NUMERICAL EVALUATION OF RING-INFILTROMETERS UNDER VARIOUS SOIL-CONDITIONS

Field evaluation of infiltrometer geometry and of soil conditions on i nfiltration measurements is difficult because of the spatial and tempo ral variability of soil properties and the disturbance of soil by infi ltrometer installation, Numerical simulation experiments provide a use ful tool for evaluating the infiltration rates measured by various con figurations of infiltrometers and soil conditions, We used an axisymme tric 3-dimensional (3D) numerical model to simulate water infiltration in single-and double-ring infiltrometers, as well as one-dimensional (1-D) infiltration for three well studied soil types representing diff erent textures and hydraulic properties, We found that the infiltratio n rates of a single-ring infiltrometer were f times greater than the 1 -D infiltration, where f is a correction factor dependent on soil init ial and boundary conditions and ring geometry, When the configuration of a typical double-ring infiltrometer was used in simulation (inner a nd outer rings were 20 and 30 cm in diameter, respectively), the simul ated infiltration rates were about 80% of the single-ring rates, When the outer-ring diameter was increased to 120 cm (inner-ring diameter k ept at 20 cm), the double-ring method-measured infiltration rates were 120 to 133% of the 1-D infiltration rates for the three test soils, C ompared with the constant head method, falling head infiltration rates dropped as much as 30% as the ponded head dropped from 5 to 1 cm in t he sandy clay loam, Layered soil can significantly affect infiltration rates, depending on the position of the wetting front relative to the textural discontinuity and the time of measurement, Time at which the layering starts playing the role can be estimated from f and the cumu lative infiltration.