A paradigm shift in the quantification of wave energy attenuation due to saltmarshes based on their standing biomass

Abstract

Most existing analytical and numerical models to quantify wave energy attenuation attributed to saltmarshes are based on the definition of a drag coefficient that varies with vegetation and wave characteristics and requires calibration, i.e., a case-specific variable. With the aim of determining a new variable to estimate wave energy attenuation without the use of calibration coefficients, wave attenuation caused by different saltmarsh species and the relationship with the ecosystem standing biomass are experimentally studied. Samples of four real saltmarshes with contrasting morphological and biomechanical properties, namely, Spartina sp., Salicornia sp., Halimione sp. and Juncus sp., are collected in the field and placed in a wave flume for testing under different regular and random wave conditions. Two meadow densities are considered, in addition to zero-density cases. Thus, wave damping coefficients are obtained in vegetated cases, β, and bare soil cases, β_B, and wave damping produced solely by the meadow standing biomass, β_SB, is determined. The obtained wave damping coefficients are related to a new variable, the hydraulic standing biomass (HSB), which is defined as a function of the meadow mean height and standing biomass and incident flow characteristics. Linear fitting relationships between the wave damping coefficient and HSB are obtained, allowing β and β_SB estimation without the need for calibration. Therefore, the use of these new relationships facilitates direct quantification of wave energy attenuation due to saltmarshes based on incident wave conditions, mean plant height and meadow standing biomass, variables that can be obtained from aerial images or remote sensing data, extending the applicability of the approach. Another key aspect is that this approach does not depend on any calibration coefficient and can be directly applied with knowledge of the abovementioned characteristics. This may represent a paradigm shift in the estimation of wave energy attenuation attributed to saltmarshes.