全球許多地區因地下水長期超抽而產生地層下陷，威脅基礎建設與民生安全。臺灣中部濁水溪沖積扇為重要農業生產區，受降雨時空分布不均、農業灌溉需求高及地層材料異質性明顯影響，地層下陷之時間尺度與變形型態具有複雜差異性。為釐清地下水抽取引致之地陷特徵，本研究整合全球導航衛星系統(GNSS)、磁環分層式地層下陷監測井(MLCW)、地下水位、降雨、作物需水量與鑽井資料，分析2018年5月至2023年4月之月尺度時間序列，探討地下水位變化、地表垂直位移、分層壓密與農業因子之時空關係，並進一步辨識彈性與非彈性變形及壓密延遲響應。結果顯示，濁水溪沖積扇地表垂直位移與分層壓密具有明顯水文年、乾濕季與垂向分層差異。2020水文年期間下陷量較為顯著，可能與濕季降雨補注不足造成之乾旱事件與有關。濕季地下水位回升，使壓密趨緩甚至產生部分回彈；乾季則因降雨減少與農業需水量增加，使地下水位下降、地表下陷與分層壓密較為明顯。秀潭國小測站結果指出，第二、三含水層壓密量對GNSS地表垂直位移具有較高占比，顯示地層下陷與地質材料組成、層厚及地下水位變化密切相關。互相關顯示，GNSS、MLCW與地下水位之季節項呈正相關，反映地下水位變化與地層壓密、回彈之關聯；降雨、農業需水、地下水位與地層變形間存在時間差，顯示水文補注、農業抽水季節性與壓密反應之延遲。比較Riley method與預壓密水位法之判釋結果，皆顯示非彈性參數整體高於彈性參數，表示相同地下水位變化量下，低於既有預壓密水位時之非彈性壓密量較彈性壓密量大。本研究整合多源觀測資料探討水文、農業因子與壓密之時間與機制關聯，以供濁水溪沖積扇地層下陷監測與地下水管理參考。;Land subsidence induced by long-term groundwater overextraction has threatened infrastructure and public safety in many regions worldwide. The Choushui River Alluvial Fan in central Taiwan is an important agricultural area. Due to uneven spatiotemporal rainfall distribution， high agricultural irrigation demand， and high heterogeneity of materials， the temporal scale and deformation pattern of land subsidence in this area are complex. To clarify the characteristics of groundwater pumping induced land subsidence， this study integrates Global Navigation Satellite System (GNSS)， multilayer compaction monitoring well (MLCW)， groundwater levels， rainfall， crop information， and borehole data. Monthly time-series data from May 2018 to April 2023 were analyzed to investigate the spatiotemporal relationships among groundwater-level variation， surface vertical displacement， layered compaction， and agricultural behaviors， and to further identify elastic and inelastic deformation as well as delayed compaction responses. The results show that surface vertical displacement and layered compaction have clear differences among hydrological years， wet and dry seasons， and vertical layers. Subsidence during the 2020 hydrological year was relatively significant. It may be related to the 2021 drought event and insufficient rainfall recharge. During the wet season， groundwater-level recovery slowed compaction and caused partial rebound. During the dry season， reduced rainfall and increased agricultural water demand decline groundwater level， making surface subsidence and layered compaction more obvious. Results from the Shutan Elementary School station indicate that compaction in the second and third aquifers accounts for a relatively high proportion of GNSS-observed surface vertical displacement， suggesting that land subsidence is closely related to geological material composition， layer thickness， and groundwater level variation. Cross-correlation analysis shows that the seasonal components of GNSS， MLCW， and groundwater level are positively correlated， reflecting the relationship between groundwater-level variation and ground compaction or rebound. Time lags among rainfall， agricultural water demand， groundwater level， and ground deformation further indicate delayed responses among hydrological recharge， seasonal agricultural pumping， and compaction. Comparison between the Riley method and the preconsolidation-head method shows that both methods indicate inelastic parameters are generally higher than elastic parameters. This suggests that， under the same magnitude of groundwater-level change， inelastic compaction occurring when groundwater levels fall below the existing preconsolidation head is greater than elastic compaction. Overall， this study integrates multi-source observations to examine the temporal and mechanistic relationships among hydrological factors， agricultural factors， and compaction， providing a perspective for land subsidence monitoring and groundwater management in the Choushui River Alluvial Fan.
