EFFECTS OF SPATIALLY-VARIABLE INTAKE ON SURFACE IRRIGATION ADVANCE

Rational evaluation of surface irrigation systems should consider the effects of spatial variations in soil intake properties on advance tra jectories and on the uniformity of infiltrated depths. The objective w as to quantify the effects of spatial variations in infiltration param eters on the variability of advance trajectories and on infiltration d epths. The soil properties were expressed as random space functions, a nd 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 traje ctories. The expressions were tested using Monte Carlo (MC) simulation s. 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. Th is resulted in discrepancies between the simulated and the closed-form approximation for infiltration depths at large distances from the fie ld inlet. The study provides a predictive tool for the evaluation of m anagement strategies for surface irrigation in heterogeneous fields on ce the extent of spatial variability in soil intake properties has bee n estimated. Some applications for the estimation of uniformity and ap plication efficiency are illustrated.