# Video Monitoring of Shoreline Positions in Hujeong Beach, Korea
## 4 Results
Figure 10 shows another example of significant shoreline change between the beginning and end time of T4 (13 March to 15 August 2018), when \(A_{b}\) decreased \(\sim\)19%. The shoreline was generally retreated along the entire coast, but the reduction in \(y_{t}\) was particularly greater at L2 and L4. As shown in Figure 9, the shoreline accretion at L1 and L2 during T3 was due to the nearshore sandbars. Therefore, the shoreline retreat at the corresponding locations might also be related to the sandbars, which could occur when the sandbar development became weaker during T4. It should be noted that the wave conditions in T4 can be distinguished from those in periods T1-T3. The wave conditions in T4 were generally similar to those in T3 because the wave energy was moderate as \(\sim\)10% of \(H_{w}\) was higher than 2 m. However, compared to the other cases, \(D_{w}\) spread in wider angles, showing that the waves were approaching in various directions. Interestingly, \(\sim\)20% of \(D_{w}\) were SE and ESE, and this indicates that the waves approached parallel to the shore from the south. These shore-parallel waves might significantly affect the shoreline changes by transporting the sediments along the shoreline regardless of the relatively low wave energy (\(H_{w}\) < 1 m). Figure 10: Same comparison as that in Figure 6 but measured at the beginning (13 March 2018) and end (15 August 2018) of T4. Figure 9: Seabed elevation changes in Hujeong Beach between 18 November 2016 (before T1) and 12 March 2017 (after T1). The figure is taken from [17]. One evidence on the longshore transport of the sediments near the shore during T4 is found in Figure 11, in which the Google images near L1 and L2 are compared at two times, on 3 March 2018 (T4) and 20 April 2018 (T4). The two times of the captured images belong to the early stage of T4, and they could provide an implication of the littoral process in this period. In Figure 11a,b, the yellow lines mark the positions of the two sandbars as they were drawn to connect the horns and bays of the sandbars. Therefore, these lines compare the orientations of the sandbar development at the two times separated by \(\sim\)1.5 months. On 3 March 2018 (T4), the direction of the yellow lines was generally normal to the shoreline. On April 20 (T4), however, the lines were inclined to the north and the angle deviated from the shore at normal direction was \(\sim\)40\({}^{\circ}\). This indicates that the sediments piled in the sandbars moved to the north due to the shore-parallel waves, which resulted in the sandbar migration along the shore. This migration of sandbars might break the equilibrium status of the out-of-phase coupling of the bars with the shoreline. Thus, the shoreline advance at the corresponding locations of the sandbar horns during T3 became weaker, which might lead to the flatter shoreline at the end time of T4. At L4, where there is a rocky island instead of sandbars, the shoreline was also significantly retreated probably due to the same shore-parallel waves that carried the sediments along the shore, regardless of the shadowing effect of the island.