| dc.description.abstract | Choushui River alluvial fan is a severe land subsidence area due to groundwater extraction in the past decades. Although the current subsidence rate has reduced significantly, Yunlin county still has a high subsidence rate. Agricultural and industrial pumping is the main activity of groundwater use in Yunlin county, which extracts in shallow and deep aquifers. In this study, Tuku Junior High School station is a specific site to investigate the contribution of each layer compaction to the total land subsidence, and the effect of pumping in different aquifers on compaction. The finite-difference algorithm in FLAC3D software was applied to analyze the land subsidence behavior due to groundwater pumping. The predicted layer compaction will be compared to observed data in the calibration stage to verify the numerical model performance. From observation data, the compaction percentage of four aquifers from aquifer 1 to aquifer 4 is 1,1%; 20,1%; 11,9%; and 50,1%, respectively. The second and fourth aquifers contribute the most, with more than 70% of the total land subsidence. That may be due to a large thickness, a high difference in groundwater level between dry and wet seasons, and the presence of many clay-interbedded layers. The assumption of the numerical modeling would be an unlimited supply of lateral groundwater. The calibrated model suggested that the pumping rate should be less than 218 m3/day to minimize inelastic compaction at clay-interbedded layers. Pumping at aquifer 2 caused the most total land subsidence. Pumping at aquifer 1 or shallow aquifer caused more compaction on other aquifers, but pumping at deep aquifers mainly affected themselves a lot. The simulation results provide critical references to reaching an efficient management plan to mitigate subsidence in Yunlin county. | en_US |