Flexible Water Content Probe for Unsaturated Soil Column Experiments

A commercially available soil moisture probe was modified by replacing rigid electrode waveguides with flexible electrode traces that can be attached to the interior of soil column walls. This new design minimizes soil packing difficulties and potential bias in water and solute flow pathways commonly associated with rigid probe installations in column experiments. Tests demonstrated that the modified flexible electrode design maintains a voltage response that is proportional to the electrode trace length and is reduced by approximately one-half when only one side of the electrode trace is in contact with the soil media. Laboratory experiments confirmed that the longer electrode traces attached to the interior of a column wall have a comparable sensitivity of that of a commercially available rigid probe inserted horizontally across the diameter of a soil column. The replacement of the rigid electrode with a flexible electrode offers an improved method of measuring the water content in solute transport experiments while minimizing sensor intrusion into laboratory soil columns.