A Review of Ecohydrological and Hydraulic/Flood Models for Evaluating the Water Quality and Flood Mitigation Potential of Natural Infrastructure (NI) Practices in the Mississippi-Atchafalaya River Basin
Philip W. Gassman, Jerry Mount, Keith E. Schilling
July 2023 [23-SR 123]
Gassman, P.W., J. Mount, and K.E. Schilling. 2023. "A Review of Ecohydrological and Hydraulic/Flood Models for Evaluating the Water Quality and Flood Mitigation Potential of Natural Infrastructure (NI) Practices in the Mississippi-Atchafalaya River Basin." Staff report 23-SR 123. Center for Agricultural and Rural Development, Iowa State University.
Extraordinary interventions are needed to overcome the extensive flooding and water quality problems that continue to manifest within the Mississippi-Atchafalaya River Basin (MARB). The Mississippi River & Tributary levee system has resulted in successful flood control in recent decades in the Lower Mississippi River (LMRB). However, hundreds of levees have failed in other MARB subregions as a result of recent floods, and the extensive LMRB levee system and other factors are linked to the considerable loss of coastal wetlands and habitat areas in southern Louisiana. Water quality degradation continues essentially unabated across much of the MARB, especially in the Corn Belt region. Massive investment in a wide range of cropland conservation practices and other interventions has unfortunately yielded only minor improvement at best in MARB stream system water quality. Widespread adoption of natural infrastructure (NI) practices provides the potential to establish greater progress in mitigating both flood impacts and improving in-stream water quality in MARB waterways, especially if those practices are embraced in a more aggressive manner within federal and state conservation practice strategies.
The Agricultural Policy/Environmental EXtender (APEX), Soil and Water Assessment Tool (SWAT) and SWAT+ models developed at the co-located USDA and Texas A&M AgriLife laboratories in Temple, TX show the strongest overall abilities to accurately replicate these NI practice impacts. The SWAT+ model is particularly advantageous, due to the incorporation of previous APEX and SWAT modeling strengths and the current development of the National Agroecosystem Model (NAM) system. The utility of SWAT+ is further underscored by the relative ease of interfacing it with other models, such as previous studies that report model cascades between SWAT and Hydrologic Engineering Center-River Analysis System (HEC-RAS). This attribute provides the potential to expand an adapted NAM modeling system to not only capture MARB NI practice flood and water quality impacts, but also account for more detailed flood analyses if needed. It is recommended that the SWAT+/NAM modeling system be adopted for future MARB NI practice simulations. Further development will be required to implement the full suite of NI practices discussed here. This can be achieved via close collaboration with the SWAT+/NAM developers and the required investment needed to incorporate physical representation of the full suite of NI practices in future MARB applications.