Breach studies: Surge of sediment, no lasting damage

March 15, 2008

By Michelle Ma

Triplicate staff writer

Studies compiled by the California Coastal Conservancy offer an initial look at what might be the most feasible option for removal of the Klamath River dams.

The best sequence and timing for dam removal hasn't been finalized, and the state agency acknowledges these ideas are in need of more extensive research before dam removal is possible.

Still, many involved with the studies say they are confident that dam removal is affordable and feasible.

But PacifiCorp and some opponents of dam removal contend that these studies don't provide enough proof that pulling the dams is the preferred option.

Here is a look at some recommended actions.

Before the four dams are removed, the reservoirs behind them should be drained to pull downstream sediment that has accumulated behind the dams.

Sediment would make the water downstream very turbid after the fine materials are released, so scientists think it would be best to flush a good portion down all at once, instead of repeatedly hitting the lower river with sediment over a longer period.

"Biologically speaking, it's better to have one really bad event than 100 bad events," said Michael Bowen, project manager for California Coastal Conservancy's North Coast work group.

More than 20 million cubic yards of fine sediment is thought to be behind the dams, but only 4 million is predicted to actually flow downstream.

Still, that sediment would probably kill wildlife it comes in contact with in the river down to the ocean, Bowen said.

"There's just no doubt that the main stem, for that short period of time, would not be a hospitable environment," Bowen said. "It's safe to say that very little is going to be able to survive that level of turbidity."

Some fish experts are confident the sediment forced downstream wouldn't hurt fish long-term. But short-term impacts of dam removal must be further studied, including the ideal time to flush sediment down the river to affect as few fish as possible, said Troy Fletcher with the Yurok Tribe.

"There's not going to be any long-term, lasting negative impacts. We believe that, of course, or we wouldn't be doing it," said Fletcher, who has worked in fisheries since the early 1980s. "We know the Klamath River will be able to heal itself."

The water draw-down rate in each reservoir would have to be balanced so that erosion and flooding do not occur.

The dams as they stand are not used for flood control, so their removal would not make the basin more vulnerable, officials said.

After the reservoirs are drained, Copco 1 and Copco 2 would be drilled, filled with explosives and blasted to pieces. Earth-filled Iron Gate and J.C. Boyle dams would be excavated with mechanical equipment.

Pieces of the dams would be moved away from the river, later to be disposed of or recycled.

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Source:  http://www.triplicate.com/news/story.cfm?story_no=7986