Submitted to: International Journal of Sediment Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/1/2011
Publication Date: 9/30/2011
Citation: Xiao, P., Yao, W., Romkens, M.J. 2011. Effects of grass and shrub cover on the critical unit stream power in overland flow. International Journal of Sediment Research. 26:(3)387-394. Interpretive Summary: Semi-arid regions are characterized by a period of little or no precipitation. In those areas, vegetation is often sparse and consists mostly of grasses and shrubs. Occasional rainfall is often intense and of relatively short duration. As a result, erosion on sparsely covered slopes can be severe, and efforts must be made to reduce erosion hazards. The Loess Plateau in China, and also areas in the western part of the USA, are such regions. This paper reports the result of a study that was conducted in China which compared the effect of grass and shrub cover on the slopes of the Loess Plateau where annual precipitation varies from 400 mm in the northwestern part of the Plateau to about 600 mm in the southeastern part, with most of the rain falling from June to October. Rates of soil loss varied linearly with the unit stream power of runoff for both types of vegetative cover. Shrub covered plots showed greater stability to soil detachment and transport by surface flow than grass covered plots. The shrub covered plot had a greater stream power value (0.0169 m/s) than the grass covered plot (0.0127 m/s).
Technical Abstract: Improved knowledge of the effect 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 the effect of grasses and shrubs 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 degree slope subjected to rainfall intensities of 45, 87, and 127 mm/h. The results indicated that the average runoff rate 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 rate 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 losses 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. Rates 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 the grass plots and 0.0169 m/s for the shrub plots. Shrub plots showed a greater stability to resist soil detachment and transport by surface flow than grass plots.