Monitoring of Recovery Process at Yeongildae Beach, South Korea, Using a Video System

Abstract

Once a beach is eroded by storm waves, it is generally recovered under milder wave conditions. To prevent or reduce damage, it is therefore important to understand the characteristics of the site-specific recovery process. Here, we present the results, based on a data set from a video monitoring system and wave measurements, of the recovery process in a pocketed beach located inside a bay where the shoreline retreated harshly (~12 m, on average, of beach width) during Typhoon TAPAH (T1917) in September 2019. It took about 1.5 years for the beach to be recovered to the level before the typhoon. During this period, the erosion and accretion were repeated, with the pattern highly related to the wave power (Pw); most of the erosion occurred when Pw became greater than 30 kWatt/m, whereas the accretion prevailed when Pw was no greater than 10 kWatt/m. The recovery pattern showed discrepancies between different parts of the beach. The erosion during storm events was most severe in the southern part, whereas the northern shoreline did not significantly change even during TAPAH (T1917). In contrast, the recovery process occurred almost equally at all locations. This discrepancy in the erosion/accretion process was likely due to human intervention, as a shadow zone was formed in the northern end due to the breakwaters, causing disequilibrium in the sediment transport gradient along the shore. The results in this study could be applied in designing the protection plans from severe wave attacks by effectively estimating the size of coastal structures and by correctly arranging the horizontal placement of such interventions or beach nourishment. Although the application of these results should be confined to this specific site, the method using wave energy parameters as criteria can be considered in other areas with similar environments, for future planning of beach protection.

Table_1.xlsx

“…The temporal scale of the recovery process has not been estimated in Bonggil Beach yet. However, a similar observation was made in Yeongildae Beach that is located ~35 km north of Bonggil Beach (Oh et al, 2021), in which it took ~1.5 yrs for the shoreline of the beach to be recovered back to the level before the time of Typhoon Tapah's attack. Considering that Yeongildae Beach is located inside a bay, and thus the damage by Tapah was smaller than that in Bonggil Beach, it is likely that Bonggil Beach was still in the recovery process when Typhoon Mysak and Heishen affiliated the site in 2020, which was also clear from the profile measurement in Figure 5B.…”

“…For example, the data measured by a video monitoring system confirmed that the shorelines in another beach in the eastern coast of the Korean Peninsula (i.e. the beach with similar wave conditions with Bonggil Beach) significantly changed when the storm waves with maximum H s lower than 4 m attacked the site (Oh et al, 2021). This unusual phenomenon was likely related with the recovery process.…”

“…One of the other factors to consider was the wave propagation direction. Although the amount of total sediment transport depends on the wave power that is contributed by the wave height and period (Oh et al, 2021), the ratio between the cross-shore and longshore transport may be related to the wave direction, and it can result in the locality of erosional process, especially in the beaches with complex geography such as Bonggil Beach. The results in Figure 4 show that the waves were approaching the shore in E direction (~82°) consistently for ~3 days during Tapah.…”

“…Therefore, it is necessary to develop measures and plans to mitigate the damage by coastal erosion based on proper risk assessment. These assessments and measures should be carefully set up because the impact by coastal erosion is site-specific due to characteristic conditions in a coastal area and sometimes shows locality even within the same area due to the loss of equilibrium by various factors (Oh et al, 2021). Accurate analysis of sediment transport patterns is, therefore, a prerequisite to developing such measures for the site.…”

Numerical Simulation of the Locality of Erosional Damages by Storm Waves in Searching for Measures to Conserve Bonggil Beach, Korea

“…Therefore, it is necessary to develop measures and plans to mitigate the damage by coastal erosion based on proper risk assessment. These assessments and measures should be carefully set up because the impact by coastal erosion is site-specific due to characteristic conditions in a coastal area and sometimes shows locality even within the same area due to the loss of equilibrium by various factors (Oh et al, 2021). Accurate analysis of sediment transport patterns is, therefore, a prerequisite to developing such measures for the site.…”