Qual2e model for the Corumbataí River

The Corumbataí River, located in São Paulo State, Brazil, is a major water supplier to a highly populated region and has an aptitude for multiple uses. Since the beginning of year 2000, all the water consumed by the city of Piracicaba (about 320,000 inhabitants) is supplied by the Corumbataí. On the other hand, the district of Rio Claro has more than fifty industries situated around the Corumbataí and its tributaries. The majority of these industries pollute the environment. To aggravate the situation, a large amount of domestic sewage is also discharged near Rio Claro. Mathematical models are important tools for predicting the water quality of a river basin. The free-use Qual2e model is suitable for one-dimensional well-mixed rivers with constant flow. In this work, the Qual2e is applied for predicting the water quality of the Corumbataí River. To apply the model it was necessary to divide the river in reaches with similar hydraulic properties and subdivide these reaches in computational elements with the same extension. Flow rates, depths, temperatures, loads, location of pollution sources, dissolved oxygen concentrations and biochemical oxygen demands were measured in the field and formed a geo-referenced database for the water quality of the river. This database was used to supply inputs to the model and to determine a curve of the actual river water quality, measured in terms of dissolved oxygen and biochemical oxygen demand. The model coefficients were estimated by trial and error until agreement with the observed data. The model, calibrated with data corresponding to 1999 and validated with data relative to 2002, was efficient to reproduce the field measurements. A sensitivity analysis was made for the model coefficients and the water quality curves were more sensitive to the biochemical oxygen demand decay coefficient.