## 3 Results and Discussion of the Physical Experiment  
### Wave Overtopping  
The target area is densely populated with skyscrapers just 20 m from the shoreline. In addition, this area is a place that many tourists visit. For this reason, it is necessary to not only secure the right view at normal times but also to prevent wave overtopping caused by storm surges. In order to cope with wave overtopping, a movable barrier was designed for the target site. As shown in Figure 5 and Table 2, experiments were conducted for eight cases by changing the water depths and the test waves with standing or non-standing barriers. Figure 7 shows photographs taken when the water surface elevation was at its maximum, and Table 3 shows the results of the measured overtopping discharge. Figure 7a shows that a large amount of water is overtopped, even though the return period is 10 years. The allowable overtopping discharge is 0.01 m\({}^{3}\)/(m s) for areas crowded by private houses and public facilities in the hinterland, where serious disasters are expected because of the inflow of overtopped water and sprays [22]. Figure 6: Spectrum of the test waves measured at E9 to E11 in Figure 2a; (**a**) approx. highest high water (H.H.W.) and a 10-year return period; (**b**) sea level during a storm surge with sea level rise (SLR) and a 50-year return period. The overtopping discharge at a full scale is 0.03 m\({}^{3}\)/(m s), as shown in Table 2. The result of this case is greater than the allowable limit, despite the minimum value among the test cases for the non-standing barrier. Thus, for this case, the movable barrier must stand to prevent wave overtopping. As shown in Figure 7b, two bullnoses on the movable barrier were designed to efficiently reflect the incident waves to the seaside. Although stairs perform this role well, the overtopped water can still be seen because of the large incident wave condition. However, the overtopping discharge at a full scale is 0.0099 m\({}^{3}\)/(m s), which is less than the allowable limit. The developed movable barrier properly prevents wave overtopping for the designed wave with a 50-year return period. The wave energy for the 50-year return period is higher than that for the 10-year return period. As shown Table 3, for the approx. H.H.W., the relative overtopping discharges (i.e., \(\text{q}_{\text{standing}}\)/\(\text{q}_{\text{non-standing}}\)) for the 10-year return period and the 50-year return period are zero and 0.0349, respectively. This implies that the overtopping discharge increases when the wave energy increases. This result is also the same for the sea level during the storm surge with the SLR. All overtopping discharges are less than the allowable limit for the standing barrier. In order to cope with wave overtopping more efficiently, it is necessary to properly design energy dissipators on the movable barrier, such as wave return walls [23] or stepped revertments [24], to reduce the height of the barrier. Reducing the height of the barrier would be excellent in terms of utilizing the surrounding space and view. The overtopping discharge of the movable barrier is now compared with the prediction equation for the overtopping discharge of the composite vertical wall proposed by EurOtop [3]. The composite vertical wall is the most similar comparison target in the EurOtop manual, even though T.T.Ps are