Heavy flooding along the Missouri River will last throughout the summer, predict federal officials. The surging waters, created by unprecedented weather conditions, have already caused levee failures, and more are expected to come.
The Missouri River and its tributaries in Montana, North Dakota, and South Dakota are swelling with water. A confluence of factors are driving the rising waters, notably the record heavy snowfall earlier this year in the Rocky Mountain region. Snow accumulation was 140 percent above normal, says Lynn Maximuk, director of the National Weather Service in the central region.
“We do have quite an unusual set of circumstances, meteorologically,” Mr. Maximuk told reporters Monday afternoon.
The unusually heavy snows – combined with ongoing heavy rains, expected to continue all summer – will create a total runoff of some 55 million acre-feet of water, according to projections from the US Army Corps of Engineers. (An acre-foot of water is the equivalent of one foot of water covering one acre of land.)
That’s the highest runoff level since they began keeping records in 1898.
The immediate danger this week comes from heavy storms, expected to move south along the river valley. Meteorologists predict that 2 inches of rain in Montana and North Dakota and up to 3 inches of rain in Omaha, Neb., will fall over the next few days, Maximuk says.
May was the second-wettest month for northern Wyoming, Montana, and North Dakota since 1889.
To relieve pressure on the river, the Corps plans to release 150,000 cubic feet per second of water at the Oahe Dam above Pierre, S.D., on Tuesday. The other dams will be opened in succession, remaining open through mid-August.
Kevin Grode, a Missouri Basin reservoir regulation team leader with the Corps, says the amount of water released may increase, depending on the changing climate.
“We are going to be testing the system,” he stresses, “because we’ll be releasing more water than has ever been released before.”
Local officials in some states are criticizing the Corps for not opening the dams earlier, which Mr. Grode challenges. “Conditions in the basin were not as extreme as they are now,” he says. “We did not see a great need.”
Water is already surging at all six of the dams along the river, breaking records at each one. According to Grode, runoff waters are highest at Gavins Point, located near Yankton, S.D. The flow there reached 10.5 million acre-feet, breaking a previous record of 7.2 acre-feet, set in 1995.
While Grode says the dams are all “very safe,” the levee system is more vulnerable – and will likely be stressed throughout the year, he warns. Tributary systems that feed into the Missouri River are also expected to flood.
A levee breach near Hamburg, Iowa, on Sunday resulted in a mandatory evacuation of residents. Corps officials have not yet determined what caused the breach. The National Guard dropped 22 thousand-pound sandbags on the levee, as an emergency measure to keep the water from flowing through the breach. Flooding will stretch two miles inland, officials predict.
Rising river levels have resulted in sandbagging efforts and road closures in virtually every state bordering the river. In Fort Calhoun, Neb., about 20 miles north of Omaha, a nuclear power plant declared an emergency and shut down. The Omaha Public Power District, which operates the plant, said it does not expect any release of radioactive material.
Surging waters can also delay emergency efforts underway to repair the Birds Point-New Madrid Floodway in Mississippi County, Mo., which was opened in May to mitigate surging Mississippi waters traveling downstream toward Memphis.
Officials are uncertain how much the flooding along the Missouri River will deepen the waters of the Mississippi River. “Obviously, with more water coming from the Missouri River,” Maximuk notes, “there will be more water in the Mississippi River.”