Studying the Philip model capability to estimate water infiltration parameters.

Infiltration refers to the entry of water into a soil profile from the boundary. Generally, it refers to vertical infiltration, where water moves downward from the soil surface. The Philip model is one of the infiltration models with an algebraic equation based on sound physical reasoning for vertical infiltration under ponded conditions. We designed a program in Quick Basic software and wrote algorithms for three models that include Kostiakove, Modified Kostiakove and Philip. Afterwards we gathered factual infiltration data by the double ring method in 12 soil series of Saveh plain in Markazi province in Iran. After assessing model coefficients, these equations were regenerated by EXCEL software and calculations related to observations and related graphs were done. Infiltration parameters, such as cumulative infiltration and infiltration rate were obtained from the models. Then observed and determined parameters of infiltration were compared. Results showed that for seven series the Philip model could determine the infiltration parameters with a good agreement. Also the Philip model for five series of soils, after passing of time, had a curve shape as shown in the Philip model for Saveh (2), Labar (1), Harisan (2), Gharehtappeh and Anjilavand series, including 5 series with heavy to very heavy texture. The sorptivity coefficient of the Philip model became less than zero, for long times, consequently accumulative infiltration decreased during this period. Other models particularly Modified Kostiakove could quantify amounts of cumulative infiltration and infiltration rate. In the short and middle time for most series, Kostiakove and Modified Kostiakove models were better than the Philip model in estimating infiltration parameters. However for long times the Philip model could determine infiltration parameter better than the other models.