Browsing by Author "Chen, Wen-Fu"

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The assessment of high recharge areas using DO indicators and recharge potential analysis: a case study of Taiwan\'s Pingtung plain
(2015-03-01)
Tsai, Jui-Pin
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Chen, Yu-Wen
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Chang, Liang-Cheng
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Chen, Wen-Fu
;
Chiang, Chung-Jung
Identifying high groundwater recharge areas is important for the conservation of groundwater quality and quantity. A common practice used by previous studies is to estimate groundwater recharge potential (GRP) using recharge potential analysis (RPA) under different environments. These studies use the estimated GRP to identify the high potential groundwater recharge sites. However, the RPA parameters are subjectively defined for these previous studies. To remove the supposition, this study proposes a systematic approach that defines the RPA parameter values based on the theory of parameter identification. This study uses dissolved oxygen (DO) indicators to calibrate the RPA parameters. This calibration improves the correlation coefficient between the DO indicators and computed GRP values from 0.63 to 0.87. By comparing the initial values, these results indicate that the estimated RPA parameters better represent the field infiltration characteristic. This result also indicates that defining the RPA parameter values based on DO indicators is necessary and important for accuracy. These calibrated parameters are used to estimate the GRP distribution of Taiwan\'s Pingtung Plain. The GRP values are delineated into five levels. High and excellent GRP areas are defined as high recharge areas, which compose about 26.74 % of the study area. Based on the proposed method, the estimated GRP distribution can accurately represent the study area\'s field recharge characteristics. These study results can be a good reference for groundwater recharge analyses, specifically if well data is limited or difficult to obtain.
Using the Resistivity Imaging Method to Monitor the Dynamic Effects on the Vadose Zone During Pumping Tests at the Pengtsuo Site in Pingtung, Taiwan
(2016-02)
Chang, Ping-Yu
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Hsu, Shao-Yiu
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Chang, Liang-Cheng
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Chen, Wen-Fu
;
Chen, Yu-Wen
We conducted a time-lapse monitoring study during a well-pumping test at the Pengtsuo site in Pingtung, Taiwan. Water-level gauges were installed in four wells (P1, W1, O1, and O2) at the Pengtsuo site with different screen depths for the observation. We designed the pumping test to be executed in three phases: the background, the stepwise-pumping, and the continuous-pumping phases. The survey line crossed the four wells so that a comparison would be possible between the resistivity measurements and the water-level records. The resistivity differences relative to the pre-pumping background show that electrical resistivity imaging (ERI) can resolve changes due to dewatering from pumping activity. The time-lapse resistivity images reveal that the maximum resistivity increase took place at the locations in the vadose zone instead of at the ground-water surface. The variation in the resistivity differences in the vadose zone correlated to the change in groundwater level in the stepwise phase. On the other hand, the resistivity-difference change was not fully consistent with the groundwater-level change in the continuous-pumping phase. We attribute the abnormal ERI signals to the dynamic non-equilibrium of the water movement in the vadose zone. The findings suggest that pumping designs can affect the changing resistivity differences and water-content distribution patterns. We show the potential of the ER method to reveal both the water flow and water-content changes in the vadose zone with different transient boundary conditions.