Vadose zone

Cross-section of a hillslope depicting the vadose zone, capillary fringe, water table, and phreatic or saturated zone. (Source: United States Geological Survey.)

The vadose zone, also termed the unsaturated zone, is the part of Earth between the land surface and the top of the phreatic zone i.e. the position at which the groundwater (the water in the soil's pores) is at atmospheric pressure ("vadose" is from the Latin for "shallow"). Hence the vadose zone extends from the top of the ground surface to the water table. Water in the vadose zone has a pressure head less than atmospheric pressure, and is retained by a combination of adhesion (funiculary groundwater), and capillary action (capillary groundwater). If the vadose zone envelops soil, the water contained therein is termed soil moisture. In fine grained soils, capillary action can cause the pores of the soil to be fully saturated above the water table at a pressure less than atmospheric. The vadose zone does not include the area that is still saturated above the water table, often referred to as the capillary fringe (Freeze & Cherry, 1979).

Movement of water within the vadose zone is studied within soil physics and hydrology, particularly hydrogeology, and is of importance to agriculture, contaminant transport, and flood control. The Richards equation is often used to mathematically describe the flow of water, which is based partially on Darcy's law. Groundwater recharge, which is an important process that refills aquifers, generally occurs through the vadose zone from precipitation.

In speleology, cave passages formed in the vadose zone tend to be canyon-like in shape, as the water dissolves bedrock on the floor of the passage.^[1] Passages created in completely water-filled conditions are called phreatic passages and tend to be circular in cross-section.^[2]

See also

Look up vadose in Wiktionary, the free dictionary.

• Aquifer
• Epiphreatic zone
• Groundwater
• Water retention curve

References

• "Unsaturated Zone Definitions Page". USGS. Retrieved 2006-07-01. 
• "Unsaturated Zone Flow: Definitions and Details". USGS. Archived from the original on 2006-05-24. Retrieved 2006-07-01. 

Further reading

• "Vadose Zone Journal". Retrieved 2006-07-01. 

• Wilson, L.G.; Everett, Lorne G.; Cullen, Stephen J., eds. (1994). Handbook of Vadose Zone Characterization & Monitoring. CRC Press. ISBN 0873716108.