Modeling of Variably Saturated Flow in Response to Pumping from an Unconfined Aquifer: Numerical Evidence of Gravity-Delayed Drainage and Its Parameterization

Abstract

A numerical model of variably saturated axis-symmetric radial flow is employed to simulate and parameterize the gravity-delayed drainage, viewing it as the vertical accretion over falling water table. Numerical experiments are conducted to simulate the head fields at advancing discrete times as pumping is sustained at the assigned well. The head fields are invoked to generate the corresponding time series of water table elevation and the accretion rate over it. Employing these time series, the optimal structure/parameters of gravity-delayed drainage equation are estimated by the least-squares approach under a variety of hydrogeologic/geometric conditions. It is revealed that generally, a two-parameter gravity-delayed drainage equation reproduces parsimoniously the accretion time series.