Saturated-Unsaturated flow in a Compressible Leaky-unconfined Aquifer

TL;DR

This paper develops an analytical model for three-dimensional flow in a leaky unconfined aquifer, incorporating the unsaturated zone and partial well penetration, revealing significant effects of leakage and unsaturated zone properties on aquifer response.

Contribution

It extends existing models by including water flow and storage in the unsaturated zone and partial well penetration, providing a more comprehensive understanding of aquifer leakage dynamics.

Findings

Leakage causes significant deviation from no-leakage models.

Aquifer drawdown depends on unsaturated zone properties.

Wellbore storage effects influence drawdown behavior.

Abstract

An analytical solution is developed for three-dimensional flow towards a partially penetrating large-diameter well in an unconfined aquifer bounded below by an aquitard of finite or semi-infinite extent. The analytical solution is derived using Laplace and Hankel transforms, then inverted numerically. Existing solutions for flow in leaky unconfined aquifers neglect the unsaturated zone following an assumption of instantaneous drainage assumption due to Neuman [1972]. We extend the theory of leakage in unconfined aquifers by (1) including water flow and storage in the unsaturated zone above the water table, and (2) allowing the finite-diameter pumping well to partially penetrate the aquifer. The investigation of model-predicted results shows that leakage from an underlying aquitard leads to significant departure from the unconfined solution without leakage. The investigation of dimensionless time-drawdown relationships shows that the aquitard drawdown also depends on unsaturated zone properties and the pumping-well wellbore storage effects.