The Terrebonne and Atchafalaya basins occupy the central coast of Louisiana. The Terrebonne-Atchafalaya Basin has the highest rate of land loss in Louisiana, making the need to rebuild these coastal wetlands even more urgent. The area is bordered to the east by Bayou Lafourche, a former outlet of the Mississippi River, and to the west by the Chenier Plain. The basin includes the growing Wax Lake and Atchafalaya deltas of the Atchafalaya River, which is the largest remaining natural distributary of the Mississippi River. However, in Terrebonne Bay, on the eastern side of the basin, wetlands are collapsing and becoming open water as the sediment-starved land sinks and salt water intrudes into freshwater wetlands. Habitats in this basin include bottomland hardwood forests, swamps, barrier islands and freshwater, brackish and saltwater marsh.
The priority projects selected for this basin focus on reestablishing a balance of fresh and salt water as well as sediment and nutrient distribution. To accomplish this goal, the Increase Atchafalaya Flow to Terrebonne Diversion project will take advantage of the Atchafalaya River and the Intracoastal Waterway to move fresh water and sediment eastward. This project will work in conjunction with the Houma Navigational Canal Lock, a successful 2012 priority project that is moving toward construction, to reintroduce and increase the retention of fresh water into Terrebonne’s marshes. Atchafalaya River Sediment Diversion will also direct sediment and fresh water to marshes in southwest Terrebonne, restoring freshwater flows and habitats. Both diversions will provide freshwater inputs and some sediment to the Terrebonne Ridge Restoration, which will create maritime forest, improve water quality and protect marsh from storm surge and wind energy. All three of these projects will help fight saltwater intrusion by restoring freshwater inputs and natural hydrologic patterns.