## 3 Numerical Model
### Solution Domain, Boundary and Initial Conditions
It is also noticeable that the SWE results were below the RANS and experimental results for time interval 2-4 s at P2, as the reflected wave passed this measurement point. Figure 9: Comparison of experimental and numerical stage hydrographs (P1–P5 sensors) for test W1. Figure 10: Comparison between experimental (**a**) and numerical (**b**) results for test W2 (\(\alpha=0.2\)). As for the P3 sensor, the experimental data are in agreement with the numerical data for time interval 0-1 s, while a disagreement was observed until \(t\) = 4 s. The water level slightly raised immediately after the sudden removal of the gate, and a sharp rise was observed in the SWE results as soon as the reflected wave reached the P3 (\(t\) = 0-2 s). After that, both the experimental and RANS results were in good agreement generally, while small oscillations due to reflections of the negative waves from the flume walls were not well represented by the SWE (\(t\) = 2-8 s). In addition, it was observed that the reflected wave clearity of the SWE results was slower than the experimental and RANS results at P3 and P4. The highest water level for the D1 case occurred at P4, located at the downstream end, as expected and already noticeable in Figure 6. Although arrival times of the reflected wave for the experimental and RANS results were quite similar, the RANS results were not as in good agreement with the experimental results as for the other probes, and the peak level of the water was not determined by the RANS at P5 (\(t\) = 2 s). Also, actual oscillations were not detected by both the computational methods (\(t\) = 3 s), and the reflected wave  
Figure 11: Comparison of experimental and numerical stage hydrographs (P1–P5 sensors) for test W2. celerity of the SWE was slower than the other results, similar to P3 and P4. Nonetheless, the results agreed progressively with decreasing undulation after \(t=4\) s.  
Figure 8 shows the comparison between the experimental data and the numerical results of the dam-break process evolution for test W1. The experimental results are displayed on the left-hand column, whereas the second and third columns refer to the numerical results calculated by the RANS. A comparison of the stage hydrographs for the test case W1 is shown in Figure 9. After the fast removal of the suicide gate, water in the reservoir hit the tailwater and the flood wave moved downstream rapidly with a plunging type wave breaking that caused a complex flow behavior on the free surface. Significant fluctuations were observed on the surface with reflection phenomena of propagating waves from the side and the front-end wall of the channel, while also interacting with the incoming flow. It can be said that with the presence of the tailwater, more undulation occurred than D1 at all probes. The water level decreased quickly with the abrupt removal of the gate, and fluctuations occurred when the negative wavefront reached the P1. It can be noticed that the water depths predicted by the RANS simulations were lower than the experimental results for the time interval \(t=0\)-\(3\) s, which indicated that the discharge time of the upstream was not computed correctly by the RANS. After the discharge finished, the results agreed well at P1, proving that the RANS simulated the undulations properly. Also, it can be seen that the SWE discharged the upstream faster than other results at the initial phase until approximately \(t=0.1\) s. Then a peak was observed, the water level increased, and the SWE results agreed with the experimental results. Nonetheless, undulations were not well determined by the SWE, unlike the RANS. A peak was observed at the beginning of the P2 and P3 plots due to passing breaking waves, then a gradual decrease occurred in the experimental and computed results due to the finite reservoir volume. The measurement method failed for P2 (\(t=0\)-\(2\) s). After that, the water level increased with the reflected wave and a hydraulic jump occurred in the RANS and measured results, unlike SWE.