'Stacked flows' begin for endangered sturgeon

Releases from Libby Dam will be up to full powerhouse capacity of about 25,000 cubic-feet per second by Wednesday morning as "stacked flows" for the endangered white sturgeon begin.

Last week, the U.S. Army Corps of Engineers announced in a public meeting that the sturgeon recovery team had agreed to the stacked flows so as not to spill water from Libby Dam, which has a detrimental effect on the local fishery. The stacked flows provide full powerhouse capacity from the dam atop the natural peak runoff of streams and rivers below the dam to provide deeper water in the Kootenai River downstream of Bonners Ferry where the sturgeon spawn. Recovery efforts are trying to create 23 feet of depth in the river for the sturgeon.

Eventually, the Corps will do some dredging and construction on the river bottom to assist the sturgeon.

The U.S. Weather Service reported Monday morning that warmer weather is accelerating the runoff of area snowmelt swelling local streams and rivers. The Yaak River, which came within a foot of flood stage two weeks ago, is forecast to be near flood stage by the end of the week.

The river was at 6.19 feet on the flood gauge with 8 feet considered flood stage. The river was flowing at 2,680 cfs on Monday afternoon, about 1,000 cfs below the mean and well below its maximum recorded flows of about 11,200 cfs.

The Corps began ramping flows up from the dam towards full powerhouse capacity on Sunday boosting releases from 4,000 to 5,000 cfs and then up again to 10,000 cfs by Monday morning and 20,000 cfs by Tuesday.

It is expected that releases from the dam will remain at 25,000 cfs for two weeks for the sturgeon augmentation flows and longer if reservoir elevation management is needed. Corps officials said they will not exceed the river elevation 1,764 feet above sea level at Bonners Ferry.

"Biologists and water managers will re-assess the shape of augmentation flows after a peak in local inflows downstream of the dam has been observed, and will make adjustments as necessary as the sturgeon volume is expended," said Greg Hoffman, fishery biologist at Libby Dam.

Bioloigsts will be looking at water temperature, creation of a receding hydrograph limb, inflow forecast and reservoir election, sturgeon spawning response and other sturgeon needs, he said.

The Corps is using the selective withdrawl system at the dam to control water temperature on the releases for the downstream sturgeon as well as resident fish in the Kootenai River.