New Method for Determining Water-Conducting Macro- and Mesoporosity from Tension Infiltrometer

Abstract

Characterization of water-conducting porosity at and near saturation is required in understanding rainfall and snowmelt infiltration and runoff as well as chemical transport in soil. There are methods available to quantify water-conducting porosity in situ, but with serious limitations. The objective of this paper was to present a general equation for water-conducting porosity based on ponded- and tension-infiltration measurements. Some analytical solutions are developed for specific unsaturated hydraulic conductivity functions such as the Gardner's exponential and rational power models, Brooks and Corey model, and van Genuchten–Mualem model. Tension infiltrometer measurements were taken at six different pressure heads between −0.3 to −2.2 kPa and double-ring infiltrometer measurements at a pressure head of 0.35 kPa. The analytical solutions were compared with numerical solutions and existing methods for calculation of water-conducting porosity. Both the analytical and numerical solutions can reliably determine the water-conducting porosity of surface soils in situ within the practical pressure head range of the tension infiltrometer. Our method gave consistent water-conducting porosity, regardless of the width of pressure head ranges. The existing methods overestimated water-conducting macroporosity by a factor of greater than two and overestimated total water-conducting porosity by a factor of >10 for measurements taken at large pressure head intervals compared with that of our method. Combining with hydraulic parameter estimation from tension infiltrometer measurements, our method may reduce the number of tension infiltration measurements required to calculate water-conducting porosity.