Portland, Ore. -- Water managers and dam operators with the U.S. Army Corps of Engineers may further increase water levels behind Libby Dam beyond normal maximum elevations in an effort to reduce flooding impacts along the Kootenai River in Montana, Idaho and British Columbia.
This is the second time in the past week the Corps has decided to exceed the normal elevation behind Libby Dam, located in western Montana, to aid in reducing downstream flooding. The region experienced record rainfall in June, in excess of 400 percent of normal in some places.
The Corps, which operates the dam, coordinated an additional action Monday night with BC Hydro to store additional water in Koocanusa Reservoir up to elevation 2,461 feet, if necessary, to reduce flooding downstream on the Kootenai River and Kootenay Lake. 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.
A similar coordination took place last week when the two countries agreed to temporarily increase the storage level to 2,460 feet. The normal maximum elevation for Koocanusa Reservoir is 2,459 feet.
Current inflow at Libby Dam is about 60,000 cfs. Outflows from Libby Dam increased from 46,000 cfs to 48,000 cfs at 6 p.m. MDT Monday night. Elevation at Koocanusa Reservoir is 2,459.2 feet, which is 0.2 feet above the normal maximum reservoir elevation. It has been rising about 0.5 feet per day over the past several days despite very high releases from the dam. The Corps will hold releases at 48,000 cfs to help manage downstream flooding and will operate Koocanusa Reservoir up to as high as 2,461 feet, if needed.
This coordination to allow up to two feet 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 0.4 feet and the lake level at Kootenay Lake by as much as 0.1 feet compared to the operation that would occur if the maximum elevation was limited to 2,460 feet. How much of this additional foot of reservoir storage space is actually utilized will depend on future runoff conditions.
The current river stage at Bonners Ferry is 1766.3 feet; flood stage is at 1764 feet. The current elevation at Queens Bay is 1,753.8 feet, the highest level since 1974.
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 natural channel constriction at Grohman Narrows.
Record rainfall soaked the basin in June. At Bonners Ferry, June precipitation totaled 5.24 inches, more than 315 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. 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.