Assessing the size dependency of measured hydraulic conductivity using double-ring infiltrometers and numerical simulation

Saturated hydraulic conductivity measurements are important for understanding and modeling hydrologic processes at the field scale. Few systematic studies have been conducted on how the size of double-ring infiltrometers affects the measured hydraulic conductivity. To determine this size effect, we measured saturated hydraulic conductivity at seven sites using four different sizes of double-ring infiltrometers. Inner-ring diameters, d(i), were 20, 40, 80, and 120 cm. Detailed numerical investigations were also conducted to explain how the inner-ring size of a double-ring infiltrorneter influences the measured hydraulic conductivity in a heterogeneous soil. Field and simulation results both demonstrated that the variability in measured hydraulic conductivity was greater for smaller inner rings (e.g., d(i) <40 cm), and gradually decreased as the ring size increased. Our study indicates that where soil spatial variability is high, infiltrometers having a large inner ring (in general, d(i) >80 cm) are essential for reliable measurement.