Levels of Lake Oahe continue to drop

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– By Katie Zerr –

As drought conditions continue to expand across the country, reservoirs on the Missouri River basin continue to shrink.

With the lack of precipitation in the region, tributary flows into the six Missouri River Mainstem reservoirs has been greatly reduced throughout the summer.

On Lake Oahe, near Mobridge, the Moose Flats are again appearing as the water level drops below 1597 feet above mean sea level. That is more than 12 feet below what it was one year ago when the reservoir was very near capacity at just above 1619 feet above mean sea level.

Runoff into the Missouri River basin above Sioux City, Iowa during the month of August was only 64 percent of normal, according to the monthly U.S. Army Corps of Engineers report. The report shows the calendar year runoff forecast is 83 percent of normal, while July’s forecast was 85 percent of normal.

During the flooding in 2011, the runoff totaled an historic 61 MAF above Sioux City, nearly three times more than this year.

In August, runoff between the Fort Peck and Garrison dams was only 46 percent of normal with the majority of the upper basin receiving less than 50 percent of normal August precipitation.

Levels in the upper three large reservoirs, Fort Peck, Garrison and Oahe, fell 2 to 3.5 feet during the August and have continued to drop through September. On Aug. 1, Lake Oahe was at 1603.86 feet above mean sea level, ending the month at 1600.56. The reservoir has dropped another 3.4 feet in September.

According to the Corps report, drought conservation measures will be implemented beginning this winter based water storage recorded on Sept. 1.

Winter releases from Gavins Point will be at minimum levels, averaging near 12,000 cubic feet per second (cfs) from December through February.   Temporary increases above 12,000 cfs will be provided during periods of ice formation to keep water intakes along the lower river operational. When the reservoir system is full, Gavins Point winter releases are generally scheduled near 17,000 cfs, or higher if flood water is being evacuated.

The Corps reports that although the runoff forecast continues to shift downward, there is enough water in the reservoir system to continue to provide good service to all eight of the congressionally authorized purposes for the remainder of the calendar year. The purposes include flood control, navigation, hydropower, irrigation, water supply, water quality control, recreation, and fish and wildlife.

Based on the July 1 storage check, the Corps is providing a full 8-month navigation season (April 1 to Dec. 1) and full service flows, which are designed to provide a 9-foot-deep by 300-foot-wide navigation channel.



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