二維地電阻率影像剖面法在地下水測勘上之應用與分析－以海岸沙丘下淡／鹹水界面測繪為例

2-D RIP Method Employed in Groundwater Prospecting-A Case Study of Mapping the Fresh/Salt Water Interface under Coastal Dune

陳可恭(Ke-Kung Chen)

《宜蘭技術學報》 9期 (2002/12) Pp. 147-158

https://doi.org/10.6179/nit.2002.09.23

摘要

本研究探討「地電阻率影像剖面法」在地下水測勘上之應用，並援引「宜蘭海岸沙丘下淡／鹹水界面之測繪」為例以進行效能分析。經實測並以不同資料解釋法展現二維剖面，結果顯示：1. 不同解釋法各具特色，可依探測目的選擇使用：視電阻率擬似剖面法，容易獲取，但僅能表達電阻率隨空間變化的概略趨勢；以一維模型為基礎的簡易逆推法，計算較簡，但僅較適用於近似水平地層之測勘；以雙極排列法施測、二維有限法逆推，對複雜的地下構造，能展現最佳的解析效能。2. 實測案例中，可發現。壯圍鄉公館沿岸沙丘之下方，在淺部為電阻率較高的含淡水地層，且其所儲存之淡水體略呈凸鏡構造，此對海水入侵應具「屏障」之效；但在深約60-70公尺處，低於5歐姆米的等值線幾乎橫貫全剖面，推測此高鹽度的層次應與海水相通；此外，測線上在近魚塭處，其淡／鹹水界面則略見揚昇；諸此現象，均可由所獲取之二維地電阻率影像剖面清楚判讀。

關鍵字

地電阻率影像剖面法 ； 雙極排列法 ； 二維有限元素法 ； 地下水測勘

並列摘要

The purposes of this study are to investigate the efficiency of geoelectrical method (2-D RIP) employed in the groundwater prospecting, and to take a case study of mapping the fresh/salt water interface under the dune along the coast in I-lan. The results of this study lead to two conclusions shown as follows:1.Surveyed by pole-pole array and interpreted by 2-D FEM method can achieve high efficiency in mapping complicated structure such as fresh/salt water interface.2.The results of the RIP survey across the coastal dune near Gung-guan village indicate that the fresh water body is a form of lens shape. This lens-shaped fresh water body serves as a barrier against seawater intrusion. But at the depth ranging from 60 to 70 meters, the seawater has intruded landward. This can be figured out by the presence of a zone where the resistivity is lower than 5 ohm-m. In addition, the boundary between the fresh and salt water zones rises at the location of fish farm.

並列關鍵字

Resistivity image profiling (RIP) ； Pole-pole array ； 2-D FEM ； Groundwater prospecting