Scaling field‐measured soil hydraulic properties using a similar media concept

Abstract

With a view toward developing techniques for studying water flow in spatially varying soils, field data for soil water characteristic relationships and unsaturated hydraulic conductivity are scaled by using the concept of similar media. Data observed by different investigators at three geographic areas are used. The soil water characteristic data consisted of 840, 900, and 512 observations, while those for the unsaturated hydraulic conductivity (available from only one of the three sources) consisted of 2640 observations. In the process of scaling the data a best fit for the scaled data is defined in terms of a sum of squares about an ‘average’ curve using one value for the scaling parameter for each sampling location. Comparisons made between curves fitting the data and those fitting the scaled data show that scaling reduces the sums of squares by amounts varying from 34 to over 90%. For similar media the scaling parameter determined at a given sampling location for the soil water characteristic relationship (α from h(S)) should be identical to that for the unsaturated hydraulic conductivity (αr from K(S)). Although these parameters were highly correlated (r = 0.91 ) for the only set of data available, α r from h(S) values are shown to be more effective in scaling the unsaturated hydraulic conductivity data than are αr from K(S) values in scaling soil water characteristic data.

Influencia de la variabilidad del suelo en la hidrología superficial de una cuenca

“…Relación Referencias 1 θ(Ψ m ) Brooks y Corey (1964), Brutsaert (1966), Van Genuchten (1980 2 K(θ) Brooks y Corey (1964), Van Genuchten (1980, Sander et al (1988) 3 K(Ψ m ) Gardner (1958), Ritjema (1965), Ahuja y Williams (1991) 4 D(θ) Fujita (1952) -en Fuentes et al, 1992-, Gardner y Mayhugh (1958 La variabilidad espacial puede ser caracterizada, para una superficie ocupada por un tipo único de suelo, con algunas funciones de distribución que afectan a un factor de escala, como sugirieron Warrick et al (1977) al reducir numerosas observaciones en un suelo aluvial a un patrón que ellos estimaron el valor medio, con la que se relacionaban haciendo variar el parámetro de escala. Sus ajustes garantizaban la eficacia del método si bien, como Warrick (1990) reconocía más tarde, presentaba algún problema como las diferencias entre los valores de tal parámetro calculado en base a la componente matricial del potencial o en base a la conductividad hidráulica para valores de la humedad determinados.…”

A Review of Approaches for Measuring Soil Hydraulic Properties and Assessing the Impacts of Spatial Dependence on the Results

“…The validity of this hypothesis has been confirmed only through laboratory tests on sand filters (Klute and Wilkinson, 1958;Elrick et al, 1959) and, even if it finds no actual correspondence in soils, it has been used by several authors (Warrick et al, 1977b;Simmons et al, 1979;Rao et al, 1983) to relate potential and conductivity to the degree of soil saturation s and not to water content . The same authors evaluated the distribution of the similarity ratio not with reference to the microgeometry of the porous medium, but by ensuring that there was the best possible fit between the tension and conductivity curves, measured at various points.…”

“…The purpose of such techniques, generally indicated in the literature as being functional normalization (Tillotson and Nielsen, 1984), is to reduce dispersion of test data, concentrating them on an average reference curve that describes the relationship in question. Scale factors identified with such procedures often differ in each hydraulic property on which they are evaluated (Warrick et al, 1977b;Russo and Bresler, 1980;Ahuja et al, 1984).…”

Scaling the Hydraulic Functions of A Water Repellent Sandy Soil

“…They found much higher heterogeneity of saturated conductivity. Warrick et al (1977) and Russo and Bressler (1980) did not find relation between the scaling of unsaturated hydraulic conductivity and water retention. Kodesova et al (2003) presented scaling approach of two-phase capillary pressuresaturation relationships for both water-air and oil-air system.…”