英文篇名
Using 2D Time-Lapse Electrical Resistivity Tomography to Estimate the Water Table and the Specific Yield of the Unconfined Aquifer: A Case Study in the Minzu Basin
作者
張竝瑜、姚馨如、 吳昱昌、宋家宇、 林鼎竣、嚴精明、張良正、陸挽中、賴慈華
關鍵字
地電阻、地下水、比出水率、名竹盆地
摘要
本研究透過在名竹盆地,於乾濕季節重複的大區域地電阻量測,推導出每個地電阻施測剖面中,垂直方向上的相對飽和度與深度變化;再推估地下水位面深度與可能的比出水率。並與觀測井地下水位高程進行比對校正,推估本區域乾濕季節的地下水位面高程分佈變化。經過與觀測井水位比較,我們發現若使用校正係數Ks=0.98推估地下水位面深度,具有較小的平均誤差(約為0.25米),因此本研究中採用此一校正係數,作為乾濕季節重複施測資料的地下水位面推估之用。而經過推估計算,名竹盆地於2017年三月,地下水位面深度約8.5米至15.8米深、六月地下水位面深度則因進入濕季而有顯著上升,約為4.6至15米深、八月地下水位深度則維持在約3.4至13.9米深,而九月的地下水位面深度則在4.8至14.2米深。整體而言,地下水位面在乾濕季節均呈現大致由濁水溪上游向下游遞減之趨勢。然而若比較乾濕季的地下水位面變化分佈,大致呈現在Min_02、Min_03、Min_06區域附近,有一南北方向的乾濕季較低水位差區域,幾何分佈上大致與河道方向正交。檢視推估之比出水率資料,測區上游段與靠近濁水溪河道的區域,具有較高的比出水率,一般約在0.20以上;而遠離河道及中下游區段的比出水率則較小,但比出水率值亦多約在0.12至0.16之間。而Min_03與Min_06附近為相較於鄰近區域擁有較低的比出水率,而此區域亦為乾濕季地下水位變化差異較小之位置,暗示了可能存在一大致為南北方向,與車籠埔斷層在集集地震中活動破壞帶有關的水文地質構造。值得未來加強研究探討。
英文摘要
We conducted the time-lapse electrical resistivity tomography (ERT) survey for the Minzhu Basin during the wet and dry seasons of 2017. The ERT survey was designed to realize the relative saturation change with depth which were then used to estimate the location of groundwater table and specific yield. To verify the ERT results, we compared our groundwater level estimation to the data from the nearby observation well. We then applied the correction coefficient Ks=0.98 to estimate the regional groundwater level, which yielded the least average error (about 0.25 meters) relative to the observed groundwater levels. In March 2017, the groundwater level in the Minzhu Basin was about 8.5-m to 15.8-m in depth. In June, the groundwater level increased significantly due to the wet season, which was about 4.6- to 15-m in depth. The groundwater level in August remained at about 3.4- to 13.9-m, while the groundwater level in September was between 4.8- and 14.2-m. In summary, the groundwater level in the dry and wet seasons decreased gradually from the upstream to the downstream of the Zhuoshui river. However, there were three profiles (Min_02, Min_03, and Min_06) which showed a smaller difference in the groundwater level between the wet and dry seasons, compared to the other survey lines. This trend of groundwater distribution is observed at locations that are normal to the river direction. From the specific yield estimations, the upstream section of the survey area and the area near the Zhuoshui river channel have higher specific yields, whose values are above 0.20. The middle and lower reaches have smaller specific yields, which are about 0.12 to 0.16. In addition, Min_03 and Min_06 have the lowest specific yield and a smaller difference in the groundwater level, compared to the adjacent area. It might be related to the hydrogeological structure of the fault damage zone of the Chi-Chi earthquake. Our future work will focus on the characterization of this damage zone and determination of its hydrogeological properties.