Three-dimensional numerical investigation of flow pattern changes in two successive diverged and converged bends in a meandering reach of a natural river by SSIIM.2 model

Investigation of the flow pattern in meandering rivers is much more complicated than straight ones. Also, most rivers in the path of bends are not uniform due to channel width variations. Therefore, the use of a robust numerical model for simulating flow pattern in rivers is necessary. In this research, SSIIM three-dimensional numerical model was used to simulate the flow pattern in a meandering reach of ​​the Doab river in Chaharmahal and Bakhtiari province. For this purpose, after doing field measurements and model calibration the velocity values ​​calculated by the model were compared with the measured values in a relatively uniform section of bend by using RMSE and MAPE error criteria. Results obtained showed that the values of these two criteria are 0.081 and 0.075, respectively. This indicates that the model performance is good. Moreover, various flow characteristics including vertical and horizontal velocity profiles, the velocity lines in longitudinal and transverse directions and also the distribution of bed shear stress in location of two converged and diverged the bends are compared. The results of this study indicate that velocity values in longitudinal direction in converged bend is higher than diverged one. the high accuracy of the model in the study of flow pattern in the river bend. Furthermore, the density of the stream lines and the values of bed shear stress at the interval reach of two bends are maximum. As result, it can be said that flow pattern simulated well with the model