Higher Releases Planned On Missouri River

The Corps of Engineers Missouri River Basin Water Management Division said it will maintain higher-than-average releases from all projects on the system over the next several months.

“Due to higher-than-average runoff being forecast in the Missouri River Basin above Sioux City, Iowa, we have increased the service level 15,000 cubic feet per second (cfs.) above full service to facilitate the evacuation of stored flood waters,” said John Remus, chief of the division. “The increased service level means that Gavins Point releases may be increased to 42,000 cfs., and possibly higher, as downstream tributary flows recede.”

Gavins Point releases will be adjusted, when needed, in response to basin conditions, the Corps said. When necessary, the Corps will reduce releases from the system projects and utilize the available flood control space in the reservoirs, in order to lessen flooding downstream of all the projects.

Forecast Raised

The Corps has raised its 2018 runoff forecast in the Missouri River Basin above Sioux City to 33.2 million acre feet (maf.).

“The updated runoff forecast increased 3.0 maf. from April’s forecast. This was due to the continued accumulation of mountain snowpack in the upper basin as well as the delayed melt of plains snow during the first two weeks of April,” Remus said. “Based on the current mountain snowpack and temperature and precipitation outlooks, runoff into the Fort Peck and Garrison reservoirs is expected to be above average from May through August,” he said.

Flood Storage

The Missouri River mainstem reservoir system storage was 60.6 maf. as of May 1, occupying 4.5 maf. of the 16.3 maf. flood control zone. “More than 70 percent of the system’s flood storage [capacity] remains available to capture runoff from the mountain snowmelt and spring and summer rainfall events,” Remus said.

Gavins Point Dam releases averaged 34,000 cfs. during April. Releases were increased to 36,000 cfs. during early April, but were reduced near the end of the month due to higher flows downstream. Releases were increased to 37,000 cfs. in early May. Downstream conditions permitting, releases will gradually be increased until they reach the expanded navigation support levels, which are estimated at 40,000 to 42,000 cfs. The Gavins Point reservoir ended April at elevation 1207.1 feet and will remain near 1206.0 feet during May, the Corps said.

The six mainstem power plants generated 870 million kwh. of electricity in April. Typical energy generation for April is 690 million kwh. The power plants are projected to generate 12.7 billion kwh of electricity this year, compared to the long-term average of 9.3 billion kwh.