Estimating the sorptivity for a wide range of diffusivity dependence on water content

Analytical approximations of the sorptivity have previously been formulated to be accurate for rapidly-varying hydraulic diffusivities. However, investigations have indicated that the diffusitivity of undisturbed field soils varies much less rapidly than that of repacked soils commonly used in laboratory studies. In fact, for certain soils, the diffusivity may decrease with increasing moisture content. In the present paper a new analytical estimate of the sorptivity is derived which retains the accuracy of earlier approximations for rapidly-varying diffusivities while remaining accurate even for constant and decreasing diffusivities