Above average rainfall and fast-melting snow led to above average runoff in the upper Missouri River Basin in June. Runoff above Sioux City, Iowa was 6.7 million acre-feet, which is 122% of average.

"The annual forecast for the upper basin has been increased due to the rainfall and snowmelt in the month of June,” said John Remus, chief of the U.S. Army Corps of Engineers’ Missouri River Basin Water Management Division. “The mountain snowpack has completely melted out, approximately 2 weeks ahead of schedule, further increasing the June runoff. The basin will need additional rainfall to continue the trend of above-average runoff.”

The annual runoff forecast above Sioux City, Iowa is 29.2 MAF, 114% of average, and about 2.4 MAF higher than last month’s forecast. Precipitation was normal to much-above-normal for the month of June in much of Montana, southern and east-central North Dakota, and western South Dakota.  Below-normal precipitation occurred in eastern South Dakota and into the lower Basin.

“Soil conditions have improved for the western portions of the upper basin as the precipitation provided some much-needed relief, but abnormally dry or drought conditions persist in eastern South Dakota and the lower basin,” said Remus.

System storage on July 1 was 55.6 MAF, 0.5 MAF below the top of the carryover multiple use zone. “Based on the July 1 System storage, flow support for navigation increased from minimum service to 1,500 cfs below full-service level,” said Remus.

“Per the guidelines in the Master Manual, this will also result in a full navigation flow support season ending Dec. 1 at the mouth of the Missouri River. Gavins Point releases were increased to 29,000 cfs in early July to account for the increase in navigation flow support.” 

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

Navigation:

Gavins Point Dam releases will be set to provide flow support at an intermediate-service level, 1,500 cfs lower than full-service flow support at all four target locations (Sioux City, Omaha, Nebraska City, and Kansas City). The flow support season length will be a full 8-month season, ending Dec. 1 at the mouth of the Missouri River.

Mountain Snowpack:

Mountain snowpack in the upper Missouri River Basin melted quickly due to warmer-than-normal temperatures during the spring and early summer. By June 26, all the snow had melted in both the reach above Fort Peck Dam and the Fort Peck Dam to Garrison Dam reach. The mountain snowpack peaked in the reach above Fort Peck on April 24 at 117% of average, while the mountain snowpack in the Fort Peck to Garrison reach peaked on April 6 at 109% of average. Mountain snowpack normally peaks near April 17. The mountain snowpack graphics can be viewed at: http://go.usa.gov/xARQC.

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 will be held Thursday, July 13. 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 – 23,500 cfs
  • Current release rate – 29,000 cfs
  • Forecast release rate – 30,500 cfs
  • End-of-June reservoir level – 1206.8 feet
  • Forecast end-of-July 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 – 20,700 cfs
  • End-of-June reservoir level – 1356.0 feet
  • Forecast end-of-July reservoir level – 1354.9 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 – 18,400 cfs
  • Forecast average release rate – 26,200 cfs
  • Forecast reservoir level – 1420.8 feet
     
• Oahe Dam
  • Average releases past month – 18,200 cfs
  • Forecast average release rate – 26,700 cfs
  • End-of-June reservoir level – 1604.2 feet (up 2.2 feet from May 31)
  • Forecast end-of-July reservoir level – 1603.8 feet
     
• Garrison Dam
  • Average releases past month – 21,700 cfs
  • Current release rate – 22,000 cfs
  • Forecast release rate – 22,000 cfs
  • End-of-June reservoir level – 1839.6 feet (up 6.8 feet from May 31)
  • Forecast end-of-July reservoir level – 1842.6 feet
  • Notes – Releases will be maintained at 22,000 cfs through mid-September.
     
• Fort Peck Dam
  • Average releases past month – 8,300 cfs
  • Current release rate – 9,000 cfs
  • Forecast average release rate – 9,000 cfs
  • End-of-June reservoir level – 2230.6 feet (up 4.8 feet from May 31)
  • Forecast end-of-July reservoir level – 2231.2 feet
  • Notes: Releases will be maintained at 9,000 cfs through mid-September.

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 690 million kWh of electricity in June. Typical energy generation for June is 846 million kWh. The power plants are expected to generate 7.9 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