Analyzing the Effect of Temperature on DO and BOD of the Tapi River using QUAL2Kw Model

Environmental pollution and climate change is the ultimate result of rapid urbanization. The change in environmental conditions due to undesirable human activities increases local ambient temperature hence it is leading to a rise in the river water temperature. Tapi river is the main source of drinking water for Surat city, Gujarat, India. A stretch of river Tapi has been studied from Kamrej to Causeway which has a stretch of about 22.39 km. The river water quality was found to be degraded due to the excessive discharge of pollutants from various points and non-point sources. Extreme discharge of pollutants into the river decreases the dissolved oxygen (DO) concentration. At the same time due to the increase in temperature, the process of transformation of atmospheric O2 gas into dissolved form also becomes very slow. In this study, the QUAL2Kw one - dimension water quality model was applied to assess the DO and BOD at various locations. The QUAL2Kw model was calibrated and validated with observed data. The calibrated model was applied to evaluate the effects of temperature on the DO and BOD of the Tapi river. The conditions of maximum, minimum, and average temperature for March, April, and May from the year 1991 to 2021 were considered. The result revealed that the full stretch of 22.39 km was not able to maintain minimum dissolved oxygen (DO) concentration, hence biochemical oxygen demand (BOD) has subsequently increased downstream of the river stretch. It was also observed that DO and BOD levels tremendously fluctuate ambient temperature.