Study suggests diversions could lessen pressure on spillway

A Tulane University study suggests environmental challenges created by the recent frequent opening of the Bonnet Carre Spillway could potentially be eased by the addition of upper river diversions.

The study was conducted by Ehab Meselhe, a professor in the school’s Department of River-Coastal Engineering who helped build numerical models used in Louisiana’s 2012 and 2017 Coastal Master Plans. Meselhe contends that each time the spillway is opened, it impacts water quality, and that the recent cluster of openings creates a need to find alternatives in order to improve river management.  The study concludes that even mid-level sized diversions upriver would significantly relieve pressure on the spillway.

To that end, there’s good news: the state plans to build two diversions upriver from New Orleans, one in Ama and one in Union, as part of Louisiana’s Coastal Master Plan. Meselhe modeled how the planned diversions can be operated to relieve pressure and reduce the volume of water flowing through the spillway while also helping to restore coastal ecosystems. It estimated that were the two diversions to have existed and operated jointly during flood events in 2018 and 2019, it would reduce the flow volume released through the spillway by between 57 and 61 percent.

The study was requested by Restore the Mississippi River Delta, a group of non-profit conservation groups that believe the environmental conditions of today may mean more frequent openings of the spillway are here to stay. The theory is that climate change may cause the Mississippi River to flood more frequently.

For the first time ever, the spillway was opened twice in a single calendar year in 2019. The structure has opened just 16 times since 1937, when it was first created. But seven of those occasions have come within the past 10 years. The spillway has opened at least once in each of the past three years, the only time in its history that has happened.

The Bonnet Carre Spillway is opened by the Army Corps of Engineers in order to relieve pressure on levees from the rising river, and thus prevent mass flooding.


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