臺中海線地區地下水資源量化評估

臺中地區近年因縣市合併、人口增長及經濟發展下，需用水量快速成長，預計2021年就會出現供水缺口。若能妥適取用地下水做為多元水資源開發，將有助於供水的穩定。臺中地區地下水系統在台灣主要的九大地下水分區中屬於臺中地區地下水區，並可細分為三個子系統：臺中盆地、梧棲龍井海岸平原、大安大甲沖積扇，在海線地區主要的地下水系統即為梧棲龍井海岸平原。本研究以地下水蓄水量歷線法進行臺中海線地區的地下水資源量化評估，首先建立梧棲龍井海岸平原地下水系統概念分層模型與水平衡模型，然後再取地下水監測網之每日水位紀錄以及現地試驗所得之水文地質參數計算整體蓄水量，依水量變化計算得到2008～2014年間，梧棲龍井海岸平原年抽水量約0.32～0.76億噸之間，淨補注量約0.21～0.81億噸之間，抽水與補注大致維持平衡狀態，但因淨補注量僅佔降雨量的9 %～24 %之間，顯示海岸平原補注不豐，應與地質條件多細砂及不透水層有關。未來若欲開發臺中海線地區之地下水資源，需特別注意區域地質條件，應選取有連續且廣大的礫石層分布之區位優先進行開發，並且對於深度超過50 m的深井鑿設需進行管制。

關鍵字

地下水蓄水量歷線法；海岸平原；水資源量化評估

並列摘要

In recent years, due to the merger of county and city, population growth and economic development, the water consumption of Taichung increased rapidly. It was expected that there will be a water supply gap in 2021. Proper access to groundwater as a diversified water resource will help stabilize the water supply. Overall, the groundwater system of Taichung belonged to the Taichung Area Groundwater Area in 9 major groundwater areas of Taiwan and can be subdivided into three sub-systems: Taichung Basin, Yuxi-Longjing Coastal Plain, and Daan-Dajia Alluvial Fan. Yuqi-Longjing Coastal Plain is the main groundwater area of coastal areas in Taichung. In this study, the groundwater hydrograph method was used to quantitatively evaluate the groundwater resources of the coastal plain in Taichung. Firstly, the conceptual layered model and water balance model of the groundwater system in coastal plain were established. Then, the daily water level record from the groundwater monitoring network and the hydrogeological parameters obtained from the field experiments were used to calculate daily groundwater storage. According to the change of water volume, the annual pumpage is between 0.32 ~ 0.76 billion tons, and the net recharge is about 0.21 ~ 0.81 billion tons. Between the annual pumpage and recharge, the groundwater balance was maintained, but the net recharge only accounted for 9 % ~ 24 % of the rainfall, indicating that the recharge sources were limited on Coastal Plain. In the future, if we want to develop the groundwater resources of Coastal Plain in Taichung, special attention should be paid to the regional geological conditions. The location of continuous and extensive gravel layer should be selected for priority development, and deep wells with depth exceeding 50 m should be limited.