River diversions won’t save shrinking Mississippi River coastline

The land of the Mississippi River Delta is gradually vanishing, and the accumulation of sediment from river diversions may be the only solution to conserve this land. But now, researchers have found that the coast is shrinking too fast for diversion projects to make a difference.

Justin Lawrence is a program director in the National Science Foundation’s Division of Earth Sciences.

“Scientists studied how fast the Mississippi River Delta grew each year before people inhabited the area and began changing the environment,” said Lawrence.

“The researchers then compared that information with observations of how fast the delta is shrinking in modern times, and the results are striking. The findings will inform coastal policy and management in this low-lying U.S. region.”

The researchers used optical dating to analyze how fast the delta shoreline shifted seaward under natural conditions prior to human influence.

“Optical dating determines when sediment grains were deposited by measuring their last exposure to daylight,” said lead author Elizabeth Chamberlain of Vanderbilt University. “This method allowed us to date the shoreline of the Lafourche lobe of the central Mississippi Delta.”

Before the impact of human activities, the delta grew at a rate of two to three square miles per year. Over the past century, however, the rate of land loss in coastal Louisiana has averaged 15 to 20 square miles per year.

Study co-author Torbjörn Törnqvist of Tulane University said that, given the accelerating rates of sea level rise, land losses will continue for many years. He explained that even the best-executed river diversion projects would not be good enough to prevent future land loss.

“Therefore, difficult choices will have to be made about where to locate these diversions,” said Törnqvist.

The study is published in the journal Science Advances.

—

By Chrissy Sexton, Earth.com Staff Writer