ACCOUNTING FOR SOIL VARIABILITY IN THE EVALUATION OF FURROW IRRIGATION

Abstract

In surface irrigation, water infiltrates into the soil but is also transported over the soil; thus, the spatial variabilityof the soil hydraulic characteristics is one of the variables determining irrigation performance. Furrow irrigation modelsrarely 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 irrigationaccounting for spatially varying infiltration. The procedure characterizes infiltration variability by measuring the finalinfiltration rate in blocked furrow segments. This variability is then used to generate a family of infiltration curves aroundthe average infiltration curve obtained from field observations during the irrigation advance phase. Simulation results wereused to evaluate the method using fieldmeasured performance indicators. The simulation model was run considering uniformand variable wetted perimeter and soil intake characteristics. Advance time and average infiltrated depth were satisfactorilyestimated, even under the assumption of uniform infiltration parameters and wetted perimeter. The distribution uniformitywas overestimated by up to 40% when assuming uniform infiltration and wetted perimeter. When the variability was takeninto account, the estimated distribution uniformity was close on average to the measured distribution uniformity. Applicationefficiency was not greatly affected by the assumption of uniform soil and wetted perimeter. In general, the performancesimulated assuming spatially varying infiltration was more realistic than that simulated assuming a unique infiltrationfunction.