last 3.3 years. It must be noted this period
includes the effects of both Hurricane Erin and Hurricane Opal.
+ The most severe erosion is concentrated on the eastern end of the project
near Pensacola Pass. Some profiles along this reach have receded landward of their pre-project location. It is hypothesized that the tidal currents around Pensacola Pass, specifically in the deep flood channel close to shore,
contribute to the increased erosion along this reach.




* Some spreading of sand westward from the project area is observed along
the first 2,000 mn west of the project, approximately to the western edge of the National Park. Observation of the historical shorelines indicates, however, that the shoreline in this area is highly variable and subject to seasonal fluctuations. It is noted that only a very small fraction of the total volume eroded from the original project area is accountable for in the monitoring area. It is hypothesized that Pensacola Pass is a strong sink of sand for the nourishment project. Additionally, the background erosion rate that existed in the area prior to nourishment (and still exists) would tend
to offset any accretion adjacent to the project.
4 As of January, 1997, the Mean High Water shoreline within the original
project limits is an average of 53 mn wider than the original pre-project shoreline (1989). Compared to the previous monitoring survey, following Hurricane Erin, the shoreline has retreated an average of 15 m. Again,
some of this retreat can be directly attributed to Hurricane Opal.
4 Analysis of bathymetric data in the offshore berm area indicates that the
berm has lost 315,000 m3 since the last offshore survey (1993). Inspection of the berm profiles suggests that the berm may have migrated slightly landward as a result of the strong hurricane waves shearing off sand from the gulfward edge of the berm and depositing some fraction on the landward side of the berm. The migration is considered minimal and does not suggest any significant sand transport to the beach within the
foreseeable future.
Given the high degree of erosion witnessed over the last 3.3 years of monitoring, it is suggested that monitoring continue along the Gulf Islands National Seashore. The impacts of Hurricane Danny, which made landfall west of Perdido Key near Mobile Bay, AL, subsequent to the most recent monitoring survey are not addressed in this report. Given the duration and intensity of Danny, increased erosion along the Perdido Key shoreline is likely.
The extent to which the navigation channel at Pensacola Pass affects the beach nourishment project has become more pronounced as the project has evolved. The latest survey data suggest a slight lowering of the seabed west of the pass and infilling of the pass channel. Continued monitoring and research of dredging records from Pensacola Pass (or a survey of the pass with comparison to the 1989-199 1 post-dredge survey) would assist in documenting the fate of the Perdido Key shoreline, particularly near the pass.




Perdido Key Beach Nourishment Project:
Gulf Islands National Seashore 1997 Performance Monitoring Report
TABLE OF CONTENTS
EXECUTIVE SUMMARY..................................................1i
TABLE OF CONTENTS..................................................1iii
LIST OF FIGURES ...................................................... iv
1.0 INTRODUCTION................................................. 1
2.0 PHYSICAL SETTING.............................................. 3
3.0 VOLUMETRIC CHANGES ......................................... 7
4.0 SHORELINE CHANGES .......................................... 11
5.0 CHANGES TO THE OFFSHORE BERM.............................. 16
6.0 IMPACTS OF HURRICANES ERIN & OPAL .......................... 25
7.0 CONCLUSIONS.................................................. 32
8.0 REFERENCES.................................................... 34
APPENDIX A PLOTS OF BEACH PROFILES SURVEYED IN 1997
APPENDIX B PLOTS OF BEACH PROFILES EXTENDING OFFSHORE
ACROSS PROFILE NOURISHMENT AREA
APPENDIX C ANALYTICAL MODEL OF BEACH PLANFORM EVOLUTION
& ESTIMATE OF HURRICANE IMPACTS




Perdido Key Beach Nourishment Project: Gulf Islands National Seashore 1997 Performance Monitoring Report
LIST OF FIGURES
Figure 1 Location map of Perdido Key, FL, taken from NOS
nautical chart 11382......................................... 2
Figure 2 Location of survey monuments and approximate limits
of beach nourishment and offshore profile nourishment area .........4 Figure 3 Cumulative volumetric changes measured from R-30 heading
eastward for four different time periods ......................... 8
Figure 4 Time history of the percentage of volume remaining within the
original project limits for the entire project and the eastern and
western halves ............................................ 10
Figure 5 Change in position of the Mean High Water shoreline along the
project area over time. The shaded area depicts the remaining
beachfill area as of the most recent survey (January 1997)........... 12
Figure 6 Beach profile history at monument R-54 (near the center of the project) 13 Figure 7 Beach profile history at monument R-61 (near the eastern end
of the project)............................................. 14
Figure 8 Time history of the percentage of planform area remaining within
the original project limits ................................... 15
Figure 9 Beach profile history at monument R-58, indicating the offshore
area where sand was deposited for profile nourishment ............ 16
Figure 10 Contour plots of the offshore berm, or profile nourishment area,
for each of the four bathymetric surveys........................ 18
Figure 11 Contour plot showing -6 m NGVD contour of the offshore berm
area in 1992 (dashed line) and 1997 (solid line) .................. 19
Figure 12 Schematic of possible berm migration/loss scenarios.............. 20




Figure 13 Time history of the location of the horizontal centroid of the berm
cross-sectional area for the six profiles crossing the offshore berm .... 22
Figure 14 Time history of the cross-sectional area of the berm for the six
profiles crossing the offshore berm............................ 23
Figure 15 Time history of the location of the landward toe of the berm for the
six profiles crossing the offshore berm ......................... 24
Figure 16 Track lines for Hurricane Erin and Hurricane Opal. The location of
offshore buoys 42001 and 42036 are also indicated................ 26
Figure 17 Satellite image of Hurricane Opal just prior to landfall on
October 4, 1995. (Image courtesy of the National Climatic Data
Center, internet address: www.ncdc.noaa.gov)................... 27
Figure 18 Time histories of significant wave height and wind speed from
offshore buoy 42001 and WIS hindcast stations 44 and 45. The buoy wind speed data indicate gust speeds, while the hindcast
data indicate averaged speeds................................ 28
Figure 19 Schematic of analytical model applied to the Perdido Key beach
nourishment project to evaluate planform evolution ............... 30




Perdido Key Beach Nourishment Project:

Gulf Islands National Seashore
1997 Performance Monitoring Report
Albert E. Browder
Robert G. Dean
Coastal & Oceanographic Engineering Department University of Florida
Gainesville, FL
August, 1997
1.0 INTRODUCTION
This report presents the latest monitoring results of the Perdido Key beach nourishment project within the Gulf Islands National Seashore on the eastern end of Perdido Key, Florida. The nourishment project was constructed between November, 1989, and September, 1990, and included the placement of approximately 4.1 million cubic meters of sand along a 7.5 krn stretch of the Gulf of Mexico shoreline of Perdido Key (Figure 1). In conjunction with the beach nourishment, an additional 3 million cubic meters of sand were deposited in approximately 6-m water depth offshore of the beach nourishment project.
Previous monitoring reports presented performance data up through September, 1995, including the partial effects of Hurricane Erin (Dean and Lin, 1995). Reports prior to that include Otay and Dean, 1993 and 1994. The present report, sponsored by the National Park Service, updates the performance of the nourishment project with survey data collected in January, 1997, and July, 1997 (prior to Hurricane Danny). The 1997 survey includes the effects of both Hurricane Erin and Hurricane Opal'.
lHurricane Erin made landfall within 30 km east of Perdido Key on August 3,1995. The survey conducted following Erin was a wading survey only and extended offshore to water depths from 2 to 5 m. Hurricane Opal made landfall approximately 55 km east of Perdido Key on October 4-5, 1995.




21 \ 221
" 21 21

.e ---- -- \ 2\ 2,42
22 2 8 28
2 2 24
V.2, 22
26 2 6
S 22 2 3 34 34 Dep s 2s
. 28 27 \GULF OFiMEXICO \ 34
GRAPHIC SCALE
Perdido Key East
Portions of NOS Nautical Chart 11382 (1
0 1.0 2.0 3.0 km
Figure 1 Location map of Perdido Key, FL, taken from NOS nautical chart 11382.

-a
8 ~li 08 a

4\1l

S42
41 48

2 29
UMP SITE
3-\ s /
r oeS;,-

990)

,\
i
4

'v" / .-' _---umf .. ", ld:: \




2.0 PHYSICAL SETTING

Perdido Key is a sandy barrier island located southwest of Pensacola in Escambia County, the westernmost county in Florida. Figure 1 depicts a portion of a nautical chart indicating the location of Perdido Key just to the west of the entrance to Pensacola Bay. The island is bordered to the west by Perdido Pass in Alabama. This report focuses on the approximately 11 km of sandy coastline adjacent to Pensacola Pass. This stretch is a part of the Gulf Islands National Seashore ginsS), which extends some 85 km to the east to East Pass in Okaloosa County.
Tides in this area are diurnal, with one high and low water per day. Tidal datums for the Perdido Key area are listed in Table 1. These datums were published by Balsillie et al. (1987).
Table I Tidal datums for the Perdido Key area
Datum Elevation (m, NGVD)
MHHW 0.36
MHW 0.34
MTL 0.15
MLW -0.04
MLLW -0.06
NGVD National Geodetic Vertical Datum, 1929
Figure 2 illustrates the extents of the monitoring survey efforts. The beach nourishment project included the placement of 4.1 million m3 of sand between Florida Department of Environmental Protection (FDEP) monuments R-40 and R-65. This material was obtained from Pensacola Pass as a part of the deepening of the channel for the U.S. Navy Base at Pensacola. This placement resulted in a seaward advance of the shoreline of approximately 135 m. At the same time, an additional 3 million m3 of sand was deposited approximately 600 m offshore in an offshore berm (or profile nourishment). Figure 2 outlines the approximate area of this berm between R-50 and R-60. Table 2 presents the FDEP monuments included in the most recent survey (25 profiles were surveyed).




6w Pass
,,4,
C60 61 62 63 C 6
S3,354,000- s
0 Big Lagoon 5s o k s
48
" n 4 42 2 3DE
383
S3,352,000- 2 -_ _..
~25
0
z Approximate Limits of
Limits of Beach Nourishment Profile Nourishment
(width not to scale)
Gulf of Mexice
3,350,000
456,000 458,000 460,000 462,000 464,000 466,000 468,000 470,000 472,000
Easting (m, UTM coordinates)
Figure 2 Location of survey monuments and approximate limits of beach nourishment and
offshore profile nourishment area.




Table 2 Coordinate information for FDEP monuments used in surveys.
Monument IEasting Northing Elevation) Azimuth I Nor thing I Easting
N2 I SPC 4f) SPC (ft) I (m 4GV (dggrgg JUIM (m) UlM (m)

R-30 R-32 R-34 R-36 R-38 R-40 R-42 R-43 R-44 R-45 R-46 R-48 R-50 R-52 R-54 R-56 R-58 R-60 R-61 R-62 R-63 R-64 R-65 R-66 R-67

1,076,816.0 1,078,813.0 1,081,013.0 1,083,221.0 1,085,078.0 1,087,120.0 1,089,123.0 1,090,213.0
1,091,143.0 1,092,157.0
1,093,014.0 1,095,042.0 1,097,097.0 1,099,265.0 1,101,191.0 1,103,328.0 1,105,353.0 1,107,323.0 1,108,298.0
1,109,324.0 1,110,297.0 1,111,091.0 1,111,729.0
1,112,143.0 1,112,293.0

483,641.0 483,966.8
484,575.0 484,834.3 485,332.0
485,924.1 486,537.5 486,786.0 486,922.8 487,257.0 487,350.0
487,884.4 488,315.0 489,072.5
489,246.5 489,603.5
489,940.5 490,247.5 490,350.5
490,433.1 490,528.3 490,836.5
491,114.9 492,016.0 492,998.0

4.43 5.86 3.99 2.35
4.07 4.27 2.62 2.83 2.87 2.18
4.14 7.10
4.02 2.65 3.08
2.48 2.18 2.03 2.68
2.01 2.45 1.82 2.13 2.68 3.08

170.0 170.0 165.0 165.0 160.0 160.0 160.0 160.0 160.0 160.0 165.0 165.0 165.0 165.0 165.0 165.0 165.0 165.0 165.0 165.0 165.0 170.0 105.0 105.0 90.0

3,351,835.0 3,351,947.0 3,352,147.0
3,352,241.0 3,352,405.0 3,352,599.0 3,352,799.0 3,352,882.0 3,352,930.0 3,353,039.0 3,353,073.0 3,353,249.0 3,353,394.0 3,353,639.0 3,353,705.0 3,353,828.0
3,353,944.0 3,354,051.0 3,354,089.0
3,354,121.0 3,354,156.0 3,354,256.0
3,354,345.0 3,354,622.0

459,085.8 459,691.9 460,358.1
461,029.1 461,591.4 462,209.4 462,815.4 463,145.9 463,428.4 463,735.0
463,995.4 464,609.6 465,232.8 465,888.2 466,473.7 467,122.3 467,737.0 468,335.0 468,631.3
468,943.4 469,239.2 469,478.8 469,671.3 469,791.5

3,354,922.0 1469,830.5

Notes: FDEP monuments are typically listed in State Plane Coordinates (ft, NAD 1927). Universal Transverse Mercator coordinates are provided in m (NAD 1983, Zone 16). Profile azimuths are measured clockwise from magnetic north.




Seven annual or biennial surveys have been conducted as part of the monitoring efforts. Each survey was conducted by personnel of the Coastal and Oceanographic Engineering Department of IJF The surveys are as follows:

+ November, 1989
+ September, 1990
+ October, 1991
+ October, 1992
+ November, 1993
+ September, 1995
+ January/July, 1997

Pre-construction survey of beach profiles to closure depth2.
Post-construction survey of beach profiles to closure depth.
1-yr annual survey of beach profiles to closure depth, offshore bathymetric survey of profile nourishment area.
2-yr annual survey of beach profiles to closure depth, offshore bathymetric survey of profile nourishment area.
3-yr annual survey of beach profiles to closure depth, offshore bathymetric survey of profile nourishment area.
Post-Hurricane Erin survey of beach profiles to wading depth (2 to 5 mn water depth). Survey of beach profiles to closure depth, offshore bathymetric survey of profile nourishment area. The beach profiles were surveyed in January to at least 4 m depth. Due to weather restrictions, the bathymetric survey was conducted in July. No significant effect is anticipated from this delay.

Additional monitoring surveys were performed in 1991 and 1992. These intermediate surveys are not discussed in this report (refer to previous monitoring reports).
The present survey (1997) includes the effects of Hurricane Erin and Hurricane Opal. The 1995 post-Hurricane Erin survey did not include offshore bathymetry and thus did not extend completely to closure. As a result the volumetric changes between previous surveys and the 1995 survey were estimates only. Similarly, volumetric changes between the 1995 and 1997 surveys will also be estimated. For the 1997 survey, the beach profiles were surveyed in January, while the offshore profile nourishment area was surveyed in July, approximately two weeks before Hurricane Danny made landfall just east of Mobile Bay, AL.
2 Along the Perdido key shoreline, the closure depth (depth beyond which no significant sediment motion is observed) is approximately 2.5 to 3 mn. Survey closure in this context refers to the depth to which agreement of the offshore portion of the profiles is obtained (approximately 5 to 6 in). See plots of surveyed profiles in Appendix A.




3.0 VOLUMETRIC CHANGES
Figure 3 depicts the cumulative volumetric change measured alongshore beginning at monument R-30 and moving eastward toward Pensacola Pass. The plot includes information for four related time periods between September, 1990, and January, 1997. As mentioned in Section 2, survey profiles for September, 1995, did not extend offshore to closure in all cases. For these "short" profiles, a best estimate of the profile to closure was generated and volume changes computed. In Figure 3, locations where the slopes of the cumulative lines are the greatest correspond to locations of greatest volumetric change.
Figure 3 indicates that for the most recent intersurvey period (1995-1997), the shoreline within the original project limits (R-40 to R-65) lost an estimated 667,000 m3 of sand. This represents a significant fraction of the originally placed volume (16% of 4.1 M in). The measured cumulative volumetric change between 1993 and 1997 (3.1 years) was 1.14 M mn3 of erosion. Dean and Lin (1995) estimated the volumetric erosion between the 1993 annual survey and the 1995 post-Hurricane Erin survey to be approximately 200,000 m3 of erosion. This estimate was based on the shoreline change, not the actual volumetric change at each profile. Comparison of the 1995 dataset to the 1993 and 1997 surveys suggests that the actual volumetric change during that period may be much higher (as much as 470,000 m3 of sand loss).
Again it must be stressed that any volumetric changes based on the 1995 dataset are estimates only. In addition, it is acknowledged that seasonal effects may well play a role in the shoreline position measurements. While the 1993 and 1995 surveys were conducted in November and September, respectively, the January survey was conducted further into the more energetic winter storm season. In some respects the season of the survey midght only affect where the sand is along the profile, however, the effects of tidal currents in the area during the energetic winter season cannot be accounted for.
Figure 3 also indicates that since completion of the beach nourishment project in 1990, the original project area has lost approximately 1.8 M m3 of sand (44% of the originally placed volume). The figure illustrates that most of the loss is concentrated on the eastern half of the project site, adjacent to Pensacola Pass. This loss is not accounted for within the monitored area. It is presumed that a significant fraction of this material may have been deposited within the shoals and channel of Pensacola Pass. Given the minor amount of accretion measured to the west of the original project area, and the increasing losses measured heading toward the pass, this seems very likely.




58 Pensacola
52 E) Pass
50
48
34 353 3839 ) )(1) D E 30 accretion 27
4 original construction limits
E
a) -400,000 _--________0) 1 erosion
c
o -800,000
.0
E
:: -1,200,000 --- --1993-1995 (1.8 years)*
E-
> 1995-1997 (1.3 years)*
a1)
M -1,600,000 1993-1997 (3.1 years)
E 1990-1997 (6.2 years)
0 -2,000,000 I I I I I I I I I I I
12,000 10,000 8,000 6,000 4,000 2,000 0
Distance west of monument R-67 at Pensacola Pass (m)
Figure 3 Cumulative volumetric changes measured from R-30 heading eastward for four
different time periods.




It must be noted that between the 1993 and 1997 surveys, two significant hurricanes impacted the area. While it is difficult to quantify the exact impact of these storms, there can be no doubt that both hurricanes resulted in the increased loss of sand from the project area. Figure 4 depicts the percentage of sand volume remaining within the original construction limits as a function of time following project completion. The figure indicates the initial equilibration of the project during the first one-yr intersurvey period, in which the project lost roughly 10% of its original volume. During the following two years (1991 to 1993) the project loss rate began to slow to only 3 to 4% per year. During this time, Hurricane Andrew (August 1992) impacted the area, but appears to have caused only minor damage to the nourishment project.
Following the 1993 survey, however, the losses from the project area increase markedly. This is assuredly due at least in part to the impacts of Erin and Opal. Inspection of Figure 4 indicates that the project has suffered more losses in the latter half of its life (25% in the last 3.3 years) as opposed to the first half (19% lost).
Figure 4 also provides an indication that the western half of the project has fared better than the eastern half. The curves for each section in Figure 4 indicate that over 60% of the sand placed between R-40 and R-52 (the western halo remains after 6.2 years. Conversely only 54% of the sand remains on the eastern half between R-52 and R-65. This difference in performance is even more noticeable for the earlier surveys of the project. After the 1993 annual survey, over 86% of the sand remained in project limits on the western half, while roughly 76% of the volume remained on the eastern half. This behavior is attributed to the presence of the pass.
Inspection of Figures 3 and 4 suggests that the impacts of both Hurricane Erin and Hurricane Opal may have been quite substantial. Both hurricanes generated a substantial storm surge, which may have carried a significant volume of sand landward of the dune system. A more likely contributor to the increased erosion witnessed during this time is the presence of increased wave-induced currents and tidal currents during each of the storms. It is hypothesized that during both hurricanes, significant quantities of sand could have been transported out of the monitoring area by increased suspension of sand by waves and the associated strong longshore currents generated. In addition, tidal currents into and out of Pensacola Pass may have served to trap significant amounts of sand within the channel and shoals of the pass.




Pensacola
Pass

Big Lagoon


E.
o:
'E .f a5)

0 1 2 3 4 5 6 7
Time in years after project completion
Time history of the percentage of volume remaining within the original project limits for the entire project and the eastern and western halves.

8 10

Figure 4




Combined with the surge levels for Erin and Opal along Perdido Key, estimated to have been 1.5 mn and 2.4 mn, respectively, the erosion measured/estimated to have occurred between 1993, 1995, and 1997 suggests that Hurricane Opal had a very substantial impact on the island, more so than Erin. More discussion of the impacts of the hurricanes is included in Section 6.
4.0 SHORELINE CHANGES
Figure 5 presents the change in shoreline position over time relative to the 1989 preconstruction shoreline. The figure indicates that the construction of the project advanced the shoreline between R-40 and R-65 seaward an average distance of about 135 mn at the Mean High Water Line (MI-WL). This resulted in an increase in the planform area of the beach of approximately 1.01 M m2 (250 acres).
Figure 5 indicates that during the first year following project completion, the project area retreated landward an average of 37 m and lost approximately 245,000 m2 (60 acres) in planform area, with an associated loss of 400,000 m3 of sand. This was an expected phenomenon associated with the equilibration of the project profiles, in which the originally- constructed steep slope of the berm retreats landward to a more natural shape. Equilibration usually manifests itself in the transport of sand from the upper portion of the profile to the lower, submerged areas. In this case some of the material was also transported alongshore out of the monitored area (back into Pensacola Pass, or westward).
Inspection of the 1993, 1995, and 1997 shorelines in Figure 5 indicates that the center and western end of the project have fared better than the ends. The most significant shoreline retreat has occurred at profile R-62. Inspection of this profile indicates that much of the profile is at or landward of the pre-construction profile, and that some lowering of the seabed near the pass may be taking place. This lowering of the seabed, while difficult to quantify, could be related to the deepening of the navigation channel and is a contributor to the increased erosion measured during the latest inter-survey period. Additional surveys would be required to determine if this lowering is continuing.
The shaded area of FigureS5 illustrates the remaining beachfill area as of the January, 1997, survey. This area represents 435,000 mn2 (107 acres). This is 43% of the originally constructed planform area. The shoreline is an average of 53 m seaward of the 1989 pre-

-11-




Big Lagoon

10,000 8,000 6,000 4,000
Distance west of monument R-67 at Pensacola

2,000 Pass (m)

Change in position of the Mean High Water shoreline along the project area over time. The shaded area depicts the remaining beachfill area as of the most recent survey (January 1997).

E E.--0-
o *-m (Loc
U)
.co
M
3 0 0).

-50
0
50 100 150 200

Pensacola
Pass

Landward recession
Seaward advance

12,000

Figure 5




construction shoreline. Along the center of the project shoreline, between R-46 and R-58, the shoreline is an average of 80 m wider than in 1989. Compared to the last monitoring survey, in 1995, the shoreline along the project limits has receded an average of 15 m. It is noted that the construction of the project more than doubled the width of the barrier island in some places. Recall from the previous section that while only 43% of the originally constructed MIHW planform remains after 6.2 years, 56% of the sand volume remains. This is attributed to the equilibrated shape of the profile in which some sand has been transported to the lower (submerged) portions of the profile.
Figures 6 and 7 present the history of the shoreline at two beach profiles, R-54 and R-61. The plots show the pre- and post-construction profiles, along with the 1995 and 1997 surveys. The profile at R-54 indicates that over half of the original beach width remains after 6.2 years. In Figure 7, the profile at R-61 has retreated nearly to the original 1989 preconstruction shoreline. Along the extreme eastern end of the project (roughly R-60 to R-65) tidal currents associated with Pensacola Pass are expected to play an increased role in the erosion of the shoreline. Any sand suspended by waves would be carried into the pass on the flood tide. On the ebb tide this sand may be transported out onto the ebb shoals of the pass, but it is doubtful that much sand would be carried back onto the Perdido Key shoreline. Plots of all profiles surveyed in 1997 are included in Appendix A.
R-54 Escambia Co.
Nov. 1989
6 Sep. 1990
SSep. 1995
" Jan. 1997
Q9 2
z
0 100 200,Gu3f
.o of
M Mexico
-4
-6
-8 I IT T F__ -T T F T IT T T T I I I I I I t I I I I
010O0 200 300 400 500
Offshore distance from monument (m)
Figure 6 Beach profile history at monument R-54 (near the center of the project).

-13-




6 Sep. 1990
4
0" Jan. 1997
.9 2
z
0\, Guff
o of
1Mexico
> -2
a)
-4 ....
-6
0 100 200 300 400 500
Offshore distance from monument (m)
Figure 7 Beach profile history at R-61 (near the eastern end of the project).
Figure 8 plots the percentage of the originally constructed planform area of the project over time. Similar to Figure 4 for percent volume remaining (note the change in the vertical scale), Figure 8 indicates that during the first year of the project following completion in 1990, the project lost roughly 24% of the planform area above MHW. This loss is somewhat misleading, as discussed, since the project underwent a considerable degree of reshaping during the equilibration process (only 10% of the placed volume was lost). Over the next two years, the rate of areal change decreased to approximately 4%/yr.
Following the 1993 survey, the project was impacted by Hurricanes Erin and Opal, as reflected in the increased rate of planform area loss in the project limits. As in Figure 4, the % change in planform area suggests that Hurricane Opal had a larger impact on the shoreline than did Hurricane Erin. By the 1997 survey, 6.2 years after project completion, roughly 43% of the original planform area remains within the project limits.




Pensacola
Pass

Big Lagoon

I I I I

0 1 2 3 4 5 6 7
Time in years after project completion

III

8 9 10

Time history of the percentage of planform area remaining within the original project limits.

-c
E 0 cE
C
0

- Entire Project
Hurrica ne Erin
Hurricane Uanny
Hurricane
- Andra w|
Ane Hur icane
- Cp~al

Figure 8

I I I




5.0 CHANGES TO THE OFFSHORE BERM
Following the construction of the beach nourishment project in 1989-1990, an additional 3 M m3 of sand was placed in separate mounds roughly 600 to 1,500 m offshore of the nourishment area in water depths of approximately 6 m (refer to Figure 2). This offshore berm, also referred to as 'profile nourishment', has been surveyed four separate times: October, 1992, May and December, 1993, and July, 1997.
The purpose of profile nourishment is two-fold. One purpose of placing the material just offshore rather than directly on the beach is to allow nature to gradually transport sand shoreward, providing a source of sediment to sustain the beach. This can also be a less expensive means of providing sand to a shoreline. The second purpose would be to provide an added degree of sheltering to the shoreline in the lee of the berm. This section discusses the fate of the offshore berm in the context of these objectives.
Figure 9 plots the historical profiles at monument R-58. The plot indicates the location and depth of the offshore berm relative to the shoreline. Note the distorted scale of the plot; the height of the offshore berm is roughly 1.5 m above the ambient seabed.

1600

0 400 800 1200
Offshore distance from monument (m)

Beach profile history at monument R-58, indicating the offshore area where sand was deposited for profile nourishment.

Figure 9

-16-




For each survey, track lines across the berm area were surveyed at roughly 75-rn spacing. Tracklines were run in both the cross-shore and alongshore directions. Horizontal positioning was provided by microwave ranging equipment set up alongshore based on the existing FDEP monument system. Water depths were measured by fathometer. Tidal corrections were applied to the collected vertical data using tide data measured concurrently with the bathymetric survey at a tide staff located just offshore near the western end of the project. As an example, over 11,200 X,YZ datapoints were collected during the July, 1997, bathymetric survey of the profile nourishment area
Figure 10 presents shaded contour plots of the surveyed berm area for each of the four surveys. Referring to Figure 2, the 500-rn mark alongshore corresponds to the western end of the berm area roughly 500 m east of monument R-46. The lighter areas indicate higher elevations. The figure indicates that the bulk of the material was placed closer to the eastern end of the project near R-58 and R-60. The area of deposition is approximately 4,000 m in length alongshore and is 750 to 1,000 m at its widest (in the cross-shore dimension).
Figure 11 plots the changes in the 6-rn NGVD contour between October, 1992, and July, 1997. The figure indicates that the area encircled by the 6-rn contour has decreased slightly over the 4.3-yr period, suggesting that some sand may have been eroded from the area, or that spreading to lower elevations may have occurred. Volumetric changes measured along the monument profiles that extend across the berm indicate that 315,000 m3 of sand has eroded from the offshore berm area during that time. The vast majority of that loss (296,000 in), occurred between the 1993 and 1997 surveys. Not coincidentally, Hurricanes Erin and Opal occurred during this time period. It is noted that this is a very approximate indication of the volumetric change in the offshore berm area, but is considered representative of the changes that occurred.
Dean et al. (1995), in a synthesis of findings from the nourishment project, concluded that no net movement of the berm in the cross-shore direction was discernable. With the addition of the 1997 bathymetric survey, it is desirable to re-examine whether the berm has migrated either shoreward or gulfward. It is equally important to attempt to distinguish between losses from the area, spreading-out of the berm, and actual migration of the berm. To illustrate the possible changes in the berm configuration along the profile, Figure 12 presents simple schematics of four possible scenarios. These are as follows:
* No change in the cross-sectional area occurs and the berm migrates
landward without change in form. Both the leading edge of the berm and

-17-




500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 4,500 m
500
1,00
m October, 1992
1r 1 1

-2 -3 -4 -5 -6 -7 -8
Elevation Scale (m relative to National Geodetic Vertical Datum)
Figure 10 Contour plots of the offshore berm, or profile nourishment area, for each of
the four bathymetric surveys.




Big Lagoon

- 50
500

Gulf of Mexico

Figure 11 Contour plot showing -6 m NGVD contour of the offshore berm area in 1992
(dashed line) and 1997 (solid line).

45 46 144

66
6 1 2 6 3i :i i /
56
Depth (m NGVD)

1.8
- - 10/92
7/97




E) horizontal centroid of berm cross-sectional area

(a) Landward migration of berm, no losses. The centroid and the landward edge
of the berm both shift landward.
(b) Landward migration of berm accompanied by erosion losses. The centroid
moves further landward than the landward edge of the berm.
(c) Erosion of the berm causing a landward migration of the centroid, however,
the landward edge of the berm remains stationary.

(d) Spreading of the sand in the berm. The landward edge migrates landward,
but the centroid remains stationary.
Figure 12 Schematic of possible berm migration/loss scenarios.




the horizontal centroid of its cross-sectional area advance landward the
same distance (plot (a)),
4 Erosion of the cross-sectional area occurs along with a landward movement
of the berm. In this case the centroid will move further landward than the
leading edge of the berm (plot (b)),
* Erosion of the cross-sectional area but no associated landward movement
of the leading edge of the berm occurs. In this case the horizontal centroid
will move landward, but no sand moves closer to shore (plot (c)),
* No change in the cross-sectional area occurs, but the berm "spreads out,"
thus the leading edge, or toe, of the berm moves further landward. No
change in centroid location occurs (plot (d)).
Inspection of the berm based on the 6 profiles that cross the profile nourishment area indicate that case (b) of Figure 12 is the most common occurrence in the area over the entire period of monitoring. In this case, erosion of the cross-sectional area is quite noticeable, while the landward edge of the berm advances landward. It is noted that migration of a berm feature occurs by transport of sand grains from the trailing (gulfward) edge of the berm to the leading (landward) edge. Thus the berm actually rolls over itself as it midgrates. While case (b) of Figure 12 does indeed represent landward migration of the berm, it comes at the cost of the loss of total volume of sand available. Appendix B contains plots of all available profile data covering the berm area.
Based on the time history of the berm movement, it appears that the two hurricanes may be largely responsible for the measured movement and losses of the offshore berm. It is hypothesized that the large waves generated during the hurricanes, particularly Hurricane Opal, may have been close to breaking (or actually breaking) on the seaward edge of the berm area. Much of the sand that was suspended by this action was probably carried away by currents (it is not accounted for in the monitored area), but some fraction of the sand was transported forward and deposited on the landward face of the berm. The contour plot of Figure 11 suggests that this may in fact be the case. The movement of the 6-in contour along the gulf ward edge of the area highlights the erosion that occurred on the gulfward ends of the profiles, particularly along R-54 to R-58 (see plots, Appendix B).
Figures 13 through 15 present the time histories of, respectively, the position of the horizontal centroid of the cross-sectional area of the berm, the cross-sectional area of the berm, and the position of the landward edge of the berm. These three figures should be

-21-




Big Lagoon

45 46
42
41 E

800 900 1,000 1,100 1,200

8,000

I I I I

I I !

I I I

58
58 54 e
(D

Gulf of Mexico

I i I I

7,000 6,000 5,000 4,000 3,000
Distance west of monument R-67 at Pensacola Pass (m)

2,000

Figure 13 Time history of the location of the horizontal centroid of the berm cross-sectional
area for the six profiles crossing the offshore berm.

85
64 61 62

o 2 0-0
-0
'PE
Q)5 E)
0O

R0
R-- R-54
R R-5
O 1992 R-58
-- 1993 R-60
- R-52
- [] 1997

landward movement

gulfward movement

i I I I

I I 1 I




58 56

Gulf of Mexico

- r -ou

1 ,UU
n Itr

ou
600
400
200
0

8,000

I I I I I I

I I I I

I I I

7,000 6,000 5,000 4,000 3,000
Distance west of monument R-67 at Pensacola Pass (m)

accretion of berm

erosion of berm

2,000

Figure 14 Time history of the cross-sectional area of the berm for the six profiles crossing the
offshore berm.

Big Lagoon

45 46
44 q
42
419(

65
66

40 Nflf

Ca a)
_C%j
*E
o
0 00

- ~~R-54 ( '--I C) 1992 R-0; E
1993 R-52 ['
1997... , i

1 O ..v .n _

IK-bU

I I I I

I I 1




5a
56
54( (D

45 46
43 44
42 91 E
41
a

I I I I I I I I

I I I

65 60 6

Gulf of Mexico

I I I I

I I I

landward migration
A

v
gulfward migration

8,000

7,0C

I III
00 6,000 5,000 4,000 3,000
Distance west of monument R-67 at Pensacola Pass (m)

2,000

Figure 15 Time history of the location of the landward toe of the berm for the six profiles
crossing the offshore berm.

Big Lagoon

E
0 (D
.)
~0
ox.
=.E
X
CL

550 600 650 700 750 800 850 900 950

R-60
R- 0R-56 R-58 R6
R-1991R
o 1992 1993 E] 1997

I I I I




viewed together in order to determine the movement (if any) of the sand in the offshore berm area. For example, at R-50, between the 1993 and 1997, the horizontal centroid migrated landward roughly 65 mn (Figure 13). Part of this migration is due to the losses in cross-sectional area the profile suffered (91 M2, or 37% of its area in 1993, Figure 14). Since the losses occurred mostly on the gulf ward edge, the centroid will of course shift landward. Figure 15 shows that the leading edge of the berm at R-50 advanced landward in a thin lens of sand nearly 50 m. Several other profiles, such as R-56, indicate a similar behavior.
General observations of Figure 13 through 15 suggest that the berm may be migrating slowly landward, although the rate of migration and the net volume of sand transported are small. In light of this, it should be recognized that the sand within the area may be experiencing settling due to consolidation (which would throw doubt on the measured volumetric changes) and may be continuing to spread out evenly in both crossshore directions. These possibilities would not provide any significant benefit to the shoreline in the lee of the area. The degree of motion observed between the 1993 and 1997 surveys also suggests that any significant movement of the sand in the area is episodic in nature, occurring only when a large energetic storm system impacts the area (i.e., Hurricanes Erin and Opal).
6.0 IMPACTS OF HURRICANES ERIN & OPAL
Inspection of the survey monitoring data presented in Sections 3-5 indicate that both Hurricanes Erin and Opal had a significant impact on the Perdido Key shoreline. This section describes the storm conditions, primarily for Hurricane Opal, and attempts to gage the impacts the storms.
A detailed description of Hurricane Erin was provided by Dean and Lin (1995). Briefly, Eri made landfall on August 3,1995, as a category 1 hurricane roughly 30 km east of Perdido Key. Figure 16 illustrates the tracks of both Erin and Opal. Maximum wind speeds and wave heights from Erin were measured to be 98 mph (44 m/s) and 4 mn (based on National Weather Service reports and offshore buoy data (Buoy 42036, Figure 16)). As stated previously, the storm surge estimates along Perdido Key were as much as 1.5 m.
Figure 17 presents a satellite image of Hurricane Opal just prior to landfall on October 4, 1995 (courtesy of the National Climatic Data Center of NOAA). Information




ATLANTIC
OCEAN
Buoy Buoy
4200 4203 Erin, 1995 (730-86)
10 PACIFIC
OCEAN
Too 90 80 70 60 50
Longitude (degrees)
Figure 16 Track lines for Hurricane Erin and Hurricane Opal. The location of offshore
buoys 42001 and 42036 are also indicated.




compiled by the National Hurricane Center in Miami, FL, detail the formation and path of Opal. The hurricane formed as a tropical wave off the east coast of Africa on September 11, 1995. Opal proceeded to drift west-northwestward toward the Yucatan peninsula, and strengthened to tropical storm status by September 30. Turning to the north-northeast, Opal accelerated across the Gulf of Mexico, strengthening to a Category 4 hurricane early on the 4' of October. At this point, a minimum pressure of 916 mb was recorded. Following that reading, the hurricane weakened prior to landfall, striking shore between Pensacola Beach (eye center) and Panama City (edge of maximum winds) as a Category 3 hurricane. The area of maximum winds was estimated to be between Destin and Panama City, with wind speeds exceeding 115 mph (51 m/s).

Figure 17 Satellite image of Hurricane Opal just prior to landfall on October 4,1995.
(Image courtesy of the National Climatic Data Center, internet address:
www.ncdc.noaa.gov)
Figure 18 presents wave height and wind speed information from three sources in the Gulf of Mexico for the 5-day period beginning October 1,1995. The first source is a wave buoy located in deep water in the Gulf (Buoy 42001, Figure 16). This buoy, maintained by the National Data Buoy Center of NOAA, provided wind speed and wave height information on an hourly basis as the hurricane passed to its east. The second and third sources are hindcast predictions of significant wave height and wind speeds




E
. 10
T
a) a)
0

I I I

Oct. 1

I I I

I I I

I I

Time (days)

2 3 4 5
Time (days)

Figure 18 Time histories of significant wave height and wind speed from offshore
buoy 42001 and WIS hindcast stations 44 and 45. The buoy wind speed data
indicate gust speeds, while the hindcast data indicate averaged speeds.

-28-

Both Plots
Buoy 42001 (deep water)
- WIS Station 45 Hindcast (28 m)
WIS Station 44 Hindcast (5 m) ,
A I
I
- I
_ \
_ #I

I I I




generated by the Wave Information Study (WIS) from the Coastal Engineering Research Center (Tracy and Cialone, 1996). These hindcasts are not actual measurements of wind speed and wave height. WIS Station 44 is located just south of Pensacola Beach (east of Perdido Key) and provides a hindcast for a water depth of 5 m. Station 45 is located slightly further offshore, south of Perdido Pass, in 28 m water depth. Since the data buoy is located much further south in the Gulf of Mexico than the locations of the hindcasts, the measured peaks in the plots of Figure 18 will occur first for the buoy, then for the hindcast stations as the hurricane proceeds northward.
As Hurricane Opal passed through the gulf, a maximum significant wave height of 8.3 m was recorded by buoy 42001, early on the morning of October 4. Later in the evening on the 4'h a significant wave height of 9.9 m was hindcast for WIS station 45, in 28 m water depth. The hindcast for the shallow station 44 projected a significant wave height of 3.2 m, indicating that breaking had already occurred; note the flattened-off maximum wave height predictions for Station 44. These high wave measurements and hindcasts indicate that breaking was indeed very possible along the seaward side of the offshore berm area, located in approximately 6 to 7 m water depth.
The lower plot of Figure 18 indicates the measured and hindcast wind speeds for the buoy and WIS stations. The measured wind speed at Buoy 42001 reached a peak gust speed of 75 mph (33.6 m/s). According to the hindcasts for Stations 44 and 45, peak wind speeds reached 85 mph (38 m/s). Further east, WIS Station 40 recorded only a 85 mph maximum speed, thus the wind speed hindcasts do not reflect maximum gusts, or may be slightly underestimated. The National Hurricane Center reports that Hurlburt Field near Fort Walton Beach (to the east) recorded a maximum wind gust of 144 mph (64 m/s).
Estimates of the storm surge from Hurricane Opal range from a measured surge of 2.5 m at the Panama City Beach pier to 4.3 m marks measured inside buildings in Walton and Okaloosa counties. These values do include the effects of wave setup nearshore, but do not include the increased water levels caused by the passage of individual waves. Along Perdido Key, Dean and Lin (1995) estimated the surge level to be roughly 2.5 m.
To examine the impacts of the hurricanes in a different perspective, an analytical model was used to estimate the required increase in the average breaking wave height between surveys necessary to create the increased erosion measured between 1993 and 1997. Appendix C contains the development of a simple analytical model to predict the




planform evolution of the project as a function of time. The method employs the diffusion equation, a second-order linear partial differential equation, to model the changes in planform of the project that occur as a result of longshore processes only, and does not include explicitly the effects of currents through Pensacola Pass.
Briefly, the model begins with a 7,500 m-long rectangular deposit of sand adjacent to Pensacola Pass. The model assumes that the shoreline at Pensacola Pass remains fixed. This is achieved by placing another artificial, or virtual, deposit in an antisymmetric fashion adjacent to the first at Pensacola Pass. The equation is then solved for various times into the project's life (Figure 19). By dividing the evolution of the project into separate time periods corresponding to the monitoring surveys, the longshore diffusivity (diffusion coefficient) for various time periods can be found and compared.

Pensacola
Pass
-150
E _Fixed shoreline
a 0 -at R-65 at
. 100 Pensacola Pass
0
Ila rn -5oe 1 \
0
i at tim
.... 3 nti symm'etri c
50 f i
4" planform .
0 1 5 0 I_ I' I' I 'I1
12,000 8,000 4,000 0 -4,000 -8,000
Distance west of R-67 at Pensacola Pass (m)
Figure 19 Schematic of analytical model applied to the Perdido Key beach
nourishment project to evaluate planform evolution.
The analytical model was applied to the time period 1991 to 1993 to establish a baseline condition for the longshore diffusivity by matching the average shoreline retreat for each period. The diffusivity value depends strongly on the breaking wave height. The




model was then applied to the 1991-1997 and 1993-1997 periods to obtain separate diffusivity values. The three values were then compared to determine the increase in average breaking wave height necessary over the latter 3.3 years of the project to match the 1997 shoreline.
Results of the model indicate that to account for the increased erosion measured between the 1993 and 1997 surveys, the average breaking wave height along the project shoreline would have had to increase by 10% for the entire 3.3 year period, for 0.60 m between 1991 and 1993 to 0.66 m between 1993 and 1997. In other words, every wave striking shore between the 1993 and 1997 surveys would need to be 10% higher than the average between 1991 and 1993 to account for the hurricane impacts.
The increase in average breaking wave height is assumed to be the averaged effects of Hurricanes Erin and Opal over that period. It must be stressed of course that this model extremely simplifies the processes at work along the shoreline, combining all processes into sand transport by an average breaking wave. It does not consider the effects of currents or cross-shore processes. It is merely a tool to provide a degree of insight into the significant impact of the hurricanes. The reader is referred to Appendix C for details of this development.




7.0 CONCLUSIONS
The performance of the beach nourishment project along the eastern 7.5 km of Perdido Key, FL, has been monitored on an annual or biennial basis since project construction began in November, 1989. This report presents the results of the most recent monitoring survey, conducted in January and July of 1997. The construction of the project included the placement of 4.1 n-dllion m3 of sand directly on the shoreline between 1989 and 1990, and the additional placement of another 3 million m3 of sand in an offshore berm roughly 600 m from the shoreline in approximately 6 m water depth between 1990 and 1991.
Conclusions and observations from the latest monitoring efforts include:
As of January, 1997, approximately 56% of the original volume of sand placed as beach nourishment (4.1 M m) remains within the original construction limits. In terms of platform area, the project has retained roughly 43% of its placed area. It is noted that the natural and expected equilibration of the project profiles is partially responsible for the reduction
in platform area.
The latest monitoring survey data suggest that of the 44% of the volume eroded from the project area, approximately 25% of that volume (over 1 million m) eroded during the last 3.3 years. It must be noted this period
includes the effects of both Hurricane Erin and Hurricane Opal.
The most severe erosion is concentrated on the eastern end of the project near Pensacola Pass. Some profiles along this reach have receded landward of their pre-project location. It is hypothesized that the tidal currents around Pensacola Pass, particularly in the deep flood channel close to shore,
contribute to the increased erosion along this reach.
Some spreading of sand westward from the project area is observed along the first 2,000 rn west of the project, approximately to the western edge of the National Park. Observation of the historical shorelines indicates, however, that the shoreline in this area is highly variable and subject to seasonal fluctuations. It is noted that only a very small fraction of the total volume eroded from the original project area is accounted for in the monitoring area. However, prior to project construction, a background erosion existed which would tend to offset any accumulation of sand




transported to areas adjacent to the project. It is also hypothesized that
Pensacola Pass is a strong sink of sand for the nourishment project.
As of January, 1997, the Mean High Water shoreline within the original project lin-dts is an average of 53 m wider than the original pre-project shoreline (1989). Compared to the previous monitoring survey, following Hurricane Erin, the shoreline has retreated an average of 15 m. Again, some
of this retreat can be attributed directly to Hurricane Opal.
Analysis of bathymetric data in the offshore berm area indicates that the berm has lost 315,000 m 3 since the 1993 survey. Inspection of the berm profiles suggests that the berm may have migrated landward slightly as a result of the strong hurricane waves shearing off sand from the gulfward edge of the berm and depositing some fraction on the landward side of the berm. Additionally, some consolidation of the berm may have occurred resulting in a volumetric reduction without loss of sand mass. The migration of the berm is considered minimal and does not suggest any
significant sand transport to the beach within the foreseeable future.
Given the high degree of erosion witnessed over the last 3.3 years of monitoring, it is suggested that monitoring continue along the Gulf Islands National Seashore. The impacts of Hurricane Danny, which made landfall west of Perdido Key near Mobile Bay, AL, subsequent to the last monitoring survey, are not addressed in this report. Given the duration and intensity of Danny, increased erosion along the Perdido Key shoreline is likely.
The extent to which the pass at Pensacola Pass affects the beach nourishment project appears to have become more pronounced as the project has evolved. The latest survey data suggest a slight lowering of the seabed in the vicinity of the pass. Continued monitoring and research of dredging records from Pensacola Pass (or a survey of the pass with comparison to the 1989-1991 post-dredge survey) would assist in documenting the fate of the Perdido Key shoreline, particularly near the pass.




8.0 REFERENCES
Balsillie, J.H., Carlen, J.G., and Watters, T.M., Transformation of Historical Shorelines to
Current NGVD Position for the Florida Panhandle Gulf Coast, Division of Beaches and Shores, Florida Department of Natural Resources (presently Bureau of Beaches and Coastal Systems, Florida Department of Environmental Protection), Tallahassee, FL.
Technical and Design Memorandum 87-4.
Dean, R.G., Otay, E.N., and Work, P.A., 1995, Perdido Key Beach Nourishment Project: A
Synthesis of Findings and Recommendations for Future Nourishments, Coastal and Oceanographic Engineering Department, University of Florida, Gainesville, FL.
UFL/COEL -95/011.
Dean, R.G., and Lin, L., 1995, Response of the Perdido Key Beach Nourishment Project to
Hurricane Erin, Coastal and Oceanographic Engineering Department, University of
Florida, Gainesville, FL. UFL/COEL -95/026.
Otay, E.N., and Dean, R.G., 1993, Perdido Key Beach Nourishment Project: Gulf Islands National
Seashore, 1992 Annual Report, Coastal and Oceanographic Engineering Department,
University of Florida, Gainesville, FL. UFL/COEL -93/005.
Otay, E.N., and Dean, R.G., 1994, Perdido Key Beach Nourishment Project: Gulf Islands National
Seashore, 1993 Annual Report, Coastal and Oceanographic Engineering Department,
University of Florida, Gainesville, FL. UFL/COEL -94/007.
Tracy, B.A., and Cialone, A., 1996, Wave Information Study Annual Summary Report, Gulf
of Mexico 1995, Waterways Experiment Station, U.S. Army Corps of Engineers,
Vicksburg, MS. WIS Report 37, November, 1996.




APPENDIX A
PLOTS OF BEACH PROFILES
SURVEYED IN 1997




R-30

I I I I I I I I

I I I I

Escambia Co.

I I I I

200 300
Offshore distance from monument (m)

I I I I

400

R-32 Nov. 1989 Sep. 1990 A- Sep. 1995
Sep. 1997
Gulf
of
____________Mexico

I I I 1

I I I I

I I

I I I I I I I I

200 300
Offshore distance from monument (m)

400

Figure A.1 Surveyed beach profiles at FDEP monuments R-30 and R-32.

Nov. 1989 Oct. 1991 Sep. 1995 Jan. 1997
Gulf
of
Mexico




R-34

I I I I

I I I I

I I I

200 300
Offshore distance from monument (m)

R-36

0 100

200 300
Offshore distance from monument (m)

Figure A.2 Surveyed beach profiles at FDEP monuments R-34 and R-36.

Nov. 1989 Sep. 1990
-Sep. 1995
-Jan. 1997
Gulf
of
Mexico

I I I I

400

400

I= mhi n

I I I I




Nov. 1989 6 Sep. 1990
SSep. 1995
-" Jan. 1997
- 2
z
C Gulf
o of
MMexico
> -2
_.)
w
-4
-6
-8
0 100 200 300 400 500
Offshore distance from monument (m)
8 __R-40
Nov. 1989 6 Sep. 1990
- ----- Sep. 1995
4
Sep. 1997
>
(. 2 __ _-z
0 Guf
.o of
-2 \ Mexico3
cu -2
U
w
-4
-6
-8
0 100 200 300 400 500
Offshore distance from monument (m)
Figure A.3 Surveyed beach profiles at FDEP monuments R-38 and R-40.




Nov. 1989 Sep. 1990 Sep. 1995 Jan. 1997
Gulf
of
. Mexico

I I I I

I I I I

I I I I

200 300
Offshore distance from monument (m)

0 100

200 300
Offshore distance from monument (m)

Figure A.4 Surveyed beach profiles at FDEP monuments R-42 and R-43.

I I I I

I I I I

400

R-42

Escamnbia Co.




0 100 200 300 400
Offshore distance from monument (in)

R-45

0 100 200 300 400
Offshore distance from monument (in) Figure A.5 Surveyed beach profiles at FIDEP monuments R-44 and R-45.




0 100 200 300 400
Offshore distance from monument (in)

R-48

0 100 200 300 400
Offshore distance from monument (in) Figure A.6 Surveyed beach profiles at FIDEP monuments R-46 and R-48.




Nov. 1989 Sep. 1990 ----- Sep. 1995
_ Jan. 1997
Gulf
of
_Mexico

I I I I I I I I

I I I I

I I I I

200 300
Offshore distance from monument (m)

R-52

0 100

200 300
Offshore distance from monument (m)

Figure A.7 Surveyed beach profiles at FDEP monuments R-50 and R-52.

I I I

400

R-50

Escamnbia Co.




0 100 200 300 400
Offshore distance from monument (in)

R-56

0 100 200 300 400
Offshore distance from monument (in) Figure A.8 Surveyed beach profiles at FIDEP monuments R-54 and R-56.




R-58

I I I I

I I I i

I I I I

Escambia Co.

I I I I

200 300
Offshore distance from monument (m)

R-60

I I I I

400

0 100 200 300 400
Offshore distance from monument (m) Figure A.9 Surveyed beach profiles at FDEP monuments R-58 and R-60.

Nov. 1989 Sep. 1990 SSep. 1995
_I Jan. 1997
Gulf
of
___________ ____________Mexico
- ''3). -




8
Nov. 1989 6 Sep. 1990
- Sep. 1995
_ 4
o Jan. 1997
z
E- 0
- 0 Gulf
.o of
-U Mexico
> -2
-4
-6
-8 I I I I II I 1
0 100 200 300 400 500
Offshore distance from monument (m)
8 -R-62
Nov. 1989 6 Sep. 1990
------ Sep. 1995
4
Jan. 1997
9 2
z
Gulf
0 of
-2_ _\ Mexico
u
-6
-8
0 100 200 300 400 500
Offshore distance from monument (m)
Figure A.10 Surveyed beach profiles at FDEP monuments R-61 and R-62.




I I I I

Escambia Co.

I I I I

I I I I

200 300
Offshore distance from monument (m)

0 100

200 300
Offshore distance from monument (m)

Figure A. 11 Surveyed beach profiles at FDEP monuments R-63 and R-64.

R-63

Nov. 1989 Sep. 1990 ----- Sep. 1995
Jan. 1997
Gulf
of
_____Mexico

R-64

(D 2
z
0
-2
Z
-4
-6
-8

400

I I I J

I I I I




Nov. 1989
6 Sep. 1990
SSep. 1995 o Jan. 1997
z
z _____ _____ ____0) Gulf
0 -of
a -2Mexico
w
-4
-6
-8
0 100 200 300 400 500
Offshore distance from monument (m) R-66
8
Nov. 1989 6 Sep. 1990
- -----Sep. 1995
Jan. 1997
z
Gulf
.0 of
Mexico
'i
-4
-6
-8 I I I I
0 100 200 300 400 500
Offshore distance from monument (m)
Figure A.12 Surveyed beach profiles at FDEP monuments R-65 and R-66.




R-67

0 100 200 300 400
Offshore distance from monument (m)

Figure A. 13 Surveyed beach profiles at FDEP monument R-67.




APPENDIX B
PLOTS OF BEACH PROFILES EXTENDING
OFFSHORE ACROSS PROFILE NOURISHMENT AREA




R-50

I I I I I I I I I

I I 1 1 1 1 1 1

I I I I I I I I I I I I I I I

I I I I I

I I I I I I I II

Escambia Co.

I I I I i I I I I I I I I

600 800 1000
Offshore distance from monument (m)

1200

1400

1600

R-50
Nov. 1989 Gulf Oct. 1991
of
Mexico Oct. 1992
SDec. 1993 Jan. 1997
- -

I I I i

I I I I

I I I I

900 1000 1100
Offshore distance from monument (m)

I I I I

1200

1300

1400

Figure B-1 Surveyed beach profile at R-50, extending offshore beyond the area of profile
nourishment. The lower plot focuses on the profile nourishment area.

-_ _Nov. 1989
--_ Oct. 1991
. Oct. 1992
__ __- ___., Gulf Dec. 1993
Profile nourishment area of Jan. 1997
Mexico

600

I I I I

I I I I




- _Nov. 1989 ...-.Oct. 1991
Oct. 1992
Gulf Dec. 1993
Uf Profile nourishment area Jan. 1997
Mexico
_ _A

1 111 1 1 1 1 I 11 1 1 1 1 1

I I I I I I l

I l I I I I I l l I

200

600 800 1000
Offshore distance from monument (m)

1200

1400

1600

R-52
Nov. 1989 Guff Oct. 1991
of
Mexico Oct. 1992
SDec. 1993 Jan. 1997

I I I I

I I I

900 1000 1100
Offshore distance from monument (m)

1200

I I I I

1300

1400

Figure B-2 Surveyed beach profile at R-52, extending offshore beyond the area of profile
nourishment. The lower plot focuses on the profile nourishment area.

I I I I I I

I I I I I I I I

I I I I I I

600

R-52

Escambia Co.




R-54

I I I I I I I I I

I l 1 1 1 1 1 1 1

I I I I I I I

I I III II IPI II II II I

I I I I I I I I I

Escambia Co.

I II IIII IIIII IIII

600 800 1000
Offshore distance from monument (m)

R-54

1200

1400

1600

1400

600 700 800 900 1000 1100 1200 1300
Offshore distance from monument (m)
Figure B-3 Surveyed beach profile at R-54, extending offshore beyond the area of profile
nourishment. The lower plot focuses on the profile nourishment area.

--_Nov. 1989 ...Oct. 1991
(,-A Oct. 1992
Gulf- Dec. 1993
- ___ _,,_Gulf Profile nourishment area Dec. 1993
Mexco Jan. 1997
- ... _m




Escamnbia Co.

___________ _____ Nov. 1989
____________Oct. 1991 Oct. 1992
----------------------------------------- ------Dec. 1993
U1______I_ Profile nourishment area_ a.19
__ ~~MexicoJa.19

I I I I I I I I I

I I I I I I I I I

I I I I I I I I I

SI I I I I I I I I I I I I

I I I I I I I I

I Ii I I I I I I I I I 1

600 800 1000
Offshore distance from monument (in)

I I I I

800

I I I I

900 1000 1100
Offshore distance from monument (in)

1200

1200

1400

1300

Figure B-4 Surveyed beach profile at R-56, extending offshore beyond the area of profile
nourishment. The lower plot focuses on the profile nourishment area.

R-56

1600

R-56 ___Guff Nov. 1989
of Oct. 1991
Mexico
-- Oct. 1992
------------------------------------ Dec. 1993
Jan. 1997

I I I

600

1400

i I I I




R-b5 Escambia Co.
Nov. 1989
-- --__Oct. 1991
Vv- Oct. 1992
Gulf Profile nourishment area ------- Dec. 1993
f, Jan. 1997
Mexico

I I I I I 1 1 1 1

I I I I I I I I I

I I I I I I I I

I I I I I I

I I I I I I I I I I I I I I I I

200

R-58

600 800 1000
Offshore distance from monument (m)

1200

1400

1600

1400

600 700 800 900 1000 1100 1200 1300
Offshore distance from monument (m)
Figure B-5 Surveyed beach profile at R-58, extending offshore beyond the area of profile
nourishment. The lower plot focuses on the profile nourishment area.

1 1 1 1 1 Mq I I I I I I I I




R-60

! 1 1 1 1 1 1 1 1 I I I I I I l

I I I I I I

i i i i I

I I I I I II

i i i 1 i i 1i i

Escambia Co.

I I I I I I I I I I I I I I I I

400

600 800 1000
Offshore distance from monument (m)

1200

1400

1600

R-60
Gulf Nov. 1989
of ___-_ Oct. 1991
Mexico
Oct. 1992
------Dec. 1993
Jan. 1997
--

I I I I

I I I I

I I I I

I I I

I I I I

900 1000 1100
Offshore distance from monument (m)

I I I I

1200

I I I I

1300

1400

Figure B-6 Surveyed beach profile at R-60, extending offshore beyond the area of profile
nourishment. The lower plot focuses on the profile nourishment area.

-__ Nov. 1989
- __---_-_Oct. 1991 Oct. 1992
Gu lf Dec. 1993
_.__,_,._lPf EProfile nourishment area
Mexico Jan.1997
_. ..Mexic---.... -o -- --.=_ ._ ._._

i I I I




APPENDIX C
ANALYTICAL MODEL OF
BEACH PLANFORM EVOLUTION
&
ESTIMATE OF HURRICANE IMPACTS




APPENDIX C
The data presented in the monitoring report indicates that Erin and Opal had a significant impact on the Perdido Key beach nourishment project, particularly Hurricane Opal. No direct measurements of wave heights or water levels along the project area were made during Erin or Opal. The 1995 beach profile survey was conducted just days prior to Opal's landfall, and approximately 8 weeks after Hurricane Erin.
In order to quantify the measured impact in perspective with average wave conditions along the Perdido Key shoreline, a simple analytical model was applied to the measured shoreline data to estimate the required increase in the average daily breaking wave height between the measured survey dates.
The analytical technique uses the diffusion equation (Equation (1)), to model the planform evolution of a beach nourishment project as a function of time.
)y G a2y(
at ax2
Here y = shoreline position, G = longshore diffusivity coefficient, t = time, and x = alongshore distance. This technique was applied to beach nourishment planform prediction by Dean and Yoo (1992) who attribute the technique first to Pelnard-Considere (1956). The solution of the partial differential equation involves the use of the error function (erf(x,4(Gt)), where G is defined as:
KHb g (2)
8(s-1)(1 -p)(h,+B)
Where K = non-dimensional sediment transport proportionality factor (=0.77), Hb = breaking wave height, g = acceleration due to gravity, K= proportionality constant (= 0.78), s = specific gravity of sand (=2.65), p = porosity of sand (=0.35), h. = limiting depth of sediment motion, B = berm height (maximum height of active profile). The independent variables x and t represent the alongshore coordinate and time variable, respectively.
Dean and Dalrymple (in preparation), state that with this method, the planform of a nourishment project does not depend on the storm sequence during the project's life, rather the planform depends only on:
0fo G(t') dt/ (3)




This implies that the planform of the project (i.e., the shoreline position at any time during the life of the project) can be determined as the sum of several integrals of the form of equation (3). For example, the Perdido Key shoreline position in 1997 can be represented by one integral from 1990 to 1997, or the sum of two integrals from 1990 to 1993 and from 1993 to 1997, etc. Since in this example we have only discrete survey dates, the quantity G will be held as a constant for each integral. In fact this quantity varies with time (or with each wave). Thus the value of G determined for each intersurvey period can be considered as an average G for that period.
To model the shoreline, and to determine the value of G for each time period, the beach nourishment project is modeled as a rectangular fill, 98 m in width (the average beach width in 1991). The fill is placed adjacent to Pensacola Pass. The presence of the pass affects the analysis in that any spreading from the project toward the east will fall into the channel and not return. In order to model this effect with the simple diffusion equation, it is assumed that the shoreline at the east end of Perdido Key will remain fixed. To achieve this, an antisymmetric (i.e., negative) fill is placed adjacent to the modeled nourishment project. The antisymmetry of the problem assures a fixed shoreline at the pass (taken to be R-65). The measured and modeled shorelines from each time period are matched using the average shoreline change along the project length for each time period. Figure C-1 presents a schematic of the modeled problem.

Figure C-1 Schematic of modeled beach nourishment project used to predict planform
evolution of the Perdido Key beach nourishment project.

C-2

Pensacola ............ P ass

-150
E Fixed shoreline
0) ~~~at R-65 at______.-'100 Pensacola Pass
U)
-50
-5 r Planform
2 aY ttfie ,
C o
-, antisymmetric
"n 50 .fill (virtual fill
0100
Initial modeled
50" TZ VT F.V planforr
0 150 1 IT --FI I- I i I J -T IF
12,000 8,000 4,000 0 -4,000 -8,000
Distance west of R-67 at Pensacola Pass (m)




To indicate the effects of the hurricanes, the following procedure will be used. The longshore diffusivity, G, will be determined for the time period 1991 to 1997. The starting point, 1991, was chosen to avoid any confusion with equilibration effects, although this is not absolutely necessary. The factor G will then be determined for the periods 1991 to 1993 and 1993 to 1997. In this way, the value of G91-97 can be compared to, G91-93. Applying equation (3) yields:
G91-97*(5.3yrs) = G91 93*(2.Oyrs) + G93-97*(3.3yrs) (4)
G9-7can be then be isolated and the corresponding average breaking wave height over that time period determined. In this application, the time period between 1991 and 1993 is considered to be the calibration, or baseline, condition. If the shoreline computed by this analytical method is matched to the measured 1993 shoreline, the resulting average breaking wave height can be found. Similarly the corresponding breaker height from G93-97 can be compared to the baseline value. The increase or decrease in breaker height can be thought of as the effects of the two hurricanes (and any other above-baseline condition storms) spread out over the entire 3.3 yr period.
Figure C-2 plots the results of the simulation between 1991 and 1993. Again, this period is considered to be the calibration or baseline period, since no major storm damage was observed during this time.' The figure indicates the initial rectangular configuration of the model, along with the measured and modeled 1993 shoreline. The value of G91-93 computed from this calibration yielded an average breaking wave height for the two-year period of 0.60 m. The model also predicts more spreading and an obviously smoother shoreline than in nature, however, the average shoreline retreat and general behavior of the model appear quite reasonable.
Figure C-3 presents the results of the modeling for the 5.3-yr period between the 1991 and 1997 monitoring surveys. The plot includes the 1997 measured shoreline along with two modeled 1997 shorelines. The first modeled shoreline indicates the predicted position of the shoreline if a constant value of G is used for the entire 5.3 yr period. The second shoreline includes a separation of the 5.3-yr period into two separate integrals, as in equation (4). The second method matches the measured shoreline retreat (45 m) between 1991 and 1997 by increasing the value of G between 1993 and 1997. Solving for Hb from the computed value of G93-97 yields an average breaking wave height of 0.66 m.
Using this simple model, it appears that the impacts of Hurricane Erin and Hurricane Opal to the shoreline of Perdido Key can be equated to an increase in the average breaking wave height over the 3.3 yr-period between the 1993 and 1997 surveys of 10% over the baseline breaker height. This would mean that, if the wave conditions were constant, every wave breaking on shore every day would have to be 10% larger to equal the impact of the storms, each of which occurred in a 24 to 48-hr period.
111 is noted that Hurricane Andrew impacted the Florida Panhandle in August, 1992. Impacts to the nourishment project were not considered significant.

C-3




Big Lagoon

12,000

10,000 8,000 6,000 4,000 2,000
Distance west of monument R-67 at Pensacola Pass (m)

Comparison of measured and modeled shoreline positions for the 1991 to 1993 monitoring period (calibration period).

E E.-(D,
CO
M 0)o CD CO
a)

0
50 100 150 200

Pensacola Pass

Landward recession
Seaward advance

Figure C-2




Big Lagoon

original construction limits

Pensacola
Pass

Landward recession
Seaward advance

10,000 8,000 6,000 4,000 2,000
Distance west of monument R-67 at Pensacola Pass (m)

Comparison of measured and modeled shoreline positions for the 1991 to 1997 period, using one constant G value for the entire period (broken line), and two separate G values for 1991-1993 and 1993-1997 (solid line).

E E
-Z
Soc
M*- =- 0
cn CU C' 2
U 0) oa
a-~

0
50 100 150 200

12,000

Figure C-3