Preliminary Assessment of Sedimentation and Erosion in Eagle River Flats, South-Central Alaska

Abstract : The physical processes of sedimentation and erosion within the tidal mudflats and salt marshes of Eagle River Flats (ERF), an area used as an artillery impact range by the U.S. Army since 1945, must be understood to evaluate potential treatments of a high duck mortality resulting from ingestion of white phosphorus (WP) particles. The WP originates from smoke-producing devices detonated here. A preliminary assessment of erosion and sedimentation during May to September 1992 indicates that the physical system is complex and the intensity of these processes spatially variable. Deposition from suspension sedimentation generally varied with morphology and elevation, increasing inland from levees on the Eagle River (1 to 2 mm) across vegetated (3 to 6 mm) and unvegetated (5 to 12 mm) mudflats, and into ponds (10 to 19 mm) and salt marshes (10 mm). Resedimentation rates in ponds ranged from 8 to 16 mm. Recession rates of eroding gully headwalls were highly variable, ranging from negligible to over 3.9 m. White phosphorus particles may be in suspended transport through gullies during ebb. Further studies are necessary to better define annual sedimentation and erosion rates, with improved sampling techniques used at an expanded number of sites. Basic data on tidal inundation, sediment influx and efflux, and WP particle transport are required to develop appropriate treatment methods. Alaska, Estuary, Sedimentation, Cook Enlet, Fort Richardson, Subarctic, Erosion, Pollution, Tidal flat.