Land subsidence of Jakarta (Indonesia) and its geodetic monitoring system

Jakarta is the capital city of Indonesia with a population of about 10 million people, inhabiting an area of about 25 x 25 km. It has been reported for sometime that locations in Jakarta are subsiding at different rates. Up to the present, there has been no comprehensive information about the characteristics and pattern of land subsidence in the Jakarta area. Usually land subsidence in Jakarta is measured using extensometers and ground water level observations, or estimated using geological and hydrological parameters. To give a better picture about land subsidence, geodetic-based monitoring systems utilizing leveling and GPS surveys have also been implemented. The land subsidence characteristics of Jakarta and its surrounding area are investigated using data from three repeated leveling surveys performed in 1982, 1991, and 1997, and two repeated GPS surveys conducted in 1997 and 1999. Leveling surveys detected subsidence up to about 80 cm during the period of 1982-1991, and up to about 160 cm during the 1991-1997 period; while GPS surveys observed subsidence up to about 20 cm during the period of 1997-1999. Comparison with the hydrological data shows that land subsidence in Jakarta is strongly related to excessive groundwater extraction.