A COMPARISON OF THREE FIELD METHODS FOR MEASURING SATURATED HYDRAULIC CONDUCTIVITY

The saturated hydraulic conductivity, Ks, was measured on a loamy sand, a fine sandy loam, a silt loam and a clay at four 100-m2-area sites in southern Ontario. Twenty measurements of Ks were obtained by each of three different measurement techniques at each of the four sites. The techniques included: (1) the air-entry permeameter method; (2) the constant head well permeameter method using the Guelph Permeameter; and (3) the falling-head permeameter method applied to small soil cores. The Ks data were found to be better described by the log-normal frequency distribution than by the normal frequency distribution. Statistical comparison of the mean Ks values [Formula: see text] indicated significant differences between some or all of the methods within each site. This site-method interaction was interpreted in terms of the influence of macropores and air entrapment on each of the measurement techniques. The measured Ks values ranged over an order of magnitude on the sand, one to two orders of magnitude on the loams, and three orders of magnitude on the clay. The [Formula: see text] estimates averaged over the three methods were: 3 × 10−5 m∙s−1 for the sand; 2 × 10−6 m∙s−1 for the loams and 1 × 10−7 m∙s−1 for the clay. Although all techniques were able to discriminate between the three soil types, the best choice of method for any particular situation appears dependent on the required type and accuracy of the Ks measurement, soil type, and the various practical constraints on the investigation. Key words: Air-entry permeameter, Guelph Permeameter, falling-head permeameter, spatial variability, macropores, entrapped air