CHICAGO/DES MOINES (Reuters) - Levees hastily erected along the Missouri River in central South Dakota were holding on Sunday as flooding caused by heavy spring rains and a melting winter snowpack continued to raise the waters toward record levels, officials said.
But hundreds of miles downstream, in southwest Iowa, residents were ordered out after a levee on the flood-swollen river began to breach.
A top Iowa official warned the Missouri’s waters may spill beyond its banks into the state as far as two miles in the coming weeks.
Tim Albrecht, a spokesman for Iowa Governor Terry Branstad called it “an increasingly serious situation.”
A Black Hawk helicopter was dispatched Sunday to dump 1,000-pound sandbags on the failing earthen berm near Hamburg, Iowa in hopes of closing a “boil” in it.
Hill said the one- to one-and-a-half inch hole is creating a small geyser of water to shoot onto the dry side of the levee because of the water pressure.
“We use a helicopter rather than putting personnel on the levee because of the danger of ... a larger levee breach occurring,” said Derek Hill, head of the Iowa Homeland Security and Emergency Management division.
Fremont County Emergency Management said a mandatory evacuation was in effect for the areas between Hamburg and the river, and residents need to be out of the area within 24 hours.
The National Weather Service issued a flash flood warning for the area around Hamburg, a town of about 1,200 near the border with Missouri and Nebraska.
Officials warned the flooding could affect portions of Interstate 29, between mile markers 1 and 10 inside Iowa.
Pressure on the earthen berms upriver in Pierre and Fort Pierre, South Dakota — and the anxiety of area residents — will continue to increase through Tuesday, when the water being released at a dam just above the two towns reaches its peak of 150,000 cubic feet (4,247.5 cubic meters) per second, nearly double the 85,000 cubic feet per second being released last week.
On Sunday, the U.S. Army Corps of Engineers said the dam was dumping 130,000 cubic feet (3,680 cubic meters) of water per second into the Missouri, whose waters have already risen more than a foot over the past week.
Officials in South Dakota have not yet ordered mandatory evacuations in the state. But as many as 3,000 Pierre and Fort Pierre residents, and more than 800 of the 1,100 homes over 250 miles away in Dakota Dunes, are threatened.
So far, the releases from the Oahe Dam have raised water levels along the Missouri in the state more than a foot.
“All the levees are holding at this hour,” said Nathan Sanderson, spokesman for the Southeast Incident Management Team, which is warily watching the creeping floodwaters in Dakota Dunes in the extreme southeastern part of the state.
Sanderson said the evacuations there continued to be voluntary but added that officials were “encouraging people to leave.”
Police have tried to reassure wary residents that their homes will be watched and access to their neighborhoods controlled.
Record snowfall at the Missouri’s headwaters this winter and record rainfall this spring have swollen the Mississippi tributary and pushed the dams and reservoirs along it that are designed to control the usual seasonal surge this time of year to their limit.
So to protect them, the U.S. Army Corps of Engineers has been slowly opening up the dams and reservoirs upstream, gradually lifting river water levels downstream from North Dakota and South Dakota,
The U.S. Coast Guard has closed a more than 180-mile (290-kilometer) stretch of the river from near Sioux City, Iowa, south due to high water.
Farther downstream, the river is beginning to swell beyond its banks in Nebraska and Missouri as well as Iowa, and officials braced for evacuations and built levees. The maximum planned release rates could push the river up to seven feet above flood stage at Sioux City, Omaha and Kansas City.
The result is a creeping problem expected to continue into July.
The Missouri is expected to continue to rise rapidly in Pierre until Tuesday, when controlled releases from the Oahe reach maximum levels — where they may hold for weeks.
Hill, the head of the Iowa Homeland Security and Emergency Management division, said he has seen maps which indicate the Missouri may flood as far as two miles into Iowa at some locations.
“This water is coming,” Hill said. “...If they have vehicles or farm equipment that are out there, or anhydrous tanks, they need to be moving them to higher ground so they’re not floating downriver.”
According to Hill, there are about 30,000 people who live outside of cities or towns and in the rural areas of the six Iowa counties that will be inundated. “The Missouri River at a few points is going to be extremely broad,” he said.
Additional reporting by David Bailey in Minneapolis; Editing by Jerry Norton