A record-high water supply and high flows on the Kootenai River are expected to override a planned spill from Libby Dam to optimize spawning conditions for endangered white sturgeon.
A 2008 Libby Dam Biological Opinion settlement agreement requires the U.S. Army Corps of Engineers to conduct late spring “spill tests” to determine if additional flows from the dam’s spillway will cause changes in sturgeon migration and spawning behavior. The intent is for higher flows to induce adult sturgeon to move into a stretch of prime spawning habitat called the braided reach upstream from Bonners Ferry, Idaho.
But with high flows on the Kootenai River, spilling water in addition to powerhouse flows from Libby Dam is not expected to be necessary. The U.S. Fish and Wildlife Service is working with the Corps and other agencies to monitor the effects of this year’s high and prolonged flows on sturgeon spawning.
Snowpack in some parts of the Kootenai Basin has been as much as 180 percent of average. Combined with forecasted precipitation, that has prompted flood control operations at the dam.
To mitigate potential flooding from swift snowpack runoff, the Corps has been regulating discharges from the dam to maintain the river at or below flood stage at Bonners Ferry, and the Koocanusa Reservoir has been kept at a low elevation to provide storage for the spring runoff.
Reservoir inflows have recently been in the range of 50,000 cubic feet per second, but they are expected to increase to 90,000 cfs. The dam’s releases have been increased to 23,000 cfs, just short of its powerhouse capacity of 25,000 cfs.
The reservoir has been refilling at a rate of two to three feet per day, and that is expected to continue at least through mid-June. However, if inflows spike due to increased snowmelt, the reservoir could rise as much as six to eight feet per day.