Calibration and verification of a dissolved oxygen management model for a highly polluted river with extreme flow variations in Pakistan Husnain Haider & Waris Ali Received: 25 July 2011 / Accepted: 30 August 2012 / Published online: 16 September 2012 # Springer Science+Business Media B.V. 2012 Abstract A dissolved oxygen (DO) model is calibrat- ed and verified for a highly polluted River Ravi with large flow variations. The model calibration is done under medium flow conditions (431.5 m 3 /s), whereas the model verification is done using the data collected during low flow conditions (52.6 m 3 /s). Biokinetic rate coefficients for carbonaceous biochemical oxygen demand (CBOD) and nitrogenous biochemical oxygen demand (NBOD) (i.e, K cr and K n ) are determined through the measured CBOD and ammonia river pro- files. The calculated values of K cr and K n are 0.36 day -1 and 0.34 day -1 , respectively. The close agree- ment between the DO model results and the field values shows that the verified model can be used to develop DO management strategies for the River Ravi. The biokinetic coefficients are known to vary with degree of treatment (DOT) and therefore need to be adjusted for a rational water quality management mod- el. The effect of this variation on level of treatment has been evaluated by using the verified model to attain a DO standard of 4 mg/L in the river using the bioki- netic rate coefficients as determined during the model calibration and verification process. The required DOT in this case is found to be 96 %, whereas the DOT is 86 % if adjusted biokinetic rate coefficients are used to reflect the effect of wastewater treatment. The cost of wastewater treatment is known to increase exponentially as the removal efficiency increases; therefore, the use of appropriate biokinetic coefficients to manage the water quality in rivers is important. Keywords Dissolved oxygen modeling . Model calibration . Model verification . Dissolved oxygen management . Rivers . Nitrification modeling Introduction Highly polluted rivers with extreme flow variations possess certain unique characteristics with respect to hydrodynamics and water quality parameters. Under extreme low flow periods due to large wastewater discharges, the river become anaerobic as little dilu- tion is available; whereas, during high flow condi- tions, dissolved oxygen (DO) sag curve is not developed. Thus, the data collection during the periods of such extreme flows cannot be used for model cal- ibration and verification. Therefore, such rivers Environ Monit Assess (2013) 185:4231–4244 DOI 10.1007/s10661-012-2864-x H. Haider (*) School of Engineering, University of British Columbia Okanagan, 3333 University Way, Kelowna, BC V1V 1V7, Canada e-mail: husnain.haider@ubc.ca H. Haider e-mail: haider42@yahoo.com W. Ali Institute of Environmental Engineering, University of Engineering and Technology, Lahore, Pakistan e-mail: warisali@uet.edu.pk