Heavy precipitation from a series of late spring storms combined with above average and late-melting snowpack runoff have significantly increased inflows into Lake Pend Oreille and increased flood risk downstream of Albeni Falls Dam. The Pend Oreille River has exceeded flood flow and is likely to stay above that threshold for the next week.
To mitigate flood risk, U.S. Army Corps of Engineers’ officials are operating Albeni Falls Dam with all gates open in a free flow operation. Free flow is when the river flow control switches from Albeni Falls Dam to the natural constriction between Dover, Idaho and the dam, balancing flood risk on the lake and downstream. Under this operation, the outflow from Albeni Falls Dam and the level of Lake Pend Oreille may rise or fall in the coming days.
Another storm is forecasted for early next week when outflows may approach the moderate downstream flood category and lake levels could approach elevation 2,063 feet. Albeni Falls Dam is currently reducing Pend Oreille River flows by 20,000 cubic feet per second. However, despite this reduction, areas downstream of Lake Pend Oreille, such as Cusick, Newport, and Usk could be affected by high flows while Albeni Falls Dam is on free flow. These projections are based on the current forecast which can change swiftly. For the latest modeling forecasts please visit the National Weather Service’s Northwest River Forecast Center link at: http://www.nwrfc.noaa.gov/river/station/flowplot/flowplot.cgi?lid=ALFW1.
The dam will remain on free flow until it has been determined that the current event is in recession and the flood risk has passed. Seattle District is coordinating with local emergency management.
Current snowpack in the basin is about 165 percent of normal for this time of year. Given the above normal snowpack and another forecasted storm this weekend, people residing in flood-prone areas should take precautions and be prepared for flooding. People on the lake and river should be prepared for water levels to temporarily rise or fall as the event unfolds.
“Corps modeling using National Weather Service River Forecast Center hydrologic forecasts suggest we could see peak Lake Pend Oreille elevations approaching 2,063.0 feet, and outflows approaching 110,000 cubic feet per second,” said Leon Basdekas, Upper Columbia Water Manager for the Army Corps of Engineers. “As of 8 a.m., the lake is currently at about 2,061.65 feet as measured at the Hope gage with outflows at 100,800 cfs.”
In addition, Corps’ officials are advising boaters to watch for additional debris which can float just beneath the water in Lake Pend Oreille due to a breach at the Clark Fork Drift Facility. A 100-foot segment of log boom failed this week which could allow logs and smaller debris to enter the upper lake. Officials are monitoring the situation until high flows recede and emergency repairs can be made.