2013-04-18 / Top News

Lake Oahe to rise 1.4 feet in April

Dry conditions continue in the upper Missouri River basin indicating less-thannormal runoff in 2013.

Based on the current soil moisture and snowpack conditions, 2013 runoff in the Missouri River basin above Sioux City, Iowa, is forecast to be 20.5 million acre feet, 81 percent of normal. Runoff for the month of March was 55 percent of normal.

As a result of the persistent drought conditions, the Corps is providing minimum flow support for navigation as part of its drought conservation measures for the first half of the 2013 navigation season.

The total volume of water stored in the mainstem reservoir system on April 1 was 48.8 million acre feet.

“System storage is 8 million acre feet below the top of the Carryover Multiple Use Zone in the system. That zone is designed to provide service to the eight Congressionally authorized purposes, though at reduced levels, through a 12-year drought like that of the 1930s and early 1940s,” Jody Farhat, Chief of the Missouri River Water Management Division, said. “Drought conservation measures, such as minimum winter releases and reduced flow support for navigation, are implemented as the volume of water in the reservoir system declines.”

In mid-March the Corps increased releases out of Gavins Point Dam from 14,000 cubic feet per second to 25,000 cfs in support of the navigation season which began April 1 near St. Louis.

“In addition to releasing minimum flows for navigation, we will conserve water throughout the navigation season by not providing flow support in river reaches above Kansas City if there is no commercial navigation traffic using that section of the river,” Farhat said.

Minimum-service flow targets range from 25,000 cfs at Sioux City, Iowa, to 35,000 cfs at Kansas City, Mo. Minimum service flow support is generally sufficient to provide a navigation channel that is 8 feet deep by 200 feet wide although challenges may exist in localized reaches. The level of flow support for the second half of the navigation season and the season length will be determined following the system storage check on July 1.

“Flood control remains a primary consideration as we move into 2013 despite the concerns about the impacts of the drought on the basin’s resources due to the potential for flooding caused by localized thunderstorms,” Farhat said. “We will continue to monitor mountain snowpack, rainfall runoff and basin soil conditions to fine tune the regulation of the reservoir system based on the most up-to-date information.”

Mountain snowpack is currently 90 percent of normal in the reach above Fort Peck and 84 percent in the reach between Fort Peck and Garrison. Typically 97 percent of the peak mountain snowpack accumulation has occurred by April 1.

“The lower-than-normal mountain snowpack indicates that we are likely to see below normal runoff during the months of May, June and July,” Farhat said. “But it’s still early. As we learned over the last two years, conditions on the ground can change very quickly so we will continue monitoring basin conditions and make any necessary release adjustments as the spring unfolds.”

View mountain snowpack graphic here: www.nwd-mr. usace.army.mil/rcc/reports/ snow.pdf

Reservoir Forecasts

Gavins Point releases averaged 18,600 cfs during the month of March. Releases were stepped in mid-March to provide flow support for the navigation season. The reservoir behind Gavins Point Dam ended March at elevation 1205.8 feet msl. The reservoir will remain near elevation 1206 feet msl during April.

Fort Randall releases averaged 16,500 cfs during March. Releases were stepped up in mid-March corresponding with the increases in Gavins Point releases, and are currently 23,000 cfs. Fort Randall releases will be adjusted as necessary to maintain the desired elevation at Gavins Point. The reservoir ended March at elevation 1353.4 feet msl, up 2.7 feet during the month. It is expected to rise to near elevation 1355 feet msl by the end of the April.

Big Bend releases averaged 17,900 cfs during the month of March. They are expected to average 22,000 cfs this month. The reservoir will remain near its normal elevation of 1420 feet msl during April.

Oahe releases averaged 19,500 cfs during the month of March. Releases are expected to average 21,000 cfs this month. The reservoir ended March at elevation 1596.6 feet msl, up 0.2 foot during the month. The reservoir is expected to rise 1.4 feet during the month of April.

Garrison releases averaged 17,700 cfs in March. Releases were stepped down from 23,000 cfs to 15,500 cfs after the river ice was out near Bismarck. Releases were increased to 19,000 cfs at the beginning of April to help provide a rising reservoir during the forage fish spawn at Oahe. Garrison ended the month at elevation 1827.2 feet msl, down 0.2 feet from the previous month. It is expected to rise more than two feet during April.

Fort Peck releases were stepped down from 12,500 cfs to 6,000 cfs at the beginning of March. They will remain at that rate through April. The reservoir ended March at elevation 2222.5 feet msl, up 0.3 foot from the previous month. The reservoir is forecast to rise nearly two feet during April.

The forecast reservoir releases and elevations discussed above should not be assumed to be definitive. Additional precipitation or lack of precipitation in the basin could cause adjustments to the reservoir release rates.

The six mainstem power plants generated 612 million kilowatt hours of electricity in March. Typical energy generation for the month of March is 639 million kWh. The power plants are projected to generate 8.2 billion kWh of electricity this year, compared to the normal of 10 billion kWh.

To view the detailed threeweek release forecast for the mainstem dams, go to: www.nwd-mr.usace.army.mil/rcc/ reports/twout.html.

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