Influence of asymmetric tidal mixing on sediment dynamics in a partially mixed estuary

查看全文 作　　者：Zhongyong [1,2]Yang;Zhiming [1,3]Liang;Yufeng [3]Ren;Daobin [1,2]Ji;Hualong [4]Luan;Changwen [1]Li;Yujie [1]Cui;Andreas [5]Lorke 机构地区：[1]College of Hydraulic and Environmental Engineering,China Three Gorges University,Yichang 443002,China;[2]Hubei Field Observation and Scientific Research Stations for Water Ecosystem in Three Gorges Reservoir,China Three Gorges University,Yichang 443002,China;[3]Hubei Key Laboratory of Intelligent Yangtze and Hydroelectric Science,China Yangtze Power Co.,Ltd.,Yichang 443000,China;[4]River Research Department,Changjiang River Scientific Research Institute,Wuhan 430010,China;[5]Institute for Environmental Sciences,University of Koblenz-Landau,Landau 76829,Germany 出　　处：《Acta Oceanologica Sinica》索引2023年第42卷第9期,共15页 基　　金：The National Natural Science Foundation of China under contract Nos U2040220, 52079069, 52009066, 52379069,52009079, 42006156 and U2240220;the CRSRI Open Research Program under contract No. CKWV20221003/KY;the Open Research Program of Hubei Key Laboratory of Intelligent Yangtze and Hydroelectric Science under contract No. ZH2102000109;the Outstanding Young and Middle-aged Scientific and Technological Innovation Team in Universities of Hubei Province under contract No. T2021003;the Hubei Province Chutian Scholar Program (granted to Andreas Lorke)。 摘　　要：To investigate the influence of asymmetric tidal mixing(ATM) on sediment dynamics in tidal estuaries, we developed a vertically one-dimensional idealized analytical model, in which the M_2 tidal flow, residual flow and suspended sediment concentration(SSC) are described. Model solutions are obtained in terms of tidallyaveraged, and tidally-varying components(M_2 and M_4) of both hydrodynamics and sediment dynamics. The effect of ATM was considered with a time-varying eddy viscosity and time-varying eddy diffusivity of SSC. For the first time, an analytical solution for SSC variation driven by varying diffusivity could be derived. The model was applied to York River Estuary, where higher(or lower) eddy diffusivity was observed during flood(or ebb) in a previous study. The model results agreed well with the observation in both hydrodynamics and sediment dynamics. The vertical sediment distribution under the influence of ATM was analyzed in terms of the phase lag of the M_2 component of SSC relative to tidal flow. The phase lag increases significantly in estuaries with typical ATM(higher diffusivity during flood and lower diffusivity during ebb) for the case of seaward-directed net bottom shear stress(e.g., strong river discharge). In contrary, the phase lag is reduced by ATM, if the tidally-averaged bottom shear stress is landward(e.g., strong horizontal density gradient). The dynamics of sediment transport was analyzed as a function of ATM phase lag to identify the time of highest sediment diffusivity, as well as a function of the residual flow, to evaluate the relative importance of seaward and landward residual flows. In estuaries with relative strong fresh water discharge or weak tidal forcing(in case of flood season or neap tide), the near bottom SSC could be higher during ebb than during flood, since the bottom shear stress is higher during ebb due to seaward residual flow. However, landward net sediment transport can be expected in these estuaries in case of a typical ATM, because higher diffusivity causes higher SSC and landward transport during the flood period, while both SSC and seaward transport could be lower during ebb. On the contrary, seaward sediment transport can be expected in estuaries with landward tidally mean bottom shear stress in case of a reverse ATM,where sediment diffusivity is higher during the ebb. 关 键 词：idealized model asymmetric sediment diffusivity vertical sediment phase lag sediment transport