名竹盆地位於台灣中部的濁水溪區域中游，地理位置在南投縣名間鄉與竹山鎮間，在名竹大橋以下，本區淺層地質以未固結礫石層為主要地層組成，因此擁有良好的水文地質條件，深具地下水的開發潛能。然而本區內尚缺乏空間密度夠高的觀測井資料，為了解此區域淺層地下水水位面分佈與季節變化，本研究利用二維地電阻剖面法（ERT）調查並建立名竹盆地淺層地下水位面分佈與隨季節之變化情形及比出水率。本研究於盆地區域內，於豐枯季節中，利用Wenner及Schlumberger陣列進行施測，每次施測於名竹盆地區域內佈設之十三條二維地電阻測線，於2016年十二月至2018年三月乾濕季中反覆進行共七次試驗，並於名竹盆地內唯一一口地下水觀測井-新民觀測井旁進行試驗，以便進行地下水位推估比較。於本研究中，所測得之電阻率利用archie’s law 轉換成相對含水率，並利用保水曲線推估地下水位深度。並可利用飽和及殘餘含水率計算比出水率。本研究發現於測區內地下水位的分佈，於測區中地下水位呈現上游較高下由較低的趨勢，地下水等位線大致垂直於濁水溪主河道，地下水位至河道邊有些微上升趨勢，推測於名竹盆地內主要地下水位補助來源為河流補助。測區內比出水率值約為0.16至0.26間，靠近濁水溪下游的地區比出水率較低，與鑽井資料進行比對，發現因靠近下游地區地層內泥含量較高，導致區域內比出水率略為下降。比較不同季節地下水位變化，發現於濕季轉乾季時，水位會大幅上升，於下游地水位變動較上游大，與比出水率推估結果相同。 ;The Minzu Basin is located at the central part of Taiwan, which is bounded by the Changhua fault in the west and the Chelungpu thrust fault in its east. The Chuoshui river flows through the basin and brings in thick unconsolidated gravel layers deposited over the Pleistocene rocks and gravels. Thus, the area has a great potential for groundwater developments. However, there are not enough observation wells in the study area for a further investigation of groundwater characteristics. Therefore, we tried to use the electrical resistivity Tomography (ERT) method for estimating the depth of the groundwater table and the specific yield of the unconfined aquifer in dry and wet seasons. We have deployed 13 survey lines with the Wenner-Schlumberger array in the study area from December 2016 to March 2018. Based on the data from the ERT measurements and the nearby Xinming observation well, we turned the resistivity into the relative saturation with respect to the saturated background based on the Archie’s Law. With the depth distribution curve of the relative saturation, we found that the curve exhibits a similar shape to the Soil-Water Characteristic Curve. Hence we attempted to use the Van-Genuchten model for characterizing the depth of the water table. we also tried to calculated the specific yield by taking the difference between the saturated and residual water contents. According to the results, we can depict the the water level distribution in the study area. In general, the ground water in upriver is higher than downriver, slightly raise near the river and the groundwater equipotential lines is vertical to the river. The specific yield in the study area is 0.16 to 0.26 which in downriver is small because the stratum has more clay material. Therefore, the water table in downstream raise higher than upstream.
