# Monitoring of Recovery Process at Yeongildae Beach, South Korea, Using a Video System
## 4 Discussion
During the recovery process after October 2020, however, the imbalance between the two ends was reduced, and the shoreline was advanced almost equally at all parts--southern, middle, and northern--of the beach. The reason for this is still unclear, but the northern end could be protected from erosion due to the shadow zone formed by the breakwaters of Duho Port, in which the wave energy was attenuated, especially when the high-powered storm waves attacked the site. In the southern end, the breakwater of Pohang Port does not form a shadow zone, considering that most of the waves approached from the NE or NNE, as shown in Figure 3b. Figure 9c also shows that the propagating direction of waves during Typhoon TAPAH (T1917) or other storm waves ranged from 50\({}^{\circ}\) to 60\({}^{\circ}\), which confirms that the damage by storm waves could be focused on the southern part of the beach. In contrast, the recovery process occurred under milder wave conditions, by transporting the sediments equally at all parts of the beach. However, there was a possibility of alongshore sediment movement from the southern part to the middle and northern areas. As shown in Figure 8c, \(\left\langle y\right\rangle_{s}\) decreased but \(\left\langle y\right\rangle_{m}\) and \(\left\langle y\right\rangle_{n}\) increased during the period just after TAPAH (T1917), as marked with the grey circle. This locality of different shoreline evolution processes implies that the sediments could be transported in the longshore direction from the south to the north. The results of this study can be usefully applied in designing the protection/prevention plans against damage to the beach and nearby coastal areas, not only from the disastrous storm events but also from the processes that may break the equilibrium in the beach status. For example, the suggested criteria that could determine the erosion/accretion conditionscould be useful in planning coastal structures. The size of these structures can be effectively estimated if information on the wave conditions that affect the erosion or accretion in this specific site is known in advance. If the size of such a structure is too large, it may be cost-ineffective. In addition, the beach recovery process could be disturbed if the structure reduces too much wave energy; in this case, the minimum power required for accretion cannot be met. Similarly, the structure would not correctly function if its size is too small to reduce the wave power below the criteria for erosion. The information on the locality in the shoreline evolution process could be also useful in planning hard and soft coastal structures. If the longshore transport from the southern to the northern part is quantitatively understood (although it has not been done in this study), structures such as groins can be designed to reduce the loss of sediment in specific areas. In addition, the results of the locality analysis in this study would be useful in planning beach nourishment--in determining where to put the sand to maximize the effect of the beach fill by considering the imbalance in the beach process. For example, beach nourishment and placing some coastal structures have been planned in the study area, although they have not been finalized. The results of this study are, therefore, expected to provide useful information in determining such plans, to maximize the effect of the structures and nourishment. It should be noted that the results from this study are confined only to this specific site. This small beach is characterized as a pocketed beach, where the sediments cannot be added from or lost to other coastal cells. In addition, the beach is located inside a bay, so the waves are usually attenuated when reaching the study site such that the shoreline can reach equilibrium under lower wave energy compared to beaches on the open coast. Figure 11 compares the wave power between Yeongildae Beach (8.5 m depth) and Hwajin Beach (32.0 m depth), located ~20 km north of Yeongildae Beach.