The good news is that the snow pack will not flood the Missouri River Basin this year. The bad news is that we don’t know how much rain is coming this spring. The Army Corps of Engineers has been keeping a close eye on the snow melt happening north of here. Jody Farhat — the Army Corps’ Chief of the Water Management Division, Missouri River Basin — says this time last year the runoff was 1.2 million acre feet higher than it is today.
She says Northwest Missouri has flooded the last four out of five years, and four of those years it was from spring rains … not snow melt upstream. She says Northwest Missouri has flooded from spring rains the last four out of five years: 2007, 2008, 2010, and 2011.
Historically, localized rainfall driven flood events occur somewhere along the river almost every year, Farhat says.
Kevin Low is the senior hydrologist with the Missouri River Basin Forecast Center. He agrees that even though snow-melt is not a threat … spring rains could make all the difference.
Hydraulic Engineer Joel Knofczynski says the corps is expecting a full navigation season, which begins at the end of March, and will not implement a spring rise because of the damage to infrastructure from last year’s flooding. A spring rise, or spring pulse, would release water from upstream resevoirs to boost the breeding cycle of the endangered pallid sturgeon. The spring rises are part of a U.S. Fish and Wildlife Service plan required by the Endangered Species Act.
“It’s good news,” Farhat says. “Our goal following the Flood of 2011 was to evacuate all of the flood waters and prepare the reservoir system for the 2012 runoff season. We’ve met that goal and have slightly more than the full capacity of the system available.”
During the fall and winter of each year, the Corps completes the evacuation of stored flood water as part of its flood risk reduction efforts, she says, and the mild winter has allowed the Corps to make higher than normal releases throughout the winter.
Gavins Point releases have been set on 22,000 cfs since mid-December. Normal winter release rates are near 17,000 cfs.
System storage fell as low as 56.1 million acre feet (MAF) in late January, 0.7 MAF below the base of the annual flood control pool. However, higher than normal reservoir inflows during the month of February filled up some of the additional storage prior to March 1, the typical start of the runoff season. Runoff above Sioux City totaled 1.6 MAF in February, 153 percent of normal. This was due in part to a combination of high base flows from three consecutive years of above normal runoff and also warm temperatures which melted much of the river ice, freeing up water that usually flows into the reservoirs in March.
On March 1, system storage was 56.5 MAF, 300,000 acre feet below the base of the annual flood control zone. The annual flood control zone is the desired operating zone for the system because it allows the Corps to serve all eight congressionally authorized purposes: flood control, navigation, water supply, irrigation, hydropower, recreation, water quality control, and fish and wildlife.
The forecast for runoff above Sioux City for calendar year 2012 is 26.1 MAF, slightly above the normal of 24.8 million acre feet. Mountain snowpack above Fort Peck is currently below normal at 93 percent of average. In the reach between Fort Peck and Garrison, mountain snowpack is tracking at 104 percent of average. This time last year, mountain snowpack was 110 and 107 percent of normal in the respective reaches. Traditionally, 79 percent of the peak mountain snowpack accumulation occurs by March 1.
AUDIO: Jessica Machetta reports (1:30)