Author(s): Ernie I. H. Lee; Heidi Nepf
Linked Author(s): Heidi M. Nepf
Keywords: Nature-based solutions Salt marshes Wave attenuation Coastal protection Wave-modeling Benefit-cost analysis Ecosystem services
Abstract: A marsh-fronted seawall is a hybrid nature-based solution for coastal protection. The marsh attenuates wave energy, reduces erosion, and provides valuable ecosystem services. However, there is a limited understanding of how to monetize the marsh wave attenuation benefits for economic analysis. In this study, the economic benefit of the marsh was quantified by the avoided seawall heightening cost that would otherwise be required to deliver the same overtopping rate without vegetation. A vegetation drag model that accounts for species-specific morphology and structural stiffness was applied in a 1-D wave model and validated with field wave height measurements. The 1-D model was used in a benefit-cost analysis (BCA) of marsh-fronted seawall design. In many scenarios, the benefit-cost ratio (BCR) was greater than one, indicating that marsh-fronted seawalls are economically justified. Both species and seasonal growth patterns impacted the wave dissipation benefit of the marsh, which alters the BCR. Specifically, the BCR varied by a factor of two across different marsh species and by a factor of 1.5 in response to seasonality. The wave attenuation was more sensitive to water depth than wave height. The effect of sea-level rise can be assessed through an increase in water depth and decrease in the intertidal zone where marsh vegetation grows, which reduces the feasible marsh width. Since specific plant morphology and rigidity characteristics are necessary inputs for modeling hydrodynamic drag, and thus wave dissipation, future studies consider how these parameters can be obtained by combining plant allometric relationships and drone remote sensing techniques.
Year: 2025