Effects of shrub on runoff and soil loss at loess slopes under simulated rainfall

Improved understanding of the effect of shrub cover on soil erosion process will provide valuable information for soil and water conservation programs. Laboratory rainfall simulations were conducted to determine the effects of shrubs on runoff and soil erosion and to ascertain the relationship between the rate of soil loss and the runoff hydrodynamic characteristics. In these simulations a 20° slope was subjected to rainfall intensities of 45, 87, and 127 mm/h. The average runoff rates ranged from 0.51 to 1.26 mm/min for bare soil plots and 0.15 to 0.96 mm/min for shrub plots. Average soil loss rates varied from 44.19 to 114.61 g/(min·m2) for bare soil plots and from 5.61 to 84.58 g/(min·m2) for shrub plots. There was a positive correlation between runoff and soil loss for the bare soil plots, and soil loss increased with increased runoff for shrub plots only when rainfall intensity is 127 mm/h. Runoff and soil erosion processes were strongly influenced by soil surface conditions because of the formation of erosion pits and rills. The unit stream power was the optimal hydrodynamic parameter to characterize the soil erosion mechanisms. The soil loss rate increased linearly with the unit stream power on both shrub and bare soil plots. Critical unit stream power values were 0.004 m/s for bare soil plots and 0.017 m/s for shrub plots.