The Ravi River is one of the five major rivers in Pakistan and has several beneficial uses, which include agricultural irrigation, municipal water supplies, fisheries and recreation. The study reach of the river is a stretch of about 100Km between Ravi Siphon and Balloki Headworks. Presently the River Ravi is receiving about 3,400,000 m 3 /day of wastewater form both domestic and industrial sources. Due to discharge of this large volume of wastewater, most of the Ravi River reach between Siphon to Balloki Headworks has become anaerobic and requires urgent implementation of a water quality management strategy. A framework for the development of DO model for the Ravi River is formulated considering both the CBOD and NBOD. The river study reach is segmented based on locations of wastewater outfalls, surface drains and freshwater tributaries. Hydrodynamic model is developed to estimate travel time and reaeration coefficient for DO modeling of the River Ravi. Estimation of model parameters and waste inputs is carried out through a combination of laboratory measurements, field and monitoring data and sensitivity analysis. Long-term BOD analysis of the wastewater samples collected at five outfalls and 2 surface drains are made to determine the ratio between CBOD5 and CBODU, bottle rate coefficients and ultimate values of BOD, CBOD and NBOD. The results of these analyses show strong correlations (R 2 ) ranging between 0.9 and 0.98 both for CBOD and overall BOD rate constants (i.e., K c and K d ). R 2 for K n ranges between 0.72 and 0.93. The CBOD rate coefficient K c ranges between 0.14 - 0.27 day -1 and the NBOD rate coefficient “K n ” ranges between 0.09 - 0.26 day -1 . These values are consistent with 0.1- 0.5 day -1 reported in literature. Diurnal variation in both the wastewater concentration and flows at the Main Outfall was assessed to find out the sampling time for model calibration and verification and to assess the pollution loads. Currently about 862,000 Kg/day of BOD pollution load is being discharged into the River Ravi. This total pollution (BOD) load will increase to about 1.5 times from different outfalls and surface drains by the year 2025 due to constant increase in urbanization and industrialization in the Ravi River catchments. DO model is formulated by using the wastewater loads estimated in past studies undertaken for Lahore and findings of present study. Sensitivity analysis is carried out to find the least sensitive reaeration rate coefficient relationship for the River Ravi hydrodynamic characteristics. O’Connor-Dobbins formula to calculate reaeration rate constant is found to be the least sensitive under variable flow conditions of the Ravi River. Its applicability in DO (ii)ABSTRACT modeling of the Ravi River is reflected by a close agreement between the model results and the field measurements. The DO model results considering only CBOD show that the calculated values do not correlate well with the field measurements as reflected by SSR value of 13. The DO model results with nitrification (NBOD separately with nitrification) have shown the strongest correlation between the calculated values and field measurements with SSR value of only 1.5. These results highlight the importance of NBOD in the DO modeling of the Ravi River. For the calibration of the DO model an extensive field survey was conducted to estimate deoxygenation rate coefficients for BOD, CBOD and NBOD in the River Ravi. The in-stream CBOD decay rate coefficient (K cr ) estimated from the River Ravi CBOD profile during the model calibration is found to be 0.36 day -1 . The K n value from the nitrification modeling calibrated through the concentrations of Org-N and NH 3 -N in the river was 0.34 day -1 . Both the values are in the range reported in literature (0.2 – 0.5 day -1 ) for the rivers receiving raw wastewaters. Nitrification is an associated phenomenon with DO and un-ionized ammonia toxicity beyond the acceptable limits can kill the fish. Therefore, modeling of ammonia toxicity and nitrification in Ravi River is also carried out. The DO model is verified with the IPHER (1978 – 1979) Ravi River monitoring data under low flow conditions. The results of the model calculations show reasonable agreement with the river data. Biokinetic rate coefficients change with level of wastewater treatment. The CBOD bottle rate (K) is 0.25 day -1 for raw wastewater. A slight increase to 0.27 day -1 for filtered sample is observed due to presence of readily biodegradable organic matter. A direct relationship of K with different levels of biological treatment has been noted wherein K value reduces from 0.27 day -1 to 0.05 day -1 with increase in biological treatment levels. NBOD rate (K n ) of 0.21 day -1 was observed for both raw and filtered wastewater samples. However, in biological treatment, K n value varies slightly between 0.08day -1 to 0.06 day -1 for treatment levels corresponding to 3 and 10 days detention times respectively in a laboratory scale aerated lagoon. As the Ravi River is currently receiving wastewater without any treatment, therefore the river rates (K cr & K n ) are reduced by a factor ranging between 1.5 to 5 depending on the level of treatment to achieve desired water quality objectives. To improve the water quality of the River Ravi wastewater control alternatives including conventional wastewater treatment, flow augmentation, wastewater transportation, low cost treatment and constructed wetlands are evaluated. Model calculations carried out for water (iii)ABSTRACT quality management of the River Ravi show that even to achieve 1mg/L of DO levels in the River Ravi at MA7CD flow (i.e., 9.2 m 3 /s) 70% BOD reduction is required. Higher removal efficiencies of 85 and 90% are required for 3mg/L and 4mg/L DO levels respectively. To achieve 5mg/L of DO standards, high removal of both CBOD and NBOD (95%) is required. Ammonia toxicity is also a water quality problem in the River Ravi. The simulation results show that 90% ammonia removal is required to meet the desired un-ionized ammonia standards. This removal results in 5mg/L DO level in the River Ravi. A flow augmentation of about 19m 3 /s through MR Link canal with 80% of CBOD removal can achieve 4mg/L DO standards with 30% lower cost than the MA7CD flow conditions. Flow required to augment the river flow to achieve 4mg/L DO standards without any treatment is 416m 3 /s. The flow that can be diverted from MR Link canal to the River Ravi will depend on availability of the water in the River Chenab and may require remodeling of MR Link canal. Transportation of wastewater from the city of Lahore trough a collector channels with primary treatment facility at the confluence point of QB Link canal is a cost effective option with about 2.5 times lower cost than the alternative with ASP at all the outfalls and surface drains. Waste stabilization ponds as an alternative for water quality management of the River Ravi comes out to be the least cost alternative, but this result in DO level of 3mg/L in the river. Furthermore, there are issues related to land acquisition that need to be resolved. However, if the effluent can be reused for irrigation, pollution load being discharged into the River Ravi can get reduced.