A Novel Approach to Characterize and Model Drywell Infiltration Capacity

Abstract

Drywells are vadose‐zone wells constructed for infiltration and recharge, typically positioned far above the water table. They provide for efficient infiltration, with high infiltration rates per land area, because the infiltration process is below the land surface. The drywell infiltration process is highly transient, with extremely high infiltration rates initially when the surrounding medium is dry, and monotonically declining rates as it wets and the hydraulic gradient decreases. The process is governed by the infiltration rate, the drywell geometry (depth, radius, casing), and the hydraulic properties of the adjacent subsurface media. This study develops a model for characterizing the drywell infiltration capacity (DIC)—the maximum infiltration rate at any time—as a unique function relating infiltration rate to cumulative infiltration. The model depends solely on the drywell's geometry and the hydraulic properties of the medium. An analytical solution is derived with the Green‐Ampt approach to describe the transient nature of infiltration and to provide a direct method to delineate the DIC function. Numerical experiments are conducted for a range of scenarios and properties, which confirm that, while the filling time of the drywell itself varies among infiltration rates, all cases converge to a single characteristic DIC curve once the well is full. Each drywell configuration, with its unique properties and subsurface settings, exhibits its characteristic DIC function. The proposed model and methodology provides a parsimonious framework for infiltration planning and real‐time management by enabling prediction of infiltration rates directly from cumulative infiltrated volume, offering a practical and robust approach for stormwater infiltration and groundwater‐recharge applications.