PLOT-SCALE RAINFALL-RUNOFF CHARACTERISTICS AND MODELING AT SIX SITES IN AUSTRALIA AND SOUTHEAST ASIA

Abstract

During major runoff events when most soil loss occurs, runoff is likely to dominate the rainfall-driven erosionprocesses. Thus accurate estimation of the runoff rate is critical to soil loss predictions. At plot scale, the Green-Amptinfiltration model is commonly assumed to be able to describe the temporal variation of the infiltration rate over a stormevent. Field measurements of both rainfall intensity and runoff rate at 1-min intervals at six sites in the tropical and subtropicalregions of Australia and Southeast Asia, however, strongly suggest that the apparent infiltration rate is closelyrelated to the rainfall intensity and it is essentially independent of the cumulative infiltration amount, features not accordwith the Green-Ampt infiltration equation. Furthermore, the storage effect and runoff rate attenuation are not negligibleat the plot scale. With an initial infiltration amount to determine when runoff begins, an exponential distribution todescribe the spatial variation in the maximum infiltration rate and a linear storage formulation to model the lag betweenrunoff and rainfall, we were able to develop a satisfactory three-parameter model for the runoff rate at 1-min intervalswithin a storm event.