Analysis of No-Flow Boundaries in Mixed Unconfined-Confined Aquifer Systems

Abstract

As human population increases, demand for water supplies will cause an increase in pumping rates from confined aquifers which may become unconfined after long-term pumping. Such an unconfined-confined conversion problem has not been fully investigated before and is the focus of this thesis. The objective of this thesis is to use both analytical and numerical modeling to investigate groundwater flow in an unconfined-confined aquifer including the no-flow lateral boundary effect and the regional flow influence. This study has used Girinskii’s Potential in combination with MATLAB to depict how changes in aquifer dimensions, hydraulic properties, regional flow rates, and pumping rates affect the size and shape of the unconfined-confined boundary. This study finds that the unconfined-confined conversion is quite sensitive to the distance between the piezometric surface and the upper confining bed when that distance is small, and the sensitivity lessens as that distance increases. The study shows that pumping rate is the dominating factor for controlling the size of the unconfined-confined boundary in comparison to the regional flow. It also shows that the presence of a no-flow boundary alters the normally elliptical shape of the unconfined-confined boundary.