Approaches for estimating unsaturated soil hydraulic conductivities at various bulk densities with the extended Mualem-van Genuchten model

Abstract

The Mualem-van Genuchten model has been widely used for estimating unsaturated soil hydraulic conductivity (Ku) from measured saturated hydraulic conductivity (Ks) and fitted water retention curve (WRC) parameters. Soil bulk density (ρb) variations affect the accuracy of Ku estimates. In this study, we extend the Mualem-van Genuchten model to account for the ρb effect with ρb-related WRC and Ks models. We apply two functions (A and B) that relate the van Genuchten WRC model to ρb and two models (1 and 2) that estimate Ks with various ρb. By combining the ρb-related WRC functions and Ks models, we develop four integrated approaches (i.e., A1, A2, B1, and B2) for estimating Ku at various ρb. Kumeasurements made on five soils with various textures and ρb are used to evaluate the accuracy of the four approaches. The results show that all approaches produce reasonable Ku estimates, with average root mean square errors (RMSEs) less than 0.35 (expressed in dimensionless unit because logarithmic Ku values are used). Approach A2, with an average RMSE of 0.25, agrees better with Ku measurements than does Approach A1 that has an average RMSE of 0.28. This is because Model 2 accounts for the WRC shape effect near saturation. Approaches A1 and A2 give more accurate Ku estimates than do Approaches B1 and B2 which both have average RMSEs of 0.35, because Function A performs better in estimating WRCs than does Function B. The proposed approaches could be incorporated into simulation models for improved prediction of water, solute, and gas transport in soils.

Influence of compost amendment rate and level of compaction on the hydraulic functioning of soils

“…Since adding compost alters the mean particle density of the material, materials at the same bulk density but with different compost amounts will have differing porosity. We chose to use porosity instead of bulk density for differentiation between compaction levels because changes in porosity are considered one of the main factors altering the soil hydraulic properties with and without the addition of compost (Tian et al, 2018(Tian et al, , 2019. Thus, by holding the porosity constant across compost levels, the direct effect of the compost addition, rather than the effect of change in porosity associated with compost addition, could be compared.…”

Urban Gardens’ Potential to Improve Stormwater Management: A Comparative Analysis among Urban Soils in Sorocaba, São Paulo, Brazil

“…The measurements were performed on unsaturated soil in situ [62]. Although the values found are below expectations in saturated soil experiments, G also had the highes conductivity (35.8 mm h −1 ) and was significantly higher than all other areas.…”

A modeling framework to quantify the effects of compaction on soil water retention and infiltration

“…The unsaturated hydraulic conductivity (K u ) was then calculated from K s and the WRC parameters. Results by Tian et al (2019) showed that Model 2 produced more accurate estimates of K u than Model 1, with Model 2 providing a better description of the WRC near saturation. Thus, we used an equation similar to Model 2 of Tian et al ( 2019) to determine K s and K u , and to be able to account for the effects of compaction on the hydraulic conductivity and water infiltration:…”

“…hydraulic conductivity. Tian et al (2019) developed two models for estimating the saturated hydraulic conductivity (K s ) at various soil bulk densities. Their first model (Model 1) was based on the Carman-Kozeny equation (Kruczek, 2016), whereas the second model (Model 2) used the Mualem and Assouline (1989) semitheoretical model and the VG water retention function (van Genuchten, 1980).…”