BISMARCK, N.D. — Electric power generation from the Missouri River's six upstream dams increased 23 percent in 2017 but the federal agency that sells the power still had to buy electricity on the open market to fulfill contracts.
The U.S. Army Corps of Engineers, which manages dams and reservoirs along the 2,341-mile river, said energy production from the dams in the Dakotas, Montana and Nebraska totaled 9.6 billion kilowatts of electricity last year, up from 7.6 billion kilowatts.
A billion kilowatt-hours of power is enough to supply about 86,000 homes for a year, said Mike Swenson, a corps engineer in Omaha, Nebraska.
The Western Area Power Administration, which buys and sells power from 56 hydropower plants around the nation, says the six Missouri River dams are WAPA's second-largest producer of energy.
The agency sells the power to rural electric cooperatives, municipal utilities, Indian tribes and other customers. A shortfall of needed hydropower to satisfy customers' contracts meant WAPA had to purchase $28.3 million of electricity on the open market, agency data show.
WAPA has spent more than $1.7 billion since 2000 to fulfill contracts, mostly due to drought years that caused shallow river levels.
Oahe Dam near Pierre, South Dakota, which holds Lake Oahe in the Dakotas, and Garrison Dam, which creates Lake Sakakawea in western North Dakota, are typically the biggest power producers in the Missouri River system.
Oahe Dam generated 2.6 billion kilowatt hours last year, equal to the long-term average, Swenson said.
Garrison Dam also generated 2.6 billion kilowatt hours of electricity last year, up from long-term average of 2.2 billion kilowatt hours, he said.
The plants have generated an average of 9.3 billion kilowatt hours of electricity since 1967, including a high of 14.6 billion kilowatts in 1997, Swenson said.
The water storage level of the six upstream reservoirs in the Missouri River system is about 56 million acre-feet at present, about equal to the ideal level.
An acre-foot is the amount of water covering one acre, a foot deep.
The corps is charged with finding a balance between upstream states, which want water held in reservoirs to support fish reproduction and recreation, and downstream states, which want more water released from the dams, mainly to support barge traffic.