Groundwater flow to a well in a strip-shaped unconfined-fractured aquifer system with a transition zone

Abstract

Semi-infinite unconfined-fractured strip shaped aquifer systems are common in alluvial plain margins, but have received little attention in the hydrogeological community. Thus, the aim of this study is to present semi-analytical solutions of flow to a well in these aquifer systems. Two conceptual models are considered: 1-An unconfined aquifer with a lateral fractured aquifer and a pumping well installed in the unconfined aquifer (model I); 2-An unconfined aquifer with a lateral fractured aquifer and a pumping well installed in the fractured aquifer (model II). A transition zone is considered between two aquifers. Three-dimensional groundwater flows are considered in unconfined, fractured and transition zone aquifers. Homogeneous, anisotropic hydraulic conductivity and instantaneous drainage water table condition are assumed first but can be relaxed to accommodate delayed drainage water table condition if needed. The point sink/source solutions are obtained via finite and infinite Fourier transforms for space and Laplace transform for time. The line sink/source solutions are obtained via integration along the desired direction. The uniform flux and uniform head boundary conditions are considered for the pumping well. The vertical distribution of the flux toward the well screen is explored. The effects of inner well condition on the variation of the dimensionless drawdown and boundary depletion volume are investigated. We investigate the influences of the hydraulic parameters of the transition zone on the spatial and temporal variations of the sensitivity of the drawdown to hydraulic parameters of the aquifer system. Furthermore, the influences of the transition zone on the spatial distribution of the drawdown are explored. The results of this study can be utilized to evaluate head distribution in the aquifer system; to calculate the water budget of the alluvial aquifers near a fractured one; to analyze the influences of a transition zone on the head and flow distribution in the aquifer system.