Snake River sediment buildup may be slowing

The buildup of sediment on the bottom of the Snake River as it passes through northern Idaho and eastern Washington may be slowing, an official with the U.S. Army Corps of Engineers says.

The agency is drafting a plan to control the sediment buildup, alleviate flood risk and keep a viable shipping channel between the cities of Lewiston, Idaho, and Clarkston, Wash.

The accumulation of sediment where the river passes through Lewiston and Clarkston has long been on the upward trend, but there is some evidence that these levels may be flattening, said Carl Christiansen, the corps' leader on the project.

The more sediment that piles up at the bottom of the river as it passes through the two cities, the more shallow the water will become and eventually flow faster, Christiansen said.

A faster-flowing streams means the sediments would be suspended in the water longer, passing through the Snake River in Lewiston and Clarkston and dropping to the bottom farther downstream, Christiansen said.

"It's hypothetical," Christiansen told the Lewiston Tribune. "We know there is a physical limit at some point. We just don't know if we have reached it."

But Tom Dechert, who coordinates the storm water program in Lewiston, said the theory that the sediment buildup is on the decline has little evidence to back it up and he's not convinced the problem is going away.

While the Army Corps of Engineers predicts a faster-moving stream will carry more of the sediment to deeper parts of the river, the agency hasn't said where the sediment will end up, Dechert said.

"They didn't show me where it is going and that is what I'm concerned about," Dechert said.

The Army Corps of Engineers is in the process of a multiyear effort to study and manage the sediment buildup, Christiansen said. Researchers are now trying to get a better idea of how much sediment is coming into the water system and how it is deposited.

The corps has outlined a number of possible solutions, including dredging to limit the amount of sediment being delivered to the lower Snake River. Christiansen said a draft of possible solutions won't be completed until 2010.

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Information from: Lewiston Tribune, http://www.lmtribune.com