MAPPING OF LAND SUBSIDENCE CHARACTERISTICS BASED ON INTEGRATION OF GEODETIC OBSERVATIONS AND ESTIMATION OF ECONOMIC LOSSES DUE TO THE LAND SUBSIDENCE IMPACTS (CASE STUDY: BANDUNG BASIN)

• Main Author: GUMILAR (NIM : 35108004); Pembimbing : Prof. Ir. Hasanuddin Z. Abidin, M.Sc., Ph.D; Prof. Ir., IRWAN
• Format: Dissertations
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/18729
• Institution: Institut Teknologi Bandung

Land subsidence has occured in many big cities around the world, including several cities in Indonesia. General causes of land subsidence are excessive groundwater extraction, building load, natural compaction, and also tectonic process. Land subsidence can yield direct impact (i.e. damage to buildings, roads, and bridges) and also indirect impact i.e. expansion of flooded area which potentially can cause economic losses. Land subsidence phenomena can be monitored and estimated using geodetic methods such as leveling and GPS Global Positioning System) surveys as well as Interferometric Synthetic Aperture Radar (InSAR) data Bandung Basin (covering the cities of Bandung and Cimahi, and Bandung District) is an area that suffers from land subsidence. Geologically, the Bandung Basin is mostly located on incompact rock. Excessive groundwater extraction from deep aquifer may eventually cause land subsidence on the ground surface. It has been widely believed that the groundwater extraction for industrial purposes is one of the main causes of land subsidence in Bandung Basin. The impacts of land subsidence are strongly indicated by the damage/cracks in buildings, roads, and bridges as well as expansion of flooding area, which is especially concentrated in southern part of Bandung. <br /> Land subsidence characteristics are closely related to the pattern and rate of land subsidence as well as its potential contributing factors, and its possible impacts. It is very useful to comprehensively understand land subsidence characteristics, since it could be valuable in determining economic losses due to the land subsidence impacts. Several relevant questions relating to mapping of characteristics land subsidence has not been answered yet, especially using integration of GPS and InSAR methods, utilization of gravity measurements, and also the estimation of economic losses. <br /> Considering the facts related to such cases, a research (dissertation) of mapping land subsidence characteristics is conducted by integrating GPS, InSAR, and gravity methods and also estimation of economic losses caused by land subsidence using Geographic Information System (GIS) technology. <br /> The results of this research show that spatial pattern and rate of subsidence derived by GPS and InSAR methods are quite similar. Several areas such as Cimahi, Gedebage, Dayeuhkolot, Banjaran, Majalaya, and Rancaekek experience the largest subsidence. Average of subsidence rate derived by GPS data during the period of 2000 – 2012 varies between 1,1 – 16,9 cm, while those derived by InSAR method varies between 0,9 – 17 cm per year in the period of 2006 – 2010. GPS and InSAR data integration with weighting concept yields better spatio-temporal characteristics. During the period of 1999 to 2010, maximum rate of land subsidence in the Bandung basin reached 2 meters which occurred in industrial areas such as in Cimahi, Katapang, Dayeuhkolot, Gedebage, and Rancaekek. There is a strong correlation between the land subsidence and groundwater extraction in Cimahi, Dayeuhkolot, Majalaya, dan Rancaekek. Result from gravity observation indicate that lowering of groundwater level has occurred in Cimahi with the rate about 1,79 m/year. Furthermore, there could also be possible existence of other causes due to natural compaction in almost all subsidence areas and tectonic processes in Dayeuhkolot, Gedebage, Cimahi, dan Majalaya. <br /> Result of field validation shows that land subsidence causes direct impacts in forms of damage/cracks in buildings, sloping of building, damage/cracks in road and bridges especially those located at differential subsidence area. Damage to the building structures which get shorter occurs in regions that has large subsidence. The most damaged areas are Cimahi, Kopo Katapang, Dayeuhkolot, Sapan, Solokan Jeruk, Majalaya, Buahbatu, Rancaekek, and Gedebage. In addition, land subsidence causes spreading of flooding area in the southern part of Bandung. Direct losses due to the land subsidence impacts reached 1,8 trillion rupiah. <br /> Flood modeling result shows that land subsidence has contributed to flooding area in 2010 around 1388 ha, which is about 21% of the total area with economic losses reaching 225 billion rupiah. The greatest losses occurred in Baleendah, Dayeuhkolot, and Rancaekek districts. Result of verification and validation show that the proposed models for flooding area and economic losses are consistent with real data derived from field observations. The economic loss due to the impact of the land subsidence in Bandung Basin in 2010 reached 2 trillion rupiah.