U.S. Army Corps of Engineers: Missouri River reservoir system prepared for 2021 runoff season

(Source: U.S. Army Corps of Engineers) — The full flood control capacity of the Missouri River Mainstem Reservoir System is available for the 2021 runoff season.

“All 2020 flood water stored in the annual flood control zone has been evacuated as of December 21,” said John Remus, chief of the U.S Army Corps of Engineers’, Missouri River Basin Water Management Division.

“The entire flood control capacity of the Mainstem System is available to capture and manage 2021 runoff, reducing flood risk while providing support to the other authorized project purposes.”

Gavins Point releases will be maintained at the winter release rate of 17,000 cubic feet per second but will be adjusted if needed in response to ice formation on the Missouri River below Gavins Point Dam.

December 2020 runoff in the Missouri River Basin above Sioux City, Iowa, was 1.2 million acre feet, 148% of average. The 2020 calendar year runoff above Sioux City was 31.1 MAF, 121% of average. Average annual runoff is 25.8 MAF.

The 2021 calendar year runoff forecast for the upper Missouri Basin above Sioux City is 23.1 MAF, 90% of average. The runoff forecast is based on significantly drier-than-normal soil moisture conditions, low plains snowpack, and below-average mountain snowpack.

“Runoff forecasts are developed using the best information as it exists today. As mountain snowpack continues to accumulate, our forecasts will be updated to reflect those changes,” added Remus.

Navigation:
Current studies indicate that flow support for Missouri River navigation will be at the full service level for the first half of the 2021 season, which begins April 1 at the mouth in St. Louis. The actual service level will be based on the total volume of water stored in the System on March 15, in accordance with the guidelines in the Master Manual. 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.

Ice Conditions:
River ice conditions below all System projects will be closely monitored throughout the winter season. Garrison releases will be maintained at 16,000 cfs until the river freezes in near Bismarck, North Dakota. Releases are typically set at 16,000 cfs prior to the freeze-in to reduce the risk of ice-induced flooding.  Releases will be gradually increased to 23,000 cfs following the formation of a stable river ice cover at Bismarck.  Basin and river conditions continue to be monitored, including plains and mountain snow accumulation, and will adjust System regulation based on the most up-to-date information. The river ice report is available at: https://go.usa.gov/xARQc.

Mountain and Plains Snowpack:
Mountain snowpack in the upper Missouri River Basin is accumulating at a below-average rate. The Jan. 3 mountain snowpack in the Fort Peck reach was 81% of average, while the mountain snowpack in the Fort Peck to Garrison reach was 82% of average. More than half of the mountain snowfall typically occurs from Jan. 1 to mid-April, and it normally peaks near April 15. The mountain snowpack graphics can be viewed at: https://go.usa.gov/xARQC. Currently, plains snowpack in the upper Missouri River Basin is sparse.

Final 2020-2021 Annual Operating Plan Released:
The final Annual Operating Plan for the Missouri River Basin for 2020–2021 has been posted at https://www.nwd.usace.army.mil/MRWM/Public-Meetings/.

Monthly Water Management Conference Calls Begin for 2021:
The first 2021 monthly conference call was held, Thursday, Jan. 7, to inform basin stakeholders of current weather and runoff forecasts and the planned operation of the reservoir system in the coming months. Presentation materials will be available via webinar. The call is intended for Congressional delegations; Tribes; state, county and local government officials; and the media. It will be recorded in its entirety and made available to the public on the Defense Video and Imagery Distribution System at https://go.usa.gov/xARQv.

Reservoir Forecasts:

  • Gavins Point Dam
    • Average releases past month – 17,000 cfs
    • Current release rate – 17,000 cfs
    • Forecast release rate – 17,000 cfs
    • End-of-December reservoir level – 1207.0 feet
    • Forecast end-of-January reservoir level – 1207.5 feet
    • Notes: The winter release rate will be at least 17,000 cfs and may be adjusted to lessen the impacts of winter ice formation.
  • Fort Randall Dam
    • Average releases past month – 13,900 cfs
    • End-of-December reservoir level – 1339.4 feet (up 1.6 feet from November)
    • Forecast end-of-January reservoir level – 1344.5 feet
    • Notes: Releases will be adjusted as necessary to maintain the desired reservoir elevation at Gavins Point. The reservoir was drawn down to 1337.5 feet near the end of November 2020 to provide space for winter hydropower generation at Oahe and Big Bend. The reservoir will refill to the base of the flood control pool by the end of February.
  • Big Bend Dam
    • Average releases past month – 15,300 cfs
    • Forecast average release rate – 19,700 cfs
    • Forecast reservoir level – 1421.0 feet
  • Oahe Dam
    • Average releases past month – 15,300 cfs
    • Forecast average release rate – 20,000 cfs
    • End-of-December reservoir level – 1607.0 feet (down 1.5 feet during November)
    • Forecast end-of-January reservoir level – 1606.3 feet
  • Garrison Dam
    • Average releases past month – 16,000 cfs
    • Current release rate – 16,000 cfs
    • Forecast average release rate – 17,100 cfs
    • End-of-December reservoir level – 1838.6 feet
    • Forecast end-of-January reservoir level – 1838.3 feet
    • Notes – Releases were set at 16,000 cfs in anticipation of the river freeze-in at Bismarck, North Dakota. Once an ice cover is established, releases will be gradually increased to 23,000 cfs.
  • Fort Peck Dam
    • Average releases past month – 10,100 cfs
    • Current release rate – 10,500 cfs
    • Forecast average release rate – 10,500 cfs
    • End-of-December reservoir level – 2235.9 feet
    • Forecast end-of-January reservoir level – 2234.7 feet
    • Notes: Releases will remain at 10,500 cfs in January and February.

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 572 million kWh of electricity in December. Typical energy generation for December is 688 million kWh. Total energy generation for 2020 was 10.1 billion kWh of electricity, compared to the long-term average of 9.4 billion kWh. Forecast generation for 2021 is 9.7 billion kWh.

To view the detailed three-week release forecast for the mainstem dams, go to https://go.usa.gov/xARQB.

MISSOURI RIVER MAINSTEM RESERVOIR DATA

Pool Elevation
(feet above mean sea level)

Water in Storage
(1,000 acre-feet)

On December 31

Change in December

On December 31

% of 1967-2019 Average

Change in December

Fort Peck

2235.9

-1.3

15,180

105

-288

Garrison

1838.6

-0.3

18,073

101

-106

Oahe

1607.0

+0.2

18,485

104

+48

Big Bend

1420.6

-0.2

1,667

98

-14

Fort Randall

1339.4

+1.6

2,295

69

+89

Gavins Point

1207.0

+0.5

350

89

+12

Total

56,050

101

-259

 

WATER RELEASES AND ENERGY GENERATION FOR DECEMBER

Average Release in 1,000 cfs

Releases in 1,000 acre-feet

Generation in Million kWh

Fort Peck

10.1

623

103

Garrison

16.0

983

143

Oahe

15.3

940

141

Big Bend

15.3

942

54

Fort Randall

13.9

852

82

Gavins Point

17.0

1,046

48

Total

571

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