Iowa county evacuates as Missouri River tops levee

DES MOINES, June 5 (Reuters) - Iowa officials ordered an evacuation in a southwestern county on Sunday after a levee on the flood-swollen Missouri River began to breach.

Record winter snowfall at the Missouri's headwaters and record rainfall this spring have swollen the Mississippi River tributary and pushed the dams and reservoirs along it that are designed to control the usual seasonal surge to their limit.

Downstream, the river is beginning to swell beyond its banks in Nebraska and Missouri as well as Iowa. Upriver, levees hastily erected in central South Dakota were holding.

A top Iowa official warned the Missouri's waters may spill beyond its banks into the state as far as two miles (3.2 km) in the coming weeks.

Tim Albrecht, a spokesman for Iowa Governor Terry Branstad, called it "an increasingly serious situation."

Fremont County Emergency Management said a mandatory evacuation was in effect for the areas between Hamburg, Iowa, and the river, and people needed to be out within 24 hours.

A Black Hawk helicopter was dispatched to dump 1,000-pound sandbags on the failing earthen berm near Hamburg in hopes of closing a "boil" in it.

The one- to one-and-a-half inch (2.5-3.8 cm) hole is creating a small geyser of water to shoot onto the dry side of the levee because of the water pressure, said Derek Hill, head of Iowa Homeland Security and Emergency Management.

"We use a helicopter rather than putting personnel on the levee because of the danger of ... a larger levee breach occurring," he said.

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 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 houses over 250 miles (400 km) away in Dakota Dunes, are threatened.

"All the levees are holding at this hour," said Nathan Sanderson of the Southeast Incident Management Team. (Additional reporting by James Kelleher in Chicago and David Bailey in Minneapolis; Editing by Doina Chiacu)