SEATTLE – Water managers at the U.S. Army Corps of Engineers, are actively managing outflows from Libby Dam to reduce downstream flood risk and have scheduled sturgeon flow increases to begin May 15.
The Corps reduced outflows from Libby dam for 18 hours starting in the evening Wednesday May 9th to minimize short term flood risk while maintaining a manageable refill rate. Current inflow at Libby Dam is approximately 55,000 cubic feet per second and outflow was held to 6,000 cfs while inflows downstream of Libby Dam had the potential to pose a flood risk at Bonners Ferry. Water managers returned outflows to 9,800 cfs on Thursday.
Elevation at Koocanusa Reservoir is 2,383 feet and it has been rising 2-3 feet per day during the past week. The reservoir is expected to continue rising by 1-3 feet per day through the end of the month
Along with federal, tribal, and state fishery biologists, have determined that spring run-off conditions warrant the commencement of required flow augmentation at Libby Dam, Montana, for endangered Kootenai River white sturgeon downstream in Idaho. The flow augmentation operation will increase Libby Dam discharge during May and June in an effort to provide river conditions that may increase sturgeon spawning success in the lower Kootenai River in Idaho.
Sturgeon flow augmentation will begin May 15, after local Kootenai River tributaries downstream of Libby Dam are forecasted to peak. The Corps considered impacts downstream, including river levels at Bonners Ferry and Kootenay Lake elevations, and worked with the regional team of sturgeon biologists to select this date. The sturgeon flow augmentation plan this year is to ramp up Libby Dam discharge over a one week period to 20,000 cubic feet per second, and then hold that flow for about three weeks. Due to above-average snowpack and high runoff conditions this year, water managers may need to increase Libby Dam discharge up to full powerhouse capacity, approximately 25,000 cfs, to manage the rate of refill of Lake Koocanusa.
The sturgeon flow augmentation operation is part of a collaborative, ongoing effort by regional biologists to enhance spawning and migration conditions for sturgeon in the Kootenai River near Bonners Ferry, Idaho. Increased flows are intended to provide river conditions that may increase sturgeon migration to the reach of river upstream of Bonners Ferry in habitat thought to be conducive to successful spawning, egg hatching, and survival of larval sturgeon. While the Kootenai Tribe of Idaho’s conservation aquaculture program has steadily increased the number of young sturgeon in the river since 1992, federal, state, and tribal partners have collaborated in recent years to construct instream habitat upstream of Bonners Ferry intended to provide conditions that will allow adult sturgeon to successfully reproduce on their own.
The sturgeon operation requires a volume of water to be released from Libby Dam based on the May water supply forecast for Lake Koocanusa. The May water supply forecast for the April to August inflow volume is 7.4 million-acre-feet, or 125 percent of average; which sets this year’s sturgeon volume at 1.20 million-acre-feet.
The dam’s flow and stage projections are based on National Weather Service ensemble forecasts and are updated frequently during runoff season as weather and conditions change. Forecast modeling includes information on elevations, outflow, and Bonners Ferry seasonal elevation and peak height for the year. To see the latest projections, visit: http://1.usa.gov/1kP1lSH.
The U.S. Army Corps of Engineers' primary consideration in operating Libby Dam is to minimize risk to human life, health, and safety, while meeting the dam’s multiple purposes and responsibilities. The Corps will closely monitor Kootenai River elevation in Bonners Ferry during the sturgeon flow augmentation and will adjust operations with the aim of staying below 1,764 feet, the local flood stage.