Hydrodynamic characteristics of the Qinjiang estuary in Guangxi during the dry season and its response to cold front
As the key region of land-sea interaction,estuaries are the main destination for river sediment and pollutants.The Qinjiang River,as the second largest river in Guangxi,holds significant importance in the development and utilization of resources,as well as the protection and restoration of the ecological environment in the Maowei Sea.To gain deeper insights into the sedimentary dynamics processes in the Qinjiang estuary area,the hydrodynamic process and water environment parameters near bed were continuously measured in the Qinjiang estuary from October 27 to December 8,2021.The measured results show that the tidal type of the estuary is regular diurnal,and shallow water over-tides are significant.The mean tidal range is 3.07 m,with the ebb tide dominance during the observation.The tidal currents are mainly characterized by diurnal current,and dominated by reciprocating flow with a mean value of 0.12 m/s.The residual current is mainly in the southwest direction.The diurnal characteristics of tide and tidal current in the estuary are more obvious than those of the outer bay and the central part of the Maowei Sea.During the dry season,the surface sediments in the estuary exhibited alternating erosion-deposition patterns with tidal action.In the vertical direction,erosion fluxes were found to be greater than settling fluxes,while in the horizontal direction,there was a net seaward transport of suspended sands.The rainfall brought by the cold front led to decrease in the salinity of near bed water in the estuary,in addition,it causes increase in turbidity,suspended sediment concentration,and sediment transport.At the meanwhile,the enhanced north wind causes the water reduction effect in the estuary and slightly increases the tidal range during the cold front southward,which further increases the estuarine hydrodynamic,enhancing the activity of surface sediment,and then enhances the intensity and frequency of bottom sediment resuspension of the estuary.
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