| Summary: | 碩士 === 國立臺灣海洋大學 === 應用地球科學研究所 === 101 === In this study we used the two-dimensional electrical resistivity imaging (ERI) method, as well as the core records of monitoring wells to help determine the groundwater recharge zone boundaries at Pingtung plain in southwestern Taiwan. Pingtung fluvial plain is one of the major groundwater resources in Taiwan which is composed of several alluvial fans deriving from the uplifted mountain area to the east and north of the plain. The thick gravel layer constitutes the main recharge area of the upper alluvial fans and the conductive clay sediments dominate most of the lower fans. With the core records, we found that, the gravel layers have higher resistivity (mostly over 200Ohm-m) and the resistivities of the clayey layers are very low (about 1~10Ohm-m). Therefore with the resistivity surveys we can have more confidence for determining the boundaries of the groundwater recharge area in the area in-between the monitoring wells. In the past two years, we have finished 29 two-dimensional electrical resistivity imaging profile lines from Meinong to Fangliao, the lines are oriented in the east-west direction, and each line was about 400 meters long. With the inverted results, we are able to characterize two major alluvial systems and their recharge zones in the Pingtung fluvial plain. The resistivities we measured almost are consistent to the core records of monitoring wells except for the Wanluan site, which shows thick gravel layer in the drilling records but has low resistivity in the nearby resistivity survey. A reasonable explanation is that the electrical resistivity is sensitive to clayey materials with lower resistivities. The intercalated clay within the gravel layers is not shown in the churn drilling records.
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