COMPARISON OF NUMERICAL TECHNIQUES SOLVING LONGITUDINAL DISPERSION PROBLEMS IN THE RIVER MONDEGO

Judicious selection of mathematical models for application in a specific river basin management can mitigate prediction uncertainty. Therefore, intervention times will be established with better reliability and alarm systems could efficiently protect the aquatic ecosystems and the public health. The main purpose of this paper is to evaluate the performance of different numerical techniques when applied to river water systems dispersion modelling. A case study was developed to assess the environmental impact of Urgeiriça mining waters in a Mondego river reach, between Caldas da Felgueira and Aguieira reservoir. A monitoring program was carried out using tracer injection (rhodamine WT) to determine the in situ dispersion river water behaviour. The present work describes the methodology used in the tracer experiments, presents the concentration-time curves obtained and the performance of finite difference method (FDM) and finite element method (FEM) in a simplified river system, and compares the results of different numerical techniques application for longitudinal dispersion coefficient estimation in this river reach. The application of DUFLOW package, that includes hydrodynamics and water quality models, showed the best agreement with experimental data, allowing a reasonable support for impact assessment of different discharges scenarios in the river water quality. KEYWORDS Environmental impact assessment, longitudinal dispersion, mathematical models, numerical methods, rhodamine WT, river Mondego, tracer experiments, water quality, water resources management