An Analytical Drawdown Solution for Constant-flux Pumping in a Confined Anticline Aquifer

• Main Author: 陳彥如
• Other Authors: Yeh, Hund-Der
• Format: Others
• Language: en_US
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/44089963183420131784

博士 === 國立交通大學 === 環境工程系所 === 99 === An anticline known as a convex-upward fold in layers of rock commonly forms during lateral compression, which may be elected as a potential site for underground waste storage or carbon sequestration. A constant-flux pumping test, which maintains a constant pumping rate at the test well, measures and analyzes the drawdown responses in one or several observation wells to determine the aquifer parameters. In this study, a mathematical model is developed for describing the steady-state drawdown distribution in the anticline aquifer during the constant-flux pumping. In the derivation, the topographical shape of the anticline is mimicked by three successive blocks. The infinite Fourier transform and finite Fourier cosine transform are applied to obtain the solution of the model in the transform spaces. The solution expressed as an integral form is then obtained from the Fourier inversion. Predicted results from the solution reveal that a thin-limbs or narrow-ridged anticline would cause a much larger head drop in the ridge zone. For a well of constant pumping rate, the dimensionless drawdown around the well increases with decreasing well screen length or/and aquifer anisotropy ratio. In examining the effect of well location, we find the partially penetrating well located at the top-middle of the ridge zone produces the largest drawdown. MODFLOW is a computer program that simulates the groundwater flow based on the block-centered finite difference method. Through the grid discretization, MODFLOW can imitate the antiform much closer to reality. The simulation for the flow in an anticline aquifer results in slightly smaller drawdown values when compared with those predicted by the present solution. The present solution can also be used to simulate the flow in a slab-shaped aquifer or a hillslope aquifer. It can be applied to identify the aquifer parameters and to design a potential site for waste disposal in the future as well.