HAMBURG, Iowa (AP) - Construction crews on Wednesday put the final touches on a makeshift levee standing between a small Iowa town and the creeping advance of Missouri River floodwater, as communities downstream took advantage of a temporary dip in water levels to bolster their own strained defenses.
Water that breached the primary river levee just south of the Missouri-Iowa border on Monday had advanced to within 500 yards of the temporary floodwall guarding Hamburg, five miles to the northeast, and was expected to reach the structure by Thursday, said Robert Michaels, the Army Corps of Engineers official who has overseen construction of the new levee.
Any hopes the breaches might alleviate the long-term flooding threat for communities downstream were short-lived, as river levels that dipped slightly from the release of pressure began their re-ascent Wednesday.
The river has been rising for weeks as the corps releases increasing amounts of water from its upstream dams to clear out heavy spring rain and snowmelt. Releases at Gavins Point Dam in South Dakota hit the maximum planned amount of 150,000 cubic feet of water per second Tuesday, and the corps wasn't planning to reduce the amount it's releasing from its dams until August at the earliest.
Parts of Montana, North Dakota and South Dakota already have been flooded, and towns and cities farther south were still bracing for the worst.
This summer's flood fight along the Missouri River will certainly be a costly one. South Dakota officials estimate the state already has spent about $10 million in the first two weeks of work to prevent flooding in Pierre, Fort Pierre and Dakota Dunes.
The hurried pace of work that went into building the new levee guarding Hamburg slowed somewhat on Wednesday as the project was completed, and most of those living in the threatened parts of town had cleared out. Fire Chief Dan Sturm said crews planned to cover the levee with plastic before the water arrived.
River towns and cities in Nebraska, Iowa and Missouri continued bolstering their own flood defenses on Wednesday, probing for any potential weakness.
"If there are weak spots, they will be shown very soon," National Weather Service hydrologist Dave Pearson said.
Officials predict the river downstream of the six dams will remain 5 to 7 feet above flood stage at most places in Nebraska and Iowa, and swell as much as 10 feet above flood stage in Missouri.
Pearson said Monday's breaches would provide only a temporary dip in river levels. Once the water spreads out, the pressure will build up and the river will rise again.
"The water is continually being replenished, so it's going to go back up again," Pearson said.
That was already the case near Brownville, Neb., just downstream of the breaches, where the river level went from 40.74 feet on Monday to 39.54 feet on Tuesday following the breaches. But the river had started rising again by 3 p.m. Wednesday when it was at 39.92 feet.
John LaRandeau, a civil engineer with the corps, said the situation along the Missouri River is distinctly different than the one along the Mississippi River earlier this spring, when the corps intentionally breached a levee south of Cairo, Ill., to reduce the risk of flooding in the city. In that case, the Mississippi water levels were expected to recede soon after the breach, whereas the Missouri levels are not.
"The pressure on the levees is going to be very, very high," he said.
The flooding threat has complicated travel in the western Iowa-Missouri border area, and state officials were preparing to close a stretch of interstate that runs between the two states.
Gary and Veronica Andrews of Ocala, Fla., were on a trip to Yellowstone National Park in Wyoming when they spotted what appeared to be a giant lake pressing up against Interstate 29. They pulled off the highway about nine miles north of Hamburg to find every gas station, restaurant and motel was closed and surrounded by sandbags and dirt levees.
"This is quite an experience," Gary Andrews said.
In Council Bluffs, two riverboat casinos permanently moored along the Missouri River are being monitored for any sign of structural problems.
Council Bluffs Mayor Tom Hanafan said if a problem is detected, the casino will be emptied. Some of the parking lots west of the Harrah's and Ameristar casinos are flooded but that's not a surprise because of their location.
Funk reported from Omaha, Neb. Associated Press writers Timberly Ross in Omaha and Chet Brokaw in Pierre, S.D. contributed to this report.
National Weather Service river forecast: http://water.weather.gov/ahps2/index.php?wfo=oax
U.S. Army Corps of Engineers Omaha District: http://www.nwo.usace.army.mil
U.S. Army Corps of Engineers Kansas City District: http://www.nwk.usace.army.mil