圖書典藏及影音數位平台

臺中地區因縣市合併後，隨著經濟發展與人口密度增加，而在臺中海線地區也隨即迅速發展，需用水量亦持續成長，以大臺中地區水資源供給量而言，主要供水來源為鯉魚潭與石岡壩，未來若開發新園區預估水資源需求量必然增加，皆顯示出臺中地區水資源困境。因臺灣降雨時空分布不均，且開發新水源不易，其中地下水資源為重要供水來源之一，目前水資源短缺的策略，未來預計以大安大甲溪水資源聯合運用工程供給大臺中地區用水，而短期內鯉魚潭水庫水源仍需供給苗栗地區使用，因此探討臺中海線地區之地下水資源，如能增加水資源供給量，將可避免持續調配農業用水解決用水短缺問題。 本計畫主要針對臺中海線地區地下水資源，以北為大安溪和大甲溪沖積扇平原，以南為梧棲、龍井海岸平原，因規模不大地下水資源不多，而臨近的臺中盆地區域，因其地質構造，推估地下水資源豐沛，有賴地表地下水關聯機制，並運用完整之整合性地表地下水耦合模擬模式，評估臺中海線地區地表水與地下水交換情況，探討臺中海線地區與臺中盆地大肚山隘口地下水資源之最適供水方式與區域，以釐清地表水與地下水互動機制與關聯，綜合評估地下水運移，透過合理的使用與管制，作為後續水資源管理調配可行性、都市計畫及國土規劃策略參考。 經濟部水利署水利規劃試驗所(以下簡稱本所)依據經濟部水利署108年11月19日經水綜字第10714072090號函「本署108年度委託服務預定計畫複審會議紀錄」會議紀錄決議，爰提本計畫書。

After the cities merging plan is conducted in Taichung, the consumption of water in people’s livelihood and industry have increased continuously due to economic development and dense population in coastal regions. Developing new water resources has been constrained and troubled because of the uneven distribution of rainfall in both spatial and temporal in Taiwan. Thus, it is accessible to take groundwater resources as supportive water supply sources. How to effectively utilize both surface and ground water in terms of hydrological characteristics in different spatial and temporal scales would be a key issue for the country to meet the demands of the future urban development. This study focuses on the investigation into groundwater resources in Coastal Taichung. By adopting the integrated surface and ground water numerical model to simulate the flow change trend, the related mechanisms and influence characteristics are discussed. Further, the water exchanges between surface and underground, the groundwater flow directions are also evaluated comprehensively, which would be the future references of groundwater resources management. Previous literature has reported that groundwater recharge volume estimation was evaluated by vertical infiltration or Darcy’s law. The result reveals annual groundwater recharge is around 5.30 billion tons in that area. But numerical models are applied for the estimation with great accuracy in recent years, annual groundwater recharge is around 5.91 billion tons. Moreover, the current trends in water resources in Coastal Taichung is further elaborated. The groundwater has higher level due to the lateral recharge from Dadu Plateau and Alluvial fan recharge from Dajia River. The groundwater table has significant discrepancies during the rainy and dry season in Dajia alluvial fan while there have no representative variations in Qingshui Coastal Plain. Then, to further explore the flow velocities and directions, two groundwater monitoring wells is set in Dajia District and Shalu District respectively for conducting three sets of field observations. Results obtained from these experiments show that in Dajia District, the stream mainly flows from east to west which correspond with the Dajia river’s flow direction. The maximum flow velocity is 7.15×10-5 m/s which revealed the flow has significant trend in north shore of Coastal Taichung. But in Shalu District, the stream flows subtlety from south to north. The maximum flow velocity is below 3.91×10-5 m/s which represented the flow trend is not obvious owing to the flat landform in mid-south part of Coastal Taichung. In addition, according to the groundwater table measurement, on the west of Dadu Plateau has insignificant water flow fluctuation. To increase the accuracy for the simulation, the study then conducts a simulated environment for river, surface and groundwater in Coastal Taichung. In river part, the flow boundary condition and tide boundary condition are exploited for the upstream and downstream. Then in overland flow, take the watershed as the boundary to simulate the surface. Lastly, in subsurface flow, groundwater simulation is conducted by head boundary to carry out the groundwater table value as well as local?grid refinement. The result reveals the parameters the study used are adequate. Similarly, the hydrograph and regional surface inundation are both simulated effectively. The groundwater simulation also corresponds with the actual situation; the groundwater table has a steady increase trend in coastal area. However, the server variation in groundwater level can be captured due to the surface heavy rainfall in the central area of Taichung Basin. The simulation result is up to four times greater than the observation’s, which leads to the parameter adjustment later. By the presenting the significant flow velocity in the north shore, there have more water resources in the Dajia Alluvial fan due to the recharge of Dajia river, while there has no obvious flow velocity in the south shore. Thus, the initial simulated result reveals that there have more groundwater resources for scheduling in north shore to meet the commands of water consumption in Costal Taichung. Furthermore, according to the historical data, there is a stable variation in the groundwater level, the value discrepancies between the high (15%) and low rate water level (91%) is merely 0.5m. The value of minimum rate water level (47%) is also fell between the high and low rate. Therefore, the variation of groundwater table belongs to linear which is more stable, not interfered by external force in the Coastal Taichung. In the future, to sustain the management of water resources, the study will be incorporated with the groundwater mechanism by different strategies in dry and rainy period.