Sediment exchange between the created saltmarshes of living shorelines and adjacent Submersed Aquatic Vegetation (SAV)

Rising sea levels and increasing frequency of extreme events put coastal communities at serious risk. In response, shoreline armoring for stabilization has been widespread; however, this solution doesn't take ecological aspects of the coasts into account. The "living shoreline" technique includes coastal ecology by incorporating natural habitat features, such as saltmarshes, into shoreline stabilization. However, living shoreline impacts to adjacent benthic communities, like submersed aquatic vegetation (SAV), aren't yet clear. In particular, while both marshes and SAV trap sediment necessary for their resilience to environmental change, synergies between the communities aren't well understood. To help quantify the ecological and protective aspects of living shorelines, we present modeling results using Delft3D-SWAN on sediment transport between the created saltmarshes of the living shorelines and adjacent SAV. Model runs use the same domain with different wave heights and periods, vegetation density and suspended-sediment concentrations. We also investigate how the presence of riprap influences the sediment exchange between the plant communities.Study results indicate lower shear stress, lower erosion rate and higher level of bottom sediments within the SAV bed, which helps stabilize bottom sediments in the zone between the bed and the shoreline. Within the marsh, compared to the case without adjacent SAV, erosion rates are lower and accumulation rates are higher, enhancing potential resilience of the marsh to environmental change. The presence of riprap can help stabilize the shoreline at the expense of a scouring effect that occurs at the foot of the riprap; this effect grows with increasing wave height and period. Overall, the SAV helps to stabilize the bed level and the shoreline, and the riprap can even make this enhancement stronger, demonstrating how the right combination of natural and built solutions can work fine in term of ecology and coastal protection.