USGS Scientists Predict, Measure Sandy's Impacts on the Coastal Landscape
Hurricane Sandy, one of the biggest storms ever to hit the United States, struck the Eastern Seaboard on October 29, 2012. It caused dozens of deaths and billions of dollars worth of damage and displaced massive volumes of protective beach and dune sediments. Before, during, and after Sandy’s landfall, U.S. Geological Survey (USGS) scientists in St. Petersburg, Florida, predicted, then measured, the change that took place along the shore.
Days before Sandy made landfall in southern New Jersey, the USGS Hurricanes and Extreme Storms team at the St. Petersburg Coastal and Marine Science Center set out to determine how the storm was likely to affect the coastal landscape. The team used forecasted wave heights and water levels in combination with a storm-impact scale to predict the likelihood that selected stretches of coast would experience certain patterns of sediment erosion and deposition (http://coastal.er.usgs.gov/hurricanes/sandy/coastal-change/). In addition, a pre-storm Global Positioning System (GPS) ground survey was conducted for Fire Island, New York, an area that ultimately experienced substantial coastal change during the storm. Along the New Jersey coast, another area that underwent severe impacts, pre-storm topographic measurements were made using EAARL-B (Experimental Advanced Airborne Research Lidar). (Lidar, short for “light detection and ranging,” is similar to radar but uses laser light instead of radio waves to measure distances.) These pre-landfall measurements provide crucial baseline information for assessing and understanding the storm’s impacts.
After the storm, the team acquired imagery from a variety of sources. Initially, they obtained post-storm photographs and videos from news reports and social media that featured clear examples of beach and dune erosion, overwash (occurs when storm waves overtop dunes and carry sand inland), and inundation (complete submersion of beach and dunes). They used this imagery to “ground-truth” their pre-storm assessments.
Additional ground-truthing was provided by aerial photographs acquired during a 2-day mission flown along the open-coast shoreline from the Outer Banks of North Carolina to coastal Massachusetts. The aim was to compare post-storm photographs with those taken before the storm to get a qualitative look at coastal change in certain areas. To view examples, visit http://coastal.er.usgs.gov/hurricanes/sandy/photo-comparisons/. Many more photo pairs are posted at http://coastal.er.usgs.gov/hurricanes/sandy/post-storm-photos/obliquephotos.html.
In partnership with several other agencies, the team coordinated lidar topographic surveys along the same stretch of coast. These data will be compared to those taken before the storm in order to quantify the magnitude of coastal change and gauge the accuracy of their pre-storm assessments.
The group also worked closely with the National Park Service, the U.S. Fish and Wildlife Service, and the U.S. Army Corps of Engineers to coordinate a post-storm survey of Fire Island National Seashore almost immediately after the storm. This survey, conducted before any data or imagery could be collected from the air, revealed drastic changes.
“We found that there was widespread dune erosion and overwash,” said St. Petersburg-based USGS coastal geologist Cheryl Hapke. “On average, the dunes eroded back 70 feet—the equivalent of 30 years of change, which had previously been measured. Our data also showed that dunes lost as much as 10 feet of elevation.”
These rapid response data were used to help the National Park Service assess the areas of the coast that were most vulnerable to a nor’easter that struck the coast a week after Sandy.
Whether carried out from the air, on the ground, or in an office, all of this work enhances our understanding of how and why coastlines respond to storms the way they do. This understanding, gained through partnering with stakeholders and agencies at all levels of government, can help coastal managers prepare to mitigate the impacts of future storms.
Check the Hurricanes and Extreme Storms team’s website for updates and additional information: http://coastal.er.usgs.gov/hurricanes/sandy/.
To learn more about USGS responses to Hurricane Sandy, read http://www.usgs.gov/blogs/features/usgs_top_story/sandy/ and visit the USGS Newsroom, http://www.usgs.gov/newsroom/.
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