圖書典藏及影音數位平台

本計畫目的在使用地表地下水耦合模擬模式應用於地下水資源潛能評估，並以濁水溪沖積扇與屏東平原為示範區。（1）103年度配合本署「彰雲地區地下水補注推動計畫」、「台灣西部河槽地下水補注設施實施計畫」推動，辦理濁水溪沖積扇北港溪地下水補注潛能河段補注評估、地下水對豐枯水年水文極端事件之敏感度分析與長期 人為抽取地下水之衝擊評估等。（2）104年度則配合中央地質調查所「台灣南段山區地下水資源調查」之103年度「台灣南段山區地下水資源調查與評估」邊界條件側向補注量研究成果，辦理屏東平原水文地質3D模型、地表、地下水整合性數值模式建置與大潮州人工湖尚未完工營運前之地下水補注方案與成效之情境模擬等。（3）105年度執行屏東平原地下水對豐枯水年水文極端事件之敏感度分析、長期 人為抽取地下水之衝擊評估與配合大潮州人工湖於104年底第一階段50公頃完工營運後，使用地表地下水耦合模擬模式評估實際補注效益，另賴旱期氣候資訊之充分掌握，以避免過度開發使用地下水源，結合季節性預報進行模擬分析，以預先掌握枯水期地下水情勢，豐水期則應依據優勢補注區位，規劃人工補注方式，減緩枯水期超抽之衝擊等。

Groundwater is one of major water resources in Taiwan. Due to over pumping of groundwater for the past decades, both the Zhuoshui River Alluvial Fan and the Pingtung Alluvial Plain having abundant groundwater resources were faced critical issues of land subsidence and degradation of groundwater environments, such as sea water intrusion and contamination. Although subsurface water and surface water are naturally linked in view of hydrological cycles, great discrepancies in residence times and responses to different hydrological forcing are existed. Rainfall in Taiwan has great spatial and temporal variations causing significant wet and dry seasons, which limited the development of new water resources and thus brought great challenges in water resources management of Taiwan. Therefore, it is important to develop integrated methodologies for taking advantages of various spatial and temporal characteristics of surface water and subsurface water to meet the requirement of sustainable development in water resources. In the first year (2014), we analyzed observed long-term hydrological data of the Zhuoshui River Alluvial Fan to reveal variations of groundwater levels in wet and dry years and their sensitivities to extreme events. Then the integrated numerical modeling of surface water and subsurface water, the WASH123D model, was applied to simulate hydrological responses of the Zhuoshui River Alluvial Fan to long-term and event-based forcing and to investigate effects of pumping on groundwater levels. Furthermore, a series of scenario simulations were performed to suggest optimal solutions for artificial groundwater recharge near the apex of Zhuoshui River Alluvial Fan and the source area of Beigang River from options of artificial lakes, detention structure inside stream channel, ponds on the floodplain, or other candidate measures. On the part of hydrological analyses, most rainfall stations observed an increasing trend in annual rainfalls while most wells shown a decreasing trend in groundwater levels showing natural variations of groundwater has been significantly affected by human pumping. The low flows at the Hsichou Bridge are much lower than those at the Changyun Bridge from the analyses of flow exceedent probability, which should be further investigated to reveal the amount of interflow between those two stations. Significant decreases of groundwater levels in both F2 and F3 zones before changing points in the time series of groundwater levels roughly match areas having serious subsidence in Changhua and Yunlin Counties. After changing points, notable decreases of groundwater levels in the F2 zone were observed on the north side of the Puzih Creek and in the F3 zone on the south of the Wu Creek, which enlighten possibilities of subsidence in near future over both areas. In general, the low groundwater levels are in March to May and gradually rose to the peaks in September to December due to recharges of rainfall and river water in wet seasons. At both the apex and the mid of the Zhuoshui River Alluvial Fan, the lag time between groundwater level peak and rainfall peak are roughly 2 months, while 5 months lags are observed at the tail. Seasonal effects on variations of groundwater levels play more important roles than effects of wet or dry years. On the event scale, lateral movements of groundwater are more important at the apex of the Zhuoshui River Alluvial Fan. The correlations between groundwater levels and rainfall amounts are weak over the middle and the tail of the Zhuoshui River Alluvial Fan during extreme events. More studies are required to reveal effects of lateral groundwater movements and extra hydrostatic pore pressures induced by extreme rainfalls. On the part of revising conceptual hydrogeological models, a near-surface layer was newly added at the top of the Zhuoshui River Alluvial Fan. Hydrogeological units included surface mud layer (for mud depth greater than 4 meters observed in well logging), terrace, plateau, hilly red-soil, and river sediment. Hydraulic conductivities of each layer were assigned based on material types and results of pumping tests of nearby wells. With revised hydrogeological models, a 3D non-structural mesh generation procedure and a 4D visualization technique were developed based-on the GIS platform for applying the WASH123D simulations. Peak river stages and peak time of the Zhuoshui River during the Typhoon Morakot were accurately captured by the WASH123D model. Simulated long-term variations of groundwater levels reflected patterns of observed data. Lateral groundwater movements from both the Mingchu Basin and the Douliu Hill toward the Zhuoshui River Alluvial Fan are important sources of recharging regional groundwater. More water is moved in the northern and the northwestern directions toward the Changhua County than that into the Yunlin County with relatively serious subsidence. For both the midstream and the downstream areas of the Zhuoshui River and the Peikang Creek, significant groundwater recharges by river water can only be observed during extreme events. The 4D visualization of long-term simulations can improve our understanding of regional and large scale patterns of groundwater movements of the Zhuoshui River Alluvial Fan. Effects of human pumping over the past 10 years were further simulated by the WASH123D model. At the apex area, groundwater levels were mainly affected by seasonal variations. Human pumping shows significant impacts on groundwater levels over the north of the apex area, while moderate impacts are observed around the mid of the alluvial fan. Substantial impacts on groundwater levels induced by human pumping are observed over the tail area of the alluvial fan. We further analyzed differences of simulated groundwater levels between with and without pumping scenarios. Discrepancies in groundwater levels are insignificant for areas around the Zhuoshui River bank due to river recharges. On the north of the apex area also shows significant differences due to pumping. For the Changhua County, substantial groundwater differences are observed at the Lukang town, the Fuhsing township, the Puyan township, and the Fangyuan township induced by over pumping. For the Yunlin County, similar situations of over pumping are revealed at the Taihsi township, the Dongshi township, the Shuilin township, and the Peikang town. Groundwater levels of both the Dongshi township and the Liujiao township in the Chiayi County are also significantly affected by human pumping. On the part of assessments of different groundwater recharge measures under the same rainfall scenario, the man-made ponds measure at the apex can raise groundwater level for 2 meters with the maximum recharge amount of 0.8 million tons per day, the Shishuipu river segment measure can raise groundwater level for 0.8 meters with the maximum recharge amount of 0.55 million tons per day, the northern Zhuoshui River floodplain measure can raise groundwater level for 0.3 meters with the maximum recharge amount of 0.45 million tons per day, and the Peikang Creek recharge measure may have the maximum recharge amount of 0.40 million tons per day. It is noted that inundation risk should be reduced for the Peikang Creek recharge measure or other alternatives should be proposed. Based on achievements acquired in this study, hydrological analyses help reveal regional characteristics of hydrological quantities and successfully link with areas suffering subsidence hazards. The revised hydrological model is applied to the integrated numerical simulations of coupled surface water and subsurface water by the WASH123D. Regional hydrological characteristics, effects of human pumping, and assessments of groundwater recharge measures of the Zhuoshui River Alluvial Fan are numerically investigated by the WASH123D model. Our results demonstrate successful localizations of the WASH123D model, which can be served as a powerful tool for groundwater recharge assessments and to support the Water Resources Agency on decision making of groundwater resources managements.

本研究利用地表地下水整合數值模式WASH123D，針對台灣濁水溪沖積扇進行地下水資源管理應用研究。研究發現，該區域年雨量雖有上升趨勢，但地下水位卻呈現下降，顯示人為抽水影響顯著，並與地層下陷區域吻合。模式模擬結果顯示，地下水主要來自名竹盆地與斗六丘陵，並向北及西北流動。研究進一步評估了多項地下水補注方案，如人工湖、河段滯水設施等，並量化其效益，為濁水溪沖積扇的地下水資源永續經營提供決策參考。