By Michael Avok
HAMBURG, Iowa (Reuters) - A handful of downtown businesses stood open on Wednesday as contractors pushed to finish a temporary top to a floodwall that protects Hamburg's southern section from approaching Missouri River floodwaters.
Federal flood officials expect additions to the secondary floodwall to be completed by Wednesday evening, not long after water pouring from a Missouri River levee breach five miles away is expected to reach the base of the protection.
Iowa Governor Terry Branstad is scheduled to tour Hamburg, a city of 1,200 in the southwest corner of the state, Wednesday night. About 300 residents of the south side of Hamburg were under mandatory evacuation orders and water spilling from the levee breach has forced some rural residents out of their homes and the closing of parts of Interstate 29 and other roads.
At Stoner Drug, which was founded in 1896 and has one of the last old-fashioned soda fountains in the area, soda jerk Stevii Warren wondered how much longer she would be working.
"We rely on tourists," Warren said. "With the flood and the interstate closed, I don't know how long they will need me."
Warren has her boyfriend's family living temporarily in her home on high ground because their rural home is threatened.
"They didn't think they would get water, but it is right there," she said. "The water has really spread since last night."
The Missouri River basin forms the northwest portion of the Mississippi River basin that stretches from Montana to western New York and funnels water south into the Gulf of Mexico.
Heavy winter snowmelt feeding the river's headwaters in the Rocky Mountains and heavy spring rains have forced the U.S. Army Corps of Engineers to release water from six dams from Montana through South Dakota to relieve swollen reservoirs.
The Corps has planned to hold the top release rates until at least mid August, creating a long-term strain on newly constructed and existing levees that were built to varying strengths for more than 1,700 miles along the river basin.
Thousands of North Dakota and South Dakota residents also have evacuated homes from communities along the river.
CROPS AT RISK, LEVEES STRAINED
The Corps reached its maximum planned release rate Tuesday at the Gavins Point Dam along the South Dakota-Nebraska border, leaving peak flows running freely to the confluence with the Mississippi River more than 800 miles downstream.
In Omaha, the NCAA College World Series opens Saturday at a new downtown stadium near the river where some 200 parking spaces were lost to flooding. Farther north, Eppley Airfield has handled minor leaks in the levee protecting runways.
Several I-29 segments were closed due to flooding or threatened flooding, including 20 miles north from Council Bluffs, Iowa, and part in Northeast Missouri.
A second levee breach near Big Lake, Missouri, 45 miles south of Hamburg, flooded farmland and forced evacuations, but a secondary levee limited flooding, officials said.
"We don't feel that water will come over the top of the levee but we are concerned about water being high for a long period of time," Diana Phillips, clerk and flood plain manager for the village of Big Lake, said on Wednesday.
Local officials reported multiple sand boils Tuesday on a third levee, in Mills County, Iowa, southeast of Omaha and across the river from Offutt Air Force Base. The levee protects a mainly agricultural area that has a handful of homes.
The Missouri River flooding has put tens of thousands of acres of cropland at risk from Montana to Iowa. Agriculture Secretary Tom Vilsack is scheduled to tour flooded areas in Iowa and Nebraska on Friday.
Heavy rains forced the U.S. Army Corps of Engineers to raise the top planned release rate from its Fort Peck Dam in Montana to 65,000 cubic feet per second, from 50,000. It has left intact plans for top release rates of 150,000 cubic feet per second from the other five dams.
The National Weather Service sees a threat for above normal precipitation for the upper Missouri basin, the northern plains area for up to the next two weeks.
Daily showers were forecast for the U.S. Midwest through the weekend, raising the risk of more farmland to flood along the Missouri River, Mike Palmerino, a forecaster with Telvent DTN weather service, said on Wednesday.
"It's going to keep pressure on the Missouri River -- the Missouri, mid-Mississippi, Illinois river basins are continuing to be affected by the heavy to moderate rainfall," he said.
The Missouri River is expected to reach up to seven feet above flood stage at Sioux City, Omaha and Kansas City when the flows from the maximum release rates reach those areas.
(Additional reporting by Kevin Murphy, David Hendee, Christine Stebbins, David Bailey and James B. Kelleher; Editing by Greg McCune)