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Corps reports above normal May runoff in the Missouri River Basin; drought conditions improve in upper basin

Published June 5, 2015
The Missouri River Water Management office releases a report at the beginning of each month to the public documenting the monthly river forecast and release schedule. The Missouri River Water Management Division is part of the Northwestern Division of the U.S. Army Corps of Engineers and is located in Omaha, Nebraska.

The Missouri River Water Management office releases a report at the beginning of each month to the public documenting the monthly river forecast and release schedule. The Missouri River Water Management Division is part of the Northwestern Division of the U.S. Army Corps of Engineers and is located in Omaha, Nebraska.

OMAHA, NE — The U.S. Army Corps of Engineers Missouri River Basin Water Management Division reports May runoff in the Missouri River Basin above Sioux City, Iowa, was 3.7 million acre feet (MAF), 110 percent of normal.  The 2015 runoff forecast has increased to 22.5 MAF, 89 percent of normal.  Average annual runoff is 25.2 MAF.

“May runoff was above normal due to rainfall that occurred in Montana, Wyoming and the Dakotas. This slightly above normal runoff occurred despite a below normal contribution from the melting mountain snowpack and the previously dry soil conditions,” said Mike Swenson, team leader in the Missouri River Basin Water Management Office. “After a very dry March and April, drought conditions had spread over much of the upper basin.  With the above normal precipitation in May, soil moisture in the upper basin has returned to more normal conditions.”

The total volume of water stored in the Missouri River Mainstem reservoir system on June 1 was 58.4 MAF; system storage gained 1.1 MAF in May. “The total water stored in the reservoir system is 2.3 MAF above the base of the annual flood control and multiple use zone,” said Swenson. “With 14.0 MAF of the 16.3-MAF flood control storage available, the system is well positioned to capture runoff and lessen flood risk downstream.” The annual flood control zone begins at 56.1 MAF and is the portion of the reservoirs that the Corps prefers to use for normal operations.

Heavy rain fell across much of the lower basin in early June resulting in increased flows on many of the tributaries below the system of reservoirs. “Rainfall events like this can cause localized flooding downstream of the reservoir system. Gavins Point Dam releases were reduced from 28,000 cubic feet per second (cfs) to 22,000 cfs, as part of our normal flood risk reduction measures,” stated Swenson. The Corps will utilize the available flood control space in the reservoirs, if necessary, to limit downstream river levels.

According to information from the Natural Resources Conservation Service, the mountain snowpack accumulation peaked in the reach above Fort Peck Dam at 72 percent of the normal peak, and in the reach from Fort Peck to Garrison dams, it peaked at 78 percent of the normal peak.  The snowpack was 37 percent and 60 percent of the June 1 average in the reaches above Fort Peck and from Fort Peck to Garrison, respectively.

View mountain snowpack graphic here:  http://www.nwd-mr.usace.army.mil/rcc/reports/snow.pdf

USACE will continue to monitor the mountain snowpack, basin soil conditions and rainfall events to fine tune the regulation of the reservoir system based on the most up-to-date information. 

Reservoir Forecasts 

Gavins Point Dam releases averaged 27,400 cfs during May. Releases, which are currently at 28,000 cfs, are expected to remain near that level during June to prevent endangered least terns and threatened piping plovers from nesting on low sandbars. These sandbars would be flooded later in the summer when higher releases are needed to meet downstream navigation flow targets.  The nesting season runs from May to late August. The reservoir behind Gavins Point Dam ended June at elevation 1206.5 feet. The reservoir will remain near elevation 1206 feet during June.

Fort Randall Dam releases averaged 25,100 cfs during June.  Fort Randall releases are currently at 23,500 cfs, and will be adjusted, as necessary, to maintain the desired pool elevation at Gavins Point Dam. The reservoir ended May at elevation 1356.1 feet, up 0.4 feet during the month. The pool will be gradually lowered to near 1355 feet during June.

Big Bend Dam releases averaged 20,000 cfs during May. They are expected to average 20,800 cfs this month. The reservoir will remain near its normal elevation of 1420 feet in June.

Oahe Dam releases averaged 21,500 cfs during May and releases are expected to average 19,500 cfs this month. The reservoir ended May at elevation 1610.0 feet, up 2.9 feet during the month and 2.5 feet into the annual flood control zone. The reservoir is expected to rise less than 2 feet during June.

Garrison Dam releases were reduced from 23,000 cfs to 22,000 cfs during May, averaging 22,800 cfs during the month.  Releases were reduced in May to help hold the reservoir steady during the forage fish spawn. Releases were reduced to 21,000 cfs on June 2 and will remain near that rate for the remainder of the month. Garrison ended May at elevation 1838.5 feet, unchanged from the previous month and 1 foot into the annual flood control zone.  It is expected to rise approximately 1 foot during June.

Fort Peck Dam releases were increased from 8,000 cfs to 9,000 cfs on June 2. Releases will remain at that rate during June. The reservoir ended May at elevation 2236.0 feet, up 0.2 feet from the previous month. The reservoir is forecast to fall less than 1 foot during June. 

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. 

The six mainstem power plants generated 810 million kilowatt hours (kWh) of electricity in May. Typical energy generation for May is 786 million kWh. The power plants are projected to generate 9.1 billion kWh of electricity this year, compared to the normal 10 billion kWh. 

To view the detailed three-week release forecast for the mainstem dams, go to
http://www.nwd-mr.usace.army.mil/rcc/reports/twregfcast.pdf.

MISSOURI RIVER MAIN STEM RESERVOIR DATA

 

Pool Elevation

(feet above mean sea level)

Water in Storage - 1,000 acre-feet

 

On May 31

Change in May

On May 31

% of 1967-2014 Average

Change in May

Fort Peck

2236.0

+0.2

15,221

105

+57

Garrison

1838.5

+0.0

18,070

103

+17

Oahe

1610.0

+2.9

19,462

105

+934

Big Bend

1421.2

+0.7

1,704

100

+46

Fort Randall

1356.1

+0.4

3,499

91

+31

Gavins Point

1206.5

+0.2

339

90

+6

 

 

 Total

58295

103

1091

 

WATER RELEASES AND ENERGY GENERATION FOR MAY

 

 

Average Release in 1,000 cfs

Releases in 1,000 acre-feet

Generation in Million kWh

Fort Peck

7.7

475

78

Garrison

22.8

1,401

216

Oahe

21.5

1,322

202

Big Bend

20.0

1,231

74

Fort Randall

25.1

1,542

165

Gavins Point

27.4

1,685

75

 

 

Total

810




Contact
Trisha Dorsey
503-808-3710
trisha.c.dorsey@usace.army.mil

Release no. 20150605-001