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MAY RUNOFF ABOVE AVERAGE IN MISSOURI RIVER BASIN

Published June 7, 2016
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, Neb. – Runoff in the Missouri River Basin above Sioux City, Iowa, was 4.5 million acre feet (MAF) during May, 136 percent of average, according to the U.S. Army Corps of Engineers (Corps). The 2016 calendar year runoff forecast is 25.3 MAF, which is the historic average.

“Conditions in much of the Missouri River Basin were wetter than average during May. In the upper basin, heavy rains accompanied by mountain snowmelt increased runoff into the reservoir system,” said Jody Farhat, chief of the Corps’ Missouri River Basin Water Management Division. Widespread rain in the lower basin also increased flows on many of the tributaries below the reservoir system, causing tributary and Missouri River levels to rise. “Rainfall events like these can lead to localized flooding downstream of the reservoir system,” said Farhat. Gavins Point releases, which are currently set at 21,500 cfs, were lowered in May to reduce flood risk along the lower river and will be gradually increased as the downstream stages decline.

The total volume of water currently stored in the Missouri River Mainstem Reservoir System is 59.4 MAF, occupying 3.3 MAF of the 16.3 MAF flood control zone. “The reservoirs remain well positioned to capture additional runoff should further reductions in releases become necessary,” said Farhat. “We expect to provide good service to all of the authorized purposes.”  Based on the current runoff and reservoir regulation forecasts, full-service flow support is expected to be provided for the second half of the navigation season. The system storage on July 1 will determine the navigation flow support level for the second half of the season as well as the navigation season length.

Fort Randall releases also were reduced during May and early June to limit the rise of the Gavins Point reservoir level, which was impacted by high runoff from localized rain and reduced Gavins Point releases. At Fort Randall, reduced releases combined with high inflows from localized rain events resulted in the reservoir level climbing above elevation 1361.0 feet during the first part of May. The reservoir is near elevation 1359.0 feet. “Releases at the upstream dams, Oahe and Big Bend, were adjusted and will be held at lower rates for several weeks to allow the Fort Randall reservoir to be gradually lowered to the normal operating level,” said Farhat. The reservoir is about 4 feet above its normal elevation at this time of year.

The Corps will continue to monitor basin conditions and adjust the regulation of the reservoir system based on the most up-to-date information.

The mountain snowpack peaked in early April, which is about two weeks earlier than normal. The snowpack peaked at 95 percent of average above Fort Peck on April 1 and 89 percent of average in the reach between Garrison and Fort Peck on April 2. As of June 1, about one-third of this year’s peak in the reach between Fort Peck and Garrison. Normally, about 40 percent of the peak remains on June 1. View the mountain snowpack graphic at http://www.nwd-mr.usace.army.mil/rcc/reports/snow.pdf

The Corps will continue to monitor basin conditions, including rainfall and mountain snow accumulation, and will adjust the regulation of the reservoir system based on the most up-to-date information.

 

Reservoir Forecasts

Gavins Point releases averaged 18,800 cfs during May as a result of high flows below the reservoir system. Releases are expected to be stepped up gradually from 20,000 cfs to 22,000 cfs in early June as flows downstream of the reservoir system subside. Releases will be made to prevent the endangered least tern and threatened piping plover from nesting on low sandbars that would be flooded later this summer when higher releases are needed to support navigation. The nesting season runs from May to late August. The reservoir behind Gavins Point Dam ended May at elevation 1207.8 feet and will decline to elevation 1206.0 feet during June.

Fort Randall Dam releases averaged 13,200 cfs in May. Releases will be adjusted as necessary to maintain the desired elevation at Gavins Point Dam. The reservoir ended May at elevation 1358.7 feet, falling 0.9 feet during the month. The reservoir is expected to gradually be lowered, ending June near elevation 1355.2 feet.

Big Bend Dam releases averaged 8,000 cfs in May. Releases are expected to average 9,100 cfs this month. The reservoir will remain near its normal elevation of 1420.0 feet during June.

Oahe Dam releases averaged 8,700 cfs during May. Releases are expected to average 8,200 cfs this month. The reservoir ended May at elevation 1611.4 feet, rising 2.2 feet during the month. The reservoir level is expected to rise less than 3 feet in June, ending the month near elevation 1614.0.

Garrison Dam releases were increased from 14,000 cfs to 21,000 cfs in May, averaging 18,100 cfs in the month. Releases are expected to remain at 21,000 cfs during June. Garrison ended May at elevation 1839.7 feet, rising 2.1 feet during the month. The reservoir is expected to rise more than 3 feet during June ending the month near elevation 1843.0.

Fort Peck Dam releases averaged 7,400 cfs in May. Releases will be increased from 8,000 cfs to 9,000 cfs during June. The reservoir ended May at elevation 2235.9 feet, up 1.7 feet during the month. The reservoir level is forecast to rise nearly 2 feet 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 504 million kilowatt hours of electricity in May. Typical energy generation for the month of May is 786 million kWh. The power plants are projected to generate 8.1 billion kWh of electricity this year, compared to the normal of 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 Mainstem 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 1967–2015 Average

Change in May

Fort Peck

2235.9

+1.7

15,189

104

+356

Garrison

1839.7

+2.1

18,425

105

+654

Oahe

1611.4

+2.2

19,912

107

+693

Big Bend

1420.9

+0.2

1,682

98

+10

Fort Randall

1358.7

-0.9

3,737

97

-74

Gavins Point

1207.8

+1.0

368

98

+22

 

 

Total

59,313

105

+1,661

 

 

Average Release in 1,000 cfs

Releases in 1,000 acre-feet

Generation in Million kWh

Fort Peck

7.4

457

77

Garrison

18.1

1,114

172

Oahe

8.7

536

82

Big Bend

8.0

491

28

Fort Randall

13.2

811

91

Gavins Point

18.8

1,158

54

 

 

Total

504

 


Contact
Michael Coffey
503-808-3722
michael.a.coffey@usace.army.mil

Release no. 20160607