Missouri River reaches Hamburg, Iowa backup levee

Marty Stouffer walks through floodwaters to his parents' home in Cottonwood Marina, north of Omaha June 14, 2011.

HAMBURG, Iowa (Reuters) - Missouri River floodwaters have reached a levee built up this week to protect Hamburg, Iowa, after the main protection along the river failed, a county emergency official said on Thursday.

Water spread rapidly the past two days from a breach of a Missouri River levee about five miles from Hamburg on Monday and reached a secondary levee by late Wednesday where workers have raced to add height using temporary barriers.

"The water has now officially reached the secondary levee, it is about 5 feet up on it in some places ... and we haven't even got the heaviest of it to us yet," Fremont Emergency Management Director Mike Crecelius said.

The secondary levee is expected to withstand the waters and the full pace of the releases from the last dam on the river at Gavins Point on the South Dakota-Nebraska border is not expected to reach Hamburg until some time Friday, he said.

Heavy winter snowmelt feeding the river's headwaters in the Rocky Mountains, and rainstorms in May and June have forced the U.S. Army Corps of Engineers to make record water releases from six dams from Montana through South Dakota.

The Corps reached a planned peak rate of 150,000 cubic feet per second at the southernmost Gavins Point Dam on Tuesday. It plans to hold that rate through at least mid August and keep high flows until December, straining levees for months.

Potentially heavy rains are expected over parts of the Missouri River valley in the next several days which could worsen the situation, officials said.

Thousands of residents have evacuated homes along the Missouri from around capital cities and other communities in North Dakota and South Dakota.

A new levee built to protect Dakota Dunes downstream of Gavins Point had a partial collapse on Thursday that was repaired, but forced South Dakota officials to delay plans to allow residents back into the affluent community on Thursday.

"Property owners proceed at their own risk when entering the evacuated area, and must recognize that a major failure of the levee remains possible," South Dakota Governor Dennis Daugaard said in a statement.

LONG TERM STRESS, RAIN FORECASTS

Levee stresses have been reported from Iowa to Missouri. A second full breach was reported in Big Lake, Missouri, 45 miles south of Hamburg, flooding farmland and forcing some evacuations. A secondary levee has limited the impact.

The breach has forced evacuations of some rural homes and closed parts of Interstate 29 and other roads at Hamburg.

Flooding also has closed I-29 for several miles south of Hamburg into Missouri and for 20 miles north from Council Bluffs, Iowa, across the river from Omaha, Nebraska.

Peak flows at Omaha are expected to stay well below the tops of levees, leaving the focus on the long-term stress. City officials are optimistic that flooding will have little impact on the NCAA College baseball World Series, which has opening events Friday at a new downtown stadium near the river.

North of Omaha, staffers scrambled to remove more than 500,000 artifacts including clothing, metal and wood displayed or stored at the DeSoto National Wildlife Refuge museum from the steamboat Bertrand. The boat sank in 1865 on a trip to Montana and the wreck was rediscovered in the 1960s.

The museum and visitor center sits at the river's edge and Iowa officials reported a boil on a refuge levee on Wednesday.

A broad front could bring up to 2 inches of rain to parts of eastern Montana through western North Dakota Thursday night into Friday and up to 1 inch across eastern South Dakota and parts of Nebraska and Iowa into northern Missouri, said Bruce Sullivan, a meteorologist for the National Weather Service.

Flash flooding in Montana and North Dakota is possible with that system and heavy rains are forecast across the northern plains from Sunday and lingering into Tuesday, Sullivan 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.

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.

(Additional reporting by David Hendee and David Bailey; Editing by Greg McCune)