Responses of riverbed morphology to the hydrological regime in anabranching reaches of the downstream Three Gorges Reservoir
摘要
To explore the evolvement characteristics and driving mechanism of a anabranching river channel under the influence of a water control project, this study classifies the branching river channel on the basis of the dynamic split ratio and measured hydrology and topography data for the lower reach of the Three Gorges Reservoir. The regulation rules of the primary branching river channel, secondary branching river channel, and low river island and their effects on the hydrological process are also investigated. The results reveal the following points. First, when the Three Gorges Reservoir is impounding, the low river island of the anabranching river channel shrinks. The branching river channel shows the specific rule of coexistence of "primary branching river channel goes up and secondary branching river channel goes down" and "primary branching river channel goes down and secondary branching river channel goes up." Second, on the basis of the dynamic split ratio of the classification of the branching river channel, these evolutionary differences are summarized as follows:the development rate of the dry-water-prone branching river channel is greater than that of the flood-prone branching river channel, and the flood-prone branching river channel has basically been characterized by siltation since 2008. Third, the decrease in flood and the continuous increase in the medium flow are the driving factors for the adjustment of channel. The erosion and sedimentation of the branching river channel show a stable pattern of the primary and secondary branching river channels, which is compatible with the hydrological process of decreasing the coefficient of runoff variation.