Abstract
A twin disc infiltrometer is developed to simultaneously measure one-dimensional cumulative infiltration. The assumption that flow at early times is essentially one-dimensional is shown to introduce error when estimating sorptivity, resulting in estimates that are greater than the true one-dimensional sorptivity. In contrast, sorptivity calculations using our recently developed three-dimensional infiltration equation give quite precise estimates of sorptivity. The difference between three-dimensional and one-dimensional infiltration is used to calculate the value of the infiltration parameter γ from the twin disc experiment. This parameter, together with the correct one-dimensional sorptivity, provide the information necessary to calculate the contribution of gravitational flow during three-dimensional infiltration. It is shown that when three-dimensional infiltration is dominated by capillary effects, as is often the case, estimation of hydraulic conductivity using quasi-steady-state solutions may not be possible.