SEATTLE – Water managers at the U.S. Army Corps of Engineers, along with federal, tribal, and state fish biologists, determined forecasted inflows are sufficient to provide a second pulse of powerhouse releases to provide flow augmentation at Libby Dam, Mont., for endangered Kootenai River white sturgeon downstream in Idaho.
While this year’s flow augmentation for sturgeon does not include spilling additional volume from the dam, plans include increasing flows to full powerhouse capacity for about a week, on two separate occasions, in an effort to provide river conditions that may foster sturgeon spawning.
Sturgeon flow augmentation began May 16 when local Kootenai River tributaries downstream of Libby Dam were forecasted to peak, the trigger for initiating releases from the dam in support of sturgeon spawning activity. Flow augmentation increased releases to full powerhouse capacity, approximately 24,500 cubic feet per second, and remained at that level for about one week before decreasing to 18,000 cfs. Monday, releases were again increased to powerhouse capacity as part of the sturgeon flow augmentation for at least one week.
This second week-long pulse of powerhouse capacity flows is part of the sturgeon operation but also benefits the controlled refill of Libby Dam. Current projections show that the powerhouse flows will likely need to be extended another week in order to save space in Libby Dam for the end of June. While this extension of the powerhouse releases is considered part of the sturgeon operation, the main goals are to control refill and mitigate flood risk.
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 undertake a series of actions to benefit sturgeon, including constructing 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. The May water supply forecast for the April to August inflow volume is 7.0 million-acre-feet, or 119 percent of average; which set this year’s sturgeon volume at 1.17 million-acre-feet.
While most of the snowpack melted in western Montana and northern Idaho, the snowpack is still well above average in the upper Kootenai Basin above Libby Dam.
The latest projections indicate that flood risk has diminished from prior predictions due to increased certainty with Kootenay Lake elevations, and since most of the snow in the southern part of the Kootenai Basin has already melted. Seattle District Water Management still considers the flood risk to be elevated from average because of the existing higher-than-average snowpack above Libby Dam, and the potential for June precipitation events.
Libby Dam 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.
Public information meetings for Libby Dam operations are scheduled for:
· June 9 at Lincoln Electric Cooperative, Eureka, Mont., from 6-8 p.m.
· June 11 at Lincoln County Credit Union, Libby, Mont., from 7-9 p.m.