This glossary defines some of the special words found on this Web site. An extremely detailed and far more comprehensive glossary of hydrology and water terms is available at Science in Your Watershed, hosted by the USGS.
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A 100-year flood does not refer to a flood that occurs once every 100 years, but to a flood so severe it has a 1% chance of occurring in any given year.
acre-foot (acre-ft) The volume of water required to cover 1 acre of land to a depth of 1 foot. Equal to 325,851 gallons.
aquifer A geological formation that stores and/or transmits water to wells and springs. Use of the term is normally restricted to formations capable of yielding water in sufficient quantity and pressure to constitute a significant supply.
The use of water for motels, hotels, restaurants, office buildings, other commercial facilities and institutions. Water for commercial uses comes both from public-supplied sources, such as a county water department, and self-supplied sources, such as local wells.
cubic feet per second (cf) A measure of flow rate, equal to a volume of water 1-foot high and 1-foot wide, flowing a distance of 1 foot in 1 second. One "cfs" is equal to 7.48 gallons of water flowing each second.
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discharge The volume of water that passes a given location within a given period of time. Usually expressed in cubic feet per second.
donor A person who makes a charitable contribution to a land trust. The contribution can be a gift of land, property rights or funding.
domestic use The use of water for household purposes, such as drinking, food preparation, bathing, washing clothes and dishes, flushing toilets, and watering lawns and gardens. Also called residential water use. The water may be obtained from a public supply or may be self supplied. (see public supply and self-supplied water)
drawdown A lowering of groundwater caused by pumping.
drought A shortage of moisture severe enough to have a negative effect on vegetation, animals and humans over a large geographic area.
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groundwater 1. Water that flows or seeps downward and saturates soil or rock, supplying springs and wells. The upper surface of the saturated 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. (see surface water)
hydroelectric use The use of water to generate electricity at plants where turbines are driven by falling water. (see thermoelectric use)
industrial use The use of water for industrial purposes such as fabrication, processing, washing and cooling. The water may be obtained from a public supply or may be self supplied.
instream use The use of water for industrial purposes such as fabrication, processing, washing and cooling. The water may be obtained from a public supply or may be self supplied.
irrigation Controlled, artificial application of water to assist in the growth of crops and pastures, or to maintain vegetative growth in recreational lands such as parks and golf courses.
irrigation district A cooperative, self-governing public corporation set up as a subdivision of a state government, with definite geographic boundaries, organized and having taxing power to obtain and distribute water for irrigation of lands within the district; created under the authority of a state legislature with the consent of a designated fraction of the landowners or citizens.
kilowatt-hour (kwh) A unit of energy equivalent to 1,000 watt-hours; a power demand of 1,000 watts for one hour. Power company utility rates are typically expressed in cents per kilowatt-hour. Watt-hour (wh) is a measure of electrical energy equal to one watt of power supplied to, or taken from, an electrical circuit steadily for one hour.
livestock use Water for livestock watering, feedlots, dairy operations, fish farming and other on-farm needs.
million gallons per day (mg) A rate of flow of water equal to 133,680.56 cubic feet per day, or 1.5472 cubic feet per second, or 3.0689 acre-feet per day. A flow of one million gallons per day for one year equals 1,120 acre-feet (365 million gallons).
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prior appropriation The system for allocating water to private individuals used in most Western states. Prior appropriation is based on the concept of "First in Time, First in Right." The first person to take a quantity of water and put it to beneficial use has a higher priority of right than a subsequent user. Under drought conditions, higher-priority users are satisfied before junior users receive water. These rights can be lost if not used; they can also be sold or transferred apart from the land. (see riparian water rights)
public supply Water withdrawn by public and private water suppliers and delivered to users. Public suppliers provide water for a variety of uses, such as domestic, commercial, industrial, and public water use.
public use The use of water from a public-water supply for such purposes as firefighting, street washing, and municipal parks and swimming pools. (see public supply)
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return flow 1. That part of a diverted flow that is returned to its original source or another body of water. 2. (Irrigation) Drainage water from irrigated farmlands that re-enters the water system to be used further downstream.
riparian water rights The rights of an owner whose land is in contact with water. In general, people who own land adjacent to a stream have the right to make reasonable use of the stream. Riparian users of a stream share the streamflow among themselves, and the concept of priority of use does not apply. Riparian rights cannot be sold or transferred for use on non-riparian land. (see prior appropriation)
self-supplied water Water withdrawn from a surface or groundwater source by a user rather than being obtained from a public supply. An example would be homeowners getting their water from their own well.
surface water Water that is on the Earth's surface, such as in a stream, river, lake or reservoir. (see groundwater)
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thermoelectric use The use of water by power generation plants that burn coal or oil, often converting water to steam, which then drives turbines. (see hydroelectric use)
water cycle The circuit of water movement from the oceans to the atmosphere, to the Earth and back to the sea. Water moves through the cycle via processes such as precipitation, interception, runoff, infiltration, percolation, storage, evaporation and transportation.
water table The top of the water surface in the saturated part of an aquifer.
watershed The land area that drains water to a particular stream, river, or lake. It is a land feature that can be identified by tracing a line along the highest elevations between two areas on a map, often a ridge. Large watersheds, like the Columbia River Basin, contain hundreds of smaller watersheds.
withdrawal Water removed from the ground or diverted from a surface-water source for use.