Saturated hydraulid conductivity (Ks) is a central soil physical property in determining water movement and contaminant transport through soils; hence modeling this system requires an accurate determination of K. Decimeter-scale KS measurements employing cores or infiltrometers are used frequently, but field-scale KS values are required to encompass the full range of operational flow processes. The objective of this study was to determine the utility of small-scale measurements in describing field-scale permeability. Four tile-drained fields in the Willamette Valley, Oregon; were studied for drainage rate and contaminant transport from field-applied chemicals to ground water and surface water. Decimeter-scale Ks was measured using 137 cm3 undisturbed soil cores collected at depths of 30, 60, 90 and 120 cm. Field-scale KS is estimated using a classic solution to the time-dependent non-linear Boussinesq equation developed by Polubarinova-Kochina (P-K) for the shape and evolution of a water table draw down in response to parallel horizontal drains overlaying an impermeable layer. Piezometers were installed along a perpendicular transect crossing two drains to observe water table fluctuations. These data were fitted to the P-K model to determine K. Key observations included a good fit of the observations to the model, and a dramatic permeability increase, exceeding 10 fold, seen at the field-scale compared to the decimeter-scale. This indicates that transport through soils will occur much faster than estimated using decimeter-scale measurements of Ks. The P-K approach is a practical, low cost method to obtain field-scale permeability.
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