Effectiveness of soil and water conservation of greening mulch of roadside slope

Soil erosion is one of the most serious environmental problems in the world. The acceleration of soil erosion is mainly caused by land use changes, and highway construction is an important land use change. Mulch is a good alternative before the establishment of vegetation on slopes, which can reduce the direct impact of rainfall on the slopes and increase the infiltration of rainwater, reducing runoff and soil erosion. In this study, a rainfall simulator was made which is of simple structure and is easy to operate. Rainfall intensity, rainfall uniformity and raindrop diameter were all calibrated and could reach the experimental requirements well. Ten 20-minute rainfall simulations were carried out on each simulated road slope (30°) which was covered variously with shade net, non-woven fabrics, straw mats and nothing, respectively, in order to examine the effects of three kinds of mulch, shade net, non-woven fabrics and straws mat on road slopes in decreasing runoff and soil loss. The aim was to obtain the best effectiveness of soil and water conservation in the process of green construction of road slope. The process of runoff production on the slope was strongly influenced by the effects of the underlying surface conditions. The ANOVA showed that there were significant differences among the hydrological responses of the slopes depending on the different mulch. The surface runoff curves are logarithmic. The highest average runoff coefficient was determined for the bare slope (21.3%). Runoff coefficients of slopes with shade net and non-woven fabrics were 13.5% and 18.9% respectively. Average runoff coefficients were lower on the slope with straw mats (6.4%). The three kinds of mulch were all successful in reducing the runoff rate. The average runoff rates were 4.2 mL/s, 5.8 mL/s and 1.9 mL/s for slopes with shade net, non-woven fabrics and straw mats, respectively, which were all much lower than that of bare slope (6.6 mL/s). The same behavior was observed for the peaks of runoff rate. Some differences were also detected in the sediment concentration in runoff water. The greatest erosion was detected on the bare slope, where average sediment yield was 5.7 g/L and total soil loss was 44.2 g/m2. The soil loss from the slopes covered with shade net and non-woven fabrics was approximately 8 g/m2 and 5 g/m2 respectively. The lowest erosion was determined for the slope covered with straw mats (with 1.0 g/L as an average sediment yield and 1.5 g/m2 as a average total soil loss). Sediment yield data were also higher for the bare slope (5.7 g/L) than for the slopes covered with shade net (2.4 g/L) and non-woven fabrics (1.9 g/L). The same behavior was observed for the peaks of sediment yield: the highest value for the bare slope was 8.1 g/L, and the lowest value for the slope with straw mats was 1.8 g/L. The three kinds of mulch all significantly (P=0) decreased runoff and soil loss rates compared with the bare slope. What is more, straws mat had the best effect as it induced the lowest runoff (1.9 mL/s), runoff coefficient (6.4%) and soil loss (1.5 g/m2).