Dry March Leads to Reduction in Annual Basin Runoff Forecast

The updated 2026 calendar year runoff forecast for the Missouri River Basin above Sioux City, Iowa, continues to be below average. March runoff in the Missouri River Basin above Sioux City was 1.7 million acre-feet, 56% of average.

“Runoff into the reservoir system was below average for the month of March and conditions across most of the basin remain dry,” said John Remus, chief of the U.S. Army Corps of Engineers’ Missouri River Basin Water Management Division. “Mountain snowpack has decreased as well and is currently below the 30-year minimum accumulation. We are forecasting a below-average runoff year for the basin.”

The 2026 calendar year runoff forecast above Sioux City is 17.8 MAF, 69% of average. The runoff forecast is based on current soil moisture conditions, plains snowpack, mountain snowpack, and long-term precipitation and temperature outlooks.

The volume of water stored in the Missouri River Mainstem Reservoir System is currently 49.5 MAF, 6.6 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.

Navigation:

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 5,500 cfs below full-service for the first half of the 2026 season, which 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 storage in the System on July 1.

Mountain and Plains Snowpack:

Mountain snowpack in the upper Missouri River Basin is accumulating at below average rates. The April 2 mountain snowpack in the Fort Peck reach was 71% of average, while the mountain snowpack in the Fort Peck to Garrison reach was 65% of average. By April 1, about 96% of the total mountain snowfall has typically accumulated. Mountain snow normally peaks near April 17. The mountain snowpack graphics can be viewed at: https://go.mil/mr-mtn-snowpack.

Reservoir Forecasts:

• Gavins Point Dam
  • Average releases past month – 17,300 cfs
  • Current release rate – 24,000 cfs
  • Forecast release rate – 24,800 cfs
  • End-of-March reservoir level – 1206.1 feet
  • Forecast end-of-April reservoir level – 1206.0 feet
  • Notes: The Gavins Point release will be adjusted as needed to provide navigation flow support on the lower Missouri River.
• Fort Randall Dam
  • Average releases past month – 15,500 cfs
  • End-of-March reservoir level – 1353.9
  • Forecast end-of-April reservoir level – 1355.1 feet
  • Notes: Releases will be adjusted as necessary to maintain the desired reservoir elevation at Gavins Point and to back up the Gavins Point release increases.
• Big Bend Dam
  • Average releases past month – 20,800 cfs
  • Forecast average release rate – 24,600 cfs
  • Forecast reservoir level – 1420.4 feet
• Oahe Dam
  • Average releases past month – 20,800 cfs
  • Forecast average release rate – 24,600 cfs
  • End-of-March reservoir level – 1601.4 feet
  • Forecast end-of-April reservoir level – 1600.5 feet
• Garrison Dam
  • Average releases past month – 16,000 cfs
  • Current release rate – 14,000 cfs
  • Forecast average release rate – 14,000 cfs
  • End-of-March reservoir level – 1827.3 feet
  • Forecast end-of-April reservoir level – 1827.6 feet
• Fort Peck Dam
  • Average releases past month – 4,900 cfs
  • Current release rate – 5,000 cfs
  • Forecast average release rate – 5,000 cfs
  • End-of-March reservoir level – 2222.3 feet
  • Forecast end-of-April reservoir level – 2222.9 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 596 million kWh of electricity in March. Typical energy generation in March is 636 million kWh. Forecast generation for 2026 is 7.3 billion kWh compared to the long-term average of 9.3 billion kWh.

To view the detailed three-week release forecast for the mainstem dams, go to: https://go.mil/mr-3wk-fcast.