Abstract:Surface soil hydraulic properties are key factors controlling the partition of rainfall and snowmelt into runoff and soil water storage, and their knowledge is needed for sound land management. The objective of this study was to evaluate the effects of three land uses (native grass, brome grass and cultivated) on surface soil hydraulic properties under nearsaturated conditions at the St Denis National Wildlife Area, Saskatchewan, Canada. For each land use, water infiltration rates were measured using double-ring and tension infiltrometers at 0Ð3, 0Ð7, 1Ð5 and 2Ð2 kPa pressure heads. Macroporosity and unsaturated hydraulic properties of the surface soil were estimated. Mean field-saturated hydraulic conductivity K fs , unsaturated hydraulic conductivity at 0Ð3 kPa pressure head, inverse capillary length scale ˛ and water-conducting macroporosity were compared for different land uses. These parameters of the native grass and brome grass sites were significantly p < 0Ð1 higher than that of the cultivated sites. At the 0Ð3 kPa pressure head, hydraulic conductivity of grasslands was two to three times greater than that of cultivated lands. Values of˛were about two times and values of K fs about four times greater in grasslands than in cultivated fields. Water-conducting macroporosity of grasslands and cultivated fields were 0Ð04% and 0Ð01% of the total soil volume, respectively. Over 90% of the total water flux at 0Ð06 kPa pressure head was transmitted through pores >1Ð36 ð 10 4 m in diameter in the three land uses. Land use modified near-saturated hydraulic properties of surface soil and consequently may alter the water balance of the area by changing the amount of surface runoff and soil water storage.

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.

The majority of landscapes, natural or cultivated, are nonlevel. However, specifically designed instruments are not available for estimation of soil hydraulic properties in sloping landscapes. The objective of this study is to examine if tension and double‐ring infiltrometers are suitable for determination of soil hydraulic properties on sloping soil surfaces. A field experiment was conducted in a silt loam soil (Typic Haplustolls) in Saskatchewan, Canada to explore the usefulness of tension and double‐ring infiltrometers for the determination of soil hydraulic properties in sloping landscapes. Soil surfaces were created to represent four treatments, 0 (level), 7, 15, and 20% slopes. For each treatment, water infiltration rates were measured using a double‐ring infiltrometer and a tension infiltrometer at −3, −6, −10, −13, −17, and −22 cm water pressure heads. In addition, three‐dimensional computer simulation studies were performed for a tension infiltrometer with various disc diameters and water pressure heads for different surface slopes. Steady‐state infiltration rate, field‐saturated hydraulic conductivity, unsaturated hydraulic conductivity as a function of water pressure head, macroscopic capillary length parameter, and water‐conducting macro‐ and mesoporosity were compared for different surface slopes. These parameters were not significantly different (p < 0.05) between level and sloping lands. Experimental and numerical results of this study suggest that both tension and double‐ring infiltrometers are suitable for characterization of surface soil hydraulic properties in landscapes with slopes up to 20%.

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trenches. Tracer studies with tensiometers, piezometers, and suction lysimeters have been used to identify sub-The majority of landscapes, natural or cultivated, are nonlevel. surface flow pathways in a steep watershed by Harr However, specifically designed instruments are not available for esti-These methods, however, are time-consuming, tedious of this study is to examine if tension and double-ring infiltrometers are suitable for determination of soil hydraulic properties on sloping to perform under field conditions, and sometimes resoil surfaces. A field experiment was conducted in a silt loam soil quire laboratory derived hydraulic parameters for deter-(Typic Haplustolls) in Saskatchewan, Canada to explore the usefulness mination of hydraulic conductivity. The hillslope infilof tension and double-ring infiltrometers for the determination of soil trometer, which is open at the bottom, top, and downhill hydraulic properties in sloping landscapes. Soil surfaces were created sides, was introduced by Mendoza and Steenhuis (2002) to represent four treatments, 0 (level), 7, 15, and 20% slopes. For for determination of vertical and horizontal saturated each treatment, water infiltration rates were measured using a doublehydraulic conductivity of soil horizons in steep lands. ring infiltrometer and a tension infiltrometer at Ϫ3, Ϫ6, Ϫ10, Ϫ13, The installation of this device requires the carving of a Ϫ17, and Ϫ22 cm water pressure heads. In addition, three-dimensional soil block that is slightly smaller than the infiltrometer computer simulation studies were performed for a tension infiltrom-(36 cm in length, 30.5 cm in width and 41 cm in height) eter with various disc diameters and water pressure heads for different and excavation of a trench around the block for ease surface slopes. Steady-state infiltration rate, field-saturated hydraulic of installation of the device and water collectors. This conductivity, unsaturated hydraulic conductivity as a function of water particular method is destructive, time-consuming, and pressure head, macroscopic capillary length parameter, and watersomewhat cumbersome for routine field use. conducting macro-and mesoporosity were compared for different surface slopes. These parameters were not significantly different (p Ͻ Tension and single-ring or double-ring infiltrometers 0.05) between level and sloping lands. Experimental and numerical are primarily designed and tested on horizontal surfaces. results of this study suggest that both tension and double-ring infiltro-However, the equipment has been extensively used in meters are suitable for characterization of surface soil hydraulic propthe past to obtain saturated and near-saturated soil hyerties in landscapes with slopes up to 20%. draulic properties on sloping lands. Watson and Luxmoore (1986) and Wilson and Luxmoore (1988) used tension infiltrometers in conjunction with double-ring