Figure 5(a) shows the boundary conditions applied to numerical models. Six-sided boundary conditions are implemented in FLOW-3D. The upstream and downstream boundaries are set as pressure (P). The lateral sides such as Y_min and Y_max are set as wall (W) boundaries which indicate no-slip conditions, and zero tangential & normal velocity (u = v = w = 0)) on the wall, where u, v, and w are the velocity in x, y, and z directions, respectively. Upper boundary (Z_max) is set as atmospheric pressure with a fluid fraction (0) to allow water as null von Neumann. The lower boundaries (Z_min) is set as symmetrical. Additionally, to deactivate the empty cells on the downstream side and to minimize the simulation time, the model applied a domain-removing component as shown in Figure 5(b). The cell's deactivation region was defined from gate to the end of the stilling basin and it was ensured that the domain-removing region is not containing the flow. Table 3 shows the upstream and downstream initial conditions given to models for gated flow (44 m³/s). Three different downstream elevations and a constant upstream fluid elevation of 136.24 m were implemented to run various models.