Flood control work in the Mississippi River and its tributaries has likely made floods worse in Louisiana and Mississippi, researchers say.
Using 500 years of data from tree rings and sediment in oxbow lakes—bends that once were part of the Mississippi River but became lakes after the river changed its path—researchers say the river has flooded more often and poured more water into these states over the past 150 years than any previous period.
Climate change may be responsible for about one-quarter of the difference, they estimate. Engineering—like building levees and creating a straighter, more narrow channel for navigation—is likely responsible for the rest, researchers from Massachusetts, Illinois, Alabama, South Carolina, Texas and Liverpool, England, say in today’s journal Nature.
Some outside scientists praise the paper, while others are casting doubts about the conclusion that flood engineering is the main reason floods are worse in Louisiana and Mississippi.
“It’s a good paper. And the study is solidly built on data, solidly executed,” says Professor Yi-Jun Xu, head of LSU’s hydrology lab.
Upmanu Lall, director of the Columbia Water Center at Columbia University, says the work linking “floodiness” to climate cycles over five centuries is exciting, but the argument about river engineering as the main driver is weak.
Recent floods have included some very low and very high floods, Lall says. Small floods also probably didn’t leave sediment or tree ring records. The recent flood analysis also doesn’t include any analysis of likely causes and ignores whether increased rainfall or changes in the landscape, such as Midwestern farm drainage, might be among them, he says.
Researchers studied three oxbow lakes: Lake Mary, west of Woodville, Mississippi; False River Lake, northwest of Baton Rouge; and Lake St. John in Louisiana,
