Maryam Hakimzadeh - M.sc Student in Environmental Engineering, Department of Civil Engineering, Sharif University of Technology, Tehran, Iran
Habib Hakimzadeh - Professor in Coastal Engineering , Faculty of Civil Engineering, Sahand University of Technology , Tabriz

Dispersion of contaminated open sea or coastal waters in the estuaries is generally a serious problem for the people who living nearby these tidal basins. Then, daily life of the residents of these regions may gradually and/or abruptly be affected by dispersion of contaminated waters along the estuaries. In addition to human beings, pollution, which is probably the most important threat to quality of water in estuaries, can affect estuarine organisms, such as commercially important fish and shellfish. The most important pollutants that have greatest impacts on the health of estuaries include toxic substances such as chemicals and heavy metals, nutrient pollution and pathogens such as bacteria or viruses [1]. The volume of contamination in the estuary is controlled by two main factors, which are tides and volume of receiving body. Tides are driven by the gravity of Moon and Sun and results in a bulge in the water on the Earth’s surface [2]. For this study, numerical code was developed to simulate the tidal dispersion of a contamination in an estuary. The model was first verified for the mass conservation of the contamination in a channel [3]. Therefore, an experimental flume with 20 meters length has been selected as a model estuary. First, it is assumed that there is a steady state current in the flume and the magnitudes of diffusion coefficient and velocity are 0.01m2/s and 0.05m/s, respectively. In addition to considering constant values for the diffusion and velocity, these parameters have been assumed to be oscillating sinusoidal for the tidal flows. Time period of the sinusoidal oscillation is then assumed to be 60 seconds.computational programming. Furthermore, an explicit method rather than implicit one is selected in solving the discretized equation because of its simplicity and being computationally fast. Generally, for the explicit methods, the numerical stability criterion is an important issue that can be achieved through a stability analysis (e.g., von Neumann method). For the adopted explicit method, it is accurate enough to take xx equal to 0.05 and tt equal to 0.025. Accordingly, these time and distance steps are taken here. Further details of the numerical schemes and solution process were outlined in [3] and are not given herein for brevity. In order to verify the numerical model results, mass conservation at the inlet and outlet of the channel has been investigated. Then, the accuracy of mass conservation implies that the model works accurate enough. For instance, by having a concentration pattern equal to C=100mg/l for 30 seconds and calculating the concentration at the outlet, it is derived that mass is equal to 3.0000e+03 at the inlet of the channel and 2.9975e+03 at the outlet of channel, which can validate the accuracy of the model implemented here [3].