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Posted 6/5/2018

Release no. 18-035


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

OMAHA, NE - The U.S. Army Corps of Engineers (Corps) Missouri River Basin Water Management Division plans to maintain higher-than-average releases from all System projects, including Gavins Point, over the next several months. “Due to the water currently being stored in the reservoirs and the higher-than-average runoff being forecast in the Missouri River Basin above Sioux City, Iowa, the service level will remain 15,000 cubic feet per second (cfs) above full service to facilitate the evacuation of stored flood waters. The increased service level means that Gavins Point releases will be increased from 42,000 cubic feet per second (cfs) to 44,000 cfs, and possibly higher, as downstream tributary flows recede,” said John Remus, Chief of the Missouri River Basin Water Management Division. Gavins Point releases will be adjusted, when needed, in response to basin conditions. When necessary, the Corps will reduce releases from the System projects and utilize the available flood control space in the reservoirs, in order to lessen flooding downstream of all the projects. It is important to note that the ability to significantly reduce flood risk along the lower Missouri River diminishes at locations further downstream due to the large uncontrolled drainage area and the travel time from Gavins Point Dam.

The 2018 runoff forecast in the Missouri River Basin above Sioux City, Iowa, is 34.6 million acre feet (MAF), 136 percent of average according to the Corps. May runoff in the Fort Peck and Garrison reaches was the second highest on record. “The updated runoff forecast reflects the rapid melting of mountain snowpack in the upper basin as well as widespread rainfall throughout the basin,” said Remus.

As of June 1, the mountain snowpack was 91 percent of average in the reach above Fort Peck and 88 percent of average in the reach from Fort Peck to Garrison. The mountain snowpack peaked on April 19 in the Fort Peck reach and on April 15 in the Fort Peck to Garrison reach. Compared to 2011, the mountain snowpack in 2018 had a lower peak snow water equivalent in both reaches and melted earlier. Both reaches have approximately 6.0 inches of snow water equivalent remaining while at this same time in 2011, there was 19 inches remaining above Fort Peck and 22 inches remaining in the Fort Peck to Garrison reach. View the mountain snowpack graphic here: http://www.nwd-mr.usace.army.mil/rcc/reports/snow.pdf.

The Missouri River mainstem reservoir system (System) storage was 63.4 MAF as of June 1, occupying 7.3 MAF of the 16.3 MAF flood control zone. “More than 50 percent of the System’s flood storage remains available to capture runoff from the remaining mountain snowmelt and summer rainfall events. On June 1, 2011, 12 percent of the total flood control storage was available. The considerable amount of vacant flood control storage provides flexibility to lessen downstream flooding should suddenly-developing large rainfall events occur anywhere in the basin,” said Remus.

Weekly updates on basin conditions, reservoir levels and other topics of interest can be viewed here: http://www.nwd-mr.usace.army.mil/rcc/reports/pdfs/weeklyupdate.pdf.

The Corps will continue to monitor basin and river conditions, including rainfall and mountain snowmelt, and will adjust the regulation of the System based on the most up-to-date information.

Reservoir Forecasts

  • Gavins Point Dam releases averaged 39,500 cfs during May. Releases were increased to 42,000 cfs during May. Downstream conditions permitting, releases will be increased until they reach the expanded navigation support levels, which are estimated at 44,000 cfs. The Gavins Point reservoir ended May at elevation 1205.8 feet and will remain near 1206.0 feet during June.
  • Fort Randall Dam releases averaged 37,200 cfs in May. Releases will be adjusted as necessary to maintain the desired reservoir elevation at Gavins Point. Due to on-going maintenance at the project, planned releases will require releases from the powerhouse and outlet tunnels. The reservoir ended May at elevation 1358.0 feet, falling 0.6 foot during the month. The reservoir will gradually fall to near 1357.0 feet during June.
  • Big Bend Dam releases averaged 31,500 cfs in May. Releases are expected to average 37,100 cfs during June. The reservoir will remain near its normal elevation of 1420.0 feet during June.
  • Oahe Dam releases averaged 34,100 cfs during May. Releases are expected to average 37,200 cfs in June. The reservoir ended May at elevation 1611.1 feet, rising 0.8 foot during the month. The reservoir level is expected to rise 2.8 feet during June.
  • Garrison Dam releases averaged 36,800 cfs during May, ranging from 32,000 cfs to 39,000 cfs during the month. Releases will be increased to 44,000 cfs in early June. Garrison reservoir is forecasted to rapidly rise during the first two weeks of June, peaking near elevation 1851.5 ft.
  • Fort Peck Dam releases averaged 14,200 cfs during May. Releases were increased throughout May, reaching 18,000 cfs at the end of May. Releases were increased to 20,000 cfs in early June. The planned release is greater than the maximum powerhouse release, so releases will be required from both the powerhouse and spillway. The reservoir ended May at elevation 2244.4 feet, rising 4.5 feet during the month. The reservoir is expected to rise 2.1 feet during June ending the month near elevation 2246.5 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.

The six mainstem power plants generated 871 million kWh of electricity in May. Typical energy generation for May is 928 million kWh. The power plants are projected to generate 12.7 billion kWh of electricity this year, compared to the long-term average of 9.3 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 1967-2017 Average

Change in May

Fort Peck

2244.4

+4.5

17,122

119

+1052

Garrison

1846.7

+4.3

20,776

117

+1463

Oahe

1611.1

+0.8

19,856

112

+352

Big Bend

1419.8

-1.0

1,622

95

-41

Fort Randall

1358.0

-0.6

3,671

110

-11

Gavins Point

1205.8

-1.3

322

82

-30

 

 

Total

63,369

115

+2785


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

14.2

873

115

Garrison

36.8

2,264

353

Oahe

34.1

2,097

320

Big Bend

31.5

1,938

113

Fort Randall

37.2

2,287

158

Gavins Point

39.5

2,426

71

 

Total

1,130