Missouri River Flood Threat Recedes As Rain Eases

Although Upper Midwest soils are still wet, and some tributaries are still experiencing high water, moderate precipitation this spring has eased flood fears on the Missouri River and led the Corps to reduce runoff from Gavins Point Dam beginning May 7 from 35,000 cubic feet per second to 33,000 cfs. The reduction followed a lowering of forecast 2020 upper basin runoff.

Since January, precipitation in the upper basin has been well below normal. Some areas of the Dakotas received less than half of their normal precipitation during the first four months of 2020.

The 2020 calendar year upper basin runoff forecast has been reduced to 32.2 million acre-feet (maf.).

“This is still an above-average runoff forecast,” said John Remus, chief of the U.S. Army Corps of Engineers’ Missouri River Basin Water Management Division. “The upper basin runoff for the remainder of 2020 depends on mountain snowmelt and rain events.”

Although this forecast is a reduction of 3.3 maf. from the April 1 forecast, it is still in the top 25 percent of the 122 years of runoff record. Average annual runoff for the upper basin is 25.8 maf. The runoff forecast is updated on a monthly basis, and more often if basin conditions warrant.

Soil moisture conditions continue to be wet in much of the upper Missouri River Basin, which increases the potential for above-average runoff in the upper basin, the Corps said. The potential for flooding remains, particularly in the lower river, due to continued high river stages on many of the uncontrolled tributaries downstream of the Missouri River Mainstem Reservoir System.

When possible, additional adjustments to Gavins Point releases may be made to offset tributary flows from heavy rain events. As of May 4, the total volume of water stored in the system was 58.7 maf., up 0.2 maf. since April 1, occupying 2.6 maf. of the system’s 16.3 maf. flood control zone.