Calibration of mathematical water quality modeling applied to a basin located in central region of the state of São Paulo, Brazil

Abstract Mathematical water quality models are support tools widely used in the management of water resources, as they may provide a broad view of the water system studied. In this way, the present study aimed to calibrate the “State Water Resources Plan Application” (APERH), applied in the São Paulo State Water Resources Plan 2023–2030, at the Jacaré-Pepira River, located in the Jacaré/Tietê River Basin (BH-TJ), central region of the state of São Paulo. The calibrated parameters were biochemical oxygen demand (BOD), dissolved oxygen (DO) and total phosphorus (P), which results showed that k1, k2 and b4 coefficients were within the range of typical values described in the literature, while s5 was higher than typical ranges. When evaluating the adjustments of the curves estimated by APERH with water monitoring data from Environmental Company of São Paulo (CETESB), visual analysis showed that BOD and DO had satisfactory adjustments between the estimated data and monitored data, while P was adequate at two of the three monitoring stations. Through the statistical method, it was observed that both BOD and DO indicated reliability between the estimated and monitoring data, while P had the opposite result. Thus, there is an understanding that APERH achieved the proposed objectives of this study, obtaining a first knowledge of BH-TJ, since there is a lack of water quality modeling studies in this region. The next step of this study is to apply the calibrated parameters to all BH-TJ and introduce the sociohydrology concept in this basin.