A method was developed for determining infiltration equations of the form y = Kta and y = St½ + A t from rate-of-advance data using solutions of the Lewis-Milne border irrigation equation, plotted in dimensionless form on logarithmic paper. Rate-of-advance data are superimposed on the solutions and the coefficients are determined from the matching factors for the best fit curve. If sufficient data are available the technique can be extended to determine the average depth of flow on the surface.