Shoreline Response to Offshore Shoals and Storms, Low Beach, Nantucket, MA

Low Beach is located on the southeast side of Nantucket Island, which is approximately 20 miles offshore from the Cape Cod mainland. It is currently the site of a municipal wastewater treatment facility for the Town of Siasconset. This study investigated relationships between erosion at Low Beach and changing offshore bathymetry. An analysis of historical and recent shorelines was conducted to quantify the trends of shoreline change for the study area. Additionally, the forcing functions responsible for shoreline change at the site were evaluated. Incident wave climatology and storm frequency (tropical and extra-tropical) were compared to observed changes in the shoreline. Bathymetric data offshore of the site were collected to provide the morphology and location of offshore shoals. These bathymetric data were compared with bathymetry taken from historical nautical charts to investigate the the impacts of changes in shoal morphology and location on shoreline change. Analyses of wave refraction patterns at the site suggest a linkage between changing offshore shoal conditions and episodic erosion at the study site. A cause and effect relationship was established between shoreline erosion and changes in offshore shoal positions. However, it was not possible to link erosional events at the study site to changes in incident wave climatology or to changes in storm intensity or frequency.