| Summary: | 碩士 === 國立中央大學 === 地球物理研究所 === 87 === Direct vertical electrical soundings with a Schlumberger array at 90 locations were carried out in Ping-Tung Plain. Incorporating the sounding data with the lithology data of wells, the environmental changes and hydrogeological characteristics in the study area can be recognized.
Based on the final results, several conclusions are drawn:
1. The Ailiao stream once flowed southwestward toward Chaochou, then the Ailiao stream was divided into two branches; the northern branch moved northward gradually between Chiuju and Pingtung, then flowed into the Kaoping stream. Finally, it became the present Ailiao stream. The south branch of old Ailiao stream became former Tungkang stream. The change of course of Ailiao stream can be attributed to the fault action nearby.
2. The main pattern of VES curves is K type and its shape varies greatly from north to south. The VES curves collected in the Ailiaochi Alluvial Fan is KHK type and it changes to KQ type in the southeast and muti-layers type in the southwest.
3. The decrease of resistivity from depth of 30 m to 100 m indicates that a trangression from 10000 to 6000 years ago. It is comparable to the Tainan transgression, therefore, the whole west coastal plain of Taiwan was affected by this trangression.
4. The sediments deposited in Aquifer F3-1 were mainly from the Ailiao stream and the Laonung stream before the Holocene. Far from the coastal area, the ground water has low salinity, it is good for the irrigation of crops with lower sensitivity to saltwater. The salinity of the ground water near the coastal area is higher than other areas, it has to be paid more attention to this fact.
5. Based on the geoelectrical characteristics of Aquifer F3-1, two hydrogeological regions are recognized, each aquifer was formed either by the deposition of the Ailiao stream or the Laonung stream.
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