Study on the sediment deposition in Yuanyuansha reach of 12. 5m deepwater channel in Yangtze Estuary

Yuanyuansha( YYS) deepwater channel in Yangtze Estuary,with a length of 15. 44 km,is located between the diversion-mouth of the deepwater channel regulation project and Hengsha Passage. This artificial channel is constructed and maintained by dredging without regulation project. However,the dredging volume has increased obviously after dredging of the 12. 5m deepwater channel. By analyzing the series of hydrology,sediment and topography data observed in situ during recent years,the mechanism for sediment deposition in12. 5m YYS reach deepwater channel are studied based on hydrodynamic conditions,sediment deposition,river regime conditions and local terrain changes. The elevation difference of the main channel and floodplains has increased after dredging to 12. 5m in the YYS channel from the natural depth which is less than 10m; the velocities and sediment transport dynamics of the ebb flows has decreased after construction of the project of reduce deposition in North Passage; crossing angle between the navigation channel and the direction of bottom current has existed because YYS channel is located in the distributary and confluence reach of ebb and flood tide. Those reasons are the main causes of deposition increase. Finally,methods are proposed to reduce deposition from resisting sediment and strengthening flow.