## 5 Results and Discussion
### Configurations Guide Vanes  
The second aspect in the model tests is to outline and assign dimensions to the guide vanes. Because the sediment is efficiently flushed at high flows, the design is based on the low and medium flows (cases 1 and 2). With a number of test combinations and comparisons, it is decided that the cross-channel axis of the vane array is placed at \(X=220\) m, i.e., along the CS3 section, and the vane number is set to be seven with \(c=10.0\) m. The spacing between two neighboring vanes is so determined that their flow fields should not interfere much with each other. By trial and error, it is chosen that \(a=10.0\) m, \(b=0.5\) m, and the vane crest is put 2.0 m below the DRWS. The vane orientation (\(\alpha\)) is a primary parameter that needs to be evaluated.  
The first step is to find the acceptable \(\alpha\) range (\(\alpha\geq 0\)). All the vanes are given the same angle. In the model, the vanes are installed in such a way that is easily adjustable to another angle. Figure 13 showcases the flow patterns in the presence of the vanes at \(\alpha=0^{\circ}\) and \(30^{\circ}\) (case 2). At \(\alpha=0^{\circ}\), the vanes follow virtually the flow direction, and their effect is limited. With a step-up in \(\alpha\), they bend the flow in a more efficient way and the flow is more directed away from the right bank and towards the middle of the shuice. The two zones of flow circulations also become suppressed in size. The layout at \(\alpha=30^{\circ}\) is, for example, more effective than the one at \(\alpha=20^{\circ}\). However, the \(\alpha=30^{\circ}\) vanes generate local flow separations and moderate vortex wakes in the middle portion of the river. In consideration of potential deterioration at high discharges, the angle \(\alpha=30^{\circ}\) is seemingly the upper limit of the vane arrangement.  
The choice of \(\alpha\) is a trade-off between attaining a favorable flow pattern in the reservoir and avoiding unacceptable risk of erosion around the vanes. In the second step, repeated tests show that \(\alpha\) should preferably be in the range of 10-20\({}^{\circ}\). For both cases, Figure 14  
Figure 13: Modified flow patterns with the guide vanes (case 2). (**a**) \(\alpha=0^{\circ}\); (**b**) \(\alpha=30^{\circ}\).  
presents the resulting flow patterns at \(\alpha\) = 15\({}^{\circ}\). Obviously, the flow patterns are, in a noticeable manner, improved, with the flow directed towards the gates and the zones of circulation suppressed to much smaller dimensions. In case 1, for example, the left circulation zone shrinks from \(\sim\)335 to \(\sim\)195 m in length and from \(\sim\)80 to \(\sim\)45 m in width. In similar river studies, [PERSON] [4] stated that the typical \(\alpha\) range is 10-20\({}^{\circ}\) and the use of larger angles should be handled with caution.  
At a given flow rate, the flow patterns are similar within the \(\alpha\) = 10-20\({}^{\circ}\) range. It is not easy to discern which angle is more favorable. Limited by laboratory conditions, it is not possible to experiment with suspended load in the model. To be convincing in the choice of vane layout, sediment deposition (amount) should be taken into consideration, which is the task of numerical modeling.