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  • 學位論文

穩定氫氧同位素於地下水資源評估之研究

Application of Stable Hydrogen and Oxygen Isotopes on Groundwater Resources Assessment

指導教授 : 陳世楷
共同指導教授 : 劉振宇

摘要


臺灣因地形陡峻、河川湍急且降雨時空分佈不均,水資源常無法有效利用,加上近年極端氣候和降雨特性的改變,導致區域性水文歷程和地面水/地下水交互補注特性皆有所變化,直接或間接影響地下水補注效益和形態,因此瞭解流域上游山區至下游沖積扇之相互交補關係,成為地下水資源經營管理的重要課題。 本研究藉由現地採樣、穩定氫氧同位素/化學離子示蹤法和地下水數理模式,探討濁水溪沖積扇上游山區及扇頂區域雨水、河水與地下水之時空變異關係和影響機制,並考量水文/地文特性,研判地下水補注來源及補注量,作為判斷水文歷程之依據。根據豐/枯水期分析雨水、河水與地下水之穩定氫氧同位素/化學離子組成,藉由氧同位素質量平衡法估算地下水補注來源比例,結果顯示豐/枯水期地下水來源皆以河水流入為主,且此現象枯水期較為顯著;應用氫氧同位素天水線及化學離子多變量統計之群集分析,將地下水補注水源分成山區北區、山區南區及扇頂區域三個群組,局部區域地下水有較輕之δ18O值,應為濁水溪河水之側向補注和上游山前補注之影響;最後以穩定基流分析法及數值模擬Modflow模式估算濁水溪沖積扇上游山區及扇頂區域地下水年補注量分別為10.95及2.49(億噸/年),結合氫氧同位素質量平衡法,推估濁水溪沖積扇上游山區雨水/河水之年補注地下水比例分別為25.9%及74.1%、扇頂區域則為37.3%及62.7%,顯示濁水溪流域上游山區河水補注地下水之趨勢較扇頂區域顯著,並將其比例量化估算上游山區雨水/河水年補注地下水補注量分別為2.83及8.12(億噸/年)、扇頂區域則為0.93及1.56(億噸/年)。 本研究綜合應用現地採樣分析及區域水文定性/定量評估,探討不同時空之地面水/地下水交互補注機制並量化區域性地下水補注量,研究成果可作為擬定區域性地下水資源經營管理計畫之參考。

並列摘要


Effective use of limited water resources is often difficult in Taiwan due to the steep topography, swift flows in steams and uneven temporal/spatial distribution of precipitation. In addition, the extreme weathers and the following changes of precipitation characteristics in recent years lead to the changes in local hydrologic history and surface water/groundwater interactions, which create direct or indirect impacts on the quantity and morphology of groundwater recharge. Therefore, it is critical for groundwater resource management to find out the interactive recharge from upstream mountain blocks of river basin to the alluvial fan at downstream. In-situ sampling, stable oxygen and hydrogen isotope/chemical ion tracer method and mathematical groundwater model were applied to determine the relationship between the temporal/spatial variation in rainfall, river water and groundwater at upstream mountain blocks and proximal-fan area of the Choushui river and the relative influence mechanisms. Hydrologic/physiographic characteristics were considered to identify the source and quantity of groundwater recharge as the basis for hydrologic history interpretation. The composition of stable oxygen and hydrogen isotopes/chemical ions sampled from rainwater, river water and groundwater in high and low flow periods was analyzed. The percentage of groundwater recharge source was estimated using oxygen isotope mass balance method. The results showed that the groundwater mainly recharging from river water both in high and low flow periods and more significant in low flow period. The sources of groundwater recharge were grouped into northern mountain blocks, southern mountain blocks, and proximal-fan using the meteoric water line for oxygen and hydrogen isotopes and multivariate statistical analysis for chemical ions. More lighter δ18O discovered in groundwater at certain local regions indicating that recharge sources may come from the lateral recharge of Choushui river and the upstream mountain block. Annual groundwater recharge amount estimated from stable base flow analysis and numerical analysis of Modflow model were 1.095 billion tons/year and 249 million tons/year for upstream mountain blocks and proximal-fan, respectively. Based on the analysis results from oxygen isotope mass balance method, the percentages of annual groundwater recharge from rainwater and river water in upstream mountain blocks were 25.9% and 74.1%, respectively, and 37.3% and 62.7%, respectively, at proximal-fan area. By quantifying the percentages, it was estimated that the quantity of groundwater recharge was 283 and 812 million tons/year from rainwater and river water, respectively, at upstream mountain blocks, and 93 and 156 million tons/year, respectively, at the proximal-fan area. In-situ sampling analysis and qualitative/quantitative evaluation of local hydrology were combined for the investigation on the interactive recharge mechanism between surface water and groundwater in different temporal/spatial settings and for the quantification of regional groundwater recharges. The results may serve as a reference for formulating a regional groundwater resource management plan.

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