Shoreline position and coastal topographical change monitoring at Assateague Island National Seashore: 2005–2020 trend report

Abstract

This trend report summarizes the results of shoreline position and coastal topography surveys conducted semi-annually from the spring of 2005 through the fall of 2020. Shoreline position was collected in the Assateague Island National Seashore (ASIS), the Assateague State Park, and the Chincoteague National Wildlife Refuge, whereas coastal topography was collected only in the Assateague Island National Seashore and the Assateague State Park. The assembled datasets are processed to provide spatial depictions and statistical analyses of annual changes, 5-year changes, and the extended 15-year changes. Although there were considerable variations in the alongshore dimensions of change, the largest and most consistent vectors of annual shoreline position and coastal topography changes were produced by storm impacts, such as Hurricane Sandy and the winter storms in 2016, followed by the subsequent recovery. As a result of Hurricane Sandy (October 2012), the entire oceanside shoreline position of Assateague Island was displaced inland, and there was a loss of total cross-section area in the profiles. There was variable recovery post-Hurricane Sandy in both the shoreline position and coastal topography profiles. The winter of 2016 was also particularly stormy and had a higher mean net landward shoreline position displacement than post-Hurricane Sandy. Throughout the survey period, the termini of the island were exceptionally dynamic. The northern 2.5 km of Assateague Island National Seashore had a mean net seaward displacement, whereas the southern portion of the Chincoteague National Wildlife Refuge was the site of major inland displacement along the oceanside and as well as downdrift seaward extension of Toms Cove Hook. From 2005 through 2020, the only section of the oceanside shoreline position that had a positive trend of mean net displacement was the northernmost portion of Assateague Island, associated with local conditions created by the presence of the ebb tide delta and the Ocean City inlet jetty. All other parts of the ocean shoreline position had a negative trend of change; the highest rate of erosion occurred at the southern portion of Chincoteague National Wildlife Refuge. Contrary to the oceanside shoreline position, a portion of the Toms Cove Hook shoreline had a trend of seaward displacement as the spit extended in the direction of sediment transport. Other trends occurred in the areas where profiles were surveyed. Most of the dune area in ASIS gained in cross-section over time, except for portions of Assateague State Park. The dune elevation tended to gain in ASIS North and lower in ASIS South. Other than the profiles in Assateague State Park, the total cross-section area increased, with the highest rate of cross-section area gain in the northern portion of Assateague Island.