Dredging to deepen the navigation channel in the Snake and Clearwater rivers could begin as soon as this winter.
The U.S. Army Corps of Engineers found the work, which will remove an estimated 258,000 cubic yards of sand and other sediment from the channel and areas around the ports of Lewiston and Clarkston, will not significantly affect fish, water quality or the environment. The agency released an environmental analysis of the proposed work and its “finding of no significant impact” Thursday and has opened a 30-day public comment period.
The Corps is authorized by Congress to maintain the channel at a depth of 14 feet and width of 250 feet. It and the four dams on the lower Snake River make tug-and-barge transportation of commodities like wheat between the Tri-Cities and Lewiston possible.
But the Corps and other federal agencies are also tasked with minimizing impacts of the dams on threatened and endangered runs of Snake River salmon and steelhead. The two tasks often conflict, and past efforts to dredge the navigation channel have served as a proxy of the larger battle between fish and dams and whether the dams should be retained or breached.
Dredging last occurred in 2015 and was slowed by litigation.
The navigation channel regularly fills with sediment washed downstream from the mountains of Idaho, northeastern Oregon and southeastern Washington. The sand and silt settle out of the current when the flowing rivers, backed up by the dams, turn to slackwater.
According to the Corps’ environmental assessment, the channel at the confluence of the two rivers is only 9 feet deep in places and there are some places in front of the ports that are fewer than 4 feet deep. The agency is proposing to dredge the areas and dispose of the spoils at Bishop Bar, about 20 miles downstream of Lewiston and near Blyton Landing, where the river is about 68 feet deep. The agency maintains dredging is needed to keep navigation safe and efficient.
The channel and port areas are on a roughly 7-year dredging schedule. During the previous two dredging actions, the Nez Perce Tribe and environmental groups filed lawsuits attempting to halt the action. For example, in 2015 the tribe argued in court that the Corps had not adequately considered the harm dredging may cause to juvenile Pacific lamprey. A federal judge ultimately allowed the dredging to proceed.
The federal government’s plan to balance the functions of the dams with the needs of the fish calls for the Snake River to be maintained at what is known as a “minimum operating pool” — essentially, at the lowest elevation that still allows for navigation, hydropower production and fish ladders. Doing so incrementally increases the speed of the river and reduces travel times for migrating juvenile salmon and steelhead.
Over the past few years, the Corps has held the river three feet above the minimum operating pool because of the accumulation of sediment in the navigation channel.
Absent litigation or other delays, Corps officials hope to begin dredging this winter. The work must take place between Dec. 15 and March 1, when it is least likely to affect salmon and steelhead.
Alan W. Feistern, deputy district engineer for the Corps at Walla Walla, said via email to the Tribune the work is expected to cost between $5 million and $10 million. It will be paid for partially out of the Corps’ regular maintenance and operations budget and from the $550 billion Infrastructure Investments and Jobs Act approved by Congress and signed by President Joe Biden last year.
The ports are responsible for paying for the dredging to their berthing areas and access channels and obtaining their own permits for the work.
The draft environmental analysis and “finding of no significant impact” can be downloaded at bit.ly/3orkumM.