A soil‐water retention function that includes the hyper‐dry region through the BET adsorption isotherm

Abstract

[1] Most existing full-range soil-water retention functions extend standard capillary pressure curves into the dry region to zero water content at a finite matric pressure. A description of dryness is commonly taken as oven-dry conditions given by a matric suction of about 10 9 Pa at zero liquid saturation. However, no finite pressure can be exerted by a zero amount of water, so a possibly more realistic situation necessarily implies that as water content approaches zero, suction tends to infinity. In this study we propose a full-range water retention function that takes advantage of the physical consistence of the Brunauer-Emmett-Teller (BET) adsorption isotherm to describe the very dry end, and preserves the capillary behavior of the classical Brooks and Corey function in the wet range. The transition from capillary to adsorption mechanisms is accounted for by a generalization of the Bradley's isotherm. Tests on seven widely studied soil data sets show that the experimental water retention curves are well fitted by the proposed retention model. In order to test the present approach, our simulations were compared to experimental data, for water transport under dry conditions, found in the literature. The present model was also compared with a recently proposed extended retention function in a hypothetical experiment designed to test the influence of predicted soil humidity on solute volatilization. These comparisons showed that, under severe dryness, the water dynamics is well described by the proposed model. Moreover, in these conditions the retention function determines the soil humidity, to which solute volatilization calculations can be very sensitive.Citation: Silva, O., and J. Grifoll (2007), A soil-water retention function that includes the hyper-dry region through the BET adsorption isotherm, Water Resour. Res., 43, W11420,

A new theoretical model accounting for film flow in unsaturated porous media

“…However, the commonly used soil hydraulic models that account for capillary forces do not deal well with the flow process that occurs under very dry conditions [e.g., Rossi and Nimmo, 1994;Silva and Grifoll, 2007]. One important reason for the poor performance in dry conditions is that the common conceptual models for unsaturated hydraulic conductivity on which these flow models rely, e.g., the frequently used model of Mualem [1976a], are unsuitable under dry conditions.…”

“…Peters and Durner [2008] presented a model that combines Mualem's capillary flow model with a simple film flow function using film flow conductivity as a function of the effective saturation. The disadvantages of this simple model are that it lacks a physical basis and that it must be coupled with a common SWRC models (e.g., the van Genuchten model used in that paper), which may be invalid at lower water contents [Nimmo, 1991;Rossi and Nimmo, 1994;Silva and Grifoll, 2007]. By combining the film model developed by Langmuir [1938] with scaling analysis, Tokunaga [2009] developed a formula for estimating hydraulic conductivity that results from film flow in media consisting of smooth uniform spheres.…”

Folyadék-visszatartás, folyadékvezetés és porozitás összefüggései vízzel és/vagy szerves folyadékkal telített talajokban I. Folyadék-visszatartó képesség — Szemle

“…A multimodális illesztési eljárások ugyan lehetővé tették a makroporozitás hatá-sának figyelembevételét a víztartó-képesség meghatározása során, a századforduló-ra érve azonban továbbra is kérdéses maradt, hogy az SWRC görbék száraz végpon-ti értékeinek becslése hogyan pontosítható (ROSS et al, 1991;CAMPBELL & SHIOZAWA, 1992;KHLOSI et al, 2006;SILVA & GRIFOLL, 2007). A kapillaritás mellett jelentős szerepe van a folyadékvisszatartó-képesség értékek alakulásában a gőz-és folyadékfázisú adszorpciós folyamatoknak is (pl.…”

Estimation of soil water retention curve: An asymmetrical pore-solid fractal model

“…Different kinds of empirical models have been established to characterize the soil water retention function [1][2][3][4] . However, because of the high variability and complexity of soils, it is necessary to explore meaningful interpretations of the parameters in the empirical models.…”