Assessing marsh terrace design parameters impacts on hydrodynamics

Changes in natural hydrodynamics along the Louisiana coast (US) have led to significant marsh loss over the past hundred years, threatening ecological balance and communities seeking protection from storm surges. Wetlands provide critical environmental services, including shoreline protection and flood mitigation, wildlife habitat, and water filtration. One nature-based feature that has gained popularity across the Gulf of Mexico is building marsh terraces to combat wetland loss. Marsh terraces are earthen berms strategically arranged in shallow coastal areas, often around wetlands or former wetlands, to reduce wave velocity and prevent erosion while also providing a natural habitat for wetland-dependent wildlife. While these structures have proven effective in building/maintaining marshland, no formal/unified guidelines exist for their design or for assessing design parameters; thus, practitioners rely on design approaches based on local knowledge and experience. Therefore, this study assesses various marsh terrace design parameters in an idealized domain to improve understanding of these parameters and their relationship to local hydrodynamics. The Advanced CIRCculation (ADCIRC) model and the Simulating WAves Nearshore (SWAN) model were used to estimate the hydrodynamic variables and their influence on the design modifications. The analysis compares various wind scenarios against physical qualities of marsh terraces, including shape, linear length, and field density. Results show that marsh terraces exhibit the greatest reduction in significant wave height, and that terrace shape has the strongest influence on this reduction. This study highlights each parameter's influence on overall performance and can serve as a foundation for developing tools that efficiently design future projects.