Effects of Spatially Variable Intake on Surface Irrigation Advance

Abstract

Rational evaluation of surface irrigation systems should consider the effects of spatial variations in soil intake properties on advance trajectories and on the uniformity of infiltrated depths. The objective was to quantify the effects of spatial variations in infiltration parameters on the variability of advance trajectories and on infiltration depths. The soil properties were expressed as random space functions, and small perturbation analysis was applied to analytical solutions for the advance phase. This resulted in closed-form expressions relating the variability in soil properties to the variability in advance trajectories. The expressions were tested using Monte Carlo (MC) simulations. The results show good agreement between the analytical expressions and the simulated mean and variance of advance trajectories for a wide range of intake variabilities. In all cases, a sharp increase in the variance of advance times was observed toward the end of the field. This resulted in discrepancies between the simulated and the closed-form approximation for infiltration depths at large distances from the field inlet. The study provides a predictive tool for the evaluation of management strategies for surface irrigation in heterogeneous fields once the extent of spatial variability in soil intake properties has been estimated. Some applications for the estimation of uniformity and application efficiency are illustrated.