Discussion of “Application of a Nonstandard Explicit Integration to Solve Green and Ampt Infiltration Equation” by Damodhara R. Mailapalli, Wesley W. Wallender, Rajendra Singh, and Narendra S. Raghuwanshi

Mailapalli et al. (2009) presented an explicit numerical scheme for calculation of solutions to the 1D Green and Ampt (1911) infiltration equation. They compared their numerical solution to a numerical solution obtained using the Newton-Raphson method (e.g., Rao et al., 2006) and the “approximate explicit solutions” of Salvucci and Entekhabi (1994) and (iii) Barry et al. (1995d). It is shown that (i) that the Green-Ampt model can be approximated very accurately using a simple formula, (ii) that the effective hydraulic conductivity mentioned by the authors is consistent with another infiltration model and (iii) that their numerical scheme becomes more accurate if the short-time expansion of the Green and Ampt model is used to provide that starting value of the infiltration.