Atchafalaya Diversions

The Atchafalaya Diversions 2023 Coastal Master Plan project consists of two proposed projects diverting water and sediment from the Atchafalaya River: Atchafalaya River Diversion and Increase Atchafalaya Flow to Terrebonne.

The Atchafalaya River Sediment Diversion will provide basin-wide benefits to marshes in southwest Terrebonne Parish. This project will see sediment and fresh water diverted into the marshes to help build land and sustain other nearby projects planned for construction like the Mauvais Bois Ridge Restoration. The wetlands in Terrebonne Basin provide critical protection for the cities of Houma and Morgan City against hurricanes and storm surge. This project will have the greatest benefits to freshwater habitats, such as forested areas, flotant and fresh and intermediate marsh, which are threatened by saltwater intrusion and sediment starvation.

The Increase Atchafalaya Flow to Terrebone project is a hydrologic diversion that stretches from the Atchafalaya River to the Houma Navigation Canal, which is part of the Gulf Intracoastal Waterway system. The marshes in the influence area are nearly an equal distance from the Mississippi and Atchafalaya rivers and are blocked from significant amounts of river water and sediment. These marshes have been rapidly converted to open water because of saltwater intrusion and sediment starvation. This project would dredge and deepen a portion of the Gulf Intracoastal Waterway to increase the flow of fresh water from the Atchafalaya River to help sustain Terrebonne marsh. Additional benefits from this project include using the dredged material to create marsh and increase flow capacity using two southern-flowing canals (Minor’s and Bayou Copasaw.) On the basis of 30% design findings, this project is being shelved and will not proceed to the final stages of design at this time.

Between 1932 and 2016, the Terrebonne Basin lost more than 500 square miles (300,000 acres) of wetlands. A dam was completed across Bayou Lafourche in 1904 to prevent flooding in Donaldsonville, but this dam also cut off the steady flow of fresh water and sediment to the wetlands. This wetland loss stands in direct contrast to the neighboring Wax Lake Delta, which is an example of the land building potential of the Atchafalaya River.

Projects such as the Atchafalaya River Sediment Diversion and the Increase Atchafalaya Flow to Terrebonne Diversion, along with the Houma Navigation Canal Lock Hydrologic Restoration, would increase the flow and retention of fresh water eastward to the central part of the basin to sustain existing marshes.