Experimental Study On The Determining Critical Conditions For Entrainment Of Fine Sediment In The Three Gorges Reservoir Area

The construction of the Three Gorges reservoir plays an important role in the sustainable development of the social economy in China,and the sediment of the Three Gorges reservoir has a thinning trend,and the median particle size is about 0.01 mm.In the past,the fine particles were attributed to the purpuration and did not participate in the bed making,and once the silting was difficult to clean up,it brought great pressure to the function and maintenance of the normal function of the channel.Therefore,it is of great significance to find the critical condition of fine sediment scour and the combination function of the flow condition which can be used to judge the erosion and siltation in the Three Gorges Reservoir area,which is of great significance to the solution of fine sediment deposition in the Three Gorges Reservoir area and the theoretical study.A two-dimensional flow mathematical model combined with theoretical analysis is applied to study the scouring and silting changes in the Huanghua Island section of the Three Gorges Reservoir area.The main achievements include:(1)By analyzing the data of large section water and sediment in the Huanghua river section for 2000-2012 years and the situation of sediment erosion and siltation,we can see that the Three Gorges Reservoir area presents the characteristics of "water and less sand",and the sediment is gradually refined.The overall erosion and silting law of the reservoir area is scouring in the flood period and the period of deposition and falling in the dry period.The erosion area and the silting area show intermittent alternating distribution,and are still in the alternation of erosion and siltation.(2)According to the measured data of the continuous time series of the Huanghua City Waterway in 7-10 months of 2012,the topography method is used to draw the change map of the scouring and silting of the river section,and the corresponding position and thickness of the erosion and siltation are clearly defined,and the characteristic sections are selected.At the same time,a two-dimensional flow mathematical model is established.The flow conditions corresponding to scouring and silting thickness of each point are obtained by verifying the field test data.(3)The scouring and silting gradient of water flow conditions is established according to the thickness of each section,and the critical depth of each characteristic section is found,and the influence of water depth on the starting of fine particles is explored.(4)It is verified whether the existing sand carrying formula satisfies the actual erosion and siltation law of Huanghua City Waterway,and determines the formula parameters of the sand carrying capacity of Huanghua City Waterway,and obtains the criteria for determining the water and sediment conditions that can be applied to the Huanghua City Waterway and can represent the change of the erosion and siltation.