The Herculean task of repairing the rocky structures that tame the Missouri River has begun.
Last summer's flooding washed away tons of rocks critical to corralling the river. Now the Army Corps of Engineers is left with the $40 million job of filling gaps in dikes and revetments — the man-made rock structures used to channelize the river.
A million tons of rock — enough to fill 77 football fields 6 feet deep — will be hauled from regional quarries, towed up and down the river and carefully laid in place.
“This is a massive undertaking,” said Laura Bentley, the project manager for the corps' Omaha district.
Dikes are rock berms that extend into the river at nearly right angles to the flow, pushing the water back to the middle of the river. Revetments are rock walls built along bends where the river's channel is most likely to cut across land during flooding.
The dikes and revetments suffered significant blows last summer.
But they did their job. The river didn't cut a new channel anywhere along the 735-mile stretch where they have been built. Repairs are planned along more than 500 miles, but the most highly damaged areas were from south of Kansas City into Nebraska and Iowa.
Without the stone structures, the Missouri would wander unpredictably, creating havoc for towns and industries that rely on its water, making barge travel impossible and washing away roads, highways and farmland.
Repairing the structures isn't an exact science. Experience guides excavators at each site, Bentley said. But there is a precision and art to the process, which will be repeated again and again during the roughly four-year project:
Rocks from each quarry are tested annually to ensure that the rock meets freeze-thaw standards. Individual rocks are sliced into about three-inch slabs, which are then frozen and thawed about 20 times in a water-based solution. That simulates about 20 to 25 years along the river. No more than 25 percent can degrade.
Ninety percent of the rock must be 10 inches to 25 inches in diameter and weigh 140 pounds to 750 pounds.
Digging and hauling
The rock is loaded onto barges and motored to repair sites by tugboat. Once there, the tug sinks two poles into the mud to anchor the operation, and work begins, one shovelful at a time. The equivalent of 8,000 train loads ultimately will be hauled to repair sites.
Getting it just right
For areas above water, the rock must be laid in place; it cannot be dropped. For repairs below water, the rock can be dropped no more than 3 feet.
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