By David Hendee
OMAHA (Reuters) - The Army Corps of Engineers is warning Missouri River states to brace for possible summer flooding, as it prepares to open dams straining under the pressure of heavy spring rains and above-normal Rocky Mountain snowpack melt-off.
The warning raises the specter of a second bout of disruptive and potentially devastating flooding in an already soggy section of the country.
The Missouri, which crosses 10 states at it makes its way from Gallatin, Montana to St. Louis, is a major tributary of the Mississippi River, which has already experienced historic flooding of its own this spring.
"There's no good news," said Jody Farhat, chief of the Corps' Missouri River Basin Water Management Division in Omaha.
Farhat said the Corps is approaching the top of the gauges at its three upper basin dams --- Fort Peck in Montana, Garrison in North Dakota and Oahe in South Dakota.
"Basically, there is little or no storage left in our reservoirs," she said.
The record water releases are being triggered by steady rain in the northern Plains and an above-normal mountain snowpack.
For the Bismarck, North Dakota, area, Garrison releases will be 30 percent more than the record set in 1975. The dam was built in the 1950s.
"It moves us into uncharted territory," Farhat said.
The Pierre, South Dakota, area below Oahe Dam will experience flood stages not seen since the dam was constructed.
Farther south, at Gavins Point Dam on the South Dakota and Nebraska border, Farhat expects June 1 flows to be 7 percent above a record set in 1997. Additional releases in early June are expected to push the total up to 21 percent above the 1997 record, she said.
"This is the situation where we are today," Farhat said, "but it's not the worst case scenario because snowmelt and additional heavy rainfall may mean even higher releases."
Snowpack in the reach above Fort Peck hit 141 percent of normal peak, with current conditions at about 108 percent of the normal peak accumulation.
The snowpack above Garrison Dam reached 136 percent of normal peak, but is slow to melt, with 132 percent of the normal peak accumulation remaining and actually gaining snow in some of the higher elevations, the Corps said.
(Editing by James B. Kelleher and Jerry Norton)