Missouri River Releases Remain Above Average

Higher-than-average releases from all Missouri River Mainstem System projects, including Gavins Point Dam, will continue through November, the Corps of Engineers reported November 5.

“Gavins Point releases will remain near 58,000 cubic feet per second (cfs.) for the remainder of the navigation season,” said John Remus, chief of the Corps’ Missouri River Basin Water Management Division. “To ensure all stored 2018 runoff is evacuated prior to the 2019 runoff season, most of the releases must occur before the river ices over in reaches predominantly upstream from Lake Oahe.”

The 2018 runoff forecast in the Missouri River Basin above Sioux City, Iowa, is 41.4 million acre feet (maf.), 163 percent of average. If this forecast is realized, that will be third highest runoff since the Corps began keeping records in 1898. Only 1997 and 2011 exceeded that total.

The October runoff above Sioux City was 1.9 maf., 160 percent of average. Due to heavy September and October rainfall, the total two-month runoff in the unregulated reach between Gavins Point Dam and Sioux City was 1.7 maf., which is the highest September–October runoff in that reach in 120 years of record-keeping.

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The Missouri River mainstem reservoir system storage was 59.6 maf. as of November 1, occupying 3.5 maf. of the 16.3 maf. flood-control zone. “System storage declined 2.6 maf. in October and will continue to gradually decline in November,” Remus said. System storage peaked on July 8 at 68.4 maf., occupying 12.3 maf. of the designated flood-control storage. “Reservoir releases will be adjusted as necessary to provide downstream flood risk reduction and continue evacuation of stored flood water,” said Remus.

Releases from Gavins Point will be reduced to near 50,000 cfs. in late November before being reduced 3,000 cfs. per day until reaching the winter release rate of 20,000 cfs. around December 11. Navigation flow support at the mouth of the Missouri River will end on December 11.