Union Freshwater Diversion

Proposed within the 2017 Coastal Master Plan with a maximum capacity of 25,000 cubic feet of water per second, the Union Freshwater Diversion is meant to deliver nutrient-rich freshwater from the Mississippi River to the fresh-forested, flotant and freshwater marsh environment in Maurepas Swamp to prevent saltwater intrusion and encourage vegetation growth. As proposed, it would be designed to operate at maximum capacity when the river’s flow reaches one million cubic feet per second.

The diversion would convey fine sediment to nourish existing wetlands and create new wetlands in Maurepas swamp, which has the ability to increase elevation and reduce inundation time allowing for vegetative growth.

Ascension, Livingston, St. James and St. John the Baptist Parishes are all expected to receive flood-reduction benefits from this project. The diversion would also divert water into the Lake Pontchartrain Basin upriver from the Bonnet Carre Spillway, allowing excess nutrients to filter out in the wetlands surrounding lakes Maurepas and Pontchartrain. This would reduce the potential of harmful algal blooms sometimes associated with opening the spillway.

Working alongside other diversions like the River Reintroduction into Maurepas Swamp Project, the Union Diversion will help maintain the Manchac Landbridge — a natural feature that provides critical storm surge protection to nearby communities, including Baton Rouge. Together, the two would also reconnect the river to disappearing forested habitats.

When operated in conjunction, the Union Diversion, River Reintroduction into Maurepas Swamp and the Ama Diversion planned downriver could divert up to 77,000 cubic feet of water per second from the Mississippi River. This, according to a recent Tulane study, would reduce the duration of Bonnet Carre Spillway openings by 47 days and the water quantity moving through the spillway between 57 to 61 percent.

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. Read more about the Upper Basin Diversion Program