Potential Exists for River Flooding Too Soon to Predict Says Corps
OMAHA – Heavy snow and ice over much of the upper Missouri River basin and below normal snow in the mountains will probably result in heavy runoff in March and April and much less in May and June.
The heavy snowpack on the plains is creating high potential for flooding on many of the rivers in North Dakota, South Dakota, Nebraska and western Iowa. In addition, because of the large buildup of ice on the rivers, ice jams may add to the potential flooding issues.
“It’s still too early to make reliable forecasts on potential flooding because so much depends on how much more snow accumulates, how fast it melts, and how much rain adds to the runoff,” said Jody Farhat, chief of the Water Management Office. “Total storage in the reservoir system is less than our target for this time of year, which means we have plenty of room to collect runoff and hold water in the reservoirs when downstream river levels are high.”
The mountain snowpack is only 71 percent of normal for this time of the year.
Traditionally, 79 percent of the peak accumulation occurs by March 1. Runoff for 2010 is currently forecast to total 117 percent of normal.
“Pulses” of water from Gavins Point Dam to benefit the endangered pallid sturgeon will be conducted in March and May, downstream river flows permitting. The March pulse will coincide with the annual increase in releases to provide navigation flows. The 2-day peak is forecast to start March 22. The second pulse will be conducted in the period May 1-19.
Fort Randall reservoir rose 3.5 feet in February as it received hydropower releases from Oahe and Big Bend. It ended February at 1349 feet. It will climb about 6.2 feet in March, ending the month near elevation 1355.2 feet.
Big Bend reservoir will remain in its normal range of 1420 to 1421 feet. Releases will be adjusted to meet hydropower needs. Oahe reservoir gained less than half a foot for the month ending at elevation 1608 feet, 0.5 feet into the annual flood control zone. It will climb more than 5 feet in March, ending near elevation 1613.1 feet. The reservoir is currently 11.8 feet higher than it was last year at this time.
The “annual flood control zone” is the portion of the reservoir that the Corps prefers to use for normal operations. Ideally, each of the three biggest reservoirs is at the base of the zone on March 1.
