Hurricane Sandy - Forecast and Documentation of Coastal Change

Hurricane Sandy made landfall on October 30, 2012, and impacted a long swath of the Mid-Atlantic coastline. Many areas that had been hit by Hurricane Irene in August 2011 were again battered by strong waves and surge. The barrier islands were breached in a number of places and erosion of the beach and dunes occurred all along the Mid-Atlantic coast. 

Response Activities

• Forecast of potential coastal-change impacts 
• Pre- and post-storm photo comparisons 
• Comparison of pre- and post-storm lidar topography and coastal change
• Field Observations and Measurements of Coastal Change

Forecast of Potential Coastal Change

As Hurricane Sandy moved northward along the U.S. Atlantic coast in October 2012, U.S. Geological Survey scientists worked to determine where and how the storm's waves and surge might dramatically reshape the beaches and dunes that stand between the storm and coastal developments. Through a complex modeling process that uses coastal elevations, wave forecasts, and potential storm surge, they predicted coastal change hazards, such as shoreline and dune erosion, that might be expected during a Sandy landfall.

The coastal change forecast model predicts the probability of where and how 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 and more information about the model can be found here: https://www.usgs.gov/centers/spcmsc/science/scenario-based-assessments-used-coastal-change-hazard-forecasts. 

Screen shot of the Coastal Change Hazards Portal showing potential coastal change impacts during a direct landfall of Hurricane Sandy based on NHC Advisory 29, 1100 AM EDT MON OCT 29 2012. The model forecast is available from the Coastal Change Hazards Portal and more information about the model can be found at https://www.usgs.gov/centers/spcmsc/science/scenario-based-assessments-used-coastal-change-hazard-forecasts. Photos of coastal change caused by Hurricane Sandy are shown in the galleries below. (Public domain.)

Pre-and Post-Storm Photo Comparisons and Lidar Elevation Maps

Following landfall, oblique aerial photography and lidar surveys of beach elevations were used to document the changes that occurred as a result of the storm. In addition, field measurements of the beaches and dunes were collected immediately after the storm. Comparisons of data collected before the storm show the nature, magnitude and spatial variability of the coastal response. These data will be used to further refine predictive models for storm-induced erosion.

All of the pre- and post-storm photos for Hurricane Sandy are available in the Oblique Aerial Photography Viewer.

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Field Observations and Measurements of Coastal Change - Fire Island, New York

As Hurricane Sandy moved up the eastern U.S. coast and the forecasts were predicting significant impacts to the south shore of Long Island, a field team went to Fire Island on the south shore of Long Island, New York, to survey the beach, dunes and shoreline. The pre-storm survey was conducted on October 28, 2012. Following the storm, surveys were conducted over several days (November 1 and 2, 2012) to measure beach and dune erosion.

The impacts to the island were extensive. The majority of oceanfront homes in the communities within Fire Island National Seashore were damaged or destroyed. Enormous volumes of sand were carried from the beach and dunes to the central portion of the island, forming large overwash deposits, and the island was breached in 3 locations. With few exceptions, lower-relief dunes were overwashed and flattened. High dunes, which are more commonly found within undeveloped portions of the island, experienced severe erosion and overwash. The elevation of the beach was lowered and the dunes form vertical scarps where they survived.

Hurricane Sandy caused damage of oceanfront houses along western Fire Island. (Public domain.)

Dunes were severely eroded and the beach elevation lowered during Hurricane Sandy. (Public domain.)

Some key findings of the field data collection effort indicate that:

• 50% of the dunes on Fire Island were overwashed during the storm, carrying large volumes of material to the interior portion of the island
• In locations where the dunes remained intact, they eroded an average of 22 meters in cross-beach position
• Dune elevation losses were as high as 5meters and the berm of the beach was lowered by as much as 3meters

The USGS worked closely with personnel from the National Park Service (NPS) to gain access to the island, and to survey and measure the dramatic changes to the barrier system. The post-storm data was used to help the NPS assess the areas of the coast that were most vulnerable to a nor'easter that impacted the coast a week after Sandy.

Cross-shore profiles from before and after hurricane Sandy for western Fire Island. (Public domain.)

Results from field surveys of net shoreline change and dune toe change (NSM) from Hurricane Sandy along western Fire Island. The locations of the cross-shore profiles are shown in red. The gray boxes on the plot are areas where the dunes were overwashed. The gain in the shoreline is due to rapid recovery of the lowest portion of the beach in the days following the storm (Photo: NOAA, 2012). (Public domain)

Cross-shore profiles from before and after hurricane Sandy for central Fire Island. (Public domain)

Results from field surveys of net shoreline change and dune toe change from Hurricane Sandy along central Fire Island. The locations of the cross-shore profiles are shown in red. The gray boxes on the plot are areas where the dunes were overwashed The gain in the shoreline is due to rapid recovery of the lowest portion of the beach in the days following the storm (Photo: NOAA, 2012). (Public domain.)