After Near-Record Year, Corps Prepares Missouri River Reservoirs For 2020 Runoff
As part of its preparation for the 2020 runoff season, the Corps of Engineers’ Missouri River Basin Water Management Division announced February 6 that Gavins Point releases were increased from 30,000 cubic feet per second (cfs.) to 35,000 cfs. Gavins Point Dam winter releases normally range between 12,000 and 17,000 cfs.
“All water from 2019 emptied from the system in late January. The higher-than-average winter releases from Gavins Point will allow us to maintain more flood storage for a longer period,” said John Remus, chief of the Corps’ Missouri River Basin Water Management Division. “This will provide flexibility to respond to runoff events downstream of Gavins Point, while giving consideration to the ongoing levee rehabilitation construction efforts.”
“Conditions permitting, releases from all projects will likely remain high during the remainder of winter. We will continue to monitor the basin conditions and will remain aggressive in our releases to the extent it is practicable,” he added.
The 2019 calendar year runoff was 60.9 million acre-feet (maf.), the second highest runoff in 121 years of record-keeping (1898–2018), exceeded only by the 61.0 maf. of runoff observed in 2011.
Based on current soil moisture conditions, current plains and mountain snowpack, and long-term temperature and precipitation outlooks, the 2020 calendar year runoff forecast is 36.3 maf. above Sioux City, Iowa, 141 percent of average. Average annual runoff is 25.8 maf. Runoff forecasts will be updated monthly, and more often if warranted, throughout 2020.
As of February 3, the total volume of water stored in the system is 56.3 maf., occupying 0.2 maf. of the 16.3 maf. combined flood control storage zones. System storage reached 56.0 maf. on Jan. 22, 0.1 maf. below the base of the combined flood control zone.
The potential for above-normal runoff, coupled with above-normal stages on many uncontrolled tributaries that join the Missouri River below Gavins Point Dam, increases the potential for flooding, particularly south of Omaha.
Current studies indicate that Missouri River navigation will be supported above full-service levels for the first half of the 2020 season, which begins April 1 at St. Louis, Mo. The actual service level will be based on the total volume of water stored in the system on March 15, in accordance with the guidelines in the Master Manual. Flow support for the second half of the navigation season, as well as navigation season length, will be based on the July 1 system storage.
River ice conditions below all System projects will be closely monitored throughout the winter season. The Corps will also continue to monitor basin and river conditions, including plains and mountain snow accumulation, and will adjust System regulation based on the most up-to-date information. The river ice report is available at: https://go.usa.gov/xpZZX.
The mountain snowpack accumulation period is underway. Mountain snowpack is currently about average in both reaches; however, the mountain snowpack accumulation has approximately two months remaining. The mountain snowpack normally peaks near April 15. The mountain snowpack graphics can be viewed at: https://go.usa.gov/xE6wT.
Until now, the winter has been milder than normal throughout the Missouri River basin. In a February 6 conference call, NOAA officials forecast lower than normal temperatures and higher than normal precipitation for February.
Weekly updates on basin conditions, reservoir levels and other topics of interest can be viewed at: https://go.usa.gov/xE6wa.
The first spring flood outlook will be released February 13.