Physically Based Modeling of Interacting Surface–Subsurface Flow During Furrow Irrigation Advance

Surface–subsurface flow during furrow irrigation is analyzed employing both a laboratory experiment and a surface– subsurface flow model. The proposed model overcomes the restrictions of traditional furrow irrigation models by rigorously describing the subsurface flow at computational nodes using the physically based two-dimensional (2D) model Hydrus-2D. Surface flow is portrayed by an analytical zero-inertia model. In order to couple both models efficiently, an iterative procedure was developed. Using a sensitivity analysis we investigated the space interval separating 2D infiltration computations. This variable showed little effect on model performance, thus permitting the selection of rather generous distances. Due to the similarity of the hydrographs at neighboring cross sections we investigated transferring the results of Hydrus-2D computations to the next downstream location. This was performed by interpolating cumulative infiltration using infiltration opportunity times. This procedure uncovered other dependencies, making the interpolation strategy unattractive. To validate the coupled surface–subsurface model, an irrigation furrow was set up in a 26.4 m long, 0.88 m wide, and 1.0 m deep tank, filled with 50 t of sandy loam soil and equipped with surface and subsurface measurement devices. Although the model results compared favorably with the observed data, the study also showed an important impact of surface cracking and preferential flow during the irrigation experiments.