DIGITAL SHORELINES AND GIS: A SEMI-QUANTITATIVE EVALUATION OF FRAMEWORK GEOLOGIC INFLUENCES ON HISTORICAL SHORELINE CHANGE RATES

This study presents a statistical comparison of historical shoreline changes to framework geology and coastal geomorphology along a portion of the South Carolina coast. Situated along a dominantly mainland attached barrier system, we utilize a wide array of directly and remotely sensed geological framework data collected as part of a larger coastal erosion program. Using a geographic information system (GIS), shoreline positions have been gathered from historical data, aerial photography, and LIDAR surveys. The framework geology data that define and categorize the near-surface geologic architecture have been incorporated into the GIS and include geomorphic parameters; subbottom profile surveys; sidescan sonar mosaics; vibracore, geoprobe, and rotosonic cores; and exposures on- and offshore. These data in turn have been reduced into interpreted geologic data layers, cross-sections, and volumes.

Scripts and extensions for ArcView currently being used in the USGS National Shoreline Change Program were modified to collect shoreline, framework geology and geomorphic data at 50-m intervals along the coastline. The integrated geologic framework data and the shoreline change parameters were extracted from these transects and statistically compared using principal components analysis and discriminant analysis to more clearly categorize relationships between historical shoreline change trends and framework geology.

Outside areas typically associated with hot spots of erosion (e.g. tidal inlets), critical trends in shoreline change point to non-hydrodynamic influences as a major source of variance in shoreline change trends. These influences include modern dune ridge truncation, intersection of the coast to obliquely trending Pleistocene beach ridges, and proximity to partially indurated strata in the near surface. These influences can be seen at typically block-scale or smaller regions. Continued studies combining high-resolution subaerial and submarine subsurface stratigraphic data with high-resolution shoreline and shoreface change models will further help communities mitigate future and imminent coastal issues. This project has been created through a cooperative arrangement between the U.S. Geological Survey, South Carolina Sea Grant Consortium, and academic institutions in South Carolina and Georgia.