Tulane researchers see a ‘win-win’ in finding alternatives to using the Bonnet Carre Spillway to prevent flooding

Two proposed river diversions could build wetlands, study finds
Updated: Feb. 16, 2022 at 5:25 PM CST
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NEW ORLEANS (WVUE) - A new study from Tulane University finds two proposed Mississippi River diversions could reduce the need to operate the Bonnet Carre Spillway while providing benefits for Louisiana’s coast.

“We’re reducing the potential impact from large releases from Bonnet Carre, while we’re actually making better use of these resources,” said Tulane professor Ehab Meselhe.

The Bonnet Carre, the giant relief valve the U.S. Army Corps of Engineers operates upriver from New Orleans, has prevented river flooding since the 1930s.

However, critics complain it produces collateral damage, pumping trillions of gallons of fresh water and nutrients into Lake Pontchartrain and surrounding bays and harming sea life.

Repeated openings of the spillway in recent years have increased calls, including from the Mississippi Gulf Coast, to look for alternatives.

Meselhe and his team used digital modeling to show how the proposed Union Diversion on the east bank and the Ama Diversion on the west bank could improve river management and reduce the volume of water flowing through the spillway.

Three-dimensional computer models were used to forecast the effects of river water flowing into the marsh and swamps

“On both sides, they are fresh swamps,” Meselhe said. “So, providing them with fresh water and nutrients will help them against salinity intrusion.”

The study was funded by the Environmental Defense Fund, which has been a vocal supporter of the concept of using the river to build back wetlands.

In the decades ahead, scientists warn Louisiana’s coast will face even more threats as sea levels rise and the delta sinks.

The Union Diversion would supply a drink of fresh water to a cypress swamp threatened by too much salt water, eventually flowing from Lake Maurepas into Lake Pontchartrain and into the Mississippi Sound.

“Definitely, it will have a positive impact on the salinity regime for the state of Mississippi,” Meselhe said.

“In theory, yes, the marsh is supposed to cleanse things,” said Dr. Moby Solangi, President and Executive Director of the Institute for Marine Mammal Studies in Gulfport and a critic of river diversions.

Solangi fears the system “may be overwhelmed.”

He argues for more frequent use of the Morganza Spillway north of Baton Rouge.

“The Bonnet Carre Spillway opening in 2019 was a major factor in people realizing the damage these diversions can cause,” Solangi said. “I think it was a watershed moment.”

Meselhe and other supporters of the two diversions hope the Army Corps will eventually jump onboard, “to see also if they can consider adjusting how the river is being managed.”

The projects, even if approved by Congress, would take years to engineer, design, and build.

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