Repeated rounds of heavy rain across Montana and the Dakotas, coupled with far above normal mountain snowpack, have pushed reservoirs to a level which calls for aggressive water releases from Missouri River mainstem dams, said Jody Farhat, chief of the Corps' Missouri River Basin Water Management Division in Omaha.
�The upper Missouri River is seeing dramatic increases in flows, particularly after as much as eight inches of rain fell over the weekend in portions of eastern Montana and western North Dakota," Farhat said. "Unusually heavy precipitation, combined with late season heavy snowpack in parts of the Missouri Basin, means we will see near-record runoff in the Missouri basin.�
Farhat thinks it is possible that Garrison Dam may be within a foot of the top of its spillway gates by this time next week. "We're beginning to make some major adjustments to water releases, starting with Fort Peck south to Gavins Point Dam and expect to do so for some time since the extended forecast is calling for more of the same."
Garrison Dam releases were increased to 60,000 cubic feet per second (cfs) today and will be stepped up until they reach 75,000 cfs on Wednesday. At the same time, releases from the upstream reservoir Fort Peck will be reduced from the current rate of 20,000 cfs to 10,000 cfs to help stem the rise of Garrison reservoir. Garrison reservoir is expected to reach 1853 feet by this weekend due to the high flow on the Yellowstone and Little Missouri Rivers. Fort Peck reservoir is also climbing rapidly due to weekend�s rainfall and low elevation snowmelt. It is expected to rise 2 feet this week, reaching 2246 by the weekend.
Oahe Dam releases will transition from 60,000 cfs today to 70,000 cfs by mid-week. Farhat expects the Oahe reservoir to reach 1618 feet by the weekend and continue to slowly drift upward over the next few weeks, perhaps peaking in mid-June. The record pool at Oahe is 1618.7 feet, set in 1995 and repeated in 1996. The peak pool level in 1997 was 0.1 foot lower at 1618.6.
Fort Randall has some space to store water, but the river reach between there and Gavins Point is already at bankfull. Gavins Point releases were increased to 60,000 cfs this afternoon and will be slowly ramped up over the coming days, possibly reaching 75,000 cfs in June unless conditions improve. This will eventually necessitate a similar magnitude increase in Fort Randall�s releases.
Travel time for water released from Garrison Dam to reach the Bismarck area is about 36 hours. River managers are expecting stages of approximately 16.5 to 17 feet in the Bismarck area when the river stabilizes. The Corps' Omaha District office has deployed technical teams to help prepare for flood fighting around Bismarck and to assess the flood potential in the Pierre area.
�As already seen in other parts of the nation, high water years always bring pain and suffering with them,� said Farhat. �We are doing everything we can to protect people and their property and reduce the extent and impact of flood stages along the Missouri. The situation in the Missouri River basin is changing rapidly and planned releases are subject to change with little notice.� Residents who live and work in flood-prone areas should remain vigilant and be prepared to follow recommendations from their local emergency management offices.
For more information, visit the Spring 2011 Flood Response site at www.nwo.usace.army.mil.