June Missouri Basin Runoff Was 159 Percent Of Average

Much-above average runoff in the upper Missouri River basin (above Sioux City, Iowa) extended into June following widespread and heavy rainfall in South Dakota and Nebraska. Additionally, widespread and heavy rainfall in the lower basin, particularly in Kansas, has resulted in high tributary and Missouri River flows downstream of the six main stem reservoirs on the Missouri River, the Corps of Engineers reported.

June runoff in the upper basin was 8.7 million acre feet (maf.), which is 159 percent of average. The average June runoff is 5.4 maf. Runoff remained particularly high in the Fort Randall to Gavins Point and Gavins Point to Sioux City reaches, which were three and four times average, respectively.

The 2019 upper basin runoff forecast is 49.9 maf. If realized, this runoff total would be the second highest runoff in 121 years of record-keeping, only surpassed by 2011 (61.0 maf.) and exceeding the 49.0 maf. observed in 1997. Upper basin runoff in 2018 was 42.1 maf., which is currently third highest.

“System releases from Gavins Point Dam are currently 70,000 cubic feet per second (cfs.), which is more than twice the average release for this time of the year,” said John Remus, chief of the Corps’ Missouri River Basin Water Management Division. “We will maintain Gavins Point releases at this rate to continue evacuating water from the Missouri River mainstem reservoir system.”

The system was storing 68.0 maf. as of July 1, occupying 11.9 maf. of the 16.3 maf. flood control zone. System storage normally peaks in early July. Fort Peck and Garrison are currently in their respective exclusive flood control zones. As a result of the high reservoir levels and the forecast above-average runoff during the summer and fall, releases from all system projects will be above average for the next several months, and possibly as late as November, to ensure evacuation of all stored flood waters.