Below average runoff forecast for the upper Missouri River Basin in 2021

Nebraska City News-Press

The updated 2021 calendar year runoff forecast for the Missouri River Basin above Sioux City, Iowa, continues to be below average. 

“Despite runoff being slightly above average in January, we expect 2021 runoff to be below average,” said John Remus, chief of the U.S. Army Corps of Engineers’, Missouri River Basin Water Management Division. “Both plains snowpack and mountain snowpack continue to lag behind seasonal averages, and soil moisture continues to be much drier-than-normal.”

January 2021 runoff in the Missouri River Basin above Sioux City was 1.1 million acre-feet, 141 percent of average. The above-average January runoff was primarily due to above-normal temperatures melting any accumulated plains snowpack and inhibiting river ice formation.

The 2021 calendar year runoff forecast above Sioux City is 22.9 MAF, 89 percent of average. The runoff forecast is based on soil moisture conditions, plains snowpack, mountain snowpack, and long-term precipitation and temperature outlooks.

Gavins Point releases will be maintained at the winter release rate of 17,000 cubic feet per second but will be adjusted if needed in response to ice formation on the Missouri River below Gavins Point Dam.

“System storage remains slightly below the base of the annual flood control zone.  The System is in good position to serve all Congressionally authorized purposes including flood control, navigation, and water supply during 2021,” Remus added. 

Navigation

Current studies indicate that flow support for Missouri River navigation will be at the full service level for the first half of the 2021 season, which begins April 1 at the mouth in St. Louis, Missouri. The actual service level will be based on the total volume of water stored in the System on March 15, in accordance with the guidelines in the Master Manual. Flow support for the second half of the navigation season, as well as navigation season length, will be based on the actual July 1 System storage.

Ice Conditions

River ice conditions below all System projects will be closely monitored throughout the winter season. The Missouri River froze in at Bismarck, N.D. near the end of January.  Garrison releases are gradually being increased from 16,000 cfs to 22,000 cfs.  Garrison releases are typically increased following the formation of a stable ice cover to benefit winter hydropower generation. 

Basin and river conditions continue to be monitored, including plains and mountain snow accumulation, and System regulation will be adjusted based on the most up-to-date information. The river ice report is available at: http://go.usa.gov/xARQc.

Mountain and Plains Snowpack

Mountain snowpack in the upper Basin is accumulating at below-average rates. The Jan. 31 mountain snowpack in the Fort Peck reach was 78 percent of average, while the mountain snowpack in the Fort Peck to Garrison reach was 79 percent of average. By February 1, about 60 percent of the total mountain snowpack has typically accumulated. Mountain snowpack normally peaks near April 15. The mountain snowpack graphics can be viewed at: http://go.usa.gov/xARQC. Currently, plains snowpack in the upper Basin is light.

Final 2020-2021 Annual Operating Plan Released

The final Annual Operating Plan for the Missouri River Basin for 2020–2021 has been posted at https://www.nwd.usace.army.mil/MRWM/Public-Meetings/.