Freshwater Diversion

Union Freshwater Diversion

  • Project TypeFreshwater Diversion
  • Project BasinPontchartrain-Maurepas Basin

Union Freshwater Diversion will move fresh water from the Mississippi River into Maurepas Swamp near Burnside. With a maximum capacity of 25,000 cubic feet of water per second, the diversion will deliver nutrient-rich freshwater to the fresh-forested, flotant and freshwater marsh environments to prevent saltwater intrusion and encourage vegetation growth. It will be designed to operate at maximum capacity when the river’s flow reaches one million cubic feet per second.

Over 50 years, the $876 million Union diversion is expected to build or maintain 141,824 acres of wetlands and positively impact about 6,000 acres within the first 20 years of operation.

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


What does a future without action look like?
What does a future with action look like?


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, 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 would reduce the duration of Bonnet Carre Spillway openings and the quantity of water that moves through the spillway. 

Modeling done in a new Tulane study suggested that when Ama North and Union were operated jointly, the volume of water flowing through the spillway reduced by 57 to 61 percent and reduced the duration of the opening by 47 days, or over a month.

The Union Sediment Diversion project is still conceptual but the planning and engineering is estimated to take five years. Construction is estimated to take three years.