利用定水頭試驗推估含水層參數

單井抽水試驗與微水試驗爲傳統單井試驗方法。單井抽水試驗只能求得T值，無法求得S値，微水試驗則僅能決定井旁鄰近地層的K值。定水頭試驗是在一口井中維持一固定水頭，藉此水頭與與周邊地下水頭差，驅動地下水流動。因爲水頭固定，定水頭井中地下水流量隨時間變化，量測此流量變化產生推估T值與S値所需資料。定水頭試驗過去並未受到廣泛注意，因為地下水流量不易測定且定水頭水井水力學較抽水試驗或微水試驗相關理論複雜。本研究建立受壓均質模式之理論基礎與分析方法，並發展地下水流量量測系統，執行定水頭試驗，且利用定水頭試驗之結果推估含水層之T值與S値，而推估之結果均相當合理。由敏感度分析得知，定水頭試驗中，水頭變化無法推估含水層參數，必須由地下水流量變化推估之。而由單一口定水頭井之流量變化即可決定含水層之T値與S値。單井定水頭試驗因此可節省觀測井的設置費用及土地取得的困難。

關鍵字

定水頭試驗；地下水流量；敏感度分析

並列摘要

A constant-head test involves the maintenance of a constant head, h_w, in a well and the measurement of the time-dependent flow rate, Q_w(t). Parameter sensitivity analysis verifies that the storage coefficient, S, and the transmissivity, T, can be uniquely determined using the data of h_w/Q_w(t) without extra measurements on observation wells. Considering the extra costs and difficulties of acquiring land use permission associated with constructing observation wells, the constant-head test warrants more attention. A device using an electric balance for the measurement of the weight of overflow from top of the well is developed to determine Q_w(t). Data analysis is made use of the numerical inversion of the Laplace-domain solutions of appropriate constant-head well hydraulics. A graphic method valid for large time only and a least-square fitting method for all time are used to estimate T and S for a field experiment. The values of T and S obtained by these two methods are reasonable.

並列關鍵字

Constant head test ； Groundwater flowrate ； Sensitivity analysis

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