宜昌至杨家脑河段河床形态冲刷调整特点分析

针对三峡工程蓄水后宜昌至杨家脑河段河床形态的冲刷调整特点,基于实测资料,对该河段的冲刷分布及河床形态特点进行了分析,并讨论了二者之间的关系,最后采用分形维数对河段深泓纵剖面形态调整进行了量化分析。结果表明,其河床形态冲刷调整的最大特点是纵向的冲刷下切具有明显的不均衡性,即存在若干深泓较高、具有一定抗冲性的纵向节点,且多以分汊河段为主,通过对各分汊河段的比较发现,年内交替型分汊河段的深泓节点比非交替型分汊河段更为稳定,由于纵向节点的控制以及河段其他部位深泓的下切,使得该河段深泓纵剖面分形维数逐年加大,纵向形态变得更为复杂,使枯水糙率有所增加,对宜昌枯水位的下降起到了抑制作用。

Features of riverbed erosion adjustment process in Yichang-Yangjianao reach

To study the effects of Three Gorges Project(TGP) on its downstream Yichang-Yangjianao reach of the Yangtze River,this paper analyzes the adjustment process of riverbed erosion caused by TGP’s operation based on field observation data,and discusses the relationship between erosion distribution over this reach and its channel morphology.Fractal dimension method is used for quantitative analysis on the adjustment of thalweg profile of the reach.Results reveal that the most remarkable feature of erosion is significant disproportion in bed downcutting,so that many nodes of strong anti-scour capability and higher thalweg elevation are formed along the channel.Most of these stable nodes are located in the braided reaches.A comparison of various braided reaches indicates that the nodes in the braided reach of alternating-type are more stable than the ones of other types.Under the control of stable nodes and the scour of thalweg in other reaches,the fractal dimension of thalweg longitudinal profile increases constantly and the longitudinal morphology becomes complex,causing an increase in low-water roughness.This phenomena restrains the decline of water stage at Yichang in low-water season.