Sturgeon flows incorporated within flood management operations at Libby Dam
by U.S. Army Corps of Engineers
May 27, 2011
While the U.S. Army Corps of Engineers continues to regulate Libby Dam for flood risk management, conditions are such that many attributes for a previously planned sturgeon spill are likely to be achieved without spill.
The 2008 Libby Dam Biological Opinion Settlement Agreement requires the Corps to conduct a late spring "spill test" to determine if additional Kootenai river flows will cause changes in the sturgeon's migration and spawning behavior. It is hoped that increased flow will ultimately coax Kootenai sturgeon to migrate to, and spawn over, rocky substrates that exist upstream of Bonners Ferry, Idaho.
However, since current record-high water supplies in the Kootenai River basin are likely to increase flows beyond what had been planned for with a "spill test," discharges in addition to powerhouse flows from Libby Dam may not be necessary. The U.S. Fish and Wildlife Service is working with the Corps and others to monitor the effects on endangered Kootenai River white sturgeon.
Unusually high snowpack, as much as 80 percent above average in some areas of the Kootenai River basin, combined with forecasted precipitation, have increased the risk of flooding downstream of the dam in Libby, Mont.
To mitigate potential flooding from swift snowpack runoff, the Corps is regulating discharges from the dam to maintain the Kootenai River at or below flood stage elevation of 1,764 feet at Bonners Ferry, beginning May 28. By keeping the river at or near flood stage in June, Koocanusa Reservoir will have more space available for late season snowmelt or rain inflows.
Inflows to the dam are approximately 50,000 cubic feet per second and discharges are 16,000 cfs. Inflows are predicted to increase to more than 90,000 cfs in the coming days. This weekend releases will increase to approximately 23,000 cfs.
Koocanusa Reservoir is currently refilling at a rate of two to three feet per day, which is expected to continue at least through mid-June. However, if inflow rates spike from increased snowmelt, the reservoir could rise as much as six to eight feet per day as more inflows are held behind the dam to prevent flooding downstream.
The Corps' primary consideration in operating Libby Dam is minimizing risk to human life, health and safety, while meeting the project's multiple purposes. Flood risk management operations at the dam always take precedence over sturgeon operations.
Residents and businesses in the river basin should continue to be prepared for potential flooding as snowpack begins to melt. As flows approach flood stage, the National Weather Service and downstream communities have plans in place to promptly alert potentially affected people about the situation and what action to take. Citizens are encouraged to contact local emergency managers and work with them to determine the best path to prepare for potential flooding.
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