水流驱动下不同灌草格局对泥沙分选特征的影响

Effects of Different Shrub-Grass Patterns on Size Selectivity of Sediment Under Flow-driven

泥沙的颗粒大小分布体现了土壤侵蚀的基本信息,分析泥沙分选特征有助于解释坡面土壤的侵蚀过程及其作用机理。通过野外冲刷试验(流量为15,20,30L/min),以砒砂岩区灌丛位于坡上(SU)、坡中(SM)、坡下(SL)的灌草地和无灌丛草地(GL)为研究对象,裸地(BL)为对照,探讨水流驱动条件不同灌草格局泥沙分选特征及其作用机理。结果表明:(1)植被可以通过影响水动力参数来影响泥沙颗粒的分布,不同格局泥沙颗粒随冲刷时间及流量的增大呈粗化趋势,粉、砂粒是该区侵蚀泥沙的主要颗粒。(2)水流剪切力、水流功率和单位水流功率均与泥沙DV呈负相关关系,与D0、D1呈正相关关系;3种冲刷流量下,泥沙DV均值分别为2.422,2.381和2.348,不同灌草格局下DV表现为GL<SU<SM<SL,而D0、D1趋势与DV相反。(3)泥沙分形维数与水动力参数的关系可用指数函数和对数函数来描述,回归分析表明,水流功率是描述泥沙分布特征的最佳水动力参数,运用水流功率和单位水流功率可以较好的模拟砒砂岩区坡面泥沙分选特征。研究结果为今后进一步完善砒砂岩区坡面土壤侵蚀模型提供理论依据。

The particle size distribution of sediment reflects the basic information of soil erosion.Researching the characteristics of sediment separation will improve better understanding to the process and mechanism of soil erosion on the slope.Field scouring experiments were conducted in four different shrub-grass patterns at three different flow rates(15 L/min,20 L/min and 30 L/min)on the 8°slope in the Pisha sandstone area.This study taken the shrub grassland on the upper slope(SU),shrub grassland on the middle slope(SM),shrub grassland on the lower slope(SL)and grassland without shrub(GL)as the research objects,and bare land was taken as contrast in the Pisha sandstone area.The results showed that:(1)Vegetation could affect the distribution of sediment particles by affecting the hydrodynamic parameters.The sediment particles in different vegetation patterns tended to coarsen with the increasing of scouring time and flow.Silt and sand were the main particles of erosion sediment in this area.(2)The flow shear force,flow power and unit flow power all were negatively correlated with sediment DV,and positively correlated with D0 and D1.The mean DV of sediment was 2.422,2.381 and 2.348 under three flow rates,respectively.The DV under different vegetation patterns followed the order of GL<SU<SM<SL,while the trend of D0 and D1wasopposite to DV.(3)The relationship between fractal dimension of sediment and hydrodynamic parameters could be described by exponential function and logarithmic function.Regression analysis showed that flow power was the best hydrodynamic parameter for describing sediment distribution characteristics,and using flow power and unit flow power could better simulate the sediment separation characteristics on slope of Pisha sandstone area.This study provided a theoretical basis for further improvement of soil erosion model on slope in Pisha sandstone area in the future.