Comparison of methodological uncertainties within permeability measurements

Permeability measurements are critical to the calculation of water‐flow within hillslopes. Despite this, errors in permeability measurements are often ignored, and can be very large particularly in disturbance‐sensitive gley soils. This work compares the uncertainties associated with six field methods of permeametry applied to a gleyed soil in upland Britain. Slug tests, constant‐head borehole permeametry, and falling‐head borehole permeametry were undertaken on established piezometers. Additionally, ring permeametry and two types of trench tests were evaluated. Method‐related uncertainty due to proximity of impeding layers of high sorptivity soils produces under‐ and over‐estimates of permeability by a factor of up to 0·2 and 5, respectively. This uncertainty band is smaller than the observed effects of anisotropy and temporal variability. Had smearing and soil‐ring leakage errors not been minimized, the methodological uncertainties would have been so large that they would have distorted the true spatial field of permeability and its estimated impact on the balance of vertical and lateral flow. Copyright © 2007 John Wiley & Sons, Ltd.