## 3 Results and Discussion of the Physical Experiment
### Uplift Pressure and Wave Pressure  
In this section, the uplift pressure and the wave pressure acting on the movable barrier are analyzed to confirm the occurrence of impulsive pressures. Barriers should be in the \"standing state\" for all cases, considering the results of the wave overtopping in Table 3. However, the uplift pressure is measured on the assumption that the designed sea level is the approx. H.H.W. and that the barrier will not stand during the 10-year return period in this section. A non-standing barrier is important to analyze the uplift pressure acting on the bottom of the barrier. An impact on the bottom of the barrier occurs when a large incident wave propagates to the barrier. For this reason, the movable barrier can be broken, making the hinterland more dangerous. Figure 10 shows the result of the uplift pressure at p\({}_{4}\) in Figure 5a for the 10-year return period and the approx. H.H.W. (No. 1, Table 2). The y-axis is the uplift pressure nondimensionalized by the hydrostatic wave pressure for the maximum wave height, H\({}_{\text{max}}\). The maximum wave height is 19.5 cm. The total generation time is 30 min. This figure shows results in the range around the maximum pressure. Relative uplift pressures greater than 1 occur about 20 times during the total generation time. The maximum relative uplift pressure is 2.12, as shown in Figure 10. This means that the impulsive pressure acts on the bottom of the movable barrier. The impulsive pressure is inversely proportional to its duration. The impulsive pressure becomes especially higher when the incident wave height increases, and the distance between the water surface and the horizontal structure (i.e., non-standing barrier) decreases. If the weight of the movable barrier is increased to secure the barrier's stability, additional ground reinforcements on the target site may be needed. However, adding such reinforcements is difficult and costly work. To ensure stability, three options are possible: (1) The movable barrier could be installed closer to the landslide to avoid impulsive pressure from acting on the bottom of the non-standing barrier; (2) the distance between the water surface and the non-standing barrier could be increased; (3) the number of armor units could be increased at the seaside to reduce the wave's energy. The movable barrier stands by the rise of the sea level and the wave overtopping during storms, which is needed to determine the wave pressure acting on the movable barrier facing the outer sea in an abnormal state. Figure 11 shows the results of the wave pressure at p\({}_{4}\) and p\({}_{5}\) in Figure 5b for the 50-year return period and the sea level during the storm surge with the SLR (No. 4, Table 2), because the maximum wave pressure acting on the movable barrier is important in terms of a design perspective. The maximum wave height of the y-axis is 23.4 cm. Relative wave pressures greater than 2 occur four times during the total generation time. The maximum relative wave pressures at p\({}_{4}\) and p\({}_{5}\) are 3.84 and 3.50, respectively. Furthermore, it can be seen that the maximum impulsive pressures  
Figure 9: Comparison of the relative overtopping discharge between the measured data and the prediction equation suggested by EurOtop. continuously occur from p4 to p5, with a time difference of 0.01 s. As the result of this experiment, the movable barrier should be designed while considering impulsive wave pressure. To avoid the impulsive pressure for the standing movable barrier, a slit structure needs to be installed under the movable barrier, and the number of armor units should be increased to the seaside to reduce the wave energy. An impulsive wave can be of a Wagner type or a Bagnold type [25; 26; 27]. The impulsive pressure of the Wagner type shows a momentary peak and is caused by the direct impact of the water mass. The impulsive pressure of the Bagnold type has two characteristics: (1) A vibration occurs after the peak; (2) air pockets are created by being entrapped by the breaking wave.