The U.S. Army Corps of Engineers is increasing water releases at the four hydropower projects on the Missouri River to reduce flood risks from heavy late summer rains.
The Corps' Missouri River Basin Water Management Division said the higher releases will evacuate flood water stored in the mainstem reservoir system, preparing the system to capture next year's anticipated runoff. The excess water also is to allow the Corps to extend the Missouri River navigation season by 10 days, to Dec. 10, and provide higher winter releases, which will benefit winter hydropower generation and reduce risks to water intakes from ice formation.
The Corps said runoff above Sioux City, Iowa, was 3.2 million acre-feet in August, 241 percent of normal. The 2014 runoff forecast is 35.6 million acre-feet, 141 percent of normal. Average annual runoff is 25.2 million acre-feet.
"Rains in the upper basin have swelled tributary rivers and increased runoff into the reservoir system," Jody Farhat, chief of the Missouri River Basin Water Management Division, said. "August runoff was the third highest since 1898. The Corps' reservoir system remains within normal operating levels, but the higher runoff has resulted in the need to evacuate water from the system this fall above the rate required for navigation."
Releases will be increased at the 786-MW Oahe, 494-MW Big Bend, 320-MW Fort Randall and 132.3-MW Gavins Point projects. The Corps said this will ensure the entire flood control capacity of the system is available for next year's runoff.
The total volume of water stored in the reservoir system is 61.3 million acre-feet. About 5.2 million acre-feet of the 16.3 million acre-feet combined flood control storage is occupied.
The Missouri's six mainstem hydropower plants -- also including 185.3-MW Fort Peck and 517.8-MW Garrison -- generated 962 million kWh in August. Typical generation for August is 1.001 billion kWh. The hydro plants are projected to generate 9.9 billion kWh this year, compared to a normal of 10 billion kWh.
The Corps said it would post in late September its 2014-2015 Draft Annual Operating Plan for the Missouri River Mainstem Reservoir System on its Internet site at www.nwd-mr.usace.army.mil/rcc/aop.html. Fall public meetings are to be held in five cities throughout the basin in the last week of October to discuss and take comments on the draft.