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.
SaLIS is a scientific journal devoted to reporting research and new work conducted to advance geodetic surveying, land surveying, large-scale mapping, and geographic information systems designed to advance the development and management of the cadastral parcel data layer and other land information applications. SaLIS publishes research articles, technical papers, technical notes, papers on the current state of surveying education, surveying history, book reviews, and current literature reviews. Every four years, the journal publishes the U.S. Report to the International Federation of Surveyors (FIG). The Proceedings of the Surveying Teachers Conference are published bi-annually.