Accurate parameterization of the soil hydraulic properties represents a key issue for the modeling of soil water transport processes. The more complex the soil structure, the more crucial this requirement becomes. In dealing with this problem for structured and well-aggregated soils, we have pursued the general objective of developing hydraulic relationships whose parameters characterize the soil's pore size distributions, thereby providing a physically based framework for the hydraulic relationships of bimodal soils. In our work, we assumed that the soil water retention function is determined by linear superposition of two distinct pore domains, which can be associated with textural and structural retention behaviors, respectively. Tlie composite soil water retention function was described by Kosugi's lognormal function, with parameters being directly associated with the mean and variance of the soil pore size distribution for each pore domain. The two components of soil water retention were linked by a weighting factor to which a physical meaning can also be given. An important and practical advantage of the proposed bimodal water retention funcrion is that a closed-form analyrical expression is obtained for the bimodal hydraulic conductivity function using pore size distribution parameters. TTiis is relevant because we suggest that soil hydraulic properties can be characterized by the soil particle size distribution. Sensitivity analysis and comparisons with experimental data were used to evaluate the proposed bimodal lognormal hydraulic Functions and to demonstrate their increased effectiveness in predicting the hydraulic conductivity charactensdc of soils.
[1] Well-type flow takes place in a heterogeneous porous formation where the transmissivity is modeled as a stationary random space function (RSF). General expressions for the covariances of the head and flux are obtained and analyzed. The second-order approximation of the mean radial flux is represented as the product between the solution q ð0Þ r ðrÞ valid in a homogeneous domain and a distortion term É q ðrÞ, which adjusts q ð0Þ r ðrÞ according to the medium heterogeneity. The spatial dependence of the function É q ðrÞ is studied. In view of the formation identification problem, the equivalent T (eq) and apparent T
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