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UFL/COEL-98/014
VOLUME, BEACH WIDTH AND SAND FENCE ACCRETION
COMPARISONS FOR THE FLORIDA PANHANDLE REGION
by
Carrie Lynne Suter
Thesis
1998
VOLUME, BEACH WIDTH AND SAND FENCE ACCRETION COMPARISONS
FOR THE FLORIDA PANHANDLE REGION
By
CARRIE LYNNE SUTER
A THESIS PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
MASTER OF ENGINEERING
UNIVERSITY OF FLORIDA
1998
ACKNOWLEDGMENTS
I would like to express my sincere thanks and gratitude to everyone in the Coastal
and Oceanographic Engineering Department for all of their assistance, advice and
support. Thanks go to Dr. Mehta and Dr. Thieke for serving on my supervisory
committee. Their comments and suggestions have contributed greatly to the quality of
this thesis. Dr. Dean has provided knowledge, encouragement and guidance on numerous
occasions. Someone once told me that the greatest lesson learned from Dr. Dean was on
how to be a good person, and I emphatically agree. I would also like to thank Becky
Hudson. She always knew the answer to all of the questions that I asked and also had the
answers to the questions that I didn't know enough to ask.
Thanks go to to all of the people who participated in the lengthy field trips
required for this study: Kerry Anne Donohue, Gus Kreuzkamp, Al Browder, Wendy
Smith, Mike Greene, Tom Glasser, Jamie MacMahan, Roberto Liotta, Phinai Jinchai,
Nicholas Grunnet and Guillermo Simon-Fernandez. Thanks also go to the lab staff for
always being so helpful with equipment problems and reservations.
I would also like to thank all of my friends and classmates who have helped along
the way. Whether the problem was in my personal life or on a PDE's homework
question, I really appreciate everyone and all of their helpful counsel.
Finally, this thesis is dedicated to my family, for without their love,
encouragement and support, the completion of this master's degree would not have
occurred. My parents have always been there for me, to give me helpful suggestions or to
just listen. My sister and brother have contributed greatly in making me the person that I
am today. My grandparents, aunt and uncles have also been unflagging in their prayers
and inspiration. Thanks go out to all of these special people in my life.
TABLE OF CONTENTS
ACKN LEDGM ENTS .............................................................................................. ii
ACKNOWLEDGMENTS ......................................... ii
LIST OF TABLES.............................................................................................vi
LIST OF FIGURES.................................................................................................. vii
ABSTRACT............................................................................................................. x
CHAPTERS
1 INTRODUCTION................................................................................................. 1
Purpose...................................................................................................................... 1
Report Organization............................................................................................ 1
2 M OTIVATION FOR THIS STUDY............................ ................................. 3
Importance of Beaches......................................................................................... 3
Physical Processes Associated with Storms and Dune Recovery.............................. 3
M maintenance of Beaches..................................... ............... ............................... 4
3 HURRICANE OPAL............................................................................................ 6
Statistics of the Storm.......................................................................................... 6
Effects and Damages............................................................................................ 6
4 BACKGROUND ON PREVIOUS STUDIES....................................... ........... 8
5 STUDY AREAS................................................................................................... 11
"Opal" Study Area............................................................................................... 11
Perdido Key............................................................... ........................................ 11
6 NATURAL VS. DEVELOPED BEACHES......................................... ............ 15
M monitoring Efforts by the U university of Florida........................................................ 15
Results........................................................................................................................ 16
Beach Profiles........................................................................................................ 16
Beach V olum es and W idths................................................. .......................... 19
D iscussion.................................................................................................................. 24
Effect of February 1998 Survey................................................ ......................... 32
Conclusions............................................................................................................... 33
7 AEOLIAN TRANSPORT..................................................... 67
M ethodology.............................................................................................................. 67
Conclusions................................................................................................................ 69
REFEREN CES.............................................................................................................. 73
BIO G RAPHICA L SK ETCH ......................................................................................... 75
LIST OF TABLES
Table pg
1. "Developed" and "Natural" Areas for Hurricane Opal
M monitoring by COE.................................. ..................... ........... 16
2. Shoreline Change as Determined from Aerial Photographs Between
October 1995 and May 1996.............................................. ........... 25
3. Beach Volume and Width Trends as Determined by the Least
Squares M ethod.................................................. ........................... 26
LIST OF FIGURES
Fiure pael
1. Hurricane Opal Study Area ............................................. ................ 13
2. Perdido K ey Study A rea .................................................................................... 14
3. Beach Profile in Natural Area of Santa Rosa County,
Monument Number R-188......................................... ............. 17
4. Cumulative Change in Average Volume for All Profiles in
Escambia County ................................................... ....................... 20
5. Beach Profile in R-194.5 in Developed Area of Santa Rosa County
Showing Artificially Placed Berm ................................................ ...... 23
6. Cumulative Change in Average Volume for All Counties ........................... 37
7. Cumulative Change in Average Volume for All Developed Profiles ............ 38
8. Cumulative Change in Average Volume for All Natural Profiles ................ 39
9. Cumulative Change in Average Distance from the Monument to
the Water Line for All Counties.................... ........................... 40
10. Cumulative Change in Average Distance from the Monument to
the Water Line for All Developed Profiles ......................................... 41
11. Cumulative Change in Average Distance from the Monument to
the Water Line for All Natural Profiles .............................................. 42
12. Cumulative Change in Average Volume for All Profiles in
Escambia County.................................................... ..................... 43
13. Cumulative Change in Average Volume for All Developed Profiles in
Escambia County................................................. ........................... 44
14. Cumulative Change in Average Volume for All Natural Profiles in
Escam bia County................................................................................. 45
15. Cumulative Change in Average Distance from the Monument to the
Water Line for All Escambia County Profiles ................................... 46
16. Cumulative Change in Average Distance from the Monument to the
Water Line for All Developed Profiles in Escambia County............... 47
17. Cumulative Change in Average Distance from the Monument to the
Water Line for All Natural Profiles in Escambia County................... 48
18. Cumulative Change in Average Volume for All Profiles in
Santa Rosa County ................................... ................................... 49
19. Cumulative Change in Average Volume for All Developed Profiles in
Santa Rosa County............................................. .......................... 50
20. Cumulative Change in Average Volume for All Natural Profiles in
Santa Rosa County............................................ .......................... 51
21. Cumulative Change in Average Distance from the Monument to the
Water Line for All Santa Rosa County Profiles............................. 52
22. Cumulative Change in Average Distance from the Monument to the
Water Line for All Developed Profiles in Santa Rosa County.............. 53
23. Cumulative Change in Average Distance from the Monument to the
Water Line for All Natural Profiles in Santa Rosa County................... 54
24. Cumulative Change in Average Volume for All Profiles in
W alton County........................................................................... 55
25. Cumulative Change in Average Volume for All Developed Profiles in
W alton County................................................ ............................. 56
26. Cumulative Change in Average Volume for All Natural Profiles in
W alton County .................................................. .......................... 57
27. Cumulative Change in Average Distance from the Monument to the
Water Line for All Walton County Profiles ........................................ 58
28. Cumulative Change in Average Distance from the Monument to the
Water Line for All Developed Profiles in Walton County ................. 59
29. Cumulative Change in Average Distance from the Monument to the
Water Line for All Natural Profiles in Walton County........................ 60
30. Cumulative Change in Average Volume for All Profiles in Bay County......... 61
31. Cumulative Change in Average Volume for All Developed Profiles in
B ay C ounty.................................................................................. ... 62
32. Cumulative Change in Average Volume for All Natural Profiles in
Bay County .................................................. .................... 63
33. Cumulative Change in Average Distance from the Monument to the
Water Line for All Bay County Profiles ......................................... 64
34. Cumulative Change in Average Distance from the Monument to the
Water Line for All Developed Profiles in Bay County ............... 65
35. Cumulative Change in Average Distance from the Monument to the
Water Line for All Natural Profiles in Bay County ...................... 66
36. Beach Profile in Perdido Key Showing Accretion at Sand Fence, R-48....... 71
37. Perdido Key Data Correlation: Active Beach Width vs Sand
Fence Accretion............................................ ........................... 72
Abstract of Thesis Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Master of Engineering
VOLUME, BEACH WIDTH AND SAND FENCE ACCRETION COMPARISONS
FOR THE FLORIDA PANHANDLE REGION
By
Carrie L. Suter
August 1998
Chairman: Robert G. Dean
Major Department: Coastal and Oceanographic Engineering
This thesis presents the data and results concluding a two year monitoring study
by the University of Florida Coastal and Oceanographic Engineering Department (COE)
in the wake of Hurricane Opal. Surveys conducted from May 1995 to February 1998
studied the poststorm response in the following counties: Escambia, Santa Rosa, Walton
and Bay. Each surveyed region encompassed "natural" and "developed" areas that were
compared volumetrically and also in terms of beach width.
The survey data were plotted for each survey control monument. By plotting
several surveys on the same graph, erosional or accretional trends become evident. An
average-end method of the distance and elevation values was used to compare the volume
and beach width changes that occurred between each survey taken for an individual
monument. The changes were averaged for each county and each subdivision of
developed and natural areas within each county. The average changes were then
combined to obtain the cumulative beach response throughout the entire survey period.
The data were plotted for the individual counties, developed areas, natural areas,
and an average of all of the counties. A linear "best fit" straight line was plotted for the
data sets so that the slope of the line represents the prevailing trend. Overall, the trend is
slightly erosive for the studied areas, and the natural sites erode marginally less than the
developed sites. There is a strong correlation between the volumetric and beach width
changes observed for each county and subdivision of natural or developed beaches. The
beaches fluctuate both in response to seasonal variations and storm events. The presence
of certain poststorm features suggest that the time scale for total recovery from a severe
storm like Hurricane Opal may exceed the observation time included in this study period.
Farther east in Escambia County, Perdido Key was studied to determine a
correlation between the active beach width and the amount of aeolian sediment trapped
by a sand fence. The same process of analyzation was used to determine the change in
sediment volume in the immediate vicinity of sand fences. The average volumetric rate
of change per year was plotted with the corresponding active beach width, and a linear
"best fit" line was plotted for the data set. A strong correlation was found between the
active beach width and the volume of sediment trapped by a sand fence.
CHAPTER 1
INTRODUCTION
Purpose
This thesis examines the recovery of natural and developed beaches after Hurricane
Opal and a correlation between active beach width and aeolian sand transport. Varying
mechanisms of sand transport from different locations and perspectives will be
considered as possible explanations of beach recovery and sand transport. This report
uses beach profiles obtained from survey data from the Florida Panhandle region.
Changes in beach volume and/or beach width from each surveyed profile are compared
for each survey conducted. Trends for beach recovery are investigated and contrasted
between several different counties and also the subdivisions within each county. Finally,
a correlation between active beach width and accretion at sand fences is examined.
Report Organization
This thesis is arranged in the following manner. Chapter 2 discusses the importance
of beaches for economic, protective and recreational benefits. The dynamic nature of
beaches in response to storms and physical recovery is presented, and a brief outline of
several methods of maintaining beaches via "hard" and "soft" structures is examined.
Chapter 3 contains information on statistics, effects and damages to the Florida
Panhandle region in October 1995 from Hurricane Opal. A literature review of previous
studies is chronicled in Chapter 4. Authors such as Davidson-Amott (1988), Davidson-
Arnott and Law (1996), Grant (1948), Illengberger and Rust (1988), Hunter, Richmond
and Alpha (1983) and Bauer, Davidson-Arott, Sherman, Nordstrom and Jackson (1996)
are outlined with reference to sand transport mechanisms and explanations. Chapter 5
provides information on the specific areas studied on the Gulf Coast. Location,
classifications of subdivisions, sediment composition and tidal cycles are addressed for
both the "Opal" and Perdido Key study sites. Chapter 6 describes the "Opal"
investigation, beginning with methods and procedures and ending with conclusions based
on the analysis of the data. Finally, Chapter 7 presents a summary and conclusion for
correlations between aeolian transport and varying beach widths.
CHAPTER 2
MOTIVATION FOR THIS STUDY
Importance of Beaches
Beaches are important to maintain and protect because they have economic,
protective and recreational benefits. The United States has spent approximately $15
million per year for the past 44 years to protect its beaches (NRC, 1995). Travel/tourism
is the largest employer and the largest industry in the United States. Eighty-five percent
of tourism revenues are spent in coastal states. The increase in tourism related jobs is
greater than the increase in all manufacturing jobs in the United States, and beaches are
an integral part of the tourism industry. Agricultural export is the only industry with a
trade surplus higher than travel/tourism. For the tourism industry, beaches are the leading
attraction in the country. The public highly values beaches for residential areas and
visitation. In fact, forty percent of Americans cite beaches as preferred vacation
destinations (Houston as sited in NRC, 1995). As a result of this preference, both the
value of coastal property and coastal populations are increasing (Culliton et al.,1990;
Edwards, 1989; Houston, 1995 as cited in NRC, 1995).
Physical Processes Associated with Storms and Dune Recovery
Beaches are dynamic systems that are constantly changing, shifting and moving.
The beach width and elevation may change drastically in response to natural forces such
as storms. Large storm surges may completely overwash beaches for certain periods of
time under conditions such as hurricanes and other extreme storms (NRC, 1995). It may
take only hours for a beach to erode, but decades to recover.
Usually, sand is moved offshore by the strong wave energy during storms. Much of
the sand is returned during the spring and summer months when the beaches are under the
influence of milder wave activity. In addition to offshore sand movement, sand can also
move parallel to the shore. It is transported in this manner by oblique waves and
alongshore currents. This alongshore sediment movement acts upon inlets, generally
causing them to migrate, unless the inlet position is fixed by a jetty or similar method
(NRC, 1995).
Maintenance of Beaches
All beaches are under the influence of conditions that will remove sand from the
active beach system. Unless a beach is also being influenced by conditions favorable to an
influx of sand, the beach will erode. The rate of erosion will vary according to storms
and sand supply (NRC, 1995). The erosional processes are aggravated by the gradual
increase in sea level and interference from humans with the geologic processes at work
(Boesch, 1982; NRC, 1987, 1992 as cited in NRC, 1995). An example of human
practices contributing to erosion is the construction of dams that inhibit the flow of
sediment from inland sources. Additionally, structures built to stabilize inlet positions
interfere with the sand supply from alongshore transport (NRC, 1995).
There have traditionally been two choices for the protection and maintance of
beaches: "hard" structures or beach fill ("soft" structures). Hard structures, such as:
bulkheads, jetties, seawalls, breakwaters, groins and revetments, are being used less
frequently because of aesthetic reasons, maintenance costs and increased downdrift
erosion rates.
Beach nourishment is considered a "soft" (i.e., nonpermanent) structure that adds
sand to the beach. The increase in the total amount of sand in the system effectively
displaces the shoreline seaward. Beach fill with periodic renourishment is becoming the
preferred method of beach preservation, and it is popular because it preserves the natural
beach resource. Both the increase in volume and the larger surface area of a nourished
beach allow increased interaction with the waves and wind. The increased interaction
results in a decrease in wave energy effects on the beach system as a whole. Instead of
concentrating wave energy upon structures located on the shore, the energy is dissipated
on the wider beach. While beach nourishment does not eliminate the erosional effects on
the beach, it does provide a temporary relief for the erosional symptoms experienced by a
beach. The background erosion rate in an area is one factor in the length of time between
renourishment events.
Natural or constructed sand dunes can help prevent the damaging and costly effects
of coastal flooding and wave runup. They are an effective barrier to flooding, erosion and
damage to inland structures. Properly vegetated sand dunes that are protected by a wide
beach face can minimize damage from storms. Sand fencing can help contribute to the
durability of the vegetation and also act as a trap for sand, thus creating a miniature sand
dune (NRC, 1995).
CHAPTER 3
HURRICANE OPAL
Statistics of the Storm
On October 4, 1995 at approximately 6:00 p.m. central daylight time, Hurricane
Opal made landfall near Navarre Beach, which is located on Santa Rosa Island in Santa
Rosa County. In the most active storm season since 1933, Hurricane Opal was the 15th
named storm out of 21 total tropical storms or hurricanes. At landfall, the winds reduced
to 110 mph from the maximum sustained surface winds of 150 mph, which had placed
the hurricane at a Category 4 status on the Saffir- Simpson scale. As determined by the
Beaches and Shores Resource Center of Florida State University, the hurricane had a
central pressure deficit of 2.16 in. mercury, a radius of maximum winds estimated at
approximately 30 miles and a forward speed of 23 knots in a north- northeast direction
(Leadon, 1995).
Effects and Damages
Storm surge data collected from a National Oceanic and Atmospheric
Administration (NOAA) tide gauge located on the Panama City Beach pier showed a
peak water level of 8.3 feet above National Geodetic Vertical Datum (NGVD), which was
nearly 8 feet above the normal predicted astronomical tide. High water mark surveys
conducted by Florida Department of Environmental Protection (DEP) staff showed a
storm surge ranging from 8-11 feet above NGVD between Pensacola Beach and Fort
Walton Beach and approximately 12-20 feet above NGVD between Destin and Seagrove
Beach (FEMA, 1996). In Panama City Beach, evidence of wave impacts and sand
deposition was found in first-floors of structures up to 17-18 feet above NGVD during
post-storm inspections conducted by the DEP (Leadon, 1995).
Hurricane Opal caused extensive damage to the beach and dune systems. Eight
million cubic yards of sand were lost from above sea level due to breaking waves,
extensive flooding, a substantial storm surge and vast overwash in lower dune areas. East
of Fort Walton Beach, portions of Highway 98 were washed away, and most of the survey
control monuments maintained by the Bureau of Beaches and Coastal Systems (BBCS) of
the DEP were destroyed (Leadon, 1995). The approximately $2 billion damage to
structures during Hurricane Opal rank it as one of the most costly natural disasters to
affect the United States (FEMA, 1996). It caused more structural damage along the
Florida coast than all of the hurricanes and tropical storms combined in the last 20 years
(Leadon, 1995).
CHAPTER 4
BACKGROUND ON PREVIOUS STUDIES
Throughout the history of coastal research, investigators have attempted to predict
and monitor the rate of aeolian sediment transport. On a sandy beach, aeolian transport is
a function of several factors. Beach width, moisture content, sediment size and wind
speed have all been investigated to determine the significance of their contribution to
aeolian sediment transport rates.
Davidson-Amott and Law (1996) attempted to obtain accurate measurements of
sediment transport from the beach system to the dunes to determine the significance of
factors such as wind, beach width and moisture content. An island in Lake Erie was
studied for 6 years to determine the sand transport rates. They found that beach width
significantly affects sediment transport and was a better indicator of deposition rates than
potential transport found from wind equations. Little similarity was found between wind
speed and sediment deposition, but a strong similarity (95% confidence) was found
between beach width and sediment deposition.
Sediment transport rates were found to decrease with decreasing beach width. The
beach width can also be a significant factor, combined with the level of sediment above
the water table, in determining the volume of sediment available for transport.
Additionally, the beach width can affect the beach form and slope, thereby changing the
9
boundary layer development (Short and Hesp, 1982; Hsu, 1987; Bauer et al., 1990; Bauer
et al., 1996 as cited in Davidson-Amott and Law, 1996).
In 1988, Davidson-Amott found that the beach width is a major control of sediment
supply that can vary temporally and spatially according to fluctuating lake levels. Low
lake levels corresponded to periods of dune repair and the growth of foredunes. In
contrast, high lake levels induced erosion and overwash deposits. Wide beaches, in
addition to supplying the beach or dune with available sediment, also acted to protect the
beach from erosion and overwash activity.
Moisture content is an important factor in aeolian sand transport. Therefore, it is
also important to recognize that the water table level of the beach can influence erosion or
accretion. Grant (1948) found that a dry beach induces deposition by both reducing
backwash flow velocity via percolation and perpetuating the existence of laminar flow.
When all of the uprush water percolates through the dry beach, the sediment load is
necessarily deposited on the beachface, causing an ever steepening slope. Eventually, the
steep slow will induce a high backwash velocity that prevents further deposition.
Several studies have attempted to correlate wind speed with sediment transport.
Illengberger and Rust (1988) investigated a dunefield in Alexandria, South Africa to
determine the sediment transport rate. The source of the sand was a sandy beach that is
transported onshore by a high energy wind field. The sediment transport varied
considerably with distance from the water line. The rate at the seaward edge of the
dunefield was 30 m3 m-' yr1- but decreased to 15 m3 m-~ yr' at the landward edge. This
decrease in the sand transport rate with increasing distance from the waterline was
10
probably due to a decrease in wind speed over land resulting from an increased boundary
layer drag.
Hunter et al. (1983) studied a dunefield in Oregon of similar scale to the dunes
studied by Illengberger and Rust, but analyzed the effect of rain on sand transport. Sand
can be eroded and transported by wind even during a heavy rain (Hunter 1980 as cited in
Hunter et al., 1983). When dry conditions were assumed, the predicted value of sand
transport overestimated the actual transport by three times. This was probably a result of
the significantly wet conditions that this region experiences. Wind was still a
contributing factor to sand transport, and the transport rate, approximately 24 m3 m'I yr',
drops significantly in portions of the dunefield that are sheltered from the wind by nearby
forests or the dunefield itself.
The inaccurate predictions of aeolian beach transport from wind transport equations
were assessed by Bauer et al. (1996). Some constraints found to affect the accuracy of the
predictions were: using shear stress as the sole variable; simplifying complex wind
profiles associated with beach winds to a single layer, thereby ignoring boundary layer
effects; and changes in sediment transport patterns caused by differences in surface
roughness, beach slope, temperature, moisture content, grain-size distribution and
mineralogical composition.
CHAPTER 5
STUDY AREAS
The Gulf coast has fine, approximately 0.30 mm mean grain size, white quartz sand
and an extensive barrier island/dune system. The wave climate is relatively calm in the
absence of major storm events such as hurricanes. Astronomical tides are diurnal and on
the order of half of a meter, NGVD. This low lying region is subject to large storm surges
(NRC, 1995).
"Opal" Study Area
Data and results will be presented that conclude an intensive two year monitoring
study conducted in the wake of Hurricane Opal by the University of Florida's Department
of Coastal and Oceanographic Engineering (COE). Four specific shoreline sites, each
including both developed and natural areas in the Panhandle of Florida, were surveyed
from May 1996 to February 1998. In total, five surveys from the COE and five surveys
from the Bureau of Beaches and Coastal Systems (BBCS) provide the basis for both
volumetric and beach width changes in the following counties, see Figure 1, from west to
east: Escambia, Santa Rosa, Walton and Bay.
Perdido Key
The Perdido Key survey data will be used to determine if a correlation exists
between active beach widths and aeolian sand transport trapped by sand fences. Located
in the western Panhandle region of Florida, Perdido Key is a barrier island in the Gulf of
12
Mexico, see Figure 2. This island is located southwest of Pensacola, in Escambia
County, and is bordered by Pensacola Pass on the east and Perdido Pass on the west. The
study area is 11 kilometers of sandy beach on the eastern portion of Perdido Key and is
within the Gulf Islands National Seashore. The tides are diurnal, one high tide and one
low tide per day (Browder, 1997). The monitoring surveys conducted by the University
of Florida that are used in this study were conducted in September 1990, October 1991,
October 1992, November 1993, September 1995 and January 1997.
3390000 county lines are approximate
SANTA ROSA OKALOOSA WALTON WASHINGTON
3370000 A
__ _-. .-- - -BAY
East
3350000 Pensacola ESCAMBIA CO. SITE SITE
Pass SITE
BAY CO. SITE
3330000 -
St. Andrews
Bay Entrance
3310000
3290000
Gulf of Mexico
3270000 I I I I
450000 470000 490000 510000 530000 550000 570000 590000 610000 630000 650000
EASTING (m, UTM Zone 16, NAD 1983)
Figure 1- Hurricane Opal Study Area Location Chart
I
. .....
0 5 km
Figure 2- Perdido Key Study Area Location Chart
(Work, 1992 p. 2)
CHAPTER 6
NATURAL VS. DEVELOPED BEACHES
Monitoring Efforts by the University of Florida
For the Hurricane Opal study area, the five monitoring surveys were conducted by
the COE in: May 1996, October 1996, March 1997, July 1997 and February 1998. The
four areas surveyed in Escambia, Santa Rosa, Walton and Bay Counties each contained
approximately 20 survey control monuments, with varying amounts of "natural" and
"developed" areas in each county. The monuments were located approximately 500 feet
apart, and the surveys were carried out with standard rod and level land based survey
techniques from the monument out to wading depth limits.
An area was deemed "natural" if there were no structures located immediately
landward of the monument marker and "developed" if there were. Walton County was
the one exception to this definition, as the entire study area was situated in a local city.
Therefore, Henderson State Park and four other monuments were included in the
"natural" category, even though they would not normally be considered "natural" due to a
parking lot adjacent to the beach. The deciding factor for this inclusion was the protection
and vegetation of the dunes from the parking lot to the beach berm.
The following table presents the list of "developed" and "natural" areas, identified
by their corresponding BBCS monument numbers.
Table 1- "Developed" and "Natural" Areas for Hurricane Opal Monitoring by COE
County "Developed" "Natural"
Escambia R133 to R138.5 R139 to R144
Santa Rosa R192.5 to R197 R187 to R192
Walton R1 to R2, R4.5 to R6A.5 R2.5 to R4, R7 to R8.5
Bay R85 to R91. R93 R91.5 to R97 (except R93)
Results
Beach Profiles
The survey data were plotted for each monument. A typical profile for the natural
areas of Santa Rosa County is plotted in Figure 3 for Monument Number R-188. By
plotting several surveys on the same graph, erosional or accretional trends are evident. To
better illustrate these trends, Santa Rosa County R-188 will be discussed in detail.
The monument location is plotted as zero on the horizontal axis, and all subsequent
horizontal positions are relative to the monument position. At this particular location in
Santa Rosa County, the dune system is extensive, as indicated by the 17 foot height of the
primary dunes. The dune heights in this area decrease with increasing proximity to the
developed areas, which are located 5,000 feet farther east. The solid line plotted on the
graph represents the only DEP survey (February 1996) used in the Santa Rosa County
data. This survey was taken 4 months after Hurricane Opal and illustrates some storm
effects. The very steep dune scarp with the distinct cut at the base is a result of waves
impacting this dune during the hurricane. Each subsequent survey shows an increasingly
milder slope, probably due to sloughing of the sediments to approach a more natural
February 1996
May 1996
20 .-.-... October 1996
........... March 1997
----- July 1997
.-. February 1998
15
z 10
[-U
S "' ...... Gulf of Mexico
-5
0 100 200 300 400 500
Distance seaward of monument (ft)
Figure 3- Beach Profile in Natural Area of Santa Rosa County, Monument Number R-188
angle of repose, i.e. the steepest angle that a loose sediment of a given size can remain
stable.
The seasonal fluctuations are most evident in the vicinity of the beach face, which is
located approximately 180-260 feet from Monument R-188 at the gulfward limit of the
berm. For the surveys that would typically be considered "summer" profiles, the October
1996 and July 1997 surveys, the beachface locations do not extend as far seaward as the
other surveys, thus resulting in a narrower beach for the summer surveys. Two of the
winter profiles, (May 1996 and March 1997) comparatively, consist of somewhat wider
beaches with larger volumes. This is contrary to the normal definition of "summer" and
"winter" profiles that are normally associated with sandy beaches in the eastern United
States.
The February 1998 survey was conducted immediately after two northeasters
impacted the area. The narrowed beach width, a steep scarp in the vicinity of the high
water lines of the storms (located at approximately 220 feet) and an offshore bar are all
signs of a post-storm beach. The sand in the offshore bar was eroded from the beach face
during the storm, but will most likely be redeposited back on the beach after a period of
milder wave activity.
Due to the varying tidal and wave conditions during the surveys, each survey ends at
a different distance from the monument. For example, the DEP survey was conducted
farther offshore than any of the COE surveys. However, the volumetric computations
were extended only out to the farthest common point seaward of the monument marker
for all surveys. For monument number R-188, the last data point for the July 1997
survey, at approximately 250 feet, is the limiting distance for volumetric computations.
Beach Volumes and Widths
The distance and elevation values for each survey were analyzed to quantify changes
in beach volume and beach width, i.e. the distance from the monument to the NGVD
water line. These changes were compared throughout the entire survey period. The
changes were averaged for each county and for each subdivision of "developed" and
"natural" areas within each county, as noted in the figure title of each graph. Finally, the
average changes that occurred between each survey were combined to obtain a
cumulative beach response throughout the entire survey period. For illustrative purposes,
the graph for the average change in volume for Escambia County, see Figure 4, will be
used for reference in the following paragraphs.
Analysis of the data concentrated on the amount of change that occurred between
each survey. However, the number of monuments surveyed within each time period were
sometimes different from one monitoring survey to the next. Some monuments were lost
through construction or damage, and only half of the monuments had been set prior to the
COE October 1996 surveys. In the graphs, the numbers in parentheses beside each date
signifies the number of monuments that the previous survey and the survey in question
have in common. In Figure 4, there were twenty common surveyed profiles between the
October 1996 survey and the March 1997 survey. However, three monument markers
were not found during the July 1997 survey, so there are only seventeen common profiles
between March 1997 and July 1997. The number of common profiles can also be
40 -.
SD- \D
3-0 0
cc
-20
E-,
-20
6 -30
I -40 ---
5 0.0 0.5 1.0 1.5
E
E Time (years)
0
I 0)
7.5
-~ 0)
Best Fit Trend Line
S2.0 2.5
Figure 4- Cumulative Change in Average Volume for All Escambia County Profiles
21
considered an approximate measure of the confidence level, for an increase in the number
of common data points yields a higher confidence in the results.
For each monument, the changes were calculated by subtracting the values from the
previous survey from those for the subsequent survey. "Empty" data sets occur when a
particular location was not surveyed on one trip, but was surveyed on a later trip. A
different method of comparing the data is required when the data set is not complete. The
following example will illustrate this method: a monument is surveyed in May 1996 and
October 1996, not surveyed in March 1997, but is surveyed again in July 1997 and
February 1998. The difference between the October 1996 and the May 1996 surveys is
calculated. Because there is no March 1997 data available for comparisons, both the
October 1996- March 1997 comparison and the March 1997-July 1997 comparison are
"empty" data sets for this particular monument. The difference in the February 1998 and
the July 1997 surveys is determined and recorded. For this particular example, there are
two "empty" data sets and two data entries.
All of the differences for a particular time interval are averaged based on the total
number of data sets available. The number of data sets used is noted in the graphs, as
previously discussed. The results for developed or natural subdivisions are obtained by
averaging the appropriately designated monuments according to the total number of data
sets available for each respective classification.
Additional surveys conducted by the DEP were used in some instances to
supplement the data set. The DEP surveys used were: for Escambia and Santa Rosa
Counties, February 1996; for Walton County, May 1995 and March 1993; and for Bay
22
County, February 1996 and October 1996. In the graphs, the asterisk next to some of the
dates indicates that the data were obtained from DEP surveys, instead of COE surveys.
For Figure 4, the February 1996 survey was conducted by the DEP, and the remaining
five surveys were conducted by the COE.
The May 1996 survey is the earliest survey conducted that is common for all of the
profiles. Thus, for congruency purposes, all of the data are referenced to this common
starting point. The cumulative averaged changes are all shifted to zero at May 1996 for
plotting purposes, and the best fit trend lines of the data begin with May 1996 (see
Figure 4).
Between the March 1997 and the July 1997 surveys, a berm with a nominal volume
of 6 yd3/ft was placed in Santa Rosa County in the "developed" locations, from R-193-
R-197. A typical monument profile which experienced this berm placement, R-194.5, is
shown in Figure 5. Note the obvious volumetric addition of the berm with reference to
the preceding surveys. Because the nourishment would have been the primary volumetric
component of change instead of natural recovery, no volumetric comparisons were made
for those monuments between those two survey dates. The post-nourishment surveys,
July 1997 and February 1998, were compared as usual. After the placement, the volume
of sand in the vicinity of the berm placement should remain approximately consistent,
even though there was some redistribution of the sand from the initial shape, see Figure 5.
There is no data set listed for the developed sites for the July 1997 survey, since the beach
at every developed monument was manipulated. No placement of sand occurred in the
natural areas in Santa Rosa County, so the associated data are unaffected. Finally, all of
*....... October 1996
........... March 1997
J----- uly 1997
'-" February 1998
Artificial Berm
Equilibrating B rm f Equilibrating Berm
A-ue
------------- -- _____ /_____________
I j
' .
""">. :*... "2- Gulf of Mexico
..
l~~~~~~~ i ii i i i
100
200
300
400
Distance seaward of monument (ft)
Figure 5- Beach Profile R-194.5 in Developed Area of Santa Rosa County Showing Artificially Placed Berm
20
15
Z10
0
4-'
500
24
the data points are used for the beach width comparisons for Santa Rosa County because
the artificial nourishment was considered to have minimal effect on the beach width.
The time line is congruent for all of these graphs, i.e. the time of 1 year on the
horizontal axis will always correspond to the May 1996 survey, regardless of the county,
see Figure 4. Time "0" is the earliest survey data used, which is the DEP survey of
Walton County conducted in May 1995. It is important to note that this is a pre-Opal
survey. Finally, the scale of the vertical axis for both the volumetric changes and the
changes in beach width are the same for all counties to allow easy visual comparison.
The plots for beach widths contain an additional data point for October 5, 1995.
This data point was obtained by measuring the distance between the monument and the
wet sand line on aerial photographs. Because of the small tidal range in this area, the
location of the NGVD water line can be reasonably estimated from the aerial
photographs. The purpose of these data points is to define the beach conditions as well as
possible immediately post-Opal. Table 2 presents the shoreline changes between
October 5, 1995 and May 1996. It is seen that the short term shoreline recovery (October
1995 to May 1996) was substantial for all counties except for Walton County. The all
county shoreline advancement is 36.3 feet. The average advancements for the developed
and natural areas are 34.2 and 42.1 feet, respectively.
Discussion
The average of all of the data was plotted to provide an general overview of the
results. A linear "best fit" straight line was plotted for the data sets so that the slope of
Table 2- Shoreline Change as Determined from Aerial Photographs Between October
1995 and May 1996
County- Subdivision Shoreline Change from October 1995 to
May 1996 (ft/yr)
All Counties- Average 36.3
Developed 34.2
Natural 42.1
Escambia- Average 49.6
Developed 41.2
Natural 62.3
Santa Rosa-Average 54.7
Developed 56.9
Natural 52.8
Walton- Average 8.3
Developed 6.1
Natural 11.1
Bay- Average 32.7
Developed 32.7
Natural insufficient data
Table 3- Beach Volume and Width Trends as Determined by the Least Squares Method
County- Subdivision VolumeTrend (yd3/ft/yr) Beach Width Trend (ft/yr)
February 1998 included February 1998 included
Yes No Yes No
All Counties- Average -2.65 0.06 -8.75 2.70
Developed -2.75 -0.04 -10.57 -0.86
Natural -2.42 0.19 -7.42 5.79
Escambia- Average -2.5 0.00 -16.4 -12.0
Developed -2.0 0.7 -14.5 -8.2
Natural -3.2 -1.3 -19.2 -17.7
Santa Rosa- Average -2.6 -1.3 -11.9 -4.9
Developed 0.00 1.7 -7.4 -6.7
Natural -5.2 -4.2 -14.6 -4.2
Walton- Average -0.3 5.3 5.7 34.7
Developed -1.5 4.9 -0.00 30.7
Natural 0.7 5.3 10.0 36.5
Bay- Average -4.5 -3.2 -14.5 -9.7
Developed -5.4 -4.6 -15.9 -12.7
Natural -0.8 2.9 -10.6 3.1
(Note: there are varying amounts of natural and developed areas in each of the four
counties, so a straight averaging method can not be used).
27
the line represents the prevailing trend, see Figures 6-35. As Table 3 and Figure 6 show,
the average rate of volume loss, overall, is 2.65 yd'/ft/yr.
There is no significant difference between the developed and natural areas, both
volumetrically and in terms of beach width. Due to natural variability and a level of
uncertainty in the data, any noticeable trends observed between the developed and natural
areas in one county was balanced by an opposite trend in another county. The developed
areas, Figure 7, are eroding at a rate of 2.75 yd3/ft/yr, and the natural areas, Figure 8, are
eroding at a slightly lower rate of 2.42 yd3/ft/yr. The overall change in beach width for all
of the counties, Figure 9, is decreasing at a rate of 8.75 ft/yr. The developed beaches, see
Figure 10, are decreasing at a rate of 10.57 ft/yr, and the natural areas are decreasing a
rate of 7.42 ft/yr, see Figure 11.
In Escambia County, the beach width and volume changes in the developed and
undeveloped areas are approximately the same, see Table 3 and Figures 12-17. Although
natural areas are slightly more erosive than the developed areas, the small difference is
probably not significant. The natural areas show a greater recessional trend than the
developed areas in terms of beach width.
Santa Rosa County has an overall negative trend for volume and beach changes, see
Table 3 and Figures 18-23. The developed areas are stable, and the natural areas are
eroding. Both the developed and the natural areas show a negative trend in beach width
change, but the developed beach width change is less erosional than the natural areas.
Overall, Walton County has the lowest erosion rate of any county studied, Table 3
and Figures 24-29. The developed sites are slightly erosional, and the natural sites
28
display a positive volumetric trend. The developed areas have a stable beach width trend,
and the natural areas have a positive trend. Therefore, Walton County is the only county
to have a positive overall beach width trend.
Bay County is the one of two areas studied (Walton County is the other) where the
natural areas had a less negative trend in volume change than the developed areas, Table
3 and Figures 30-35. This trend is reflected in the beach width changes, also. The beach
width change trends are moderately large compared to the other areas surveyed.
The paragraphs below summarize, in detail, each county's overall trends in volume
and beach width for the county's average, developed and natural areas.
Escambia County experiences both positive and negative volume changes, see
Figure 12, with an overall rate of sand loss at 2.5 yd3/ft/yr. Due to the fluctuations, the net
change is approximately zero until the February 1998 survey. There was a loss in volume
from the February 1998 survey of about 5 yd3/ft of sand from the beach. In general, the
Escambia County beaches are fairly stable, with only small seasonal fluctuations. The
summer surveys, October 1996 and July 1997, are more erosional. In contrast, the winter
survey of March 1997 has an accretional signal. The developed and natural sites show
similar trends, see Figures 13-14. They both fluctuate around the zero line and are fairly
stable with some seasonal variability. The natural sites, Figure 14, fluctuate slightly more
overall than the developed sites and have a slightly more negative trend ( -3.2 yd3/ft/yr)
than either the average (-2.5 yd3/ft/yr) or the developed areas (-2.0 yd3/ft/yr).
In terms of beach width, Escambia County oscillates around the zero line with
seasonal fluctuations, Figure 15, for profiles in both developed and natural areas. The
29
February 1998 survey shows a decrease in the beach width, with an average loss of 16.4
ft/yr. The developed areas, Figure 16, show similar trends and have a loss rate of 14.5
ft/yr. In general, the beach width change for the natural areas, Figure 17, is more negative
than either the average or developed areas, at a rate of-19.2 ft/yr. The beach width
fluctuates seasonally, and the February 1998 survey is the most erosional survey in the
natural areas of Escambia County.
Overall, with the exception of the February 1998 survey, the average net volume
change in Santa Rosa County is slightly positive, but the general trend is moderately
negative (-2.6 yd3/ft/yr) due largely to the volume reduction associated with the February
1998 survey, see Figure 18. After a significant volume increase in May 1996, the volume
is reasonably constant until February 1998. The developed areas also increase in May
1996 and then level off, see Figure 19. February 1998 is not as noticeably erosive as in
the other graphs; the volume of sand on the developed beach is reduced only slightly from
the March 1997 survey. The beach volume is stable; it is neither accreting nor eroding.
The absence of the July 1997 data due to placement of the artificial dune was explained in
Chapter 6. For the natural areas of Santa Rosa County, Figure 20, the data fluctuates
around the zero line, with the February 1998 data set more erosive than any other natural
area surveyed. The reduction in volume occurs at a rate of approximately 5.2 yd3/ft/yr for
the natural areas.
In general, the beach width trends for Santa Rosa County are erosive, Figure 21. The
erosive nature of the February 1998 data contributed to a negative trend of 11.9 ft/yr. The
fluctuation patterns in the beach width correspond to the changes in volume. The
developed areas also show a decrease in beach width. The rate of beach change for
developed areas in Santa Rosa County is -7.4 ft/yr, see Figure 22. The beach width in the
developed areas decreases from May 1996 and then remains fairly constant. The February
1998 decrease is not as large for the developed areas it is for the natural areas of Santa
Rosa County. The beach loss rate for the natural areas is 14.6 ft/yr, see Figure 23. This
rate corresponds to the relatively large loss in volume for the natural areas of this county.
Walton County's prevailing tendency is only nominally erosive at a rate of 0.3
yd3/ft/yr, see Figure 24. Even though the data includes pre-Opal survey data, only the
post-Opal data, starting with May 1996, were used to obtain the trend lines. The average
results shows the greatest erosion for the October 1996 and February 1998 surveys and
the greatest accretion for the March 1997 survey, which corresponds to the seasonal
fluctuations in this Panhandle region. The developed and natural sites, see Figures 25 and
26, follow the same pattern as the county average. The developed sites are eroding at a
rate of 1.5 yd3/ft/yr. The natural sites, Figure 26, are the only accretional areas studied,
with a positive rate of 0.7 yd3/ft/yr. However, due to the nature of the beaches that were
included in the "natural" category, this should be expected. The natural areas in Walton
County, as previously discussed, are composed of areas where the dunes were protected
from beach goers by walkovers, surrounded by sand fences and highly vegetated. All of
these factors probably contributed to the positive volumetric change.
Walton County's average beach width changes are positive at a rate of 5.7 ft/yr, see
Figure 27. As previously discussed, even though the data collection begins before Opal,
the trend lines are only based on post-Opal results. The beach width fluctuates
31
seasonally, and the March 1997 survey is the widest beach observed throughout the COE
survey period. The developed beach width trends are stable, see Figure 28. Overall, the
natural areas studied are wider than the developed beaches, Figure 29, and show the only
positive trend for beach width changes at a rate of 10.0 ft/yr.
Bay County, see Figure 30, had two surveys conducted in the month of October
1996, one by the DEP and one by COE. There is not a significant difference between the
two surveys. Throughout all of the graphs, there is virtually no change between the May
1996 and the DEP October 1996 surveys.
The average rate of loss in volume for Bay County is 4.5 yd3/ft/yr. The last four
surveys, all conducted by the COE, show a relatively stable beach with little change. As
seen previously, the beach volume decreases in the February 1998 survey. The developed
areas, Figure 31, are consistently erosional, with an erosional tendency overall at a rate of
5.4 yd3/ft/yr. This is the largest erosion rate for the areas studied. The natural areas
fluctuate around the zero line, and the February 1998 survey ends the study period with a
deficit of sand, see Figure 32. The relatively small erosion rate for the natural areas of
Bay County is 0.8 yd3/ft/yr.
The average beach width changes for Bay County (Figure 33) show a slight seasonal
trend, similar to the volumetric changes. The rate of beach loss is 14.5 ft/yr for all of Bay
County. The February 1998 survey indicates a narrower beach than in the previous
surveys. The developed areas have seasonal fluctuations, see Figure 34, and an erosional
rate for beach width of 15.9 ft/yr. There were no natural areas surveyed in May 1996, so
the comparisons begin with the DEP October 1996 survey as the baseline, see Figure 35.
The fluctuations are seasonal, and the February 1998 survey is negative. The natural
areas decrease in beach width at a rate of 10.6 ft/yr.
Effect of February 1998 Survey
The discussions of the trends in volumetric and shoreline changes have emphasized
the role of the erosive conditions documented in the February 1998 survey. In order to
quantify the effect of this storm on the overall results, the data for all of the counties were
reanalyzed excluding the February 1998 survey data set. The results are presented in
Table 3 where it is seen that the February 1998 data are a significant contribution to the
overall erosive trends of this study.
The average volumetric trend becomes positive at a rate of 0.06 yd3/ft/yr if the
February data are neglected, instead of-2.65 yd3/ft/yr. The developed beaches also have
a less negative trend, -0.04 yd3/ft/yr verses -2.75 yd3/ft/yr. The natural beach trend
becomes positive at a rate of 0.19 yd3/ft/yr, compared to a trend of-2.42 yd3/ft/yr when
the February data are included. Without the February 1998 data set, the volumetric
changes for the study area are basically zero.
The greatest impact of the February 1998 data is evident in the beach width changes.
The average beach width change becomes positive when the erosive February 1998 data
set is not included, changing from -8.75 ft/yr to 2.7 ft/yr. The developed beach has a
similar less negative trend, decreasing from -10.57 ft/yr to -0.86 ft/yr. The natural
beaches have a notably positive trend without the February 1998 data set. The natural
beach trend, including the erosive data set, is -7.42 ft/yr, but excluding the February 1998
set changes the trend to a positive 5.79 ft/yr.
33
For Escambia County, excluding the February 1998 data set turns the slightly erosive
volumetric trend into a stable trend. The developed beaches accrete instead of erode, and
the natural beaches have a slightly less erosive trend. The beach width trends, in the case
of the average, developed and natural areas of Escambia County, all erode significantly
less than they would if the February 1998 data set were included.
In Santa Rosa County, the data trend becomes less negative when the February 1998
data is removed. The developed beaches have a positive trend, and the natural beaches
have a less negative trend. The beach width trends become less erosive with the
elimination of the February 1998 data.
Walton County's trend becomes positive for all subdivisions of both volume and
beach width change. The beach width change was especially affected by the removal of
the February 1998 data set. Even though the trends for beach width were already positive
or stable, they become very large positive trends when excluding the erosive data set.
For Bay County, the overall and developed site's volumetric change becomes
slightly less negative when the February 1998 data set is removed. The natural area's
trend changes from slightly negative to moderately positive. The beach width change
trends follow the same pattern as the volumetric change trends. The overall and
developed sites become less erosive than they originally were, and the natural beaches
become positive.
Conclusions
In general, the change in beach width correlates very strongly with the volumetric
changes for each county and each subdivision, i.e. if an area shows a decrease in the
volume of sand, there is usually a corresponding decrease in the distance between the
monument and the NGVD water line. The fluctuations in the graphs and the magnitudes
of change are similar for both the volumetric and beach width changes. However, the
largest erosive trend for the volume may not correspond to the largest recessional trend
for the beach width when comparing the natural and developed areas. One possible
reason that the linear trends do not match the overall net changes is that the strongly
erosive February 1998 survey may have skewed the results to varying degrees for the
different areas. For example, a beach that suffered considerable loss of beach width but
not a corresponding reduction in volume may indicate that the sand was removed from
the system from an upland dune area and deposited in a shallow nearshore sand bar.
The alternating cycles of erosion and accretion throughout the study period indicate
seasonal trends in the dry beach erosion and accretion. For the surveys reported herein,
the winter profiles are characterized by wider beaches with larger volumes when
compared to the summer profiles. This is contrary to the normal definition of"winter"
and "summer" profiles associated with sandy beaches in the eastern United States. Wave
hindcast data provided from the United States Army Engineer Waterways Experiment
Station were analyzed to determine if the seasonal fluctuations are characteristic of this
area. The average wave heights from two stations located in the vicinity of this study
from 1956-1975 show higher wave heights in the winter months than in the summer
months. From October through March, the average wave height is 1.18 meters, and from
April to September, the average wave height is 0.93 meters. Because larger wave heights
are typically more erosive to the beachface, the winter profiles should have narrow
beaches and the summer profiles should have wider beaches, according to the wave
hindcast data. Because the profiles obtained during this study period do not support this
prediction, the observed conditions may be anomalous to this area or just during the
duration of the monitoring period.
The areas studied show a slight erosional trend, with the no significant difference
between the developed and natural areas, overall. One possible explanation for this
general erosional trend is that the final survey was conducted immediately after two
northeasters impacted the area. If the final survey is not included in the analysis, the
general trend is slightly positive. The natural areas still perform better than the
developed areas, and even show a small level of accretion, while the developed areas
remain slightly erosive.
At the February 1998 survey, there were sandbars present at almost every monument
surveyed. This suggests that while the beach width, and to a lesser degree, the subaerial
volume, has decreased, much of the "lost" sand was merely transported to and deposited
in a nearshore bar. Again, this is possibly the result of a succession of northeasters. If
another survey were conducted several months later, after sufficient time for milder
waves to redeposit the sand back on the beach face, it is likely that the beach width
conditions would be neutral or show accretion.
The slight variability in volumetric and beach width changes between individual
county's developed and natural areas can be explained by a level of uncertainty in the
data. Also, the effects of homeowner manipulation on the developed beaches fronting
their houses via sand fences and extensive vegetation may take a longer time period than
included in this study to demonstrate their effectiveness in stimulating beach recovery.
Overall, the natural variability in the beaches and the duration of this study, which is
considered short relative to natural recovery processes, combine to result in a difficulty in
identifying with confidence any differences in recovery processes in the natural and
developed areas.
The October 5, 1995 data points for beach width change plots provide useful
information regarding initial beach recovery following Hurricane Opal. The first post-
Opal survey data, obtained four months after the hurricane, shows significant beach
recovery. Therefore, although the two year duration of this study appears to have been
too short to quantify substantial long-term trends, the additional data obtained from aerial
photography has established short-term post hurricane recovery.
40
30
20
10
0
-10
-20
-30
-40
0.0
0.5 1.0 1.5
Time (years)
Figure 6- Cumulative Change in Average Volume for All Counties
Best Fit Trend Line
Best Fit Trend Line
2.0
2.5
40 .
M) 0)
, 30 0, Fi ,- L e
20 0
0.0 0.5 1.0 1.5 2.0 2.5
0Time (
. -30 -
"-?
-30
3 -40 Best----Fit Trend ---- Line---
S0.0 0.5 1.0 1.5 2.0 2.5
Time (years)
Figure 7- Cumulative Change in Average Volume for All Developed Profiles
40
30
20
10
0
-10 -
-20
-30
-40
0.0
1.0 1.5
Time (years)
Best Fit Trend Line
Best Fit Trend Line
0.5
2.0
2.5
Figure 8- Cumulative Change in Average Volume for All Natural Profiles
100 r ,-
0) 0
80 -- 0
0) ccc
a 60 2 75
C 40 -
._ 20
a)
C : 0...... I..'.lo. .............
a -20 ,I
-40 Best Fit Trend Line
-60
-80
-1 0 0 I I I I I
0.0 0.5 1.0 1.5 2.0 2.5
Time (years)
Figure 9- Cumulative Change in Average Distance from the Monument to the Water Line for All Counties
100
80
60
40
20 -
0
-20
-40
-60
-80
-100
0.0
o>
Ow-
0)o>
co N-
0) L- M CO
o -. 0
OU'
u-
Best Fit Trend Line .
Best Fit Trend Line "
0.5
1.0 1.5 2.0 2.5
Time (years)
Figure 10- Cumulative Change in Average Distance from Monument to Water Line for All Developed Profiles
100 r
0)
80
0 60 -
40 0
o
.20
U -20
I Best Fit T
-40
E -60
-80
-100 '
0.0 0.5 1.0 1.5
Time (years)
rend Line
2.0 2.5
Figure 11- Cumulative Change in Average Distance from Monument to Water Line for All Natural Profiles
O
-0
0) 0) (D
) 30 0
t-Z
!0)
^ 20
S0.0
-20
a,
S-30 -0
>-40
S0.0 0.5 1.0 1.5
E
3 Time (years)
O
0) 0
0) C0
3-
0)
75
Best Fit Trend Line
2.0 2.5
Figure 12- Cumulative Change in Average Volume for All Escambia County Profiles
I I g
40 0
S30 L.
S lca
S 20 -LL
20
S10
0 . . . . .. . . . . . . . . . ." ,
) Best Fit Trend Line
-20
| -30
I -40
0.0 0.5 1.0 1.5 2.0 2.5
Time (years)
Figure 13- Cumulative Change in Average Volume for Developed Profiles in Escambia County
Figure 13- Cumulative Change in Average Volume for Developed Profiles in Escambia County
C.J
-.
-I
0
c
oa
05
E
-5
a,
0
0)
40
30
20
10
0
-10
-20
-30
-40
0.0
Best Fit Trend Line
0.5 1.0 1.5 2.0 2.5
Time (years)
Figure 14- Cumulative Change in Average Volume for Natural Profiles in Escambia County
1
S 5- 5
80- ( M
8 60 .0 C c 0)
S40-
S 20 LL.
CO
-100 '.. '. .. '. .
0.0 0.5 1.0 1.5 2.0 2.5
-Time (years)
Figure 15- Cummulative Change in Average Distance from Monument to Water Line for All Escambia County Profiles,
October 1995 Position Based on Aerial Photographsend Line
E -60
-80
-100
0.0 0.5 1.0 1.5 2.0 2.5
Time (years)
Figure 15- Cummulative Change in Average Distance from Monument to Water Line for All Escambia County Profiles,
October 1995 Position Based on Aerial Photographs
M M
0) 0
O) LL
to
0
100
80
60
40
20
0
-20
-40
-60
-80
S.........
Best Fit Trend Line
-100 L
0.0
0.5 1.0 1.5 2.0
Time (years)
Figure 16- Cummulative Change in Average Distance from Monument to Water Line for Developed Profiles in
Escambia County, October 1995 Position Based on Aerial Photo.
4/
2.5
CO
c0
0)
IL
-D
U)
100
80
60
40
20
0
-20
-40
-60
-80
1.0
1.5
Time (years)
2.0
2.5
Figure 17- Cummulative Change in Average Distance from Monument to Water Line for Natural Profiles in Escambia
County, October 1995 Position Based on Aerial Photo.
B F T.r..n L
Best Fit Trend Line
-
-100'
0.
0
0.5
40 (C
e, .0 a
30 o
OO
20 LL
I 10 -
0 ......
S-10 Best Fit Tre
2 -20
E
= -40
- 0.0 0.5 1.0 1.5
E
= Time (years)
O
Figure 18- Cumulative Change in Average Volume for All Santa Rosa County Profiles
n d ... ..e .... .......
!nd Line r
2.0 2.5
S230 -
3 0 a
I.0i >, 5 "
r Best Fit Trend Line
-20
- -30
1-40
*I -4 --------------------
0.0 0.5 1.0 1.5 2.0 2.5
Time (years)
Figure 19- Cumulative Change in Average Volume for Developed Profiles in Santa Rosa County
0
tM 10
c: Z-/
40 c o a
00)
LI.. a
D 2.0 CD M
30 I-"
0 o O
0 -20
E
I 10
-20
~ -30
-40 -40
0.0 0.5 1.0 1.5 2.0 2.5
Time (years)
Figure 20- Cumulative Change in Average Volume for Natural Profiles in Santa Rosa County
0)
00
0)
U-
U-
I
0
100 -
o 60 D U
C: o0
)- 40 --
0
c 20 -
0)
o 0 .............. ....
0 -20
S_-b40 Best Fit Trend Line
c 4 -4
E
-60
-80
-100 1 '
0.0 0.5 1.0 1.5 2.0 2.5
Time (years)
Figure 21- Cumulative Change in Average Distance from Monument to Water Line for All Santa Rosa County
Profiles, October 1995 Position Based on Aerial Photographs
00
V-
U-
0)
LL
)
100 _
80 c -
a 60-
S60 a)
I 40 n
0 0 0a Li
c:20
-20 -
S -40 Best Fit Trend Line
1 -60
0
-80
-100 L '
0.0 0.5 1.0 1.5 2.0 2.5
Time (years)
Figure 22- Cumulative Change in Average Distance from Monument to Water Line for Developed Profiles in
Santa Rosa County, October 1995 Position Based on Aerial Photographs
L()
100 r ICD
80 -, ,-
U 0U
8 60 Cr
S40 I LL
20 -
0 ... ....
/- ...-.............. ..........
i 2- i n in i BesFit Trend Line
S-60
-80 -
-100
0.0 0.5 1.0 1.5 2.0
Time (years)
Figure 23- Cumulative Change in Average Distance from Monument to Water Line for Natural Profiles in
Santa Rosa County, October 1995 Position Based on Aerial Photographs
2.5
.. .
40 0
40 *May 1995
S- 0) C) 0)
m 30 (Pre-Opal) "
20
M 10
10
S0 1 0
cu Best Fit Trend Line -
N
0 -20
6 -30
> -40
0.0 0.5 1.0 1.5 2.0
E
3 Time (years)
O
Figure 24- Cumulative Change in Average Volume for All Walton County Profiles
2.5
- S 4 0 I C
^ 30 ) "-- 0)
20- l 2 0
m 10
S*May 1995
S-10 (Pre-Opal) Best Fit Trend Line
U -20
S 40
FI -C30---- Cag----u
0.0 0.5 1.0 1.5 2.0
Time (years)
O
Figure 25- Cumulative Change in Average Volume for Developed Profiles in Walton County
2.5
40 0
S40 0) (0 s-
S0) 0)
0) v 0)
20
0 0
m 10 i
M ,*May1995 1
) 0 (Pre-Opal)
S-10 B
C'.
c0
o -20
E
-30
a)
-40
5 0.0 0.5 1.0 1.5 2.
E
STime (years)
Figure 26- Cumulative Change in Average Volume for Natural Profiles in Walton County
Figure 26- Cumulative Change in Average Volume for Natural Profiles in Walton County
est Fit Trend Line
0 2.5
*May 1995
(Pre-Opal)
0o
1 I
\ ^
0.5
co
0)
D 0)
0D Best Fit Trend Line
0.
1.0 1.5 2.0 2.5
Time (years)
Figure 27- Cumulative Change in Average Distance from Monument to Water Line for All Walton County
Profiles, October 1995 Position Based on Aerial Photographs
100
80
60
40
20
0
-20
-40
-60
-80
-100
0.0
*May 1995 O
100 (Pre-Opal) o
oD (0
> 0) 0)
80 co
8 60 ,r 0) s 0 )
I 40 -
c 20
S *............. .. ........ ... .. ... . .. .
)
o -20
S.' S Best Fit Trend Line
S o 0
-40
S-60 -
0 -10 0)
-80 -
O a
-100
-100 1--1--1-1------1-1--M I--I-----
0.0 0.5 1.0 1.5 2.0 2.5
Time (years)
Figure 28- Cumulative Change in Average Distance from Monument to Water Line for Developed Profiles in
Walton County, October 1995 Position Based on Aerial Photographs
-B
Best Fit Trend Line LL
. 4........- .
100
80
60
40
20
0
-20
-40
-60
-80
-100
1.5
Time (years)
2.0
2.5
Figure 29- Cumulative Change in Average Distance from Monument to Water Line for Natural Profiles in
Walton County, October 1995 Position Based on Aerial Photographs
co
(D
0)
CA
-
S*May 1995
(Pre-Opal) o- or
Ic
w 75
0.0
0.5
1.0
% 40r 0
S30 -
0) ,,
a) -0
20 0
0 ........
10 I
-20 Best Fit Trend
E 0)
S-30 -
a) O
S-40 I L l
3 0.0 0.5 1.0 1.5 2.0 2.5
E
Time (years)
O
00
()
Line
Figure 30- Cumulative Change in Average Volume for All Bay County Profiles
40 co
S30 o -
0-)o
20
20 0) c)
SBest Fit Trend Line 5
0 -20 o (
-30 -
m O
S-40
Time (years)
O
Figure 3 1- Cumulative Change in Average Volume for Developed Profiles in Bay County
-Co
40
30
20
10
0
-10
-20
-30
-40
1.0
1.5
Time (years)
Figure 32- Cumulative Change in Average Volume for Natural Profiles in Bay County
0 Best Fit Trend Line
O i
*a
-U-
0' M)
(0 7 -
0) 0) 0I
0) 0) 0)
--'
o .C 5
0.0
0.5
2.0
2.5
(0 -(0 00
100 o0 -
.0- (20 0
8'- 0) 0) -V- O
80 '-.
v" "r > *a oo
60 5 0 CD
-60 O o0 oU
40 |
-60 o Best Fit Trend Line
2 0 -0
-80 C)
-100 '---'-'--------
0.0 0.5 1.0 1.5 2.0 2.5
Time (years)
Figure 33- Cumulative Change in Average Distance from Monument to Water Line for All Bay County Profiles,
October 1995 Position Based on Aerial Photographs
CD
o ,
0)
CO
0
) C
g v
.2. N- .
o 0
00i
Best Fit Trend Line
-100 L
0.0
0.5 1.0
1.5
2.0
2.5
Time (years)
Figure 34- Cumulative Change in Distance from Monument to Water Line for Developed Profiles in Bay County,
October 1995 Position Based on Aerial Photographs
100
80
60
40
20
0
-20
-40
-60
-80
100
80 -
| 60
20
S-20
40 Best Fit
c- 20 -
cm 0-" .............' ---..
; -40 -" Best Fit
I -60 -
-80 -
O .
-100 '
0.0 0.5 1.0 1.5 2.0 2.
Time (years)
Figure 35- Cumulative Change in Distance from Monument to Water Line for Natural Profiles in Bay County
CO)
%oo
00
0)
0)
LL
Trend Line
5
CHAPTER 7
AEOLIAN TRANSPORT
Methodology
Field books from surveys conducted by COE personnel in the Perdido Key study
area were examined for notes describing the location of sand fences, if they existed, at
each monument profile. A list of the monuments and the corresponding sand fence
location was made, and the survey data were plotted for the appropriate profiles. A
typical profile for Perdido Key is plotted in Figure 36 for Monument Number R-48
(Escambia County). For this profile, the sand fence is located approximately 360 feet
seaward of the monument. Each profile that contained a sand fence was analyzed
individually to determine the cross-shore limits of accretion around the sand fence. A
distance of thirty feet in the seaward and landward direction of the sand fence was used as
a general rule of thumb for the accretion range. In some instances, the accretion range
was estimated as the distance between the sand fence and the location where the most
recently surveyed profile intersected the previous profile, both landward and seaward of
the sand fence. For Figure 36, an accretion range of 310-475 feet from the monument was
used.
As discussed previously for the Hurricane Opal study area, analysis of the data
concentrated on the change that occurred between each survey. In the Hurricane Opal
study, the entire beach width was analyzed for changes. For the Perdido Key study area,
however, only the change that occurred in the accretion range around a sand fence was
considered.
The distance and elevation values for each survey were analyzed to quantify changes
in beach volume only around the sand fence region. For each monument, the volume
changes were determined from one survey to the next. These changes were compared
throughout the entire survey period. The change in volume between each survey was
divided by the number of months that had elapsed between the given surveys for each
monument. This yielded a volume change rate per month. At each monument location,
the volume change rates throughout the entire survey period were averaged to obtain an
average rate of change per month for that particular monument location. Finally, the
average rate of change per month was multiplied by twelve to produce the average rate of
change per year for each separate monument.
This study attempts to determine a correlation between the active beach width and
the amount of aeolian sediment trapped by a sand fence. The beach width discussed
previously for the Hurricane Opal study differs slightly from the active beach width used
in this correlation of Perdido Key. The beach width used earlier for the Hurricane Opal
study area is defined as the distance from the monument to the NGVD water line.
However, the Perdido Key study defines the active beach width as the distance from the
sand fence to the NGVD water line. In instances of fields of sand fences, the farthest
seaward sand fence was used to determine the active beach width.
Conclusions
For each monument location, the average volumetric rate of change per year was
plotted with the corresponding active beach width in Figure 37. A linear "best fit"
straight line was plotted for the data set. There is a strong correlation between the active
beach width and the volume of sediment trapped by the sand fence. The sediment on
wider beaches has a lower moisture content due to increased distance from the water line
and the water table. The drier sediment is thus more easily transported by the wind. If the
beach is void of vegetation, sand fences or other mechanisms to sufficiently slow the
wind speed, then a wide beach could become erosive due to wind transport more readily
than a narrower beach.
O'Brien proposed a simple sand transport equation based on field measurements:
G=0.036U,
where G is the transport rate in pounds per day per foot width and U5 is the wind speed
five feet above ground level in ft/sec (Belly, 1964). For the average G of the Perdido Key
data points, the necessary wind speed to transport the sediment load is 9.66 ft/sec. From
Work and Dean 1990 and Work, Lin and Dean 1991, the average sustained winds in the
Perdido Key area are approximately 10-16 ft/sec. Thus, the observed aeolian transport
rate is consistent with the O'Brien formula.
The sand transport is lower in the Perdido Key study site than in the areas studied by
Illengberger and Rust (1988) and Hunter et al. (1983). The site in Oregon had a sand
transport rate range of 6-12 yd3 ft-' yr', and the Alexandria site had a sand transport rate
70
of approximately 10 yd3 ft'' yr"'. Although the beach widths for these sites are not known,
they are probably in the same general range of the Perdido Key beach widths.
Differences in wind speed, moisture content and grain size may be contributing factors
for the discrepancy. For an average beach width of 250 ft in the Hurricane Opal study
area, accretion rates of approximately 1 yd3 ft' yr-' could be extrapolated from the data
presented in Figure 37. However, studies have not been conducted to verify this
prediction.
November 1989
S.......... September 1990
S Sand FEnce --..-. October 1991
10- ---S--- October 1992
S1- November 1993
.. .-.- September 1995
i January 1990
|.' ___ -- _.... __
> P
0 ~ ~
/cc tion Range \
0 \
SGulfofMexico
-5
\\ \, . .
0 100 200 300 400 500 600 700 800 900 1000
Distance seaward of monument (ft)
Figure 36- Beach Profile in Perdido Key Showing Accretion at Sand Fence, R-48
I 2-
0
I -1 II I
100 200 300 400
Active Beach Width (ft)
Figure 37- Perdido Key Data Correlation: Active Beach Width vs Sand Fence Accretion
REFERENCES
Bauer, B.O., Davidson-Amott, R.G.D., Sherman, D.J., Nordstrom, K.F. and Jackson,
N.L. 1996. Indeterminacy in Aeolian Sediment Transport Across Beaches. Journal
of Coastal Research. 12: 3: 641-653.
Belly, P.-Y. 1964. Sand Movement by Wind. U.S. Army Corps Eng. CERC. Tech. Mem.
1. Washington, D.C.
Browder, A.E. and Dean, R.G. 1997. Perdido Key Beach Nourishment Project: Gulf
Islands National Seashore. 1997 Performance Monitoring Report, University of
Florida, Gainesville, FL.
Davidson-Amott, R.G.D. 1988. Temporal and Spatial Controls on Beach/Dune
Interaction, Long Point, Lake Erie. Journal of Coastal Research. Special Issue No
3, Dune/Beach Interaction, edited by N.P. Psuty, 131-136.
Davidson-Amott, R.G.D. and Law, M.N. 1996. Measurement and Prediction of Long-
Term Sediment Supply to Coastal Foredunes. Journal of Coastal Research. 12:3:
654-663.
Federal Emergency Management Agency (FEMA), 1996. Hurricane Opal in Florida: a
Building Performance Assessment, FEMA 281.
Grant, U.S. 1948. Influence of the Water Table on Beach Aggradation and Degradation.
Journal of Marine Research, VII:3: 655-660.
Hubertz, J.M. and Brooks, R.M. 1989. Gulf of Mexico Hindcast Wave Information.
Department of the Army, U.S. Army Corps of Engineers, WIS Report 18,
Waterways Experiment Station, Vicksburg, MS.
Hunter, R.E., Richmond, B.M., and Alpha, T.R. 1983. Storm-controlled Oblique Dunes
of the Oregon Coast. Geological Society of America Bulletin, 94: 1450-1465.
Illengberger, W.K. and Rust, I.C. 1988. A Sand Budget for the Alexandria Coastal Dune
Field, South Africa. Sedimentology, 35: 513-522.
74
Leadon, M.E. 1995. Hurricane Opal: Damage to Florida's Beaches, Dunes and Coastal
Structures. Florida Bureau of Beaches and Coastal Systems, Tallahassee, FL.
National Reseach Council. 1995. Beach Nourishment and Protection. Marine Board,
Commission on Engineering and Technical Systems. Washington, D.C.: National
Academy Press.
Work, P.A. and Dean, R.G. Perdido Key Beach Nourishment Project: Gulf Islands
National Seashore, 1991 Annual Report. University of Florida, Gainesville, FL,
1992.
Work, P.A., Lin, L. and Dean, R.G. Perdido Key Beach Nourishment Project: Gulf
Islands National Seashore, 1990 Annual Report. University of Florida,
Gainesville, FL, 1991.
BIOGRAPHICAL SKETCH
The author was born in Cleveland, Ohio, and moved to Conyers, Georgia when
she was two years old. With support from a loving family, she moved far away from
home to study Marine Science at Jacksonville University in Jacksonville, Florida. She
graduated three short years later, and a slight career change ensued. The University of
Florida's Coastal and Oceanographic Engineering Department and the chance to study
with Dr. Robert Dean next enticed the author. Six semesters later, she will graduate with
a Master of Engineering degree. After a brief break from school, she plans to enter law
school to specialize in environmental or coastal law.
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