The Study of Seawater Intrusion in Pearl River Estuary Area by a River Network-Estuary-Costal Ocean Coupled Numerical Simulation System

摘要

In this paper, a river network-estuary-coastal ocean coupled numerical simulation system is developed to study the increasing problem of seawater intrusion in the Pearl River delta and estuary area since it is greatly influenced by the coupled effects of river discharge and oceanic forcing conditions. A numerical model based on one-dimensional Saint-Venant equation is used to resolve the hydrodynamics of the whole river network which involves more than one hundred natural rivers and artificial channels to provide upward boundary conditions for the estuary-coastal ocean model. In order to accurately satisfy the irregular coastlines and numerous islands as well as meet the need of grid flexibility and higher resolution, the three-dimensional unstructured-grid Finite-Volume Coastal Ocean Model (FVCOM) is applied to simulate the interacting processes of tidal forcing and river discharge. By establishing a communicational mechanism, these two models are integrated into a simulation system. Then, the simulation system is well calibrated and validated using field measurement and remote sensing data. The results show that the simulation system can correctly capture the dynamic processes of interactions between river discharge and oceanic and meteorological forcings. Based on the validated simulation system, several process-oriented numerical experiments are conducted to study the dynamic process and find out the relationship between these effecting factors such as river discharge, tidal forcing, wind, bathymetric etc. Simulation results indicate that fresh water drifting westward during ebb tide and seawater directly intruding during flood tide is the controlling dynamic process leading seawater intrusion. These important effects on the seawater intrusion from the dynamic interactions have never been investigated and have largely been neglected in the previous investigations of seawater intrusion in the Pearl River Delta and Estuarine area for its complexity of dynamics, which is characterized as "hundreds of interlaced rivers and eight connected outlets to South China Sea".