Modeling the Roughness Effect of Blown-sand-controlling Standing Vegetation in Wind Tunnel

The roughness properties of standing vegetation and their influential factors were studied in wind tunnel by using artificial plant models. It was found that with any wind velocity the roughness factor (\%Z\-0\%) in the log law wind profile increased with the vegetation density by power function, the exponent1; and decreased with wind velocity by some kind of exponential function. The predicted \%Z\-0\% values by the multivariate model including wind velocity and vegetation density based on experiment data matched those measured reasonably well. Therefore, the \%Z\-0\% in the log law is a physical dimension reflecting the interaction of the near surface airflow and surface conditions, correcting the common view that \%Z\-0\% is only determined by the surface conditions. It is suggested that cautions should be taken in applying the concepts of aerodynamic roughness and surface roughness.