Effects of grass-shrub vegetation and litter on overland flow resistance coefficients

Vegetation communities can drastically influence the hydrodynamic characteristics of the overland flow, change the overland flow resistance mechanism, and regulate soil erosion. To investigate the effect of grass-shrub vegetation and litter combinations on overland flow resistance, simulated rainfall experiments were carried out. The experiments involved a 15° gradient slope, five rainfall intensities (I = 60–120 mm h−1), five grass-shrub coverages (Cgs), and six litter volumes (Cl). The results showed that the mean values of form resistance under Cgs = 15%–75% ranged from 0.195 to 1.775, and the mean values of form resistance under Cl = 5–25 g m−2 ranged from 0.609 to 2.160. The form resistance of grass-shrub slopes with the addition of litter was 1.82–12.47 times higher than that under a single grass-shrub cover. The order of magnitude of the factors influencing the slope form resistance coefficients of the grass-shrub + litter was Cl > Cgs > Cl × Cgs > I. With varying vegetation kinds and coverage rates, I had diverse effects on form resistance. The resistance superposition principle does not hold under combined vegetation cover conditions. The degree of difference (Δfform) in form resistance was inversely proportional to I and directly proportional to Cl. Through dimensional and multiple nonlinear regression analyses, a general model for calculating form resistance was established (Adj. R2 = 0.99, NSE = 0.97). Theoretically, the results of this study can be used to evaluate soil and water conservation during vegetation community succession and restoration.