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濁水溪沖積扇之地下水文特徵研究-地下水位退水線探勘分析

A Study on the Characteristics of Groundwater in Choushui River Alluvial Fan - Analysis of Groundwater Decline

摘要


本研究在藉由分析地下水位退水線隨地下水位的抬升與下降所產生的變化,探討地下水系統受河川及抽水的影響,並以濁水溪沖積扇為研究區域。濁水溪沖積扇為台灣西半部重要的地下水區,若能充分了解該區域之地下水系統特徵,尤其是與主要河川之互動及抽水情形,將有助於整體流域之分析與合理之管理規劃。地下水系統與外界的水量交換主要是人為抽水、降雨補注及鄰近河川或系統邊界所產生之交換作用等。枯水期時,降雨補注少,系統內外交換量主要為抽水與河川及邊界交換兩個機制,一般而言會造成系統內的水量淨流失及水位下降(退水),因此枯水期的退水線,為兩大機制的綜合效應。原則上若河川之影響較大時,則水位越高水力梯度越大,流失量越大(退水線較陡),惟若是人為抽水為主時則反之。基於上述原因,地下水位之退水線為地下水系統之重要特徵,可為探討地下水系統尤其是在枯水期時與外界互動之重要依據。惟退水線分析以往需以人工方式分析,易流於主觀且費時費力,本研究乃以Python程式語言配合基本統計分析方法,開發自動化分析模組,可對研究區域大量地下水位資料進行即時資料探勘分析,經由分析各觀測井水位之平均退水線斜率,及退水線斜率隨水位變化情形,可得枯水期水位下降在扇頂地區主要受天然河川影響,扇央以下尤其是雲林沿海則抽水效應明顯,此結論與以往相關研究一致,本研究成果不但對濁水溪沖積扇地下水系統受外界天然或人為之影響,提出另一更直接的資訊,此分析方法並可推廣應用於其他地區。

並列摘要


The characteristics of groundwater system in Choushui River alluvial fan are explored via analysis of groundwater decline curves. The pumping influence area is thoroughly analyzed during drought periods. Choushui River alluvial fan is an important groundwater source for the western Taiwan. The fan tail area is excessive use of groundwater. However the fan top area still has water supply potential. Therefore, the groundwater resources management can be improved if the groundwater planning is considered based on the whole groundwater system. The groundwater exchange between systems is basically resulted from the artificial pumping, the rainfall recharge, and the exchanges at the boundaries. During drought periods, the rainfall recharge volume decreases. The other two mechanisms have major influences and result in net water loss of the groundwater system and the decline of groundwater level. Therefore, the decline curves during drought periods are the combination of these two mechanisms. Larger river influence results in larger groundwater level gradient and groundwater loss, which mean steeper groundwater decline curves. By contrast, mild decline curves are observed when the artificial pumping has major influence. Hence, the groundwater decline curve is an important characteristic of a groundwater system. The decline curve information is traditionally obtained using manually time-consuming processes. In this study, the Python programming language is used to develop a real-time statistical analysis model for exploring the decline curve information. The developed model provides real-time average decline slope for each observation well and the variation of the decline curves in the studied area. The fan top area is majorly influenced by rivers while the artificial pumping dominates the central and tail areas of the groundwater system. The pumping influence is clearly observed at the coastal area at Yunlin which is consistent with previous studies. This study provides a direct information to distinguish the artificial influence from the natural influence in a groundwater system. This developed can be applied to other groundwater systems.

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