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Storm surge and wave damage along Florida's Gulf Coast from Hurricane Elena

Material Information

Title:
Storm surge and wave damage along Florida's Gulf Coast from Hurricane Elena
Creator:
Bodge, Kevin R.
Kriebel, David L.
Affiliation:
Coastal and Oceanographic Program -- Department of Civil and Coastal Engineering
Place of Publication:
Gainesville
Publisher:
Dept. of Coastal and Oceanographic Engineering, University of Florida
Publication Date:

Subjects

Subjects / Keywords:
Hurricane Elena, 1985.
Hurricanes -- Mexico -- Gulf Coast ( LCSH )
Storms -- Florida
Spatial Coverage:
North America -- United States of America -- Florida

Notes

Funding:
This publication is being made available as part of the report series written by the faculty, staff, and students of the Coastal and Oceanographic Program of the Department of Civil and Coastal Engineering.

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Source Institution:
University of Florida
Holding Location:
University of Florida
Rights Management:
All rights reserved, Board of Trustees of the University of Florida

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Full Text
UFL/COEL-85/015

STORM SURGE AND WAVE DAMAGE ALONG FLORIDA'S GULF COAST FROM HURRICANE ELENA
by
Kevin R. Bodge and
David L. Kriebel

1985




STORM SURGE AND WAVE DAMAGE
ALONG FLORIDA'S GULF COAST
FROM HURRICANE ELENA
ABSTRACT
Hurricane Elena's unusual path through the Gulf of Mexico affected almost all of Florida's Gulf coast counties over Labor Day weekend, 1985. The most severe concentration of damage occurred in Pinellas County where many seawalls and upland strucutures were destroyed. The maximum surge in this area represented less than a 10-year event. The greatest levels of surge, (25-30 year events), were recorded at Cedar Key and in the vicinity of Alligator Point. In these areas, roadway damage, slab-on-grade construction failures, and flooding
resulted from the storm. Measurements of beach profiles in the Clearwater area indicate that initial recovery of the berm after the storm is very rapid--then tapers off considerably one or two days after the storm passes. The profiles demonstrate the toe scour at the base of a seawall associated with a storm event, but also suggest that, in at least some cases, the presence of a seawall does not considerably alter the beach recovery process.
I. INTRODUCTION
The University of Florida Coastal and Oceanographic
Engineering Department initiates and executes a variety of coastal-related research efforts for the State of Florida. One part of the Department's mission is the collection of surge, wave, and coastal processes data along Florida's coasts during severe storms.
Storm data collection is rarely an easy task, and Hurricane Elena presented even more difficulties than most storms. Its unusual path flirted with Florida for five days over the Labor Day weekend of 1985. The storm immediately affected half of Florida's 34 coastal counties while it feinted landfall all over the central and eastern Gulf coasts.
Elena qualified as a "Category 3" storm on the Saffir/Simpson scale. The National Weather Service calls this a
"major storm." The maximum sustained winds of Elena reached 125 mph, and the lowest recorded central presure was 28.08" Hg., (Figure 1).

2




This paper presents a partial summary of the data which the Coastal and Oceanographic Engineering (COE) Department collected regarding the impact of Hurricane Elena on the Florida coastline. A brief description of the methods which the
Department (and its Laboratory) uses to collect storm data is also presented. Observations of beach profile recession and recovery in Pinellas County after the storm are discussed in Section VI.
II. STORM DATA COLLECTION
A variety of systems intended to collect severe storm data have been developed at the University of Florida's Coastal
Engineering Department. The effort to obtain storm surge and wave data is partly addressed by the Florida Coastal Data Network (CDN) which the Department operates out of its
Laboratory located in Gainesville, (1). The network presently includes twelve wave monitoring stations located one-half to fifteen miles offshore around the state, (Figure 2). The
stations at Vero and Venice were under repair at the time of Hurricane Elena. Each station consists of a pressure transducer
"package" mounted near the seabed in water depths of 20 to 60 feet. The "package" monitors and reports (or records) the waves
and mean water level during a 17-minute period every one to six hours.
Stations which are close to shore communicate with the network computer in Gainesville via an underwater cable and the state's telephone lines. In the event of an approaching storm, a station may be instructed to dissociate itself from the
computer and land-based power facilities. When this occurs, the station begins to act independently: it draws power from its own battery source and stores data internally on a cassette tape. The data tape is retrieved by SCUBA divers after the storm passes.
Stations which are further from shore operate independently all of the time. Once installed by divers, these stations operate with battery power and store their data on internal cassettes for about three months at a time.
A radio link is under development for the station located 15 miles offshore of Steinhatchee. Here, a buoyant, tethered tower has been designed and installed by COE to transmit data and instructions between the underwater wave monitoring "package" and the network computer. The tower uses solar power and is designed to withstand hurricane-related forces. During

3




Elena, however, an independent commercially-purchased "package" was in place at this station in lieu of the radio link. This "package" failed unbeknownst to the laboratory several days before Elena's appearance in the Gulf.
Storm surge data is also collected by deploying simple gauges along the coast in anticipation of a storm's landfall. These "storm surge gauges" are constructed from an 8-foot section of steel pipe which is banded to a pier piling or utility pole close to the water. The pipe is closed except for small holes in the bottom, (and near the top). As the sea level rises up to the gauge, the small holes dampen the wave actvity so that only the mean level of the water stands inside the pipe. The rising water level activates a powerful dye which stains a wooden stick inside the pipe. The highest water level reached is thereby recorded onto the stick, and this level is surveyed-in after the storm passes.
The Laboratory is also developing inexpensive electronic surge gauges. A prototype was installed on the coast during Elena; unfortunately, the surge never reached it. Whereas the standard gauges record only the peak water level associated with the storm, the new type of gauge records a time history of the water level's rise and fall. Pairs of electro-chemical "clocks" at several different levels inside the gauge sense the presence
(or non-presence) of water. At each level, one "clock" records the time at which the water level first reached that level, and
the other "clock" records the length of time which the water remained there, (2).
The Laboratory uses traditional data gathering techniques in addition to the Coastal Data Network and surge gauges. Laboratory personnel locate and survey high water marks in flooded areas immediately after the storm. Sustained wind data around the coast is recorded using anemometers which are deployed in the anticipated storm path. Both the storm and its damage are also documented by video, aerial, and ground-truth photography crews dispatched by the Department. Finally, beach profiling crews monitor selected areas in order to address research problems relating to storm-induced erosion and recovery processes.
III. HURRICANE ELENA STORM TRACK
Figure 3 illustrates the path of Hurricane Elena through the Gulf of Mexico. The tropical disturbance which spawned the Hurricane originated off the Atlantic coast of Africa. Elena

4




was classified as a hurricane just after dawn on Thursday, August 29, 1985, after brushing over eastern Cuba and turning towards the central Gulf. It initially appeared that Elena might strike Louisiana, but through Thursday evening, the storm veered east and slowed from 15 mph forward speed to 5 mph. By early Friday morning, the storm was 170 miles south of Pensacola with maximum sustanied winds of 95 mph. The easterly trend intensified through Friday as Elena passed 100 miles southwest of Apalachicola by dusk--marking a clear course towards Cedar Key. At Saturday's dawn, August 31, Elena was 70 miles south of Apalachicola. The storm continued slowly towards the Big Bend area, then remained stationary 55 miles WSW of Cedar Key from 10:00 Saturday morning through dawn on Sunday. Elena had built
to 110 mph sustained winds before beginning a westerly, then northwesterly course away from Cedar Key. At 6 p.m., Sunday night, the storm was back within 40 miles of Apalachicola and moving at 10 mph towards Pensacola. Elena passed 60 miles south of Destin with 125 mph sustained winds around midnight on Sunday. By 6:00 Monday morning, September 2, the hurricane was 30 miles south of Mobile on its way to landfall near Biloxi, Mississippi, one hour later.
The indecisive path of Elena was particularly troublesome for emergency personnel and coastal residents from Charlotte through Escambia counties. Out of over 700 tropical storms and hurricanes near Florida since the late 1800's, Elena is in the company of only about one or two dozen other storms with very erratic paths, (i.e., storms which turn dramatically several times and feint landfall repeatedly at one or more locations).
Although Hurricane Elena's path was unusual, its flirtation with the Flordia panhandle was not. Statistics based on
historical records indicate that the shoreline between Pensacola and Apalachicola is more likely to experience a landfalling hurricane or tropical storm than any other area of the United States Gulf and Atlantic coasts. The 100 mile stretch between Pensacola and Panama City, or between Panama City and Apalachicola, can expect a landfalling hurricane or tropical storm at least once every five years, (3).
IV. WIND, WAVE, AND SURGE DATA
Winds around the Florida coast were fairly light, (less than 30 mph), until Elena neared Cedar Key. Winds gusted to over 100 mph at Cedar Key during Saturday, August 31, while the storm was stationary nearby. At the same time, winds just north of the area, (at Keaton Beach and Steinhatchee), were less than

5




30 mph. However, peak gusts at Apalachicola, Clearwater and Tampa International Airport were 67 mph, 69 mph, and 45 mph, respectively. On Sunday, and through Sunday night, as Elena moved along the Panhandle for the second time, (more than twice as close as during the first pass), peak gusts of 67 mph were again reported at Apalachicola, while 93 mph gusts were reported at Pensacola Airport, (with sustained winds estimated at 50 mph). There were unofficial weather service estimates of 90 mph sustained winds on Perdido Island late Sunday night.
Figure 4 illustrates the significant wave height measured by CDN during Hurricane Elena. Significant wave height refers to the height of the waves which an observer would estimate if he or she were watching the sea; that is, it is the average value of the one-third highest waves measured.
The largest significant wave height on the southeast
Florida coast, (4.1 feet at Miami and 5.2 feet at West Palm Beach on August 28, 6 p.m. E.S.T.), occurred when the center of the storm was approximately 120 miles south of Key West. At this time, the southern Atlantic Coast of Florida was subject to strong onshore winds associated with the storm's NE quadrant.
The highest waves measured elsewhere occurred while Elena was just offshore of Cedar Key. At Clearwater, peak significant
wave height reached 8.2 feet at 2 p.m., August 31. Earlier that morning, waves along the northest coast of Florida reached 10.5 feet at Jacksonville and 7 feet at Marineland. Meanwhile, the south Atlantic coast was fairly quiet. This was due to the strong onshore winds at Clearwater and along the northeast Florida coast while Elena was off Cedar Key--whereas the winds were southerly around south Florida, (Figure 5).
Wave modal periods were fairly consistent around the state at 4 to 6 seconds without the influence of Elena--and 10 seconds in those instances when the storm generated its largest waves. Figure 6 illustrates the wave periods measured at Clearwater during the time of the storm.
The maximum storm surge recorded was + 9.2 ft (MSL) at Cedar Key, (inside the Sea Breeze restaurant which fronts the Gulf). Peak standing water levels of + 8 ft (MSL) were measured in the town about 1 mile from the Gulf-front. Wave crest elevations of approximately 2.2 ft were measured atop these water levels in town. Elena is at least the third hurricane in the past century for which storm surge levels exceeded 9 feet at Cedar Key.

6




The surge just north of Cedar Key is estimated to have been slight, (tides 1 to 2 feet above normal). Much of the water damage in these areas was likely due to heavy rainfall.
Directly across the Gulf, however, at Panacea, Alligator Point, and the central-eastern Gulf side of St. George Island, the mean storm water levels reached 8.0 ft., 9.0 ft, and 8.5 ft above MSL, respectively. The highest surge in this area, 9.0 ft, represents a 25-year event for Alligator Point, (4). By contrast, the maximum sustained inland winds in this area represent less than a 5-year event, (4).
The maximum surge at Clearwater was south of Cedar Key, estimated as + 4.6 ft. MSL, (August 31 at 11:00 a.m. E.S.T.). This approximately represents a seven-year event for Clearwater,
(5).
Figure 7 illustrates the mean water level over time
reported by the CDN Station at Clearwater. Also shown in Figure 7 is the corresponding predicted astronomical tide, (6). The water levels reported by the CDN underwater package correspond to a position offshore--seaward of the surf zone. The presence of breaking waves can increase the water level at the shoreline by 20-50% of the breaking wave height, (7). Accordingly, the upper curve in Figure 7 includes an additional anamolous surge, (called "set-up"), which was conservatively calculated as 20% of the reported significant wave height.
The moderate levels of surge south of Cedar Key and the low levels just north of Cedar Key--as well as the extreme water levels at Cedar Key and around Apalachicola--correspond
reasonably to the idealized wind field around the storm when it was stationary offshore of Cedar Key, (Figure 5).
V. OVERVIEW OF STORM-RELATED DAMAGE
In terms of gross structural damage, Hurricane Elena had the greatest impact on Pinellas County. Over 2.6 miles of seawall were completely destroyed or sustained major damage and another 2.2 miles were somewhat damaged. Inspection indicated that many of the sewall failures were due to poor or lacking toe-scour protection, inadequate maintenance, insufficient toe penetration into the bed, and/or poorly embedded tie-backs. The variety of seawalls, the inconsistency of seawalled lots next to non-seawalled lots, and the insufficient cap elevation of almost
all of the seawalls allowed considerable flanking and overtopping--which contributed significantly to the seawall failures. In virtually all cases inspected, the seawall

7




structures which were of higher-quality construction faired well. Older bulkheads of inferior toe design and improperly maintained concrete failed or were severely damaged. In those cases where the seawall remained intact, overtopping posed a problem to the upland residents in the form of sizeable sand deposits, (overwash), amidst homes, yards, and parking area.
Flooding was probably the chief problem for residents of Cedar Key--where the maximum storm surge exceeded + 9.0 feet MSL. Many of the buildings had 3 to 4 feet of standing water in them. Several restaurants located on the waterfront faced directly into Elena's winds. Damage assessements were much lower for those restaurants of more recent construction, (1984), which were built at high elevation upon concrete pilings with smaller windows of severe-storm-rated construction. The Sea Breeze Restaurant, however, was of lower elevation, (about +6 ft. MSL), with very large standard sliding-glass doors all
around the dining area. These doors blew out early in the storm and allowed the full force of the winds and waves to enter the restaurant atop the surge. The small, low-elevation, piled house next to the restaurant lost its floor and, of course, everything inside. The decks of all the piers in the area were similarly completely destroyed.
The predominant failures at Alligator Point typified the upland damage all around the Gulf coast: slab-on-grade
construction suffered total or severe failures in contrast to piled structures.
Road damage was severe along County Highway 370 at Alligator Point and along Rt. 98 between Appalachicola and Carabelle. The town of Eastpoint, along Rt. 98 suffered considerable waterfront damage even with its low-elevation
breakwater offshore. Further west, on Dog Island, there were many failures of indequately designed or poorly maintained structures.
The causeway to St. George Island failed on the east sides at those areas where the earth-supported roadway meets the bridges. The failures here were due to surge and wave overtopping of the low-elevation bulkheads. St. George Island was very nearly (but not completely) overwashed in many areas.
The remainder of the Panhandle survived the storm with relatively little damage. There were some instances of
downburst wind damage and a few isolated instances of impending or progressive structural collapse due to beach erosion along

8




the western Panhandle. Table 1 lists a partial summary of the damage around the Florida coast.
VI. POST-STORM BEACH MONITORING
Following Hurricane Elena, beach profile monitoring was initiated in Pinellas County to document the rate and extent of natural post-storm beach recovery. In addition, the surveys provided data on the effects of seawalls on beach profile development and on the behavior of a beach nourishment project in response to a minor hurricane.
On the morning of September 2, post-storm beach profiles were obtained from the north end of Sand Key at the southern end of Clearwater Beach. Wading profiles were initially taken at 6 and 15 hour intervals, then at intervals of several days or weeks until natural recovery processes were interrupted by beach
scraping in mid October. As shown in Figure 8, five profiles were monitored along an 850 meter segment of the coast. Two profiles were taken off DNR survey monuments in a "natural" sandy area with no exposed seawalls. These monuments are actually located on the cap of a seawall that is now buried under a reconstructed dune and which forms the landward limit of a beach nourishment project. Two additional profiles were taken
seaward from a surviving seawall that was exposed to storm waves. A fifth profile was taken 30 meters north of the exposed seawall in a sandy area that was eroded during the storm.
Natural post-storm beach recovery processes are depicted in Figure 9 in a comparison of the measured post-storm profile from September 2 and a subsequent profile from September 10. On September 2, a continuous longshore bar was present over the entire survey area. The bar crest elevation was below the spring high tide elevations and with each incoming wave, sand and shell fragments were carried landward over the bar crest and deposited on the steep landward face of the bar. By September 10, the bar crest had grown vertically approximately 0.5 meters and, while the bar crest position remained stationary, the bar width increased 5-10 meters.
In Figure 10, the recovery processes in front of the exposed seawall were nearly identical. On both seawalled and non-seawalled profiles, initial deposition occurred on the bar and little sand reached the base of the seawall or the landward beach face. As the bar crest elevation increased, fewer waves were able to overtop the bar crest, thus preventing further landward migration of the bar. In the week after the storm,

9




during the neap tidal cycle, no additional changes in the bar crest or landward slope occurred although some changes occurred on the seaward slope.
Based on the first five surveys (September 2 to September 10) an average of 5.8 m3/m was transported landward and deposited on the bar above mean sea level. Of this volume, an average 5.5 m3/m was deposited by September 3; after September 3 periodic erosion and deposition occurred resulting in a slow net
deposition above mean sea level. Since the first survey was completed 10 to 20 hours after the storm effects began to subside, some recovery had occurred before the September 2 survey. It is not clear whether the bar formed during the storm or during the initial recovery phases; however, the profile was actively recovering during the high tide prior to the first survey.
Recovery processes are clearly linked to both the water level and wave conditions. Based on data presented in Figure 4 and 7, the peak water level and wave heights occurred over August 31 to September 1 and it is probable that the maximum erosion occurred about mid-day on September 1. From September 1 through September 2, during the most active recovery, wave heights exceeded 1.0 meter; after September 3 wave heights dropped to 0.3 meters and recovery slowed substantially. Recovery seemed to occur in two phases: 1) the immediate rapid post-storm "healing" of the eroded beach which occurs while the storm is still affecting wave-conditions and 2) a long term slow recovery which occurs over several weeks, months, or years in response to normal wave conditions.
In 1983-1984 a beach nourishment and dune restoration project was completed in the study area. Profiles R-58 and R-59 were within the main nourishment area, profiles R-60A, R-60B, and R-60C were located at the southern end of the nourishment project. On these southern profiles, no dune was constructed and instead, a "feeder" beach was designed with a broad berm which could gradually erode and continuously replenish downdrift beaches to the north. Profile R-60C was located near the tapered transition between the feeder beach and the unnourished beaches to the south; therefore, the shoreline in this area is closer to the exposed seawall than on profiles R-50A or R-60B.
Comparisons of pre-nourishment, post-nourishment, and poststorm profiles for R-58 and R-59 are given in Figures 11 and 12. In 1974 most of the profile was below mean sea level, there was no recreational or storm protection beach, and the seawall

10




was exposed to direct wave attack. In November 1984, a 40-60 meter wide beach and a nearly 3 meter high dune were placed seaward of the seawall. Total fill volumes of 106 m3/m and 188 m3/m were placed on R-58 and R-59 respectively; of these volumes 45 m3/m and 70 m3/m were placed above mean sea level.
After the storm on September 2, 1985, profile R-58 showed a
net gain of 3.2 m3/m while R-59 had a net loss of 34.8 m3/m Both profiles showed a loss of the reconstructed dune and berm with a bar offshore. While few conclusions can be drawn, longshore sediment transport seems to have resulted in a
redistribution of sand from south to north, resulting in a net loss to R-59 and a net gain to R-58. Between these two profiles an average loss of 15.8 m3/m occurred between November 1984 and September 2, 1985. It is not known what portion of this volume was lost during the storm versus prior to the storm.
Although not shown in Figures 11 and 12, between September 2 and September 10 post-storm recovery returned a net volume of 3.8 m3/m and 7.3 m3/m to R-58 and R-59 respectively, for an
average recovery of 5.1 m3/m. Thus based on average values, the net loss to the profiles between November 1984 and September 10, 1985 is 10.7 m3/m or about 7% of the initial average beach fill volume. It should be noted that these figures are based on
wading profiles; however, spot checks of the offshore profiles with a fathometer showed no bars or large depositional features.
The effects of seawalls on beach profile response are
illustrated in Figure 13, in a comparison of three post-storm profiles influenced by the exposed seawall. Profile R-60A, located 30 meters from the end of the seawall, was found to have a similar form to R-58 and R-59 and did not exhibit any local effects due to the proximity of the seawall. Profile R-60B, located 60 meters to the south in front of the seawall, exhibits the increased toe scour associated with open coast seawalls. The offshore portions of the profiles are nearly identical
however and the seawall does not seem to have had an effect on the bar formation or seaward slope.
The seawall performed its intended function of preventing upland property from eroding. It is interesting to compare the volume of the increased toe scour attributed to the seawall with the volume of material the seawall prevented from eroding. There is an approximate balance between these volumes. This seems to indicate that the seawall did not cause any additional loss of volume from the profile than would otherwise have
occurred, losses were simply concentrated at the toe of the seawall.

11




Profile R-60C, located 180 meters to the south of R-60B in front of the seawall, shows dramatically the depth of the erosion that can occur at the toe of a seawall. As noted, the tapering of the beach fill causes the shoreline and the bar to be closer to the seawall at the south end than at the north end; however, the form of the bar and the seaward sand slopes are the
same as in all other profiles. At the toe of the seawall, the erosion extends 1.6 meters below the sand level of profile R-60A adjacent to the seawall. This clearly illustrates the need for proper embedment of the seawall to ensure structural stability to prevent toe failure and undermining.
VII. SUMMARY
The greatest extent of damage due to Hurricane Elena was realized in Pinellas County, although the greater potential for damage was probably at the lesser-developed areas of Cedar Key and Apalachicola through St. George Island. The maximum
measured surge around Florida was at Cedar Key and in the region of Panacea, Alligator Point, and St. George Island. Surge in these areas were at approximately 25-30 year levels.
While Elena entered the Gulf of Mexico, south of the Keys, maximum significant wave heights off of Miami and West Palm Beach were between 4 and 5.2 feet. The largest significant wave heights around Florida were recorded while the storm was stationary 55 miles WSW of Cedar Key: 8.2 ft at Clearwater and 10.5 ft at Jacksonville. Modal wave periods associated with Elena were approximately 10 seconds.
The highest winds along the Florida coast were at Cedar Key, Appalachicola, and the Panhandle barrier islands. Maximum sustained winds were not thought to have exceeded 100 mph. However, gusts of between 70 mph to at least 100 mph were reported from Clearwater through Cedar Key, and from Apalachicola to Pensacola.
The storm damage was characterized by:
1. failure of low-elevation, poorly constructed seawalls with
inadequate toe penetration or protection and/or inadequate
tie-back design or protection;
2. slab-on-grade construction failures;
3. blow-out (and subsequent damage) due to large non-hurricanerated windows and doors;
4. flooding of low-elevation structures, (piled and non-piled);
5. road damage due to inappropriate elevations of roadways
and/or protective revetments and bulkheads;

12




6. overwash; and
7. structural designs, in general, which were not compatible
with severe storm conditions.
Post-storm monitoring of beach profiles in Pinellas County indicates the capacity of sand beaches to respond to a severe storm. During the storm a net transfer of sand occurred from the berm and dune offshore. After the storm, much of this sand was returned and deposited as a bar above mean sea level. Beach profile response in front of a seawall was similar with a net transfer of sand from the toe of the seawall to offshore areas during the storm. Post-storm recovery has likewise returned much of this sand to the beach face. While it is difficult to state conclusively the impact of the seawall on beach changes in
the area, the localized erosion at the toe of the seawall can be significant, and certainly contributed to the failure of many seawalls in Pinelas County.
The Sand Key beach nourishment and artifical dune
construction project seems to have been successful in absorbing wave energy by "remolding" during the storm. While the constructed dunes eroded almost completely, this sand moved offshore during the storm and has subsequently moved back onshore to the beach face. In areas where the dune was
constructed and the beach was nourished, the only storm damage was due to sand overwash into swimming pools and parking lots; no structural damage occurred due to storm waves.
REFERENCES
1. Howell, G. L., "Florida Coastal Data Newtork," Proceedings
of the 17th International Conference on Coastal
Engineering, Sydney, Australia, ASCE; 1980.
2. Bodge, K. R., and Broward, C., "The E-Cell Time-Recording
Storm Surge Gauge," University of Florida Coastal and Oceanographic Engineering Department UFL/COEL TR/057,
Gainesville, FL 32611; August, 1985.
3. "Tropical Cyclones of the North Atlantic Ocean, 18711980," National Oceanic and Atmospheric Administration (NOAA), National Climatic Center, Asheville, NC;
Amended, 1984.

13




4. "Feasibility Report Protection of Highway 370, Alligator
Point Fla.," U.S. Army Corps of Engineers, Mobile
District; March, 1985.
5. "Beach Erosion Control Project Review Summary and
Environmental Impact Statement for Pinellas County,
Florida, U.S. Army Corps of Engineers, Jacksonville
District: July, 1984.
6. "Tide Table, East Coast of North and South America Including
Greenland," U. S. Dept. of Commerce, National Oceanic and Atmospheric Administration, National Ocean Survey;
1985.
7. Lo, J. M., "Surf Beat: Numerical and Theoretical Analyses,"
Ph.D. Dissertation, University of Delaware, Newark, DE;
1981.

14




Table 1. Partial Summary of
Hurricane Elena,
Resources, Division

Structural Damage Sustained from (from Florida Dept. of Natural of Beaches and Shores).

PINELLAS COUNTY

2.66 miles of vertical bulkheads destroyed or severely
damaged.
2.15 miles of vertical bulkheads sustained minor damage.
44 single family dwellings destroyed, 31 damaged.
4 condominium/hotel units destroyed.
9 condominium/townhouse/motel buildings damaged.
5 pools destroyed, 3 damaged.
3 fishing piers destroyed, 2 damaged.

MANATEE COUNTY

0.22 miles of vertical bulkheads destroyed, 0.08 damaged.
5 single family dwellings destroyed, 2 damaged.
SARASOTA COUNTY
0.2 miles of vertical bulkhead; destroyed or damaged.
1 single family dwelling destroyed.
0.6 miles of road damaged.
FRANKLIN COUNTY

0.5
0.06
20
1 1
0.3 123,100 58,000 130,000

miles of vertical bulkhead destroyed or damaged. miles rock revetment destroyed or damaged. single family dwellings destroyed or damaged. community recreation building destroyed mile of road destroyed (Alligator Pt., St. Island), 3.9 miles damaged (St. Geo. Island). mi es causeway damaged (St. Geo. Island). ft3 pavement U.S. 98 destroyed. yd3 fill lost from St. Geo Island Causeway. yd fill lost form U.S. 98

miles

Geo.

GULF, BAY, WALTON, OKALOSSA, ESCAMBIA, CHARLOTTE, LEE, AND
COLLIER COUNTIES No major damage.

15




Itr.O

10101000
(n
990w980
(n
w 970960-

950F

OC"^

26 27 28 29 30 31 1
AUGUST

2 3 4
SEPTEMBER

Figure 1: Minimum pressure and maximum winds of Hurricane
Elena. (source: National Weather Service, Tampa Bay Area;
Ruskin, FL.).

STMARYSENTRANCE 1983 IJACKSONVILLE 1981 WMARINELAND 1977

EINHATCHEE
CLEARWATER 1978

VENICE 1984,

CAPE KENNEDY 1977 01983
VERO BEACH 1980
PALM BEACH
1979
MIAMI 1977

Figure 2: The Florida Coastal Data Network wave monitoring
stations (and year of installation of each site). Solid lines indicate a hard-wire station link to Gainesville, dashed lines indicate a radio link, and no line indicates
that the station stores its data internally.

16

PRESSURE
Wi n d

70
60 50
z
40 30 :E 20 M 10




9/2
8/31
8/30 9
8/29--V =4
8/28
-7
Figure 3: Hurricane Elena storm track, 1985. The dates shown
indicate the position of the center of the storm at noon
E.S.T.
I--3
-- JACKSONVILLE
9' ARINELAND3
S' E
CANAVERAL
U
3' CLO WATER2
2 -- -- 0
26 27 2B 29 30 31 1 2 3 4
AUGUST 1985 SEPT. ..S EST
ALM---- --- 0
MIAMI 3
26 27 2B 293 0 31 3 AU GUST( 1985 SEPT. Figure 4: Significant wave heights measured by the Florida Coastal Data Network during Hurricane Elena, 1985.

17




cyclonePeloctedofofCdrKyFoia.
- ytono
- Ft Pie
- Miami
Figure 5: Idealized wind field associated with a tropical
cyclone located off of Cedar Key, Florida..
1' 10
(L
4
27 28 29 3 2 3 AUGUST SEPTEMHER Figure 6: Wave periods at Clearwater during Hurricane Elena, 1985.

18




7I I I
Shoreline Water Level (calculated)
6 -----Offshore Water Level (measured)
- Astronomical Tide (predicted)
5
3-
- 2
-JI i \I\ / % I
29 30 31
AUGUST 1985 SEPT
Figure 7: Storm surge hydrograph at Clearwater during Hurricane
Elena, 1985.
N
R-58
Srall Pier
0' t-Reconstructed Dune R-59
Bar Formed DrinSeawoll Buried Uider Dune
Post-Storm 0
Recovery
* Appioioe Mean SeaAShoreline
-R-60A
R-60B
Exposed Seowall
-R-60 C
Figure 8: Location of post-storm monitoring of beach processe;

19




R-59
BEACH NOURISHMENT WITH ARTIFICAL DUNE

POST STORM
RECOVERY SEPT. I0,t985 SEPT2,1985
DISTANCE FROM MONUMENT(M)
- -

20

60 80

Beach recovery on nourished beach, profile R-59.
R- 608
BEACH NOURISHMENT WITH SEAWALL

t SEAWALL

POST STORM RECOVERY
SEPT 10, 3985 SEPT 2, 1985

DISTANCE FROM SEAWALL (M)

80

Figure 10: Beach recovery in front of seawall, profile R-60B.

20

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0
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Figure 9:
3 r

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31

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R-58
SAND KEY BEACH NOURISHMENT PROJECT
3 -PROFILE WITH ARTIFICAL DUNE
E
-j
w
Nov. 1984 Post Nourishment
w Sept 2,1985
(n Post Hurricone Eleno
z
44
s distance from rmfisro -8 terms)
0
_j Before Nourishment
w
Figure 11: Comparison of pre-nourishment, post-nourishment, and
post storm profiles, profile R-58.

R-59
SAND KEY BEACH NOURISHMENT PROJECT
PROFILE WITH ARTIFICAL DUNE
Nov 1984 Post Nourishment
i l I | distpce from monumn (mrs)
2o 40 6 0
Sept. 2,1985
Pbst Hurricone Ekeno
Oct 1974
Before Nourishment

Figure 12: Comparison of pre-nourishment, post-nourishment, and
post storm profiles, profile R-59.

21

E
w
w U)
z
w
0
z
0
w
-j
w

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-2




3
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-20

z -I

.21

COMPARISON OF PROFILES AFFECTED BY SEAWALL

SEAWALL
PROFILE R-60A NORTH OF SEAWALL
PROFILE R-608 WITH SEAWALL

DISTANCE FROM SEAWALL (M)

so

40 60
- PROFILE R- 60 C WITH SEAWALL

Figure 13: Comparison of profiles affected by seawall.

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Full Text

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UFL/COEL-85/015 STORM SURGE AND WAVE DAMAGE ALONG FLORIDA'S GULF COAST FROM HURRICANE ELENA by Kevin R. Bodge and David L. Kriebel 1985

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STORM SURGE AND WAVE DAMAGE ALONG FLORIDA'S GULF COAST FROM HURRICANE ELENA ABSTRACT Hurricane Elena's unusual path through the Gulf of Mexico affected almost all of Florida's Gulf coast counties over Labor Day weekend, 1985. The most severe concentration of damage occurred in Pinellas County where many seawalls and upland strucutures were destroyed. The maximum surge in this area represented less than a 10-year event. The greatest levels of surge, (25-30 year events), were recorded at Cedar Key and in the vicinity of Alligator Point. In these areas, roadway damage, slab-on-grade construction failures, and flooding resulted from the storm. Measurements of beach profiles in the Clearwater area indicate that initial recovery of the berm after the storm is very rapid--then tapers off considerably one or two days after the storm passes. The profiles demonstrate the toe scour at the base of a seawall associated with a storm event, but also suggest that, in at least some cases, the presence of a seawall does not considerably alter the beach recovery process. I. INTRODUCTION The University of Florida Coastal and Oceanographic Engineering Department initiates and executes a variety of coastal-related research efforts for the State of Florida. One part of the Department's mission is the collection of surge, wave, and coastal processes data along Florida's coasts during severe storms. Storm data collection is rarely an easy task, and Hurricane Elena presented even more difficulties than most storms. Its unusual path flirted with Florida for five days over the Labor Day weekend of 1985. The storm immediately affected half of Florida's 34 coastal counties while it feinted landfall all over the central and eastern Gulf coasts. Elena qualified as a "Category 3" storm on the Saffir/Simpson scale. The National Weather Service calls this a "major storm." The maximum sustained winds of Elena reached 125 mph, and the lowest recorded central presure was 28.08" Hg., (Figure 1). 2

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This paper presents a partial summary of the data which the Coastal and Oceanographic Engineering (COE) Department collected regarding the impact of Hurricane Elena on the Florida coastline. A brief description of the methods which the Department (and its Laboratory) uses to collect storm data is also presented. Observations of beach profile recession and recovery in Pinellas County after the storm are discussed in Section VI. II. STORM DATA COLLECTION A variety of systems intended to collect severe storm data have been developed at the University of Florida's Coastal Engineering Department. The effort to obtain storm surge and wave data is partly addressed by the Florida Coastal Data Network (CDN) which the Department operates out of its Laboratory located in Gainesville, (1). The network presently includes twelve wave monitoring stations located one-half to fifteen miles offshore around the state, (Figure 2). The stations at Vero and Venice were under repair at the time of Hurricane Elena. Each station consists of a pressure transducer "package" mounted near the seabed in water depths of 20 to 60 feet. The "package" monitors and reports (or records) the waves and mean water level during a 17-minute period every one to six hours. Stations which are close to shore communicate with the network computer in Gainesville via an underwater cable and the state's telephone lines. In the event of an approaching storm, a station may be instructed to dissociate itself from the computer and land-based power facilities. When this occurs, the station begins to act independently: it draws power from its own battery source and stores data internally on a cassette tape. The data tape is retrieved by SCUBA divers after the storm passes. Stations which are further from shore operate independently all of the time. Once installed by divers, these stations operate with battery power and store their data on internal cassettes for about three months at a time. A radio link is under development for the station located 15 miles offshore of Steinhatchee. Here, a buoyant, tethered tower has been designed and installed by COE to transmit data and instructions between the underwater wave monitoring "package" and the network computer. The tower uses solar power and is designed to withstand hurricane-related forces. During 3

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Elena, however, an independent commercially-purchased "package" was in place at this station in lieu of the radio link. This "package" failed unbeknownst to the laboratory several days before Elena's appearance in the Gulf. Storm surge data is also collected by deploying simple gauges along the coast in anticipation of a storm's landfall. These "storm surge gauges" are constructed from an 8-foot section of steel pipe which is banded to a pier piling or utility pole close to the water. The pipe is closed except for small holes in the bottom, (and near the top). As the sea level rises up to the gauge, the small holes dampen the wave actvity so that only the mean level of the water stands inside the pipe. The rising water level activates a powerful dye which stains a wooden stick inside the pipe. The highest water level reached is thereby recorded onto the stick, and this level is surveyed-in after the storm passes. The Laboratory is also developing inexpensive electronic surge gauges. A prototype was installed on the coast during Elena; unfortunately, the surge never reached it. Whereas the standard gauges record only the peak water level associated with the storm, the new type of gauge records a time history of the water level's rise and fall. Pairs of electro-chemical "clocks" at several different levels inside the gauge sense the presence (or non-presence) of water. At each level, one "clock" records the time at which the water level first reached that level, and the other "clock" records the length of time which the water remained there, (2). The Laboratory uses traditional data gathering techniques in addition to the Coastal Data Network and surge gauges. Laboratory personnel locate and survey high water marks in flooded areas immediately after the storm. Sustained wind data around the coast is recorded using anemometers which are deployed in the anticipated storm path. Both the storm and its damage are also documented by video, aerial, and ground-truth photography crews dispatched by the Department. Finally, beach profiling crews monitor selected areas in order to address research problems relating to storm-induced erosion and recovery processes. III. HURRICANE ELENA STORM TRACK Figure 3 illustrates the path of Hurricane Elena through the Gulf of Mexico. The tropical disturbance which spawned the Hurricane originated off the Atlantic coast of Africa. Elena 4

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was classified as a hurricane just after dawn on Thursday, August 29, 1985, after brushing over eastern Cuba and turning towards the central Gulf. It initially appeared that Elena might strike Louisiana, but through Thursday evening, the storm veered east and slowed from 15 mph forward speed to 5 mph. By early Friday morning, the storm was 170 miles south of Pensacola with maximum sustanied winds of 95 mph. The easterly trend intensified through Friday as Elena passed 100 miles southwest of Apalachicola by dusk--marking a clear course towards Cedar Key. At Saturday's dawn, August 31, Elena was 70 miles south of Apalachicola. The storm continued slowly towards the Big Bend area, then remained stationary 55 miles WSW of Cedar Key from 10:00 Saturday morning through dawn on Sunday. Elena had built to 110 mph sustained winds before beginning a westerly, then northwesterly course away from Cedar Key. At 6 p.m., Sunday night, the storm was back within 40 miles of Apalachicola and moving at 10 mph towards Pensacola. Elena passed 60 miles south of Destin with 125 mph sustained winds around midnight on Sunday. By 6:00 Monday morning, September 2, the hurricane was 30 miles south of Mobile on its way to landfall near Biloxi, Mississippi, one hour later. The indecisive path of Elena was particularly troublesome for emergency personnel and coastal residents from Charlotte through Escambia counties. Out of over 700 tropical storms and hurricanes near Florida since the late 1800's, Elena is in the company of only about one or two dozen other storms with very erratic paths, (i.e., storms which turn dramatically several times and feint landfall repeatedly at one or more locations). Although Hurricane Elena's path was unusual, its flirtation with the Flordia panhandle was not. Statistics based on historical records indicate that the shoreline between Pensacola and Apalachicola is more likely to experience a landfalling hurricane or tropical storm than any other area of the United States Gulf and Atlantic coasts. The 100 mile stretch between Pensacola and Panama City, or between Panama City and Apalachicola, can expect a landfalling hurricane or tropical storm at least once every five years, (3). IV. WIND, WAVE, AND SURGE DATA Winds around the Florida coast were fairly light, (less than 30 mph), until Elena neared Cedar Key. Winds gusted to over 100 mph at Cedar Key during Saturday, August 31, while the storm was stationary nearby. At the same time, winds just north of the area, (at Keaton Beach and Steinhatchee), were less than 5

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30 mph. However, peak gusts at Apalachicola, Clearwater and Tampa International Airport were 67 mph, 69 mph, and 45 mph, respectively. On Sunday, and through Sunday night, as Elena moved along the Panhandle for the second time, (more than twice as close as during the first pass), peak gusts of 67 mph were again reported at Apalachicola, while 93 mph gusts were reported at Pensacola Airport, (with sustained winds estimated at 50 mph). There were unofficial weather service estimates of 90 mph sustained winds on Perdido Island late Sunday night. Figure 4 illustrates the significant wave height measured by CDN during Hurricane Elena. Significant wave height refers to the height of the waves which an observer would estimate if he or she were watching the sea; that is, it is the average value of the one-third highest waves measured. The largest significant wave height on the southeast Florida coast, (4.1 feet at Miami and 5.2 feet at West Palm Beach on August 28, 6 p.m. E.S.T.), occurred when the center of the storm was approximately 120 miles south of Key West. At this time, the southern Atlantic Coast of Florida was subject to strong onshore winds associated with the storm's NE quadrant. The highest waves measured elsewhere occurred while Elena was just offshore of Cedar Key. At Clearwater, peak significant wave height reached 8.2 feet at 2 p.m., August 31. Earlier that morning, waves along the northest coast of Florida reached 10.5 feet at Jacksonville and 7 feet at Marineland. Meanwhile, the south Atlantic coast was fairly quiet. This was due to the strong onshore winds at Clearwater and along the northeast Florida coast while Elena was off Cedar Key--whereas the winds were southerly around south Florida, (Figure 5). Wave modal periods were fairly consistent around the state at 4 to 6 seconds without the influence of Elena--and 10 seconds in those instances when the storm generated its largest waves. Figure 6 illustrates the wave periods measured at Clearwater during the time of the storm. The maximum storm surge recorded was + 9.2 ft (MSL) at Cedar Key, (inside the Sea Breeze restaurant which fronts the Gulf). Peak standing water levels of + 8 ft (MSL) were measured in the town about 1 mile from the Gulf-front. Wave crest elevations of approximately 2.2 ft were measured atop these water levels in town. Elena is at least the third hurricane in the past century for which storm surge levels exceeded 9 feet at Cedar Key. 6

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The surge just north of Cedar Key is estimated to have been slight, (tides 1 to 2 feet above normal). Much of the water damage in these areas was likely due to heavy rainfall. Directly across the Gulf, however, at Panacea, Alligator Point, and the central-eastern Gulf side of St. George Island, the mean storm water levels reached 8.0 ft., 9.0 ft, and 8.5 ft above MSL, respectively. The highest surge in this area, 9.0 ft, represents a 25-year event for Alligator Point, (4). By contrast, the maximum sustained inland winds in this area represent less than a 5-year event, (4). The maximum surge at Clearwater was south of Cedar Key, estimated as + 4.6 ft. MSL, (August 31 at 11:00 a.m. E.S.T.). This approximately represents a seven-year event for Clearwater, (5). Figure 7 illustrates the mean water level over time reported by the CDN Station at Clearwater. Also shown in Figure 7 is the corresponding predicted astronomical tide, (6). The water levels reported by the CDN underwater package correspond to a position offshore--seaward of the surf zone. The presence of breaking waves can increase the water level at the shoreline by 20-50% of the breaking wave height, (7). Accordingly, the upper curve in Figure 7 includes an additional anamolous surge, (called "set-up"), which was conservatively calculated as 20% of the reported significant wave height. The moderate levels of surge south of Cedar Key and the low levels just north of Cedar Key--as well as the extreme water levels at Cedar Key and around Apalachicola--correspond reasonably to the idealized wind field around the storm when it was stationary offshore of Cedar Key, (Figure 5). V. OVERVIEW OF STORM-RELATED DAMAGE In terms of gross structural damage, Hurricane Elena had the greatest impact on Pinellas County. Over 2.6 miles of seawall were completely destroyed or sustained major damage and another 2.2 miles were somewhat damaged. Inspection indicated that many of the sewall failures were due to poor or lacking toe-scour protection, inadequate maintenance, insufficient toe penetration into the bed, and/or poorly embedded tie-backs. The variety of seawalls, the inconsistency of seawalled lots next to non-seawalled lots, and the insufficient cap elevation of almost all of the seawalls allowed considerable flanking and overtopping--which contributed significantly to the seawall failures. In virtually all cases inspected, the seawall 7

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structures which were of higher-quality construction faired well. Older bulkheads of inferior toe design and improperly maintained concrete failed or were severely damaged. In those cases where the seawall remained intact, overtopping posed a problem to the upland residents in the form of sizeable sand deposits, (overwash), amidst homes, yards, and parking area. Flooding was probably the chief problem for residents of Cedar Key--where the maximum storm surge exceeded + 9.0 feet MSL. Many of the buildings had 3 to 4 feet of standing water in them. Several restaurants located on the waterfront faced directly into Elena's winds. Damage assessements were much lower for those restaurants of more recent construction, (1984), which were built at high elevation upon concrete pilings with smaller windows of severe-storm-rated construction. The Sea Breeze Restaurant, however, was of lower elevation, (about +6 ft. MSL), with very large standard sliding-glass doors all around the dining area. These doors blew out early in the storm and allowed the full force of the winds and waves to enter the restaurant atop the surge. The small, low-elevation, piled house next to the restaurant lost its floor and, of course, everything inside. The decks of all the piers in the area were similarly completely destroyed. The predominant failures at Alligator Point typified the upland damage all around the Gulf coast: slab-on-grade construction suffered total or severe failures in contrast to piled structures. Road damage was severe along County Highway 370 at Alligator Point and along Rt. 98 between Appalachicola and Carabelle. The town of Eastpoint, along Rt. 98 suffered considerable waterfront damage even with its low-elevation breakwater offshore. Further west, on Dog Island, there were many failures of indequately designed or poorly maintained structures. The causeway to St. George Island failed on the east sides at those areas where the earth-supported roadway meets the bridges. The failures here were due to surge and wave overtopping of the low-elevation bulkheads. St. George Island was very nearly (but not completely) overwashed in many areas. The remainder of the Panhandle survived the storm with relatively little damage. There were some instances of downburst wind damage and a few isolated instances of impending or progressive structural collapse due to beach erosion along 8

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the western Panhandle. Table 1 lists a partial summary of the damage around the Florida coast. VI. POST-STORM BEACH MONITORING Following Hurricane Elena, beach profile monitoring was initiated in Pinellas County to document the rate and extent of natural post-storm beach recovery. In addition, the surveys provided data on the effects of seawalls on beach profile development and on the behavior of a beach nourishment project in response to a minor hurricane. On the morning of September 2, post-storm beach profiles were obtained from the north end of Sand Key at the southern end of Clearwater Beach. Wading profiles were initially taken at 6 and 15 hour intervals, then at intervals of several days or weeks until natural recovery processes were interrupted by beach scraping in mid October. As shown in Figure 8, five profiles were monitored along an 850 meter segment of the coast. Two profiles were taken off DNR survey monuments in a "natural" sandy area with no exposed seawalls. These monuments are actually located on the cap of a seawall that is now buried under a reconstructed dune and which forms the landward limit of a beach nourishment project. Two additional profiles were taken seaward from a surviving seawall that was exposed to storm waves. A fifth profile was taken 30 meters north of the exposed seawall in a sandy area that was eroded during the storm. Natural post-storm beach recovery processes are depicted in Figure 9 in a comparison of the measured post-storm profile from September 2 and a subsequent profile from September 10. On September 2, a continuous longshore bar was present over the entire survey area. The bar crest elevation was below the spring high tide elevations and with each incoming wave, sand and shell fragments were carried landward over the bar crest and deposited on the steep landward face of the bar. By September 10, the bar crest had grown vertically approximately 0.5 meters and, while the bar crest position remained stationary, the bar width increased 5-10 meters. In Figure 10, the recovery processes in front of the exposed seawall were nearly identical. On both seawalled and non-seawalled profiles, initial deposition occurred on the bar and little sand reached the base of the seawall or the landward beach face. As the bar crest elevation increased, fewer waves were able to overtop the bar crest, thus preventing further landward migration of the bar. In the week after the storm, 9

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during the neap tidal cycle, no additional changes in the bar crest or landward slope occurred although some changes occurred on the seaward slope. Based on the first five surveys (September 2 to September 10) an average of 5.8 m3/m was transported landward and deposited on the bar above mean sea level. Of this volume, an average 5.5 m3/m was deposited by September 3; after September 3 periodic erosion and deposition occurred resulting in a slow net deposition above mean sea level. Since the first survey was completed 10 to 20 hours after the storm effects began to subside, some recovery had occurred before the September 2 survey. It is not clear whether the bar formed during the storm or during the initial recovery phases; however, the profile was actively recovering during the high tide prior to the first survey. Recovery processes are clearly linked to both the water level and wave conditions. Based on data presented in Figure 4 and 7, the peak water level and wave heights occurred over August 31 to September 1 and it is probable that the maximum erosion occurred about mid-day on September 1. From September 1 through September 2, during the most active recovery, wave heights exceeded 1.0 meter; after September 3 wave heights dropped to 0.3 meters and recovery slowed substantially. Recovery seemed to occur in two phases: 1) the immediate rapid post-storm "healing" of the eroded beach which occurs while the storm is still affecting wave-conditions and 2) a long term slow recovery which occurs over several weeks, months, or years in response to normal wave conditions. In 1983-1984 a beach nourishment and dune restoration project was completed in the study area. Profiles R-58 and R-59 were within the main nourishment area, profiles R-60A, R-60B, and R-60C were located at the southern end of the nourishment project. On these southern profiles, no dune was constructed and instead, a "feeder" beach was designed with a broad berm which could gradually erode and continuously replenish downdrift beaches to the north. Profile R-60C was located near the tapered transition between the feeder beach and the unnourished beaches to the south; therefore, the shoreline in this area is closer to the exposed seawall than on profiles R-50A or R-60B. Comparisons of pre-nourishment, post-nourishment, and poststorm profiles for R-58 and R-59 are given in Figures 11 and 12. In 1974 most of the profile was below mean sea level, there was no recreational or storm protection beach, and the seawall 10

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was exposed to direct wave attack. In November 1984, a 40-60 meter wide beach and a nearly 3 meter high dune were placed seaward of the seawall. Total fill volumes of 106 m3/m and 188 m3/m were placed on R-58 and R-59 respectively; of these volumes 45 m3/m and 70 m3/m were placed above mean sea level. After the storm on September 2, 1985, profile R-58 showed a net gain of 3.2 m3/m while R-59 had a net loss of 34.8 m3/m Both profiles showed a loss of the reconstructed dune and berm with a bar offshore. While few conclusions can be drawn, longshore sediment transport seems to have resulted in a redistribution of sand from south to north, resulting in a net loss to R-59 and a net gain to R-58. Between these two profiles an average loss of 15.8 m3/m occurred between November 1984 and September 2, 1985. It is not known what portion of this volume was lost during the storm versus prior to the storm. Although not shown in Figures 11 and 12, between September 2 and September 10 post-storm recovery returned a net volume of 3.8 m3/m and 7.3 m3/m to R-58 and R-59 respectively, for an average recovery of 5.1 m3/m. Thus based on average values, the net loss to the profiles between November 1984 and September 10, 1985 is 10.7 m3/m or about 7% of the initial average beach fill volume. It should be noted that these figures are based on wading profiles; however, spot checks of the offshore profiles with a fathometer showed no bars or large depositional features. The effects of seawalls on beach profile response are illustrated in Figure 13, in a comparison of three post-storm profiles influenced by the exposed seawall. Profile R-60A, located 30 meters from the end of the seawall, was found to have a similar form to R-58 and R-59 and did not exhibit any local effects due to the proximity of the seawall. Profile R-60B, located 60 meters to the south in front of the seawall, exhibits the increased toe scour associated with open coast seawalls. The offshore portions of the profiles are nearly identical however and the seawall does not seem to have had an effect on the bar formation or seaward slope. The seawall performed its intended function of preventing upland property from eroding. It is interesting to compare the volume of the increased toe scour attributed to the seawall with the volume of material the seawall prevented from eroding. There is an approximate balance between these volumes. This seems to indicate that the seawall did not cause any additional loss of volume from the profile than would otherwise have occurred, losses were simply concentrated at the toe of the seawall. 11

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Profile R-60C, located 180 meters to the south of R-60B in front of the seawall, shows dramatically the depth of the erosion that can occur at the toe of a seawall. As noted, the tapering of the beach fill causes the shoreline and the bar to be closer to the seawall at the south end than at the north end; however, the form of the bar and the seaward sand slopes are the same as in all other profiles. At the toe of the seawall, the erosion extends 1.6 meters below the sand level of profile R-60A adjacent to the seawall. This clearly illustrates the need for proper embedment of the seawall to ensure structural stability to prevent toe failure and undermining. VII. SUMMARY The greatest extent of damage due to Hurricane Elena was realized in Pinellas County, although the greater potential for damage was probably at the lesser-developed areas of Cedar Key and Apalachicola through St. George Island. The maximum measured surge around Florida was at Cedar Key and in the region of Panacea, Alligator Point, and St. George Island. Surge in these areas were at approximately 25-30 year levels. While Elena entered the Gulf of Mexico, south of the Keys, maximum significant wave heights off of Miami and West Palm Beach were between 4 and 5.2 feet. The largest significant wave heights around Florida were recorded while the storm was stationary 55 miles WSW of Cedar Key: 8.2 ft at Clearwater and 10.5 ft at Jacksonville. Modal wave periods associated with Elena were approximately 10 seconds. The highest winds along the Florida coast were at Cedar Key, Appalachicola, and the Panhandle barrier islands. Maximum sustained winds were not thought to have exceeded 100 mph. However, gusts of between 70 mph to at least 100 mph were reported from Clearwater through Cedar Key, and from Apalachicola to Pensacola. The storm damage was characterized by: 1. failure of low-elevation, poorly constructed seawalls with inadequate toe penetration or protection and/or inadequate tie-back design or protection; 2. slab-on-grade construction failures; 3. blow-out (and subsequent damage) due to large non-hurricanerated windows and doors; 4. flooding of low-elevation structures, (piled and non-piled); 5. road damage due to inappropriate elevations of roadways and/or protective revetments and bulkheads; 12

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6. overwash; and 7. structural designs, in general, which were not compatible with severe storm conditions. Post-storm monitoring of beach profiles in Pinellas County indicates the capacity of sand beaches to respond to a severe storm. During the storm a net transfer of sand occurred from the berm and dune offshore. After the storm, much of this sand was returned and deposited as a bar above mean sea level. Beach profile response in front of a seawall was similar with a net transfer of sand from the toe of the seawall to offshore areas during the storm. Post-storm recovery has likewise returned much of this sand to the beach face. While it is difficult to state conclusively the impact of the seawall on beach changes in the area, the localized erosion at the toe of the seawall can be significant, and certainly contributed to the failure of many seawalls in Pinelas County. The Sand Key beach nourishment and artifical dune construction project seems to have been successful in absorbing wave energy by "remolding" during the storm. While the constructed dunes eroded almost completely, this sand moved offshore during the storm and has subsequently moved back onshore to the beach face. In areas where the dune was constructed and the beach was nourished, the only storm damage was due to sand overwash into swimming pools and parking lots; no structural damage occurred due to storm waves. REFERENCES 1. Howell, G. L., "Florida Coastal Data Newtork," Proceedings of the 17th International Conference on Coastal Engineering, Sydney, Australia, ASCE; 1980. 2. Bodge, K. R., and Broward, C., "The E-Cell Time-Recording Storm Surge Gauge," University of Florida Coastal and Oceanographic Engineering Department UFL/COEL TR/057, Gainesville, FL 32611; August, 1985. 3. "Tropical Cyclones of the North Atlantic Ocean, 18711980," National Oceanic and Atmospheric Administration (NOAA), National Climatic Center, Asheville, NC; Amended, 1984. 13

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4. "Feasibility Report -Protection of Highway 370, Alligator Point Fla.," U.S. Army Corps of Engineers, Mobile District; March, 1985. 5. "Beach Erosion Control Project Review Summary and Environmental Impact Statement for Pinellas County, Florida, U.S. Army Corps of Engineers, Jacksonville District: July, 1984. 6. "Tide Table, East Coast of North and South America Including Greenland," U. S. Dept. of Commerce, National Oceanic and Atmospheric Administration, National Ocean Survey; 1985. 7. Lo, J. M., "Surf Beat: Numerical and Theoretical Analyses," Ph.D. Dissertation, University of Delaware, Newark, DE; 1981. 14

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Table 1. Partial Summary of Structural Damage Sustained from Hurricane Elena, (from Florida Dept. of Natural Resources, Division of Beaches and Shores). PINELLAS COUNTY 2.66 miles of vertical bulkheads destroyed or severely damaged. 2.15 miles of vertical bulkheads sustained minor damage. 44 single family dwellings destroyed, 31 damaged. 4 condominium/hotel units destroyed. 9 condominium/townhouse/motel buildings damaged. 5 pools destroyed, 3 damaged. 3 fishing piers destroyed, 2 damaged. MANATEE COUNTY 0.22 miles of vertical bulkheads destroyed, 0.08 miles damaged. 5 single family dwellings destroyed, 2 damaged. SARASOTA COUNTY 0.2 miles of vertical bulkhead; destroyed or damaged. 1 single family dwelling destroyed. 0.6 miles of road damaged. FRANKLIN COUNTY 0.5 miles of vertical bulkhead destroyed or damaged. 0.06 miles rock revetment destroyed or damaged. 20 single family dwellings destroyed or damaged. 1 community recreation building destroyed 1 mile of road destroyed (Alligator Pt., St. Geo. Island), 3.9 miles damaged (St. Geo. Island). 0.3 miles causeway damaged (St. Geo. Island). 123,100 ft3 pavement U.S. 98 destroyed. 58,000 yd3 fill lost from St. Geo Island Causeway. 130,000 yd3 fill lost form U.S. 98 GULF, BAY, WALTON, OKALOSSA, ESCAMBIA, CHARLOTTE, LEE, AND COLLIER COUNTIES -No major damage. 15

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1020l1i 1i i I 1 s80 1010-70 1000-60( i 990 -50 960--40 (nl W D W 970-30 a 96020 M Wind 950 --10 Z it 0 94Qr-~--I~---I~n---------1-l-0 27 28 29 30 31 I 2 3 4 AUGUST SEPTEMBER Figure 1: Minimum pressure and maximum winds of .Hurricane Elena. (source: National Weather Service, Tampa Bay Area; Ruskin, FL.). \ STMAR ENTRANCE 1983 *-. JcKSONVILLE 1981 MARINELAND 1977 STEINHATCHEE CAPE KENNEDY 1977 .1983 CLEARWATER 1978 VEROBEACH 1980 VENICE 1984 pALM BEACH • 1979 MIAMI 1977 Figure 2: The Florida Coastal Data Network wave monitoring stations (and year of installation of each site). Solid lines indicate a hard-wire station link to Gainesville, dashed lines indicate a radio link, and no line indicates that the station stores its data internally. 16

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9/2 8/31 8/29\ 2 -7 Figure 3: Hurricane Elena storm track, 1985. The dates shown indicate the position of the center of the storm at noon E.S.T. SJACKSONVILLE / .. \ ... S9'|. ARINELAND E .CANAVERAL ; UL 0[ : 0 26 27 28 29 30 31 2 3 4 .. AUGUST 1985 SEPT. CUT /E ALM-.MIAMI 3 26 27 29 30 31 1 2 3 AUGUST 1985 SEPT. Figure 4: Significant wave heights measured by the Florida Coastal Data Network during Hurricane Elena, 1985. 17

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Reooolo Vetce Pi Miami Figure 5: Idealized wind field associated with a tropical cyclone located off of Cedar Key, Florida. 12'(L S64 27 28 29 30 31 I 2 AUGUIST SEPTEMHtR Figure 6: Wave periods at Clearwater during Hurricane Elena, 1985. 18

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-Shoreline Water Level (calculated) 6 -----Offshore Water Level (measured) ---Astronomical Tide (predicted) -24.j3W 2 ail 29 30 31 I AUGUST 1985 SEPT Figure 7: Storm surge hydrograph at Clearwater during Hurricane Elena, 1985. N R-58 Smoll Pier .o *o / -Reconstructed Dune Recovery Appoximote Mean S Level Shoreline I R-60A R-6OB -:C 2 R-60 Figure 8: Location of post-storm monitoring of beach processea 19 19

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R-59 BEACH NOURISHMENT WITH ARTIFICAL DUNE 2-J .POST STORM RECOVERY SEPT. 10,1985 L.UW -SEPT.2,1985 DISTANCE FROM MONUMENT(M) E 20 40 60 80 -2Figure 9: Beach recovery on nourished beach, profile R-59. R608 3 BEACH NOURISHMENT WITH SEAWALL S/SEAWALL S/POST STORM RECOVERY SEPT IO,1985 S/ /SEPT 2,1985 DISTANCE FROM SEAWALL (M) 060 0 -2 Figure 10: Beach recovery in front of seawall, profile R-60B. 20

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R-58 SAND KEY BEACH NOURISHMENT PROJECT 3 PROFILE WITH ARTIFICAL DUNE w SNov. 1984 SPost Nourishment U1 wI _Sept 2,1985 SPost Hurricone Eleno z 4 > Oct. 1974 -/ Before Nourishment -2Figure 11: Comparison of pre-nourishment, post-nourishment, and post storm profiles, profile R-58. R-59 SAND KEY BEACH NOURISHMENT PROJECT 3 -PROFILE WITH ARTIFICAL DUNE w SNov. 1984 S\ / Post Nourishment 2Se : i i s o distlce from monument ( ters) I "20 / 40 ^ ^60 80 < s LSept. 2,1985 z ^ Fst Hurricone Eleno 2 Oct. 1974 J -J Before Nourishment Figure 12: Comparison of pre-nourishment, post-nourishment, and post storm profiles, profile R-59. 21

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COMPARISON OF PROFILES AFFECTED BY SEAWALL 2 SEAWALL PROFILE R-60A NORTH OF SEAWAU. PROFILE R-608 WITH SEAWAU. DISTANCE FROM SEAWALL (M -2o 40 60 O Z -I 'PROFILE R60 C WITH SEAWALL -2 Figure 13: Comparison of profiles affected by seawall. 22