Spring Precipitation Brings Improved Missouri Basin Conditions, Corps Says
The latest 2023 calendar year runoff forecast for the Missouri River Basin above Sioux City, Iowa, is showing improvement, the Corps of Engineers reports.
“Spring precipitation, including increased mountain snowpack and late-season plains snow, has provided improved runoff conditions in the upper basin,” said John Remus, chief of the Corps’ Missouri River Basin Water Management Division. “We prefer to see a slower plains snowmelt to improve soil conditions. The longer the snow persists, the greater risk of flooding caused by rapid snowmelt from a spring rain event.”
The 2023 calendar year runoff forecast above Sioux City is 26.4 million acre-feet (maf.), 103 percent of average. The runoff forecast is based on current soil moisture conditions, plains snowpack, mountain snowpack and long-term precipitation and temperature outlooks. March runoff in the Missouri River Basin above Sioux City was 1.7 maf., 57 percent of average.
System storage is currently 46.8 maf., 9.3 maf. below the top of the carryover multiple use zone.
“Despite these improvements, the system is still recovering from drought, and it will take time to return system storage to the top of the carryover multiple use zone while continuing to serve all congressionally authorized purposes during 2023,” Remus said.
Beginning in mid-March, releases from Gavins Point Dam were adjusted to provide flow support for Missouri River navigation. Navigation flow support for the Missouri River is at minimum service for the first half of the 2023 season, which began April 1 at the mouth of the river near St. Louis, Mo. The service level was based on the total volume of water stored within the system on March 15, which was 46.3 maf., 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 storage in the system on July 1.
Mountain snowpack in the upper Missouri River Basin improved during March. The April 1 mountain snowpack in the Fort Peck reach was 117 percent of average, while the mountain snowpack in the Fort Peck to Garrison reach was 108 percent of average. By April 1, about 95 percent of the total mountain snowfall has typically accumulated. Mountain snow normally peaks near April 17.
The plains snowpack, which typically melts from mid-February into April, is hanging on longer in 2023, and the plains snow on April 1 showed widespread areas of 4-8 inches of snow-water equivalent (SWE) across North Dakota and eastern South Dakota following a blizzard that occurred in late March. The blizzard that occurred April 4-5 in the upper plains was not included in this forecast.