One‐Dimensional Model to Evaluate the Performance of Wick Samplers in Soils

Abstract

AbstractWick samplers have become a valuable device for collecting soil pore water samples from the unsaturated zone. However, one of the problems with wick samplers has been that water and solutes bypass the samplers. Little work has been done on the nature of soil‐wick interrelations. Based on an analytical solution for a layered soil profile, a steady‐state solution was developed to predict the pressure head in a wick‐soil continuum. The solution was also used to match wick properties to a given soil type in order to minimize the bypass flow. The results of this analysis show that for a good match between wick and soil types, (i) their capillary length (α−1) needs to be similar, and (ii) the ratio of their saturated hydraulic conductivities should be similar to the inverse ratio of their cross section for flow. Examples for wick type selection based on these two requirements are given for two soil types and two wick types. For sandy soils, the optimal wick length is 30 to 40 cm, while for silt loams, the optimal length is >100 cm. Sampling with wick samplers in coarse‐textured soils was found to be less disturbing of the soil pressure head and moisture profile than sampling in fine‐textured soils. Hydraulic properties of fine‐textured soils require a large sampling area in order to create an undisturbed zone above the wick sampler.