Abstract: Based on the vertical profile data of current velocity and suspended sediment concentration (SSC) measured in the North Passage of the Changjiang Estuary from 26th October to 9th November in 2013, the vertical distribution patterns of SSC during the neap and spring tides are studied, and the impacts of current velocity and vertical salinity gradient on the SSC profiles are analyzed. The results show that there are remarkable difference in the hydrodynamic condition between the neap tide and spring tide, with weak current velocity, low SSC, large vertical salinity gradient and strong density stratification in the neap tide, and with contrary situation in the spring tide. Affected by large salinity gradient and weak current velocity, the vertical profiles of SSCin the neap tide mainly exhibit two types, i.e., ladder type and L type. Sediment diffusion in the neap tide was strongly suppressed by the intense salinity-induced stratification, with greater SSC appeared in the lower water column and smaller SSC appeared in the upper water column. Under the influence of strong current velocity and weak stratification, the SSC profiles in the spring tide mainly display linear distribution, and suspended sediment was well mixed in the latter half of the ebb phase, with constant concentration in the whole water column. The low correlations of lnC and ln[h -z/z] reveal that the observed SSC profiles deviate from the Rouse equation significantlyin the survey period. Due to the linear distribution in the water column, most of SSC profiles in the spring tide fit the Souls by equation, and can be accurately predicted by it.

Key words: suspended sediment concentration profile, salinity gradient, Rouse equation, Soulsby equation, Changjiang Estuary