利用持久性散射體合成孔徑雷達干涉技術與數值模型探討台北盆地地下水引起的地表變形與水力參數

Abstract

Taipei basin is located in the northern Taiwan. In the historic records of groundwater level, it reveals that groundwater was overexploited in 1950s and has risen since the prohibition by government in 1970s. As for last decade, groundwater level change shows a high correlation with short-term ground surface deformation. In this study, we apply PSInSAR technique to detect land surface deformation by using 29 Cosmo-Skymed (CSK) satellite images in a period from 2011/5/21 to 2015/4/2. The result shows a basin-scaled uplift during the whole period, however, the time-series also indicate that the basin went through a subsidence stage and a following uplift stage. With the land deformation information, this study further make the comparison with groundwater level data and extract the elastic storage coefficients (Ske) for each well. The evaluated Ske values in confined aquifer are ranged from 4.2×10−4 to 8.91×10−3. Then, we integrate the Ske values and PSInSAR data into the estimation of groundwater maps and storage variations under two periods: reduction period (2011/12/27~2012/8/11) and recovery period (2012/8/11~ 2013/2/19). Taking the advantage of high density of PS points, the spatial uncertainty can be reduced and the volume of water expelled in the extraction period can be quantitatively evaluated. The estimated storage loss in the reduction period is about 1.6 million cubic meters. The estimated storage variation result indicate that the study area is generally featuring elastic behavior with no severe storage loss after the reduction-recovery cycle, but there are still a little regions with slight storage loss that we can pay attention to. Furthermore, based on the referenced hydraulic head map achieved from numerical model through MODFLOW, we integrate the estimated Ske values and observed deformation derived from PSInSAR to retrieve the groundwater level map in specific date through whole basin. Note that the hydrogeological conceptual model is based on deep drilled borehole data and horizontal grid sizes 500×500 meters are adopted. The observed groundwater level data in March 2012 is adopted in steady-state calibration.