Vadose Water

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Vadose water is subsurface water between the land surface and the saturated zone below the water table. The vadose (or unsaturated) zone includes soil water, which is immediately available to the biosphere. It acts as a controlling agent in the transmission of water and other substances between various components of the earth system: aquifers, land surface, bodies of water, atmosphere, and so on. As an accessible body of material near the earth's surface, the vadose zone is a focus of much human activity, including agriculture, mining, construction, and waste disposal. Thus, it is affected by anthropogenic modifications of its chemical and physical components. Modern hydrology must consider interactions not only among the natural constituents, but also with a wide variety of contaminants, including pesticides, fertilizers, irrigation wastewater, sewage, toxic chemicals, radioactive substances, bacteria, mine wastes, and organic liquids.

The dynamics of vadose water are complicated by the presence of multiple phases. At least three drastically different substances – water, air, and solid mineral – are critical to vadose zone processes. Unsaturated flow phenomena are extremely sensitive to the proportions of those phases, especially the fluid phases, as natural variations in the relative amounts of water and air can cause a property like hydraulic conductivity to vary over many orders of magnitude.

This article describes the main phenomena related to the state and dynamics of vadose water, including means of measuring or estimating the properties that affect vadose water. Further, it describes roles of vadose water in the hydrologic cycle.

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