This study investigated the use of effective soil hydraulic properties (expressed in terms of hydraulic parameters) applicable to large‐scale transient infiltration problems in a landscape with horizontally heterogeneous soil hydraulic properties. The heterogeneous landscape was conceptualized as an equivalent homogeneous medium with effective hydraulic properties. The main objectives were to investigate: (i) which effective soil hydraulic property schemes are suitable to represent average behavior of large‐scale infiltration processes, (ii) how the effective hydraulic parameters are sensitive to the process time frame, and (iii) how hydraulic parameter variability and correlation impact the effective hydraulic parameters. The heterogeneous landscape was represented by a series of vertically homogeneous stream tubes or parallel columns. Large‐scale average infiltration behavior in the heterogeneous soils was quantified through Monte Carlo simulations of multiple realizations (stream tubes) of local‐scale infiltration. The optimal effective hydraulic parameters were then calculated with an inverse procedure that minimized the difference between average cumulative infiltration and cumulative infiltration based on a single set of effective parameters. Three scenarios were used to optimize either two hydraulic parameters simultaneously or only one hydraulic parameter while using the arithmetic mean for the other parameter. Results indicate that while the effective hydraulic parameters could simulate average infiltration more closely when multiple parameters were optimized together, the effective parameter values were more variable as time evolved. Optimizing only one hydraulic parameter while keeping the arithmetic mean for the other parameter produced more uniform effective hydraulic parameters with time, but this approach did not represent average infiltration behavior of the heterogeneous soils as well as when multiple hydraulic parameters were optimized simultaneously.
Zhu, J. and Sun, D. 2010. Capillary pressure-dependent anisotropy of layered unsaturated soils. Can. J. Soil Sci. 90: 319Á329. This paper presents an approach based on a conceptualization of combining the neural network based pedo-transfer function (PTF) results with the thin layer concept to explore capillary-pressure-dependent anisotropy in relation to soil texture and soil bulk density. The effects of capillary pressure (or saturation degree) on the hydraulic conductivity anisotropy of unsaturated soils are still poorly understood. The main objective is to examine how anisotropy characteristics are related to the relationships between hydraulic parameters and the basic soil attributes such as texture and bulk density. The hydraulic parameters are correlated with the texture and bulk density based on the pedo-transfer function (PTF) results. It is demonstrated that non-monotonic behavior of the unsaturated soil anisotropy in relation to the capillary pressure is only observed when the saturated hydraulic conductivity and the shape parameter are both related to the particle diameter. Therefore, it is suggested that this behavior is mainly due to the coupled dependence of the layer saturated hydraulic conductivities and the shape factors on the texture and bulk density. The results illustrate that the inter-relationships of soil texture, bulk density, and hydraulic properties may produce vastly different characteristics of anisotropic unsaturated soils.Key words: Anisotropy, unsaturated soils, capillary pressure-dependent Zhu, J. et Sun, D. 2010. Anisotropie attribuable a`la pression capillaire dans les sols stratifie´s insature´s. Can. J. Soil Sci. 90: 319Á329. Les auteurs recourent a`une approche articule´e sur une conceptualisation qui combine une fonction de pe´dotransfert (FPT) reposant sur les re´seaux neuronaux et le concept des couches minces pour explorer l'anisotropie associe´e a`la pression capillaire et les liens de cette dernie`re avec la texture et la masse volumique apparente du sol. On comprend mal l'incidence de la pression capillaire (ou degre´de saturation) sur l'anisotropie de la conductivite´hydraulique dans les sols insature´s. L'objectif principal consistait a`e´tablir comment les proprie´te´s anisotropes influent sur les liens entre les parame`tres hydrauliques et les proprie´te´s fondamentales du sol, comme la texture et la masse volumique apparente. Les parame`tres hydrauliques sont corre´le´s à la texture et a`la masse volumique apparente selon les re´sultats de la FPT. L'anisotropie des sols insature´s ne suit un comportement non monotone par rapport a`la pression capillaire que lorsque la conductivite´hydraulique au point de saturation et le parame`tre de forme sont relie´s au diame`tre des particules. C'est pourquoi on pre´sume que ce comportement re´sulte principalement du fait que la conductivite´hydraulique des diffe´rentes strates au point de saturation et les coefficients de forme de´pendent tous deux de la texture et de la masse volumique apparente. Les re´sultats indiquent q...
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