ABSTRACT
ABSTRACT: Jakarta is the capital city of Indonesia with a population of about 9 million people, inhabiting an area of about 660 km2. It has been reported for many years that several places in Jakarta are subsiding at different rates. Over the period of 1982-1997, subsidence ranging from 20 to 200 cm is evident in several places in Jakarta. There are four different types of land subsidence that can be expected to occur in the Jakarta basin, namely: subsidence due to groundwater extraction, subsidence induced by the load of constructions (i.e. settlement of high compressibility soil), subsidence caused by natural consolidation of alluvial soil and tectonic subsidence. In addition to the levelling surveys, GPS survey methods and InSAR measurements have been used to study land subsidence in Jakarta. This paper describes the characteristics of subsidence in Jakarta over the period of 1982 to 2007 as observed by the three methods. In general land subsidence in Jakarta exhibits spatial and temporal variations, with rates of about 1 to 15 cm/year. A few locations can have subsidence rates up to about 20-25 cm/year. It was found that the spatial and temporal variations in land subsidence correlate with variations in groundwater extraction, coupled with the characteristics of sedimentary layers and building loads above it. The observed subsidence rates in several locations show a positive correlation with known volumes of groundwater extraction. However, the relative magnitude and spatial variability of the effect of groundwater extraction on land subsidence in the whole Jakarta basin is not yet fully understood. In the coastal areas of Jakarta, the combined effects of land subsidence and sea level rise also introduce other collateral hazards, namely the tidal flooding phenomena.
