Conservation and improvement of water quality in water bodies is an important matter to maintain all of its uses as well as other human necessities like microclimate regulation and leisure. Lakes and reservoirs have a complex circulation behavior with vertical temperature profiles changes along the time, resulting in differences in water density and a vertical stratification condition. This characteristic can directly affect the water quality conditions perturbing its main indicators. This study aims to evaluate the quasi-3D models' capacity to represent the hydrodynamic behavior of a tropical lake and its effects on the main variables that characterize its water quality. To achieve this objective, high-frequency monitoring data were collected, the lake was represented in a quasi-3D model, and the accuracy of the result was evaluated by applying statistical indices. The evaluation showed good agreement between field measures and simulated results when compared with other applications. The connections between hydrodynamic behavior and water quality were seen with the simulations results analysis, which showed that mixing events and long stratification periods perturb the water quality, the first with re-suspended bed material and the second blocking the surface and bottom exchanges. The application of a 3D model gives the capacity to reproduce the reservoir spatial variability and its vertical profiles, which is necessary to study the constituents' distributions across the water column. Therefore, the hydrodynamic and water quality behavior of lakes was accurately represented by the model, as well as the importance of improving high-frequency monitoring techniques.

RESUMO A questão da qualidade da água nos corpos d’água urbanos é complexa, pois passa pelo controle de cargas poluidoras pontuais e difusas. As cargas pontuais ainda são um problema recorrente no Brasil, porém são mais facilmente identificáveis. As cargas difusas não têm um ponto de lançamento específico, o que torna seu controle mais difícil, pois ocorrem principalmente em função da lavagem das superfícies durante as chuvas. Os corpos d’água em áreas urbanas são severamente afetados por tais descargas, que se refletem na qualidade das águas e em seus usos. Nesse contexto, este trabalho apresenta elementos do monitoramento da qualidade da água do rio Pinheiros nos últimos dez anos; analisa os resultados do monitoramento da Companhia Ambiental do Estado de São Paulo (Cetesb); verifica se há relação com resultados do monitoramento diário do projeto Avaliação da Qualidade das Águas do Sistema Pinheiros-Billings com o Protótipo Flotação; e, por fim, avalia o uso de sistema de biorretenção, que apresenta resultados significativos de reduções da carga poluidora do escoamento superficial chegando, em alguns casos, a mais de 90%. Essa solução é uma alternativa para a redução da poluição difusa na bacia do rio Pinheiros.

Periods of drought are impactful in terms of surface water quality, as there is less mass available to dilute the released contaminants. However, it has now been determined that the cause of substantial effects on water and aquatic habitat is surface runoff caused by rainfall-flow process. Although not receiving as much attention, diffuse pollution (runoff, deforestation, fertilizers from farmland, etc.) is just as harmful as point pollution (from treatment plants, industrial discharges, etc.). Thus, the coupling of hydrological, load and hydrodynamic models related to water quality is becoming increasingly important. The development of the CABC-QUAL model in this work was thought to help with these complex issues, which include the multiples uses of the watershed and the variability of precipitation itself, the different forms of sanitary systems and the seasonality of the constituents. In addition, a tool was included to manage Best Management Practices (BMP) through in situ Treatment Units, which proved to be a great helper for positioning these practices to reduce pollution in surface waters. In the two case studies used to validate the developed model, the CABC-QUAL demonstrated its ability to perform all its tasks accurately, quickly and completely. It also demonstrated results on an annual time scale, discussing all the complexity of the variation in constituent concentrations distributed across the basin. This tool will be essential to represent the complexity of water quality more accurately and will serve as support for depollution programs.

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