Numerical study of effects of soil pipes on the constant-head well permeameter test

The Guelph Permeameter (GP) method is a widely used in-situ test for estimating field-saturated hydraulic conductivity (Kfs). However, its applicability to forested hillslopes, where large macropores such as soil pipes are often present, remains insufficiently examined. This study investigated the effects of pipes on GP measurements using three-dimensional infiltration simulations. Two pipe representations were assessed, namely, a seepage face boundary and a highly permeable porous medium. Simulation results indicated that pipes contribute to a significant increase in the infiltration rates only when they are directly connected to a well. Sensitivity to pipes was found to be influenced by the size of saturated bulbs (SBs), which differs according to soil texture. When pipes are located at a distance of more than 2.0 cm from a well, the increase in infiltration remains within 6%, regardless of soil texture. These findings indicate that GP measurements primarily reflect the properties of the soil matrix, rather than structures such as pipes and macropores.