Abstract
The representative anisotropic parameters for an aquifer located at the campus of the National Yunlin University of Science and Technology in Taiwan have been acquired. A constant-rate pumping test was carried out, and drawdown-time data were collected from ten observation wells. Applications of the conventional aquifer test analysis, which assumes aquifer homogeneity for each observed well hydrograph, yielded spatially varying transmissivity and storage coefficient estimates, contradicting the homogeneous assumption. A direct approach and a nonlinear-least squares minimization of distance-drawdown data were then employed to analyze anisotropy of the transmissivity of an equivalent homogeneous aquifer. Results show that the direction and values of anisotropic transmissivities vary with time and the estimates depend on the number of observation wells used. These field results are consistent with results from recent theoretical investigations which questioned the suitability of the conventional aquifer test analysis.
Résumé
Les paramètres anisotropiques représentatifs d'un aquifère situé sur le campus de la National Yulin University of Science and Technology à Taïwan ont été obtenus. Un pompage d'essai à débit constant a été mis en œuvre, et les données de temps et rabattement ont été collectées sur dix piézomètres. L'application d'interprétations conventionnelles de pompages d'essai, qui supposent l'homogénéité de l'aquifère pour chaque courbe d'observation, aboutit à des transmissivités et coefficients d'emmagasinement variables spatialement : ceci est en contradiction avec l'hypothèse de l'homogénéité. Une approche directe et la minimisation des moindres carrés non-linéaires des données de distance et rabattement ont été utilisées pour analyser l'anisotropie de la transmissivité dans un aquifère équivalent homogène. Les résultats montrent que la direction et les valeurs des transmissivités anisotropiques varient dans le temps et que les estimations dépendent du nombre de piézomètres utilisés. Ces résultats pratiques sont cohérents avec les résultats d'études théoriques récentes, qui remettaient en cause la pertinence des interprétations conventionnelles de pompages d'essai.
Resumen
Se obtuvieron los parámetros anisotrópicos representativos de un acuífero localizado en el campus de la Universidad Nacional Yunlin de Ciencia y Tecnología en Taiwán. Se llevó a cabo un ensayo de bombeo a .caudal constante, y se obtuvieron los datos tiempo-depresión a partir de 10 pozos de observación. Las aplicaciones de los análisis convencionales de ensayos de acuífero, que suponen la homogeneidad del acuífero para cada hidrograma observado de un pozo, arrojaron estimaciones de coeficiente de almacenamiento y transmisividad espacialmente variables, contradiciendo la suposición homogénea. Se emplearon un enfoque directo y una minimización no lineal de mínimos cuadrados de los datos depresión-distancia para luego analizar la anisotropía de la transmisividad de un acuífero homogéneo equivalente. Los resultados muestran que la dirección y los valores de las transmisividades anisotrópicas varían con el tiempo y las estimaciones dependen del número de pozos de observación. Estos resultados de campo son consistentes con los obtenidos a partir de investigaciones teóricas recientes que cuestionan la viabilidad aplicabilidad de los análisis convencionales de los ensayos de acuífero.
摘要
本研究取得了位于国立云林科技大学的一含水层的各向异性参数的代表性值。进行了定流量抽水试验, 并取得了十口观测井的水位降深-时间数据。传统抽水试验分析假定每口观测井的水位曲线都是均质含水层的反映, 但得到的导水系数和储水系数存在空间变化, 这同含水层均质的假定相悖。然后应用直接方法和对距离-降深数据进行非线性最小二乘法处理分析等效均质含水层导水系数的各向异性。结果表明, 方向和非均质导水系数值是随时间变化的, 计算值取决于采用的观测井的数量。这些现场试验结果与最近的理论研究是一致的。这些理论质疑了传统抽水试验适用性。
Resumo
Foram obtidos parâmetros anisotrópicos representativos de um aquífero localizado no campus da National Yunlin University of Science and Technology, em Taiwan. Foi desenvolvido um teste a caudal constante e foram obtidas séries temporais dos rebaixamentos em dez piezómetros de observação. A aplicação de métodos de análise convencionais, que assumem a homogeneidade do aquífero para cada furo, forneceu transmissividades e coeficientes de armazenamento variáveis espacialmente, contrariando a hipótese da homogeneidade assumida. Uma análise directa e uma análise não-linear por mínimos quadrados da distância vs. rebaixamentos foi utilizada em seguida para analisar a anisotropia da transmissividade num aquífero homogéneo equivalente. Os resultados mostraram que a direcção e os valores das transmissividades anisotrópicas variam com o tempo e que as estimativas dependem do número de furos de observação utilizados. Estes resultados de campo são consistentes com os resultados de investigações teóricas recentes que questionam a adequabilidade dos testes convencionais de análise de aquíferos.
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Acknowledgements
The authors express gratitude to the National Science Council for the funding through grants NSC 96-2221-E-224-029, NSC 95-2221-E-224-005 and NSC 94-2211-E-224-011. Site pumping tests which were conducted by Mr. Ho-Da Chung and support from National Yunlin University of Science and Technology are greatly appreciated. The third author would like to acknowledge support from National Cheng-Kung University during his visit in 2006 and 2007. Support from the Strategic Environmental Research and Development Program (SERDP) as well as by funding from the National Science Foundation (NSF) through grants EAR-0229713, EAR-0229717, IIS-0431069, IIS-0431079, EAR-0450336, and EAR-0450388 are acknowledged.
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Wen, JC., Wu, CM., Yeh, TC.J. et al. Estimation of effective aquifer hydraulic properties from an aquifer test with multi-well observations (Taiwan). Hydrogeol J 18, 1143–1155 (2010). https://doi.org/10.1007/s10040-010-0577-1
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DOI: https://doi.org/10.1007/s10040-010-0577-1