冲积扇发育过程中砾石颗粒对砂坝和沟流的控制作用——基于冲积扇水槽模拟实验

Dominations of gravel particles to sandbar and channel in process of alluvial fan development based on alluvial fan flume experiment

通过观察和记录冲积扇自旋回沉积模拟实验,研究在冲积扇的发育过程中,砾石颗粒对冲积扇在沉积过程中的控制机理。研究表明:在同一期洪水期的中期—后期,在冲积扇扇根片流带中,沟流发育的优势方向与砾石颗粒初期分布有着重要关系,同时砾石颗粒的分布还控制着沟流改道;在冲积扇的扇中发育过程中,由于砾石颗粒是在牵引流的搬运作用下运动,因此对沟道的控制作用便更多体现在对沟道形态的改造与砂坝的形成上。通过对比冲积扇剖面中出现的多期辫流水道叠置、砂坝和沟道的分布状态,就能够验证实验过程中冲积扇表面发生的现象。在实验过程中,冲积扇形成的规模是与碎屑流的动力、携带沉积物和沉积时间呈正比关系。在碎屑流的动力与携带的沉积物相对没有变化的稳定期内,扇根的砂坝与沟流、扇中的沟道都与砾石颗粒的作用密切相关。

In this paper, the controlling mechanism of gravel particles in the deposition of alluvial fan during the development of alluvial fan was studied by observing and recording the simulation experiment of simulating alluvial fan autogenetic cycle deposition.The results show that： in the middle-late period of one same flood period and in the alluvial fan laminar flow zone, advantage direction of channel development has an important relationship with gravel particles early distribution. In addition, the distribution of gravel particles controls the diversion of channel; in the process of mid-alluvial fan development, because the gravel particles were transported by the traction flow, the controlling effect on the channel is more embodied in the form transformation of channel and the form of the sand dam. Comparing the distributions of multi-stage braided channel, sand bar and channel distribution in alluvial fan profile, we can verify the phenomenon of alluvial fan surface during the experiment. It is found that the scale of alluvial fan is proportional to the magnitude of debris flow, the quantity of sediment and the time of deposition. In the stable period with relatively unchanged debris flow power and sediments, the cause of sand dam and channel in the middle and bottom fan is closely related to gravel particles.