Våtfront

Våtfront, or the wetting front, is a term used in soil physics and hydrology to describe the moving boundary between wetter, more saturated soil and drier soil during infiltration from rainfall or irrigation. It marks the depth at which water has just begun to invade the soil profile, with moisture content and matric potential changing markedly across the boundary. In practice, the transition is typically diffuse rather than a sharp interface, forming a gradient zone that broadens with time.

The progression of the våtfront depends on soil properties such as porosity, hydraulic conductivity, texture, and structure, as well as driving conditions including rainfall intensity, irrigation rate, and gravitational and capillary forces. Its movement is analyzed using models of unsaturated flow, often governed by the Richards equation. Practically, researchers and practitioners use infiltration curves and depth to estimate how far the front has penetrated at a given time, as well as how deep water has saturated the soil.

Measurement and observation methods include soil moisture sensors, tensiometers to monitor matric potential, and time-domain reflectometry to infer moisture distribution. Tracking the våtfront is important for irrigation management, drainage design, and soil salinity control, as it informs decisions to maximize water use efficiency, prevent waterlogging, and reduce runoff.

Variations in soil texture and layering affect front behavior: coarse soils tend to allow faster, sharper fronts, while fine-textured or nested soil layers produce slower, more diffuse fronts. Preferential flow along permeable layers can also alter the shape and advance of the våtfront.

See also: infiltration, unsaturated flow, Richards equation, soil moisture measurement.