Technical Abstract: Coupling the unsteady open-channel flow equations of surface irrigation with the equation of variably saturated porous media flow is a computationally complex problem, because of the dependence of infiltration on flow depths. Several models of this coupled process have been developed, all of which solve the surface and subsurface iteratively at each time step of the surface flow solution. This study presents an alternative strategy, in which surface and subsurface flow calculations are conducted sequentially and iteratively at the level of the duration of the irrigation event. At each iteration, the subsurface flow results are computed based on the surface flow depths generated by the surface flow model at the previous iteration. These infiltration results are then fed back to the surface flow model, as an empirical infiltration function. The proposed strategy, labeled external iterative coupling, was prototyped for border and basin irrigation systems using the WinSRFR and HYDRUS 1-D models. The proposed procedure produced irrigation performance results comparable to those generated with an internally coupled model. Results also show that the procedure can produce reasonable results even when using a single representative location to calibrate the empirical infiltration equation used by the surface flow model.