By David Bailey
MINNEAPOLIS (Reuters) - Authorities rushed on Thursday to complete levees to hold back historic flooding on the Missouri River in North and South Dakota and urged many residents to evacuate their homes, possibly for two months.
Officials have less than a day to finish flood protections along the Missouri before the U.S. Army Corps of Engineers on Friday rapidly increases the release of water being held in reservoirs from Montana to South Dakota.
Heavy rains in May coupled with a deep melting snowpack left reservoirs near capacity on the Missouri River and levels high across the basin and nearby river systems from Idaho to North Dakota and down through South Dakota.
Flooding along the Souris River, a Red River tributary, has forced a mandatory evacuation for up to 12,000 Minot, North Dakota, residents -- more than one-quarter of the city. Levels there have exceeded damaging floods in 1976 and 1969.
"We're keeping our fingers crossed," said Paulette Nelson, who was staying with relatives after evacuating her Minot home Tuesday and lived through the 1969 flood. "I remember a lot of people were left with just the clothes on their backs."
Flows from most Missouri River reservoirs already were at record levels on Thursday and the accelerated releases will add several feet to the high river levels deep into summer.
Residents in Nebraska, Iowa and Missouri also are braced for widespread flooding with the maximum planned release rates expected to push the Missouri River up to seven feet above flood stage at Sioux City, Omaha and Kansas City.
Agribusiness Cargill was laying sandbags and building a berm or sloping wall around a corn mill in Blair, Nebraska, north of Omaha and had stopped accepting loads of corn and soybeans at an elevator in Council Bluffs, Iowa, across from Omaha due to rising waters.
South Dakota officials said levees were nearly complete to protect the capital of Pierre and nearby Fort Pierre. North Dakota officials said around-the-clock levee construction to protect the capital of Bismarck was also progressing.
"We need to be careful that we do not become complacent if the levees are holding," South Dakota Governor Dennis Daugaard said on Thursday. "The force of the Missouri River is mighty."
"Not since the construction of the dams has the height and breadth of the Missouri been this great," he said.
HIGH LEVELS 'FOR QUITE SOME TIME'
Daugaard has called for residents of flood threatened areas in Pierre, Fort Pierre and in Dakota Dunes downriver near Iowa, to evacuate their homes by later on Thursday. He has stopped short of making the evacuations mandatory.
Those suggested evacuations cover up to 3,000 Pierre and Fort Pierre residents and more than 800 of the 1,100 homes in Dakota Dunes.
Planned releases from the Oahe Dam above Pierre are set to reach a maximum rate on Tuesday, not quite doubling from Thursday, raising river levels by four feet gradually.
That level is expected to be held "for quite some time," said Eric Stasch, Corps operations manager at the Oahe Dam.
Even with the releases, the Oahe reservoir is expected to peak within half a foot of the top of its spillway gates, he said. The Corps has no plan to use an emergency spillway on the Oahe reservoir, but is preparing the area as a precaution.
The Corps plans to reach maximum release rates by mid June at the reservoirs. It is unclear when the rates will slow.
"Nobody really knows the time frame, it could continue well into July simply because the mountain snowpack has to come out," said Jim Scarlett, meteorologist in charge for the National Weather Service in Aberdeen, South Dakota.
In Montana, forecasts for more rain on Thursday came as water managers stepped up spills from Fort Peck Dam to make room for expected melting of record mountain snows.
High water in Missouri river tributaries has displaced 500 Montana residents and is blamed for two drowning deaths.
The Crow Nation in southeastern Montana has been among areas hardest hit by flooding, which forced hundreds of tribal members to American Red Cross of Montana shelters in Billings.
Tribal leaders and the Red Cross on Thursday said the residents will be shifted on Friday to a multi-purpose building on the reservation to serve as a shelter.
The Missouri River basin forms the northwest section of the Mississippi River system that stretches from the Rockies to western New York in the north and funnels water down through Louisiana to the Gulf of Mexico.
The Corps held water in the Missouri reservoirs to reduce the impact from record Mississippi River flooding earlier this year. Mississippi flood stages are expected to be extended a few weeks by the releases, but not raised.
(Additional reporting by Laura Zuckerman in Salmon, Idaho, and Michael Hirtzer and Christine Stebbins in Chicago)