Browsing by Author "Chen, You-Cheng"

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Basin-scale groundwater response to precipitation variation and anthropogenic pumping in Chih-Ben watershed, Taiwan
(2012-05-01)
Hsu, Kuo-Chin
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Yeh, Hsin-Fu
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Chen, You-Cheng
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Lee, Cheng-Haw
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Wang, Chung-Ho
The sustainable use of groundwater has become increasingly challenging due to extreme hydrological events and anthropogenic activity. In this study, the basin-scale groundwater response to precipitation variation was analyzed using an integrated model that comprises lumped models for land and river recharges and a distributed model for groundwater. The integrated model was applied to the Chih-Ben watershed, Taiwan, using 20 years (1988-2007) of data. The hydrological data were analyzed for trends using statistical tests. Based on decreasing trends in precipitation and groundwater levels and an increasing trend in stream flow, the oblique-cut method was applied to precipitation and excess infiltration to assess land and streambed recharge. Distributed numerical groundwater modeling was used to simulate the basin-scale groundwater responses to precipitation variation and anthropogenic pumping. The model was calibrated using stable-isotope and groundwater-level data. The safe yields were estimated for the Chih-Ben watershed for dry, wet, and normal precipitation scenarios. The safe yield of groundwater was shown to vary with precipitation, which does not guarantee the sustainable use of groundwater resources. Instead, water resources should be assessed at a basin scale, taking into account the whole ecosystem, rather than only considering water for human consumption in the alluvium.
Boron-doping effect on the super-high density Si quantum dot thin films utilizing a gradient Si-rich oxide multilayer structure
(2019-05-01)
Huang, Pin-Ruei
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Chen, You-Cheng
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Kuo, Kuang-Yang
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Lee, Po-Tsung
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光電工程學系
Boron (B)-doped gradient Si-rich oxide multilayer (GSRO-ML) structure is utilized to realize super-high density Si quantum dots (QDs) thin films with large carrier tunneling probability by co-sputtering. The B-doping effect on crystalline, optical, electrical and photovoltaic (PV) properties of Si QD thin films is investigated in this study. With increased B-doping concentration, the preserved high crystallinity of Si QDs and the reduced optical bandgap are observed. An optimized doping condition is found for the electrical and PV properties. Further increasing the doping concentration leads to increased inactive B atoms and interfacial over-diffusion. The issue of interfacial over-diffusion can be efficiently improved by inserting lowly B-doped GSRO-ML thin films. Our results show the feasibility and great potential for high efficiency Si-based solar cells integrating Si QDs by properly doped B atoms in GSRO-ML thin film structure.
Estimating Hydraulic Conductivity Fields in Composite Fan Delta Using Vertical Electrical Sounding
(2018-11-01)
Chen, You-Cheng
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Tsai, Jui-Pin
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Chang, Liang-Cheng
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Chang, Ping-Yu
;
Lin, Helen
Hydraulic conductivity (K) is crucial for groundwater studies and is conventionally obtained through pumping tests, which are costly due to well installation, resulting in a limited amount of data. Recent studies have addressed this limitation by estimating K through the integration of a pumping-test K and electrical resistivity measurements. While this approach is suitable for local areas, it cannot readily be applied to determine K fields for the composite fan delta. This study proposes and demonstrates an advanced method to estimate the K's spatial distribution of a composite fan delta. The proposed method included data classification, linear regression, and kriging interpolation. Data classification was conducted using a physical-based zonation method. The K and formation factor (F) data pairs were classified into several groups. Linear regression was used to develop K-F mapping for each group. The regression results showed a good correlation between K and F in each group. These K-F mappings were verified by additional pumping tests. These results indicate that estimation errors were between 7 m/day and 58 m/day, and the correlation coefficient of each data group was greater than 0.8. Based on these regression equations and ordinary kriging method, the detailed K spatial distribution of the study area was derived. According to these results, the proposed method is efficient and economical to delineate K's spatial features for regional groundwater systems and can benefit groundwater-related studies.
Features of spatiotemporal groundwater head variation using independent component analysis
(2017-04-01)
Hsiao, Chin-Tsai
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Chang, Liang-Cheng
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Tsai, Jui-Pin
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Chen, You-Cheng
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土木工程學系
The effect of external stimuli on a groundwater system can be understood by examining the features of spatiotemporal head variations. However, the head variations caused by various external stimuli are mixed signals. To identify the stimuli features of head variations, we propose a systematic approach based on independent component analysis (ICA), frequency analysis, cross-correlation analysis, well selection strategy, and hourly average head analysis. We also removed the head variations caused by regional stimuli (e.g., rainfall and river stage) from the original head variations of all the wells to better characterize the local stimuli features (e.g., pumping and tide). In the synthetic case study, the derived independent component (IC) features are more consistent with the features of the given recharge and pumping than the features derived from principle component analysis. In a real case study, the ICs associated with regional stimuli highly correlated with field observations, and the effect of regional stimuli on the head variation of all the wells was quantified. In addition, the tide, agricultural, industrial, and spring pumping features were characterized. Therefore, the developed method can facilitate understanding of the features of the spatiotemporal head variation and quantification of the effects of external stimuli on a groundwater system. (C) 2017 Elsevier B.V. All rights reserved.
Spatial-temporal pattern recognition of groundwater head variations for recharge zone identification
(2017-06-01)
Tsai, Jui-Pin
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Chang, Liang-Cheng
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Chang, Ping-Yu
;
Lin, Yuan-Chien
;
Chen, You-Cheng
The delineation of groundwater recharge zones is crucial for the conservation of groundwater quality and quantity. To objectively estimate groundwater recharge zones, many field surveys are required that are costly in both time and money. To facilitate the assessment of recharge zones with high efficiency and low expense, this study proposes a 'fast-filter' approach based on empirical orthogonal function analysis and applies it in a synthetic case study and to Taiwan's Yilan Plain. In the synthetic case study, we demonstrate that the proposed method can effectively identify the recharge area by considering the head variations driven by rainfall recharge. For the case of Yilan Plain application, the field investigations (i.e., collected wellbore logs and electrical resistivity tomography [ERT] surveys) and a groundwater simulation model support the recharge zones estimated by the proposed method. The study results show that within the estimated recharge zone, all of the collected wellbore logs consist of coarse grains, and thick and continuous high resistivity zones were shown in the ERT profile images. Moreover, the groundwater model indicates that the recharge within the estimated recharge zone is 57.6% of the total recharge despite that the area of the estimated zone is only 26.8% of the study area. Therefore, the proposed method is shown to delineate recharge zones at low cost. (C) 2017 Elsevier B.V. All rights reserved.
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
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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.
The development of a real-time flooding operation model in the Tseng-Wen Reservoir
(2014)
Chen, Yu-Wen
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Tsai, Jul-Pin
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Chang, Liang-Cheng
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Ho, Chih-Chao
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Chen, You-Cheng
Typhoon events occur frequently in Taiwan resulting in flood-related disasters. A well-operated reservoir can reduce the severity of a disaster. This study incorporates a genetic algorithm, a river hydraulic model, an artificial neural network and a simulation model of Tseng-Wen Reservoir to propose a real-time flooding operation model. The model includes two parts: an optimal flooding operation model (OFOM) and a reservoir inflow forecasting. Given an inflow condition, the OFOM is run based on the safety of the dam structure, reservoir flooding operation rule, and minimization of the downstream loss due to flood. A simple and robust model for reservoir inflow forecasting, which automatically chooses the most similar event from a typhoon event database as the future inflow, is developed. This study compares the model results with the real operations during Typhoons Sepat, Krosa, Kalmaegi, Fung-wong, Sinlaku, and Jangmi. This study compares the performances of the proposed model with the practical operation operated by the management center of Tseng-Wen Reservoir. The proposed model indicates shorter flooding duration in the downstream area. For example, the flood durations of the model output are 4 and 3 hours shorter during Typhoon Krosa and Sinlaku, respectively, than the practical operations.