Characterization of surface soil hydraulic properties in sloping landscapes

Abstract

Saturated and near-saturated surface soil hydraulic properties influence the partition of rainfall and snowmelt into infiltration and runoff. The goal of this study was to characterize near-saturated surface soil hydraulic properties and water-conducting porosity in sloping landscapes. The specific objectives included exploration of tension and double-ring infiltrometers for estimation of soil hydraulic properties in sloping landscapes, development of an improved method for determining water-conducting porosity, and the application of these methods in characterizing soil hydraulic properties and water-conducting porosity under three land use. Water infiltration from a double-ring infiltrometer and a tension infiltrometer at water pressures between -2.2 and -0.3 kPa was measured in a cultivated field with 0, 7, 15, and 20% slopes at Laura and under three land use (native grass, brome grass and cultivated) at St. Denis in Saskatchewan, Canada. Three-dimensional computer simulation studies were also performed for tension infiltrometer with various disc diameters, water pressures, and surface slopes. Steady infiltration rates and estimated field-saturated hydraulic conductivity (Kfs), hydraulic conductivity-water pressure relationship (K(h)), and inverse capillary length parameter were compared for different slopes and land use. These parameters were not significantly different (p 1×10-3 m in diameter) of the cultivated land and the grasslands, respectively. Experimental and simulation results of this study indicated that both tension and double-ring infiltrometers are suitable for characterization of saturated and near-saturated surface soil hydraulic properties in landscapes up to 20% slope. The new method can be used to characterize water-conducting porosity from in situ tension and double-ring infiltrometers measurements more adequately and efficiently than the existing methods. Application of these methods for three land use indicated that land use modified surface soil hydraulic properties and consequently may alter the water balance of an area by affecting the partition between, and relative amount of infiltration and surface runoff.