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Toutle River sediment

Step 1 of the Corps of Engineers' volcano flood control plan is to raise the spillway of the sediment dam on the North Fork of the Toutle River.

Roger Werth / The Daily News

The U.S. Army Corps of Engineers’ final long-term plan for controlling sediment washing out of the Toutle River Valley has been delayed at least a year.

The delay will push back any flood control work until at least 2018, the agency said.

The corps had intended to issue a final environmental impact statement on its three-pronged plan this winter. Fisheries agencies want the corps to make sure it retains fish passage up the North Fork of the Toutle River and minimizes the impact of its work on endangered salmon runs.

“Because these are endangered species fish, we need to get a biological opinion from NOAA Fisheries,” Cowlitz-Toutle project manager for the corps Tim Kuhn said by phone Wednesday. “They have a disagreement on what they think we need to do or not do. We have to work through that process.”

Representatives from fisheries agencies did not return phone calls last week.

A 400-page draft version of the EIS released in August 2014 included a 21-year plan for managing sediment in the river to reduce floods risks along the Cowlitz River. Under the plan, the corps would roll out its plan in three phases:

• Raise the spillway of the existing sediment-retaining dam on the North Fork of the Toutle River up to 23 feet.

• Build weirs and other structures on the sediment plain above the dam to slow the Toutle and force it to drop silt.

• Dredge the Cowlitz River.

Controlling silt is vital to keeping it from clogging the Cowlitz. For now, Kuhn says, flood protection levels for lower Cowlitz River cities exceed authorized levels.

The corps built a 125-foot-tall dam on the Toutle’s north fork between 1986-1989 to trap sediment dumped into the valley during the May 18, 1980 eruption of Mount St. Helens. But debris filled the dam quickly, and the structure was essentially ineffective for more a decade. This forced the corps to find temporary measures to deal with the problem, including raising the spillway by 7 feet in 2012.

As additional material builds behind the dam, Kuhn said it could impact at least one of the North Fork tributaries where fish can be found.

“We’ve proposed to improve fish release sites. That’s a component of the mitigation. There’s a lot of interest by other entities that we should provide unconstrained fish passages,” Kuhn said.

The silt control plan was designed to be flexible to adapt to changing volumes of volcanic debris washing out of the Toutle River Valley. If the silt flow slows down significantly, parts of the $192 million plan may never be undertaken, according to corps officials.

An increase of 23 feet (combined with some additional work) would keep the dam passable for upstream-bound steelhead and salmon, according to the corps. This is an essential consideration to fishery agencies and the Cowlitz Tribe.

Kuhn said the agency is also working through all of the comments it received during the public comment period for the draft EIS while also working with NOAA Fisheries and the Washington Department of Fish and Wildlife on fish passage issues.

Contact Daily News reporter Shari Phiel at 360-577-2510 or sphiel@tdn.com.

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