Missouri River Nav Season To Be Extended 10 Days

Higher-than-average releases from all Missouri River mainstem system dams will continue through the fall, and the navigation season on the river will be extended by 10 days in December, the Army Corps of Engineers announced September 6.

“Due to this year’s high runoff and the water currently being stored in the reservoirs, Gavins Point releases will remain near 58,000 cubic feet per second (cfs.) for the remainder of the navigation season to ensure evacuation of all stored flood waters prior to the 2019 runoff season,” said John Remus, chief of the Missouri River Basin Water Management Division.

The 2018 runoff forecast in the Missouri River Basin above Sioux City, Iowa, is 39.8 million acre feet (maf.), 157 percent of average. August runoff was 1.8 maf., 138 percent of normal.

The Missouri River mainstem reservoir system storage was 64.7 maf. as of September 1, occupying 8.6 maf. of the 16.3 maf. flood control zone. “System storage declined 2.7 maf. in August and will continue to gradually decline in September,” said Remus. System storage peaked on July 8 at 68.4 maf.

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“Reservoir releases will be adjusted as necessary to provide downstream flood risk reduction and continue evacuation of stored flood water,” said Remus.

He added that it’s important to note that the ability to significantly reduce flood risk along the lower Missouri River diminishes at locations further downstream, due to the large uncontrolled drainage area and the travel time from Gavins Point Dam.

Based on the September 1 reservoir system storage, winter releases from Gavins Point will be at least 17,000 cfs. Based on the latest reservoir studies, there will be a 10-day extension to navigation flow support and a Gavins Point winter release of 20,000 cfs. Navigation flow support at the mouth of the Missouri River will end on December 11.

In late September, the Corps will issue the 2018–2019 draft Annual Operating Plan for the Missouri River Mainstem System. The agency also will present a synopsis of its 2018 operations and plans for regulating the reservoir system in 2019 at public meetings in six cities throughout the basin in early November. Meeting times and locations will be announced when additional details become available.