Finite element modeling of seawater intrusion into well-mixed estuaries

Estuaries are main water resources for various drinking, agricultural and industrial purposes in coastlines. With increasing water demand in these areas, the discharge of industrial and municipal wastewater into rivers and estuaries has increased. On the other hand, seawater intrusion into estuaries has decreased water quality which becomes more severe under the high tides. In order to reduce the undesirable impacts of seawater intrusion, recognition of the influential mechanisms and prediction of their impacts is essential. To achieve this, computer models are usually considered as the main tools. Throughout this paper a novel finite element model has been developed which is particularly applicable in the simulation of the flow hydrodynamics and salt transport in well-mixed estuaries. The presented model consists of two steps, that is, in the first step hydraulic parameters of estuary under tidal wave is computed and in the second step salt concentration at different points during a tide is determined. Continuity and momentum equations are governing equations in the first part while the advection-diffusion equation is used in the second part. Taylor-Galerkin Finite Element technique is applied to the formulation associated with the developed model. According to this approach, governing equations are descritized by Galerkin weighted residual method with respect to space while temporal discritization is implemented by finite difference method. To evaluate the accuracy of the model several analytical and numerical examples have been studied. A comparison between the obtained and expected results indicates the favorable performance of the model and its capability for simulation of seawater intrusion into this type of estuaries.