Improvements in the prediction of unsaturated soil hydraulic conductivity using bimodal lognormal relationships.

We propose to improve the estimation of soil hydraulic properties by first using a bimodal analytical relationship to describe the water retention function. Basically a superposition of structural and textural unimodal components represents the behavior of bimodal pore-size distribution. Each of these water retention functions is described by a Kosugi-type log-normal function, with parameters being associated to the soil pore-size distribution. The two components of the water retention response are linked by a weighting factor, w to which a physical meaning can also be given. The model of Mualem is then used to obtain an analytical closed-form expression for the unsaturated hydraulic conductivity. Comparisons with experimental data demonstrate the effectiveness of better predicting the hydraulic conductivity characteristic not only for clayey, well structured soils, but also in case of soils showing a textural component comparable with the structural component.