Spatiotemporal Variations of the Skeletal Specific Storage in Choushui River Aquifer System, Taiwan

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Title:	Spatiotemporal Variations of the Skeletal Specific Storage in Choushui River Aquifer System, Taiwan
Authors:	阮玉清武;Vu, Nguyen Ngoc Thanh
Contributors:	應用地質研究所
Keywords:	彈性骨架比儲水係數;非彈性骨架比儲水係數;地下水位變化;土體壓密;地層下陷潛勢;濁水溪沖積扇;Elastic skeletal storage coefficient;Inelastic skeletal storage coefficient;Groundwater level variation;Soil compression;Land subsidence potential;Choushui River Alluvial Fan of Taiwan
Date:	2024-01-19
Issue Date:	2024-09-19 17:32:38 (UTC+8)
Publisher:	國立中央大學
Abstract:	地層下陷是一個影響廣大的地質災害，包括可能引起水資源的枯竭與土地資源的流失、建築損壞和財物損失等。台灣的濁水溪沖積扇地區面臨嚴重地層下陷的問題，主要受到自然和人為因素引起的土體壓密所致。要深入瞭解含水層系統變形和孔隙水壓力之間的相關性，就得深入理解土水力學特性。本研究的目標是評估不同深度地層中骨架比儲水係數(skeletal specific storage coefficient, Ssk)的空間和時間變化，以了解地層下陷與地下水位變化之間的關係。研究中的儲水係數包括彈性骨架比儲水係數(Sske)和非彈性骨架比儲水係數(Sskv)，這兩係數隱含地層下陷的壓縮速度和可壓縮性。研究中蒐集水利署提供的38口地下水井和31個分層式地層下陷監測井資料，以地下水位變化資料和累積土體壓縮資料，透過線性迴歸分析來推估兩儲水係數值。研究結果顯示，儲水係數隨季節有所變化，枯水期估計值一般較高，第一分層和第四分層的彈性骨架比儲水係數值範圍分別為9.30×10-6 ~ 1.15×10-4 m-1和8.60×10-6 ~ 8.50×10-5 m-1；而豐水期則相對較低，第一層和第四層的值範圍分別為1.00×10-5 ~ 6.68×10-5 m-1和8.10×10-6 ~ 5.00×10-5 m-1。此外，不同位置和地層中的儲水係數，受到區域土水力學特性變化而存在差異，特別是濁水溪沖積扇的扇央區域具有最高的儲水係數值，表示該區域比其他地區具有更容易壓密的特性。當含水層系統孔隙水壓下降時，該地區具有相當高的地層下陷潛勢。本研究展示了儲水係數在濁水溪沖積扇的時空變化特性，該成果可評估濁水溪沖積扇地區的地層下陷潛勢，並有助於該地區的地下水資源管理。關鍵字：彈性骨架比儲水係數、非彈性骨架比儲水係數、地下水位變化、土體壓密、地層下陷潛勢、濁水溪沖積扇。 ;Land subsidence represents a significant geohazard with potential implications, including the depletion of water and land assets, structural damage, and financial disturbances. The Choushui River Alluvial Fan (CRAF) experiences issues of land subsidence largely attributed to soil compaction, influenced by both natural and human-made factors. A detailed comprehension of the hydro-mechanical characteristics that dictate the correlation between aquifer system deformation and pore water pressure is crucial. This research focuses on evaluating the spatial and temporal variations of skeletal storage parameters across multiple strata to understand the patterns of land subsidence linked to alterations in groundwater levels. Investigated storage parameters in this research encompass both elastic skeletal specific storage (Sske) and inelastic skeletal specific storage (Sskv), indicative of the pace and likelihood of land subsidence. Utilizing linear regression analysis, the storage parameters were deduced from fluctuations in groundwater levels and accumulated soil compression data, gathered from 38 groundwater wells and 31 multi-layer compaction wells, as provided by the Water Resources Agency, Taiwan. Findings reveal fluctuating skeletal specific storage values, with high estimations in the dry period and low estimations in the wet period. During the dry period, layers 1 and 4 have the highest values range from 9.30×10-6 ~ 1.15×10-4 m-1 and 8.60×10-6 ~ 8.50×10-5 m-1, respectively, while during the wet period, layers 1 and 4 have values range from 1.00×10-5 ~ 6.68×10-5 m-1 and 8.10×10-6 ~ 5.00×10-5 m-1, respectively. Additionally, spatial variations were observed, displaying differences in skeletal specific storage across various locations and geological strata, specifically that the central region of the CRAF has the highest storage values means that this area has a higher ability to absord and release water than other areas. This can be inferred that there is a high susceptibility of subsidence when the aquifer system is dehydrated. This research elucidates that hydro-mechanical parameters are subject to spatiotemporal changes, which can aid in assessing the potential for land subsidence in the CRAF, Taiwan. Keywords: Elastic skeletal storage coefficient, Inelastic skeletal storage coefficient, Groundwater level variation, Soil compression, Land subsidence potential, Choushui River Alluvial Fan of Taiwan.
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