Vadose zone

The vadose zone is the subsurface region between the land surface and the water table, where pore spaces contain both air and water.

Infiltration: The entry of water at the land surface into soil or other porous material. It supplies water that moves downward through the vadose zone.
Water table: The surface in an unconfined aquifer where water pressure equals atmospheric pressure. It forms the lower boundary of the vadose zone.
Contaminant transport: The movement of harmful chemicals through environmental media such as soil, water, and air. Pollutants can travel downward through the zone toward aquifers.
Phreatic zone: The saturated subsurface region in which pore spaces are filled with water. It lies below the water table, unlike the partly air-filled vadose zone.
Unsaturated flow: Fluid flow through porous material whose pores are not completely filled with liquid. It describes how water moves while air-filled pore space remains.
Porosity: The fraction of a material's volume occupied by pores. Pore space provides storage for both air and water in the zone.
Soil salinity: The accumulation of soluble salts in soil to levels that affect plants or soil processes. Evaporation and irrigation in the vadose zone can concentrate salts near the surface.
Confined aquifer: A permeable water-bearing formation bounded by low-permeability layers and containing water under pressure. Its groundwater is confined beneath an aquitard rather than directly beneath the vadose zone.
Soil water potential: A measure of the energy state of water in soil, governing its movement and availability. Potential gradients drive water through the zone toward roots and the water table.
Soil moisture: Water held in soil, including water in pores and on particle surfaces. Its amount and distribution determine how wet the vadose zone is.

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