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August inflows much below average in northern Missouri River Basin

Missouri River Water Management Division
Published Sept. 3, 2020
Missouri River Water Management Monthly Update - Each month, from January through the end of the runoff season, Missouri River water managers and weather forecasters report the conditions of the Missouri River Basin.

Missouri River Water Management Monthly Update - Each month, from January through the end of the runoff season, Missouri River water managers and weather forecasters report the conditions of the Missouri River Basin.

August precipitation was well-below normal in the Missouri River Basin, particularly in the western and far northern portions, which received less than 25% of normal precipitation.

The lack of precipitation and dry soil conditions resulted in 74% of average August runoff in the Missouri River Basin above Sioux City, Iowa (upper Basin). The 2020 calendar year forecast for the upper Basin, updated on Sept. 1, is 30.6 million acre-feet (MAF), 119% of average. Average annual runoff for the upper Basin is 25.8 MAF. Runoff in the upper Basin during the remainder of 2020 is forecast to be below average.

“Reservoir inflows in August, particularly into Fort Peck and Garrison, were much lower than average due to ongoing warmer-than-normal and drier-than-normal conditions. For the remainder of the year, we expect below-average inflows in the upper reservoir reaches due to the warmer-than-normal and drier-than-normal climate outlook and the intensifying drought conditions.  We will begin reducing releases from Fort Peck and Garrison in mid-September,” said John Remus, chief of the U.S. Army Corps of Engineers’ Missouri River Basin Water Management Division. “We plan to adjust Gavins Point Dam releases throughout the fall in order to meet full-service navigation flow targets through the end of the navigation season,” Remus added.

As of Sept. 3 the total volume of water stored in the System was 60.1 MAF, occupying 4.0 MAF of the System’s 16.3-MAF flood control zone. System storage peaked at 61.8 MAF on July 16 and is forecast to decline during the fall. All 16.3 MAF of flood control storage is expected to be available prior to start of the 2021 runoff season. If fall runoff continues to be below average, System storage may fall below the base of the annual flood control zone by the start of the 2021 runoff season.

According to the National Drought Mitigation Center (NDMC), drought degradation is occurring across much of the upper Basin. Wide-spread areas of drought classified as Extreme and Severe are evident in Colorado and portions of Wyoming and Iowa. Abnormally Dry conditions are affecting most of the upper Basin and areas of the lower Basin.

Navigation

The July 1 System storage check indicated flow support for the second half of the navigation season would be at least at the full service level for a full-length season. Full service flow support is designed to provide a 9-foot deep by 300-foot wide navigation channel from Sioux City, Iowa to the mouth of the river near St. Louis, Missouri. Full service flow support will be provided for an 8-month season from April 1 through Dec. 1 at the mouth. During a full-length season, Gavins Point releases are reduced beginning around Nov. 22.

Fort Peck and Garrison Fall Release Reduction

Due to below-average August inflows into Fort Peck and Garrison reservoirs and a below-average runoff forecast for the remainder of 2020, Fort Peck and Garrison releases will be reduced in mid-September. The Fort Peck release will be stepped down from 11,000 cfs to 6,000 cfs from Sept. 15-17. The release reduction will result in a Missouri River stage reduction of about 2.5 feet at Wolf Point and Culbertson, Montana. The Garrison release will be reduced from 26,000 cfs to 20,000 cfs from Sept. 6-8 and then stepped down to 14,000 cfs from Sept. 13-15. The release reduction from 26,000 cfs to 14,000 cfs will result in a Missouri River stage reduction of about 3 feet at Bismarck, North Dakota. 

Winter Release Rate

The winter release rate is determined based on the Sept. 1 System storage. Per the Sept. 1 System storage, winter releases from Gavins Point Dam will be at least 17,000 cfs.

Fall Public Meetings

Fall public meetings will be held virtually due to current restrictions for public meetings related to COVID-19. Plans for the meetings and meeting format will be announced in the coming weeks.  

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 last call for 2020 was held on Thursday, June 4. These monthly calls will resume in January 2021. All calls are recorded in their entirety and are available to the public on the Defense Video and Imagery Distribution System at www.dvidshub.net/unit/usace-nwd.

2019 Summary of Actual Regulation

The Summary of Actual 2019 Regulation of the Missouri River Mainstem Reservoir System Summary is available here: https://go.usa.gov/xwWTY. This document contains a summary of the actual regulation of the Missouri River Mainstem Reservoir System for the 2019 calendar year.

Reservoir Forecasts:

  • Gavins Point Dam
    • Average releases past month – 30,000 cfs
    • Current release rate – 30,500 cfs (as of Sept. 1)
    • Forecast release rate – 31,500 cfs (month of September)
    • End-of-August reservoir level – 1206.8 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 – 27,200 cfs
    • End-of-August reservoir level – 1355.3 feet
    • Forecast end-of-September reservoir level – 1353.3 feet
    • Notes: Releases will be adjusted as necessary to maintain the desired reservoir elevation at Gavins Point.
       
  • Big Bend Dam
    • Average releases past month – 24,000 cfs
    • Forecast average release rate – 26,500 cfs
    • Forecast reservoir level – 1420.6 feet
       
  • Oahe Dam
    • Average releases past month – 25,100 cfs
    • Forecast average release rate – 26,800 cfs
    • End-of-August reservoir level – 1612.3 feet
    • Forecast end-of-September reservoir level – 1610.7 feet
       
  • Garrison Dam
    • Average releases past month – 27,000 cfs
    • Current release rate – 26,800 cfs
    • Forecast average release rate – reduce to 14,000 cfs by Sept. 15 
    • End-of-August reservoir level – 1840.8 feet
    • Forecast end-of-September reservoir level – 1839.8 feet
       
  • Fort Peck Dam
    • Average releases past month – 10,000 cfs
    • Current release rate – 11,000 cfs
    • Forecast average release rate – reduce to 6,000 cfs by Sept. 17
    • End-of-August reservoir level – 2238.7 feet
    • Forecast end-of-September reservoir level – 2237.2 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 934 million kWh of electricity in August. Typical energy generation for August is 1,013 million kWh. The power plants are projected to generate 10.1 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.

MISSOURI RIVER MAINSTEM RESERVOIR DATA

 

Pool Elevation
(feet above mean sea level)

Water in Storage
(1,000 acre-feet)

 

On August 31

Change in August

On August 31

% of 1967-2019 Average

Change in August

Fort Peck

2238.7

-1.4

15,797

109

-319

Garrison

1840.7

-2.8

18,783

105

-897

Oahe

1612.3

0.0

20,237

114

+41

Big Bend

1420.7

+0.5

1,674

98

+25

Fort Randall

1355.2

-2.7

3,433

103

-207

Gavins Point

1206.8

-0.6

345

88

-14

 

 

Total

60,269

109

-1,371

 

WATER RELEASES AND ENERGY GENERATION FOR AUGUST

 

Average Release in 1,000 cfs

Releases in 1,000 acre-feet

Generation in Million kWh

Fort Peck

10.0

614

103

Garrison

27.0

1,662

255

Oahe

25.1

1,543

241

Big Bend

24.0

1,475

78

Fort Randall

27.2

1,673

182

Gavins Point

30.0

1,845

75

 

 

Total

934


Contact
Eileen Williamson
402-996-3802
eileen.l.williamson@usace.army.mil

Release no. 20-123