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 in past decades, critical issues of land subsidence and degradation of groundwater environments, such as sea water intrusion and contamination, were occurred in both the Zhuoshui River Alluvial Fan and the Pingtung Alluvial Plain which formerly have abundant groundwater resources. Although subsurface water and surface water are naturally linked with each other, 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. Therefore it is important to develop integrated methodologies for taking advantages of various spatial and temporal characteristics of surface water and subsurface water to support sustainable development in water resources. In the second year (2015), we first analyzed past assessments of potential surface and subsurface water resources of the Pingtung Alluvial Plain, including setting of boundary conditions and hydrogeological parameters. Annual groundwater recharges are in a rage of 1.1~1.4 billion tons with an average of 1.211 billion tons. The difference between wet year and dry year may reach 0.25 billion tons. Annual groundwater pumping amounts are in a rage of 1.0~1.3 billion tons with an average of 1.124 billion tons. Although long-term averages recharges are greater than pumping amounts of the entire Pingtung Alluvial Plain, some local pumping amounts are much greater than naturally recharges and induced severe degradation of groundwater environments. The next task is to develop the digitalized 3D hydrogeological model of Pingtung Alluvial Plain by integrating drilling data of Central Geological Survey (CGS) and Water Resources Agency. We followed the same concept of the CGS not considering geological differences between the Recent epoch and Pleistocene epoch. Hydraulic conductivities of each aquifer were given as zone A of gravels, zone B of very coarse and medium coarse sands, zone C of fine sands and muds, aquitards, surface muds, river sediments, and Linco gravel rocks. Horizontal hydraulic conductivities were given as 10 times of vertical hydraulic conductivities, while no difference between them was considered for rock materials due to they are relatively homogeneous. The third task is to develop coupling surface water and subsurface water numerical models with the WASH123D model. Three hydrological events were selected to calibrate and validate parameters. The 1-D river modules include Chishan Creek, Laonong Creek, Ailiao Creek, Gaoping Creek, Donggang Creek, Linbian Creek, and Lili creek. The 2-D surface water module contains triangular elements to descried topographic variations with setting of fine elements for hilly terrain on left and right sides of the Pingtung Alluvial Plain, mostly around Meinong, Longdu, and Sinwei, to reflect elevation variations The 3-D subsurface module covers 4 aquifers, namely the F1 aquifer, the F2 aquifer, the F3-1 aquifer, and the F3-2 aquifer, as developed by the hydrogeological concept model. Simulated water stages and peak times were acceptable in comparison with observed data. Simulated surface inundations were consistent with post-event field investigations. Responses of simulated groundwater levels with respect to observed variations were overall consistent. Developed coupling surface water and subsurface water numerical models were successfully calibrated and validated. We further analyzed simulated groundwater variations during three hydrological events. Significant variations of groundwater levels were found in mountain areas around Laonong Creek, Ailiao Creek, and Linbian Creek, showing increase of pressure heads and high groundwater velocities due to existence of high permeable surface layer promoting event infiltrations. Those areas are worthy to conduct further investigations for promoting groundwater exploitation and usages, such as recharge projects of Gaoping Manmade Lakes and Dachaojhou Manmade Lakes. The last task is to apply the developed integrated model to perform scenario assessments of groundwater recharges of the Dachaojhou Manmade Lakes prior to the completion of constructions. Based on event simulation results, significant groundwater recharges were found around areas of rivers entering flat plane. High vertical groundwater velocities indicating favorable recharges were caused by reduced surface gradients and permeable surface layers. The Dachaojhou Manmade Lakes were selected from areas promoting groundwater recharges. In view of the extreme events like the Typhoon Morakot has abundant surface water can be used as the water source of the Dachaojhou Manmade Lakes, scenario simulations were performed and found groundwater recharges mainly occurred in both the F1 and F2 aquifers. On the south sides of the lakes have larger recharge areas than those of other sides around the lakes. And the groundwater recharges were diffusively toward Donggang Creek. It can be concluded that during the period of recharges simulations, rising of pressure heads about 0.65 m, and mainly occurred in an area of 24 km2 around the lakes with a recharge amounts of 9.6 million tons. Based on tasks completed in this year, the hydrogeological conceptual model and coupling surface water and subsurface numerical models of Pingtung Alluvial Plain were successfully developed and applied to study hydrological responses to event forcing, which are very supportive to understand hydrological characteristics of regional surface water and subsurface water, as well as their interactions in events. Quantitative assessments with tools developed in this study are important to decisions of major engineering constructions and can be applied to support planning of groundwater management measures to achieve visions of sustainable development and conservation of national land and water resources.