| 摘要: | 濁水溪沖積扇是台灣面積最大的沖積扇，由北港溪、新虎尾溪、舊虎尾溪等多條河流的沖積作用形成，具有優越的水文地質條件。近年來，該地區由於過度抽取地下水而面臨各種問題，其中地層下陷問題最為嚴重。人工地下水補注被視為解決這一問題的有效方案，但在實施前，我們需要先了解該區域地下的水文地質結構。
本研究採用地球物理勘探技術中的時間域電磁波方法（TDEM），使用50x50公尺的發射線圈和3x3公尺的接收線圈，並試用圈內配置，在整個雲林地區共布設64個站點。我們對獲得的數據進行反演算，得到各測點在不同深度下的真實電阻率分佈資料，然後通過內插法建立地下的三維模型。這一方法的應用使我們能夠利用地下不同電阻率物質的分布來描繪該地區的水文地質結構。
基於模型的分析結果顯示，該區域存在至少兩個含水層和兩個難透水層。通過對一維反演結果的觀察，我們發現地下材料的電阻率呈現相對的高-低-高-低的分布特徵，與鑽探數據相符。同時，三維模型的建立還展示了礫石、砂和黏土的分佈情況。
通過將二維切面與先前研究中的剖面進行對比，我們成功確定了20米、50米、110米和150米深度處的含水層和不透水層的界限。在水平切面中，我們還發現了一個電阻率較低的區域，深度約為10米，這可能暗示著古代河道的存在，古河道通常會保留較高含水量的沉積物，例如細沙和泥。這些含水沉積物具有較低的電阻率，因此在地球物理測量中顯示為低電阻率區域。此外，在50米、100米和150米深度的水平剖面上觀察到的沉積物分佈模式表明了海退的跡象。
;The Choushui River Alluvial Fan is the largest alluvial fan in Taiwan, formed by the sedimentation of multiple rivers such as the Beigang River, New-Huwei River, and Old-Huwei River. It possesses favorable hydrogeological conditions. In recent years, the region has faced various issues due to excessive groundwater extraction, with land subsidence being the most severe problem. Artificial groundwater recharge is considered an effective solution to address this issue. However, before implementation, it is necessary to understand the hydrogeological structure of the area.
In this study, we employed the Time-Domain Electromagnetic (TDEM) method. We used a 50x50-meter transmitter loop and a 3x3-meter receiver loop, applying the central mode configuration. A total of 64 stations were deployed throughout the Yunlin region. The obtained data were subjected to inversion algorithms to obtain the true resistivity distribution at different depths for each measurement point. Subsequently, a three-dimensional model of the subsurface was constructed using interpolation techniques. This approach successfully depicted the hydrogeological structure of the study area.
Based on the analysis of the model, at least two aquifers and two aquitards were identified in the region. Through the observation of the one-dimensional inversion results, it was found that the resistivity distribution of the subsurface materials exhibited a high-low-high-low pattern, consistent with the drilling data. Additionally, the three-dimensional model revealed the distribution of gravel, sand, and clay.
By comparing the 2D profiles with previous studies, the boundaries of the aquifers and aquitards at depths of 20 meters, 50 meters, 110 meters, and 150 meters were successfully determined. On the horizontal map, a lower resistivity zone at a depth of approximately 10 meters was observed, possibly indicating the presence of ancient river channels. Furthermore, the sediment distribution patterns observed on the horizontal profiles at depths of 50 meters, 100 meters, and 150 meters indicated signs of marine regression. |
