An In-Depth Examination of the Philip Equation for Cataloging Infiltration Characteristics in Rangeland Environments

Abstract

The objective of this study was to investigate the use of Philip's equation coefficients (which have, in theory, direct physical meaning) to characterize infiltration on rangelands. It was found that a least squares regression approach to estimating Philip equation parameters (S and A) essentially reduces A, and perhaps S, to empirical coefficients. However, the Philip equation does provide a model that fits infiltrometer data reasonably well and reflects significant differences between infiltration curves. The effects of land management and temporal variables (e.g., soil moisture, season) may be associated with changes in S and A for particular sites. Indexing of infiltration curves by model coefficients allows for infiltrometer data from different researchers to be pooled and provides a basis for simulation modeling of infiltration and runoff on small watersheds. Coefficients are tabulated for a variety of rangeland plant communities for easy reference by practicing rangeland hydrologists. Researchers who present infiltration data in the future are urged to represent their data, at least in part, in the form of S and A coefficients to expand results tabulated from this study.