Rainfall-infiltration Process And Simulation In Typical Erosion Regions In The Loess Plateau

Large-scale?grain of green?ecological construction has profoundly changed the vegetation cover and the underlying surface conditions on the Loess Plateau,significantly changed the soil physical and chemical properties,and had a significant impact on the mechanism of runoff generation and convergence and the hydrological process of the surface.It is of great scientific significance to study the driving effects of the change of environmental conditions on the underlying surface,especially the driving effects of the change of soil physical characteristics on the surface hydrological process under vegetation restoration in the Loess Plateau,in order to reveal the runoff generation and convergence process in watershed.This paper based on long-term dynamic monitoring of soil moisture at the same location,multiple depths,stable and continuous to study infiltration process under different rainfall types in slope of typical erosion regions and uphill,downhill of slope-gully system,compared the difference among infiltration processes.Meanwhile,Used Horton model,Mezencev model,Kostiakov model and USDA-NRCS model to simulate infiltration processes under different rainfall types,and constructed Pedotransfer functions of soil physical properties and cumulative infiltration amount,steady infiltration rate,in order to comprehensive understanding Characteristics and rules of rainfall-infiltration process in typical erosion regions.The specific results and conclusions are as follows:?1?The response levels of soil moisture changes to rainfall events are significantly different on the Loess Plateau.The response levels of grassland in the slope of the Qiaogou watershed in the Loess Hilly and Gully Region are:rapid change layer?0?60 cm?,active layer?70?140 cm?,stable layer?150?200 cm?;the response levels of the grassland in the Dongzhuanggou watershed of the Loess Plateau Gully Area are:rapid change layer?0?40 cm?,active layer?50?110 cm?and stable layer?120?200 cm?.More than 90%of the infiltration amount is stored in the rapid change layer in the Qiaogou watershed of the Loess Hilly and Gully Region and the Dongzhuanggou watershed of the Loess Plateau Gully Area.In addition,among the different rainfall types,only the long-duration light intensity type and the short-duration large intensity type can drive the soil moisture response of the active layer,while the other rainfall types can only affect the rapid changing layer.?2?The 0?20 cm soil layer frequently alternates with wet and dry with rainfall in the slope-gully system of Qiaogou watershed in in the Loess Hilly and Gully Region.More than 80%of the infiltration amount is stored in the 0?60 cm soil layer.Moreover,soil moisture is sensitive to the response to rainfall events,the deepest level affected by the rainfall process is 140 cm.Therefore,0?140 cm can be used as the key hydrologic level of the slope-gully system in Qiaogou watershed.In addition,the change of soil moisture on both uphill and downhill showed an exponential decreasing trend in depth?Adj-R²>0.96?.?3?The rainfall is mainly based on short-duration moderate intensity type and short-duration light intensity type in the slope-gully system.The depth of the wetting front is deeper with the extreme rainfall and long-duration light intensity type,followed by the short-duration heavy intensity type,the shallowest by the short-duration light intensity type.The response time of soil moisture under different rainfall types showed different degrees of hysteresis,and there are significant differences.On the whole,the response of downhill is faster than uphill.Compare with the uphill,wetting front depth of downhill of each rainfall type is about 5?10 cm deeper than the uphill on average.?4?The 130?140 cm soil layer is critical to the soil hydrological process in the profile,with average water storage being 26.49%higher than that of the 150?200 cm soil layer.The soil water storage of that layer could reach as high as 225.99 mm,1.37 times its initial water storage capacity?95.37 mm?.Thereinto,the 0?100 cm soil layer is the one with available soil water closely related to its grass cover.In this area,soil infiltration depends on physical properties of the soil.Soil steady infiltration rate decreases with increasing soil bulk density,and the decrease declines in magnitude with rising bulk density,too.The attenuation is high in rate in the initial period and turns low.The infiltration rate varies exponentially with time.Cumulative infiltration?Adj-R²=0.99,P<0.01?shows a logarithmic relationship with wetting front movement process?Adj-R²=0.99,P<0.01?along the time series.During the severe rainstorm event,the mechanism of runoff generation is still dominated by infiltration excess runoff on hillslopes of the region.?5?Horton model,Mezencev model,Kostiakov model and USDA-NRCS model can effectively simulate the soil moisture infiltration process of different rainfall types?Adj-R²>0.88,NSE>0.90?.And the simulation results of Horton model and Mezencev model are slightly better than Kostiakov model and USDA-NRCS model.Based on artificial neural network,the Pedotransfer functions of 10 infiltration environmental elements and infiltration characteristic parameters was constructed,and the simulation accuracy from high to low was:stable infiltration rate?f_c?>1h cumulative infiltration?I₁?>3h cumulative Infiltration volume?I₃?>7h Cumulative infiltration volume?I₇?.This function can be used to predict the characteristic parameters of infiltration rapidly and efficiently in a specific region.