應用多重監測資料探討濁水溪沖積扇地區地表變形之時空演化;Space-Time Evolutions of Land Subsidence in the Choushui River Alluvial Fan from Multiple-Sensor Observations

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Title:	應用多重監測資料探討濁水溪沖積扇地區地表變形之時空演化;Space-Time Evolutions of Land Subsidence in the Choushui River Alluvial Fan from Multiple-Sensor Observations
Authors:	陳怡安;Chen, Yi-An
Contributors:	地球科學學系
Keywords:	濁水溪沖積扇;地層下陷;雷達干涉量測;GPS;水準測量;地陷監測井;Choushui River Alluvial Fan;land subsidence;SAR interferometry;global positioning system;precise leveling;multi-layer compaction monitoring well
Date:	2022-01-25
Issue Date:	2022-07-13 18:29:24 (UTC+8)
Publisher:	國立中央大學
Abstract:	臺灣西部平原地區由於經濟快速發展，水資源需求大幅增加，加上地下水取用方便，使得西部平原區超抽地下水的情形普遍，進而導致地層下陷問題的發生。本研究利用長期的雷達干涉量測資料整合區域內GPS、精密水準測量及地陷監測井等多重觀測資料，以建構濁水溪沖積扇地區內地表變形之完整輪廓，並嘗試釐清歷年地層下陷區域之時空分布變化情形、下陷最嚴重的彰化大城鄉地表變形情形、區域內高速鐵路沿線的下陷情況，以及深度300 m以下的深層壓縮分布情形。由研究成果顯示，濁水溪沖積扇內長期地表變形以地層下陷型態為主，在1993～2019年間，以彰化大城鄉區域內累積下陷量最大，達210 cm，其次為雲林的土庫、元長與褒忠地區，最大累積下陷量達160～180 cm之間。彰化大城鄉地區主要壓縮深度位在地下52～180 m之間，參考西港地下水位站資料與相互比對後可發現，當地地層下陷行為主要與含水層2（西港水位98 m）與含水層3（西港水位171 m）深度範圍的水位波動有關，而影響該深度水位起伏的主因應與當地水產養殖抽水量的多寡有關。彰雲地區高鐵沿線主要有3個明顯的沉陷中心，由北而南依次為彰化溪州地區、雲林虎尾-土庫地區及雲林土庫-元長地區。由鄰近雲林土庫-元長地區的秀潭國小地陷監測井資料顯示，該區位主要壓縮範圍集中在地表至深度50 m之間，由於該地區淺層0～60 m之間富含有易壓縮性的細砂、粉砂及黏土，因此未來需特別注意該地區附近的土地利用狀況與淺層用水行為，以避免危及高鐵的行車安全。濁水溪沖積扇內深層壓縮主要發生在彰化溪州鄉與雲林土庫鎮地區，由於近年針對區域內深層抽水井進行減抽與封填等處置措施，整體深層壓縮速率已有明顯降低，其中主要壓縮區彰化溪州鄉的最大壓縮速率由23.0 mm/yr下降至19.1 mm/yr，而雲林土庫鎮的最大壓縮速率則由24.5 mm/yr下降至17.0 mm/yr。;Land subsidence is a significant problem in the world that can induce the increasing risk of flood, building and infrastructure damage, and economic loss. Hence the continual monitoring of subsidence is important for early detection, mechanism understanding, countermeasure implementation, and deformation prediction. In this study, the analysis of the multiple-sensor observation, e.g., continues Global Positioning System, SAR interferometry, precise leveling, multi-layer compaction monitoring well, and groundwater level observation well, demonstrates the spatial and temporal detail of land subsidence in the Choushui River Alluvial Fan (CRAF) during 1993-2019. Significant land subsidence appears along with coastal areas in CRAF, and most of the inland subsidence areas also experience higher subsidence rates (> 30 mm/yr). The analysis of subsidence along the Taiwan High Speed Rail reveals a newly formed subsidence center between Tuku and Yuanchang areas in Yunlin with high subsidence rates ranges from 30-70 mm/yr was detected and documented. Moreover, the distribution map of deeper compaction (deeper than 300 m depth) in CRAF was proposed firstly in this study.
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