Testing laboratory methods to determine the anisotropy of saturated hydraulic conductivity in a sandy-loam soil

Anisotropy, a (the log of the ratio of horizontal to vertical conductivity, log10(Kh/Kv)), of saturated soilhydraulic conductivity, Ks, affects transport processes in soil but is not routinely measured, probably becausepractical and validated methods are lacking. The objective of this investigation was to determine the effectsof different constant-head laboratory and sampling procedures on anisotropy of saturated hydraulicconductivity measurements. The sequence of Ks measurements was varied (vertical conductivity, Kv, first,then horizontal, Kh, second and vice versa) for an experimental set-up considering five variables: 1) waterponding type (Mariotte or siphon); 2) saturation state prior to experiment start (unsaturated or saturated);3) experiment duration (long or short); 4) sample geometry or extraction (cube or core); and 5) samplevolume. The Mariotte, unsaturated/saturated, long experiment for a single soil cube resulted in unreliablemean anisotropy results, where a differed in sign. Generally, the sequence of measurements had a negligibleimpact on a for a siphon, saturated, short experiment for a soil cube. Furthermore, different a were obtainedby varying the undisturbed soil sample collection procedure (cube vs. core). The conclusion of thisinvestigation was that using a siphon and a short-duration run on an initially saturated cube of soil encasedin foam is generally expected to yield reliable bi-directional Ks results. However, a check of the independenceof the estimated anisotropy on the order of measurements for the sampled soil is recommended. Analternative procedure to determine a mean anisotropy for an area of interest would be to measure Kv and Khon different soil cubes. Finally, the ratio between the mean Kh and Kv results varied from a not statisticallysignificant factor of 1.02 to a statistically significant factor of 1.95 during the one-year investigation period(five sampling dates). Therefore, anisotropy of this sandy–loam soil varied with time but it was always lowor negligible.