Analysis of short-time single-ring infiltration under falling-head conditions with gravitational effects

Analytical solutions of the flow equation for infiltration offer an interesting tool for the hydrodynamic characterization of non-saturated soils by optimization of the hydraulic conductivity, Kfs, and the capillary sorptivity, So. However, the experimental conditions have to satisfy the governing assumptions. For falling head infiltration tests the initial water height, Ho, is a third unknown parameter that has to be optimized. For the short-time, the classic solution expresses the depth of water infiltrated as a function of time as a term that depends only on the sorptivity. This, however, neglects gravitational effects. We improved the falling head infiltration problem, after a period of constant head infiltration, for the case of rigid materials without any assumptions for a particular hydraulic conductivity relationship and taking into account gravity effects. A comparison of two solutions, i.e., the equation of one and two terms, was made using the results of falling head infiltration tests. Neglecting the effects of gravity in the infiltration equation leads to an overestimation of the hydrodynamic parameters, Ho and So, and a concomitant underestimation of Kfs compared to our improved solution developed here. Consequently, the depth of ponded water predicted by the one term infiltration equation is higher than that calculated by the improved two term solution. Unfortunately, the actual depth of water infiltrated into the soil cannot be independently verified. To accomplish this, it is recommended that future studies include a measure of the change in stored soil water content at the test site, or a continuous measure of the variation in soil water content by a non-destructive method.