What Happened During Sandy on Fire Island?
As Cheryl Hapke, a USGS research geologist and lead author of the after-study pointed out, “Sandy profoundly altered the shape and position of the barrier island, shifting it landward and redistributing large amounts of sand.”
Essentially, three things occurred:
- The island was breached in three locations;
- The beaches and dunes of the island were severely eroded and enormous volumes of sand carried from the beach and over 50 % of the protective dunes to the central portion of the island, forming large overwash deposits; and
- There was widespread damage and destruction of coastal infrastructure, including private residences as flood waters rushed through.
Even before the storm hit a USGS pre-storm field team went to Fire Island and took before pictures. There were also pre-storm photos acquired during a baseline survey on May 21, 2009 and post-storm photos were acquired. On November 4-6, 2012, after the storm hit, the field team took specific oblique aerial photographs of the resultant damage.
Measurement and analysis of the damage followed in the form of profiles and 3D Lidar topography imaging, a remote sensing technology that measures distances by illuminating a target with a laser and analyzing the reflected light.
While there was some recovery in the early spring when 18 percent of the pre-Sandy beach volume returned, during the preceding winter months, Fire Island’s shoreline position shifted up to 57.5 meters (189 feet) inland.
Hurricane Sandy Beach Damage: Implications
Obviously, by eroding beaches and dunes, elevated water levels and waves during tropical storms can lead to dramatic coastal changes.
The USGS uses a storm-impact scale to predict the probability of coastal change. The result is three coastal change regimes:
- Collision- when waves attack the base of dunes and cause dune-front erosion;
- Overwash- under higher surge or wave runup conditions, waves can overtop dunes
- Inundation- storm surge and wave setup exceeds the elevation of the primary dune or beach berm (low, narrow islands may breach).
The probabilities of each of the above were assessed by calculating coastal probabilities. The parameters included were:
- Modeled total water levels- tide, surge, wave runup
- Dune or berm elevations
The probabilities were mapped with white representing a low probability (0-10 %) and dark red a high probability (90-100%). High probabilities leave the impacted areas more vulnerable to future storms.
Fire Island: Vulnerable and Ever-Changing
So, this island, founded as a whaling center in the 18th century and now a destination for artists, actors and musicians “puts the fear of god in Fire Islanders whenever a storm approaches. With Hurricane Sandy, for many, our worst fears were realized,” says Jane L. Rosen.
And so it should. Fire Island’s shores and elevations constantly shift in a sort of equilibrium among mighty natural forces. The beaches are destroyed by the power of erosion – as Alida Thorpe’s photos attest- while, on the other hand, the island is being built up by the deposits carried to the ocean-front by longshore drift. The USGS is limited to providing scientific advice.
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