Experimental Research On Characteristics Of Fine Sediment In Nanhui Marginal Bank Of Yangtze River Estuary

Nanhui marginal bank is located in a distinctive terrain which is in the interaction of Yangtze River Estuary, Hangzhou Bay and out sea. Plenty of fine sediments from the up reach of Yangtze River flocculate when they meet strong electrolyte seawater at the junction of salt and fresh water of Nanhui marginal bank. Flocs speed up sedimentation, thus forms silting.The flocculation has close relationship with the basic characteristics of fine sediments. By using sediment deposition experiments in static water, this article analysis the basic characteristics of sediment at Nanhui marginal bank. The sediments are clayey silts. Medium grain size is 0.0416mm.The optimal flocculation salinity is around 15‰.The critical particle size of flocculation is around 0.0325mm.When the sediment concentration is 1.0kg/m~3, the capacity of flocculation achieves maximum. The higher the organic matter content is in sediments, the weaker the flocculation is. High water temperature intensifies flocculation and decreases the optimal flocculation salinity. The composition and content of clay mineral has great influence on flocculation.In the flowing water experiments in a circulating flume, the incipient velocity of the sediments at Nanhui marginal bank is 8-10cm/s and the non-silting velocity is 50-60cm/s.The influence of salinity and sediment concentration on the properties of sedimentation becomes greater when current velocity reduces. Sedimentation in flow water is in conformity to second order dynamics mode.The research on the basic characteristic of sediments at Nanhui marginal bank and the analysis on the hydrological conditions provide theoretical basis for reclamation projects.