Dam operators struggling to avoid floods

BOISE – After six years of drought, a large snowpack has dam managers across southern Idaho trying to fill reservoirs without risking flooding areas downstream.

“There’s always risk and uncertainty when you’re dealing with Mother Nature,” said Brayton Willis of the Army Corps of Engineers, which coordinates operations of the three dams that control the flow of the Boise River through the state’s capital. “She’s given us a couple of storms that have put us in the situation that we’re in now.”

On Friday, the three reservoirs have about 100,000 acre-feet too much water in them for this time of year.

Two other reservoirs, Magic Reservoir near Twin Falls and Owyhee Reservoir in eastern Oregon near the Idaho border, have already filled. Managers looking to get rid of excess water include those at American Falls Reservoir on the Snake River near Twin Falls, Palisades Reservoir on the Upper Snake River in eastern Idaho, and the Little Wood Reservoir near Carey.

“Southern Idaho is where the problem is this year,” said Jay Breidenbach, a National Weather Service hydrologist in Boise.

Full reservoirs mean the dams can’t provide flood control.

“That’s a really serious situation if you have an uncontrolled flow,” said Breidenbach. “It doesn’t hurt the integrity of the dam, but you could end up with much more serious flooding if you have no control of the inflow.”

How much water is in a reservoir, and how much water in the snowpack that’s expected to make it to the reservoir, can be accurately determined. “The third variable is what will weather and climate conditions be like, say a month or two months in the future,” said Breidenbach. “That’s a lot less certain.”