长江河口下段分汊口的组构模式

Combination mode of branching portions in downstream of the Changjiang Estuary

长江口自徐六泾以下呈三级分汉、四汉入海格局，比较稳定的径流过程和输沙过程、比较丰富的流域泥沙补给、中等强度的潮汐环境是长江口分汉水道形成、发育的主要水沙条件．分汉口态势变化对下游分汉水道的演变起着关键的作用．追溯了长江口南、北支、南、北港及南、北槽三个分汉口的变化过程，提挈出这三个分汊口在形态结构上的共同特征，概化出分汊口的“板块一沟槽”组构模式，阐述了诸“板块”的组合和分离、“沟槽”的生成和消失对分汊口态势变化的影响．

The Changjiang Estuary has a morphologic pattern that is characterized by three-order bifurcation and four distributary channels discharging into the sea. More stable hydrological process, richer riverine sediment supply and mesotidal environment are beneficial to formation and development of branching type in the Changjiang Estuary. Situation and change of the branching portion play a key role in evolution of downstream tributary channels. A review on change process of the branching portion in the south--north branches, the south-north channels and the south-north passages is made. There are some common features in these portions. A combination mode of the branching portions that consists of 2-3 'plates' representing sand bodies and a series of 'trenches' representing passways or ditches is summarized. Merging or separation of the plates and scouriDg or filling-up of the trenches have a significant influence on situation of bifurcation and evolution Of tributary channels.