SOLUTE DIFFUSION ANALOGY MODEL FOR PREDICTING UNSATURATED HYDRAULIC CONDUCTIVITY IN REPACKED SOIL

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Abstract

Solute diffusion in soil has been shown to cease below a certain threshold water content. In this study, the threshold water content (θth) for unsaturated hydraulic conductivity (K) was investigated, with the purpose of establishing a relationship between θth and the Campbell soil water retention parameter, b. A model for predicting K in sieved, repacked soil from the soil water retention curve using an approach similar to a newly developed model for solute diffusion in soil was developed using K data for a set of 39 sieved, repacked soils representing a wide range of textures. The new solute diffusivity analogy model for predicting K was tested against a set of independent conductivity data from six additional repacked soils and predicted the measured hydraulic conductivity values well. The comparison between the threshold water contents for solute diffusivity and hydraulic conductivity implied that the transport of water can still occur at low water contents where solute (ion) diffusion is restricted or nonexistent. This effect was found most prominent in fine textured soils such as clayey and silty soils.

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