Comparison of measured and estimated unsaturated hydraulic conductivity

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Abstract
Most studies of empirical estimates of unsaturated hydraulic conductivity functions do not account for water which may be relatively immobile under the conditions in which field measurements of conductivity are made. To investigate this, unsaturated hydraulic conductivity data were obtained for three monolith lysimeters, 80 cm in diameter by 135 cm deep, using the instantaneous profile technique. The lysimeters contained well‐structured, freely draining loam soil and moisture measurements were made using a neutron probe. Conductivity estimates were also obtained from laboratory measurements of soil moisture characteristics using the modified Millington and Quirk computational method. Ratios of the calculated to measured conductivities at a matching point near saturation were so large as to suggest that only a minor proportion of the soil pore space was contributing to flow through the whole profile.