摘要

　　本研究目的在於先以基流資料估計法推估翡翠水庫集水區之地下水補注量並探討基流量變化與雪山隧道開鑿湧水變化之相關性。再利用數值解以及解析解推估隧道開鑿之湧水量並與實際湧水量做一比較，以作為後續相關工程之參考。最後以數值方法建立翡翠水庫集水區之三維數值模式，模擬隧道東口與西口開鑿對集水區地下水位之影響藉以評估隧道開鑿湧水與翡翠水庫進流量變異之相關性相關性。

　　利用基流資料估計法與低流分析所推估出之翡翠水庫集水區地下水補注量分別為3.93億噸/年與3.0億噸/年，而根據現場量測資料隧道湧水約3.75~5.09百萬噸/年，共佔地下水補注量約1.25~1.70%。根據1996至1998逐月基流量變化與湧水量變化之關係則可看出在1996/03至1996/07、1997/05至1997/10與1998/03至1998/12間兩者增減變化的趨勢是相同的，意味翡翠水庫集水區與隧道沿線可能存在有地下的連通管道，故兩者間會有相互之影響。

　　在推估隧道湧水量方面，以解析模式推估TBM第十次受困處(里程39K＋074)之隧道湧水量約為163~168L/sec之間，與實際湧水量150~180L/sec相符。不過以數值模式推估出之二維與三維湧水量分別為12.00與1.68L/sec與實際湧水量差異甚大。

　　以數值方式所建構出翡翠水庫集水區之三維模擬場模擬隧道東段與西段開挖湧水對集水區地下水位之影響結果顯示，東段因為位於頭城端之集水區，所以雖然湧水量較西段大，但是影響相當輕微，模擬90天後僅造成相鄰邊界約1%的水位變化。而西段在湧水範圍3公里內地下水位洩降最大亦僅有3.37%的變化，故推測雪山隧道開鑿湧水對集水區之地下水位變化影響極微。

Abstract

　Fei-Tsuei Reservoir is the main source of water supply in Taipei. The purposes of this study were to investigate the impact of the excavation of Shiue-Shun tunnel on water supply. The base-flow record method was used to estimate groundwater recharge and to separate base-flow from daily river inflow at the watershed of Fei-Tsuei Reservoir. The diversity of water amount due to the change of monthly base-flow and the excavation of Shiue-Shun tunnel was also discussed. The 2-D and 3-D hydrogeological models were established for the watershed of Fei-Tsui Reservoir. The numerical solutions with MODFLOW and analytical solutions were used to estimate the seepage during tunnel excavation and then compare it with field measurement. The model calibration was also performed in terms of groundwater level when the east and west entrances of Shiue-Shun tunnel were excavated.

　The results showed that the estimate of the groundwater recharge of Fei-Tsui Reservoir was 0.39 billion tons per year and 0.3 billion tons per year for the base-flow record method and the low-flow analysis, respectively. The filed investigated result showed that the seepage of the excavation of Shiue-Shun tunnel was about from 3.75 to 5.09 million tons per year. It indicated that the seepage of the excavation tunnel is only in the ratio range between 1.25% to 1.70% of groundwater recharge. On the other hand, according to the relationship between base-flow variation per month and the excavation change during 1996 to 1998, especially during 1996/03~1996/07, 1997/05~1997/10 and 1998/03~1998/12, it showed that the positive correlation is provided in terms of the relation between the seepage of the tunnel and the base-flow of the watershed of the Fei-Tsui reservoir. It could imply that there exit the connected channels between the watershed and tunnel.

　The results of the analytical model showed that the tunnel inflow amount at TBM 10th besieged place (mileage is 39K＋074) was in the range between 163 to 168(L/sec) with which was corresponded to the real field amount between 150 and 180(L/sec). On the other hand, results of 2-D and 3-D numerical model were provided that the inflow were 12.00 and 1.68(L/sec) respectively. It indicated that the inflow from 2-D and 3-D numerical model were difference from real field amount.

　The 3-D model was also used to simulate the impact of the inflow of tunneling excavation at eastern and western part on ground water recharge on the watershed of Fei-Tsui Reservoir. The results show that the excavated inflow of eastern part was larger than that of western part. The effect of the excavated inflow of eastern part on ground water recharge on Tou-Cheng Watershed was quietly less significant. When the tunnel was excavated after 90 days, only 1% variation and 3.37% variation of groundwater level drawdown of groundwater level at the eastern part and in the western part respectively within the range of the radius 3 kilometers. In conclusion, the effect of excavation advance of Shiue-Shun tunnel on the change of groundwater level of watershed of Fei-Tsui Reservoir is less significant.

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