Deepening of navigation channel will allow lower Snake River to operate at lower levels

The completion of sediment removal in Lower Granite Reservoir will make it easier to navigate for large crafts and small critters alike.

On Friday, the Walla Walla District of the Army Corps of Engineers announced dredging at the top end of the reservoir where the Snake and Clearwater rivers meet and the ports of Lewiston and Clarkston are sited is complete.

The agency hired HME Construction of Vancouver, Wash., under a $5.8 million contract to remove about 258,000 cubic yards of accumulated sediment from the navigation channel. The ports kicked in additional money to have sediment cleared from their dock and birthing areas.

The work will benefit ocean-bound juvenile salmon, barges hauling wheat headed for overseas markets and cruise ships calling on the Lewiston-Clarkston Valley.

With the navigation channel restored to a minimum depth of 14 feet, barges can be loaded more quickly at the ports. Hazards will be fewer for tug and cruise boat captains.

Juvenile salmon will benefit in another way. The river was last dredged in 2015. But it didn’t last long. High flows in subsequent years so choked the navigation channel and port areas with muck that the corps, at the request of ports and shippers, began raising the elevation of the reservoir to at least 736 feet above sea level to make it easier and safer for large vessels to maneuver.

But that was bad news for juvenile salmon and steelhead, many of which are protected by the Endangered Species Act. Each spring, millions of hatchery and wild salmon and steelhead migrate downstream to the ocean. The trip that once took days before dams slowed flows on both the Snake and Columbia rivers now takes weeks.

A federal plan intended to balance power and navigation with the needs of the fish, calls for the river to be operated at a lower level, roughly 733 to 734.5 feet above sea level, during juvenile fish migration season. Doing so slightly speeds the pace of the river and that helps shorten the time it takes the young fish to progress downstream.

But when the needs of navigators bumped up against the needs of fish, the corps chose navigators. Since at least 2020, the river has been held artificially high during fish migration season.

With dredging complete, the river now can be operated at levels not seen in at least the last two years.

“By bringing the reservoir back down it should help,” said Jonathan Ebel, a fisheries biologist with the Idaho Department of Fish and Game. “It will decrease fish travel time a little bit.”

In a short news release, the corps said the reservoir’s elevation can now fluctuate between 733 and 738 feet over the course of the years. When it’s at its lowest levels, it may affect marinas and boat ramps on the river, according to the news release.

Barker may be contacted at ebarker@lmtribune.com or at (208) 848-2273. Follow him on Twitter @ezebarker.