Louisiana Wetlands Could be Restored by Mississippi River Diversions

In Nature Geoscience, a group of geologists from the University of Pennsylvania used the Mississippi River flood of 2011 to observe how new diversions in the Mississippi River’s levees could help restore the wetlands in Louisiana.

The study conducted by geologists from the University of Pennsylvania is one of the only large-scale experiments to show how levee modifications may help restore Louisiana’s wetlands. During the 2011 floods of the Mississippi River, the Army Corps of Engineers opened the Morganza Spillway, a river-control structure, to divert water off of the Mississippi into the Atchafalaya River Basin. This action involved the deliberate flooding of more than 12,000 square kilometers and alleviated pressures on downstream levees and spared Baton Rouge and New Orleans from the worst of the flood. The opening of the Morganza Spillway allowed the Penn researchers to see how floods along the Mississippi may have occurred before engineered structures were put in place to control the river's flow.

The researchers quickly began taking advantage of the rare opportunity by examining satellite images showing the plume of sediment-laden water emerging from the mouths of the Atchafalaya and Mississippi rivers. The amount of sediment in the plumes was calculated for the duration of the flood and then field samples were taken from a boat in the Gulf of Mexico. The samples allowed the researchers to gather data on the speed of the plume and the extent to which river water mixed with ocean water.

The researchers' findings offer a large-scale demonstration of how flooding over the Atchafalaya's wide basin built up sediment in wetland areas, compared to the more-focused plume of water from the Mississippi River, which provides a convincing and reliable way of gathering data and information about how changes in the Mississippi's levees and control structures could help restore marsh in other areas of the Delta.

"One of the things that we found here is that the Atchafalaya, which is this wide, slow plume, actually produced a lot of sedimentation over a broad area," Jerolmack, an assistant professor in the Department of Earth and Environmental Science at Penn, said. "We think that what the Atchafalaya is showing us on a field scale is that this is the sort of diversion that you would need in order to create effective sedimentation and marsh building."