Written by Herald-News
The U.S. Army Corps of Engineers (Corps) Missouri River Basin Water Management Division reports runoff in the Missouri River Basin above Sioux City, Iowa, for the month of June was 8.3 million acre feet (MAF), 153 percent of normal. The 2014 runoff forecast is 33 MAF, 131 percent of normal. Average annual runoff is 25.2 MAF.
“June precipitation was generally above normal across much of the Missouri River Basin causing above normal runoff into the reservoirs. The exception was the below normal precipitation in western and central Montana that contributed to lower than expected runoff into Fort Peck Reservoir,” said Mike Swenson, team leader in the Missouri River Basin Water Management Office. “Repeated rains in the lower basin also increased tributary flows, below the system of reservoirs, resulting in lower releases from Gavins Point Dam.”
Dring June, releases from Gavins Point Dam were reduced to as low as 10,000 cubic feet per second (cfs). “Releases from Gavins Point were cut by 20,000 cfs to lessen flood risk downstream. Those reductions lowered peak river stages three to four feet in most areas,” explained Swenson. “Following the flood crest, releases have been gradually increased to 25,000 cfs to meet the navigation flow targets downstream, as the flood flows continue to recede.”
The melting of the mountain snowpack is nearly complete. In the reach above Fort Peck Dam, 6 percent of the normal peak snowpack remains, and in the reach from Fort Peck to Garrison dams 3 percent of the normal peak snowpack remains. View mountain snowpack graphic here: http://www.nwd-mr.usace.army.mil/rcc/reports/snow.pdf.
The total volume of water stored in the Mainstem Reservoir System is currently 60.5 MAF, occupying 4.4 MAF of the 16.3 MAF combined flood control storage zones. “The reservoirs remain well positioned to capture additional runoff should further reductions in releases become necessary,” stated Swenson.
The Missouri River Mainstem System Master Manual sets the navigation service level for the second half of the season and the season length based on the July 1 system storage. The July 1 storage check called for an increase in the service level for navigation flow support, as well as a full, eight-month season. “Flow support, which had been 3,000 cfs below full service from April to June, was increased to full service in July,” said Swenson. Flow targets for the second half of the season will now range from 31,000 cfs at Sioux City, Iowa, to 41,000 cfs at Kansas City, Mo. The increase in service level will provide a navigation channel 9 feet deep and 300 feet wide.
The Corps will continue to monitor basin conditions and fine tune the regulation of the reservoir system based on the most up-to-date information.
Fort Peck Dam releases averaged 8,900 cfs in June. Releases were cut from 9,000 to 7,000 cfs in early July. Releases will likely remain near 7,000 cfs in July, but may be adjusted to provide adequate irrigation support below Fort Peck. The reservoir ended June at elevation 2230.0 feet, up 1.7 feet. The reservoir is forecasted to rise less than 1 foot during July.
Gavins Point Dam releases averaged 22,800 cfs in June, ranging from 10,000 to 30,000 cfs. Releases will remain near the current rate of 25,000 cfs in early July, and will be adjusted, as necessary, to meet downstream flow targets as tributaries’ flows drop. The reservoir behind Gavins Point Dam ended June at elevation 1206.8 feet. The reservoir will remain near elevation 1206 feet during July.
Fort Randall Dam releases ranged from 2,000 to 27,000 cfs during June, averaging 19,000 cfs. Fort Randall releases will be adjusted during July, as necessary, to maintain the desired elevation at Gavins Point Dam. The reservoir ended June at elevation 1356.9 feet, up 1.6 feet during the month. The reservoir will remain near elevation 1357 feet during July.
Big Bend Dam releases averaged 18,200 cfs during the month of June. They are expected to average near 22,000 cfs this month. The reservoir will remain near its normal elevation of 1420 feet during July.
Oahe Dam releases averaged 19,300 cfs during the month of June. Releases are expected to average 21,000 cfs this month. The reservoir ended June at elevation 1612.4 feet, up 4.5 feet during the month. The reservoir is expected to rise approximately 2 feet during the month of July.
Garrison Dam releases averaged 29,700 cfs in June. Releases were reduced from 30,000 to 29,000 cfs in early July. Releases will be reduced to 28,000 cfs around mid-July. Garrison ended June at elevation 1845.2 feet, up 5.4 feet. It is expected to rise about two feet during July.
The forecasted 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 752 million kilowatt hours (kWh) of electricity in June. Typical energy generation for the month of June is 843 million kWh. The power plants are projected to generate 9.3 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.