ASSESSMENT OF THE SIMPLIFIED FALLING HEAD TECHNIQUE TO MEASURE THE FIELD SATURATED SOIL HYDRAULIC CONDUCTIVITY

The Simplified Falling Head (SFH) technique to measure field saturated soil hydraulic conductivity, Kfs, has received little testing or comparison with other techniques. Different experiments were carried out to i) determine the effect of ring size on the measured conductivity; ii) compare the SFH and Pressure Infiltrometer (PI) techniques in a clay loam soil; and iii) assess the indirect approach to estimate the * parameter used in the SFH methodology. Sampling a relatively large number of sites allowed to detect a statistically significant relationship between the Kfs values obtained with rings differing in diameter (0.15 and 0.30 m, respectively). This relationship suggested that a measurement carried out with a small ring contains enough information to make an approximate prediction of the Kfs value that would be obtained at the same site with a larger ring. The SFH and PI techniques yielded similar means but substantially different coefficients of variation (much higher for the SFH technique). The two methods should be considered complementary, being usable to determine Kfs at the beginning (SFH) and at a later stage (PI) of a ponding infiltration process. Using * values directly measured by the tension infiltrometer or indirectly estimated on the basis of a general description of soil characteristics did not modify significantly the Kfs predictions obtained with the SFH technique. In conclusion, this investigation gave support to the use of the SFH technique for a rapid and reasonably simple determination of, at least, the order of magnitude of Kfs.