Mapping of land subsidence induced by groundwater extraction in urban areas as basic data for sustainability countermeasures

Estimation of land subsidence induced by groundwater extraction has been observed by some researchers using field instrumentation as well as a spatial mapping technique. Among six Asian cities previously studied (Bangkok, Jakarta, Manila, Osaka, Seoul, Taipei, and Tokyo), the rate of land subsidence in Jakarta is the highest in the period from 1900-2010. In order to improve the applicable monitoring system and obtain comprehensive results for subsidence measurement, tools for raising the government's and society's awareness of subsidence are needed. This paper aimed to determine a benchmark and perform an analysis of sustainable counter measures for land subsidence induced by groundwater extraction in the urban areas of Jakarta city, using a continuous monitoring system and integrated data management system. Land subsidence was measured using field monitoring techniques, such as an extensometer, a leveling survey (global positioning system,GPS; geodetic measurements), and observation wells; this was conducted in some locations in north Jakarta from 1990-2016. The results from the visual observation identified an average land subsidence rate of 1.65 cm/year, while the GPS geodetic measurements ranged from 0-12 cm/year. Monitoring from seven extensometer sensors installed in different borehole elevations revealed subsidence of 0.66 cm on average. Meanwhile, the groundwater surface level ranged from 0.6 m to 44 m from the surface, with the deepest being in the area of Bintaro, South Tangerang. Data analysis was conducted using a computer simulation to investigate the inter-connection between land subsidence and groundwater extraction. Consequently, land subsidence was found to have a strong association with groundwater extraction. Integrated data management systems, including data sharing, are needed to improve the appropriate monitoring system of land subsidence in Jakarta.