Combination with precise leveling and PSInSAR observations to quantify pumping-induced land subsidence in central Taiwan

Choushui River Fluvial Plain (CRFP) is located in the western central Taiwan, where the geomaterials are composed of alluvial deposits. Because the CRFP area receives highly variable rainfall in wet and dry seasons, the groundwater becomes the main resource of residential water. The precise leveling monitoring from 1970s indicated that the coastal areas of CRFP had been threatened by serious pumping-induced land subsidence. On the basis of relatively accurate measurements of precise leveling measurements, we used cokriging technique to incorporate a number of InSAR images to quantify the surface deformation in CRFP. More specifically, the well-developed Persistent Scatterer InSAR (PSI) was employed to process 34 Envisat images (2005-2008) and the results of PSI was then used for improving the spatial resolution of data from precise leveling. The results of cokriging estimation indicate whether the rate or the area of the land subsidence slows down gradually from 2005 to 2008. The subsidence in the northern part of CRFP was influenced by the groundwater decline in aquifer III, and the southern part was influenced by groundwater decline in aquifer II and III. The cokriging estimation was also comparable with continuous GPS data, and their correlation coefficient is 0.9603 and the root mean square is 10.56 mm yr-1.