Tropical Depression Alberto

Tropical Storm Debby
Post-Debby Beach/Dune
Damage Assessment Report
Sarasota Florida
By Weiqi Lin P.E., Ph.D.
Coastal Resources/Community Services
June 29, 2012
BACKGROUND AND SUMMARY
Tropical storm Debby formed on June 23, 2012. With maximum sustained wind speed of
45 mph, the storm moved northeast very slowly at 3-4 mph. In Sarasota County, Debby
caused major coastal flooding, severe beach/dune erosion and property damage, due to its
slow movement, location, long duration of heavy rainfall, and steady winds. The storm
surge was estimated to be about 3-5 feet. On June 25 & 26, 2012, Sarasota County
Coastal Resources staff conducted beach/dune damage assessment along the county’s
Gulf shoreline, and found the following:
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Major coastal flooding occurred on north Siesta Key. A large portion of Beach
Road was flooded during the storm.
•
Severe beach/dune erosion occurred on south Siesta Key, Casey Key and
Manasota Key. There was 10-20 feet of dune erosion noted at many locations. In
some areas, more than 30 feet of dune was lost.
•
Three residential structures are imminently threatened, at the edge of the newly
eroded bluff on Manasota Key. On Casey Key, one residential structure is
threatened by coastal erosion.
•
Structural damage to decks and dune walkover structures were documented.
Many dune walkover structures were washed out.
•
Heavy loss of sea turtle nests and native dune vegetation was observed. Fallen
palm trees and Australian pine trees were also noted.
•
Significant devastation to the nesting shorebirds was reported by the Sarasota
Audubon Society. Entire colonies were lost from Longboat Key down through
Siesta Key, with similar impacts suspected on Manasota Key as well.
•
A recently constructed sandtube was exposed on Casey Key. A step seawall was
undermined by wave action on Manasota Key.
BEACH AND DUNE CONDITIONS
Siesta Key
Due to its low elevation, Siesta Key is vulnerable to coastal flooding, and has a long
history of flooding during storms. North Siesta Key has the lowest elevation of 4 to 5 ft.
NGVD and suffered major flooding during Tropical Storm Debby. Several inches to a
foot height of water was documented on Beach Road (Figs. 1-3). Most of Siesta Key
public beach was covered by waves and white-caps (Fig.4).
Severe erosion was observed at the southern most portion of Siesta Key. It is estimated
that 20-30 ft. of beach has eroded away at Turtle Beach Public Park. The boat ramp at
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Blind Pass Lagoon was flooded. South of Turtle Beach Public Park, from Fisherman’s
Cove and Fisherman’s Haven condos down to the Palmer Point Park area, most of the
restored beach and restored dune vegetation were washed away (Fig.5). The rock
revetment in front of Fisherman’s Cove and Fisherman’s Haven was exposed for the first
time since the construction of the South Siesta Key beach nourishment project. Several
feet of sand was pushed up onto the most southern residential property at 9230 Blind Pass
Road (Fig.6).
Casey Key
Casey Key has a higher elevation of 13-14 ft. NGVD. A small portion of Casey Key
Road experienced a flooding problem due to heavy rainfall. Waves over-topped a gulffront portion of North Casey Key Road. The road was covered with 2-4 feet of sand and
not passable during the storm (Fig.7).
Debby has caused severe dune/beach erosion. It is estimated about 10-20 feet of dune
erosion has occurred throughout Casey Key, due to the combined effects of high wave
energy and high tide. The residential structure at 2007 Casey Key Road was threatened
by the receding bluff line (Fig.8). A recently constructed sandtube at 2209, 2305, 2309
and 2315 Casey Key Road was exposed (Figs.9-10). More than 30 feet of dune has
eroded at that location. Dune vegetation has been washed out, and structural damage to
decks and dune walkovers was also observed. Many sea turtle nests have been overwashed.
Manasota Key
Storm surge and high waves generated by Debby have caused severe erosion on most of
Manasota Key. Up to 20 to 30 feet of dune was eroded away throughout most of
Manasota Key and North Manasota Key. Numerous sea turtle nests were over-washed
and dune vegetation was washed away. Many palm trees were laying on the beach. Big
Australian pine trees were also down. Structural damage to decks and dune walkovers
was documented. Some dune walkover structures were washed out.
The worst erosion occurred from the Sarasota/Charlotte county line north to Blind Pass
Park (Middle Beach), and from Blind Pass Park up to just south of the Pearl Motel (7990
Manasota Key Road). At least three residential structures (7160, 7110 Manasota Key
Road and 6116 Gnarled Oak Drive) were threatened, at the edge of the newly eroded
bluff line (Fig. 11 & 12). The foundation of the residential structure at 7160 Manasota
Key Road was undermined and the residence is imminently threatened (Fig.13). More
than 30 feet of dune eroded away in front of 7100 Manasota Key Road, and the steps of
the dune walk-over structure were washed away (Fig.14). A step seawall at 6110
Manasota Key Road was undermined by wave action (Fig. 15). Two decks at 6210 and
6260 Manasota Key Road were damaged. A portion of Manasota Key Road at the north
end of Blind Pass Park was threatened by dune erosion (Fig.16). The bluff has eroded all
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the way to the edge of that portion of the road (about 200-300 ft long). There is
approximately 40 feet of dune estimated to have eroded away at this location.
SUMMARY
In Sarasota County, Tropical Storm Debby caused major coastal flooding, severe
beach/dune erosion and coastal property damage. The storm produced significant impacts
on our coastal communities, coastal environments and coastal systems. In terms of
flooding and beach/dune erosion, Debby’s effects were equivalent to those of a much
higher category storm.
ATTACHED PHOTOS
Figure 1. Waves over-topped the most northern portion of Beach Road, causing major coastal
flooding in this area.
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Figure 2. Flooding at Public Beach Access#3. More than a foot of water and two feet of sand
covered this portion of Beach Road.
Figure 3. Flooded Beach Road at the exit of Siesta Key Public Beach main parking lot.
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Figure 4. Most of Siesta Public Beach was covered by waves and white-caps.
Figure 5. Restored beach, dune and native dune vegetation were washed out in front of
Fisherman’s Cove and Fishman’s Haven condos.
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Figure 6. Several feet of sand was washed on shore at 9230 Blind Pass Road.
Figure 7. Waves washed sand on top of a Gulf-front portion of North Casey Key Road. The road
was impassable during the storm.
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Figure 8. The residential structure at 2007 Casey Key Road is threatened by the eroded bluff. The
wooden deck suffered structural damage and collapsed.
Figure 9. This photo shows the beach/dune conditions in front of 2209, 2305 and 2309 Casey Key
Road on May 1, 2012. It was taken by staff during a pre-storm beach/dune condition inspection
for comparison with post-storm beach/dune inspections.
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Figure 10. This June 26, 2012 photo was provided by Mote Maine Lab showing more than 20 feet
of dune eroded away by Tropical Storm Debby. The sand tube was exposed just two years after
construction.
Figure 11. The residential structure at 7110 Manasota Key Road was threatened by beach/dune
erosion. The wooden deck collapsed and the dune-walkover was washed out. The adjacent
neighbor at 7160 Manasota Key suffered similar damage.
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Figure 12. The receding bluff line also threatened this residential structure at 6116 Gnarled Oak
Drive. The wooden deck collapsed and the dune-walkover washed away.
Figure 13. The foundation of the residence at 7160 Manasota Key Road was exposed after the
sand under the deck washed out. The residential structure is imminently threatened.
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Figure 14. More than 30 feet of dune eroded in front of the residence at 7100 Manasota Key
Road. The dune walkover structure is damaged and the steps washed away.
Figure 15. A step seawall at 6210 Manasota key Road was undermined by wave action. A big
hole was created landward of the seawall and the deck was structurally damaged.
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Figure 16. The bluff eroded all the way to the edge of a gulf-front portion of Manasota Key
Road (about 200-300 ft ) and approximately 40 feet of dune was estimated to be eroded away at
this location.
(End)
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