Environmental

Corps to begin flow augmentation for sturgeon spawning at Libby Dam

Tags
Corps to begin flow augmentation for sturgeon spawning at Libby Dam

The U.S. Army Corps of Engineers will begin flow augmentation at Libby Dam in Montana for endangered Kootenai River white sturgeon downstream in Idaho and British Columbia, Canada.

Corps water managers — along with federal, tribal and state fishery biologists — determined spring run-off conditions in the Kootenai River and its tributaries warrant starting the required flow augmentation.

Libby Dam impounds water for a 600 MW hydroelectric powerhouse.

The flow augmentation operation entails increasing outflows to provide river conditions to potentially increase sturgeon spawning success in the lower Kootenai River. Outflows will increase May 14 to 21, as local Kootenai River tributaries downstream of the dam are forecasted to peak. Discharge from the dam will increase to full powerhouse capacity, about 25,000 cubic feet per second (cfs) for about 18 days. After sturgeon flow augmentation is complete, Libby Dam discharge will gradually decrease to stable summer levels, no less than 7,000 cfs — the bull trout minimum flow associated with Koocanusa Reservoir’s inflow forecast.

This augmentation operation is part of a collaborative, ongoing effort by regional biologists to enhance spawning conditions for sturgeon in the Kootenai River near Bonners Ferry, Idaho. Increased flows provide river conditions to potentially increase sturgeon migration to the reach of river upstream of Bonners Ferry in habitat known to be conducive to spawning, egg hatching and larval sturgeon survival while providing river stage downstream of spawning areas to connect the river to off-channel habitats.

The Kootenai Tribe of Idaho’s conservation aquaculture program has steadily increased young sturgeon numbers in the river since 1992. Federal, state and tribal partners have collaborated for over a decade to build and enhance instream and off-channel habitat upstream and downstream of Bonners Ferry, to provide conditions that allow adult sturgeon, both wild and those released into the river through the conservation aquaculture program, to reproduce on their own. The sturgeon operation requires a volume of water to be released from Libby Dam based on May water supply forecasts for Koocanusa Reservoir. The May water supply forecast for April-August inflow volume is 5.13 million-acre-feet or 82% of average, which sets this year’s sturgeon volume at 0.8 maf.

The latest projections indicate a minimal chance of exceeding flood stage at Bonner Ferry, which is 1,764 feet. The dam’s flow and stage projections are based on National Weather Service ensemble forecasts that are frequently updated 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.