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，已完成濁水溪沖積扇北港溪地下水補注潛能河段補注評估、地下水對豐枯水年與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 over both the Zhuoshui River Alluvial Fan and the Pingtung Alluvial Plain in past decades, critical issues of land subsidence and degradation of groundwater environments were occurred recently. The objective of this project is to apply integrated numerical modeling of surface water and subsurface water to investigate carrying capacities of groundwater resources. 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 on water resources management in 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 third year (2016), both the Zhuoshui River Alluvial Fan and the Pingtung Alluvial Plain were included in our studies. We first analyzed observed long-term hydrological data of the Pingtung Alluvial Plain 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 Pingtung Alluvial Plain to long-term and event-based forcing and to investigate effects of pumping on groundwater levels. Seasonal forecasting, having lead time of 1 to 3 months, were adopted into simulation platforms developed in the past two years to provide groundwater outlooks with lead time of up to 3 months to support groundwater management. Scenarios of seawater intrusion were further simulated for the Pingtung Alluvial Plain to investigate differences in migration of seawater intrusion in both wet and dry seasons to support the planning of future against measures. On the part of hydrological analyses for the Pingtung Alluvial Plain, most rainfall stations observed a stationary trend in annual rainfalls while increasing trends in both annual temperature and annual evaporation were significant. Spatial patterns in annual groundwater levels were increase over the west plain and decrease over the east plain. Regions having significant decreased groundwater levels before detected changing points of groundwater levels are consistent with townships of Changing Jiadung, Fangliao, and Linbian having severe land subsidence. Decreasing trends have been observed over the Pingtung Alluvial Plain since 1998 due to over pumping. Analyses of monthly scale groundwater variations found the correlation between monthly groundwater levels and monthly rainfalls are higher over the apex of alluvial fan than those over the tail of alluvial fan. Notable correlations between monthly groundwater levels and monthly river stages were found for monitoring wells near rivers. Results of correlation analyses during extreme events found short response time and high correlations between groundwater level variations and cumulative rainfalls for events having high rainfall intensities and short durations which are suspected to be the effect of hydrostatic pressures caused by surface inundation and infiltration. On the other hand, long response time and weak correlations between groundwater level variations and accumulative rainfalls were observed for plum rainfall events. Effects of human pumping over the past 10 years were simulated by the WASH123D model. Trends of regional groundwater levels were higher on the northeast and lower on the southwest. For drought lasting for 2 to 4 months, significant differences in groundwater levels can be observed due to pumping. Rising of groundwater levels due to rainfall recharges can be observed after onset of plume rainfalls, and effects of pumping on lowering groundwater levels are less significant. Based on hydrological analyses and simulations of pumping intrusion, the most affected region on groundwater level depletions are consistent with regions having sever land subsidence. It is noted pumping over upstream of the Linbian River may reduce horizontal discharge of groundwater toward downstream coastal area. In this study, the integrated approach of combining seasonal forecasting and coupled surface and groundwater simulations were developed to provide groundwater outlooks. Taking outlooks of groundwater levels in April, May, and June as examples, the depletions in groundwater levels may reach 5 m due to changes in rainfalls from the consecutive 3 months with above normal scenarios to all below normal scenarios over the Zhuoshui River Alluvial Fan. Using the same simulation scenarios, the depletions in groundwater levels over Pingtung Alluvial Plain are less than 1 m. Seasonal variations of groundwater levels over the Pingtung Alluvial Plain are 2 m. For aquifers having chloride ions concentrations higher than 2000 mg/L, elevated groundwater levels in wet seasons may reduce chloride ion concentrations in a range of 265 to 867 mg/L. The reduction of chloride ion concentration is significant in the unconfined and high concentration areas.