Water quality modeling at Poti river in Teresina (Piauí, Brazil)

ABSTRACT The uncontrolled growth of Piauí’s capital, in Brazil, characterized mainly by the occupation of the banks of the river Poti and the existence of illegal connections of raw sewage in rainwater drainage pipes, has contributed significantly to water pollution in the basin of Parnaíba river (semiarid region of Brazil). This research aims at performing the mathematical modeling of water quality in an area of 36.8 km of the Poti river, based on the QUAL-UFMG platform. The research is presented as the first study involving modeling of water quality in said river. Modeled components were: dissolved oxygen (DO), biochemical oxygen demand (BOD) and thermotolerant coliforms (TC). The results obtained from field measurements indicated nonconformities of the parameter TC with respect to CONAMA Resolution nº 357/2005. The calibration of the decay coefficients for each parameter resulted in mean deviations between measured and modeled data of up to 20% and Nash-Sutcliffe efficiency coefficients higher than 0.75, which indicate that the QUAL-UFMG can be used as a basis for predicting the water quality in rivers of semiarid areas. The calibrated model was also compared to field data obtained from the literature. Finally, model simulations were performed for different flow scenarios (minimum and maximum), with consistent results that can be used for the management of the Piauí state water resources.