圖書典藏及影音數位平台

臺灣主要地下水分區如屏東平原及濁水溪沖積扇，由於富涵地下水資源故早已成為重要地下水資源區，迄今已投入相當資源進行水文地質架構釐清與地下水位觀測，並已完成豐碩之地下水資源相關評估工作。惟不同計畫受工作區域、評估時間以及方法限制，於地下水分區之邊界條件設定不盡相同，對於統合各地下水分區困難度高，故為建立地下水模擬分析條件之標準與共識，俾利未來地下水管理相關工作推動與執行。本計畫針對主要地下水分區的天然邊界：含麓山帶邊界、河川沖積扇及海岸邊界等，進行邊界條件釐清及研討，瞭解地下水分區邊界區域上地下水之動態以及補注或流出來源，藉由調查所得之現場資料說明主要河川與地下水之及地下水與海洋之交互作用關係，配合既有地下水位站、河川流量站等資料進行綜合評估，並於工作期間邀請學者專家，完成地下水分區邊界條件評估標準建置，作為後續相關模擬分析設定基準。

Pingtung Plain has become an important groundwater resource area due to its rich groundwater resources. It has rich hydrogeological data, investigation and research results. Therefore, the plan has carried out on-site supplementary investigation and experiment, and cooperate with existing data. It uses the groundwater division of Pingtung Plain as an example to set up the hydrogeological conceptual model of the Pingtung Plain boundary area, and the appropriate hydraulic boundary setting conditions are proposed according to the location and conditions of each station. The project first collected the 24 cases groundwater-related plans and researches of the Pingtung Plain. The numerical model boundary settings were different from the numerical model range, grid size, simulation time, and temporal setting (transient state or steady state). The boundary settings usually uses water head. However, it may cause the groundwater recharge amount too large, which affects the groundwater dynamics and leads to over-optimistic assessment of groundwater resources, and it has a great impact on the overall work results. The composition of the Pingtung Plain is mainly from the alluvial fan system of the river. Therefore, the hydrogeological structure of the alluvial fan and the groundwater flow characteristics caused by the sedimentary environment have become important considerations for the hydraulic boundary. According to the position of the alluvial fan, the plan divides the Pingtung Plain into the Fengshan hillside boundary on the west side, the Meinong River boundary on the north side, the south coastal boundary, and the alluvial fan boundary of the northeast-east side of Loaning River, Ailiao River, and Linbian River. The fan apex of the alluvial fan in Pingtung Plain is mainly composed of water permeable gravel and sand layer. The proportion of fine-grained sediment increases in the central part of fan and fan toe areas, including the silt and mud, and there is a multi-layer aquifer structure. The main groundwater source is the lateral groundwater provided by the upstream valley and the vertical infiltration caused by the surface water in the central part of fan and fan toe areas, which is the most important groundwater source in alluvial fans. At the fan apex, the bedrock is suddenly increased by shallow, and the water permeability is good. The groundwater recharge by the above supplementary source is rapidly flowed downstream by the gradient, so that the groundwater depth is deep at the fan apex, and the hydrological geological condition of the alluvial fan is formed. In order to meet the groundwater flow characteristics of the alluvial fan, the plan is aimed at the hydrogeological conceptual model of the alluvial fan of Meinong River, Ailiao River, and Linbian River. The river infiltration at the fan apex is recommended as water head boundary. However, because of the absence of observation data, the river infiltration can be set as specified head and the depth of the bedrock can be set to control the lateral groundwater recharge. The river infiltration can refer to the river water infiltration rate of each river section obtained from the existing surveys, and calculate according to the grid size. After the infiltration amount is set in the river channel grid, and corrected by the groundwater table calibration process to obtain the boundary conditions and simulation results in accordance with the simulation period. Due to the hydrogeological characteristics and long-term groundwater utilization, the coastal aquifer of Pingtung Plain has caused the water table to be lower than the sea level, and the subsidence and the seawater intrusion has occurred. For the hydrogeological numerical models, the coastal boundary has been artificially influenced. Two important factors need to be considered, the first is whether the condition of the subsidence has affected the aquifer hydraulic character. The second is that lower groundwater table and the seawater intrusion caused by human activities. Both need to be considered to incorporate with coastal boundary conditions to meet the status quo.