2.4 STUDY AREA
Korea has long coastlines and various coastal terrains, as it is surrounded by the sea on three sides. According to recent data, the lengths of the coastline for the western, southern, and eastern coasts of South Korea span approximately 4,900, 3,300, and 600 km, respectively (Ministry of Oceans and Fisheries, 2003). The west coast has numerous bays, peninsulas, capes, and islands due to the crooked and broken coastline. In particular, a ria coast is developing in the coastal areas of the Dadohae and Taean Peninsula, where the coastlines are extremely crooked. Furthermore, this is also a place where numerous soils of terrestrial origin are transported and deposited owing to the gentle the terrain slope, severe tidal differences, and the flow through of Korea’s great rivers. Consequently, large tidal flats develop along the west coast, and low hilly mountains or large and small coastal plains are distributed inland.
Among the sea areas under the influence of seawater intrusion in South Korea, this study targeted the western coast with severe tidal differences, where the coastline is long, and the terrain slope is gentle. The selected study area was a coastal area of the inland, excluding islands in the north, where urban areas are concentrated on the western coast of South Korea. The study area consists of nine administrative districts: Incheon, Asan, Ansan, Gimpo, Hwaseong, Siheung, Pyeongtaek, Dangjin, and Osan. In all of these nine areas, the manufacturing industry is developing and urbanization is accelerating, and there is a continuous influx of population. Incheon is the third-largest city in terms of population in South Korea after Seoul and Busan, and has a developed logistics industry as it hosts the Incheon International Airport and Incheon Port. Ansan is a planned industrial city, where a population of a similar size to the residential one flows during the day due to numerous manufacturing plants. The manufacturing industry was also developed in Gimpo, Hwaseong, Siheung, Pyeongtaek, Dangjin, and Osan. There is Sihwa Lake Seawall in Siheung, Hwaseong, and Ansan, where industrial clusters and tourist attractions were developed. Daebu Island, the only island in the study area, was included in the study area because it is connected to a freshwater lake through the Sihwa Lake Seawall. The total area of the study is 3976.59 km2, and the length of the coastline is 608.1 km. The automatic monitoring data and drill logs of the National Groundwater Information Center were used to assess the seawater intrusion vulnerability of the study area. There were 58 groundwater level stations in total. Further, seawater levels were observed at nine seawater level stations. Figure 2 shows the locations of the study area, rivers, coastlines, groundwater level stations, and sea water level stations.