Engineering & Design
Region 3, Terrebonne Basin, Terrebonne Parish, Wetlands in select locations along the Atchafalaya River and continuing eastward into critical areas of Terrebonne Parish Wetlands.
Due to the construction of the Atchafalaya River East Guide Levee and changes to the historic hydrology, critical marshes in central and eastern Terrebonne Parish have become sediment and nutrient deficient. The modification of the natural processes that would have nourished the adjacent wetlands to the east leaves no mechanism in place to counteract subsidence in the area. This dire situation also makes the area susceptible to saltwater increasingly intruding into the region from the Gulf of Mexico to the South. Another regional issue this project seeks to address is the overabundance of sediment that accumulates in the Port of Morgan City's Channel Maintenance Program in the Atchafalaya River. These areas are periodically dredged under the United States Army Corps of Engineers' Environmental Dredging Program, but the dredged sediments are not utilized to their fullest beneficial potential. This project will seek partnership with the Corps of Engineers with the goal of getting the maximum benefit out of this resource.
This project will consist of constructing a sediment delivery pipeline which will be used to transport sediments dredged from available sources in the Atchafalaya River to be identified during the design process. The sediment will be transported eastward from these locations into the critically sediment-deprived marshes of central and eastern Terrebonne Parish. The alignment of the pipeline will be selected in order to provide the optimum route for the installation of a long-term use pipeline to maximize the multi-purpose benefits associated with moving sediments from the Atchafalaya Basin. Potential sites for marsh creation projects utilizing the pipeline will also be identified and prioritized during the design process.
Region 3, Strategy 5: Enhance Atchafalaya River water influence to central Terrebonne marshes (Bayou Dularge to Bayou Terrebonne).
Region 3, Terrebonne Basin, Terrebonne Parish, Marshes adjacent to Falgout Canal between Bayou Dularge and Houma Navigation Canal.
The marshes located in the project area have been hydrologically isolated from historical flow patterns by construction of various navigation channels, including the Houma Navigation Canal (HNC) and the Falgout Canal. Because of these barriers, the prevailing hydrologic influence is confined to southern tidal flows, which has resulted in elevated salinity and land loss in historically fresh and intermediate marshes. The project would expand the zone of Atchafalaya beneficial influence by modifying water flow patterns to include these areas of need. The marshes are expected to benefit from reduced salinity and increased nutrients and sediment.
The project would include construction/modification of structure at a site located on the HNC north of the Falgout Canal to increase freshwater flow to marshes north of Falgout Canal and to create freshwater plume to benefit marshes south of the canal. Three sets of six 36" culverts would be installed through the road separating the Falgout Canal from the marshes to the south to introduce freshwater nutrients and sediment. Approximately 50,000 linear feet of earthen terraces would be constructed in the broad shallow open water to facilitate marsh development.
The project will reestablish historical north to south flow in which the benefits of increasing freshwater, nutrients and sediment derived from the Atchafalaya River can be extended to marshes that have suffered catastrophic loss due to hydrologic isolation and salinity intrusion. The project will also facilitate creation of new marsh by terracing large shallow open water areas receiving new freshwater flow.
Approximately 5000 acres of existing marsh can be expected to benefit from the project freshwater flow enhancements. Much of the project area has degraded to open water and with terracing and the benefits of freshwater introduction and additional 4000 acres of marsh can be expected to benefit over the project life. The 50,000 linear feet of terracing will create approximately 675 acres of new marsh. Because the southern area of the project has already converted to nearly complete open water the project should offset any further loss and through terracing result in a net gain to the area. Land loss is expected to be offset greatly in the northern area of the project area as a result of improved freshwater flow.