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Efforts to contain Mississippi floods may have made them worse

Re-creation of the river’s 500-year flood history shows the worst floods are bigger than ever

By
2:21pm, April 4, 2018
Mississippi River flooding

HIGH WATER  Floods along the Mississippi River in spring 2011 rivaled the Great Flood of 1927 in size. Human engineering of the river may be making such floods bigger.

The world’s longest system of levees and floodways, meant to rein in the mighty Mississippi River, may actually make flooding worse.

Using tree rings and lake sediments, researchers re-created a history of flooding along the lower Mississippi River extending back to the 1500s. This paleoflood record suggests that the past century of river engineering — intended to minimize flood damage to people living along the river’s banks — has instead increased the magnitude of the largest floods by 20 percent, the researchers report April 5 in Nature.

Climate patterns that bring extra rainfall to the region don’t account for the dramatic increase in flood size, the team found. “The obvious culprit is that we have really modified the river itself,” says Samuel Munoz, a geoscientist at Northeastern University in Boston.

Settlers built the first levees on the

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