A comparison of the Green-Ampt and a spatially variable infiltration modelfor natural storm events

Rainfall-runoff data collected from bare plots (20-216 m(2)) at 1-min inter vals were used to compare the performance of the Green-Ampt infiltration mo del and a spatially variable infiltration model (SVIM). The two models have the same number of parameters. For 60 natural storm events from six sites in Australia and South-East Asian countries, the average Nash-Sutcliffe mod el efficiency was 0.77 for the Green-Ampt model and 0.83 for the SVIM. At a ll sites, the SVIM consistently outperformed the Green-Ampt model when comp ared to runoff data at a range of time intervals and storm events, includin g events of very long duration. A larger hydrologic lag is needed for the G reen-Ampt model to fit the measured hydrographs in comparison to the SVIM, suggesting that the Green-Ampt model tends to underestimate the infiltratio n rate when rainfall intensity is high. Measured rainfall and runoff rates show a positive relationship between rainfall intensity and infiltration ra te. Considerable spatial variability in the infiltration capacity at the pl ot scale is implied by this positive relationship. This spatial variability clearly needs to be accommodated in infiltration models, and the SVIM repr esents a simple formulation of the infiltration rate as a function of rainf all intensity to address this spatial variability. SVIM parameters cart be related to the Green-Ampt parameters, and they could therefore be estimated directly using soil properties.