Modelling solute leaching during fingered flow by integrating and expanding various theoretical and empirical concepts

Wetting front instability (fingered flow) accelerates solute transport thro ugh the unsaturated zone to the groundwater table. Whether fingers widen or dissipate close to the groundwater is unclear. Water flow in a two-dimensi onal artificial capillary fringe below a dry layer exhibiting fingered flow was investigated. The flow diverged strongly in the wet soil, suggesting t hat fingers dissipate. Expressions for the finger radius in dry and wet soi l were combined and adapted to a soil hydraulic property parameterization p opular in numerical modelling. The modified equation provided finger radii for soils in humid and arid climates. The fingers in the arid soil were exc essively wide. The finger radii were used to model solute transport, assumi ng fingers dissipated in the subsoil. Modelling was cumbersome for the arid climate. One shower may often be insufficient to trigger fingering in arid regions with short, heavy showers. In soils with shallow groundwater, the diverging subsoil flow determines solute leaching.