應用地理資訊系統與因子分析方法於地下水補注潛勢評估─以濁水溪沖積扇為例

Abstract

由於地下水在台灣地區水資源供應上扮演著極重要的角色，因此地下水資源的保育一直是個重要的議題，其中地下水補注為影響整個地下水系統的關鍵因素之一。因此，本研究乃結合地下水補注因子分析與地理資訊系統(GIS)，以評估地下水補注潛勢的空間分布並劃分高補注區域。 前述地下水補注因子分析考量之因子，包括土地利用、表層土壤種類、河系密度、透水係數、平均年降雨量、降雨與地下水位變化相關性、單位蓄水量變化等七項因子。而補注潛勢的計算則分為三個步驟，包括各因子細項分數的給定、因子間權重的訂定以及補注潛勢總分之計算。其中因子間權重的訂定乃基於Shaban et al. (2006)提出之因子分析方法，繪製因子邏輯關係圖以給定因子間權重，而補注潛勢總分乃是各因子分數加權後之總合。前述因子細項分數的給定及補注潛勢總分之計算等皆應用GIS軟體輔助執行與展示。 本研究進一步將前述方法實際應用於濁水溪沖積扇，結果顯示扇頂區域擁有較高之補注潛勢，且由扇頂至扇尾逐漸遞減。其中高補注區與工研院能源與資源研究所於1996年以施蘭卜吉排列(Schlumberger Array)之地電阻探測法及觀測井鑽探資料所推估之補注區界線相當接近。此結果驗證了本研究提出之方法對地下水補注潛勢評估是個可靠有效的方法，亦可作為地下水資源相關管理之輔助工具。

Since groundwater, resources play a vital role in regional water supply, groundwater protection and conservation is an important issue in Taiwan. A systematic approach to assessing high recharge areas is a key factor in groundwater conservation. Therefore, this study proposes a systematic procedure that combines a factor-based method and geographic information system (GIS) to determine the spatial distribution of recharge potential and define high groundwater recharge areas. This study selects seven factors to determine recharge potential: land use, surface soil type, drainage density, average annual rainfall, the correlation between rainfall and groundwater level variation, the variation of unit aquifer storage, and hydraulic conductivity. Calculating the recharge potential requires three steps; defining all factor scores, determining the weighting of factors, and summing the weighted factor scores. The purpose of the first step is to define the recharge score for each factor. A high factor score value represents high recharge potential for that factor. Second, the determination of weighting among factors was based on Shaban et al.’s factor analysis method, in that a diagram of logical relationship among factors is defined and the factor weights are computed based on the diagram. After determining the recharge score of each factor and its weighting, the total recharge score was obtained by summing all weighted factor scores. A high total score represents a high recharge potential. This study uses a GIS system for analysis, and all the values, including recharge potential, were spatially distributed. This study applies the proposed method to Choshuihsi Alluvial Fan. Results show that the proximal area has a high recharge potential that decreases in the distal area. These results are similar to the results of prior studies using Resistivity Image Profile of the Schlumberger Array and the field investigations conducted by the Industrial Technology Research Institute of Taiwan. This case study demonstrates that the proposed procedure is a reliable and efficient method of measuring groundwater recharge potential, and is therefore a useful tool for groundwater resource management.