地下水水位的變化受到許多因素的影響，包含有氣壓、地潮、降雨及其他因素所引起的水位變化。為了深入探討降雨和地下水位變動之關聯性，需要先分離大氣壓力、地潮及其他等因素所引起之地下水位變化。本研究以雲林縣古坑鄉東和地下水井之第三含水層水位資料為研究對象，使用資料包括井位地下水水位資料、嘉義市嘉義氣壓站之氣壓資料及氣象局雨量站(包括斗六、中坑、大埔與阿丹站)之雨量資料。將 原始觀測地下水位資料利用BAYTAP-G模式分離氣壓與地潮對地下水位之影響後，再分析地下水水位變化量與降雨之關聯性。結果顯示氣壓對於東和地下水位變動的影響量大約在2.0 cm以內，而地潮的影響量大約在1.0 cm以內
本研究分析東和地區降雨與地下水位變化之關聯性結果顯示，東和地下水位日平均消散量約為116 mm。地下水位變化量 與斗六雨量站 及 的關係不明顯，但 與有效累積雨量 的關係密切，並可表示為 。以此關係式進行迴歸分析，結果顯示東和地下水位日水位變化量與其前5天至前10天累積雨量之相關係數 值較高，且各雨量站的 值差異並不大。考慮降雨影響的衰減效應下，加入一衰減權重參數 ，結果顯示以在 ，有效累積雨量 與地下水位變化量的相關性較佳。應用本文所提之 與 之關係式分析1998年至1999年所選取的四個降雨時段，結果顯示除了1999年4月29日至5月9日此段降雨之外，其餘三段降雨迴歸求得之係數A值皆很相近，於相同有效累積雨量下所引起的地下水位變化量皆很相近。造成1999年4月29日至5月9日此段降雨所引起的地下水位變化量較高之原因有待進一步探討。本文加入流域集水區外之竹山及桶頭雨量站分析東和地下水位日水位變化量 與有效累積雨量 之相關性，結果顯示，竹山雨量站有效累積雨量與東和地下水變化量相關性最高。東和地下水井之補注區並不完全在地表流域集水區內，流域集水區外之降雨對地下水井也可能會有補注的情況。因此，在探討降雨和地下水位變化之關聯性時，應再加以考慮集水區外周邊之雨量站。

The BAYTAP-G program has been used to screen out the influenced component of atmosphere and earth tide. Then, groundwater level data of Tung-Ho well station has been used to analyze the relationship between the rainfall and the variation of groundwater level. The result shows that the barometric response is about 2.0 cm and the tidal response is about 1.0 cm in the Tung-Ho well station. The daily average value of groundwater level diffusion rate (i.e., groundwater level lowering rate) is about 116 mm. The relationship between the groundwater level increment and the effective accumulative rainfall is better than the others. So we can use the equation, , to represent the relationship between the rainfall and the variation of groundwater level. A regression analysis shows that the groundwater level increment has higher relation with the accumulative rainfall of previous five days and ten days. This paper considers the decaying effect of rainfall by a weighting parameter . This result is that it has better relation when . This paper analyzes four periods of rainfall from 1998 to 1999, and result a similar value of the coefficient period A, besides the periods of April 29th to May 9th in 1999. It’s mean that the equal effective accumulative rainfall can almost cause the same groundwater level increment. A step further study is needed to find out the reason why the rainfall in the period of April 29th to May 9th in 1999 has higher groundwater level increment.

1. 余貴坤，1986，「降雨量與深井水位變動的關係研究」，台灣地區地球物理研討會，165-173頁。
2. 李友平，1997，「抽水試驗改良與即時參數鑑定」，國立成功大學水利及海洋工程研究所博士論文。
3. 謝正倫等人，2001，「地震發生前後地下水位異常變化之研究(1/5)」，經濟部水利署委辦計劃，國立成功大學防災研究中心。
4. Akaike, H., 1973, “Information theory and an extension of the maximum likelihood principle,” Second Intermational Symposium of Information Theory, pp.267-281.
5. Akaike, H., 1974, “A new look at the statistical model indentification,” IEEE Transactions on Automatic Control, AC-19, pp.716-723.
6. Akaike, H. and Nakagawa T., 1986, “Statistical analysis and control of dynamic systems ,” Kluwer Academic, Dordrecht, pp.210.
7. Bredehoeft, J. D., 1967, “Response of well-aquifer systems to earth tides,” J. Geophys. Res., pp.3075-3087.
8. Igarashi, G. and Wakita, H., 1991, “Tidal responses and earthquake- related changes in the water level of deep wells,” J. Geophys. Res., 96, pp. 4269-4278.
9. Ishiguro, M., Akaike, H., Ooe, K. and Nakai, S., 1983, “A Bayesian approach to the analysis of earth tides,” Proceeding of the Ninth International Symposium on Earth Tides, pp. 283-292.
10. Kitagawa, K. and Matsumoto, N., 1996, “Detection of coseismic changes of underground water level,” Journal of the American Statistical Association, Vol. 91, No. 434, pp. 521-528.
11. Matsumoto, N., 1992, “Regression analysis for anomalous changes of ground water level due to earthquakes,” Geophysical Res. Letters, V.19, No.12, pp.1193-1196.
12. Roeloffs, E. A., 1988, “Hydrologic precursors to earthquakes,” PAGEOPH, 126, pp.177-206.
13. Rojstaczer, S., 1988, “Determination of fluid flow properties from the response of water levels in wells to atmospheric loading,” Water Resources Research, Vol.24, No.11, pp. 1927-1938.
14. Van der Kamp, G. and Gale, J.E., 1983, “Theory of earth tides and barometric effects in porous formations with compressible grains,” Water Resour. Res., 19, pp.538-544.