Missouri River Basin Sees Better Inflows

Warm temperatures in the mountainous region of the upper Missouri River Basin has led to a quick melt of the mountain snowpack, the Corps of Engineers reports. The rapid melting combined with precipitation in the western half of the basin resulted in above-average inflow into the reservoir system.

May runoff for the basin above Sioux City, Iowa, was 4.9 million acre-feet (maf.), 144 percent of average.

“The warm temperatures in the northern Rockies has melted the snow earlier than is typical,” said John Remus, chief of the Corps’ Missouri River Basin Water Management Division in Omaha, Neb. “With much of the mountain snowpack already melted, the basin will need additional rainfall to continue the trend of above-average runoff.”

Runoff Forecast

The annual runoff forecast above Sioux City is 26.8 maf., 104 percent of average, and about the same as last month’s forecast. While portions of the basin received above-normal rainfall, precipitation was below normal over most of the basin during May.

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“The precipitation during the month of May provided some relief to the western half of the basin, but the drought continues to worsen in other areas,” Remus said. “There is some level of drought present in every state with the worst conditions in Nebraska and Kansas.”

System storage is currently 52.6 maf., 3.5 maf. below the top of the carryover multiple use zone. During May, system storage increased 2.5 maf.

“The June 1 reservoir studies indicate navigation flow support for the second half of the navigation season, based on the forecasted July 1 system storage check, will be increased to 2,500 cfs. below full service,” Remus said. Basin and river conditions continue to be monitored, and system regulation will be adjusted based on the most up-to-date information.

“As we enter into the summer months, we will continue to serve all congressionally authorized purposes while dealing with the on-going drought,” he said.

The Corps said that releases from Gavins Point Dam will provide minimum-service navigation flow support at all four target locations (Sioux City; Omaha; Nebraska City, Neb.; and Kansas City, Mo.) through the first half of the navigation season, which ends on July 1. Flow targets may be missed to conserve water if there is no commercial navigation in a given reach. Minimum-service flow targets range from 25,000 cfs. at Sioux City to 35,000 cfs. at Kansas City. Flow support for the second half of the navigation season, as well as the navigation season length, will be based on the actual system storage on July 1. The current forecast indicates that flow support 2,500 cfs. below full service will be provided for the second half of the navigation season, and flow support may be provided for the entire navigation season ending December 1 at the mouth of the river near St. Louis, Mo.