LINCOLN, Neb. — Big releases of water that have created massive Missouri River flooding should slowly begin to decline starting at the end of July, the U.S. Army Corps of Engineers said Tuesday.
Corps officials said they plan to reduce the water volume flowing out of Gavins Point Dam in South Dakota from its current 160,000 cubic feet per second to 155,000 cubic feet per second on July 30 and cut it to 150,000 cubic feet per second on Aug. 1.
Heavy rain and a large snowmelt from the Rocky Mountains have poured water into the Missouri, and the corps has been releasing large amounts of water from upstream reservoirs to limit flooding there. The water has caused flooding downstream, covering more than 500,000 acres in seven states so far. The high water is expected to linger through August, putting pressure on levees that protect homes, cities and farms.
Roger Michaels, the Omaha division's chief of construction, said the corps will trim the releases slowly so the dam can process water still coming in from upstream. The gradual drawdown also is intended to prevent further erosion of flooded farmland and roadways.
Dam releases have exceeded the previous record of about 70,000 cubic feet per second since late May. The corps is reducing the flows at upstream dams first and working its way through the system as weather permits. Any big rain in Montana or the Dakotas could force it to increase flows again.
"It's going to take a while to drain out," Michaels said. "It's a slow process."
David Rogers, an engineering professor at Missouri University of Science and Technology, said no one should get complacent as the flood begins to ebb: More levees fail when the water is declining than when it's rising, and that's especially true in a long-term flood like this one where the levees become saturated.
"The most important time to be watching the levee is after the flood peaks and while it drops," Rogers said.
It's important for the corps to try to lower the water level in the river gradually, not suddenly, to reduce the risk of levee failure, he said.
State officials said the flow reductions would not affect their immediate flood plans, which include monitoring levees and helping flood victims.
Nebraska Emergency Management spokeswoman Jodie Fawl said the state has reduced the number of personnel working out of a Lincoln-based emergency operations center, but that most were still monitoring the situation from their regular state offices. An emergency call center is reducing its hours starting next week because the call volume has dropped, she said.
"It seems that while there is going to be some diminishing of the waters, the levels will still be high," Fawl said. "This is a long-term situation that we'll be monitoring for a while."
Iowa Homeland Security and Emergency Management is keeping its focus on the state's levee network and mental health treatment for stressed-out flood victims, spokesman John Benson said. The drawn-out flood displacements are prompting some residents to return home before they should, he said.
Local officials in a few flood-threatened cities saw glimmers of hope. In Hamburg, a southwest Iowa town, local officials took control of a new levee built to shield residents from the river. Federal contractors and local crews constructed the earthen barrier after another levee closer to the river burst.
Michaels said the corps will still offer help if the levee shows signs of trouble, but he expressed confidence that the 9,000-foot-long barrier will hold until the flood subsides. Water is pushing against the newer, 18-foot-tall levee, but it has caused only minor seepage problems so far.
Officials in South Sioux City, Neb., welcomed the news about smaller water releases. City Administrator Lance Hedquist said word of the reductions could offer his northeast Nebraska city a psychological pick-me-up, even if it has no immediate impact.
"Obviously, it's good news for the community, so that's very favorable," Hedquist said. "The quicker we get the water down, the better off we're all going to be."