A modification to the van Genuchten model for improved prediction of relative hydraulic conductivity of unsaturated soils

Abstract

Modelling of flow and transport in unsaturated soils requires information on two fundamental hydraulic properties: the soil water retention curve and relative hydraulic conductivity. A soil's relative hydraulic conductivity is frequently predicted from the soil water retention curve. The most widely used combination is the van Genuchten model for the soil water retention curve and the Mualem model for relative hydraulic conductivity (VGM). Previous studies show that the VGM model underestimates measured relative hydraulic conductivity for soils with fine textures; a sharp drop in relative hydraulic conductivity can be seen near saturation. A new modification of the van Genuchten soil water retention model is proposed with the aim of improving the agreement between predicted and measured relative hydraulic conductivity. The Brooks and Corey-Burdine model is used to predict relative hydraulic conductivity from the modified van Genuchten soil water retention curve (MVG-BCB). The modified model assumes independent m and n in the van Genuchten model but with constraints n > 2 and 0 < m < 1. The MVG-BCB model is evaluated by comparing calculated and measured data for 59 soils that have widely varying soil textures, ranging from sandstone to clay. The MVG-BCB model improves the agreement between calculated and measured data for both the soil water retention curve and relative hydraulic conductivity. The MVG-BCB model is closer to measured relative hydraulic conductivity data for most of the selected soils and the sharp drop near saturation is eliminated. Both the modified soil water retention curve and relative hydraulic conductivity functions are smooth curves and can easily be incorporated into vadose zone flow and transport modellings. Highlights• A new modification to the van Genuchten soil water retention model.• The model improves the fit to measured soil water retention data.• The chosen model improves the prediction of relative hydraulic conductivity.

Migration of carbon dioxide in sandstone under various pressure/temperature conditions: From experiment to simulation

“…The VG model is widely used to give the capillary pressure and the relative permeability for CO 2 /brine transport in porous media 48–51 . The model was adopted in this study and the equations are listed below: $$\begin{equation}\overline {{S_{{\rm{bri}}}}} \eqcellsep =\eqcellsep \frac{{{S_{{\rm{bri}}}} - {S_{r,{\rm{bri}}}}}}{{1 - {S_{r,{\rm{bri}}}} - {S_{r,{\rm{C}}{{\rm{O}}_2}}}}}{\rm{\;}}\eqbreak\end{equation}$$ $$\begin{equation}\overline {{S_{{\rm{C}}{{\rm{O}}_2}}}} \eqcellsep =\eqcellsep \frac{{{S_{{\rm{C}}{{\rm{O}}_2}}} - {S_{r,{\rm{C}}{{\rm{O}}_2}}}}}{{1 - {S_{r,{\rm{bri}}}} - {S_{r,{\rm{C}}{{\rm{O}}_2}}}}}{\rm{\;}}\eqbreak\end{equation}$$ $$\begin{equation}{P_c} \eqcellsep =\eqcellsep {P_{{\rm{ec}}}}{\rm{\;}}{\left( {{{\overline {{S_{{\rm{bri}}}}} }^{ - \frac{1}{m}}} - 1} \right)^{1 - m}}\eqbreak\end{equation}$$ $$\begin{equation}{k_{r,w}} \eqcellsep =\eqcellsep {\...$$…”

“…The VG model is widely used to give the capillary pressure and the relative permeability for CO 2 /brine transport in porous media. [48][49][50][51] The model was adopted in this study and the equations are listed below:…”

Capillary rise in partially saturated rigid porous media

“…These are often expressed as soil water retention curves and relative hydraulic conductivity relationships and include well-known works by Leverett (1941), Brooks & Corey (1964), Mualem (1976) and van Genuchten (1980), as well as related ones adopted by Lockington & Parlange (2004) (but see also Bear (1972) and Hornung (1997)). More recent investigations include Kuang et al (2020) who discuss a modification to the classical van Genuchten model for relative hydraulic conductivity and the work by Soldi, Guarracino & Jougnot (2017) which has a specific focus on hysteretic features. Another recent study by Johnson, Zyvoloski & Stauffer (2019) incorporates an additional porosity dependence of these functions to be used in problems in which the porosity evolves in time (e.g.…”

Approximation of van Genuchten Parameter Ranges from Hydraulic Conductivity Data

“…Both, relative conductivity and retention function can be described by parameterizations, such as the ones proposed by Brooks and Corey (1965), Russo (1988), Gardner (1970), and Mualem (1976), Van Genuchten (1980). The latter parameterization is among the most widely used, often referred to as MvG in practice (Kuang et al 2021). Mathematically, the MvG retention function reads: where [MLT] is fluid pressure, [ML] is fluid density, g [LT] is gravitational acceleration and the effective saturation [−] is with the water content [−], the saturated water content [−] and the residual water content [−].…”