Subsidence : Semarang City (1 October 2009)

Land Subsidence Spatial Model “Subsidence Vulnerability Index” and JERS Data for Semarang Coastal City – Indonesia

A. Hartoko*, A. Wirasatriya*, M. Helmi*, B. Rochaddi* and J.T. Sri Sumantyo**
*) Spatial Database, Marine Geomatic Centre, Faculty of Fisheries and Marine Science, University of Diponegoro, Indonesia e-mail : agushartoko@yahoo.com
**) Josaphat Microwave Remote Sensing Laboratory, Center for Environmental Remote Sensing, Chiba University, Japan e-mail : jtetukoss@faculty.chiba-u.jp

Several natural phenomena that can latter become natural disaster in our daily life are phenomena of flood, tide water-flood, land-slide, mountain eruptions, tsunami, etc. While specific natural phenomena happened at Semarang city is coastal land subsidence. This specific phenomena has wide implications to the city infrastructures such as the road, drainage system, port and harbor, residential zones, airport, electri-plant zone, business and government buildings, etc. The research done based on field measurement on land contour and land height measurement since 2006 – 2009 at 60 land-height position set by Bakosurtanal (TTG-Bakosurtanal/ Height Control Point) and some other Bench Mark (BM) in Semarang city, supported with its coordinate positioning by D-GPS. Geodetic data collected was then transformed into numeric data, and then processed into spatial layer by geo-statistic method – Kriging. Another spatial data used is Shuttle Radar for Terrain Model (SRTM), JERS (1993 – 1997) and IKONOS on Semarang city for 3D-image analysis, and Landsat ETM. Spatial coastal land-subsidence model was built based on field measurement data, while “Spatial Coastal land Subsidence Vulnerability Index” (SC_SVI) has been built based on parameters of distance from coastal line; land-slope; distance from river estuary, using Arc-GIS software. Based on field data measurement and series of spatial plot revealed that subsidence-rate at Semarang City ranged from 1 – 9 cm/year. SC_SVI model had been validated using the field (actual) land subsidence control point. As consequence of the phenomena therefore the city need re-mapping and evaluation on the Spatial Zoning was inevitable.