屏東平原為台灣第二大平原，由高屏溪、東港溪等多條河流沖積而成，擁有良好水文地質條件，地下水豐沛，然而本區觀測井資料空間分布不均，因此對於區域性地下水資源之水文特性了解仍有限，為更深入了解地下水資源之水文特性，本研究運用二維地電阻影像法(ERI)，採用 Wenner 及 Schlumberger 陣列進行施測，並以測區內彭厝觀測井的地下水位觀測資料作為驗證背景資料，於2019年跨乾溼季節進行五次施測，每次佈設10條二維地電阻測線，以推估屏東扇頂地區之地下水位面在乾溼季的變化。本研究將所測得之視電阻率進行反演算，得出不同測點真實電阻率隨深度分布資料後，再利用Archie’s Law 轉換為相對飽和度空間分布，最後利用 Van Genuchten 模型推估的保水曲線來估算地下水深度，同時利用保水曲線所推估的殘餘含水量(θ_r)及飽和含水量(θ_s)推算理論比出水率(S_y)。運用上述的不同季節施測之研究結果，扇頂的彭厝地區二月時地下水深度約在地下8.6至13.7公尺之間，而五月初施測之地下水位高程分布因受乾季影響相較其它月份低，深度約9.5至14.7公尺，七月及九月則因進入溼季大量降雨緣故，相較於五月地下水位明顯上升2至10公尺，十一月為乾季初期，地下水位較濕季低，地下水深度為5至15公尺。從各月地下水位高程分布圖中發現地下水位高程分布整體趨勢由扇頂向西或向西南遞減，主要是受到扇頂補注區降雨影響，然而在濕季测區北邊的地下水位高程則有由北向南的局部性遞減趨勢，本研究認為是受到隘寮溪及過去武洛溪的河川補注架構影響。此外，本研究在濕季時發現部份测線受到暫棲水影響，使得所推估之地下水位過度低估，藉由正演模型比對出有無暫棲水影響下的誤差最高可達到11公尺，也可依此作為校正受影響之测線的地下水位參考。本研究地電阻推估之比出水率約在0.15到0.21之間，顯示區域內有良好的地下水資源開發潛勢。;The Pingtung Plain is the second largest plain in Taiwan, and also has good hydrogeological conditions and recharge source for groundwater. However, the spatial distribution of observation wells in this area are uneven. So the regional hydrological structure still has some uncertainty. In order to provide better information about groundwater hydrological structure of fan head of Pingtung plain. We conducted Electrical resistivity imaging (ERI) survey for time-lapse monitoring of the groundwater level, and also attempt to estimate the specific yield. In 2019, we deployed ten ERI survey lines with both Wenner and Schlumberger array configurations and conducted the time-lapse measurements 5 times during the wet and dry season. Based on the Archie’s law , we estimate the relative saturation change with depth on each ERI profile which then will be used to apply van Genuchten model to estimate the groundwater depth and specific yield. Afterwards, we compared our groundwater level data to the adjacent Pengcuo observation well in order to justify the result. In February, the groundwater level varies between 8.6 - 13.7 m. In May, the groundwater level decreased to 9.5 - 14.7 m. In June and September, the groundwater depth increased significantly due to the wet season, which was increased about 2 to 10 m. While the groundwater depth in November started to decrease to 5.0- 15.0 m. Overall, the groundwater level in the dry and wet seasons showed a trend of decreasing gradually from the fan head of plain to the South-West or West. However, the North part of study area showed a regional trend of decreasing gradually from North to South, which considered that was affected by the river recharge structure of Ailao river and Wuluo river. The specific yield in the study area is 0.16 to 0.26, which also indicating that there is a good potential for groundwater resources development in the area.
