河流网泥沙输移过程的瞬态特点

Transient characteristics of sediment transport in river networks

根据水流携沙力及其与河道冲淤态之间的反馈自调节机制,提出了一个枯水期河流网上的泥沙输移模型.利用该模型进行的模拟研究表明,流量改变所引起的水流携沙力同河道冲淤量的变化几乎是相反的.这实际预示着泥沙输移动力学的一种自组织特征:依据河道冲淤情况,水流携沙力所作出的自我调节将趋向于抑制河道大量冲刷或大量淤积.泥沙输移动力学过程的瞬态可以区分为对来水来沙条件改变作出快速响应的快瞬态和在稳定水沙条件下的趋向于稳态的缓慢过程,即慢瞬态.由于出流携沙力的变化相对于入流携沙力的调节滞后一个时步,从而对应流量增减时的冲淤量作相反变化.因此,流域降水的涨落对维持河道相对稳定的冲淤状态起重要作用.

Based on the sediment-carrying capacity （SCC） and the feedback mechanism between SCC and erosion-sedimentation, a dynamical model for sediment transport in river network in lower-water season was proposed. The simulated results by this model reveal that as stream flow varies the quantity of erosion-sedimentation （QES） and the sediment-carrying coefficient （representing the SCC of the stream） change respectively in nearly opposite ways. This indicates the self-organized dynamics charac- teristics： according to the QES, the self-adjustment of the SCC tends to prevent a mass of erosion or the occurence of sedimentation. The transience of the dynamical process can fall in two successive phases. The first one is a faster phase and indicates the immediate response of the SCC to the changes of runoff. The second one is a slower phase and shows the dynamic effect is leading to the steady state. The responses of QES to the increase and decrease of the branch runoff are in nearly opposite ways：the increase of the stream flow can induce the fall of QES, while the decrease of the stream flow can result in the rise of QES. Therefore, the fluctuation of the stream flow, caused by the stochastic rainfall, may play an important role in keeping the QES relatively steady.