In response to increasing mountain snowpack, the U.S. Army Corps of Engineers (Corps) Missouri River Basin Water Management Division has increased the annual runoff forecast for the Missouri River Basin above Sioux City, Iowa, to 32.0 million acre feet (MAF), 127 percent of normal. Typically, the average annual runoff volume is 25.2 MAF. Runoff during March was 4.2 MAF, 142 percent of normal, as a result of plains snowmelt runoff and ice breakup on the Missouri River and its tributaries. 

“As mountain snowpack continued to accumulate in March, our runoff forecast increased accordingly,” said Jody Farhat, chief of the Corps Missouri River Basin Water Management Division. As of April 3, mountain snowpack was 132 percent of normal in the reach above Fort Peck Dam, and 140 percent of normal in the reach between Fort Peck and Garrison Dams. The mountain snowpack typically peaks in mid-April, and runoff from the melting snow enters the reservoir system from May through July.  

“While above normal runoff is expected, the reservoirs are well positioned to manage the forecasted inflow,” said Farhat. The total volume of water stored in the Missouri River Mainstem Reservoir System is 53.2 MAF, which is still below the base of the annual flood control and multiple use zone of 56.1 MAF. “Recent snowstorms caused light plains snow accumulations across Montana and the Dakotas, but most of the plains snowmelt runoff has already accumulated in the reservoir system,” added Farhat.  

“It's important to remember that in 2011, we had high runoff from three sources in the Missouri River Basin: mountain snowpack, plains snowpack, and rainfall,” emphasizes Farhat. “Only one of those conditions exists today: the above normal mountain snowpack.” The current mountain snowpack is near the same levels as this time in 2011 yet still below the peak levels seen in 2011. Plains snowpack was generally light this year, and system storage ended March 8.5 MAF lower than in 2011. “The Corps will continue to monitor the plains and mountain snowpack, basin soil conditions, and rainfall events to fine tune the regulation of the reservoir system based on the most up-to-date information,” said Farhat.  

View mountain snowpack graphic here: https://www.nwd-mr.usace.army.mil/rcc/reports/snow.pdf. 

In mid-March, Gavins Point Dam releases were increased from 14,000 cubic feet per second (cfs) to approximately 25,000 cfs in support of the navigation season, which began April 1 near St. Louis, Mo. “Flow support for the first half of the navigation season will be 3,000 cfs below full service,” said Farhat. Full service navigation flow support is generally sufficient to provide a 9-foot deep by 300-foot wide channel; minimum service generally provides an 8-foot deep channel. Flow support for the second half of the navigation season and the season length will be determined following the system storage check on July 1. Navigation support is expected to increase to full service after the July 1 storage check.  

Reservoir Forecasts  

Gavins Point Dam releases averaged 19,500 cfs during March. Releases were stepped up in mid-March to provide flow support for the navigation season. Releases are currently at 27,500 cfs, and will be adjusted in April to meet target flows downstream. In the event of heavy rains downstream of the reservoir system, releases will be reduced to lessen flood risk along the lower river. The reservoir behind Gavins Point Dam ended March at elevation 1206.2 feet. The reservoir will remain near elevation 1206 feet during April.  

Fort Randall Dam releases averaged 17,300 cfs during March. Releases were stepped up in mid-March corresponding with the increases in Gavins Point Dam releases. Fort Randall Dam releases are currently at 25,500 cfs, and will be adjusted, as necessary, to maintain the desired pool elevation at Gavins Point. The reservoir ended March at elevation 1351.5 feet, up 2.5 feet during the month. The pool is expected to rise until reaching 1355.2 feet and will remain near that elevation through the end of April.  

Big Bend Dam releases averaged 17,600 cfs during March. They are expected to average 29,400 cfs this month. The reservoir will remain near its normal elevation of 1420 feet in April.  

Oahe Dam releases averaged 18,600 cfs during March. Releases are expected to average 28,700 cfs this month. The reservoir ended March at elevation 1605.2 feet, up 2.5 feet during the month. The reservoir is expected to rise less than 1 foot during April.  

Garrison Dam releases were stepped down from 18,000 cfs to 16,000 cfs in mid-March as the river ice went out near Bismarck, ND, averaging 16,500 cfs during the month. Releases were increased to 18,000 cfs at the beginning of April to help provide a rising Oahe Reservoir during the forage fish spawn. Releases will be gradually increased to 25,000 cfs during April. Garrison ended the month at elevation 1835.8 feet, up 4.2 feet from the previous month. It is expected to rise nearly 2 feet during April.  

Fort Peck Dam releases averaged 7,000 cfs in March. Releases will be increased from 7,000 cfs to 8,000 cfs around mid-April. The reservoir ended March at elevation 2224.6 feet, up 2.1 feet from the previous month. The reservoir is forecast to rise nearly 2 feet during April. 

The forecast reservoir releases and elevations discussed above are not definitive. Additional precipitation, lack of precipitation, or other circumstances could cause adjustments to the reservoir release rates.  

The six mainstem power plants generated 619 million kilowatt hours (kWh) of electricity in March. Typical energy generation for March is 639 million kWh. The power plants are projected to generate 9.6 billion kWh of electricity this year, compared to the normal of 10 billion kWh.  

To view the detailed three-week release forecast for the mainstem dams, go to: https://www.nwd-mr.usace.army.mil/rcc/reports/twout.html.  

      MISSOURI RIVER MAINSTEM RESERVOIR DATA  

         WATER RELEASES AND ENERGY GENERATION FOR MARCH