Managing floods

Flood Management adds to the problem

 
Last Updated: Saturday 04 July 2015

 Flooding in the USA: Embankme flood - management measures may be increasing the risk of river Mississippi and other rivers bursting their banks in the us , new research suggests.

Robert Criss and Everett Shock, researchers at the Washington University found that, for the same total amount of water flowing down the Mississippi -- its discharge -- the annual floods in the St Louis region have been getting steadily higher since 1860.

The flood of 1993, for example, was triggered by about the same discharge as that of 1903 -- but was about 3.6 metres higher, causing billions of dollars' worth of damage in the river basin. Tens of thousands of hectares of farmland were inundated and their crops destroyed, roads and bridges were damaged, and thousands of people had to flee their homes.

Today, the Mississippi is supposed to be protected by 29 locks and dams north of St Louis, hundreds of canals, and artificial embankments along its banks.

That protection, say Criss and Shock, is precisely the problem. The changes in flood hazards over time "are far more dependent on human activities than on the amount of flood water in the river", they point out.

The duo compared the rising flood levels of the middle Mississippi -- the St Louis region -- with flood records of the Ohio, the Meramec and the Missouri rivers. This other two join the Mississippi upstream of St Louis. The lower Missouri and middle Mississippi have been heavily engineered, constrained by artificial channels and high levees. Both have risen. But on the upper Missouri, above Fort Benton, there are few flood-control measures --and no evidence that flood levels have risen significantly for more than a century. The same is true of the Meramec in eastern Missouri, where locals have resisted attempts to engineer this river's course. The minimally defended Ohio river in Cincinnati has a similarly unchanged flood record.

"The evidence," say Criss and Shock, "indicates that embankments and channelisation of the lower Missouri and the middle Mississippi have greatly magnified their floods." The researchers add that "this effect is increasing and shows no signs of stopping".

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