Variability of Furrow Infiltration and Irrigation Performance in a Macroporous Soil

The study of spatial and temporal variations of infiltration in furrows is essential for the design and management of surface irrigation. A key difficulty in quantifying the process is that infiltration is dependent on the depth of flow, which varies along a furrow and with time. An additional difficulty is that under many field conditions, a large fraction of the infiltrated water flows through macropores. This study evaluates a proposed furrow infiltration model that accounts for both effects. Flow depth dependent infiltration is computed based on porous media flow theory. The macropore contribution is modeled as water that infiltrates instantaneously. Parameter estimation techniques were used to determine two of the model parameters, the hydraulic conductivity and the macroporosity term, and the Manning roughness coefficient. The methodology was tested using 30 furrow irrigation data sets collected in 6 furrows over 5 irrigation events. The analysis produced reasonable estimates for hydraulic conductivity relative to values reported in the literature. The estimated macroporosity term exhibited greater variation between irrigation events than between furrows during an event. Irrigation simulations were conducted with the estimated infiltration and roughness parameters. The observed irrigation measurements (advance, recession times, outflow rates, and flow depths) were simulated with reasonable accuracy for all events. Results show that the proposed furrow infiltration model can represent the infiltration process reasonably and that the proposed estimation procedure can yield consistent infiltration and hydraulic resistance parameters. Results also illustrate the large infiltration variability that can be encountered in furrow irrigated fields.