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Glossary of Terms

Acre-foot
The volume of water required to cover 1 acre of land (43,560 square feet) to a depth of 1 foot. One acre-foot is equal to 325,851 gallons, which is enough water for a family of four for an entire year.

Aquifer
A geologic formation (soil or rock), group of formations, or part of a formation capable of storing, receiving and transmitting water. An aquifer is capable of yielding enough water to support a well or spring.

Conjunctive Use
The combined use of surface and ground waters to serve a particular purpose. For example, during dry years in a conjunctive use program, drinking water needs are largely met with groundwater. During wet years, surface water is the primary sources of drinking water, allowing the groundwater table to replenish naturally.

Consumptive Use
Water that is evaporated, transpired by plants, incorporated into products or crops, consumed by humans or livestock, or otherwise removed from the immediate water environment. Also referred to as water consumption.

Diversion
A channel constructed across the land slope to intercept surface runoff and conduct it to an outlet.

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Drainage Basin
The land area drained by a river.

Evapotranspiration
A collective term that describes water movement back to the atmosphere as a result of plant transpiration and evaporation from soil surfaces and surface water bodies.

Groundwater
Water stored underground in rock crevices and in the pores of geologic materials that make up the Earth’s crust.

Groundwater Recharge
The replenishment of groundwater by seepage of precipitation and runoff. 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.

Injection Well
Refers to a well constructed for the purpose of injecting treated wastewater directly into the ground. Wastewater is generally forced (pumped) into the well for dispersal or storage into a designated aquifer. Injection wells are generally drilled into aquifers that don’t deliver drinking water, unused aquifers, or below freshwater levels.

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Infiltration
The downward entry of water into the Earth’s surface.

Infiltration Capacity
The maximum rate at which infiltration can occur under specific soil moisture conditions.

Million Gallons Per Day (Mgd)
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).

Overdraft
The reduction of groundwater storage that occurs when withdrawals from an aquifer exceed recharge. Sometimes referred to as mining of groundwater.

Percolation
The downward movement of water through the openings in soil or rock.

Recharge
The replenishment of groundwater by seepage of precipitation and runoff. Also stated as the process of addition of water to the saturated zone.

Return Flow
The amount of water that reaches a surface or groundwater source after it has been released from the point of use and thus becomes available for further reuse. Also called return water.

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Safe Yield
The amount of groundwater that can be withdrawn continually from an aquifer in an economical and legal manner without having any adverse effect on the groundwater resource or the surrounding environment.

Saturated Zone
The zone in a soil profile or geologic formation in which all pore spaces are filled with water.

Surface Water
Water that is on the Earth’s surface, such as streams, rivers, lakes or reservoirs.

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.

Water Table
The upper boundary or top surface of the zone of saturation in a soil profile or geologic formation.

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