OMAHA, NE – The U.S. Army Corps of Engineers Missouri River Basin Water Management Division plans to maintain higher-than-average releases from all System projects, including Gavins Point, through the summer and fall. “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, Gavins Point releases will remain near 58,000 cfs for the remainder of the navigation season to ensure evacuation of all stored flood waters prior to next year’s runoff season,” said John Remus, Chief of the Missouri River Basin Water Management Division.

The 2018 runoff forecast in the Missouri River Basin above Sioux City, Iowa, is 39.8 million acre feet (MAF), 157 percent of average according to the Corps. July runoff was 5.1 MAF, 155 percent of normal.

The Missouri River mainstem reservoir system (System) storage was 67.4 MAF as of August 1, occupying 11.3 MAF of the 16.3 MAF flood control zone. “System storage peaked on July 8 at 68.4 MAF and is gradually declining. Approximately 30 percent of the System’s flood storage remains available to capture runoff from late summer rainfall events. The current 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. 

When necessary, the releases will be reduced 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.

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 49,600 cfs during July, ranging from 26,000 to 58,000 cfs. Releases will remain near 58,000 cfs during August downstream conditions permitting. The Gavins Point reservoir ended July at elevation 1207.4 feet. The reservoir will end August near 1206.5 feet.
• Fort Randall Dam releases averaged 48,300 cfs in July. Releases will be adjusted as necessary to maintain the desired reservoir elevation at Gavins Point. Releases are being made from both the powerhouse and outlet tunnels. The reservoir ended July at elevation 1358.1 feet, falling 3.9 feet during the month. The reservoir will gradually fall to near 1356.5 feet during August.
• Big Bend Dam releases averaged 38,300 cfs in July. Releases are expected to average 54,000 cfs during August. The reservoir will remain near its normal elevation of 1420.0 feet during August.
• Oahe Dam releases averaged 43,300 cfs during July. Releases are expected to average 53,000 cfs in August. The reservoir ended July at elevation 1617.2 feet, 0.2 feet into the 3-foot Exclusive Flood Control Zone. The reservoir rose 2.9 feet during the month. The reservoir level is expected to peak near its current elevation before beginning to fall, ending August near elevation 1615.9 feet.
• Garrison Dam releases were stepped down from 60,000 to 54,000 cfs during July averaging 58,700 cfs during the month. Releases were stepped down to 50,000 cfs in early August, and will be further reduced to 46,000 cfs by mid-August. Releases in excess of the powerhouse release were transferred from the outlet tunnels to the spillway on August 6. Transferring releases from the outlet tunnels to the spillway will allow the Corps to inspect the outlet tunnels, and to test the repairs that have been made to the spillway. Releases will be made from the spillway for the next several weeks. Garrison reservoir peaked in early July at 1353.2 feet, 3.2 feet into the 4-foot Exclusive Flood Control Zone. The reservoir ended the month near 1850.7 feet. The reservoir is expected to continue falling ending August near 1846.7 feet.
• Fort Peck Dam releases averaged 17,400 cfs during July. Releases were decreased from 18,000 to 16,000 cfs near the end of July. Releases will remain at 16,000 cfs during August. Releases will be stepped down to 12,000 cfs around mid-September. Releases are currently greater than the maximum powerhouse release, so releases are being made from both the powerhouse and spillway. The reservoir peaked in early July at 2247.9 feet, 1.9 feet into the 4-foot Exclusive Flood Control Zone. The reservoir ended July at elevation 2246.1 feet. The reservoir is expected to continue falling ending August at 2243.4 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 1,336 million kWh of electricity in July. Typical energy generation for July is 943 million kWh. The power plants are projected to generate 13.3 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.