Glossary/water dictionary

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gage height

The height of the water surface above the gage datum (zero point). Gage height is often used interchangeably with the more general term, 'stage', although gage height is more appropriate when used with a gage reading.^

gaging station

A site on a stream, lake reservoir or other body of water where observations and hydrologic data are obtained. The U.S. Geological Survey measures stream discharge at gaging stations.^

geographic information system (GIS)

All information concerning a point or a group of points georeferenced on Earth’s surface, such as maps or satellite images, digitally stored, processed and manipulated by a computer program (e.g. IDRIS, MAPINFO, ARCINFO).^


A geothermal feature of the Earth where there is an opening in the surface that contains superheated water that periodically erupts in a shower of water and steam.^


A disease that results from an infection by the protozoan parasite Giardia intestinalis, caused by drinking water that is either not filtered or not chlorinated. The disorder is more prevalent in children than in adults and is characterised by abdominal discomfort, nausea and alternating constipation and diarrhea.^

gravity irrigation

A method of operating a system or part of a system using gravity alone, water being available at a sufficient level (or pressure) to ensure its conveyance or delivery to the fields or its distribution in the fields.^

greenhouse effect

The warming of the Earth’s atmosphere caused by the buildup of carbon dioxide, which allows light from the sun’s rays to heat the earth but prevents the loss of heat.^


Wastewater from clothes washing machines, showers, bathtubs, hand washing, lavatories and sinks.^


(1) Water that flows or seeps downward and saturates soil or rock, supplying springs and wells. The upper surface of the saturate zone is called the 'water table'. (2) Water stored underground in rock crevices and in the pores of geologic materials that make up the Earth's crust.^

groundwater balance

A systematic review of inflow, outflow and storage as applied to the computation of groundwater changes. It is based on the concept that all inputs of water in a defined space and time are equal to the sum of all outputs of water, and the changes of water storage, in the same space and time.^

groundwater inventory

A detailed estimate of the amount of water added to the groundwater reservoir of a given area (recharge) balanced against estimates of amounts of withdrawals from the groundwater reservoir of the area during a specific period.^

groundwater recharge (1)

Replenishment of groundwater supply in the zone of saturation, or the addition of water to groundwater storage by natural processes or artificial methods for subsequent withdrawal for beneficial use or to check saltwater intrusion in coastal areas.^

groundwater recharge (2)

Inflow of water to a groundwater reservoir from the surface. Infiltration of precipitation and its movement to the water table is one form of natural recharge. Also, the volume of water added by this process.^

groundwater, confined

Groundwater under pressure significantly greater than atmospheric, with its upper limit the bottom of a bed with hydraulic conductivity distinctly lower than that of the material in which the confined water occurs.^

groundwater, unconfined

Water in an aquifer that has a water table that is exposed to the atmosphere.^