Calculation of Sorptivity from Constant‐Rate Rainfall Infiltration Measurement

Abstract The incipient ponding time equation developed by Kutilek and Parlange and Smith were rearranged and used for calculating sorptivity under constant‐rate rainfall conditions. The equations were tested using the field‐measured data obtained in Hawaii by Dangler et al. In the calculation, the incipient ponding time is assumed equal to the time of first appearance of runoff from the experimental plot. Additionally, the A value in the Philip two‐term infiltration equation is assumed to the K sat /3. The results showed that the sorptivity values calculated from both equations have only a 1.22% difference. The accuracy of the calculated sorptivity was assessed by its use for predicting infiltration. In the comparison of cumulative infiltration, the correlation coefficient between measured and estimated values is > 0.9 with a mean error percentage of 20.09 and a median of 10.57%.