By early next week, the Omaha metro area should get its first look at the full effects of the peak water releases from Gavins Point Dam.
The U.S. Army Corps of Engineers on Tuesday morning will begin releasing 150,000 cubic feet of water per second from the dam that controls water levels along the Missouri River in Nebraska, Iowa and points south.
At 150,000 cfs, a football field would fill four feet deep in one second.
Normally, water flowing out of Gavins Point takes about two days to reach Omaha.
During flooding, however, it takes longer because the river spreads out over a wider area, said Dave Pearson, hydrologist with the National Weather Service at Valley.
Additionally, the movement of water through the floodplain is slowed by trees and other obstructions.
Although it's hard to say for sure, Pearson said Monday that he believes the river will reach 34 feet early next week. That level, 5 feet above Omaha's flood stage of 29 feet, should reflect the full impact of 150,000 cfs.
All that water will be around for a while, too.
The Corps of Engineers' Jody Farhat said water releases from the six Missouri River dams are expected to remain high until late summer, possibly longer.
The amount of water being released is subject to change, Farhat said, but the corps currently believes 150,000 cfs will be the maximum amount discharged.
“We will need to push hard on (releases) into August,'' she said, “and it really depends on rain this summer and (snowmelt) runoff.”
Communities won't be out of harm's way even when the Gavins Point releases start to drop, because the river will remain above flood stage for a period of time thereafter.
The high releases already were causing significant problems in Omaha late last week and into the weekend.
Sewage began backing up near north downtown, river water had crawled two feet up the city's emergency levee around the sewage treatment plant, and floodwater closed one of the region's most important gasoline storage sites.
The corps rapidly ratcheted up releases last week, making the problems here more obvious. Releases jumped from 115,000 cfs on Monday of last week to 140,000 cfs by Friday.
The weather service is projecting that the Missouri ultimately will reach between 34 feet and 36 feet at Omaha as it fluctuates from the effects of normal rainfall. Pearson said rains across the Missouri River basin are the “wild card” that will determine if — and when — the river goes even higher.
Precise river levels are hard to forecast because the basin north of Omaha is huge, covering 320,000 square miles.
The volume of water flowing past Omaha is greater than the amount coming out of Gavins Point because the Missouri River also picks up flows from tributaries, including the James River and the Big Sioux and Little Sioux Rivers, said Bob Swanson of the U.S. Geological Survey.
Thus, the 34-foot river stage at Omaha corresponds to a volume of water of about 175,000 cfs flowing past the city, Pearson said.
At 36 feet, the amount of water flowing through the metro area probably is around 210,000 cfs, he said.
That's more than twice the amount of water that goes over Niagara Falls in the summer.
In addition, Swanson said water in the Missouri is flowing significantly faster in the channel as a result of the volume that is moving downstream.
Normally, the river flows about 5 miles per hour. Measurements indicate it now is flowing about 8 mph, he said.
World-Herald staff writer David Hendee contributed to this report.
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