Numerical investigation of the impacts of extreme storm waves on coastal erosion in Hujeong Beach using XBeach model

Abstract

The east coast of Korea occasionally suffers from the extreme storms developed by the winter time extratropical cyclones in the East/Japan Sea. The damages from these storms are not only due to strong winds but also due to high waves that cause severe coastal erosions. In October, 2006, storm waves were observed higher than 6 meters, the highest record in the past 15 years. In this study, we performed a numerical experiment to predict possible erosion rates by simulating the 2006 storm condition in Hujeong Beach as this area is listed as one of the sites that have highest waves among the beaches along the east coast of Korea. For this we employed XBeach nearshore process model because it is specifically designed for the computation of coastal response during time-varying storm conditions. For XBeach modeling conditions, we also used SWAN model to calculate wave parameters based on the observations during the 2006 storm event. The grid spacing is set as fine as 5 m to resolve the minute changes in the nearshore region where seabed topography is complex due to sand bars. We ran XBeach for 48 hours during which the wave height at Hujeong Beach increased from ~1 to ~7m in the first 20 hours. The results show that the shoreline is retreated ~10m on average during the storm period. However, the erosion becomes more severe with maximum retreat of ~30m at the mouth of a stream where the original beach elevation was relatively lower. The eroded sediments are then cumulated outside the swash zone, which shows that the sand is conserved in the shallow region between the coastline and the sand bars. However, some of the crests of the sand bars are lost to offshore, indicating that total sand in the whole nearshore region may not be conserved under this high wave conditions.