| Summary: | 碩士 === 國立中興大學 === 水土保持學系所 === 105 === We combine the technologies of gravimetry and electrical resistivity tomography (ERT) to estimate the groundwater content in Minzhu Basin. Gravimetry and ERT can be used to obtain mass variations and groundwater levels, respectively. Four joint surveying missions combined with gravimetry and ERT were carried out in September, December in 2016, and March and June in 2017, respectively. On field surveys of gravimetry, we use the absolute gravimeter FG5 and relative gravimeter CG5 to collect the gravity observations at 19 gravity stations in Minzhu Basin; on field surveys of ERT, we lay surveying profiles on north side of Jhuoshuei River to collect the ERT observations. The gravimetry-derived and ERT-derived data will be combined with the data of 5m resolution DEM and ground water wells in Minzhu Basin area in order to estimate groundwater changes during the period from September 2016 to June 2017. Overall, the main research topics of this study include: (1) analyze the suitability of the gravity and ERT observing stations; (2) determine the best density contrast; (3) analyze the influence of gravity observation distance on groundwater change; (4) analyze the influence of groundwater level change on gravity values. Due to the obvious difference between the gravimetry-derived and ERT-derived results, accurate estimate for groundwater content is not feasible. Thus we design different simulated study cases to explorer the relations between density contrast, groundwater variation and gravity change. Based on the simulated results, the groundwater level changing above than 3m at least can be observed by CG5.
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