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St. Petersburg Coastal and Marine Science Center > National Assessment of Storm-Induced Coastal Change Hazards > Hurricane Irma

National Assessment of Storm-Induced Coastal Change Hazards

Hurricane Irma Storm Response

Pre- and Post-Storm Photo Comparisons - Southwest Florida

The coastal change forecast model predicts the probability of where and how primary sand dunes along the coast will be impacted by water levels during a storm. This includes the combined effect of surge and wave runup. The color band closest to the shoreline is the probability of dune erosion, the middle color band is the probability that sand dunes will be overtopped by waves during the storm and the outer color band is the probability that the sand dunes will be completely inundated/flooded. The model forecast is available on the coastal change hazards portal: https://marine.usgs.gov/coastalchangehazardsportal/  and more information about the model can be found here: https://coastal.er.usgs.gov/hurricanes/assessments/background.php
Below is an initial comparison of imagery collected by the National Oceanic and Atmospheric Administration (NOAA) in 2017 with similar imagery taken a few days after Hurricane Irma’s landfall (https://storms.ngs.noaa.gov/). These photos provide information about how the coastal was impacted by the storm and can be used as validation for the model.

    Predicted probabilities of dune erosion (inner strip), overwash (middle strip), and inundation (outer strip) for Hurricane Irma. Pictures are representative of coastal change observed during past storm events.
Predicted probabilities of dune erosion (inner strip), overwash (middle strip), and inundation (outer strip) for Hurricane Irma. Pictures are representative of coastal change observed during past storm events. [larger version]

Location Map
Locations of observed coastal change due to Hurricane Irma.

pre- and post-storm photos
Location 1: Even though the predicted probability of overwash was 99%, elevated water levels during Hurricane Irma did not overtop the seawall on the southern end of Marco Island, but eroded much of the beach in front. Some overwash can be seen to the north of the seawall. [larger version]



pre- and post-storm photos
Location 2: Elevated water levels during Hurricane Irma overtopped the low-elevation dunes on Keewaydin Island near Naples, depositing sand on top of and behind the dunes in overwash fans. The predicted probability of overwash in this location was 100%. [larger version]



pre- and post-storm photos
Location 3: A small breach formed at a low spot on Keewaydin Island. The predicted probability of inundation in this location was 100%. [larger version]



pre- and post-storm photos
Location 4: The beach in south Naples shows small areas of overwash where sand from the beach and dunes was deposited behind the seawall. The beach and dunes in front of the seawall were completely removed by the waves and surge of Hurricane Irma. The predicted probability of overwash was 100%. [larger version]



pre- and post-storm photos
Location 5: Elevated water levels during Hurricane Irma reopened Clam Pass on Sanibel Island and eroded most of the sand in front of the vegetation. The predicted probability of inundation for this location was 92%. [larger version]



pre- and post-storm photos
Location 6: The inlet at Cayo Costa was widened and sand transported inland by high waves and surge during Hurricane Irma. The predicted probability of inundation for this location was 90%. [larger version]



pre- and post-storm photos
Location 7: Low elevation dunes were overtopped by waves and surge from Hurricane Irma. Sand was transported landward covering vegetation and walking trails. The predicted probability of overwash in this location was 99%. [larger version]



pre- and post-storm photos
Location 8: A home on Little Gasparilla Island was swept away by Hurricane Irma’s waves and surge. The beach narrowed significantly and two more homes are now more vulnerable to future storm impacts. The predicted probability of overwash for this location was 97%. [larger version]



pre- and post-storm photos
Location 9: This beach on Palm Island illustrates varying coastal responses to elevated water levels during Irma. The southern portion of the beach experienced beach erosion, the northern portion overwashed, and the middle section was inundated. Predicted probabilities of dune erosion, overwash, and inundation were 100, 98, and 78 respectively. [larger version]

St. Petersburg Coastal and Marine Science Center > National Assessment of Storm-Induced Coastal Change Hazards > Hurricane Irma

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Page Last Modified: September 27, 2017 03:55 PM (JSG)

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