Simplified Numerical Simulation Of Saltwater Intrusion In Estuary And Its Empirical Model

Saltwater intrusion threatens security of fresh water resources utilization and ecological environment.It is possible to relieve saltwater intrusion by regulating runoff process in dry season with using large-scale reservoirs in the watershed.The key problem is how to estimate salinity characteristics rapidly under different combinations of runoff and tidal dynamics.The objective of this research is to put forward a simple and high-efficient empirical method for clorinity/salinity prediction,which can also quickly estimate the critical runoff for saltwater intrusion at the Datong Hydrological Station.And the critical runoff would contribute to restraining saltwater intrusion in the Yangtze Estuary through the Three Gorges Reservoir's operation.The main study in this paper includes:Estuary was generalized as a one-dimensional semi infinite and uniform open channel,with adopting perturbation analysis,characteristics theory,and tidal harmonic theory to analyze hydrodynamic conditions and overall features of saltwater intrusion.The change rule of clorinity/salinity in two generalized estuary types,simple-straight and bifurcated estuaries,was simulated by numerical experiment under different combinations of runoff and tide.Based on the generalized analysis above,this paper came up with a new empirical model for clorinity/salinity prediction at particular locations in estuary.The main results are as follows:(1)When water depth and fluctuation cycle approximate to constant value,intensity of saltwater intrusion is negatively correlated with velocity or flow,but positively with power function of tidal range.A linear correlation was found between the change of salinity/clorinity and cosine function of tidal range cycle.(2)The research proved that averaged-daily tidal range was approximate to semi-monthly periodic function,and put forward an estimation model for averaged-daily tidal range by using lunar calendar.The correlation between predicted value and measured value reached 0.9.(3)The salinity/clorinity amplitude of variation,and the phase of salinity/clorinity peak in one day existed some differences in two areas,area of saltwater intrusion directly and area of flowing-backward saltwater.But relationship of averaged-daily salinity/clorinity which had same saltwater source was good.(4)An empirical model for estimating averaged-daily salinity/clorinity quickly in the area where saltwater flows into the South Branch from the North Branch in Yangtze Estuary,was proposed.And the correlation between prediction values and field data reached above 0.8(5)The runoff for restraining saltwater intrusion at Datong Hydrological Station was between 41000?12000m~3/s,and the value can be 11500 m~3/s in practice.