Transport de polluants dans la lagune de Bizerte simule par un modèle de circulation de l’eau

Abstract

A numerical model simulating the dynamics of water and passive tracer advection was applied to the lagoon of Bizerte. The objective is the study of the behaviour of industrial or urban inputs into the lagoon. The model is three-dimensional and takes into account the exchanges of water, salt and heat between the waters of the lagoon and the surrounding environment. It includes a model of passive tracer advection. Numerical simulations were done considering inputs from one test then from the principal source sites around the lagoon. Simulations are forced by realistic winds and tides. The results show that tracer dispersion occurs during few hours. The tracer is transported by water circulation towards the eastern edge of the lagoon, then towards the Western edge in deeper layers. They reach the western edge after about a week. The tracer leaves the lagoon through the channel on a longer time, about 7 months. This long time results from that tide
oscillations do not allow the tracer to leave the lagoon without recycling. A large part of the tracer that leaves the
lagoon during the outflow returns back in during the inflow. The residence time of the tracer in the lagoon suggests that
an improvement of the lagoon is possible few months after the tracer input stops.