| Summary: | 碩士 === 國立臺北科技大學 === 土木工程系土木與防災碩士班 === 107 === Groundwater is one of major water resources in Taiwan. Continuously over-pumping has resulted in social and economic disasters, such as soil salinization, seawater intrusion, and land subsidence in this country. Rational use of groundwater resources has become a crucial issue for environmental protection and sustainable economic development. Therefore, it’s necessary to establish an integral hydrogeological stratification structure applied for accurate evaluation of the groundwater budget in aquifers.Considering the soil permeability plays an important role in groundwater recharge and pollution transport in vadose zone, the indicator kriging (IK) was applied to estimate spatial distributions of highly and lowly permeable soil texture ratios of aquifers in the Choshui River Alluvial Fan. First, the borehole data reported by the Central Geological Survey were statistically analyzed to establish multiple thresholds. The multi-threshold IK was then used to probabilistically estimate occurrence probabilities of highly and lowly permeable soil texture ratios of aquifers and determine the conditional cumulative distribution function (CCDF) at each cell. Finally, quartiles obtained from CCDF were adopted to determine the estimates of highly and lowly permeable soil texture ratios of aquifers and the interquartile range was employed to explore the estimate uncertainty.
The research results reveal that the highly permeable soil texture ratios of aquifers are mainly located in the proximal-fan and partial area of mid-fan (Changhua and Yunlin). The lowly permeable soil texture ratios of aquifers are primarily situated in the distal-fan and the partial mid-fan (Chiayi). In addition, the results also prove that the IK approach with multiple thresholds can reduce the smoothing effect presented in OK estimation and characterize a reliable hydrogeological pattern in vadose soils. In the future, the effects of soil layer distribution and texture on the soil water retention characteristics, deep seepage and pollution transport in groundwater can be further explored based on the study results. Moreover, comprehensive groundwater management strategies can be formulated according to the revised hydrogeological pattern with more detailed highly and lowly permeable soil textures.
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