Applicability of the Green-Ampt Infiltration Model with Shallow Boundary Conditions

Abstract

The Green-Ampt model is an approximate analytical solution to Richards’ equation that is commonly used to simulate infiltration processes in hydrological models and land surface schemes. The Green-Ampt model assumes that neither a water table nor an impermeable layer (e.g., bedrock or a frost table) exist near the soil surface. In regional-scale applications these idealized conditions will often not be met, and it is presently unclear what implications this has for regional water resource models. This paper investigates the limiting conditions under which the Green-Ampt model is appropriate and how individual assumptions about lower boundary conditions affect the validity of the model. Guided by the comparison between the Green-Ampt model and numerical solutions to Richards’ equation, various simple revisions to the Green-Ampt model are suggested. Results demonstrate that even when the traditional assumptions are relaxed, the Green-Ampt model often still provides reasonable results for regional-scale analysis and can be amended to account for conditions for which it was not intended.