The Impact Of Soil Antecedent Water Content On Runoff And Infiltration During Rainfall Simulation In A Coarse Texture Soil

It is of great significance for ecological restoration and reconstruction in the Loess Plateau watershed that the spatial-temporal characteristics of soil moisture dynamics and the affected factors, and many reports showed the soil desiccation phenomenon in the region. The dynamics of soil water content will have a great influence on the process of rainfall infiltration and runoff. On the one hand, to understand the process of the variation of the soil water content in the Loess Plateau, we chose the Liudaogou basin in the water-wind erosion crisscross region of the Loess Plateau as studying area, and analyzed the characteristic of soil water storage and the profile soil moisture under alfalfa land(12,15,17,21,26,41 a), wild grass land(15,32,41 a), abandoned farmland(12,21,41 a), kyorin land(14 a). On the other hand, in this paper, using the method of simulated rainfall field, we selected 20 mm ? h-1, 40 mm ? h-1, 60 mm ? h-1 rainfall intensities with frequent rainfall events(from first to fifth) in alfalfa land which was typical example of soil desiccation phenomenon. On basis of these rainfall events, we analyzed quantitatively the effect of rainfall intensities and rainfall frequencies on runoff and sediment concentration and infiltration characteristics under different experimental conditions. And discussed the relationship between soil water content(0-10 cm, 0-20 cm, 0-30cm) and runoff coefficient through statistical analysis, and then studied the impact of vegetation cover on runoff and sediment process. The results showed:1)Among the four modes of vegetation restoration, the order of both the average of soil water content and the soil water storage was abandoned farmland > wild grass land > kyorin land > alfalfa land. The soil water storage of 0~200 cm of the alfalfa land and the abandoned farmland increased with time rapidly firstly and then decreased gradually, and remained stably finally. Whereas the average 0~200 cm water storage of the wild grassland decreased with time; During the process of vegetation restoration in the water-wind erosion crisscross region of the Loess Plateau, the vegetation restoration modes affected the soil water content changes mainly, it was not obvious that the dynamic change of soil water moisture with time.2) Compared with 20 mm ? h-1 rainfall intensity, it began runoff earlier, larger runoff coefficient and the more total volume with the same rainfall frequencies at 40 mm ? h-1and 60 mm ? h-1 rainfall intensity. Using the same rainfall intensity, it showed a positive correlation between rainfall frequencies and runoff-sedimentation process. Through statistical analysis, we found that rainfall frequency had a significant influence on the starting time of runoff, runoff rate, runoff coefficients, sediment loss(P <0.01), it was not significant for sediment concentration(P <0.01). Rainfall intensity played an important role on runoff, sediment concentration and the runoff starting time(P = 0.00), not for runoff coefficient and sediments loss amounts(P <0.05).3) Using linear and polynomial fitting relationship between soil water content(0-10, 0-20, 0-30cm) and runoff coefficient(runoff / rainfall), we found that the fitting coefficients were higher between soil moisture of 0-20 cm depth and runoff coefficients than 0-10 cm depth both linear and polynomial regression.4) After studying the change of average infiltration rate and cumulative infiltration, Process with rainfall duration under different rainfall intensities through rainfall frequencies, it showed that soil infiltration rate is higher for the first rainfall event for three kinds of rainfall intensity, and then decreases, while the cumulative infiltration increases linearly.5) It showed a significant linear relationship between runoff depth and sediment loss amounts(P <0.01), the linear is y = 77.3x-70.3 with the fitting coefficient of 0.80. Overall, it showed the feature of more water loss and more sand loss.6) It presented that the sediment monotonically decreased with the increasing of vegetation cover from 0.20 to 0.79. Compared with the bare land, the runoff rate was less and infiltration rate was significantly higher for root system retained.