蘭陽平原位於台灣東北部，東鄰太平洋，西側與南側接雪山山脈及中央山脈。本研究地區位於蘭陽溪至羅東溪之間－大隱地區，此區位於扇頂補注區的礫石層範圍內，在水文地質方面，屬於非拘限含水層分布區域，適合地下水區。為了瞭解蘭陽平原大隱地區之地下水文特性，遂利用二維地電阻法(Electrical Resistivity Imaging, ERI/ Electrical Resistivity Tomography, ERT)調查並計算淺層地下水位深度及比出水率隨季節之變化情形。在研究區域內，每次布設十條二維地電阻測線，並於測區內之大隱地下水觀測井附近進行試驗，以利進行推估地下水位面之比較，而後將調查所得電阻率資料帶入Archie’s Law 轉換成相對含水量，並藉由van Genuchten與Brooks-Corey保水曲線推估地下水位深度，以及利用飽和及殘餘含水量計算比出水率，最後將所得結果繪製成地下水位高程分布圖。本研究區域其比出水率約0.06至0.15之間，並發現地下水位由西南向東北遞減趨勢，與羅東溪流向大致一致，推測本區分別受到山區及河流補注影響。最後，比較兩種保水曲線模型推估結果，以van Genuchten模型較為接近真實地下水位面。;The Lanyang Plain is located at the northeastern part of Taiwan, which is adjacent to the Pacific Ocean and the Hsuehshan Range, Central Range is in its south to west. The study area is located in Da-yin area which is between Lanyang River and Luodong River, which brings thick gravel layers. This area is a great potential for groundwater developments, so we tried to use geophysics method to know the hydrogeological parameters of this area. In the study, We applied 2D Electrical Resistivity Imaging (ERI) method to estimate the depth of groundwater table and specific yield of the unconfined aquifer in dry and wet seasons. We have deployed ten survey lines in the study area. And the investigation is conducted near the Da-yin groundwater observation well to compare with groundwater estimation. Based on Archie′s Law, we converted the resistivity data into relative water contents. Using the van Genuchten model and Brooks-Corey model to characterize the depth of the water table, and calculate the specific yield by the difference between the saturated and residual water contents. Finally, the results can depict the water level distribution in the study area. According to the results, the specific yield is 0.06 to 0.15 and the groundwater level decreases from southwest to northeast, which is same as the flow direction of Luodong River. It is speculated that this area is affected by the rainfall from mountain and river recharge. Finally, comparing the estimation results, van Genuchten model is closer the real groundwater table than Brooks-Corey model.
