Active rainfall patterns across the Midwest provided much needed moisture to several portions of the Missouri River Basin. Large areas of Montana, North Dakota, Wyoming, eastern South Dakota, and eastern Nebraska received more than 200% of normal precipitation for the month of May. However, central South Dakota, western Nebraska, and eastern Colorado received as little as 25% of normal precipitation.

"The month of May brought significant rainfall to the northern and eastern portions of the Missouri River Basin, resulting in slightly above average May runoff.,” said John Remus, chief of the U.S. Army Corps of Engineers’ Missouri River Basin Water Management Division.

“The runoff was higher than forecast last month.” May runoff for the Basin above Sioux City, Iowa was 3.5 million acre-feet,104% of average. The annual runoff forecast above Sioux City, Iowa is 21.0 MAF, 82% of average, and 1.8 MAF higher than last month’s forecast.

“While the precipitation provided relief for some portions of the basin, drought remains a concern as we move into the summer months.  The western portion of the basin received very little rain last month. As we enter the summer months, we will continue to serve all Congressionally authorized purposes while dealing with the on-going drought,” said Remus.

Currently, 31% of the Basin is experiencing abnormally dry or drought conditions with drought outlooks showing persisting drought conditions through the end of August. Soil moisture is below normal in Montana, North Dakota, eastern Wyoming, and Colorado and near normal in South Dakota and northern Nebraska.

System storage is currently 55.0 MAF, 1.1 MAF below the top of the carryover multiple use zone. During May, System storage increased 1.0 MAF. The improved forecast and increased storage in the reservoir system indicate the navigation flow support for the second half of the navigation season will be higher than earlier forecasts.

"The June 1 reservoir studies indicate navigation flow support for the second half of the navigation season, will be reduced to 1,000 cubic feet per second below full service,” said Remus. “However, the official Navigation flow support level for the second half of the navigation season will be based on the July 1 System storage check.”

Basin and river conditions continue to be monitored and System regulation will be adjusted based on the most up-to-date information.

Mountain Snowpack:
The mountain snowpack was below normal all season long and peaked approximately one week earlier than normal. However, additional late season storms have extended the anticipated snow melt season and increased the overall volume expected from snowmelt. On June 1, 56% of the annual peak remains in the reach above Fort Peck Dam, and 74% of the annual peak remains in the Fort Peck Dam to Garrison Dam reach. The mountain snowpack peaked in the reach above Fort Peck on April 9 at 73% of average, while the mountain snowpack in the Fort Peck to Garrison reach peaked on April 10 at 82% of average. Mountain snowpack normally peaks near April 17. The mountain snowpack graphics can be viewed at: http://go.usa.gov/xARQC.

Navigation:
Gavins Point Dam releases will continue to provide navigation flow support at 500 cubic feet per second below full service at all four target locations (Sioux City, Omaha, Nebraska City, and Kansas City) through the first half of the navigation season which ends on July 1. The current forecast indicates that flow support 1,000 cfs below full service will be provided for the second half of the navigation season and flow support may be provided for the entire navigation season ending Dec. 1 at the mouth of the Missouri River.

Fort Peck Flow Test:
Test releases from Fort Peck to assess the potential benefits of alternative management scenarios for the pallid sturgeon began on April 26 and will be completed by Sept. 1. The test includes two higher flow periods, in late April and June, with target flows at Wolf Point, Montana. The first peak in releases was completed in early May with peak flows of 18,000 cfs at Wolf Point, Montana.  Releases were reduced to 10,000 cfs by May 10. The second peak is scheduled to start in mid-June with peak flows of 22,500 cfs. The test releases will not affect river stages below Gavins Point Dam. The flow test has been extensively coordinated with local stakeholders and was discussed in depth at a public meeting held in Poplar, Montana on March 28, 2024.

The U.S. Army Corps of Engineers will host weekly virtual meetings during the flow test to update the public on test progress and planned operations. Information on accessing the public meetings can be found at https://www.nwd.usace.army.mil/MRWM/Public-Meetings/Meetings. June calls will be held June 5, 12, 19 and 26 at 1 p.m. Central (12 p.m. Mountain).

During the flow test a number of monitoring activities will be conducted to include fish monitoring, lidar and aerial photography, physical surveys, cultural resource surveys, and water quality sampling. Interested parties can also provide information through a web-based application that can be found at https://hydroviz.ca/fort-peck-feedback.

Monthly Water Management Conference Calls
Water management calls include an update from the National Weather Service’s Missouri Basin River Forecast Center, and an update on the Missouri River mainstem reservoir system operations. The next call for 2023 will be held Thursday, June 6. All calls are recorded in their entirety and are available to the public on our website at https://go.usa.gov/xARQv.

Reservoir Forecasts:

• Gavins Point Dam
  • Average releases past month – 25,300 cfs
  • Current release rate – 29,000 cfs
  • Forecast release rate – 29,000 cfs
  • End-of-May reservoir level – 1206.0 feet
  • Forecast end-of-June reservoir level – 1206.0 feet
  • Notes: The Gavins Point release will be adjusted to provide navigation flow support on the lower Missouri River.
     
• Fort Randall Dam
  • Average releases past month – 21,100 cfs
  • End-of-May reservoir level – 1355.4 feet
  • Forecast end-of-June reservoir level – 1355.0 feet
  • Notes: Releases will be adjusted as necessary to maintain the desired reservoir elevation at Gavins Point and to back up Gavins Point releases.
     
• Big Bend Dam
  • Average releases past month – 18,700 cfs
  • Forecast average release rate – 25,400 cfs
  • Forecast reservoir level – 1421.0 feet
     
• Oahe Dam
  • Average releases past month – 17,700 cfs
  • Forecast average release rate – 26,100 cfs
  • End-of-May reservoir level – 1603.0 feet (up 0.8 feet from April 30)
  • Forecast end-of-June reservoir level – 1603.0 feet
     
• Garrison Dam
  • Average releases past month – 19,600 cfs
  • Current release rate – 21,000 cfs
  • Forecast release rate – 22,000 cfs
  • End-of-May reservoir level – 1837.8 feet (up 2.3 feet from April 30)
  • Forecast end-of-June reservoir level – 1841.4 feet
  • Notes – Releases will be maintained at 22,000 cfs through mid-September.
     
• Fort Peck Dam
  • Average releases past month – 11,400 cfs
  • Current release rate – 10,000 cfs
  • Forecast average release rate – 15,200 cfs
  • End-of-May reservoir level – 2231.6 feet (up 0.3 feet from April 30)
  • Forecast end-of-June reservoir level – 2230.7 feet
  • Notes: Releases will be adjusted in accordance with the Fort Peck flow test.

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 715 million kWh of electricity in May. Typical energy generation for May is 790 million kWh. The power plants are expected to generate 8.7 billion kWh this year, compared to the long-term average of 9.4 billion kWh.

To view the detailed three-week release forecast for the mainstem dams, go to https://go.usa.gov/xARQB.

The Missouri Basin Web App provides links to these reports and others that are updated more frequently. http://go.usa.gov/xE6fC