Missouri River Basin Runoff Higher, But Only Because Of Early Snowpack Melt
A warm February led to increased snowmelt and runoff in the Missouri River Basin above Sioux City, Iowa, but didn’t do much to change the outlook for the coming year, the Northwestern Engineer Division reported March 7.
February runoff was 1.8 million acre-feet (maf.), 161 percent of average, with above-average runoff in every reach except Sioux City, which was near average.
However, the updated 2024 calendar year runoff forecast for the basin continues to be below average.
“Despite the increased runoff in the month of February and improved soil moisture conditions, we expect 2024 runoff to remain below average,” said John Remus, chief of the Corps’ Missouri River Basin Water Management Division. “The much warmer –than normal temperatures led to an early melt of the lower –than average plains snow. In addition, mountain snowpack is lower than average, resulting in the low annual runoff forecast.” Soil moisture conditions are near or above normal across most of the basin with below-normal soil moisture conditions spanning eastern portions of the basin.
The 2024 calendar year runoff forecast above Sioux City is 17.0 maf., 66 percent of average. The runoff forecast is based on current soil moisture conditions, plains snowpack, mountain snowpack and long-term precipitation and temperature outlooks.
System storage is currently 53.9 maf., which is 2.2 maf. below the top of the carryover multiple use zone. Basin and river conditions continue to be monitored, including plains and mountain snow accumulation, and system regulation will be adjusted based on the most up-to-date information.
“The system will continue to serve all congressionally authorized purposes during 2024,” Remus said.
Snowpack
Mountain snowpack in the upper Missouri River Basin is accumulating at below-average rates. The March 3 mountain snowpack in the Fort Peck reach was 73 percent of average, while the mountain snowpack in the Fort Peck to Garrison reach was 78 percent of average. Mountain snow normally peaks near April 17.
The plains snowpack, which typically melts from mid-February into April, is almost nonexistent in the basin, the Corps said. A trace to 1 inch of snow-water-equivalent is modeled in eastern North Dakota, according to the report.
Navigation Support
Beginning in mid-March, releases from Gavins Point Dam will be adjusted to provide flow support for Missouri River navigation. Navigation flow support for the Missouri River is expected to be at 500 cfs. below full service for the first half of the 2024 season, which begins April 1 at the mouth of the river near St. Louis, Mo. The actual service level will be based on the total volume of water stored within 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 storage in the system on July 1.
