Effects of exponentially decaying aquitard hydraulic conductivity on well hydraulics and fractions of groundwater withdrawal in a leaky aquifer system

• Published in: Journal of hydrology (Amsterdam) 2022-04, Vol.607, p.127439, Article 127439
• Main Authors: Zhuang, Chao, Li, Yabing, Zhou, Zhifang, Illman, Walter A., Dou, Zhi, Yang, Yun, Wang, Jinguo
• Format: Article
• Language: English
• Subjects: Exponentially decaying aquitard hydraulic conductivity; Groundwater budget; Leaky aquifer system; Semi-analytical solutions; Well hydraulics
• ISSN: 0022-1694; 1879-2707
• DOI: 10.1016/j.jhydrol.2022.127439

A hydrogeological unit with a considerable thickness usually demonstrates depth-decaying hydraulic conductivity (K) at the regional scale. In this study, we investigated transient well hydraulics (i.e., aquifer and aquitard drawdown) and groundwater budget (i.e., fractions of groundwater withdrawal including aquifer depletion, aquitard depletion and leakage from the unconfined aquifer) within a leaky aquifer system considering an exponentially decaying K of the aquitard, parameterized with a dimensionless decay coefficient (Ad). Relevant semi-analytical solutions were derived using the Laplace transform and Hankel transform techniques, while drawdown and groundwater budget characteristics and their sensitivities to Ad were theoretically analyzed. Theoretical analysis results suggested that a larger Ad consistently leads to a larger aquifer drawdown, a smaller aquitard drawdown, a larger fraction of aquifer depletion and a smaller fraction of leakage from the unconfined aquifer. Sensitivity analysis results also indicated critical effects of Ad on well hydraulics and groundwater budget. Comparative analysis revealed that none of the three typical mean values of depth-decaying aquitard K can perfectly characterize the well hydraulics and groundwater budget from early to intermediate times. However, the harmonic and geometric mean values can be feasibly used to calculate the final fractions of aquifer depletion and aquitard depletion at late times, respectively. Limitations of the newly developed analytical model have also been discussed. Practical investigations of vertical aquitard heterogeneity and further applications of this new model are recommended.