COUNCIL BLUFFS — A flexible approach to water releases in December and January opened an additional 500,000 acre-feet of flood control storage for the 2012 runoff season in the Missouri River reservoir system.
Responding to public concerns about the risks of repeat flooding, and with levee repairs still under way, the U.S. Army Corps of Engineers released additional water from the reservoirs.
"The warmer temperatures we've seen this winter provided us with a lot of flexibility," said Jody Farhat, who manages reservoir releases for the corps. "We have taken advantage of those warmer temperatures to move additional water ... and create more flood control storage."
Currently 56.3 million acre-feet of water are stored in the reservoir system. Farhat said that if temperatures are seasonal in February, the corps expects to release an additional 100,000 acre-feet of water.
Warmer-than-normal weather throughout the basin in the first half of January prevented ice formation and allowed the rivers to flow freely, resulting in above-average runoff. Runoff above Sioux City in January totaled 980,000 acre-feet, 131 percent of normal.
The first major blast of colder air moved into the basin midmonth, freezing over many rivers and temporarily reducing reservoir inflows. That typically happens in December, Farhat said. The water lost to river ice formation typically shows up after the spring thaw.
Throughout January, the corps maintained releases from Gavins Point Dam at 22,000 cubic feet per second, about 5,000 more than typical winter release rates. Releases will be held at 22,000 cfs through the end of February, barring ice-related concerns.
"So far this year, mountain snowpack has continued to accumulate at slightly below-normal rates. However, we still have a few months of winter to get through, so we will continue to monitor the weather and make adjustments to our release schedule if necessary," Farhat said.
Traditionally 61 percent of peak mountain snowpack accumulation has occurred by Feb. 1. Mountain snowpack above Fort Peck is currently below normal, at 87 percent of average.
Precipitation has remained below normal over most of the basin during the first half of winter. This, along with the higher-than-normal temperatures, has resulted in minimal snow accumulation on the northern Plains.
The runoff for the 2012 calendar year is currently forecast at 25.6 million acre feet, just above the normal, historical runoff of 24.8 million. Runoff for the 2011 calendar year totaled a record 61.2 million, 247 percent of normal — the most in the 114 years the corps has kept records.
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