Engineer Warns About Release Of Sedmient Dam Breaching Could Free Millions Of Cubic Yards Of Silt

Punching holes in four Snake River dams could unleash 75 million cubic yards of mud into Lake Wallula, an engineer said at a public hearing.

That raises concerns that too much mud could harm irrigators, not to mention the salmon that are the focus of dam-breaching discussions.

Some worry that dismantling the dams would interfere with fall Chinook swimming through work areas to spawn.

Confusion about what’s best for Snake River salmon didn’t clear up during Wednesday’s meeting arranged by the U.S. Army Corps of Engineers.

The corps is evaluating three options to help fish stocks survive: doing nothing, breaching the dams at a cost of $500 million to $850 million, or creating devices that will move fish past dams with less death and delay. The agency’s report is due next year.

Breaching the dams would return the river to a more natural state. Lower, faster waters are thought to be best for fish making their way to the ocean.

There is little doubt that the Snake River and Lake Wallula will get muddier if the dams are removed.

Gene Spangrude, corps engineer, said between 100 and 150 million cubic yards of sediment have been deposited in the reservoirs behind dams since they were constructed in the 1960s and 1970s.

Spangrude estimates that in the first few years after breaching the dams about half of the sediment - as much as 75 million cubic yards - will travel downstream.

One million cubic yards covers a square mile one foot deep.