On the variability and use of the hydraulic conductivity alpha parameter in stochastic treatments of unsaturated flow
- CSIRO Centre for Environmental Mechanics, Canberra (Australia)
The quasi-linear parameterization for unsaturated hydraulic conductivity K({Psi}) = K{sub s} exp ({alpha}{Psi}), where K is hydraulic conductivity, {Psi} is soil water matric potential, K{sub s} is saturated hydraulic conductivity, and {alpha} is a porous material parameter, has been used in both stochastic and deterministic models of unsaturated water flow in porous materials. In the stochastic approach, K{sub s} is assumed lognormally distributed, but {alpha} and the volumetric soil water capacity C = d{theta}/d{Psi}, with {theta} volumetric soil water content, are assumed normally distributed. The authors point out here that {alpha} and K{sub s} are related to the same internal pore geometry of the soil. This interrelationship ensures that if K{sub s} is lognormal, then {alpha}, and possibly C, will also be lognormal. Additionally, the authors present preliminary field results which indicate that {alpha} is better described by a lognormal than a normal distribution. The quasi-linear parameterization can be expected to be correct only in some integral sense. Predictions of increases in the variability of hydraulic conductivity with decreasing {Psi} may therefore be prejudiced by the use of the exponential form for K({Psi}). Tests of the sensitivity of stochastic model predictions to both the parameterizations adopted for K({Psi}) and the assumed distribution functions of parameters seem warranted. Reliable experimental evidence on field variability of K({Psi}) and {Psi}({theta}) at substantial negative values of {Psi} are also needed.
- OSTI ID:
- 5245133
- Journal Information:
- Water Resources Research; (United States), Vol. 28:1; ISSN 0043-1397
- Country of Publication:
- United States
- Language:
- English
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