Engineer fears levees will fail test of time
June 15th, 2011 by Ric Hanson
With the floodgates open at Gavins Point Dam, a record one-point-one million gallons of water per second are gushing into the already-flooded Missouri River. Rod Nohr, a professional engineer based in Yankton, South Dakota, says most of the temporary levees are designed — at best — to with stand a couple of weeks of high water. Nohr says those levees are likely doomed.
“Over time, I don’t care how they cover them with plastic and sandbags, the earth and that will become liquefied by long-term exposure to water and you’ll start having really serious erosion problems, especially if there’s current there,” he says.
Communities in the immediate threat zone in South Dakota, Nebraska and Iowa have ringed homes, businesses and important infrastructure with these temporary berms and floodwalls. Ever seen the Grand Canyon? When it’s water versus anything solid, the water will eventually win.
“The concerns probably aren’t going to be today or tomorrow,” he says. “It’s going to be within a week or two or three when you’re going to see sandbag walls being undermined or these temporary plastic-lined levees liquefying and starting to leak and fail.” Nohr says the water will eventually find the weak spots in temporary barriers.
He says, “Water pressure seeps in and actually liquefies the levee wall so these temporary ones that are pushed up with bulldozers, exposure to deep water and water with current over two weeks, three weeks, four weeks, five weeks, six weeks — can be a really become a really serious problem.”
Nohr, whose company works with grain-handling facilities along the Mississippi and Missouri rivers, says levees and sandbag walls have to be watched constantly as the high water pushes against them. He’s not optimistic for any of the small towns standing in the way of the flooding Missouri, especially Hamburg, in far southwest Iowa.
(Matt Kelley/Radio Iowa)