Acre-foot

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The acre-foot is a unit of volume commonly used in the United States in reference to large-scale water resources, such as reservoirs, aqueducts, canals, sewer flow capacity, irrigation water, and river flows.

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Definitions

As the name suggests, an acre-foot is defined as the volume of one acre of surface area to a depth of one foot.

Since an acre is defined as a chain by a furlong (i.e. 66 ft × 660 ft or 20.12 m × 201.17 m), an acre-foot is 43,560 cubic feet (1,233 m³).

There are two definitions of an acre-foot (differing by about 0.0006%), depending on whether the "foot" used is an "international foot" or a "U.S. survey foot".

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Application

As a rule of thumb in U.S. water management, one acre-foot is taken to be the planned water usage of a suburban family household, annually. In some areas of the desert Southwest, where water conservation is followed and often enforced, a typical family uses only about 0.25 acre-feet of water per year. One acre-foot/year is approximately 893 gallons (3.38 m³) per day.

The acre-foot (or more specifically the time rate unit of acre-foot per year) has been used historically in the U.S. in many water-management agreements, for example the Colorado River Compact, which divides 15 million acre-feet (MAF) per year (586 m³/s) among seven western U.S. states.

Water reservoir capacities in the U.S. are commonly given in thousands of acre-feet, abbreviated TAF.

Elsewhere in the world, where the metric system is in common use, water volumes can be expressed in either cubic metres (as in flow rates of cubic metres/second, or "cumecs") or, for water usage, storage or irrigation volumes, in kilolitres (kL = 1 cubic metre), megalitres (ML = 1,000 cubic metres), or gigalitres (GL = 1,000,000 cubic metres). One acre-foot is approximately equivalent to 1.233 megalitres and 1,233 kilolitres. Large bodies of water may be measured in cubic kilometres (1,000,000,000 m³, or 1000GL), with 1000 TAF or 1 million acre-feet approximately equalling 1.233 km³.

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See also

• Cubic metres per second
• Cubic feet per second
• List of unusual units of measurement
• United States customary units
• Units of measurement

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Notes

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References

Source of the article : Wikipedia