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This article in SSSAJ

  1. Vol. 51 No. 1, p. 42-47
    Received: Dec 23, 1985

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Estimating the Variability of Unsaturated Soil Hydraulic Conductivity Using Simple Equations1

  1. R. J. Wagenet and
  2. T. M. Addiscott2



Description of transient water flow requires knowledge, or estimation, of the relationship between the unsaturated soil hydraulic conductivity, K, and volumetric water content. A variety of studies have related K(θ) to the saturated conductivity Ko by equations involving the volumetric water content, θ, and its value at saturation, θo. The relationship is expressed here in terms of either the difference between θ and θo or the ratio of θ to θo, so that K(θ) is obtained by multiplying Ko by exp[β(θ − θo)] or by [θ/θo]2b + 3 respectively, with β and b being constants for any one sampling point. The quantity β in the equation involving (θ − θo) can be obtained from field data by four different mathematical methods. When this equation was used to compute distributions of lnK(θ) from measured distributions of lnKo and lnβ, the first four moments of the resulting distributions of lnK(θ) all differed considerably according to the mathematical method used, although Ko and β were derived in each case from the same set of field data. When both equations were used to estimate lnK(θ), using the same distributions of lnKo and appropriate distributions of lnβ or lnb, there were large differences between them in the moments of the resulting distributions. The estimate of lnK(θ) from the equation using θ/θo had much the larger variance, mainly because the variance of lnb was about three times that of lnβ.

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