Citation
Volume, beach width and sand fence accretion comparisons for the Florida Panhandle region

Material Information

Title:
Volume, beach width and sand fence accretion comparisons for the Florida Panhandle region
Series Title:
UFLCOEL-98014
Creator:
Suter, Carrie Lynne
University of Florida -- Coastal and Oceanographic Engineering Dept
Place of Publication:
Gainesville Fla
Publisher:
Coastal & Oceanographic Engineering Dept.
Publication Date:
Language:
English
Physical Description:
xi, 75 leaves : ill. ; 29 cm.

Subjects

Subjects / Keywords:
Coast changes -- Florida -- Florida Panhandle ( lcsh )
Sedimentation and deposition -- Florida -- Florida Panhandle ( lcsh )
Genre:
bibliography ( marcgt )
non-fiction ( marcgt )

Notes

Thesis:
Thesis (M.E.)--University of Florida, 1998.
Bibliography:
Includes bibliographical references (leaves 73-74).
Statement of Responsibility:
by Carrie Lynne Suter.

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Source Institution:
University of Florida
Holding Location:
University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
41567206 ( OCLC )

Full Text
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
A CKN OW LED GM EEN TS .............................................................................................. ii
LIST OF TAB LES .......................................................................................................... vi
LIST OF FIGURES ........................................................................................................ vii
AB STRA CT ................................................................................................................... x
CHAPTERS
I INTRODUCTION ....................................................................................................... I
Purpose ...................................................................................................................... I
Report Organization .................................................................................................. 1
2 M OTIVATION FOR THIS STUD Y ......................................................................... 3
Im portance of Beaches ............................................................................................... 3
Physical Processes Associated with Storms and Dune Recovery .............................. 3
M aintenance of Beaches ............................................................................................ 4
3 HURRICAN E OPAL .................................................................................................. 6
Statistics of the Storm ................................................................................................ 6
Effects and Dam ages .................................................................................................. 6
4 BA CKGROU ND ON PREVIOU S STUDIES ............................................................ 8
5 STU D Y AREA S ......................................................................................................... 11
"Opal" Study Area ..................................................................................................... I I
Perdido Key ............................................................................................................... 11




6 NATURAL V S. DEVELOPED BEACHES ................................................................ 15
M onitoring Efforts by the University of Florida ........................................................ 15
Results ........................................................................................................................ 16
Beach Profiles ........................................................................................................ 16
Beach Volumes and W idths ................................................................................... 19
Discussion .................................................................................................................. 24
Effect of February 1998 Survey ................................................................................. 32
Conclusions ............................................................................................................... 33
7 AEOLIAN TRAN SPORT .......................................................................................... 67
M ethodology .............................................................................................................. 67
Conclusions ................................................................................................................ 69
REFEREN CES .............................................................................................................. 73
BIOGRAPHICAL SKETCH ......................................................................................... 75




LIST OF TABLES

Table
I "Developed" and "Natural" Areas for Hurricane Opal
M onitoring by CO E ............................................................................... 16
2. Shoreline Change as Determined from Aerial Photographs Between
October 1995 and M ay 1996 ................................................................. 25
3. Beach Volume and Width Trends as Determined by the Least
Squares M ethod ..................................................................................... 26




LIST OF FIGURES

Figure pag.e
1. Hurricane Opal Study Area ......................................................... 13
2. Perdido Key Study Area............................................................. 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-l 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 C ounty .................................................................................... 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 R osa County ................................................................................ 49
19. Cumulative Change in Average Volume for All Developed Profiles in
Santa R osa County ................................................................................. 50
20. Cumulative Change in Average Volume for All Natural Profiles in
Santa R osa 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 C ounty ....................................................................................... 55
25. Cumulative Change in Average Volume for All Developed Profiles in
W alton C ounty ....................................................................................... 56
26. Cumulative Change in Average Volume for All Natural Profiles in
W alton C ounty ...................................................................................... 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
B ay C ounty ....................................................................................... 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 A ccretion ................................................................................. 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 I
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-




Amott and Law (1996), Grant (1948), Illengberger and Rust (1988), Hunter, Richmond and Alpha (1983) and Bauer, Davidson-Amott, 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. Whiile 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 hurrcanes. 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 8-1 1 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-Arnott 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-Arnott and Law, 1996).
In 1988, Davidson-Arnott 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 M1 yr-' but decreased to 15 M3 m-1 yr-1 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 duniefield 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- 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, graln-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 I I 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 199 1, October 1992, November 1993, September 1995 and January 1997.




county lines are approximate

3390000

3370000 3350000 3330000 3310000 3290000

32700001 1 1 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




f
611

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 naturala" 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 RI to R2, R4.5 to R6A.5 R2.5 to R4, R7 to R8.5
Bay R85 to R91, R93 R91.5 to R97 exceptt R9.3
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- 18 8. By plotting several surveys on the same graph, erosional or accretional trends are evident. To better illustrate these trends, Santa Rosa County R- 18 8 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
0
0
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-1 88




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- 18 8 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




Cumulative Volume Change per Unit Beach Length (yd3/ft)
1 I I I I
0 h C) C) .. --D C) C) (D
0 0 0 0 0 0 0 0 0
c O
> 0
0" 0
D *Feb 1996
O
9
o
--D -4 May 1996 (10)
a
CD
D Oct 1996 (11)
0
o
s- Mar 1997 (20)
o- Jul 1997 (17) CD
"11
- Feb 1998 (17)
CD
_ Feb 1998 (1 7)




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 44 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 yd/ft was placed in Santa Rosa County in the "developed" locations, from R-193R- 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
July 1997
February 1998
Artificial Berm
Equilibrating B rm if Equilibrating Berm
-SA
Gulf of Mexico
.. . . . . . .. .
" ': : ....:.. : : ..: .. . : . . ... ... . ,-.- .
* .
\ "\ I I I II 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
~55

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 I 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 (ftlyr)
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 6-3 5. As Table 3 and Figure 6 show, the average rate of volume loss, overall, is 2.65 yd'lft/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 yd 3/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 yd 3/ftlyr) 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 yd 3/ftlyr for the natural areas.
In general, the beach width trends for Santa Rosa County are erosive, Figure 2 1. 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 yd 3/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 yd 3/ftlyr. The natural sites, Figure 26, are the only accretional areas studied, with a positive rate of 0.7 yd 3/ftlyr. 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 ftlyr.
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 yd 3/ftlyr. The last four
surveys, all conducted by the COB, show a relatively stable beach with little change. As seen previously, the beach volume decreases in the February 1998 survey. The developed areas, Figure 3 1, are consistently erosional, with an erosional tendency overall at a rate of
5.4 yd 3/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 yd 3/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 ftlyr 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/ftlyr. 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 ftyr, 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 postOpal 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

2.0

2.5




~40
00
"oo
430 0.
c:
20-0 S20 0
o
S10
L
0)
II I
-10
0 Best Fit Trend
a)
E
=$-20
30
M
=-40 S0.0 0.5 1.0 1.5
Time (years)

Line '

2.0 2.5

Figure 7- Cumulative Change in Average Volume for All Developed Profiles




40 30 20
10
0
-10
-20
-30
-40
0.0

0.5

1.0 1.5
Time (years)

Figure 8- Cumulative Change in Average Volume for All Natural Profiles

Be t i Te........ .
Best Fit Trend Line

2.0

2.5




100 (0 ,03O) O'('3)I0) 80 ( Mo
60 (. 40
ci)
20
0 .. .. .. .. .......... .
c -20
Best FitTrend Line S-60
-80
-100' ''
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 -C 0")
)CD
80 -)
S60
oo
.6
.' 40
O
o 20
0 . . .
-20
a)
-40 Best Fit Trend L
S-60
0
-80
-100 I I0.0 0.5 1.0 1.5
Time (years)

0) U0') 00
0)

.. ..... ......... / 4 .....

2.0 2.5

Figure 10- Cumulative Change in Average Distance from Monument to Water Line for All Developed Profiles




100
0') 0")
0)0')I80
080
40
(n 40
. 20
a)
-20
a)
-I.-, Best Fit Trend Line
m -40
E
- -60
-6
-80
-100 L
0.0 0.5 1.0 1.5 2.0 2.5
Time (years)
Figure I I- Cumulative Change in Average Distance from Monument to Water Line for All Natural Profiles




0
0 C ) 03) 0)
ciD
*Ic

0 (D
0) 0) Q
OCO C3)
O
LL
Best Fit Trend Line

Figure 12- Cumulative Change in Average Volume for All Escambia County Profiles

40 30 20 10
0
-10
-20
-30
-40
0.0

0.5 1.0 1.5 2.0 2.5
Time (years)




co (o
040
o) M
ca 10
0
M 10
S 0 . . . ' '".. . . . . . . . . . .. .
-10 Best Fit Trend Line
1 0
-20
-30
> -40
0.0 0.5 1.0 1.5 2.0 2.5
5 LTime (years)
O
Figure 13- Cumulative Change in Average Volume for Developed Profiles in Escambia County




" 40 LO
S30
Cc
._1 0 .. _--20 0
a)
m 10
0
CD
a.
( 10 Best Fit Trend Line
-20 CD
6 -30
a)
> .40
- 0.0 0.5 1.0 1.5 2.0
E
Time (years)
0
Figure 14- Cumulative Change in Average Volume for Natural Profiles in Escambia County

2.5

'




0
0 0
100 ,,
80 )
C) 00 0
60 M U 1)U 0)
. 20
-4 Best FtTrend Line
-200
C-40
E
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




CD
I
Lo 0 M 0
LO
0
O)

100 80 60 40 20
0
-20
-40
-60
-80

-100
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.

(o
(0

.........Best Fit Trend Line
Best Fit Trend Line

2.5




100 "
o 60CU
a)0M 40 0 0 0
2 0 -(D0
0 ... .
40 o uT. I...
0)
2 0 "---.. ..
20
- -40
E -60
-80
-100 '
0.0 0.5 1.0 1.5 2.0 2.5
Time (years)
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.




%40
0 ) 0 )b
=- 30 ).820
M 10 .
Best Fit Tre
10
-20
E
--30
S-40 I
-3 0.0 0.5 1.0 1.5
"E Time (years)
U

.......................
nd Line

2.0 2.5

Figure 18- Cumulative Change in Average Volume for All Santa Rosa County Profiles




40 0
a) {u cu
t30 0
~a~i
U,
-8 20
0 ....." .... -.......... .... . .............
0
C',
m 10
Best Fit Trend Line
S-20
> 0,II ,I II
75 0.0 0.5 1.0 1.5 2.0 2.5
E
:3 Time (years)
U
Figure 19- Cumulative Change in Average Volume for Developed Profiles in Santa Rosa County




L0C)
, 40(0 N
0--1 BstFi Tren Lin
8 20
-6 -30
> a ,--, 0) ) 0) I,
101
- C 00 .. . . ... . . ..... . 5
a-)
m 1
-10 Best Fit Trend Line
~-30
0.0 0.5 1.0 1.5 2.0 2.5
" Time (years)
0
Figure 20- Cumulative Change in Average Volume for Natural Profiles in Santa Rosa County




0)
100
80 0
) 60 a
c 0 "
-- 40
20
C0 O-" . . . .
0 0
-20
Profiles, October 1995 Position Based on Aerial Photographsend Line
_ -40
E
:-60
-80
- 1 0 0 11 I- II - I I I I
0.0 0.5 1.0 1.5 2.02.
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

0) O)
L




100 LO
80 0) CDn0
80 (o 0
60 2U C
(U
LO 0
.t 40 0)
. 20
,U -40 Best Fit Trend Line
E60
06
-80
-100 '
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




LO
I.- CD
100 -D co0
80 -)o )M
a 60 "CA 40 L II
. 20 ,
C: 0 .......
;j ......................
c 20
a)
~Best Fit Trend Line
E
, -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




S 0)
(0 00
40 *May 1995 0) (0) 0)0) 30 (Pre-Opal)
a)
In 10
a) 0
S10
1 Best Fit Trend Line
S-20
--30
> -40
-3 0.0 0.5 1.0 1.5 2.0 2.5
Time (years)
u
Figure 24- Cumulative Change in Average Volume for All Walton County Profiles




40 L ,
i._ 0") 0)O'
o_ *May 1995
S-10 (Pre-Opal) Best Fit Trend Line
8 -20
~20 0') 0)C
-30
(1
- -40
0.0 0.5 1.0 1.5 2.0
E
o-30
a)
-~-40 I
=3 0.0 0.5 1.0 1.5 2.0
:E Time (years)
Figure 25- Cumulative Change in Average Volume for Developed Profiles in Walton County Figure 25- Cumulative Change in Average Volume for Developed Profiles in Walton County

2.5




CCD
4 20 M ('-) M0C
c3O 0)0 0) 75
a)CU 0u
__1
0
a) 0
m 10
\*May 1995
0 (Pre-Opal)
a)
c -10 Best Fit Trend L
ca
c
S-20
E
- -30
a)
> -40 '
- 0.0 0.5 1.0 1.5 2.0 2.5
E
- Time (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

ine




*May 1995
(Pre-Opal)
co
0)
CU
/L )

0.5

co
0)0
COCO3 CD 0M
M3 Best Fit Trend Line
0
o .......

1.0 1.5 2.0
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

2.5




*May 1995
_. 0
100 (Pre-Opal) _S40 'O
-40 80 CD 0)
o 60
In 40
EO
._ 20
a)
-10
cu
-0 002
u> vno Best Fit Trend Line
0Oc
M -40 -o
E T= -60 -0)
-80 8
-100 1 1 1 1 '_ '_ I 1 1 2
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




co 0U 0)
A:t-.

-D
)0
Best Fit Trend Line
.........................................4 .

100
80 60 40 20
0
-20
-40
-60
-80
-100

0.5

1.0

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

*May 1995 ,
(00
(Pre-Opal) G0) 0")O
1ca

0.0




~30
U1) .4-,.
,- 20 0
.Jo
m 10
0 ................
a)
-10
a) -20 B
1) 0
- -40 30
0.0 0.5 1.0 1.5 2.0
Time (years)
Figure 30- Cumulative Change in Average Volume for All Bay County Profiles

LO LO
0) 00
M:
7.

st Fit Trend Line

2.5




S40
(.0
.3 3 0
30 r-" "
0)
-j O ._ 0 0
20 0
Best Fit Trend Line 7
m 10
D
CL
10
U00
c) -20 -. a 0
E )
-30
>~ Ou
S-40
0240 '('' 0 ''c
E
- 000.5 1.0 1.5 2.0 2.5
- Time (years)
O
Figure 31- Cumulative Change in Average Volume for Developed Profiles in Bay County




40 30 20 10

0.5

1.0

1.5
Time (years)

2.0

2.5

Figure 32- Cumulative Change in Average Volume for Natural Profiles in Bay County

0 Best Fit Trend Line 0~
.. ................ -- -- -- ............
) M ,,O- ,
(0 c0 0) 0)11

0
-10
-20
-30
-40

0.0




100 o"
80
o-- 1.. 0). 0)
60 0 0U
0, 40
E4V
w I
._ 20 L6I
I 0 . . . .. .. ..
-20o.....
>
-40
75 (60O Best Fit Trend Line
U
-80
-1 0 0 '- I I I I I
0.0 0.5 1.0 1.5 2.0 2.5
Time (years)
Figure 33m Cumulative Change in Average Distance from Monument to Water Line for All Bay County Profiles,
October 1995 Position Based on Aerial Photographs




CD
0') CC)
0)
00 0)
CD0
L6i
0

(0
0) 0) C\
0) 0)
750
+ LL
f,% Best Fit Trend Line

-100
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
S60
o 0
C',
.n 40 o 20
0)
U
C',
~40 M -40 N
-60
-80
-100 0 O
0.0 0.5 1.0 1.5
Time (years)

C CV
0 75 0)
0)
(D IL

Best Fit Trend Line

2.0

2.5

Figure 35- Cumulative Change in Distance from Monument to Water Line for Natural Profiles in Bay County




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 ft1 yr-, and the Alexandria site had a sand transport rate




70
of approximately 10 yd' Wt yt-'. 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 yd' ft-I yr' could be extrapolated from the data presented in Figure 37. However, studies have not been conducted to verify this prediction.




November 1989
............. September 1990
A Sand Fence ........ October 1991
10- ------October 1992 10 .'-,November 1993
. .. September 1995
% % January 1990
, 5"" l
c= tion Range
0.Gulf qfMexico
- %
I T I1--I-I-I TI*I x
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




2
0
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-Arnott, 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-Arnott, 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-Arnott, R.G.D. and Law, M.N. 1996. Measurement and Prediction of LongTerm 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.