Recently, because of the influence of climate change on sea level change, there has been growing concern regarding the erosion of beaches, which play a role in reducing the damage caused by coastal disasters. However, despite these concerns, a comprehensive understanding of the morphodynamic relationship between hazard factors and beach erosion is still lacking. Therefore, in this study, a vulnerability analysis of beach erosion was conducted by applying the shoreline response model (SLRM) of bulk model type, which identifies the physical characteristics of relevant coefficients based on the suspended sediment movement processes. To characterize wave energy incidence, storm wave scenario modeling and extreme wave analysis were conducted using wave data of 40 years on the east coast of Korea provided by the National Oceanic and Atmospheric Administration. A dimensionless mathematical function representing the storm wave scenario was proposed as a function of the peak wave height. In addition, to examine whether the beach vulnerability curve (BVC) obtained from the SLRM is valid, it was compared with the long-term shoreline observation data conducted at Maengbang Beach. For the past 9 years, sand sampling and shoreline observations were performed at Maengbang Beach about 5 times a year. However, since observations were performed in time intervals of several months, the direct comparison with model results was impossible, so a comparative analysis through statistical analysis of shoreline variability was performed. The variability of the shoreline for each reference point followed a normal distribution with a standard deviation of approximately 7.1 m. As a result of comparing the BVC results obtained from these statistical characteristics with those obtained from the model, significant similarity was shown in the high wave condition. Finally, the model was performed on two factors (mean wave height and peak wave height) which appear in SWSF and three factors (wave energy at breaking point, beach response factor and beach recovery factor) which appear in SLRM, and by analyzing the results, an approximate formula for the BVC is derived. This novel BVC approximation equation provides an intuitive understanding of the factors that affect beach vulnerability as well as their importance, and estimates the beach buffer section required to prevent coastal facilities from being damaged by erosion during a specific period. The results of this study can help limit reckless coastal development and mitigate erosion damage.

Dean's equilibrium beach profile formula was used to investigate the correlation between the static shoreline position and the incident wave energy. The effect of the longshore sediment transport was neglected, and the results showed the reasonable agreement compared with the field observations of Yates et al.(2009)

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1. 서 론 연안에서 빈번히 발생하는 침식문제가 사회적 이슈로 크게 대두되고 있으며, 이를 예방 및 방지를 하고자 모니터링 및 침 식저감 기술의 필요성이 증대되고 있다. 이러한 연안침식관리 문제를 해결하기 위해서는 해안수리학 및 표사특성을 고려한 공학기술 분야의 연안침식 방지기술 개발뿐만 아니라, 목적에 따른 해안선의 개념 정립이 필요하다. 현재 연안침식 대응기술 개발(MOF, 2018) 및 연안침식 대응정책의 개선방안 연구(KMI, 2017) 등의 연구를 통해 침식 대응정책이 제도 및 정책부문 개 선을 통한 중장기 정책 수립, 대응 조직별 역할 강화, 토사종합 관리 시행 등을 제시하였다. 하지만 이는 연구의 필요성과 방향 성에 대한 내용이 주로 이루고 있는 실정이다. 또한, 해빈과정 의 해안선 변화에 관한 실험적 연구(Son and Lee, 2000), 해안선 변형 예측에 대한 수치모델 연구(Park et al., 1993), 후포해빈에 서 해안선의 장기변화 및 전연안표사량의 추정(Park and Lee, 2007), 부산 송도해수욕장의 해안선변화 특성 분석(Kim and Yoon, 2010) 등 연구가 진행되어 있지만, 해안선 관리를 위한 목적별 해안선이 정리되어 있지 않다. 해외사례를 살펴보면 영국에서는 해안을 25개로 구분하고 중 장기 해안선변화에 따라 4가지 관리정책(무간섭, 후퇴방호, 유 지방호, 전진방호) 중 하나를 채택하는 해안선 관리계획을 수립 하고 시행중에 있으며, 이 외에 미국, 영국, 호주, 유럽연합(EU) 등 선진국에서는 해안관리의 목적별로 해안선을 설정하고 이를 기초로 설계 및 정책을 수립하고 있다. 이와 같이 선진국에서는 자국의 해안을 관리하기 위해 목적별 해안선을 정립하여 다양 한 분야에 활용하고 있다. 미국은 현재 약 23개주에서 연안관리선 규정을 가지고 있 으며, 플로리다의 경우 해안선과 연안육역개발통제선(Coastal construction control line, CCCL) 사이에 연안후퇴선(Beach setback line)을 설정하여 개발을 제한하는 완충구간을 두고 있 으며, 노스캐롤라이나 주는 해양금지법(Oceanfront setback law) 을 통해 해역을 관리하고 있으며 적용 해역은 연평균 침식률이 나 개발계획을 고려하여 지정하며 관리해안선 설정시 기준선이 ABSTRACT:The average coastline and the erosion control line introduced as the management coastline, and the average shoreline (MSL) was established from the observed coastline. Also, the median grain size and the wave height of 30-years return period were applied. The erosion control line (ECL) was established through the model, HaeSaBeeN. These two lines set the coastline for evaluation. Based on the observed monitoring data along the coastline, the 1-day variation according to the normal distribution was used to estimate the regional variation, and the width of the erosion was calculated by applying the median grain size (  ) and the wave height of 30-years return period through the high-wave coastal erosion width model, i.e., HaeSaBeeN.This is an open access article distributed under the terms of the creative commons attribution non-commercial license (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Recently, the impacts of short-term erosion caused by storm waves on coastal damages are increasingly recognized as social issues, compared to those of long-term erosion from climate change or coastal development. The erosion caused by the storm wave has an episodic characteristic that the shoreline recovers gradually after retreating for a short-term. Furthermore, if shoreline changes caused by longshore sediment transport are not taken into consideration, the shoreline position is determined by following two physical parameters based on the bulk response model. The beach response factor determines converging ultimate erosion on the assumption that incident waves constantly affects a beach, which can be estimated according to the concept of Dean’s profile. On the contrary, the beach recovery factor affects the velocity of the shoreline retreat and recovery. Therefore, the parameter plays an important role to predict the peak erosion due to the storms. However, there are still insufficient researches to utilize it as an engineering design for erosion reduction. In this study, the two methodologies (i.e., approximation formula and statistical analysis) that estimates peak erosion width caused by the storms are compared to extract the beach recovery factor. During the process, it is confirmed that peak wave height has little impact on the beach recovery factor. Instead, it is mainly determined by the median grain size. Also, the beach recovery factor is estimated as a function of median grain size based on the shoreline and sand survey data conducted over ten years. Among the 41 surveyed sites along the east coast, 11 sites of straight-type shorelines that directly react to the incident waves were applied to consider only the short-term recovery process. To prove validity, the estimated applied into the real sea and then the results were compared to the shoreline data extracted from CCTV images. Using these results, the peak erosion width for a target wave event can be predicted with only median grain size. These study results are expected to be used as a concrete and practical means to manage the coast, in preparation for the current and future shoreline erosion threats.