Experimental Study On Deposition In Static Water Of Fine Sediment Of Yangtze River Estuary

This article presents the experimental research on sediment deposition in staticwater of fine sediments in the northern channel of Yangtze River estuary. There aretwo parts in this research: the first one is about the flocculation of suspendedsediments, this experiment studied the relationship between settling velocity ofsuspension sediments and several parameters including temperature, salinity andsediment concentration using new settlement barrels and advanced equipments, inwhich fine sediments and original water of Yangtze River estuary were adopted; thesecond part is about fluid mud deposition, focusing on the settling processes of mudfluid in Yangtze River estuary and high concentration sediments with different particlesize to search several physical properties about fine sediments deposition aftersedimentation. Through above analysis, it is easy to get the following conclusions.Suspended sediments settling:1. The settling velocity of sediments is between0.033mm/s and0.36mm/s in dryseason, compared with that in flood season which ranges from0.016mm/s to0.39mm/s.2. The optimal flocculation sediment concentration and the best flocculationsalinity about the fine sediments in the north passage of Yangtze River estuary are7kg/m³and7‰in dry season. However, in flood season, those are4.5kg/m3and about10‰¹2‰respectively. Sediments settling velocity increases with the increase ofsediment concentration （and salinity）. After researching the optimal flocculationsediment concentration （and the best flocculation salinity）, this velocity will decreasebefore tending towards stability. It will decrease dramatically if sedimentconcentration, the primary factor for deposition, is over10kg/m³.3. Experimental results illustrate that settling velocity will increase with water temperature increasing. This velocity in flood season is about1.2¹.5times that indry season when sediment concentration is in the range of2kg/m3⁷kg/m3. Outsidethe range of sediment concentration, water temperature has little effect on thevelocity.4. The empirical formula about sediment deposition in static water is deduced.Fluid mud settling:According to deposition experiments of high concentration sediments, fluid mudsettlement in the northern channel of Yangtze River estuary is not into consolidationand its velocity is0.31×10^-3mm/s. Settling velocities of fluid mud with sameconcentration but different particle sizes which are16μm and58μm are0.58×10^-3mm/s and0.48×10^-2mm/s. Sediment grading plays an extremely significant role onthe consolidation process: sand containing much mud settles quite slowly and theparticle size distribution remains nearly unchanged; on the contrary, sand with largeparticles settles quite fast and the particle size distribution changes obviously.Researches in this paper are reference when studying the essential characteristicsof cohesive fine sediment and the immediate cause of back silting in the YangtzeRiver estuary waterway.