Sediment Activity In The Changjiang River Subaqueous Delta

Recently,a great count of large deltas have faced the problem of erosion and silting transition caused by the decrease of sediment into the sea.Due to the influence of human engineering,the sediments in the Changjiang River subaqueous delta has dropped sharply,which is bound to cause changes in the erosion and deposition of the delta.The Changjiang River subaqueous delta is important to geology,ecology,hydrology and socio-economic.Therefore,the study of erosion and deposition changes in the Changjiang River subaqueous delta has become an important topic.Sediment activity is a suitable point,which can characterize the distribution of erosion and siltation characteristics in a wide range of subaqueous deltas,and provide measurement data for the delta geomorphological evolution model.In this study,sediment sample was collected in the range of 121°E?124°E,29°N?32°N in the Changjiang River subaqueous delta,and the critical threshold shear stress(?_cr-M)was measured using the CSM instrument,the grain size and water content were measured simultaneously.Using FVCOM model to simulate the hydrodynamic conditions.Sediment activity refers to the percentage of time that sediments on the seafloor surface are active in a certain period of time.Combining the erodibility of the sediment and the hydrodynamic features where the sediment is located,the activity situation is analyzed,and the spatial activity distribution in the Changjiang River subaqueous delta are given.Discussing the relationship among the critical threshold shear stress,water content,sediment component content and particle size,explore the dominant factors affecting the erosion resistance of the sediments.The main research results are as follows:(1)The critical threshold shear stress measured by CSM has a larger variation range than that calculated by the empirical formulas,and is closer to the critical threshold shear stress measured by other researchers.The measured activity is more in line with the current surface deposition than the theoretical activity It can be seen that using CSM to study sediment activity is feasible.(2)Under the current tidal dynamic conditions,the sediment activity is relatively stable as a whole;the sediment activity is spatially regional,the muddy zone in the subaqueous delta front area is more active,and the sediment activity in other areas is less active.Weak;in the complete tide cycle,the sediment activity is stronger at the rising and falling moments than at other moments.(3)In the muddy area of the subaqueous delta,the erosion resistance of the sediment fluctuates in the vertical direction.Comparing?_cr-M,average particle size,water content and clay content,the results show that the primary influencing factor of sediment erosion resistance is the clay content...