Below average runoff continues in the upper Missouri River basin
September precipitation was well-below normal in the Missouri River Basin. As a result, September runoff in the upper Missouri River Basin above Sioux City, Iowa was 69 percent of average.
Since January 1, precipitation in the upper Basin is well-below normal. The National Weather Service’s Climate Prediction Center is forecasting that below-normal precipitation will continue in October. The 2020 calendar year runoff forecast for the upper Basin, updated on Oct. 1, is 30.2 million acre-feet (MAF), 117 percent of average. Average annual runoff for the upper Basin is 25.8 MAF.
“Upper basin runoff was below average in September. We expect runoff to be below average during the remainder of the calendar year. Lower basin runoff has been below average as well,” said John Remus, chief of the U.S. Army Corps of Engineers’ Missouri River Basin Water Management Division. “Releases from Gavins Point Dam are being made to meet full service Missouri River navigation flow targets”, Remus added.
The navigation flow support season ends on December 1 at the mouth of the Missouri River.
As of Oct. 5, the total volume of water stored in the System was 58.6 MAF, occupying 2.5 MAF of the System’s 16.3-MAF flood control zone. System storage peaked at 61.8 MAF on July 16 and will decline during the fall. All 16.3 MAF of flood control storage is expected to be available prior to the start of the 2021 runoff season. If fall and winter runoff continues to be below average as forecasted, System storage will be about 0.8 MAF below the base of the annual flood control zone by the start of the 2021 runoff season.
According to the National Drought Mitigation Center (NDMC), drought conditions continue to worsen across much of the upper Basin. Wide-spread areas of drought classified as Extreme are evident in Colorado and Wyoming. Moderate to Severe drought conditions are present in large areas of Montana, North Dakota, South Dakota, Nebraska and Iowa.
The July 1 System storage check indicated flow support for the second half of the navigation season would be at least at the full service level for a full-length 8-month flow support season. Full service flow support is designed to work in tandem with the Missouri River Bank Stabilization and Navigation Project to provide a 9-feet deep by 300-foot wide navigation channel from Sioux City, Iowa to the mouth of the river near St. Louis, Missouri. Gavins Point releases will be reduced to winter levels beginning around Nov. 22.
Winter Release Rate
The winter release rate is determined based on the Sept. 1 System storage. Per the Sept. 1 System storage, winter releases from Gavins Point Dam will be at least 17,000 cfs.
Fall Public Meetings
Two public meetings will be conducted by webinar on Nov. 2. The purpose of these meetings is to update the region on current hydrologic conditions and the planned operation of the mainstem reservoir system during the remaining fall months as well as present the draft plans for operating the System during 2021. Meeting times and webinar information will be at the following link when it becomes available: https://www.nwd.usace.army.mil/MRWM/Public-Meetings/.