2D Surface Water Quality Model: A Forecasting Tool for Accidental Pollution in Urban River—Application to the Var River, France

In many countries, urban river is a key subsystem of urban environment and offers services for the surrounding inhabitants: drinking water, agricultural, and industrial water. Actually, the river and the urban development depend on each other. This is why the growth of population and the economic development can cause stress not only on quantity of water but also on its quality. In this context, surface water quality models can be useful tools to simulate and forecast concentrations and risks of chemical pollutants in a given water body. The Var river, located in the French Riviera in the south of France, is an urban river encompassed by various land uses: industries, agricultural fields, and urban areas. Furthermore, the alluvial aquifer, which is connected with this river provides drinking water for nearby cities by using six pumping stations. Hence, this water resource is vulnerable to accidental pollution. Indeed, the wastewater from industries could be a source of contamination and a tanker accident on one of the 6 bridges across the Var river could be occurring. This configuration appears to become a big issue for the municipality. In order to predict the transfer of chemical pollutants, the 2D hydraulic model is an appropriate tool. Actually, numerical models are able to represent hydrodynamics of the river and the pollutant effects on the surface water. This paper compares different ways to model the transfer of pollutant in the Var river. Three hydraulic modeling tools were used to simulate accidental pollutions: Mike 21, Mike 21 FM, and Telemac2D. They are presented in a first section by introducing the equations used, the required parameters and the limitations. After that, the 2D free surface flow model was built (with the three software tools) and calibrated. Then, two scenarios of accidental pollutions were simulated. For the different models the propagation time, the concentration of pollution, and the polluted surface were compared. Therefore, the objective of this study is to point out the differences among the three water quality models built by Mike 21, Mike 21 FM and Telemac2D. The calibrated parameters seem to be different from one modeling tool to another. According to the results, the peak concentration computed by Telemac2D is much lower than the one calculated from Mike 21 or Mike 21 FM. In addition, the decaying aspect appears different in the Telemac2D model. These facts can be explained by the different equations used to model the pollutant transport.