Upper Basin Runoff Forecast Lowered Due To Dry Conditions

The updated 2025 calendar year runoff forecast for the Missouri River Basin above Sioux City, Iowa, continues to be below average. April runoff in the Missouri River Basin above Sioux City was 1.4 million acre-feet, 48% of average.

“Runoff into the reservoir system was below average for the month of April, and runoff was below average in all reaches,” said John Remus, chief of the U.S. Army Corps of Engineers’ Missouri River Basin Water Management Division. “Drought or abnormally dry conditions are currently present in 75 percent of the basin, and conditions have worsened in the Fort Peck reach and parts of the Garrison reach in the last month. As a result, the runoff forecast was lowered by 1.9 MAF from last month.”

The 2025 calendar year runoff forecast above Sioux City is 20.0 MAF, 78 percent of average. The runoff forecast is based on current soil moisture conditions, mountain snowpack and long-term precipitation and temperature outlooks.

The volume of water stored in the Missouri River Mainstem Reservoir System is currently 50.4 MAF, 5.7 MAF below the top of the carryover multiple use zone.

Fort Peck releases will be increased to 10,500 cfs in mid-May. Garrison releases will be increased to 24,000 cfs around mid-May. Releases are expected to stay at those rates through the summer.

Basin and river conditions continue to be monitored, including plains and mountain snow accumulation, and System regulation will be adjusted based on the most upto-date information.

Navigation:

Gavins Point Dam releases will continue to provide navigation flow support at 4,000 cfs below full service for the first half of the navigation season. The flow support began April 1 at the mouth of the river near St. Louis, Missouri. The service level was 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.

Reservoir Forecasts: Garrison Dam: Average releases past month – 17,900 cfs Current release rate – 21,000 cfs Forecast average release rate – 24,000 cfs End-of-April reservoir level – 1830.8 feet Forecast end-of-May reservoir level – 1831.4 feet Fort Peck Dam:

Average releases past month – 6,700 cfs Current release rate – 9,000 cfs Forecast average release rate – 10,500 cfs End-of-April reservoir level – 2227.6 feet Forecast end-of-May reservoir level – 2227.3 feet The forecast reservoir releases and elevations discussed above are not definitive. Additional precipitation, lack of precipitation or other circumstances could cause adjustments to the reservoir release rates.

Hydropower:

The six mainstem power plants generated 727 million kWh of electricity in April. Typical energy generation in April is 695 million kWh. Forecast generation for 2025 is 8.6 billion kWh compared to the long-term average of 9.4 billion kWh.