Accounting for soil variability in the evaluation of furrow irrigation

In surface irrigation, water infiltrates into the soil but is also transported over the soil; thus, the spatial-variability of the soil hydraulic characteristics is one of the variables determining irrigation performance. Furrow irrigation models rarely consider the; variability of the soil intake characteristics. However, such models are used more and more for the design; evaluation, and management of surface irrigation systems. In this-article, a method is developed to evaluate furrow irrigation accounting for spatially varying infiltration. The procedure characterizes infiltration variability by measuring the final infiltration rate in blocked furrow segments. This variability is then used to generate a family of infiltration curves around the average infiltration curve obtained from field observations during the irrigation advance phase. Simulation results were used to evaluate the method using field-measured performance indicators: The simulation model was run considering uniform - and variable wetted perimeter and soil intake characteristics. Advance time and average infiltrated depth were satisfactorily estimated; even under the assumption of uniform infiltration parameters and wetted perimeter. The distribution uniformity was overestimated by up to 40%-when assuming uniform infiltration and wetted perimeter. When the variability was taken into account, the estimated distribution uniformity was close on average to the measured-distribution uniformity. Application efficiency was not-greatly affected by the assumption of uniform soil and wetted perimeter. In general, the-performance simulated assuming spatially varying infiltration was more realistic than that simulated assuming a unique infiltration. function.