| dc.description.abstract | River confluences are the morphodynamically challenging sections of river networks. Regardless of their occurrence which can be manually or naturally, they are constantly changing and are dominated by a complex flow pattern. Due to the complex structure of the three-dimensional flow, river beds undergo scouring and deposition. This complex 3D flow structure can cause problems for navigation in man-made channels, and also the lateral movement in natural channels which is important for maintance of riverine structures . In this study, the flow and sediment patterns at river confluences are investigated by using a 3D numerical method called REEF3D::CFD, which is an open-source hydrodynamic model developed at the Department of Civil and Environmental Engineering, Norwegian University of Science and Technology (NTNU). The model is solving the Reynolds-averaged Navier-Stokes (RANS) equations. In order to evaluate bed changes at the channel confluence, k-ω turbulence model, sandslide algorithm, the level set method for free surface calculation, and 5th-order weighted essentially non-oscillatory (WENO) discretization scheme have been applied. The results of sediment pattern and maximum scoure depth and point bar are compared with the available experimental data, and the promising agreement between experimental and simulation results proves the applicability of the numerical model. Then, a sensitivity analysis has been carried out for the calibration parameters including cell size, bedload equation, shear stress, and porosity. Results show that reduction of the cell size and Shields parameter as well as increasing the porosity value cause an increase in maximum scour depth. After calibration the model of the channel confluence which are the main goal of this study, the applicability of 3D modeling the collar at the channel confluence is shown by the preliminary simulations. | |