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Missouri River basin’s below-normal precipitation leads to lower runoff forecast; reduced Gavins Point releases

Missouri River Water Management Division
Published May 7, 2020
The Upper Missouri River basin has experienced below-normal precipitation since January. This map shows the precipitation departure from normal for the last 180 days from May 7, 2020. The map and data are generated by the National Weather Service's Advanced Hydrologic Prediction Service. The location of upper basin Missouri River mainstem dams has been spotlighted.

The Upper Missouri River basin has experienced below-normal precipitation since January. This map shows the precipitation departure from normal for the last 180 days from May 7, 2020. The map and data are generated by the National Weather Service's Advanced Hydrologic Prediction Service. The location of upper basin Missouri River mainstem dams has been spotlighted.

Gavins Point releases will be reduced to 33,000 cubic feet per second (cfs) on Friday, May 8 following a reduction in forecast 2020 upper basin runoff.

Since January, precipitation in the upper basin has been well below normal, which has led to a reduction in the runoff forecast. Some areas of the Dakotas received less than half of their normal precipitation during the first four months of 2020.

The 2020 calendar year upper basin runoff forecast has been reduced to 32.2 MAF. “This is still an above average runoff forecast. The upper basin runoff for the remainder of 2020 depends on mountain snowmelt and rain events,” said John Remus, chief of the U.S. Army Corps of Engineers’ Missouri River Basin Water Management Division. Although this forecast is a reduction of 3.3 MAF from the April 1 forecast, it is still in the top 25 percent of the 122 years of runoff record. Average annual runoff for the upper basin is 25.8 MAF. The runoff forecast is updated on a monthly basis, and more often if basin conditions warrant.

Soil moisture conditions continue to be wet in much of the upper Missouri River Basin, which increases the potential for above average runoff in the upper basin. The potential for flooding remains, particularly in the lower river due to continued high river stages on many of the uncontrolled tributaries downstream of the Missouri River Mainstem Reservoir System. When possible, additional adjustments to Gavins Point releases may be made to offset tributary flows from heavy rain events. “I encourage all interested parties to check the Corps’ Missouri River Basin Water Management and the National Weather Service websites on a daily basis for the most up-to-date information on System conditions and forecasted river stages,” said Remus.

As of May 4, the total volume of water stored in the System was 58.7 MAF, up 0.2 MAF since April 1, occupying 2.6 MAF of the System’s 16.3-MAF flood control zone.

Navigation:

The March 15 system storage check indicated flow support for Missouri River navigation will be at least full service for the first half of the 2020 season, which began on April 1 at the mouth. Full service flow support 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 navigation season length, will be based on the actual July 1 System storage.

Mountain Snowpack:

As of May 1, the mountain snowpack was 98 percent of average in the reach above Fort Peck and 99 percent of average in the reach from Fort Peck to Garrison. The mountain snowpack has peaked in both reaches: on April 16 in the Fort Peck reach at 109 percent of average and on April 19 in the Fort Peck to Garrison reach at 112 percent of average. The mountain snowpack graphics can be viewed here: https://go.usa.gov/xE6wT.

Weekly updates on basin conditions, reservoir levels and other topics of interest can be viewed here: https://go.usa.gov/xE6wa.

Monthly Water Management Conference Calls

Water management calls include an update from the National Weather Service’s Missouri Basin River Forecast Center, an update on the Missouri River mainstem reservoir system operations. The next call for 2020 will be held Thursday, May 7, for Congressional delegations; Tribes; state, county and local government officials, levee and drainage districts; and the media. Calls will be recorded in their entirety and made available to the public on the Defense Video and Imagery Distribution System at www.dvidshub.net/unit/usace-nwd.

Reservoir Forecasts:

  • Gavins Point Dam
    • Average releases past month – 35,000 cfs
    • Current release rate – 35,000 cfs (as of May 1)
    • Forecast release rate – 33,000 cfs (first week of May)
    • End-of-April reservoir level – 1206.3 feet
    • Forecast end-of-May reservoir level – 1206.0 feet
    • Notes: Releases will be decreased to 33,000 cfs the first week of May, basin conditions permitting.
       
  • Fort Randall Dam
    • Average releases past month – 30,200 cfs
    • End-of-April reservoir level – 1354.4 feet
    • Forecast end-of-May reservoir level – 1355.0 feet
    • Notes: Releases will be adjusted as necessary to maintain the desired reservoir elevation at Gavins Point.
       
  • Big Bend Dam
    • Average releases past month – 27,800 cfs
    • Forecast average release rate – 26,400 cfs
    • Forecast reservoir level – 1420.0 feet
       
  • Oahe Dam
    • Average releases past month – 28,100 cfs
    • Forecast average release rate – 26,800 cfs
    • End-of-April reservoir level – 1609.9 feet
    • Forecast end-of-May reservoir level – 1610.6 feet
       
  • Garrison Dam
    • Average releases past month – 24,200 cfs
    • Current release rate – 24,000 cfs
    • Forecast average release rate – 28,000 cfs (middle of May)
    • End-of-April reservoir level – 1840.3 feet
    • Forecast end-of-May reservoir level – 1840.9 feet
       
  • Fort Peck Dam
    • Average releases past month – 7,700 cfs
    • Current release rate – 9,000 cfs
    • Forecast average release rate – 9,000 cfs
    • End-of-April reservoir level – 2236.3 feet
    • Forecast end-of-May reservoir level – 2237.6 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 884 million kWh of electricity in April. Typical energy generation for April is 695 million kWh. The power plants are projected to generate 11.0 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 April 30

Change in April

On April 30

% of 1967-2019 Average

Change in April

Fort Peck

2236.3

+0.6

15,242

105

+97

Garrison

1840.3

+0.3

18,609

104

+54

Oahe

1609.9

+0.1

19,438

110

+1

Big Bend

1420.5

-0.2

1,660

97

-11

Fort Randall

1354.4

-0.2

3,360

100

-11

Gavins Point

1206.3

-0.5

334

85

-14

 

 

Total

58,643

106

+116

 

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

7.7

458

76

Garrison

24.2

1,439

222

Oahe

28.1

1,671

252

Big Bend

27.8

1,655

93

Fort Randall

30.2

1,798

191

Gavins Point

35.0

2,083

50

 

 

Total

884


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

Release no. 20-048