Numerical Simulation Of Saline Intrusion In Qinjiang River Estuary

Qinzhou Bay Maowei Sea is located in the north of the Beibu Gulf,connected with the Qin River,and is the outlet of the western Land Sea new channel(Pinglu)canal.Maowei Sea is rich in fishery resources,developed in aquaculture,and surrounded by a large number of mangroves,with high ecological value.It is significantly affected by the change of salinity distribution.However,current studies on Qinzhou Bay mainly focus on the analysis of tidal current and water quality,and few studies on the temporal and spatial changes of salinity in Qinzhou Bay.Due to the lack of long-term continuous field observation data of salinity,a three-dimensional brine intrusion model was constructed by numerical simulation method to analyze the seasonal salinity variation.Through dimensional analysis,the influence mechanism of runoff and tidal range on the upstream distance of brine is clarified.The research results have important guiding significance for the construction of Pinglu Canal salt-proof lock and provide reference for the environmental impact assessment caused by the project.The main work and contents are as follows:(1)Based on the field observation data of salinity in flood and low water periods,the vertical mixing characteristics of saline in the upstream process of Qinjiang River estuary in flood and low water periods were analyzed by using the layered type formula of salinity.The results show that the tidal power is enhanced,the vertical stratification coefficient increases,and the salinity changes from full mixing to partial mixing along the vertical direction.During ebb tide,the vertical salinity is mainly completely mixed because the direction of runoff is consistent with the direction of tidal current.(2)Based on the field measured data,the three-dimensional saltwater intrusion model from Maowei Sea to Qin River in Qinzhou Bay was built with MIKE31,and the verification of tide level,velocity and salinity was completed.The correlation analysis between simulated and measured salinity values shows that the 3D brine intrusion model established in this paper can reflect the upstream process of brine.(3)A typical year was selected to carry out a numerical simulation study on the upstream process of brine during dry,middle and flood periods,and the spatial-temporal distribution of salinity was analyzed.In the plane distribution,the upstream distance of brine changes periodically with the ebb and flow tide during dry,middle and flood periods,but the maximum upstream distance of brine decreases gradually because the average daily runoff increases gradually during dry,middle and flood periods.In the vertical distribution,the vertical stratification coefficient of salinity increases gradually in the process of high tide and decreases gradually in the process of low tide.The variation characteristics of tidal capacity in flood,middle and low water periods were analyzed,and the empirical formula of tidal capacity in Maowei Hai was established.(4)The analytical model is used to study the influence of runoff and tidal range on the upstream distance of Qin River estuary brine.The results show that there is a power function relationship between runoff,tidal range and upstream distance of brine,and the upstream distance of brine is negatively correlated with runoff,but positively correlated with tidal range.The formula of upstream distance of brine was obtained by multivariate nonlinear regression,and the reliability of the formula was verified by correlation analysis.