Army Corps plans to dredge lower Snake, Clearwater rivers

LEWISTON – The U.S. Army Corps of Engineers wants to dredge the ports of Lewiston in Idaho and Clarkston in Washington state as well as the shipping channel of the lower Snake and Clearwater rivers.

That’s according to a draft of the agency’s Programmatic Sediment Management Plan and environmental impact statement.

The agency doesn’t plan to raise levees in Lewiston to guard against flood risks, the Lewiston Tribune reported.

The release Friday of the document that exceeds 1,000 pages is being followed by a public comment period that begins next Friday. The document outlines the agency’s strategy of dealing with sediment accumulating behind the four lower Snake River dams.

Suspended sand and silt drops out of the Snake and Clearwater rivers when flows are slowed by the dams. The sediment clogs shipping channels and recreation sites, and reduces the ability of the rivers to contain floodwater.

Since 2005, the U.S. Army Corps of Engineers has been working on a plan to deal with the problem. At one time it looked like the agency might raise Lewiston’s levees about 3 feet, a possibility opposed by leaders in Lewiston concerned higher levees would cut off the community from its historic waterfront.

However, Richard Turner, project leader for the corps at Walla Walla, said studies indicate there has been no net accumulation of material in recent years in Granite Reservoir, and that no flood control action is needed in the foreseeable future.

“It is at an acceptable level right now,” he said. “We do not have to raise levees based on the conditions now.”

The agency plans to continue to monitor sediment levels for possible action in the future.

“That is what this plan does, provide tools for taking action,” said Sandy Sheline, environmental coordinator for the corps’ Walla Walla district.

Lewiston Mayor Kevin Poole said dredging should be the main option in reducing flood potential.

“Lewiston and Clarkston both always had a connection to the river,” he said. “To put that barrier there to me just doesn’t make sense when there are some other things they can do engineeringwise to handle the flood hydraulics.”

The plan calls for dredging, as soon as next winter, the shipping channel at the confluence of the Snake and Clearwater rivers, the ports of Lewiston and Clarkston and the approach to Ice Harbor Dam.