Solute transport during unsteady, unsaturated soil water flow - the pulse input

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Abstract
A general approximate analytical solution was derived for the movement and dispersion of a solute pulse during unsteady flow of water in unsaturated soils. Two types of pulse were considered: that arising from a non-uniform distribution of solute initially in the soil, and that arising from a change in concentration of solute in the water supply. The movement of pulses of tritiated water and chloride ion was investigated experimentally for the specific case of constant flux horizontal infiltration of water into a strongly aggregated, structurally stable clay soil. Good agreement between the measured distributions of tritium and those predicted using the approximate solution confirmed the validity of the approximate solution. Agreement was much poorer for chloride. The approximate analytical solution was also used to examine factors affecting the shape of solute pulses. It was found that pulses may be asymmetric at short times, but that they rapidly become symmetric as time increases.