A rapid assessment method for calculating the drag coefficient in wave attenuation by vegetation

Vegetation in wetlands is a large-scale nature-based resource that can provide multiple benefits to human beings and the environment, such as wave attenuation in coastal zones. Traditionally, there are two main calibration approaches to calculate the attenuation of wave driven by vegetation. The first method is a straightforward one based on the exponential attenuation of wave height in the direction of wave transmission, which, however, overlooks the crucial drag coefficient (CD). The other method is in accordance with more complicate equations for predicting the damping factor, which is regarded as a function of CD. In this study, a new relation, combining these above two conventional approaches, is proposed to predict the CD in an operative approach. Results show that values yielded by the new assessment method perform a strong linear relationship with a collection of historical observations, with a promising R2 value of 0.90. Besides, the linear regression derives a new predictive equation for the bulk drag coefficient. Additionally, a calibrated value of 4 for the empirical plant drag coefficient (CP) is revealed. Overall, this new equation, with the superiority of the convenient exponential regression, is expected to be a rapid assessment method for calculating wave attenuation by vegetation and predicting the drag coefficient.