A COMPARISON OF THE GEOMORPHIC EFFECTS OF HURRICANES SANDY AND IRENE ALONG ASSATEAGUE ISLAND, MD-VA, A WAVE-DOMINATED BARRIER ISLAND

Within the last two years, Assateague Island, MD-VA was affected by two major storms - Hurricanes Sandy and Irene. Hurricane Irene affected the U.S. Atlantic Coast on 27-28 August 2011, making landfall along the NC coast as a Category 1 storm. Irene moved north along the U.S. Atlantic Coast centered approximately 15 km east of the VA coast, producing a storm surge peak of 0.75 m during mean high tide conditions at Ocean City Inlet, MD. The storm yielded 20 m/s winds and a minimum atmospheric pressure of 967.3 hPa in Delaware Bay. A post-Irene flyover of the outer Delmarva Peninsula coast on 31 Aug 2011 showed that beach erosion and overwash were the main geomorphic processes resulting from Irene. A small ephemeral breach was observed on southern Assateague Island, along Swan Pool beach (north of Tom’s Cove). The breach had a throat width of 10-15 m, with a linear geometry, and shore-normal orientation. Washover fans were deposited along the northern and southernmost portions of the island. Hurricane Sandy impacted the U.S. Atlantic coast on 29 October 2012 as a Category 1 storm, passing 80 km northeast of Ocean City Inlet, before hooking west into southern NJ. A minimum atmospheric pressure of 962.7 hPa and maximum winds of 26.1 m/s were recorded at Ocean City Inlet. The storm occurred during spring tides (syzygy) and had a storm surge along the Delmarva Peninsula of 1.2 m. Two breaches were documented on Assateague Island by a USGS flyover on 6 November 2012. Once again, Swan Pool beach was breached. This breach had a maximum throat width of 30 m with a curvilinear geometry, and a shore-oblique orientation. Swan Pool beach has a width of 150 m and mean elevation of 1.5±0.5 m. This area is historically prone to breaching, with three documented events between 2010 and 2012. A second smaller breach with a throat width of 10 m occurred along the southern recurved spit of Assateague Island. This may be the first documented case of breaching within this zone. The geomorphic effects of Sandy were also characterized by large-scale overwash. A comparison of pre and post Sandy aerial photographs demonstrates large-scale washover deposits occurring within the Tom’s Cove area, as well as the northernmost sector of the island. These washover fans were much broader than those resulting from Hurricane Irene.