A constant head well permeameter formula comparison: Its significance in the estimation of field-saturated hydraulic conductivity in heterogeneous shallow soils

Abstract

We evaluate the application and investigate various formulae (and the associated parameter sensitivities) using the constant head well permeameter method to estimate field-saturated hydraulic conductivity (Kfs) in a previously glaciated temperate landscape in the Scottish Borders where shallow soils constrain the depth of augering. In finer-textured soils, the Glover equation provided Kfs estimates nearly twice those of the Richards equation. For this environment, we preferred the Glover equation with a correction factor for the effect of gravity, which does not include soil capillarity effects because: (1) the low depth to diameter ratio of the auger holes (AH) required in the shallow stratified soils of temperate glaciated environment needs a correction for gravity; (2) the persistently moist environment and the use of long pre-wetting times before measurements seem to reduce the effect of soil capillarity; (3) the Richards equation is dependent on accurate α∗ values, but the measured AH intersected soil horizon boundaries that had different soil structure and texture, causing difficulty in selecting the most appropriate α∗ value; (4) when comparing the different solutions to estimate Kfs using the constant-head well permeameter method against the AH method and ponded permeameter measurements, the Glover solution with a correction for gravity gave the best comparable result in fine-textured soil.