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Soil Science Society of America Journal Abstract -

An Improved Form of Soil-Water Diffusivity Function1


This article in SSSAJ

  1. Vol. 36 No. 1, p. 9-14
    Received: May 24, 1971
    Accepted: Aug 27, 1971

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  1. L. R. Ahuja and
  2. D. Swartzendruber2



The soil-water diffusivity D(θ) is expressed by a functional form which becomes infinite as the soil-water content approaches a constant value, such as the saturated or near-saturated value. The function begins at the origin, and shows an approximately exponential rise in the intermediate soil-water content range. When combined with a previously suggested form of unsaturated hydraulic conductivity function K(θ), qualitatively reasonable forms for the relationship between water content and suction head can be inferred. A computer program was developed to determine the characterizing parameters in the function by a least-squares fit to experimental data for horizontal water absorption. The program used an optimum seeking technique with numerical solutions of the flow equations as obtained by Philip's method. For different types of soils and several bulk densities, the new functional form was compared with the commonly used exponential expression for D(θ), and was found to be more representative, particularly for soils which show a very rapid increase in D(θ) as saturation is approached.

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