請用此 Handle URI 來引用此文件:
http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/70475
標題: | 抽水引致地層下陷造成砷釋出至地下水層之數值模擬與情境分析 Scenario Analysis and Numerical Simulation of pumping induced land subsidence causing the arsenic release to groundwater aquifer |
作者: | Bo-Cheng Pan 潘柏成 |
指導教授: | 劉振宇(Chen-Wuing Liu) |
關鍵字: | 地下水,砷,地層下陷,數值模擬,情境分析, groundwater,arsenic,land subsidence,numerical simulation,scenario analysis, |
出版年 : | 2018 |
學位: | 碩士 |
摘要: | 含砷地下水,一直為全球所關注的環保議題,於東南亞地區由於冰河時期海近海退,其地質多為沉積岩,先前研究發現天然沉積岩中砷含量高,所以該地區地層先天富有高含量的砷,大量抽取含砷地下水不僅危害人體健康,同時造成地層下陷,壓密作用可能造成黏土層或難透水層中之含高砷層間水釋出,更加惡化地下水水質,而砷釋出之物理過程及傳輸進入水體之機制,至今未有完善之研究,僅Erban et al. (2013)在東南亞地層下陷嚴重之越南湄公河三角洲,於原本砷含量較低之深水井,發現其監測井砷濃度隨井深度而增加,推測可能因地層壓縮釋出高砷層間水所致。台灣濁水溪沖積扇南翼地下水豐沛,在連續數十年密集抽水下造成嚴重之地層下陷以及水質惡化,故政府投入大量經費設置地下水及地層下陷觀測和監測站網,提供完整的地層下陷與地下水砷濃度之時空變化數據,故本研究將先彙整既有的數據,量化分析濁水溪沖積扇南翼雲林地區之地層下陷變化與該區地下水砷之時空變化趨勢及相關性,然後應用耦合三維地下水模式MODFLOW,搭配壓密模式軟體INTERBED(IBS1)及溶質傳輸模式(MT3D),模擬探討雲林地區抽水導致地層下陷,造成含水層中砷濃度增加,來確立地層下陷與砷濃度之耦合機制,以利後續地下水及水質監測管理之參考。
研究結果於含水層一顯示砷濃度釋出區域隨著主要下陷區域增加而增加,而含水層二略為增加較不明顯,但抽水導致下陷確實造成砷濃度於含水層的增加,透過情境分析進一步討論。 情境分析一:若阻水層與含水層砷濃度相近時,模擬之結果於含水層一及含水層二,皆無太大變化,證實阻水層含高砷濃度之黏土層或不透水層於物理釋出機制中扮演著穩定砷來源提供者的角色。 情境分析二:增減15%及30%全區抽水量之模擬結果,於增抽及減抽模擬中,下陷面積的改變,影響砷釋出之影響面積,證實下陷壓密阻水層中富含高砷之黏土層及不透水層,有直接影響,且抽水量作為此為此釋出機制之驅動力,當抽水量增加造成更大面積的下陷,砷釋出到被察覺時間將可能更短於Erban et al. (2013)所提出之十年。 情境分析三:透過更接近大氣變遷之情形做為假設,假設由於大氣變遷影響,夏季及秋季梅雨季節遲到或變短,造成湖山水庫蓄水量已不足供給民生所需,進而需透過抽取地下水做為補足地表水之用水,並將抽水決策分為全區增抽60%及扇頂增抽60%做比較,結果顯示增抽於扇頂,更有效於減緩主要下陷區之下陷量,砷釋出之面積及濃度亦同時受到抑制,本研究提出適合東南亞國家及本國之地下水用水策略之抽水管理決策,抽水之區位選取黏土層較少之阻水層區域進行,如砂質等,將可有效減緩下陷及砷濃度的釋出。 Groundwater containing arsenic has always been one of the most important environmental issues in the world, In Southeast Asia, due to the marine transgression and regression during the ice age, sedimentary formations were found with high arsenic content in previous studies. A large amount of groundwater extraction containing arsenic not only endangers human health and environment, but also causes land subsidence. Consolidation causes inter-layer water containing high arsenic released from clay or impermeable layer further worsening the groundwater quality. The mechanism of arsenic release and the transport process of arsenic to the groundwater have not been well studied. Erban et al. (2013) explored the land subsidence in the Southeast Asia, Mekong delta, Vietnam and found that the arsenic concentrations in wells may increase with the depth in deep groundwater, which was originally low in arsenic content. They speculated that high arsenic interlayer water may be expelled to the lower aquifer caused by land subsidence. Groundwater in the southern Choushi River Alluvial Fan of Taiwan is abundant. Due to intensive pumping over decades, severe subsidence and deterioration of groundwater quality were found. Government invested a large fund to set up groundwater/subsidence monitoring stations, which may provide valuable spatiotemporal data of subsidence and groundwater arsenic concentration. This study first analyzes the correlation of the land subsidence and groundwater arsenic changes in the Choushi River Alluvial Fan of Yunlin area. Secondly, a three-dimensional groundwater model MODFLOW coupled with the compaction mode software complex process of INTERBED (IBSI) and solute transport mode (MT3D) was developed to simulate the groundwater flow, land subsidence and arsenic transport in Yunlin. The simulation results demonstrate that the intensive pumping leads to subsidence and the increase of arsenic concentration in the deep groundwater aquifer. The inter-related processes among groundwater pumping, subsidence and increase of arsenic concentration identified herein may be useful to the management of groundwater resource in the Yunlin area and other Southeast Asian countries. The results of the study also show that the arsenic concentration in the aquifer one significantly increases in the major subsidence area, while the aquifer two only with less noticeable increase. The implication of the developed model can further explore the consequences of subsidence caused by groundwater pumping and an increase the arsenic concentration in the deep aquifer using Scenario Analysis. Scenario Analysis One: If arsenic concentration level is similar in both aquifer and aquitard, the results of the arsenic concentration do not vary much in the aquifer one and the aquifer two after intensive pumping and land subsidence. Scenario One confirmed that the clay or the impermeable layer containing high arsenic concentration plays an important role to furnish stable arsenic sources to lower aquifer after compaction. Scenario Analysis Two: Increase or decrease the total pumping volume of 15% and 30%. In the results of increase or decrease pumping affects the subsidence area and arsenic concentration, which confirmed the physical process of arsenic release from aquitard to the lower aquifer was attributed to subsidence. Also, intensive pumping causes an expanding of subsidence area which is the driving force of arsenic release. The affecting time of arsenic to lower aquifer may be shorter than 10 years proposed by Erban et al. (2013). Scenario Analysis Three: The climate changes may delay or shorten the rainy season causing insufficient domestic water supply by the Hushan Reservoir in Yunlin. The groundwater is considered as a supplement water resource. Two pumping schemes are proposed, one is by placing the 60% increase of total pumpage in mid-fan and distal-fan, the other is by placing the 60% increase of total pumpage in proximal-fan. The result shows increasing pumping in proximal-fan is most effective in reducing subsidence and arsenic concentration in the main subsidence area. This study proposes a sound groundwater pumping strategy in Taiwan and other Southeast Asian countries is to select the pumping area with free or loss aquitard layer, which can effectively reduce the subsidence and arsenic release and warrant the safe use of groundwater. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/70475 |
DOI: | 10.6342/NTU201803127 |
全文授權: | 有償授權 |
顯示於系所單位: | 生物環境系統工程學系 |
文件中的檔案:
檔案 | 大小 | 格式 | |
---|---|---|---|
ntu-107-1.pdf 目前未授權公開取用 | 14.15 MB | Adobe PDF |
系統中的文件,除了特別指名其著作權條款之外,均受到著作權保護,並且保留所有的權利。