With August precipitation only about half of what it normally is in Eastern Montana, the U.S. Army Corps of Engineers is having to boost flows from its lower Missouri River dams to float barges through the navigation season.
The scenario is the exact opposite of last year when the Corps struggled with a record-setting runoff — 61 million acre feet, or nearly three times this year's runoff.
"During August, runoff in the upper basin was significantly below normal, especially in the reach between the Fort Peck and Garrison dams where it was only 46 percent of normal," said Jody Farhat, chief of the Missouri Water Management Division.
Aside from a few areas in northern Montana and central North Dakota that have received slightly above normal precipitation, the majority of the upper basin received less than 50 percent of normal August precipitation.
As a result, reservoir levels in the upper three large reservoirs, Fort Peck, Garrison and Oahe, fell 2 to 3.5 feet in August. The total volume of water stored in the system on Sept. 1 was 54.2 million acre feet, down from 56.4 maf on Aug. 1. The base of the flood control and multiple use zone is 56.8 maf. The annual flood control pool is the desired operating zone for the system because it allows the Corps to serve all eight congressionally authorized purposes — flood control, navigation, hydropower, irrigation, water supply, water quality control, recreation and fish and wildlife.
"Drought conservation measures will be implemented beginning this winter based on the Sept. 1 storage check," Farhat said. "Winter releases from Gavins Point will be at minimum levels, averaging near 12,000 cfs from December through February."
Fort Peck releases averaged 10,900 cfs in August. Releases will remain near 10,000 cfs in September with the exception of higher flows early in the month for spillway testing. The reservoir ended the month at an elevation of 2,233.9 feet, down 2 feet from the previous month. It is expected to decline by 1.9 feet this month, ending the month near 2,232 feet.