The Contrastive Study About The Transport Mechanism And The Characteristics Of Water And Suspended Sediment Of Flood And Ebb Channels In The Changjiang Estuary

Study of the hydrological character , suspended sediment character, and the transport mechanism of flood and ebb channels is not only an important content in estuarine dynamic, but also is a practical problem nearly related to the selection of harbor sites, regulation of sea-entering waterway, and even the comprehensive exploitation of estuaries. Taking the Xinqiao Channel and the South Branch as study objects, systematically features of tide current and suspended sediment, the transport mechanism are studied by applying hydrological statistics and dynamic analysis. The Laser In Situ Scattering and Transmissometry-100(LISST-100) is used to study the character of grain size of suspended sediment flocs in the Xinqiao Channel. According to this data, further research of character of grain size of flood and ebb channels can be done.Based on the analysis of the data collected during neap tide of dry season in April, 2005, combining with data collection during the spring and neap tides in the flood season, the spatial-temporal character of water and suspended sediment in flood and ebb channels. The results show the complex hydrological features in the flood channel. There are not only the variation between the flood and dry seasons but also the variation between the neap and spring tides. As the change of water dynamic, suspended sediment character of flood and ebb channels is obviously different.The maximum velocity and average velocity of flood current are greater than those of ebb current in flood channel, and also greater than those of ebb current in the same cross section. The flood channel only presents flood-dominated feature during the spring tide of the dry season.,the flood current discharge per unit width is more than the ebb current discharge per unit width in the flood channel. In flood season and neap tide of dry season, the flood current discharge per unit width is more than the e bb current discharge per unit wi dth in the flood channel. The direction of residual currents in the flood channel points to land in spring tide of flood season , to sea in neap tide of flood season and dry season.The maximum and average sediment concentration of flood channel are greater than those of ebb channel in flood and dry seasons. During ebb times, The maximum and average sediment concentration of ebb current in flood channel are greater than those in ebb channel in neap tide of dry season, in neap and spring tides of flood season it is opposite. In vertical direction, suspended sediment of ebb channel is still in underside layer, while it changes in flood channel during flood and dry season, suspended sediment of flood channel is in underside layer during spring tide of flood season, partly in upside layer in neap tide of flood season, mostly in upside layer in neap tide of ebb season. In upriver of the Xinqiao Channel, the dominant sediment is always smaller than 50% ,and flood dominant sediment of dry season is greater than that of flood season.The contribution of advection to sediment transport in ebb channel is greater than that in flood channel. The R of flood and ebb channels in flood season is larger than that in dry season. In spring tide of flood season, the direction of advection to sediment transport points to land in flood channel, while in spring tide of flood season and neap tide of dry season to sea.In downriver area of the Xinqiao Channel, from surface layer to bottom layer, the average and middle mean grain size becomes larger. The average and middle mean grain size in surface layer is smaller than that in bottom layer. The distribution of volume concentration of fine suspended sediment flocs are consistent with suspended sediment concentration in the vertical direction. Mean grain size of suspended sediment is dominant to clayey silt. The average volume concentration is 69.5%.