Manchac Landbridge Diversion

Manchac Landbridge Diversion, as proposed in the 2017 Coastal Master Plan, would be constructed within the existing western guide levee of the Bonnet Carre Spillway. When the Bonnet Carre Spillway is opened to reduce river flood risk in New Orleans, all sediment, fresh water and nutrients are directed into Lake Pontchartrain, wasting these vital resources and causing water quality issues. The Manchac Diversion will direct some of these flows into degraded swamps and marshes adjacent to the spillway to increase nutrient input and improve water quality, fostering vegetation growth.

Located near Lakes Pontchartrain and Maurepas, the diversion could benefit a variety of habitats, from freshwater forests to brackish marsh. The restoration of these habitats will help St. Charles and St. John the Baptist parishes become more resilient to flooding and storms. The Manchac landbridge is identified by the Army Corps of Engineers (Corps) as a vital landscape feature that serves as a critical line of defense from storm surge for nearly 1.5 million people in eight parishes, especially the Greater Baton Rouge region, and the cities of New Orleans, Laplace, Madisonville, Mandeville and Slidell.

Note: This project is included for consideration and additional modeling/research in the 2023 Coastal Master Plan’s Upper Basin Diversion Program – Pontchartrain. As such, it does not appear by name/Project ID in the most current edition of the Master Plan.