Modeling Soil Matrix Hydraulic Properties for Variably-Saturated Hydrologic Analysis

Abstract

This article presents a method to estimate soil matrix hydraulic properties to be used for variably-saturated hydrologic analysis, such as rainfall/runoff and stormwater management analyses, among others. The methods are described and verified with the U.S. Department of Agriculture’s Unsaturated Soil Database (UNSODA), and the resultant soil hydraulic properties are presented. For conservative estimates of soil infiltration, a filter is recommended to remove soils from the analysis with high-saturated hydraulic conductivity that are likely to be macropore-dominated, and it is confirmed that the removed soils contain substantially more macropore influence than the retained soils. It is shown with the UNSODA database that good estimations of the soil matrix hydraulic conductivity function may be obtained by using the modified van Genuchten-Mualem model normalized to the saturated hydraulic conductivity with an immutable model parameter he=−0.1 cm if data are not available to calibrate he; this allows for the hydraulic conductivity curve to be estimated without laboratory-measured unsaturated data and overcomes some of the limitations of the van Genuchten-Mualem model.