Rainfall in the Missouri River Basin above Sioux City, Iowa, was above normal for the month of August, resulting in above average runoff. However, due to drier-than-normal conditions in previous years, the total storage in the Missouri River mainstem reservoir system remains lower than normal. Based on the Sept. 1 system storage, winter releases from Gavins Point Dam will be 13,000 cubic feet per second, per the criteria in the Master Manual. This release rate is slightly above the minimum rate of 12,000 cfs.

"Rainfall in the month of August provided some welcome inflow into the upper Missouri Basin Reservoir System,” said John Remus, Chief of the U.S. Army Corps of Engineers’ Missouri River Basin Water Management Division. “Several precipitation events occurred during the month, with some areas receiving 400% of normal rainfall. Despite this fact, drought conditions continue, and are predicted to persist and expand throughout the basin in the coming months.”

August runoff was 1.7 million acre-feet (MAF), 121% of average above Sioux City. The updated 2023 calendar year forecast for the upper Basin is 29.1 (MAF), 113% of average. Average annual runoff for the upper Basin is 25.7 MAF.

As of September 1, the total volume of water stored in the System was 55.5 MAF, which is 0.6 MAF below the base of the System’s flood control zone. System storage is expected to continue to decline through the fall. The updated reservoir studies indicate that the System storage is expected to be approximately 3.7 MAF below the base of flood control at the start of the 2022 runoff season.

Navigation

Gavins Point Dam releases will be set to provide navigation flow support at a level 1,500 cfs below full service at all four target locations (Sioux City, Omaha, Nebraska City, and Kansas City). Flow targets may be missed to conserve water if there is no commercial navigation in a given reach. Season support will end on Dec. 1 at the mouth of the Missouri River.

Winter Release Rate

As per the criteria in the Maser Manual, the winter release rate is determined based on the September 1 System storage. Per the Sept. 1 System storage, winter releases from Gavins Point Dam will be at least 13,000 cfs. In anticipation of the low winter releases, a letter will be sent in September to water users below Gavins Point Dam making them aware of the planned releases and encouraging them to assess the risk to their facilities.

Monthly Water Management Conference Calls

Water management calls include an update on the Missouri River mainstem reservoir system operations. The next call for 2023 will be held on Thursday, Sept. 7.  The focus of this call will be winter release rates and the preparation for a possible Fort Peck Flow Test. All calls are recorded in their entirety and are available to the public on our website at https://go.usa.gov/xARQv.

Fall Public Meetings

The Northwestern Division will host a series of public meeting the week of Nov. 6. The date and locations of the meetings are still being finalized.

Reservoir Forecasts:

• Gavins Point Dam
  • Average releases past month – 30,900 cfs
  • Current release rate – 34,500 cfs (as of September 5)
  • Forecast release rate – 34,800 cfs (month of September)
  • End-of-August reservoir level – 1206.3 feet
  • Forecast end-of-September reservoir level – 1207.5 feet
  • Notes: Releases will be adjusted as necessary to meet all downstream navigation targets.
     
• Fort Randall Dam
  • Average releases past month – 28,800 cfs
  • End-of-August reservoir level – 1354.6 feet
  • Forecast end-of-September reservoir level – 1353.6 feet
  • Notes: Releases will be adjusted as necessary to maintain the desired reservoir elevation at Gavins Point.
     
• Big Bend Dam
  • Average releases past month – 28,300 cfs
  • Forecast average release rate – 31,200 cfs
  • Forecast reservoir level – 1420.7 feet
     
• Oahe Dam
  • Average releases past month – 27,900 cfs
  • Forecast average release rate – 31,900 cfs
  • End-of-August reservoir level – 1602.8 feet
  • Forecast end-of-September reservoir level – 1600.3 feet
     
• Garrison Dam
  • Average releases past month – 22,100 cfs
  • Current release rate – 22,000 cfs
  • Forecast average release rate – reduce to 17,000 cfs by mid-September
  • End-of-August reservoir level – 1841.4 feet
  • Forecast end-of-September reservoir level – 1840.6 feet
     
• Fort Peck Dam
  • Average releases past month – 7,800 cfs
  • Current release rate – 7,500 cfs
  • Forecast average release rate – 7,500
  • End-of-August reservoir level – 2229.4 feet
  • Forecast end-of-September reservoir level – 2228.4 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 907 million kWh of electricity in August. Typical energy generation for August is 1,009 million kWh. The power plants are projected to generate 7.9 billion kWh of electricity 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 http://go.usa.gov/xVgWr.