At 895,000 acres, the Atchafalaya Basin is the nation’s largest swamp wilderness, containing nationally significant expanses of forested wetlands. M&N is currently supporting The Nature Conservancy’s (TNC) stewardship and ecosystem restoration efforts in the Atchafalaya Basin by developing a hydrodynamic model of the basin to accurately simulate the distribution of flows out of the Atchafalaya River into the surrounding floodplain through secondary channels and the regulation of backwater swamp inundation by vertical features (spoil banks, etc.). The Atchafalaya Basin Model is a high-resolution, flexible mesh hydrodynamic model with updated topo bathymetric sources that is calibrated to the latest hydrologic monitoring data, including United States Geological Survey (USGS) discharge measurements along secondary channels. A Cypress/Tupelo Swamp Ecology Module, modeled after the wetland morphology modules in the Louisiana Coastal Master Plan ICM, was also developed to model the impacts of varying Atchafalaya Basin flows and inundation extents/durations on cypress/tupelo germination, survival, and regeneration. Additional development extended model capabilities to include simulation of water quality proxies that capture the influence of stagnant water on ecological health. The Atchafalaya Basin Model and coupled ecology module are together used to examine regeneration potential under current hydrologic conditions and to characterize changes in suitability for fresh forested wetlands over time associated with different Atchafalaya Basin water management strategies.

Since creation of the model, TNC has engaged in the Sustainable Rivers Program (SRP), where M&N model results have been instrumental in informing discussion and restoration planning. The Sustainable Rivers Program (SRP) is a national partnership between the U.S. Army Corps of Engineers (USACE) and TNC to improve the health and life of rivers by changing the operations of existing water management structures to restore and protect ecosystems, while maintaining or enhancing authorized uses and other project benefits. The Atchafalaya River was added to the SRP portfolio in 2020, prompting the identification of stakeholders, establishment of the stakeholder engagement process, and identification of hydrologic, hydrodynamic, and habitat models and other tools to help identify ecological opportunities within the Atchafalaya River Basin. In March 2025, an environmental flow (e-flow) development workshop was held to develop e-flow recommendations for the Old River Control Structure that could result in benefits to forest health, water quality (flow/exchange), and fish and crawfish habitats within the Atchafalaya Basin, culminating in combined recommendations for alternative flow management that could improve basin ecosystems.