OMAHA, NE - The U.S. Army Corps of Engineers (Corps) Missouri River Basin Water Management Division increased releases from Gavins Point in late-May as tributaries downstream of Gavins Point receded. Releases from Gavins Point had been reduced to 20,000 cubic feet per second (cfs) in mid-May to lessen flooding along the lower Missouri River due to widespread, heavy rainfall in parts of Nebraska, Kansas, and Missouri.  Releases are expected to remain at the current rate of 33,000 cfs through June.

The mainstem reservoir system began the 2017 runoff season with the full 16.3 million acre-feet (MAF) of flood control storage available. The total volume of water stored in the reservoir system is currently 60.5 MAF. “System storage currently occupies 4.4 MAF of the 16.3 MAF flood control zone,” said Jody Farhat, chief of the Corps’ Missouri River Basin Water Management Division.   “With more than 70 percent of the flood control storage remaining, the reservoirs are well positioned to capture runoff from the mountain snowmelt and to allow future reductions in Gavins Point releases in response to summer rainfall events in the lower basin if needed.”

The 2017 runoff forecast in the Missouri River Basin above Sioux City, Iowa, is 29.9 MAF, 118 percent of normal. Runoff above Sioux City, Iowa in May was 4.3 MAF, 129 percent of normal. The mountain snowpack peaked about two week later than normal.  The snowpack peaked at 99 percent of the normal peak in the reach above Fort Peck on April 29 and 148 percent of the normal peak in the reach from Fort Peck to Garrison on May 2. As of June 5, approximately 25 percent of this year’s peak snow accumulation was remaining in the reach above Fort Peck and 35 percent of the peak accumulation was remaining in the reach from Fort Peck to Garrison. View the mountain snowpack graphic here: http://www.nwd-mr.usace.army.mil/rcc/reports/snow.pdf.

Navigation flow support for the start of the navigation season was at full service levels, which is designed to provide a 9-feet deep navigation channel. In mid-April Gavins Point releases were increased to a level slightly above full service due to the higher-than-normal forecasted runoff and System and tributary storage levels. “Based on the current runoff forecast, navigation flow support will continue to be at a level slightly above full service to provide beneficial use of the excess runoff while reducing flood risk,” said Farhat.

Weekly updates on plains and mountain snowpack 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 conditions, including rainfall and mountain snowpack, and will adjust the regulation of the reservoir system based on the most up-to-date information.

Reservoir Forecasts

• Gavins Point Dam releases averaged 28,100 cubic feet per second (cfs) during May. Releases were increased in May to approximately 33,000 cfs to evacuate the above average runoff in the upper basin while preventing the endangered least terns and threatened piping plovers from nesting on low sandbars. These sandbars could be inundated later in the summer if higher releases are needed to meet downstream navigation targets or to evacuate flood water. The Gavins Point reservoir ended May at elevation 1205.5 feet and will remain near 1206.0 feet during June.
• Fort Randall Dam releases averaged 25,200 cfs in May. Releases will be adjusted as necessary to maintain the desired reservoir elevation at Gavins Point. The reservoir ended May at elevation 1356.1 feet and will average near elevation 1355 feet in June.
• Big Bend Dam releases averaged 22,500 cfs in May. Releases are expected to average 28,700 cfs this month. The reservoir will remain near its normal elevation of 1420.0 feet during June.
• Oahe Dam releases averaged 24,100 cfs during May. Releases are expected to average 28,500 cfs in June. The reservoir ended May at elevation 1609.8 feet, rising 1.5 feet during the month. The reservoir level is expected to rise during June due to increased Garrison releases, and is expected to end the month near elevation 1611.1 feet.
• Garrison Dam releases averaged 32,200 cfs during the month of May. Releases were increased from 30,000 cfs to 35,000 cfs in mid-May. Garrison reservoir ended May at elevation 1843.1 feet, rising 1.6 feet during the month. The reservoir level is expected to rise to elevation 1847.2 feet during June.
• Fort Peck Dam releases averaged 8,700 cfs during May. Releases were increased to 10,000 cfs in early June. The reservoir ended May at elevation 2239.0 feet, rising 1.8 feet during the month. The reservoir is expected to rise during June ending the month near elevation 2241.5 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 898 million kWh of electricity in May. Typical energy generation for May is 786 million kWh. The power plants are projected to generate 10.5 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

WATER RELEASES AND ENERGY GENERATION FOR MAY