Study On The Effects Of Rainfall Spatial And Temporal Characteristics On Runoff And Soil Erosion Processes

Rainfall spatial and temporal charateristics are one of the key factors affecting the runoff and soil erosion processes.Due to the shortage of the study on the effect of rainfall spatial and temporal charateristics on the runoff and soil erosion processes,this study used physical-based numerical simulation method combining with an indoor rainfall simulation experiment to systematically analyze the effects of rainfall spatial and temporal characteristics on runoff generation and soil erosion processes.Combining the overall response of the study area with the spatial distribution characteristics of the internal runoff and soil erosion processes,this study has obtained a more comprehensive influence rule on the runoff and soil erosion processes.The result of this study improved the understanding of the rainfall runoff and soil erosion mechanisms,and have great application value in the fields of soil and water conservation,disaster prevention and agricultural management.The main contents are summarized as follows:(1)Using numerical simulation method,adopting the distributed hydrological model InHM,the effects of rainfall patterns on runoff generation and soil erosion were systematically studied on the slope scale.Through the analysis of the hydrographs,sedigraphs and distributed infiltration and erosion depth characteristicson the slope,it was found that the rainfall pattern has a great influence on the runoff and erosion processes.The difference in total runoff and soil erosion between different rain patterns at the same slope can reach 74%and 160%,respectively.The runoff and erosion peaks of the increasing pattern are the largest,while the peak discharge of the convex-upward pattern was formed later than the peak of the rainfall.Compared with concave-upward pattern,the infiltration of constant pattern was more concentrated in the upstream of the slope,while the erosion in the downstream of the slope was greater.Compared with the increasing pattern,the convex-upward pattern had less infiltration and more erosion in the downstream of the slope.(2)Using numerical simulation method,a comprehensive study was conducted on the differences in runoff and soil erosion processes caused by different rainfall movement conditions on both the slope scale and basin scale.The research systematically analyzed the effects of different rainfall movement directions and moving speeds on hydrograph,sedigraph and infiltration,total runoff and total transported sediment.Through the analysis of the distributed runoff and infiltration data in the study area,the influence of specific runoff processes caused by different rainfall movement directions on the infiltration process was clarified.The results showed that at the slope scale,the infiltration time and volume were larger due to the longer runoff process under upstream-moving rainfall,resulting in less total runoff than the downstream-moving rainfall.This conclusion can be extended to the basin scale.In the hillslope facing downstream outlet and the main channel,the infiltration time and volume of the upstream-moving rainfall was larger.Since the hillslopes of studied watershed was mostly facing downstream,the total infiltration of the upstream-moving rainfall was greater.The total soil erosion of upstream-moving rainfall was also less than that of downstream-movign rainfall.(3)Taking the process of surfaces sealing as the entry point,using the indoor artificial rainfall simulation experiment,the different spatial processes of surface sealing and the resulting differences in rainfall runoff and soil erosion processes caused by different rainfall moving directions were comprehensively studied on the easily sealed loess slope.The study found that,in the absence of the impact of the antecedent rainfall,due that the upslope-moving rainfall generated seal on the downstream slope in the early stage of the event,it produced more runoff than downslope-moving rainfall.The difference between the runoff of the two moving rainfalls decreased significantly as the slope increases from 15 degrees to 25 degrees.When considered the influence of the antecedent rainfall,since the surface seal had formed,the runoff coefficient of the upslope-moving rainfall was close to the downslope-moving rainfall.In both pre-states,the erosion of the downslope-moving rainfall was more severe than the upslope-moving rainfall.