Study On Slope Soil Erosionresponse And Model Simulationin Beijing Mountainous Area

Slope is the basis unit of the surface process development, also one of fundamental units of river basin, as well as the source areas of soil erosion and channelsediment. We conducted the study by runoff plots location observation and the artificial rainfall simulation test in field and indoor, our object is:to analyzethe response of slope soil erosion to the effects of multi-factors including rainfall pattern, topography, vegetation cover, soil and water conservation measures and so on; to build the runoff-erosion model in slope scale under the condition of rainfall runoff through improving the antecedent precipitation index model, runoff curve model and slope soil erosion model, then conducted the quantified study and modeling of slope soil erosion process by these models, and indicated the process and mechanism of slope rainfall erosion. The study provide theoretical basis for slope soil erosion and related model in Beijing mountain areas.The main conclusions are as follows:(1)The rainfall events in study areas were divided into three different rainfall patterns. The first rainfall pattern is short-term, small-amount, high-intensity and high-frequence rainfall event; third rainfall pattern is long-term, large-amount, low-intensity and low-frequence rainfall event; and the second pattern is between these two rainfall patterns. We analyzed the seasonal distributions of different rainfall patterns, and the characteristics of soil erosion under these patterns, the results indicated that the first rainfall pattern play a dominant role in slope soil erosion.(2)Some differences existed in the change discipline of runoff and erosion in runoff plots with different gradient, which showed the increased trends with increased gradients. The variations of runoff and erosion were different in runoff plots with different slope length, runoff decreased with the increase of slope gradient, while soil erosion showed increase firstly and then reduction. Slope runoff and erosion were closely correlated with rainfall amount and maximum30min rainfall intensity in different slope gradients and lengths, which showed positive relationships.(3)The analysis of soil erosion characteristics under different land use pattern and soil and water conservation measures indicated that:the differences of soil erosion were significant in five land use patterns, the sediment reduction rate of farmland, artificial grassland, banning wild grassland and forest reached63.88%-99.63%contrasting with bare land;2.soil erosion of terrace were95.2%smaller than slope cropland, which demonstrated remarkable effect of soil and water conservation;3. soil erosion of horizontal bar and scale-hole measures were83.56%and96.53%smaller respectively, indicated significant effects of decreasing erosion.4. soil erosion of banning wild grassland were98.25%smaller than artificial grassland, that could effectively control soil erosion. So the engineering measures of soil and water conservation were very usefully through increasing aboveground vegetation cover, reducing human interference and the proper configuration of terraces.(4)The variation of soil water fading coefficient were analyzed in different seasons and soil depths based on the study of soil moisture dynamics, and optimized depending on the characteristics of erosive rainfall. The rainfall index model were improved by soil water fading coefficient. The processes of rainfall-runoff, which was affected by antecedent soil moisture, were analyzed quantitatively using the antecedent rainfall index of rainfall events,which is the representation of soil water condition. The results indicated that:the antecedent rainfall index model could perfectly reflect the processes of slope rainfall-runoff under the effect of antecedent soil water, suggested antecedent rainfall index model has good applicability in Beijing mountain areas.(5)Modeling slope runoff by improved runoff curve model. Firstly, the key model parameter was optimized, the optimal values of early damage coefficient (λi) on different land use types were determined using anti-inference method; then the model structure was improved by introducing the antecedent soil moisture(M), and the revised antecedent rainfall index model was used to calculate the effective rainfall in early stage (P5). Lastly, the modeling results of slope runoff, by the model of improved runoff curve, indicated that there was the validity of model simulation due to the very closed value between slope runoff simulation and measured runoff.(6)Improved the model of Revised Universal Soil Loss equation (RUSLE). Rainfall-runoff erosivity index was added in the model structure, determined by the parameter of slope runoff simulation calculated by the model of improved runoff curve. The results of soil erosion, which was determined by developed slope erosion model, indicated that the validity of model simulationwas very obvious, the soil erosion were very closed between simulation and actual measurement.