Estimation of river Tigris dispersivities using a steady-state numerical model

The present work suggests a simple approach for simulating the dispersion of pollutants in rivers and streams with the aid of computational fluid dynamics technique. The two-dimensional advection-dispersion equation was solved using FlexPDE code to predict the biochemical oxygen demand (BOD) and the total dissolved solids (TDS) concentrations at the confluence of Diyala with Tigris Rivers. In this model, two sets of data were used for calibration and validation processes. Various values of longitudinal and transverse dispersion coefficients were adopted in the model to determine the suitable value using the trial-and-error method. The results revealed that the best agreement between simulated and measured values was observed when the longitudinal and transverse dispersion coefficients are close to 10 and 5 m(2)/s, respectively. The results showed that the proposed methodology is more suitable for TDS, while for BOD, it needs an accurate representation of the chemical or biological transformations.