| dc.description.abstract | 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. | en_US |