Laboratory Observations and Numerical Simulations of Wave Height Attenuation in Heterogeneous Vegetation: Fid-Bau Portal

Laboratory Observations and Numerical Simulations of Wave Height Attenuation in Heterogeneous Vegetation

Blackmar, Philip J. / Cox, Daniel T. / Wu, Wei-Cheng

Abstract

Quarter-scale physical model experiments and a phase-resolving numerical model (FUNWAVE) were used to evaluate random wave attenuation through two types of synthetic vegetation. The experiment was performed with two peak periods, three water depths, and two stem densities. For each combination of parameters, free surface time series were collected at seven locations throughout the vegetation field and one location seaward of the vegetation. Each combination of wave conditions was evaluated for the following four different cases: Case A with no vegetation; Cases B and C with short and long specimens, respectively; and Case D with mixed vegetation. The wave height decay for each case was fit to two existing wave height attenuation prediction equations. The decay equations provided reasonable predictions for the normalized wave height attenuation, with an average root-mean-square error (RMSE) of 0.015. The linear combination of attenuation coefficients obtained for the cases of the individual plants provided a reasonable prediction of the attenuation coefficient for the cases of the combined, heterogeneous vegetation. FUNWAVE was used to model wave attenuation for these tests using a bottom friction factor calibrated for each run. The numerical attenuation followed the same trends as the measured data, with an average RMSE of 0.017. Similar to the physical model study, it was found that summing the calibrated model friction factors for the cases of the individual plants reasonably predicted the wave height attenuation for the cases of the combined vegetation with an average RMSE of 0.032.