Pollution distribution in the rivers is one of the most important problems in the environment. The main sources of surface water pollutants are urban wastewater and industrial sewage. The one of the problems of pollutants entering to the river is reduction the concentration of dissolved oxygen. It is necessary to predict the amount of dissolved oxygen for management of water resources. Modeling is considered as a proper and effective tool for determining and evaluating the effects of various pollutants on the water supplies. The various models have been applied in order to develop the dissolved oxygen in the rivers such as CSP, M and AQUAL2 series. The base of developed model in this investigation is convection-diffusion of solute equation in soil. For this purpose, two term including production and decay of dissolved oxygen were added to this equation. Final equation was discretized using finite difference method with implicit scheme. With applying the initial and boundary conditions, the equation set was solved by Thomas algorithm. The calculations was done by programming in MATLAB software. In order to calibration and validation of the model, data obtained from two reaches of Zayanderoud river including steel melt factory and Mobarakeh Steel Complex were used. The temporal and spatial variations of dissolved oxygen were plotted and compared with real data and results of the MSP and CSP models. Results showed that concentration of the dissolved oxygen can be well predicted through solving convection-diffusion equation with introducing two terms for decay and production of oxygen.The comparison between the results of the model and two other models showed that the model gives better results than the MSP and CSP models. Sensitivity analysis of model coefficients showed that coefficents had the most effect on model’s prediction. Since is dependent on hydraulic parameters, the sensitivity of the depth and velocity of the river were checked out. Finally the depth of the river was introduced as the most sensitive variable. Keywords : dissolved oxygen, Thomas algorithm, Zayandehrud, Advection- Dispersion Equation, MATLAB
