Effects of grass and shrub cover on the critical unit stream power in overland flow

Abstract Improved knowledge of the effects of grass and shrub cover in overland flow can provide valuable information for soil and water conservation programs. Laboratory simulated rainfall studies were conducted to determine effects of grass and shrub on runoff and soil loss and to ascertain the relationship between the rate of soil loss and the unit stream power of runoff for a 20 o slope subjected to rainfall intensities of 45, 87, and 127 mm/h. The results indicated that the average runoff rates ranged from 4.2 to 73.1 mm/h for grass plots and from 9.3 to 58.2 mm/h for shrub plots. Runoff rates from shrub plots were less than those from grass plots for all but the 45 mm/h rainfall intensity regime. Average soil loss rates varied from 5.7 to 120.3 g/min.m 2 for grass plots and from 5.6 to 84.4 g/min.m 2 for shrub plots. Soil loss rates from shrub plots were generally lower than those from grass plots. Runoff and soil loss were strongly influenced by soil surface conditions due to the formation of erosion pits and rills. The rate of soil loss increased linearly with the unit stream power of runoff on both grass and shrub plots. Critical unit stream power values were 0.0127 m/s for grass plots and 0.0169 m/s for shrub plots. Shrub plots showed a greater stability to resist soil detachment and transport by surface flow than grass plots.