COASTAL EVOLUTION IN THE COLUMBIA RIVER LITTORAL CELL

The Columbia River littoral cell, a 165-km long stretch of sandy barrier beaches and coastal plains separated by three large tidally dominated estuaries, has been characterized by shoreline progradation for the majority of the twentieth century. In the 1990s, several beach erosion crises threatened community infrastructure, resource-based industries, public access, and public and private property. Initial attempts to address these crises identified a paucity of basic data and information needed for decision-making on project engineering, resource management, and hazard mitigation. This need motivated the Southwest Washington Coastal Erosion Study, a multi-disciplinary investigation co-sponsored by the U.S. Geological Survey and the Washington Department of Ecology.

The study was designed to investigate the coastal region from a systems perspective and include assessments of the relative influences of sediment supply, regional tectonics, climatic forcing, and human intervention on the evolution of the coast. The primary goals of the study are to: understand regional sediment system dynamics; determine natural and anthropogenic influences on the littoral system; and predict coastal behaviour at management scales (i.e. decades and tens of kilometers).

The coastal system, including the estuarine flood and ebb delta shoals, the nearshore bars and inner shelf, and the shoreline evolve at all time scales from seasonal to decadal to millenia. These changes are predominantly linked to coastal oceanographic processes at shorter time scales, sediment supply at intermediate scales, and tectonics and sea-level rise at longer time scales.

Results of this study are now being used by state and local governments to aid in mitigating existing erosion problems, as well as in long-term planning for future coastal development. The science and products developed through the study serve as a basis for improved coastal management and policy at the local and state level, as well as support a better scientific understanding of the geologic and oceanographic processes responsible for large-scale coastal change.