SEATTLE -- Water managers at the U.S. Army Corps of Engineers, 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 includes increasing outflows to provide river conditions that may increase sturgeon spawning success in the lower Kootenai River.
Outflows will increase May 16 as local Kootenai River tributaries downstream of Libby Dam are forecasted to peak. Discharge from Libby Dam will increase to full powerhouse capacity, approximately 25,000 cubic feet per second (cfs), for about three weeks, followed by a week of 20,000 cfs flows. Once the flow augmentation operation is complete, outflows will decrease to a summer flow no less than 9,000 cfs, the bull trout minimum flow associated with Koocanusa Reservoir’s inflow forecast.
The sturgeon flow augmentation operation is part of a collaborative, ongoing effort by regional biologists to enhance migration and spawning 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 known 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, both wild and those released into the river through the conservation aquaculture program, 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 Koocanusa Reservoir. The May water supply forecast for April-August inflow volume is 6.74 million-acre-feet, or 111 percent of average, which sets this year’s sturgeon volume at 1.18 million-acre-feet.
The latest projections indicate a minimal chance of exceeding flood stage at Bonner Ferry, Idaho, which is 1,764 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: https://www.nwd-wc.usace.army.mil/nws/hh/www/pend_esp.html
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.