31 Coastal and Nearshore Processes Affecting Our National Parks

Monday, 15 March 2010
8:00 AM - 12:05 PM
Pratt A/B

HISTORICAL SHORELINE CHANGE ASSESSMENT FOR THE U.S. NEW ENGLAND AND MID-ATLANTIC COASTS

Paper number: 31-2
Program: Theme Sessions
Time: 8:05 AM – 8:25 AM

Authors

Abstract

The US Geological Survey has been compiling historical shoreline position data and assessing changes to the ocean coastlines of the United States as part of a nationwide study of coastal change hazards. To date, rates of shoreline change have been completed for sandy shorelines along the Gulf of Mexico, the Southeast Atlantic, California, and most recently, the New England and Mid-Atlantic regions, which extend from the southern border of Virginia to central Maine. Shoreline position data were compiled from NOAA T-sheets (1800s-1970’s), Global Positioning System field-based shoreline surveys (1990s-2000s), orthophoto-derived shorelines (1970s-2000s) and shorelines derived from LIDAR data (1990s-2000s). The Digital Shoreline Analysis System (DSAS v. 4.0) was used to calculate the shoreline rates of change in ArcMap. Long-term shoreline change rates (90+ yrs) were calculated using linear regression of several (≥4) historical shoreline positions and short-term rates were computed using only a shoreline from 25-30 years ago and the most recent position (end point rate).

The greatest erosion rates in the Mid-Atlantic are observed at the southern portion of the Delmarva Peninsula, in Virginia. The averaged long-term erosion rate for this subregion (from Wallops Island, VA to the Chesapeake Bay entrance) is -4.0±2.5m/yr. Retreat rates exceed -17±2.5m/yr along the southern ends of the Hog and Parramore barrier islands. In New England, the highest rates of change are found on the eastern shores of Cape Cod, Massachusetts. The high rates of change are found adjacent to dynamic shorelines that have experienced historic breaches, such as South Beach at Chatham Inlet, which has one of the largest short-term rates of retreat (-21.6±0.7 m/yr). The highest short-term accretion rates occur nearby, immediately to the south (58.9±0.7m/yr) due to the southern migration of the South Beach spit and welding to North Monomoy Island.

The shoreline positions and rates will be publically available for the New England and Mid-Atlantic regions as part of the U.S. Geological Survey’s National Assessment of Shoreline Change Project. The data, which has been compiled using a standardized method of mapping and analysis, can be used to quantify and understand the historical trends of shoreline change within these regions.