應用補注井群改善海水入侵之可行性研究

地下水是雲林地區農業、工業及民生用水之重要來源。多年來在沿海地區大量從地下含水層抽水使雲林地區產生了地層下陷及海水入侵等嚴重問題。本文採用三維有限元素地下水流及傳輸模式FEMWATER，可以同時模擬含水層中地下水流況及氯離子之傳輸，探討應用補注井群改善海水入侵之可行性。根據水文地質調查資料將雲林西部地區地層劃分爲三層含水層及一層黏土層，雲林東部地區爲單一深層之礫石層。模式輸入之抽水量及水文地質參數經由檢定與驗證後，將井距訂爲300公尺及600公尺之補注井群搭配0.0255、0.017及0.0085立方公尺／秒之淡水補注量配置於麥寮及口湖沿海地區，模擬六組補注井群進行補注兩年後之地下水水位及氯離子濃度之等值分佈。另外將沿海六鄉之抽水量減少三分之一使其總抽水量不超出地下水天然補注量後，設置300公尺井距及0.017立方公尺／秒作爲第七組補注井群之模擬。研究結果顯示雲林麥寮沿海地區及口湖沿海地區防治海水入侵之補注井群之井距以300公尺較適合，每口井之補注水量應高於每秒0.017立方公尺，並以第七組之補注井群防治海水入侵效果最佳。

關鍵字

回注井群；海水入侵；雲林

並列摘要

Groundwater is an important water resource to the agricultural, domestic and industrial water demand in Yun-Lin. Excessive withdrawal of ground water has led to serious adverse effects such as land subsidence and sea water intrusion. A three dimensional finite element flow groundwater and transport model, FEMWATER, is used for the simulations of regional groundwater movement and chloride transport. According to geological evidences, the western area is divided to three aquifers and a clay layer. The eastern part of Yun-Lin consists of one thick gravel layer. The input parameters including, the hydraulic conductivity, dispersion coefficient and pumping rate of the model are first calibrated and verified, then six fresh water injection well systems with different well spacing and injection rate are set for a series of simulations. The spacing of the wells are 300 m and 600 m and the injection rate are 0.0255 cms, 0.017 cms, and 0.0085 cms, respectively. Simulations of these six systems are conducted to determine the groundwater level contour and the distribution of chloride concentration after 2 years' injection operation. Results of simulation show that the performances of the injection well system with 300 m well spacing are better than those with 600 m. For each well at least 0.017 cms injection rate is needed to stop seawater intrusion. The seventh injection well system which reduce one third of the pumping rate in the six coastal town with injection rate of 0.017 cms and well spacing of 300 m has the best performace result in reducing seawater intrusion.

並列關鍵字

Injection wells ； Seawater intrusion ； Yun-Lin

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