苜蓿草地侵蚀产沙过程及其水动力学机理试验研究

Experimental study on erosion process and hydrodynamics mechanism of alfalfa grassland

利用人工模拟降雨试验,定量研究了不同降雨强度(45mm/h、87mm/h、127mm/h)下20°陡坡苜蓿草地的产流产沙变化规律,分析了苜蓿草地侵蚀产沙的水动力学机理。试验结果表明,苜蓿草地累积径流量和累积产沙量与降雨时间呈良好的幂函数关系,随着降雨时间的增大而增大。在45mm/h和87mm/h降雨强度时,草地径流量和侵蚀产沙量呈高-低-稳定的变化趋势;在127mm/h降雨强度时,草地径流量和侵蚀产沙量呈高-低-高的变化趋势。苜蓿草地的水土保持作用通过改变土壤的入渗特性实现,草地坡面入渗率与径流量和产沙量呈明显负线性相关。从水动力学角度对苜蓿草地径流剪切力和单位水流功率与输沙率的关系进行了分析,得出试验条件下苜蓿草地的临界径流剪切力值为2.857N/m2,临界单位水流功率值为0.0114m/s,输沙率随径流剪切力和单位水流功率的增大而增大。

The runoff and erosion processes as well as its hydrodynamics mechanism of alfalfa grassland was studied under rainfall intensities of 45mm/h,87mm/h and 127mm/h with 20° slope gradient by rainfall simulation experiment.The results show that the cumulative runoff and the cumulative sediment yields of alfalfa grassland are varied in a power function with rainfall duration and increase with the duration.Under rainfall intensity of 45mm/h and 87mm/h,runoff and sediment of alfalfa grassland maintain a trend of high- low-constant.Under rainfall intensity of 127mm/h,runoff and sediment of alfalfa grassland keep a process of high-low-high.The function of soil and water conservation of alfalfa is realized by its changing soil infiltration rate.The infiltration rate of alfalfa grassland has a negative relation with runoff as well as sediment yield.The relationship between flow shear stress,unit stream power and sediment delivery rate are analyzed based on hydraulic theory.The sediment delivery rate increased with the increase of flow shear stress or unit stream power