Dredging Of Lower Snake River Channel, Ports, Begins This Month, First Time Since 2015

Dredging will begin in areas of the lower Snake River this month that will solve an issue raised in recent years by federal, state and tribal fisheries managers – how to drop the Lower Granite Dam pool to improve summer conditions for salmon and steelhead that are at risk at the same time the Port of Clarkston needs more depth in the river to unload barges. 

The U.S. Army Corps of Engineers says it will spend $5.8 million of Corps and federal Infrastructure money on the dredging and will begin this month upstream of Lower Granite Dam at the confluence of the Snake and Clearwater rivers near Clarkston, WA and Lewiston, ID. In addition, it will dredge downstream of Ice Harbor Lock and Dam near Pasco, WA. Dredging in both areas is needed to remove accumulated sediment from the federal navigation channel, to deepen the channel and to dredge sediment from the port.

Alex Colter, the Corps’ dredging project manager, said the money to pay for the project comes from a combination of Corps Operations and Maintenance funds and from the Bipartisan Infrastructure Law fund. The money was allocated in May 2022.

Further, the area being dredged near Ice Harbor Lock and dam will use $60,000 from Corps Operations & Maintenance funds and the area near the confluence of the Snake and Clearwater Rivers near Clarkston, WA and Lewiston, ID will use funding predominantly from the Bipartisan Infrastructure Law, Colter said.

The Corps at times operates the Lower Granite Dam reservoir level at minimum operating pool (MOP) plus an additional three feet to ensure it can maintain a 14-foot depth in the federal navigation channel at the Port of Clarkston, a multi-year issue that arises when Snake River flows are low. Silting and shallow water in the Port prevents barges from fully-loading.

When the MOP +3 operation is put into effect by the Corps, fisheries managers grow concerned about the effects of a higher and slower pool on juvenile salmon and steelhead travel times through the four lower Snake River dams. They also get concerned that the slower and larger pool heats up faster than would a smaller faster-flowing pool.

In the past, when fisheries managers have asked the Corps to lower its elevation back to minimum pool, the Corps has said no because of the impacts on navigation and the ports’ operations (including the Port of Lewiston).

All dredged sediment will be disposed of at an in-water location near Bishop Bar (north shore) located at River Mile 118 on the lower Snake River in Washington, the Corps said. The contract for the dredging was awarded to HME Construction Inc., a general contractor in Vancouver, WA. Work will begin this month and be done during the in-water work window Dec. 15, 2022 to March 1, 2023.

In July, the Corps released a Draft Finding of No Significant Impact and the Lower Snake River Channel Maintenance Immediate Need Dredging for Commercial Navigation Environmental Assessment and opened public comment for 30 days.

In the FONSI it proposed to dredge this winter to meet the immediate need of providing a 14-foot navigation channel depth as measured at minimum operating pool (MOP) at four locations in the lower Snake River and lower Clearwater River. One site is the downstream navigation lock approach for Ice Harbor Dam, while the other three sites are located at the confluence of the Snake and Clearwater rivers in the Lower Granite reservoir.

Although the ports of Clarkston and Lewiston are responsible for dredging at their respective berthing areas (50 feet in front of any dock/terminal), the Corps included such dredging in its proposal. The ports will fund that portion of the work.

The footprint for dredging the federal navigation channel is smaller than it has been in the past, according to the draft FONSI. Due to the decreased navigation channel footprint and location, it is now necessary to dredge access channels to connect the navigation channel to the Port of Clarkston docks. The Port of Clarkston and the Port of Lewiston dock berthing areas will also be dredged.

Channel maintenance by dredging has occurred periodically since 1961 but has not been done since the Dec. 4, 2014 to March 15, 2015 timeframe, Colter said.

Shoaling in the channel and port berthing areas has become critical in the channel and at the Snake/Clearwater confluence. Survey results from 2021 show that areas shallower than 14 feet where the dredging will occur (at minimum operating pool) have increased since 2015. Some areas at the confluence are as shallow as 9 feet. The berthing areas at the Port of Clarkston and Port of Lewiston are now as shallow as 4 feet and 11 feet, respectively, based on a MOP water surface elevation.

A biological assessment by the Corps has documented potential impacts to ESA-listed species that may occur from these maintenance activities. Up to 300,000 cubic yards of sand, silt, and gravel/cobbles, across 100 acres, will be dredged. The dredged sediment will be disposed of in water at one site.

The proposed action: may affect, and is likely to adversely affect Snake River spring Chinook, Snake River fall Chinook, Snake River B-steelhead, and bull trout; may affect, but is not likely to adversely affect Snake River sockeye; may affect, and is likely to adversely affect designated critical habitat for Snake River spring Chinook, Snake River fall Chinook, Snake River B-steelhead, Snake River sockeye, and bull trout, according to the draft FONSI.

The Corps is authorized by the Flood Control Act of 1952 to maintain a 14-foot-deep, and 250 feet wide, federal channel, with wider areas authorized at bends and turning places to support the safe, efficient movement of vessels. The 14-foot minimum depth is required to safely pass large boats and barges.

For background, see:

— CBB, JULY 28, 2022, CORPS SEEKING COMMENT ON PROPOSAL TO DREDGE NAVIGATION CHANNEL IN LOWER GRANITE DAM RESERVOIR, PORTS’ BERTHING AREAS, HTTPS://CBBULLETIN.COM/CORPS-SEEKING-COMMENT-ON-PROPOSAL-TO-DREDGE-NAVIGATION-CHANNEL-IN-LOWER-GRANITE-DAM-RESERVOIR-PORTS-BERTHING-AREAS/

— CBB, August 13, 2020, RIVER MANAGERS REJECT REQUEST TO RAISE LOWER GRANITE POOL TO AID BARGE LOADING AT CLARKSTON PORT; CONCERNS ABOUT TEMPERATURE IMPACTS TO SALMON, HTTPS://CBBULLETIN.COM/RIVER-MANAGERS-REJECT-REQUEST-TO-RAISE-LOWER-GRANITE-POOL-TO-AID-BARGE-LOADING-AT-CLARKSTON-PORT-CONCERNS-ABOUT-TEMPERATURE-IMPACTS-TO-SALMON/

— CBB, August 11, 2017, TEMPERATURES TO COOL IN LOWER SNAKE RIVER, RIVERBOAT NEEDS HIGHER POOL AT PORT OF CLARKSTON https://www.www.www.columbiabasinbulletin.org/temperatures-to-cool-in-lower-snake-river-riverboat-needs-higher-pool-at-port-of-clarkston/

— CBB, Feb. 27, 2015, CORPS DREDGING OF FEDERAL NAVIGATION CHANNEL COMPLETED FOR SNAKE, CLEARWATER RIVERS, TWO PORTS https://www.www.www.columbiabasinbulletin.org/corps-dredging-of-federal-navigation-channel-completed-for-snake-clearwater-rivers-two-ports/

— CBB, Feb. 12, 2016, FEDERAL JUDGE UPHOLDS CORPS’ LOWER SNAKE RIVER SEDIMENT MANAGEMENT PLAN (DREDGING) https://www.www.www.columbiabasinbulletin.org/federal-judge-upholds-corps-lower-snake-river-sediment-management-plan-dredging/

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