Land subsidence monitoring with a network of continuously operating GPS stations in Yunlin County, Middle Taiwan

Land subsidence in western Taiwan has been an issue since 1970´s due to over extraction of ground water for aquaculture. This problem became serious in Yunlin County because high-speed rail way transects the center of land subsidence which may cause safety problem. Leveling survey is applied annually. A more efficient method with 6 continuous GPS stations is used in this study to observe the subsidence. The effectiveness and advantages are compared with leveling survey and underground monitoring wells in the period from 2007 to 2012. It is concluded that the trend of the subsidence can be fully observed by the GPS network and the observation frequency of GPS prevails the annual survey of traditional approach which is an important factor for early warning purposes.