Assessment of Seasonal Variations of Pollutant Decay Coefficient of Babolrood River

Simulation of self-purification and investigation the pollutant decay coefficient of rivers is one of the most important requirements of surface water resources pollution monitoring and treatment. In this paper, self-purification capacity and the pollutant decay coefficient values of Babolrood River, IRAN, was investigated based on field measurements of qualitative parameters including; DO, BOD, pH, EC, nitrate, phosphate and temperature in four seasons, 2018. To achieve this aim, QUAL2Kw software used. In this paper not only the modelling results and analyzes are presented but the measured data of the studied river are also presented, which can be used in the future researches. Based on the results, the average amount of dissolved oxygen of Babolrood River in all seasons except summer are varied between 6.55 and 7.65 mg/l, while the average of that is equal to 5.93 mg/l in summer. Also, the average value of BOD in summer, due to an increase in temperature, is recorded equal to 3.17 mg/l and in other seasons were recorded between 2.17 to 2.93 mg/l. The decay coefficient of the Babolrood River was estimated equal to 5.5(1/day) in summer and in other seasons it varied between 0.5 and 4(1/day), applying QUAL2Kkw simulations. According to the dissolved oxygen diagram and involving the Streeter-Phelps method, no reduction in dissolved oxygen during spring and fall, in this river, was recorded. However, in winter and summer, the dissolved oxygen was reduced to 6.5 and 5.7 mg/l, respectively.