Assessing the feasibility of managed aquifer recharge through unsaturated zone modeling with VS2DTI in a multilayer system

Abstract

Managed aquifer recharge (MAR) is one of the interventions examined at the Medina del Campo demonstration site, where decades of over-abstraction have left the groundwater body and its dependent wetlands under stress. Whether recharge is feasible at a given location depends less on the aquifer itself than on what happens in the unsaturated zone above it: whether water can move through the profile at all, and how long it takes.

The study used the VS2DTI finite-difference code of the U.S. Geological Survey, which solves the Richards equation for flow and the advection-dispersion equation for transport in variably saturated porous media, to represent infiltration at local scale. Twelve two-dimensional models were simulated, covering three lithological zones — two in the Trabancos sub-basin and one in the Zapardiel — each run in both isotropic and anisotropic form, and each under two abstraction restriction scenarios. Hydraulic parameters were taken from the VS2DTI database and checked against the Rosetta Stone Advantage program and published values.

The results distinguish the parts of the system where recharge is hydraulically plausible from those where the unsaturated zone would delay or divert it, and provide the local-scale evidence that the Medina del Campo recharge assessment is built on.