# Monitoring of Recovery Process at Yeongildae Beach, South Korea, Using a Video System
## 3 Results
### Locality in the Erosion/Accretion Process
In particular, the extreme \(L_{t}\) values (\(<\!-\!3\)) occurred when TAPAH (T1917) afflicted the beach. This pattern of \(L_{t}\) distribution indicates that the shoreline was more severely eroded in the southern part of the beach, compared to that in the northern part, when storm waves attacked the site. In Figure 9c, the distribution of wave direction, \(D_{p}\), is also plotted in terms of \(L_{t}\). The \(x\)-axis denotes the wave propagation angles, which increase clockwise from the origin (0\({}^{\circ}\)) at the north. Therefore, 45\({}^{\circ}\) and 90\({}^{\circ}\) denote the NE and E, respectively. The high-powered waves generally approached the beach from \(\sim\)NE. In the case of Typhoon TAPAH (T1917), the wave propagation direction ranged between 50\({}^{\circ}\) and 60\({}^{\circ}\). Considering the shoreline in Figures 1c and 3a, the storm waves during the typhoon directly attacked the southern part, with a slight slope from the normal direction, whereas a shadow zone was likely formed in the northern part of the beach due to the breakwaters of Duho Port. The discrepancy in the erosion/accretion pattern between the southern and northern parts of the beach can be also observed in the plane view of shoreline changes. In Figure 10, the beach widths of all 34 baselines are compared at three different times, as they correspond to the times of T1, T2, and T3 in Figures 6 and 7. The figure clearly shows that the reduction  
Figure 9: Distribution of (**a**) wave power, (**b**) probability of occurrence, and (**c**) wave propagation direction in terms of \(L_{t}=\int(\partial y/\partial t)dx\). The red circles in (**a,c**) mark \(P_{w}\) and \(D_{p}\) for Typhoon TAPAH (T1917), respectively. in the beach width from T1 to T2 was greatest in the southern end (# of baseline \(<\)6), where the maximum reduction distance along baseline #2 was \(\sim\)40 m. In contrast, the beach width in the northern end (# of baseline \(>\)28) was not significantly changed from T1 to T2, as the maximum change in the beach width was no greater than 5 m along baseline #29. At the baselines higher than #30, the change was minimal and not observed. During the recovery process from T2 to T3, the beach width increased at most of the baselines. However, the locality is also clearly observed, as its magnitude at T3 was smaller than that at T1 for the baselines #2-#20, indicating the shoreline was not fully recovered to the level before the typhoon attack in the southern part of the beach. In contrast, the beach width at T3 was greater than that at T1 for the baselines higher than #28. This result indicates that the shoreline in this northern area was not eroded significantly during the attacks of storm waves but advanced under milder wave conditions, leading to an accretion of the shoreline in general. In the present study, the wave data were measured in location M1, which led to the assumption that the wave conditions were uniform along the coast of the beach. Therefore, alongshore variation of sediment transport caused by the spatial difference in the wave conditions could not be detected using the present data sets. As described, the locality in the results was induced by the shadowing by breakwaters and the curved shoreline, which might produce alongshore discrepancies in the shoreline evolution pattern, as implied from the locality parameter, \(L_{t}\), in Figure 8d. The impacts of alongshore variation of wave conditions can be established, in future studies, by employing an array of wave gauges in the longshore direction.