Monitoring of Coastline Changes in Gerokgak Sub-District In 1995-2020 Using Grid Method

Coastal areas have conditions that are under a lot of pressure from various phenomena and activities that occur both on land and sea. One of the consequences of the many phenomena that occur in coastal areas is changes in coastlines. Of the several factors that cause coastlines changes, abrasion is one of the most detrimental factors and can be categorized as a disaster because it has destructive characteristic, such as threatening ecosystems or buildings behind the coastlines. This study aimed to monitor changes in coastlines every five years within a period of 25 years as a basis for disaster mitigation analysis. After the results of the coastlines extraction were monitored, it was then generally concluded the amount of abrasion that occurs at each observation point that was made using the grid method with a distance of 500m along the coastlines in Gerokgak Sub-district. Coastline changes that occur at each point of observation are in the form of varying and not linear values, for example abrasion occurs in the first 5 years and it is possible that accretion occurs in the second 5 years. This research produces information about the point with the largest shoreline change in the form of abrasion at observation point 23 with the abrasion as far as 151.98m and the point with the change in the shoreline in the form of the largest accretion at the observation point 61 with an accretion as far as 107.07m.