Annual Investigation of the Karun River Reaeration Rate Coefficient (From Mollasani to Kot-e Amir)

One of the most important factors of the water quality management is the rate of dissolved oxygen. Reaeration coefficient describes the rate of absorption of oxygen from atmosphere into water. The rate of dissolved oxygen in water quality modelling shows great sensitivity even to the smallest changes in reaeration rate coefficient. The main target of this paper is to evaluate the best equations of the reaeration rate coefficient, among 29 most used equations based on the dissolved oxygen modelling for Karun River, IRAN, in different seasons. In order to achieve this aim 91 km length of river, from Molasani to Kut-Amir stations was modeled. Modelling was performed based on monthly quality and quantity data of this river, from 2010 to 2011 and also 2011-2012, involving Qual2Kw5.1 software. According to the results Thyseen (TH) equation in the autumn, Lau (LA) in winter and spring and finally Jha (JH) equation in summer have the best estimations for the reaeration rate coefficient, while the accuracy of the modeled DO values were evaluated using RMSE between simulated and observed data, which were equal to 0.35, 0.48, 0.29 and 0.29, respectively. Also the MBE values were equal to 1.78, 0.43, -2.47 and -0.67, respectively, which show very good agreement. Finally, the relevant modeled reaeration rate coefficients for the above mentioned seasons were equal to 0.62, 0.23, 0.33 and 1.59 (1/day), respectively.