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.

摘要 巴西皮奥伊州首府出现无序扩张现象，主要表现为波蒂河（Poti）岸线被违规占用，且存在原生污水非法接入雨水排水管道的问题，该状况显著加剧了帕纳伊巴河（Parnaíba）流域（巴西半干旱地区）的水体污染。本研究基于QUAL-UFMG平台，针对波蒂河36.8公里河段开展水质数学建模，系该河段首次水质建模相关研究。本次建模涵盖的指标包括溶解氧（DO）、生化需氧量（BOD）与耐热大肠菌群（TC）。野外实测结果显示，耐热大肠菌群参数不符合巴西国家环境委员会（Conselho Nacional do Meio Ambiente，简称CONAMA）第357/2005号决议的要求。对各参数的衰减系数进行校准后，实测数据与模拟数据的平均偏差最高可达20%，纳什-萨特克利夫效率系数高于0.75，表明QUAL-UFMG模型可作为半干旱地区河流水质预测的可靠工具。校准后的模型还与公开文献中的野外实测数据进行了对比验证。最后，本研究针对最小、最大流量两类不同情景开展了模型模拟，所得结果一致性良好，可用于皮奥伊州水资源管理工作。