| Summary: | 碩士 === 國立臺灣大學 === 生物環境系統工程學研究所 === 105 === The abundant groundwater is an import resource in Taiwan. However, characteristics of rainfall plus the high-slope terrain, as well as seasonal over-exploitation greatly affect the groundwater recharge and result in severe problems. To make sustainable groundwater management plans, this study chose the Pingtung Plain as the study area to investigate how rainfall and geomorphology affect the changes in the groundwater level. Located in the southwest of Taiwan, the Pingtung Plain is rich in groundwater resources and has thick and highly permeable aquifers across the basin. This study collected the rainfall and groundwater level data from 1999 to 2015 in 121 stations in the plain and applied statistical methods to explore the relationship among rainfall, groundwater level and geochemical conditions using the monthly scale, so that the mechanisms of hydrology and sources of groundwater recharge can be better understood. Then this study applied two Self-Organizing Maps (SOMs) to explore the patterns of each clustering based on the connective algorithm between the neurons, and further separated and categorized the characteristics of regional groundwater level stations in wet and dry seasons. Analysis results indicated that: (1) There was an excessive and uneven temporal distribution of precipitation, to which the groundwater level variation was highly related; (2) The results of SOM appeared a spatial distribution reflecting the permeability of the geology across the plain that greatly influenced the groundwater recharge in both the wet and the dry seasons. Nonetheless, during the dry seasons, the Dexing 2 station was the only one station located in the coastal area with severe seawater intrusion problems in clustering D; (3) According to the temporal distribution of the SOM, results showed that rainfall in the wet seasons was one of the main sources for groundwater recharge. Moreover, the average groundwater level variations during the 10-day period (MA2) showed greater correlation with the trends of the rainfall in low-permeability clusters. Additionally, the average groundwater level variations during the 10-day period were similar to the rainfall in the high-permeability clusters, and the groundwater level rose rapidly particularly in the initial stage. In the dry seasons, the groundwater level descended much faster in the clusters A, B and C that reflected the reality of large groundwater exploitation by various human activities during the dry seasons. In the cluster E, the high permeability characteristics of this cluster made the outflow rates of the groundwater high when the groundwater level was high. On the contrary, the outflow rates declined when the groundwater level became lower due to the over-exploitation of the groundwater in the dry seasons. In conclusion, this study assessed the variation of the groundwater level in wet and dry seasons. It can be used to provide important information for sustainable groundwater resource management in the Pingtung Plain.
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