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。

Due to the difficulty in hydrogeological data survey, the numerical model is a widely used tool to supplement the regional groundwater flow field data to complete the hydrogeological framework, and the boundary hydraulic conditions are the most important items to control the groundwater flow field﹐ especially it is an important factor to control the inflow and outflow. However, it is limited by the source of the data. The setting of the hydraulic boundary often needs to be simplified to simplify the existing data, or to select a neighboring station for setting. Therefore, the reasonable and correct hydraulic boundary becomes an important task of the simulation work. 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. According to various data, the main groundwater recharge sources in the Pingtung Plain ate the north and east river alluvial fans, while the groundwater level in the recharge area varies greatly. The groundwater level in some sections is located deeper, indicating that the river is the suspended river. Therefore, the river in the alluvial fan should be the source of recharge of groundwater. At the center of the alluvial fan, the groundwater level gradually approaches the river and is transformed into a groundwater replenishment river. Therefore, the focus of the alluvial fan position, including:1. Investigation of groundwater level on the river bank and exploration of groundwater recharge in rivers; 2. The exchange area between groundwater and surface water in the section channel; 3. Analysis of groundwater recharge by river water at the top of the fan; 4. Appropriate hydraulic boundary position determination. This project proposes the basis for setting the hydrogeological boundary of the Pingtung Plain, as well as the groundwater level station set by the boundary conditions and the infiltration rate parameter of the river. The hydraulic boundaries and setting considerations recommended in this project include: (1) East side boundary- river alluvial fan The results of the survey and analysis show that there are four main alluvial fan areas in Pingtung Plain. Along the eastern side of the Chaozhou fault section is the bedrock of the foothill, and the west side is the recent alluvium. Therefore, except for the alluvial fan apex of the river, the amount of recharge in the foothill is very low, and the no flow boundary can be adopted. The river level of the alluvial fan apex is higher than the groundwater level, and the river water is replenished with groundwater. The groundwater also has lateral replenishment from the upstream valley and vertical replenishment of the river water. Therefore, it can be set by using the water head boundary of the river and the river filling conditions. (2) North side boundary- the Meinong River area In the Zhongtan Bridge area, Meinong River is the junction of the north terrace deposits and the recent alluvium on the south side. The alluvial layer on the north side is muddy and the bedrock is shallow. The investigation showed that the boundary is for the groundwater replenishment of the river water, so it is recommended to set the water head boundary. (3) West side boundary -Fengshan hill In the past, the Fengshan hill was often used as the no flow boundary as well as the Gaoping River was used as the constant head boundary for the western boundary of the Pingtung Plain. There is a multi-layer aquifer structure below the middle and lower reaches of Gaoping River. The river water head should be limited to the first aquifer with better connectivity. The second and third aquifers are not suitable for the water head. Therefore, it is recommended to use Fengshan hill as the no flow boundary. (4) South Coastal Boundary Due to the stable head of the coastal boundary, if the simulation range is the entire Pingtung Plain, the coastal boundary is recommended to be set along the coastline with the fixed water head. However, there are many artificial influences on the coast of Pingtung Plain, so this project is evaluated separately. However, there are many artificial influences on the coast of Pingtung Plain, so this project provides four suggestions based on the different requirements of simulation target, including (a) analysis of tidal zone, (b) extrapolation of coastal boundary, (c) change of hydraulic parameters caused by ground compaction, and (d) artificial use of simulation programs. (5) Pingtung Plain boundary demarcation and setting case The important work of this project is to propose the appropriate boundary design and condition setting of the Pingtung Plain. This project provide boundary demarcation and setting reference according to different simulation ranges. The west and south boundaries may refer to the west and south boundary of the Pingtung Plain announced by the Water Resources Agency, namely the Fengshan hill and the coastal area. The Meinong area on the north side of the boundary is bounded by the junction of terraces and the modern alluvial layers. The scope can be set by referring to the geological data integration query database of the Central Geological Survey. The eastern part of the Pingtung Plain is bounded by the Chaozhou fault. The lower part of the Chaozhou fault is the Miocene sedimentary rock. However, the Miocene sedimentary rocks in the Pingdong plain are not exposed, so the fault location is based on the topography, while the hydrogeological model will taking the boundary between the rock disk and the sedimentary plain as the boundary. Therefore, the east side proposes to take the 200 m contour line of the foothill as the boundary, and define the boundary between the Xinwei Bridge, and define the boundary between the Xinwei Bridge, the contour line and the junction of the terrace and the modern alluvium layer on the north side.