Three-Parameter Soil-Water Transient Equations in Horizontal Water-Transport Analysis
- Ivan A. Guerrini and
- D. Swartzendruber
For data obtained from horizontal soil column experiments, the determination of soil-water transport characteristics and functions would be aided by a single-form equation capable of objectively describing water content θ vs. time t at given position xt. Our study was conducted to evaluate two such possible equations, one having the form of the Weibull frequency distribution, and the other being called a bipower form. Each equation contained three parameters, and was fitted by nonlinear least squares to the experimental data from three separate columns of a single soil. Across the θ range containing the measured data points obtained by gamma-ray attenuation, the two equations were in close agreement. The resulting family of θ(xf,t) transients, as obtained from either equation, enabled the evaluation of exponent n in the tn dependence of the positional advance of a given θ. Not only was n found to be <0.5 at low θ values, but it also increased with θ and tended toward 0.5 as θ approached its sated (near-saturated) value. Some quantitative uncertainty in n(θ) does arise due to the reduced number of data points available at the higher water contents. Without claiming non-Boltzmann behavior (n < 0.5) as necessarily representative of all soils, we nonetheless consider n(θ) to be worthy of further study for evaluating its significance and implications.
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