Modification and evaluation of Green–Ampt model: Dynamic capillary pressure and broken-line wetting profile

Abstract

The Green–Ampt (GA) model, which assumes a rectangular saturated piston flow and homogeneous isotropic soil with uniform initial water content, is one of the most widely used models for describing infiltration processes. However, these assumptions severely limit the applications of the model. Thus, a modified GA model has long been a topic of interest. This study mainly investigates the effects of the broken-line wetting profile and dynamic capillary pressure on the GA model of a horizontal soil column. The aim is to provide a reasonable correction term for the hydraulic conductivity and suction head. The correction term is considered to be 0.4 when the dynamic capillary pressure (CGA model) is neglected. When the dynamic capillary pressure is taken into account, the correction term is a special function (FGA model). Moreover, the results of the CGA model, FGA model, Richards equation, and Mao model are compared with respect to the measured data for sandy loam, silt loam, and silty clay loam. Richards equation cannot accurately describe the infiltration of water into silt loam, and part of the reason is the high infiltration velocity. Although the Mao model can perfectly simulate the infiltration process in a short time (approximately 50 min in this study), its results gradually deviate from the actual situation after 50 min. The CGA model can predict the entire infiltration processes relatively accurately except in the dry sand with zero water content. However, as in the traditional GA model, small errors can still occur during the early infiltration stage. The FGA model is considered to be the most suitable approach for describing infiltration processes. In this paper, the characteristics of these models are explained, and the parameters of the FGA model are discussed in detail.