Prevention and control of grass strips distribution on soil and water loss and its optimal configuration of slope-gully system

Understanding of the spatial configuration of vegetation regulated erosion and sediment transport of slope–gully systems is the key to manage erosion and sediment yield as well as to regulate the sediments in a watershed. A slope–gully system is the basic component of a watershed. Understanding the occurrence and development of erosion in slope–gully systems remains an essential problem in research related to the mechanisms of soil erosion dynamic, as well as the key to prevent soil and water loss in a watershed. Revealing the occurrence and development mechanism of the water erosion process in slope–gully systems, clarifying the regulation mechanisms of vegetation on the water erosion process in slope–gully systems, and proposing reasonable regulation and control modes have become the focuses of current studies on soil erosion. In this study, the slope-gully system was used as the object, using indoor simulated rainfall experiments combined with three-dimensional laser scanning technology and microtopography analysis technology. Such system discriminated the soil and water conservation function, dynamic regulation approach on water and sediment, and proposed the optimal vegetation pattern for regulation on the erosion at low vegetation coverage. The results showed that grass strips in different positions performed better in direct sediment interception function than performed in water storage function considering the water and sediment reduction. However, considering the water erosion dynamics, the grass strip could respectively exert runoff retardation sediment interception function on runoff and sediment from up-slope and exert runoff detention elimination energy function on runoff and sediment in the lower part during water erosion dynamic process and erosion sediment process. The regulation scope and strength of the two functions on water erosion dynamics were closely related to the configuration mode. When the grass strips were placed at the middle-lower part of the slope, they could play a better dual role in soil and water conservation functions. The erosion from the slope above the grass strip can be effectively mitigated by the effect of retarding runoff and intercepting sediment. In addition, the rapid increase in runoff velocity and “peak discharge” into the gully could be effectively weakened by the effect of retaining runoff and eliminating energy, thereby significantly reduced the sediment yield on the lower part of the slope and in the gully. A quadratic function could be used describe the relationship between the relative position of vegetation and sediment yield in the slope–gully system. The relative position indicator was between 0.571-1.200, which was the optimal regulation scope of vegetation on erosion. When grass strip was planted in the area, it could effectively exert both the best soil and water conservation effect of runoff retardation sediment interception function and runoff detention elimination energy function, and the regulation scope could extend each section from the slope to gully to achieve better effect of erosion reduction. The relative position indicators still need to be corrected and perfected based on experiments and observations. The information can be useful for better understanding the effect of vegetation on erosion sedimentation processes and hydrological processes in a slope-gully system.