Study On Soil Erosion Of West Poplar Valley Small Watershed Based On Artificial Simulated Rainfall

Soil erosion has hindered the restoration and development of pasture ecosystems in semi-arid areas.Affected by short-term strong rainfall in mountainous areas,coupled with low vegetation coverage and inappropriate extensive management models,a large amount of fertile soil has been lost in the West Poplar Valley region.Comprehensive management of small watersheds increases the difficulty.The purpose of this study is to quantify the initial soil erosion,study the time-varying characteristics of runoff and sediment associated with different vegetation coverage and soil erosion,and try to provide suitable ideas for the management of regional soil erosion.Based on this,a simulated rainfall test was used in West Poplar Valley to evaluate the effects of vegetation factor,rain intensity factor,and slope factor on hydraulic erosion,and 60 simulated rainfall events were conducted in August 2019.By studying 3 rainfall intensities（10mm/h,20mm/h,30mm/h）,5 vegetation coverages（bare slopes,15%,35%,55%,75%）,and 4 representative slopes（5°,10°,15°,20°）conditions of runoff and sediment production process,using wavelet transform and R/S method to study the multi-scale time variation characteristics of runoff sediment during simulated rainfall erosion,The following main conclusions are drawn:（1）The law of runoff time（T）changing with slope is T_20°<T_15°<T_10°<T_5°.The initial runoff time of chestnut soil exposed slopes decreases with the increase of rain intensity,slope,and vegetation coverage.The regularity of runoff time（T）with rain intensity is T_30mm/h<T_20mm/h<T_10mm/h,the decrease range is 28%～60%.The law of runoff time（T）changing with vegetation coverage is T bare slope<T_15%<T_35%<T_55%<T_75%.（2）The results of the flow change process under the condition of bare chestnut soil show that when the slope is 5°,10°,15°,20°,the slope surface under the rain intensity of10mm/h,20mm/h,30mm/h The runoff rate increases with increasing precipitation time.The variation of sediment yield under different slopes and different rain intensities shows that when the slope condition is 5°,the sand yield increases with the increase of rain intensity.When the slope of the steel trough increases to 10°,15°,and 20°,the yield There is a clear difference between the amount of sand and the slope of 5°.The trend of runoff rate under the conditions of 10mm/h,20mm/h,and 30mm/h rain is roughly the same,showing a single peak change that increases rapidly in the early period and decreases in the later period.（3）Regression analysis of cumulative runoff,cumulative sediment yield and rainfall time respectively,the results show that the relationship between cumulative runoff,cumulative sediment yield and rainfall time is a power function or a linear function relationship,and the fitting relationship is good.For the soil erosion of chestnut soil bare slopes,by calculating the contribution rate of rain intensity and slope in the rainfall process,a critical value of slope appears near 20°.（4）Under different slopes,with the extension of rainfall duration,the runoff rate of Elymus dahuricus slope shows a consistent trend under different vegetation coverage conditions:rapid rise in the initial stage of runoff generation-runoff Slowly increasing after stabilization-the trend of steady decline at the end of rainfall.The change of sand production rate under different vegetation coverage conditions is relatively complicated.When the slope condition is 5°,the sand production rate of Elymus spp.Slope decreases with the increase of vegetation coverage,at 10°,15°,20°slope The sediment yield rate of each vegetation coverage increased rapidly first and then steadily declined.（5）When the vegetation coverage is low,the average sediment reduction benefit is also low,which is a slow growth trend,which is the same as the average vegetation reduction effect.The optimal vegetation coverage to control soil erosion should be controlled at 35%～55%,The planting slope is not greater than 10°,and the critical vegetation coverage is between 75%and 80%.（6）Through the time series analysis and wavelet analysis of runoff and sediment production in Elymus grassland,according to the R/S analysis results of runoff and sand production,the Hurst index H of runoff is between 0.572 and 0.875,and the amount of runoff The index H is between 0.525 and 0.832,and the time series of runoff and sediment production show a long-range and positive correlation.Therefore,the time series of E.sativa runoff and sediment production is a continuous time series.The main theme of future runoff and sediment changes shows a clear consistency with the current trend.（7）The main cycle of runoff and sediment production on the Elymus dahuricus slope increases first and then decreases with the increase of vegetation coverage,with a shock period of 5～15min.The maximum peak value of the main cycle of runoff is 8～15min.There is a main cycle change at the 5～15min scale,and the wavelet real contour of some sediment yield exceeds the 15min scale change period.In the subsequent study,the length of the time series should be increased.