A simplified model for the transient water budget of a shallow unsaturated zone

Abstract

A simplified model describing the transient water budget of a shallow unsaturated soil profile is presented and applied to an example of long-term climatic conditions for a site near Coshocton, Ohio. Its conceptualization is simplified because the instantaneous redistribution of infiltrated water in a uniform soil profile is imposed. The model's formulation is a revision of that originally presented by Kim et al. [1996]. Runoff from a soil profile with uniform hydraulic properties is described by using an infiltration equation derived by Salvucci [1996] for ponded conditions. During storm periods the infiltration rate equals the rainfall intensity, unless that rate exceeds the saturated hydraulic conductivity, and then the input rate is determined by the infiltration equation for ponded conditions, with the excess applied water being accounted for as runoff. During interstorm periods, when the soil profile is drying due to evapotranspiration (ET) and drainage, the ET rate equals the potential evapotranspiration rate E(p), until the soil profile relative saturation s drops below a certain falling value of saturation S(f). When s