Numerical Simulation of the Transverse Dike (Epi) and Islands effect over Water Flow Pattern in Natural Meandering of the Tajan River

The transverse dike has many applications for River bank erodibility stabilization and consolidation. Water flow pattern, erosion and sedimentation around the transverse dike are dependent of various factors, Such as transverse dike type, geometry sections, sediment transport capacity and etc. In This study With regard to the significance role of the flow velocity and shear stress forces on river bank erosion, two-dimensional numerical modeling as CCHE2D was performed to Numerical Simulation of the Transverse Dike and Islands effect over Water Flow Pattern in Natural Meandering of the Tajan River (in the north of Sarakhs and downstream of Noruzababd village- Razavi Khorasan Province, Iran).

In the first step of this study, a large topographic scale map was prepared with scale 1: 2000. And in three sections of the surveyed sections, the flow parameters were measured. Using topographic data obtained from field surveys and then the geometry model and the computational mesh (grid) with different dimension and also field measurements of flow characteristics such as velocity and depth, the two-dimensional hydrodynamic model was run. Simulated data were compared with observed ones in order to assess the velocity horizontal profile gradients, the distribution of shear stress and the flow depth condition in curved parts of the river channel and around the transverse dike and islands.Furthermore, two statistical criteria (RMSE and MAPE) were used to evaluate the performance of the model.

The results indicated that the simulated values are in good agreement with the field measurements. In the study area, water flow pattern around the transverse dike and islands is dependent of hydraulic conditions and at various discharges has different impact on the flow pattern. due to transverse dike and islands, cross-sections reduce, reason increasing the depth, speed and shear stress, sediment transport capacity and bed load.

The results of this study show that for Observation discharge (47 m3/s) and discharge with a return period of less than 25 years, transverse dike have local effects on the deviation of the flow, and they cannot lead to the diversion of floods with a return period of less than 25 years to the eastern banks. Because the high density of vegetation and high roughness on the east coast, prevents the distribution of flow to the two natural canals. Key words: Transverse Dike (Epi), Island, CCHE2D, Meandering, Tajan riverKey words: Transverse Dike (Epi), Island, CCHE2D, Meandering, Tajan river