All 2017 stored flood waters were evacuated from the Missouri River mainstem reservoir system (System) as of Jan. 15, when the total volume stored in the System reached 56.1 million acre-feet (MAF), according to the U.S. Army Corps of Engineers (Corps) Missouri River Water Management Division.
“The System stands ready to capture spring runoff, reducing flood risk while providing support to other authorized project purposes,” said John Remus, Chief of the Missouri River Basin Water Management Division.
Over the last few weeks, periods of intermittent warming have caused some of the plains snowpack to melt and enter the System,” said Remus. System storage is currently 56.3 MAF. The latest annual runoff forecast for the Missouri River basin above Sioux City, Iowa, is 26.4 MAF, 104 percent of average.
“While the forecasted annual runoff is near average, the timing and distribution of runoff in individual reaches varies. Runoff in the reaches between Garrison and Gavins Point is expected to be below normal during February through April, the months when plains snowpack normally melts,” said Remus. “Runoff into Fort Peck and Garrison is expected to be slightly above average during May through July due to the above average mountain snowpack.”
Plains snowpack in the upper basin has been widespread, but light, so far this winter. Currently, some areas in central and eastern Montana are reporting 1 to 3 inches of liquid content while isolated areas in northeast Nebraska are reporting 1 to 2 inches of liquid content in the snowpack. However, there is light to no snow cover throughout the remainder of the upper and lower basin. The Corps is cooperating with other agencies to acquire plains snow measurements in the upper basin.
As of Feb. 1, the mountain snowpack was 114 percent of average in the reach above Fort Peck and 124 percent of average in the reach from Fort Peck to Garrison. Normally 64 percent of the total mountain snowpack accumulation has occurred by Feb. 1. Mountain snowpack will continue to accumulate over the next few months and normally peaks in mid-April.
Winter releases from Gavins Point are expected to remain at 18,000 cubic feet per second (cfs) during February, but will be adjusted if needed in response to basin conditions. Flow support for Missouri River navigation will likely be at full service levels for the first half of the 2018 season, which begins on April 1 at the mouth. The actual service level will be based on the total volume of water stored in the System on March 15, in accordance with guidelines in the Master Manual. Flow support for the second half of the navigation season, as well as the navigation season length, will be based on the actual July 1 System storage. Weekly updates on basin conditions, reservoir levels and other topics of interest can be viewed  at: http://www.nwd-mr.usace.army.mil/rcc/reports/pdfs/weeklyupdate.pdf.