IDENTIFICATION OF FURROW INTAKE PARAMETERS FROM ADVANCE TIMES AND RATES

This paper analyzes the convergence of a numerical model for the quantification of lumped furrow infiltration parameters. The model minimizes the squared difference of observed and model-predicted advance times as a function of distance. An alternative objective function was formulated in terms of velocity of the advancing wave. Predicted values were obtained with a hydrodynamic irrigation model with wetted-perimeter-dependent infiltration. Solutions were computed with the Marquardt method. The three parameters of the empirical extended Kostiakov equation were estimated when nonuniformity of infiltration was the only source of variability in the advance curve. Faster convergence and larger radius of convergence resulted from fitting velocities rather than advance times. Measurement errors and system perturbations impeded the simultaneous identification of three parameters, while computation of two coefficients from highly variable velocities required the application of weighted least squares. Similar parameters were obtained from few or many observations, but convergence improved with smaller data sets.