GROUND PENETRATING RADAR AS A REGIONAL GEOMORPHIC MAPPING TOOL: SHORELINE ACCRETION/EROSION ALONG THE COLUMBIA RIVER LITTORAL CELL

Over the past century, the shoreline along the Columbia River littoral cell (southwest Washington to northwest Oregon) has been substantially accretional. Recently, however, the growth trend has slowed throughout the region and has reversed in at least one area (Grays Harbor jetties), yielding the potential for costly damages. The large study area and the lack of longterm (prehistoric) shoreline change data, created the need for a regional subsurface database. Therefore, an extensive ground penetrating radar (GPR) survey was conducted to study prehistoric and historic barrier accretion and erosion.

The goal of the Coastal Erosion Study is to provide solid technical data and analysis about the littoral system to local communities and agencies who, armed with the information, can tackle landuse decisions with a regional perspective. In addition, GPR imaging and radar facies analysis across the barrier complexes in the Columbia River littoral cell provide stratigraphic details of the coastal geomorphology and documents prehistoric and historic shoreline positions. The data also reveals regional variation in apparent barrier growth, which might reflect fundamental processes of net longshore transport, sediment supply, and response to co-seismic subsidence. The collected GPR profiles will also aid in sand volume budgeting of the Columbia River littoral cell.