- - - Assistant Professor, Department of Water Engineering, Faculty of Agriculture, Fasa University, Fasa, Iran.
- - - M.Sc, Department of Irrigation and Reclamation Engineering, University of Tehran, Tehran. Iran.
- - - Associate Professor, Department of Water Engineering, Faculty of Agriculture, University of Kurdistan, Sanandaj, Iran.

The two-point method is the most commonly used method of calculating the coefficients of the Kostiakov-Lewis infiltration relationship, which is based on the volume balance equation. Using the two-point method of Elliott and Walker (EW), the coefficient of the power relation of water advance can be determined by initially utilizing data from the midpoint and endpoint of the field. Subsequently, the coefficients of the infiltration relationship can be determined. In this study, all the advance data were used to determine the power relation coefficients of water advance. Also, in this research (TR), the point where its infiltration opportunity is equal to the average infiltration opportunity time of the advance phase was considered as the midpoint in the two-point method for determining the infiltration coefficients. The relative error index and Root Mean Square Deviation (dRMS) index were used to assess the accuracy of the advanced relationships and infiltration equations derived from TR and EW methods. The results showed that the advanced relationships obtained from the TR method have higher accuracy than the EW method. The average relative error index of the infiltration depth indicated that the infiltration relations obtained from the TR method with an average relative error of ۲.۴% is more accurate than the EW method.

Surface irrigation, Infiltration coefficients, Volume balance, Two point method