Some moisture characteristics of a small column of sand

Abstract

Interest in soil-water relationships in the unsaturated zone has increased in the last decade because of the concern that contaminants may have moved into the soil and the water in that zone. Characterization of the soil-water relationships in the unsaturated zone is complicated by hysteresis and the variation of soil moisture with depth. When modelling the movement and storage of water in the unsaturated zone, it is necessary to evaluate various parameters including: matric potential, soil moisture content, and most importantly unsaturated hydraulic conductivity. Soil moisture retention curves developed from soil moisture and matric potential data aid in the evaluation of unsaturated hydraulic conductivity. The Brooks-Corey and the van Genuchten models are often employed to estimate the unsaturated hydraulic conductivity as a function of volumetric soil moisture content. This report documents a series of experiments performed as part of a senior report project. To demonstrate the variation of soil moisture content with depth, several short stacked columns of sand were permitted to drain under the influence of gravity. An outflow method was employed to measure the soil matric potential and soil moisture of a sample of loose sand. Data collected from the outflow experiments was used to numerically estimate the relative unsaturated hydraulic conductivity as a function of moisture content. The van Genuchten model and the Brooks-Corey model were both used to calculate the relative unsaturated hydraulic conductivity. These experiments have demonstrated the complexity of processes associated with soil-water relationships in the unsaturated zone. However, the basic principles of the soil-moisture relationships for a sample of sand were characterized.