Experimental work has clearly shown that the effective hydraulic conductivity (Ke) or effective infiltration rate (fe) on the local scale of a plot cannot be considered as constant but are dependent on water depth and rainfall intensity because non-random microtopography-related variations in hydraulic conductivity occur. Rainfall–runoff models generally do not account for this: models assume that excess water is uniformly spread over the soil surface and within-plot variations are neglected. In the present study, we propose a model that is based on the concepts of microtopography-related water depth-dependent infiltration and partial contributing area. Expressions for the plot scale Ke and fe were developed that depend on rainfall intensity and runon from upslope (and thus on water depth).
To calibrate and validate the model, steady state infiltration experiments were conducted on maize fields on silt loam soils in Belgium, with different stages and combinations of rainfall intensity and inflow, simulating rainfall and runon. Water depth–discharge and depth–inundation relationships were established and used to estimate the effect of inundation on Ke. Although inflow-only experiments were found to be unsuitable for calibration, the model was successfully calibrated and validated with the rainfall simulation data and combined rainfall–runon data (R²: 0.43–0.91).
Calibrated and validated with steady state infiltration experiments, the model was combined with the Green–Ampt infiltration equation and can be applied within a two-dimensional distributed rainfall–runoff model. The effect of water depth–dependency and rainfall intensity on infiltration was illustrated for a hillslope. Copyright © 2012 John Wiley & Sons, Ltd.