GPS Monitoring Ground Subsidence Associated with Seasonal Underground Water Level Decline: Case Analysis for a Section of Taiwan High Speed Rail

Ground subsidence induced by heavy withdrawal of underground water has resulted in environmental hazard and potential risk in Taiwan, particularly in the Chuo-Shui River alluvial fan where the Yun-Lin section of the Taiwan High Speed Rail is being constructed. In this paper, seasonal effects of ground subsidence occurring in the study area are investigated. The rate of ground subsidence was estimated using a regression analysis of a series of weekly GPS height solutions. The average rate of ground subsidence in the study area over the period of 1995-2001 was 3 cm/year, with a high correlation coefficient of 0.9. Based on data collected at the piezometer, the variation of ground subsidence rate appears to be associated with an unstable underground water level, which drop gradually during winter and either remains constant or rises during summer time. As a result, ground subsidence rates vary considerably from 1.5 cm/year for the summer data to 9.0 cm/year for the winter data. The seasonal effect of the GPS height variation is borne out by correlation coefficients ranging from 0.3 to 0.7.