由過去中央地質調查所的地質鑽探資料顯示，台中盆地在200公尺以內深度地下沉積物，以未固結的全新世沖積礫石層，與經過壓密作用的更新世礫石層為主要組成。由於資料顯示台中盆地可能具有良好之非拘限含水地層，為進一步提供台中盆地地區的地下水保護與劃設補注敏感區，本研究採用地電阻方法，配合區域地質鑽井資料，進行由大肚-烏日一帶至霧峰一帶之地下調查。地電阻電極排列方式使用溫奈-施蘭卜吉方法，在台中盆地中部太平沖積扇與烏溪沖積扇一帶區域，收集23條二維地電阻剖面，平均探測深度約為60公尺。比對現有地質岩心鑽井資料，發現在探測深度內，太平沖積扇的霧峰鑽井與烏日鑽井附近之地電阻反應顯示有較厚的低電阻的泥質地層存在，電阻率約在40 Ωm以下，而在其餘地區地電阻剖面均呈現大於300 Ωm之高電阻率礫石層反應；而在烏溪沖積扇施測結果顯示地下電阻率均為大於300 Ωm，研判為礫石層反應，並未出現泥質地層之低電阻反應。本研究另外也將一維地電阻資料，利用地質統計的克利金法與距離反比法，繪出二維電阻率模型。藉由二維模型與鑽井資料之驗證，而認為台中盆地中部，在60公尺深度範圍內的泥質地層分布並未呈現大面積連續分佈，僅局部分布於烏日與霧峰一帶，且地下泥質地層屬於薄層分布，因此台中盆地之淺層水文地質主要架構應為以非拘限的礫石含水層為主，而此一厚層的非拘限含水層，可以作為潛在的天然補注地下水庫，作為未來的水資源管理與利用。;This research used Electrical Resistivity Imaging (ERI) method and near geological drilling data to investigated hydrogeology between Datu-Wurih area to Wufong area in the Taichung Basin. The sediments are consisted of unconfined Holocene conglomerate and compact Pleistocene conglomerate in the uppermost 200 m in the Taichung Basin from the drilling data of the Central Geological Survey. We used the Wenner-Schlumberger array in the Taiping alluvial fan and Wurih alluvial fan. We conducted 23 2D Electrical Resistivity Imaging(ERI) measurements and investigated 60m of depth. Compared with near geological drilling data from the observation wells, we found that there was a mud layer with a resistivity lower than 40 Ωm in Taiping alluvial fan near Wurih and Wufong observation wells. On the other hand, in the region with thick conglomerates exhibits resistivity values that are higher than 300 Ωm. In order to delineatethe recharge area which has no insulating mud layers from the resistivity measurements, we used 1D electrical resistivity data for geostatistical spatial modeling, including the krigging and inverse-distance modeling. We compared the 2D resistivity model with drilling data in the basin to show the possible recharge area with thick gravel and conglomerates. The results show that sporadic mud layers only located from the surface to a depth of 60m near the Wurih and Wufong area. Therefore, the majority of the sediments in the Taichung Basin may be consisted of the unconfined conglomerate and serve as the unconfined aquifer in the Taichung basin. The thicker unconfined aquifer where can be natural groundwater recharge area. It can be the alternative water resources for the domestic usage in the future.
