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Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
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Volume 21, issue 2
Hydrol. Earth Syst. Sci., 21, 1251–1262, 2017
https://doi.org/10.5194/hess-21-1251-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Hydrol. Earth Syst. Sci., 21, 1251–1262, 2017
https://doi.org/10.5194/hess-21-1251-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 02 Mar 2017

Research article | 02 Mar 2017

On the coupled unsaturated–saturated flow process induced by vertical, horizontal, and slant wells in unconfined aquifers

Xiuyu Liang1, Hongbin Zhan2, You-Kuan Zhang3, and Jin Liu1 Xiuyu Liang et al.
  • 1School of Earth Sciences and Engineering, Nanjing University, Nanjing, Jiangsu 210093, P. R. China
  • 2Department of Geology & Geophysics, Texas A & M University, College Station, TX 77843-3115, USA
  • 3School of Environmental Sciences and Engineering, South University of Science and Technology of China, Shenzhen, Guangdong 518055, P. R. China

Abstract. Conventional models of pumping tests in unconfined aquifers often neglect the unsaturated flow process. This study concerns the coupled unsaturated–saturated flow process induced by vertical, horizontal, and slant wells positioned in an unconfined aquifer. A mathematical model is established with special consideration of the coupled unsaturated–saturated flow process and the well orientation. Groundwater flow in the saturated zone is described by a three-dimensional governing equation and a linearized three-dimensional Richards' equation in the unsaturated zone. A solution in the Laplace domain is derived by the Laplace–finite-Fourier-transform and the method of separation of variables, and the semi-analytical solutions are obtained using a numerical inverse Laplace method. The solution is verified by a finite-element numerical model. It is found that the effects of the unsaturated zone on the drawdown of a pumping test exist at any angle of inclination of the pumping well, and this impact is more significant in the case of a horizontal well. The effects of the unsaturated zone on the drawdown are independent of the length of the horizontal well screen. The vertical well leads to the largest water volume drained from the unsaturated zone (W) during the early pumping time, and the effects of the well orientation on W values become insignificant at the later time. The screen length of the horizontal well does not affect W for the whole pumping period. The proposed solutions are useful for the parameter identification of pumping tests with a general well orientation (vertical, horizontal, and slant) in unconfined aquifers affected from above by the unsaturated flow process.

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