The infiltration envelope: Results from a theoretical infiltrometer

Abstract The theoretical partial differential equation for unsaturated soil moisture flow is solved by a versatile numerical scheme designed for accurate simulation of infiltration from various patterns of rainfall. This model is used to study the independent effects of soil type, initial soil moisture, rainfall rate and rainfall pattern. The results of the investigation are expressable as a simple parametric model for vertical infiltration. Infiltration from a suddenly ponded surface is shown to be an asymptotic limit to increasing rainfall rates. A single dimensionless formula is found to accurately describe the infiltration decay curves for all soils, initial conditions, and rainfall rates tested, and another dimensionless relation predicts time to ponding under arbitrary rainfall patterns as a function of infiltrated rainfall depth. The effect of initial soil moisture is shown to be well described by a simple linear effect on the normalizing time in the dimensionless system. Uses and implications of these results are discussed.