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Drought conditions driving lowered runoff forecast

Missouri River Water Management Division
Published May 6, 2021
Runoff can enter the Missouri River anywhere and anytime in the basin. Only when runoff occurs in the upper Missouri River basin can it be captured by the mainstem system of dams. Even then, where runoff is captured depends upon where precipitation falls.

Runoff can enter the Missouri River anywhere and anytime in the basin. Only when runoff occurs in the upper Missouri River basin can it be captured by the mainstem system of dams. Even then, where runoff is captured depends upon where precipitation falls.

The six dams on the main stem of the Missouri River capture runoff from parts of Montana, North Dakota, South Dakota, Wyoming, and northern Nebraska.

The six dams on the main stem of the Missouri River capture runoff from parts of Montana, North Dakota, South Dakota, Wyoming, and northern Nebraska.

Very dry conditions in April resulted in very low runoff in the upper Missouri River Basin.

The upper Basin runoff was 44% of average, which was the 9th driest April in 123 years of record. The updated 2021 upper Basin runoff forecast is 17.8 million acre-feet (MAF), 69% of average, which, if realized, would rank as the 22nd lowest calendar year runoff volume.

“The extremely dry April, current drought conditions, and below-normal mountain snowpack has led our office to significantly lower the 2021 calendar year runoff forecast,” said John Remus, chief of the U.S. Army Corps of Engineers’, Missouri River Basin Water Management Division. “Based on this forecast, the May reservoir monthly studies indicate reduced flow support for navigation during the second half of the navigation season and a 12,000-cfs Gavins Point winter release rate. I urge all water users, particularly intake owners, to begin preparing for the possibility of lower river levels later this summer and during the fall and winter.”

System storage is currently 55.3 MAF, 0.8 MAF below the base of the Annual Flood Control and Multiple Use Zone. System storage is expected to remain in the Carryover Multiple Use Zone during 2021. 

Mountain Snowpack:

Mountain snowpack in the upper Basin has peaked and melting is underway. The mountain snowpack peaked above Fort Peck in late March at 86% of the normal peak, while the mountain snowpack in the Fort Peck to Garrison reach peaked in late April at 96% of average. Mountain snowpack normally peaks near April 15. The mountain snowpack graphics can be viewed at: http://go.usa.gov/xARQC.

Navigation:

Gavins Point Dam releases will provide full-service navigation flow support at all four target locations (Sioux City, Omaha, Nebraska City, and Kansas City) through July 1. Full-service flow support, in combination with the Bank Stabilization and Navigation Project, is generally sufficient to provide a 9-foot-deep by 300-foot-wide channel. Flow support for the second half of the navigation season, as well as the navigation season length, will be based on the actual July 1 System storage. If the May 1 runoff forecast is realized, navigation flow support would be lowered below the full-service levels, to an intermediate-service level, for the second half of the season, and the season length would be a full 8-month season.  

Winter Release Rate:

The winter release rate is determined based on the Sept. 1 System storage. Per the reservoir studies, if the May runoff forecast is realized, the winter releases from Gavins Point Dam will be 12,000 cfs.

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 2021 will be held on Thursday, May 6. All calls are recorded in their entirety and are available to the public on our website at https://go.usa.gov/xARQv.

Spring Public Meeting:

The spring public meetings were held virtually on Tuesday, April 6 by conference call and webinar. The purpose of this meeting was to update the region on current hydrologic conditions and the planned operation of the mainstem reservoir system during the coming months. Links for a recording of the virtual public meeting and meeting slides can be found here: https://go.usa.gov/xARQv.

Reservoir Forecasts:

  • Gavins Point Dam
    • Average releases past month – 28,600 cfs
    • Current release rate – 29,000 cfs
    • Forecast release rate – 29,500 cfs
    • End-of-April reservoir level – 1206.5 feet
    • Forecast end-of-May reservoir level – 1206.1 feet
    • Notes: The Gavins Point release will be adjusted to provide full-service navigation flow support on the lower Missouri River.
       
  • Fort Randall Dam
    • Average releases past month – 24,600 cfs
    • End-of-April reservoir level – 1354.9 feet (down 0.1 feet from March)
    • Forecast end-of-May 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 – 24,200 cfs
    • Forecast average release rate – 24,200 cfs
    • Forecast reservoir level – 1420.8 feet
       
  • Oahe Dam
    • Average releases past month – 24,100 cfs
    • Forecast average release rate – 24,700 cfs
    • End-of-April reservoir level – 1606.4 feet (down 0.8 foot from March)
    • Forecast end-of-May reservoir level – 1606.3 feet
       
  • Garrison Dam
    • Average releases past month – 21,200 cfs
    • Current release rate – 21,500 cfs
    • Forecast release rate – 22,000 cfs
    • End-of-April reservoir level – 1835.2 feet
    • Forecast end-of-May reservoir level – 1835.0 feet
    • Notes – Releases will be increased to 22,000 cfs in mid-May.
       
  • Fort Peck Dam
    • Average releases past month – 7,400 cfs
    • Current release rate – 7,500 cfs
    • Forecast average release rate – 8,500 cfs
    • End-of-April reservoir level – 2233.0 feet
    • Forecast end-of-May reservoir level – 2231.9 feet
    • Notes: Releases will be increased to 9,500 cfs in mid-May.

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 767 million kWh of electricity in April. Typical energy generation for April is 699 million kWh. The power plants are expected to generate 9.0 billion kWh this year, compared to the long-term average of 9.5 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.

MISSOURI RIVER MAINSTEM RESERVOIR DATA

 

Pool Elevation
(feet above mean sea level)

Water in Storage
(1,000 acre-feet)

 

On April 30

Change in April

On April 30

% of 1967-2020 Average

Change in April

Fort Peck

2233.0

-0.4

14,572

100

-86

Garrison

1835.2

-1.5

17,086

96

-439

Oahe

1606.4

-0.8

18,343

103

-229

Big Bend

1420.4

-0.3

1,657

97

-17

Fort Randall

1354.9

-0.1

3,403

102

-4

Gavins Point

1206.5

0.0

340

87

+2

 

 

Total

55,401

100

-773

 

WATER RELEASES AND ENERGY GENERATION FOR APRIL

 

Average Release in 1,000 cfs

Releases in 1,000 acre-feet

Generation in Million kWh

Fort Peck

7.4

443

72

Garrison

21.2

1,262

186

Oahe

24.1

1,431

216

Big Bend

24.2

1,442

79

Fort Randall

24.6

1,463

160

Gavins Point

28.6

1,702

54

 

 

Total

767


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

Release no. 21-020