## 3 Comparison between Flow-3D, MIKE 3 FM, and 1D Exact Riemann Solver Predictions
### Water Depth Variations  
The evolution of the initial reservoir water levels of \(h_{0}=0.4\) m under the dry- and wet-bed conditions from [PERSON] et al. [39] are shown in Figures 10 and 11, respectively. Figure 10 shows the water level variations at different gauges, including upstream and downstream of the gate; there is satisfactory consistency between the experimental data and the numerical results. Positions G1 and G2 represent the water level variations in the reservoir, and they displayed a progressive reduction in the water depth variation. It was also observed that the sudden upstream water depth reduction \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{
\begin{tabular}{c} **Water Depth** \\ **Ratios** \\ \end{tabular} } & \multirow{2}{*}{**Time \(T\) (-)**} & \multicolumn{3}{c}{**RMSE**} \\ \cline{3-5}  & & **Analytical Solution** & **Flow 3D** & **MIKE 3 FM** \\ \hline \multirow{3}{*}{0} & 9.899 & 0.03 & 0.03 & 0.04 \\  & 14.845 & 0.04 & 0.04 & 0.04 \\  & 49.497 & 0.26 & 0.02 & 0.02 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: RMSE values for the free surface profiles observed by [PERSON] et al. [39]. resulted in a flow depth of \(\sim\)4/9 of the initial water depth, which the expected analytical result was first presented by [PERSON] [5]. According to [PERSON] et al. [44], the water level curve of the analytical solution was separated from the experimental curve from \(t=3\) s. Thus, for \(t\geq 3\) s, the analytical solution approached the constant value of the water depth of 4/9, while the experimental data decreased gradually owing to reservoir depletion. The reduction in the water depth was slow at G1 and G2, at approximately \(t=1\)-5 s when the downstream water began to enter the reservoir backwater. A sharp variation of the water level immediately downstream of the dam behaved similarly, and it involved a decrease in the maximum water level at locations G3, G4, G6, and G8. As expected, the water level increased for \(t<3\) s and then exhibited an identical reduction. The RMSE values for Flow-3D and MIKE 3 FM are quite satisfactory (Table 3), with the maximum RMSE for Flow-3D being 0.03 and that of MIKE 3 FM being 0.04. Figure 10: Measured and computed water level hydrograph at various positions for dry-bed by [PERSON] et al. [39]: (**a**) G1 (\(-\)0.5 m); (**b**) G2 (\(-\)0.1 m); (**c**) G3 (0.1 m); (**d**) G4 (0.8 m); (**e**) G6 (1.2 m); (**f**) G8 (5.5 m). Figure 11 shows the evolution of the water level with time for the wet-bed case with a tailwater level of \(h_{1}=0.08\) m; that is, \(\alpha=0.2\). Upstream and downstream for the wet-bed, the physical downgrade of the water depth was strongly interrupted by the reflected wave at the downstream end of the testing flume (as seen in Figure 11). At points G1 and G2 in the reservoir, no obvious difference was found in the variation of the water level until approximately \(t=15\) s, because of the wave reflected against the downstream weir. For points G4 and G5, at \(t<15\) s, the reflected waves became visible. When they struck the weir, they were partially reflected, and these reflected waves moved the upstream boundary, yielding the aforementioned water depth results. The simulated results using MIKE 3 FM and Flow-3D appeared to have a quicker velocity of propagation than the measurement when the wave was reflected at approximately \(t>15\) s. This slight delay in the measured data can be attributed to the fact that the actual opening of the gate was not instantaneous. Figure 11 also demonstrates that the numerical results are reasonably consistent with the experimental data for the propagation speed of the wavefront and the water depth variation. The water level obtained with the two numerical models decreased more rapidly than in the experiments. Moreover, the wavefront in the numerical simulation was propagated sooner than the experimental results. It can be clearly observed from Table 3 that the  
Figure 11: Measured and computed water level hydrographs at various positions for the wet-bed by [PERSON] et al.