By Eric Barker
April 26, 2021
LEWISTON – The Army Corps of Engineers is operating the lower Snake River at a water elevation that decreases survival of protected salmon and steelhead but provides safer navigation conditions for tug and barge operators.
Fish managers have protested the move intended to increase the depth of the navigation channel near Lewiston and argued the needs of the fish should take precedence over transportation of grain and other products. For example, the Nez Perce Tribe suggested that river transportation be temporarily halted or the location of the shipping channel shifted to deeper areas of the reservoir as alternatives to raising the elevation.
“The point of our concern really kind of boils down to, yes, (navigation) is one of the many purposes the Corps of Engineers has for the system, but we are also dealing with fish listed under the Endangered Species Act here,” said David Johnson, director of the Nez Perce Tribe’s Department of Fisheries Resources Management. “In our mind, especially with as low as these (salmon and steelhead) returns have been the last several years, the Corps and (Bonneville Power Administration) could be giving a lot more consideration to how they are operating these dams.
“In times of healthy returns, (a trade-off like raising the river) is something that should be considered, but a trade-off in times of horrible returns shouldn’t be balanced on the backs of the fish.”
Dredging of the navigation channel last occurred in 2015. Since then, sediment at and near the confluence of the Snake and Clearwater rivers has accumulated to the point that, in some places, the channel no longer maintains its federally prescribed minimum depth of 14 feet, raising the risk of barges running aground.
Port of Lewiston Manager David Doeringsfeld said the turning basin in front of the port is also becoming shallow, but the berthing areas are sufficiently deep.
In response to the sedimentation, the Corps opted to raise the river above the elevation prescribed by the latest biological opinion – a federal document that spells out measures designed to ensure salmon and steelhead protected under the Endangered Species Act aren’t pushed further toward extinction.
The agency intends to keep the river 3 feet above that level, known as minimum operating pool, when flows are less than 50,000 cubic feet per second, 2 feet higher when flows are between 50,000 and 79,000 cfs, 1 foot higher between 80,000 and 119,000 cfs, and at the prescribed minimum operating pool when flows are 120,000 cfs or higher. At each of the levels, the agency is permitted 1½ feet of flexibility, meaning the elevation could be even higher at times.
“(The Corps) will operate Lower Granite Dam to temporarily hold water to a higher level when flows are low to maintain the federal navigation channel, until sediment can be removed,” agency spokesman Matt Rabe at Portland said via a prepared statement. “The District continues to develop plans to perform work to remove sediments which are impacting the federally authorized navigation channel.”
Juvenile salmon and steelhead depend on river current to flush them downstream. The biological opinion calls for a lower elevation from April 1 to Aug. 14 because it helps the reservoir to behave more like a free-flowing river.
“When the pool is lower, at minimum operating pool, that allows the fastest water velocity through the reservoir, which then results in faster fish travel time, which then results in higher survival,” said Jay Hesse, director of biological services for Tribe’s Department of Fisheries Resources Management. “As the pool elevation rises, the water velocity slows down and the fish travel time slows down and the survival decreases.”
Hesse said the Corps has agreed to try to shrink its 1½-foot operational flexibility down to 1 foot.
When the river hits the reservoir and its current slows, the sediment carried by the water drops out and accumulates on the bed. The agency typically dredges every seven to 10 years to clear the channel.
“Based on existing conditions and anticipated sedimentation, a dredging action to address immediate navigation needs is expected to be required to maintain safe navigation conditions while the other efforts are underway,” Corps spokesman Joseph Saxon at Walla Walla said. “In the meantime, the (Corps) will operate Lower Granite Dam to temporarily hold water to a higher level when flows are low to maintain the federal navigation channel, until sediment can be removed.”
Dredging is controversial. It adds to the cost of operating the federal hydropower system and some argue the in-water disposal of spoils in deeper areas of the reservoir downstream of Lewiston can harm protected fish as well as unlisted juvenile Pacific lamprey that live in the sediment. Fish advocates, including the Nez Perce Tribe, have gone to court in the past to stop dredging.