Providing the volume balance equation for the new two-point method

Advance data and infiltration parameters are used to evaluate surface irrigation. Philip infiltration equation is one of the most widely used equations in surface irrigation. For the first time, Shepard et al. (1993) presented a one-point method to determine the parameters of the Philip infiltration equation in surface irrigation. In recent years, a new two-point method has been proposed to determine the parameters of Philip infiltration equation. In the new method, the volume balance equation is not presented. As a result, the Shepard et al. (1993) volume balance equation is used to determine the advance phase (Ebrahimian-Sheppard method). In this study, the volume balance equation for the new two-point method is presented. The volume balance equation presented in this study was evaluated with five independent furrow irrigation data sets and different input conditions. Results showed that mean value of root mean square error in Shepard et al. (1993), Ebrahimian-Shepard (2010) method and new two points were 40.5, 30.3 and 10.9, respectively. The absolute mean error of prediction had the lowest equilibrium of 9.6% in the new two-point method followed by the Ebrahimian-Sheppard (2010) and Sheppard et al. (1993) methods with 19.5 and 20.4%, respectively. The coefficient of determination for all three methods was more than 0.97. In general, it can be concluded that the method presented in this study predicts the advance curve with higher accuracy compared to the other two methods.