Experimental study on the correction factor of surface overland flow velocity

Abstract

The correction factor (α) of surface overland flow velocity is a significant parameter for determining the mean flow velocity in the study of soil erosion. A series of experiments with six types of surface roughness, five types of rainfall intensity, ten types of grass cover density, and three types of grass-shrub communities were conducted to quantify the influence of surface roughness, rainfall intensity, and grass cover on α. These results confirmed that for smooth surfaces, there is a negative correlation between α and the slope gradient in a large slope gradient range of 0.087–0.4226. The low critical value of Re (Rel) that resulting the influence of Re on α is not significant may be less than 170. There was a significant negative correlation between α and roughness (p < 0.001). In addition, whether on a smooth or rough surface, the rainfall increased α. When the grass cover density (C) was smaller than 3.45%, α increased with an increase in C; when C was larger than 3.45%, α showed the opposite trend as C increased. This is because as C increased, us did not continue to decrease but increased slightly. In addition, the mean flow velocity decreased significantly. This leads to a decrease in α. The rainfall intensity, roughness, and grass cover density had significant effects on α. Finally, the prediction equation of α quantifying the influence of rainfall and roughness on α was obtained with a high R2 (0.84) and low RRMSE (14%). h is a significant parameter for predicting α under grass-cover conditions. The prediction equation of α quantifying the influence of grass cover on α was also obtained with a high R2 (0.87) and low RRMSE (13%). These equations should be further validated when applied beyond the scope of the conditions under which they were developed.