The sharp rise of the upper Missouri has forced officials to release unprecedented amounts of water from a series of dams that normally control the flow of the river, leading to the evacuations of homes and the construction of emergency levees in downriver communities, including the capital cities of North Dakota and South Dakota. The river is expected to remain at high levels for at least six weeks.
“Many communities along the river will experience flooding in proportions they haven’t seen,” said Jody Farhat, chief of the Missouri River Basin water management division of the Army Corps of Engineers.
Navigated by the explorers Lewis and Clark as they journeyed west through the middle of the country, the Missouri River remains a vital economic and recreational hub for the Great Plains region. The flooding, especially if it lasts as long as predicted, threatens to swamp freshly planted cropland, displace thousands of residents and define a summer normally spent celebrating events like the Prairie Rose State Games in Bismarck, N.D.
Floods, like the record one that soaked communities along the Mississippi River last month, are often slow, unfolding disasters. Despite its magnitude, this one is provoking less suspense because the release of water is being regulated by the Army Corps of Engineers, which has warned leaders as far away as Omaha and Kansas City as to the likely impact.
“It’s very unusual to deal with a predicted flood,” said Gov. Dennis Daugaard of South Dakota, where a number of cities have been scrambling to prepare.
Mr. Daugaard said the warning had given state and local leaders more time to build earth and sandbag barriers, like those put up around Pierre, Fort Pierre and Dakota Dunes. He called for voluntary evacuations of affected areas in all three towns.
“They don’t call it the Mighty Missouri for nothing,” he added.
There are six major dams along the upper stretch of the river that allow federal officials to slow down the sometimes violent rush of water that accompanies the melting snowpack in the region.
This year, though, torrential rains unexpectedly filled the reservoir to levels that had been reserved for a record-breaking snowpack, forcing the dams to begin releasing water to make room for the coming melt.
“We still have snow, lots of it and it’s just now starting to melt,” said Kevin Low, a river forecaster with the National Weather Service. Mr. Low said the entire river was likely to remain “above to well above flood stage” for weeks.
Each of the dams has begun releasing more water than at any time since the system was built more than a half century ago, and is scheduled to continue increasing the discharge in the coming days to the maximum level.
That influx of water, which represents as much as a fivefold increase over the normal flow into the river, is scheduled to remain at the maximum level for at least six more weeks. More rain or a fast melt would aggravate the risk.
“Even though we have these historic releases, the dams are continuing to provide some flood-risk reduction,” Ms. Farhat said.
The threat from the river provoked a mix of reactions in the states that it passes through. Al Berndt, the assistant director of the Nebraska Emergency Management Agency, said his many concerns included charts that showed that 10 of 14 levee systems could be topped, as well as the possible impact on two nuclear power plants along the river, both of which are taking protective measures.
Mayor Jim Suttle of Omaha, however, was confident that a local levee system that reaches well above the highest predicted levels would keep the city dry, particularly given the advance notice that has allowed workers time to fortify the wastewater treatment plant.
“It let us plan,” Mr. Suttle said. “Plan the work and work the plan. That’s why I can say, in all candor, we’re going to proceed with business as usual.”
Even as the Missouri continued to rise, the experience along the Mississippi River offered reason for both fear and hope. In southern Louisiana, evacuation orders were lifted and residents were returning; some found their homes destroyed, others undisturbed. The flooding threat is not over — and waters have been slow to recede in parts of the Delta — but it has been far less damaging than initially feared.
Campbell Robertson contributed reporting from New Orleans.
