Upscaling Hydraulic Properties and Soil Water Flow Processes in Heterogeneous Soils: A Review

Abstract

This review covers, in a comprehensive manner, the approaches available in the literature to upscale soil water processes and hydraulic parameters in the vadose zone. We distinguish two categories of upscaling methods: forward approaches requiring information about the spatial distribution of hydraulic parameters at a small scale, and inverse modeling approaches requiring information about the spatial and temporal variation of state variables at various scales, including so-called "soft data". Geostatistical and scaling approaches are crucial to upscale soil water processes and to derive large-scale effective fluxes and parameters from small-scale information. Upscaling approaches include stochastic perturbation methods, the scaleway approach, the stream-tube approach, the aggregation concept, inverse modeling approaches, and data fusion. With all upscaling methods, the estimated effective parameters depend not only on the properties of the heterogeneous flow field but also on boundary conditions. The use of the Richards equation at the field and watershed scale is based more on pragmatism than on a sound physical basis. There are practically no data sets presently available that provide sufficient information to extensively validate existing upscaling approaches. Use of numerical case studies has therefore been most common. More recently and still under development, hydrogeophysical methods combined with ground-based remote sensing techniques promise significant contributions toward providing high-quality data sets. Finally, most of the upscaling literature in vadose zone research has dealt with bare soils or deep vadose zones. There is a need to develop upscaling methods for real world soils, considering root water uptake mechanisms and other soil-plant-atmosphere interactions.

Column-scale unsaturated hydraulic conductivity estimates in coarse-textured homogeneous and layered soils derived under steady-state evaporation from a water table

“…There are different approaches with regard to scaling of soil hydraulic properties and soil water processes in heterogeneous porous media such as averaging methods (Kitanidis, 1990;Zhu et al, 2004;Zhu and Mohanty, 2006), inverse solutions (van Dam et al, 1994;Hopmans and Simunek, 1999;Zhang et al, 2004;Javaux and Vanclooster, 2006;Vrugt et al, 2008;Erdal et al, 2012), percolation theory (Hunt, 1998;Samouelian et al, 2007;Hunt and Idriss, 2009), homogenization theory (Neuweiler and Cirpka, 2005;Neuweiler and Eichel, 2006;Neuweiler and Vogel, 2007), hybrid mixture theory , 1980, similar media scaling theory (Miller and Miller, 1956;Warrick and Amoozegar-Fard, 1979;Kosugi and Hopmans, 1998;Sadeghi and Jones, 2012;Ojha et al, 2014), dissimilar media scaling methods (Sadeghi et al, 2012b,c), stochastic methods (Yeh et al, 1985;Zhang and Lu, 2002), and renormalization methods (King, 1989;Saucier, 1992;King and Neuweiler, 2002). Many of these methods and their strengths and limitations have been previously reviewed and discussed (e.g., Wen and Gomez-Hernandez, 1996;Pachepsky et al, 2003;Cushman et al, 2002;Chen, 2006;Vereecken et al, 2007).…”

Spatial time domain reflectometry and its application for the measurement of water content distributions along flat ribbon cables in a full‐scale levee model

“…Field measurements are often the basis for inversely determined hydraulic properties [Abbaspour et al, 2000;Ferré et al, 2002;Vereecken et al, 2007]. TDR has been proven as a useful tool for the collection of site-specific information, especially for intensive soil sampling [Long et al, 2002;Stenger et al, 2007].…”

Kalman filters for assimilating near-surface observations into the Richards equation – Part 1: Retrieving state profiles with linear and nonlinear numerical schemes

“…These "optimal" soil hydraulic parameters are to be considered as effective values at the scale of the observation or of the modelled system, respectively (Vereecken et al, 2007).…”