A constant-head well permeameter method for measuring field-saturated hydraulic conductivity above an impermeable layer

Abstract

Hydrologic understanding of mountainous and northern regions of Canada is poor owing to the lack of critical field data such as hydraulic conductivity. A portable field instrument, the Guelph permeameter (GP), is a promising tool for measuring field-saturated hydraulic conductivity in remote watersheds inaccessible by motorized vehicles. In order to extend the applicability of the GP method to relatively thin soils underlain by impermeable bedrock or permafrost, a new set of shape factors was determined by numerical simulation. The new shape factors gave accurate values of field-saturated hydraulic conductivity when tested in the laboratory. The impermeable layer causes flow around the auger hole to be primarily horizontal. Therefore, the GP method measures a predominantly horizontal field-saturated hydraulic conductivity in these thin soils. The measured conductivity represents a weighted average of the soil surrounding the submerged surface of the auger hole. In layered soil, the weight is greater for the layers close to the bottom of the hole than for those close to the top. Key words: Guelph permeameter, hydraulic conductivity, forest hydrology, permafrost, peat