Effects of different grass distribution patterns and coverage combinations on overland flow resistance mechanisms

To clarify the relationship between grass cover and water flow resistance, laboratory-simulated  rainfall experiments were conducted. Five rainfall intensities and three degrees of slope were  applied to six degrees of grass cover and six distribution patterns to elucidate the response of overland resistance to the experimental design factors and hydrodynamic parameters and to  establish a predictive model. The results indicated that as grass coverage increases, the resistance  coefficient also increases; however, with increases in the rainfall intensity and slope, the resistance  coefficient decreases, with no apparent critical slope or rainfall intensity. Overland resistance was  higher for the horizontal vegetation pattern than the vertical pattern. The flow Reynolds and Froude numbers were negatively correlated with the resistance coefficient. The water flow path index was  useful for characterizing overland resistance, reflecting the influence of different grass cover types,  and was positively correlated with the resistance coefficient. Based on a dimensional analysis and  the π theorem, a model of overland flow resistance was developed. This model effectively predicted overland resistance and quantified the contribution of each factor to the  resistance coefficient. The contributions of the slope, rainfall Reynolds number, flow Reynolds  number, Froude number, and water flow path index to overland resistance were 12.78%, 6.02%, 34 9.77%, 15.04%, and 56.39%, respectively, with grass cover playing a key role. Simulated rainfall  experiments with different degrees of grass coverage and distribution patterns revealed the  dynamic mechanisms of overland hydraulic erosion.