An analysis of hydrodynamic dispersion accompanying constant flux absorption of KCl solution by an initially relatively dry soil, is developed for the case when the hydrodynamic dispersion coefficient is pore water velocity‐independent. It is shown that in this process both the water content and the soil water salt concentration are uniquely defined by θ(X,T) and C(X,T), where X = vox and T = vo2t are space and time‐like coordinates, and vo is the constant surface flux of water.Quasi‐analytical methods based on the flux‐concentration relation predict θ(X,T) while an error‐function solution, based on a material coordinate Q labeling parcels of water, predicts the salt profile.The analysis is demonstrated using a chemically inert sandy soil. The results show that during transient, unsaturated flow a simple piston‐flow model described the process over a range of water contents. The method may be extended to explore dispersion in structured and chemically reactive soils.

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