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

<p>To clarify the relationship between grass cover and water flow resistance, laboratory-simulated&nbsp; rainfall experiments were conducted. Five rainfall intensities and three degrees of slope were&nbsp; 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&nbsp; establish a predictive model. The results indicated that as grass coverage increases, the resistance&nbsp; coefficient also increases; however, with increases in the rainfall intensity and slope, the resistance&nbsp; coefficient decreases, with no apparent critical slope or rainfall intensity. Overland resistance was&nbsp; 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&nbsp; useful for characterizing overland resistance, reflecting the influence of different grass cover types,&nbsp; and was positively correlated with the resistance coefficient. Based on a dimensional analysis and&nbsp; the &pi; theorem, a model of overland flow resistance was developed. This model effectively predicted overland resistance and quantified the contribution of each factor to the&nbsp; resistance coefficient. The contributions of the slope, rainfall Reynolds number, flow Reynolds&nbsp; 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&nbsp; experiments with different degrees of grass coverage and distribution patterns revealed the&nbsp; dynamic mechanisms of overland hydraulic erosion.</p>