HISTORICAL COASTAL CHANGE HAZARDS FOR THE UNITED STATES: INITIAL PROGRESS UNDER THE USGS NATIONAL ASSESSMENT

As growing population, sea level rise, and the potential for increases in the intensity of storms continue to threaten natural and developed coastal resources, it is increasingly important to understand historical coastal change. Shoreline change rates provide state and local authorities with information necessary to make informed land use decisions, to set development limits, and to establish economic and legal coastal policies. Since the last national compilation of historical shoreline change more than 20 years ago, significant coastal changes have occurred and new methods for delineating shoreline position and comparing shoreline rates of change have been developed.

The need for updated information regarding shoreline movement at a national scale prompted development of a long-term coastal change effort as part of the USGS National Assessment of Coastal Change Hazards. Primary objectives of this effort are 1) to provide an updated assessment of historical coastal change for the conterminous US and Hawaii, 2) to develop a standardized methodology for computing long-term shoreline change, and 3) to improve our understanding of the mechanisms forcing long-term coastal change. We are currently working on the first two objectives with an initial focus on the northern and eastern shores of the Gulf of Mexico coastline.

To maintain consistency and inter-comparability across diverse regions, we are using shorelines from 4 different time periods, i.e. mid-late 1800s, 1930s, 1970s and 1995 - 2000s, to compute long-term rates of change. Digital shorelines for the 3 earliest time periods, primarily derived from t-sheets, have been largely compiled from various state agencies and universities throughout the US. A digital shoreline for the most recent time period is being acquired with airborne lidar in cooperation with NASA. Products of this effort will include regional maps depicting rates of historical coastal change, written summaries of historical shoreline change rates for the nation, and a database that will be integrated with other information to improve our understanding of the mechanisms forcing long-term, large-scale coastal change.