Monitoring Land Subsidence and its Effect on Surabaya Coastal Inundation by Utilizing GPS Campaigns Data

Land subsidence is a process of land movement based on a certain datum (geodetic reference frame) in which there are various variables causing it. This phenomenon occurs in many big cities in Indonesia, which is the city of Surabaya. The Surabaya city has a type of soil in the form of alluvial soil which is prone to movement. The accumulation of land subsidence that occurs will certainly cause its own losses. As a result, it can damage urban infrastructure so that in the future it can cause disruption to the environment, economic activities, and social life in the region. In addition, the Surabaya area is also a coastal area. Coastal areas have characteristics where this area will be strongly influenced by natural events. One of the natural events that affect the oceans and coastal areas is global temperature changes. The phenomenon of global temperature changes can affect sea level rise. If sea level rise occurs accompanied by an increase in the rate of land subsidence, this can result in flooding or inundation in coastal areas. Considering that the city of Surabaya is a metropolitan city that has a high population density and a continuous level of development, mitigation efforts are important in following up on land subsidence in this area. One of the efforts that can be applied is by conducting GPS observations. The outcomes of the GPS observations were then processed using scientific software in the form of GAMIT/GLOBK. According to the study’s findings indicated that Surabaya is experiencing land subsidence in the northern and eastern coastal areas with a range of 0.2 – 83.3 mm/year. The point that experienced a significant decline was in the border area of Tandes and Asemrowo, namely station BM35. Furthermore, land subsidence conditions influence the extent of tidal inundation, where in 2032 tidal inundation will inundate 105.411