By Michael Avok
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 full 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 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.
The secondary levee is expected to withstand the waters.
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.
In North Dakota and South Dakota, where thousands of residents have evacuated homes along the Missouri from around the capital cities and other communities, has shifted to levee maintenance with the construction phase completed.
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 flooding has put tens of thousands of acres of cropland at risk. Agriculture Secretary Tom Vilsack is expected to tour flooded areas in Iowa and Nebraska on Thursday and Friday.
Thunderstorms made work on Hamburg flood barriers hazardous Thursday. The breach has forced evacuations of some rural homes and closed parts of Interstate 29 and other roads.
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.
Rain remains a focus.
A broad area of up to 1 inch in rains was expected Thursday night to Friday from Eastern Montana to central North Dakota, South Dakota and into southeastern Missouri, according to the Hydrometeorological Prediction Center.
Scattered rain is expected across the river valley through the weekend. Significant rain in spots is possible from late Sunday to early next week in the northern and central plains.
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)