Draft Supplemental Environmental Assessment to Fiscal Years 2012 Through 2019 Maintenance Dredging of the Upper Duwamish Waterway for Spokane Street Bridge Shoal.

摘要

This Supplemental Environmental Assessment (EA) evaluates the environmental effects of shoal removal in the Lower Duwamish Waterway opposite the southwestern shore of Harbor Island in the vicinity of the Spokane Street Bridge, slightly over one mile upstream of where the Duwamish Waterway (West Waterway) enters Elliott Bay. The project site is located in the industrial district of Seattle, about two and one-half miles south of downtown Seattle in King County, Washington. The Duwamish Waterway is a constructed channel within the Duwamish River that was built by the U.S. Army Corps of Engineers (Corps). Construction and deepening of the Duwamish Waterway straightened the original meandering channel of the Duwamish River to allow access by deep draft vessels. The Duwamish Waterway is important to commerce including cargo receiving and exporting, boat building, vessel repair, and vessel storage. The Corps periodically removes accumulated sediment from a settling basin at the upstream end of the Duwamish Waterway (Corps 2011a) in an effort to minimize maintenance dredging in the lower portions of the waterway. The area around the Spokane Street Bridge has not been dredged for at least 80 years. Over that time a shoal has developed that is causing cargo vessels to be light loaded (reducing vessel draft) which costs local businesses time and money.