Numerical Simulation of Water Quality and Self-Purification in a Mountainous River Using QUAL2KW

Abstract

Understanding the water quality in mountainous rivers is critical for sustainable water resources management. By using the rivers’ self-purification to improve water quality is also the most economical and sustainable way to clean water. In the present study, the QUAL2KW model is applied to investigate the water quality and self -purification capacity in a mountainous river. The Abbasabad River in Iran is used as the study site. The river is divided into two interva ls based on the main purpose of water usage: drinking and agriculture. The model is calibrated and validated using field data from five monitoring stations along the river. Six parame ters, COD, BOD, DO, P-PO4, N-NO3, and N-NH4 are calculated and compared with field data. The Margin of Safety (MOS) is presented and added to the value of each parameter for better water resources protection. The sensitivity analysis is conducted to identify the m ost influential parameters in water quality simulation for mountainous rivers. It is revealed that the parameters of oxidation rate, nitrification rate, and denitrification rate have the maximum influence on water quality simulation for mountainous rivers using QUAL2KW. Additionally, three scenarios are tested for water quality and self-purification. It is found that the river flow rate has a stronger impact for water self - purification in mountainous rivers and the location of point-source pollution has very limited impact.

Keywords: margin of safety (MOS), mountainous river, QUAL2KW, self-purification, TMDL, water quality