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Acre-foot
Non-SI unit of volume From Wikipedia, the free encyclopedia
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The acre-foot is a non-SI unit of volume equal to about 1,233 m3 commonly used in the United States in reference to large-scale water resources, such as reservoirs, aqueducts, canals, sewer flow capacity, irrigation water,[1] and river flows.
An acre-foot equals approximately an eight-lane swimming pool, 82 ft (25 m) long, 52 ft (16 m) wide and 9.8 ft (3 m) deep.
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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 (1,233.5 m3).
There have been two definitions of the acre-foot (differing by about 0.0006%), using either the international foot (0.3048 m) or a U.S. survey foot (exactly 1200/3937 meters since 1893). On December 31, 2022, the National Institute of Standards and Technology, the National Geodetic Survey, and the United States Department of Commerce deprecated use of the US survey foot and recommended conversion to either the meter or the international foot.[2]
| 1 acre-foot | = 43,560 cubic feet |
| = 75,271,680 cu in | |
| = 325,851+3⁄7 US gal[a] | |
| international | ≈ 1,233.4818 m3 (using the 0.3048 m foot) |
| U.S. survey | ≈ 1,233.4892 m3 (using the 1200/3937 m foot) |
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Application
As a rule of thumb in US water management, one acre-foot is taken to be the planned annual water usage of a suburban family household.[b] In some areas of the desert Southwest, where water conservation is followed and often enforced, a typical family uses only about 0.25 acre-foot per year (310 m3/a) of water per year.[4] One acre-foot/year is approximately 119 cu ft/d (3.38 m3/d).
The acre-foot per year has been used historically in the US in many water-management agreements, for example the Colorado River Compact, which divides 15 million acre-feet per year (19 cubic kilometres per year) among seven western US states.
Water reservoir capacities in the US are commonly given in thousands of acre-feet, abbreviated TAF or KAF.
In most other countries except the US, the metric system is in common use and water volumes are normally expressed in liter, cubic meter or cubic kilometer. One acre-foot is approximately equivalent to 1.233 megaliters. Large bodies of water may be measured in cubic kilometers (1,000,000,000 m3, or 1000 gigaliter), with 1 million acre-feet approximately equalling 1.233 km3.
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See also
Explanatory notes
Citations
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