Acre-foot
| acre-foot | |
|---|---|
 An acre-foot volume (not drawn to scale) | |
| General information | |
| Unit system | US Customary units |
| Unit of | Volume |
| Symbol | ac⋅ft |
| Conversions | |
| 1 ac⋅ft in ... | ... is equal to ... |
| SI units | ≈ 1,233.5 m3 |
| US customary units | 43,560 cu ft |
| US customary units | ≈ 325,850 US gal |
| Imperial units | ≈ 271,330 imp gal |
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.
Definitions
[edit]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 has 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. 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 |
| 1 international acre-foot | = 43,560 international cubic feet |
| = 1,233.48183754752 m3 | |
| = 325,851+3⁄7 US gal | |
| 1 U.S. survey acre-foot | = 43,560 U.S. survey cubic feet |
| ≈ 1233.4892384681 m3 | |
| ≈ 325,853.383688 U.S. gal[a] |
Application
[edit]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 15×106 acre⋅ft/a (590 m3/s) 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.
See also
[edit]
- Cubic meter per second
- Cubic foot per second
- List of unusual units of measurement
- United States customary units
- Unit of measurement
Explanatory notes
[edit]- ^ This conversion assumes the international foot is used to define the U.S. gallon and the U.S. survey foot to define the acre foot. If the same foot is used for both, the result is the 325,851+3⁄7 U.S. gal figure as obtained previously.
- ^ The state of Montana assumes 1.0 acre-foot per year (1,200 m3/a) for a family of five.[3]
Citations
[edit]- ^ "NM OSE Glossary". Archived from the original on 14 November 2005. Retrieved 15 March 2014.
- ^ "U.S. Survey Foot". National Institute of Standards and Technology. 4 January 2023. Retrieved 4 April 2024.
- ^ Water Rights Bureau; state of Montana (13 April 2004). "Form No. 627 R8/03 Notice of Water Right" (PDF). Archived from the original (PDF) on 25 January 2008. Retrieved 30 January 2008.
- ^ Santa Fe, New Mexico rate averages 0.25 acre-foot per year per household. See Planning Division, Planning & Land Use Department, City of Santa Fe, New Mexico (February 2001). "Water Use in Santa Fe: A survey of residential and commercial water use in the Santa Fe urban area". Archived from the original (PDF) on 22 July 2012. Retrieved 30 January 2008.