侵蚀基准面下降对水系发育与产沙影响的实验研究

在3556mm/hr·cm²定雨强的人工降雨条件下,组成物质中径为0.021mm,侵蚀基准面两次下降的流域发育对比实验表明,水系发育以增加河道(沟道)数目及流域出口段河道下切、溯源侵蚀延伸长度两种方式进行最小消能,产沙过程具有明显的复杂响应特征。流域侵蚀产沙与水系分形维数间存在显著的非线性特征,分数维值与产沙量间呈不对称双曲线的关系。侵蚀基面下降导致流域势能的相对增大,在消能过程中,第一次基面下降带来的影响比第二次基面下降带来的影响要显著,在空间上,其影响随远离流域出口而减弱

Influence of base level lowering on sediment yield and drainage network development:an experimental analysis

In this paper an experimental study on influence of base level lowering on non linear relationship between sediment yield and drainage network development has been completed in the Lab of Fluvial Geomorphology in the Institute of Geographic Sciences and Natural Resources Research,Chinese Academy of Sciences The area of flume drainage system is 81.2 m² ,the longitudinal gradient and cross section slope are from 0.0348 to 0.0775 and from 0.0115 to 0.038, respectively Three experiments are a background drainage development (Run I) and drainage developments influenced by the first (Run II) and second (Run III) base level lowering, respectively They are covered by the same model materials with a medium diameter of 0.021 mm At the beginning of each experiment the (shaped small network is dug in the flume,an artificial rainfall equipment is a sprinkler system composed of 7 downward nozzles, distributed by hexagon type and a given rainfall intensity is 35.56 mm/hr cm² . Three experiments are designed by process response principle Running time span for each experiment is 720 minutes The background experiment shows that the sediment yield process is characterized by delaying with a vibration During network development the energy of a drainage system is dissipated by two ways, of which one is to increase the numbers of channels (rill and gully),and the other one is to enlarge the channel length As the first base level lowering occurs the channel at the model drainage outlet is down cut and enlarged and the sediment yield process appears a complex response with double peaks at first and then decreases When the second base level lowering occurs the phenomena was duplicated, but the influence of the second base level lowering on intensity and amplitude is smaller than that of the first base level lowering The fractal dimension of a drainage network is exactly an index of energy dissipation of a drainage morphological system Change of this index with time is an unsymmetrical concave curve Comparative result of the three experiments explains that the influence of base level lowering is reducing with the elapse of time and far away from the outlet of model drainage basin