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U.S. and Canada coordinating to reduce flood impactsPosted: June 29, 2012
Water managers and dam operators may exceed normal water level limits behind Libby Dam in western Montana in an effort to reduce flooding impacts along the Kootenai (Kootenay) River in Montana, Idaho and British Columbia, announced the US Army Corps of Engineers Northwestern Division June 28.
The U.S. Army Corps of Engineers, which operates the dam, coordinated the action with BC Hydro to store additional water in Koocanusa Reservoir up to elevation 2,460 feet, if necessary, to reduce flooding downstream on the Kootenai River and Kootenay Lake. The normal maximum elevation for Koocanusa Reservoir is 2,459 feet. Because the Columbia River Treaty also has requirements for the operation of Libby Dam, the Corps and BC Hydro have coordinated this action with their respective entities under the Treaty.
Current inflow at Libby Dam is approximately 70,000 cfs. Outflows from Libby Dam increased from 40,000 cfs to 42,000 cfs at 7 p.m. MDT Wednesday night (June 27) and again to 46,000 cfs at midnight. Elevation at Koocanusa Reservoir is 2,456.7 feet and it has been rising 1-1.5 feet per day since June 23. The Corps will hold releases at 46,000 cfs with the potential of exceeding elevation 2,459 feet in Koocanusa Reservoir.
This coordination to allow up to one foot above the normal maximum will enable the Corps to maintain a lower release from Libby Dam than would otherwise be required. It is estimated that this may reduce the river stage for the Kootenai River at Bonners Ferry by as much as .2 feet and the lake level at Kootenay Lake by as much as .2 feet compared to the operation that would occur if the maximum lake elevation was limited to 2,459 feet. Whether this additional foot of reservoir storage space is actually utilized will depend on future runoff conditions.
A number of actions are underway to minimize flood damage in both countries. BC Hydro continues to hold the Duncan Dam discharges at minimum, reducing flows into Kootenay Lake. BC Hydro and FortisBC continue to discharge the maximum amount from Kootenay Lake, limited only by the channel constriction at Grohman Narrows. All of these actions are helping to reduce flooding and minimize damage in the Kootenai River system.
Record rainfall has soaked the basin in June. At Bonners Ferry, current precipitation for the month of June is 5.2 inches, more than 300 percent of the June average which is 1.66 inches. The previous June record for precipitation at Bonners Ferry was set in 1981 when it was measured at 3.96 inches.
Heavy June rainfall in the Kootenai Basin also resulted in a high water level on Kootenay Lake, downstream of Libby Dam. The current elevation at Queens Bay is 1,753.1 feet, the highest level since 1974. Libby Dam operations are being managed to reduce downstream flood damage for both the Canadian and U.S. portions of the Kootenai Basin.
Residents and businesses in the river basin should be prepared for potential flooding. 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.
US Army Corps of Engineers
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