长江河口浮泥形成机理及变化过程

THE FLUID MUD TRANSPORTATION PROCESSES IN CHANGJIANG RIVER ESTUARY

1976年以来 ,在长江河口盐水楔和最大浑浊带活动的河道进行了 2 0余次现场观测。本文在现场观测资料基础上 ,确认长江河口浮泥由细颗粒泥沙组成 ,中值粒径在8— 1 1 5μm ,小于 2 μm的粘土占 2 8 1 8%— 36 39%。长江河口浮泥是悬沙在盐淡水混合环境中絮凝沉降于近底和风暴潮再悬浮泥沙形成的高浓度浑水层。在成因类型上分为憩流浮泥、盐水楔浮泥和风暴潮浮泥 ,第 1种在涨或落潮转流期低流时形成 ,规模大 ,厚度薄 ;第 2种在盐水楔发育时形成 ,规模较小 ,厚度较大 ;第 3种在大风后形成 ,规模大 ,范围广 ;若三者相遇 ,则浮泥厚度和范围最大。浮泥具有洪枯季、大小潮和风暴周期变化规律。长江河口河道宽浅 ,但河槽中动力作用较强 ,自然状态下浮泥层比较薄 ,在人工疏浚河槽中可以出现 1 0m多厚的浮泥层。浮泥层的变化与河口拦门沙的冲淤有良好的正相关。

In this observations since 1976, show that the fluid mud of the Changjiang River Estuary consists of fine sediment ranging from 8 to 11.5μm including 28.18 to 36.39 percent of clay finer than 2μm. The composition of the clay is illite, chlorite, kaolinite and montmorillonite. The fluid mud in the Changjiang River Estuary is a layer of sediment with high concentrations near the bed, resulting from flocculation due to salt and fresh water mixing. There are three kinds of fluid muds according to the dynamic conditions. The first one was formed at slack water during flood and ebb tides with a large scale but small thickness. The second was formed at area of grows saltwater wedge with small scale and thick depth. The third was formed following a storm with large scale and thick depth. The fluid mud is generally thin, but at a dredging channel it can be up to 1 m. In general, fluid mud will change with the factors of spring and neaptides, flood and dry seasons, and storms. At the same time, the changing of fluid mud is related to erosion and deposition of the mouth bar in the Changjiang River Estuary.