OMAHA, Neb. — June runoff in the Missouri River Basin above Sioux City, Iowa, was 4.1 million acre feet (MAF), 74 percent of average, according to the U.S. Army Corps of Engineers (Corps). The 2016 calendar year runoff forecast is 23.0 MAF, which is 91 percent of the historic average.
“Mountain snowpack in the reaches above Fort Peck and Garrison reservoirs peaked in early April slightly below normal and melted quickly this spring, with the bulk of the runoff entering the reservoirs during May and early June,” said Jody Farhat, chief of the Corps’ Missouri River Basin Water Management Division. “That, coupled with below normal precipitation and above normal temperatures across the upper basin, reduced inflow to the reservoir system during June.” The melting of the mountain snowpack is complete. View the mountain snowpack graphic at http://www.nwd-mr.usace.army.mil/rcc/reports/snow.pdf.
The total volume of water currently stored in the Missouri River Mainstem Reservoir System is 59.9 MAF, occupying 3.8 MAF of the 16.3 MAF flood control zone. “The reservoirs are currently occupying 23 percent of the available flood control storage and remain well positioned to capture additional runoff should reductions in releases become necessary,” said Farhat. System storage peaked at 60.1 MAF on June 22.
Based on the July 1 System storage check, the navigation service level will remain at full service for the second half of the navigation season. In addition the navigation season length will be a normal 8-month season with navigation flow support ending on December 1 at the mouth of the Missouri River near St. Louis, Mo. The September 1 system storage check will determine the winter releases from Gavins Point.
The Corps will continue to monitor basin conditions and will adjust the regulation of the reservoir system based on the most up-to-date information.
Gavins Point releases averaged 23,900 cfs during June. Releases are expected to remain near 25,000 cfs in July but will be increased if needed to meet navigation targets in reaches with commercial traffic as flows on tributaries in the lower basin recede. The reservoir behind Gavins Point Dam ended June at elevation 1206.2 feet and will remain near elevation 1206.0 feet during July.
The forecast reservoir releases and elevations discussed above are not definitive. Additional precipitation, lack of precipitation or other circumstances could cause adjustments to the reservoir release rates.