Flocculation properties of cohesive fine-grained sediment in the Three Gorges Reservoir under variable turbulent shear  

作　　者：LIU Jie SHEN Ying WANG Xin 

机构地区：[1]National Inland Waterway Regulation Engineering Research Center,Chongqing Jiaotong University,Chongqing 400074,China [2]Tianjin Research Institute for Water Transport Engineering,Tianjin 300000,China [3]National Key Laboratory of Hydraulic Engineering Simulation and Safety,Tianjin University,Tianjin 300072,China

出　　处：《Journal of Mountain Science》2022年第8期2286-2296,共11页山地科学学报（英文）

基　　金：funded by National Natural Science Foundation of China(No.51809130,No.5210090851);Opening Fund of State Key Laboratory of Water Simulation and Safety,Tianjin University(No.HESS-1720);Natural Science Foundation of Chongqing(No.cstc2019jcyjmsxmX0599);Special funded project for basic scientific research business expenses of central public welfare scientific research institutes(TKS 190104)。

摘　　要：Sediment flocculation is a key process for the deposition of fine-grained sediments in the Three Gorges Reservoir(TGR)of China.Sediment flocculation influences the evolution of the river regime,but also hampers the smooth navigation in the long term.However,the flocculation process and its controlling factors are poorly understood.We experimentally determined the flocculation properties of cohesive sediment of samples from the TGR(predominantly a mixture of clay and silt)over a range of turbulent shear rates and sediment concentrations.The experiments were conducted in an almost isotropic turbulence field,which was simulated by an array of horizontal oscillating grids in a water tank.Sediment flocculation was recorded by a camera and investigated by image analysis.Our new data indicate that flocculation is generally a response in equilibrium median floc size(d_(f,50))to the increase of the shear rate G.The peak value is attained at G=16.5 s^(-1),where d_(f,50) is 81.3μm(for the suspended sediment concentration(ssc)=0.4 g/L)and 107μm(for ssc=0.7 g/L),respectively.At low shear rates(G<16.5 s^(-1)),the equilibrium floc sizes d_(f,50) increase with rising shear rate G and isinversely related to the Kolmogorov micro length scale η.We attribute this variability to an insufficient deposition time of the sediment flocs in the water tank.Settling velocities,calculated from our experimental data of the floc sizes,are almost consistent with in-situ measured settling velocities,and are ten times larger than the terminal settling velocity of primary particles as calculated from Stokes'law.

关 键 词：Cohesive sediment flocculation Floc properties Settling velocity Turbulent shear rate Three Gorges Reservoir(TGR) 

分 类 号：TV145[水利工程—水力学及河流动力学]