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Estimation of the Philip Infiltration Parameters from Rainfall Simulation Data¹

ABSTRACT

A new, simple technique for estimating the parameters of the two-term Philip infiltration equation was developed and tested using field-measured data obtained in the northern Chihuahuan desert of New Mexico. The technique simultaneously provided information on the relationship between the Philip equation parameter A, and the field-measured hydraulic conductivity. The equation was reformulated as I – cK_f = 1/2St^–1/2, where I is the infiltration rate, S the sorptivity, t the time, K_f the field-measured final infiltration rate, and c, a coefficient relating K_f to the Philip parameter A. The final, steady infiltration rate measured in the field was used for the value of K_f. Regressions of (I – cK_f) vs. (1/2t^–1/2) for values of c between 0 to 1 resulted in optimum c values for each treatment along with their corresponding S values. For the soils in this area, values for the coefficient c were sometimes outside the suggested range of 0.33 to 0.67, and were different for each study site. The regression analysis also showed that the value of S can be highly sensitive to changes in c. Using the values of S and c determined by the proposed method, a comparison was made between computed infiltration rates and measured infiltration rates. The results of this study showed that the prediction method provided adequate fits to field-measured data, and that the choice of an appropriate c factor is important in determining infiltration parameters from field data.

¹ Journal Article 1171, Agricultural Experiment Station, New Mexico State Univ., Las Cruces, NM 88003. Funded in part through NSF grant no. BSR-8114466-02.

² Graduate Student and Professor, respectively, Dep. of Crop and Soil Sciences; Associate Professor, Dep. of Civil Engineering, New Mexico State Univ., Las Cruces, NM 88003. The senior author is presently with the USDA-ARS, Fort Collins, CO 80522.

Received for publication June 25, 1985.