Acre-foot

The acre-foot is a non-SI unit of volume equal to about Template:Cvt commonly used in the western United States in reference to large-scale water resources, such as reservoirs, aqueducts, canals, sewer flow capacity, irrigation water,<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> and river flows.

An acre-foot equals the volume of water needed to fill approximately an eight-lane swimming pool, Template:Cvt long, Template:Cvt wide and Template:Cvt deep.

Definitions

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

Since an acre is defined as a chain by a furlong (i.e. Template:Convert), an acre-foot is Template:Convert.

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 Template:SfracTemplate:Nbspmeters 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.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

1 acre-foot	= 43,560 cubic feet
	= 75,271,680 cu in
	= Template:ConvertTemplate:Efn
international	≈ Template:Round m3 (using the 0.3048 m foot)
U.S. survey	≈ Template:Round m3 (using the Template:Sfrac m foot)

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.Template:Efn In some areas of the desert Southwest, where water conservation is followed and often enforced, a typical family uses only about Template:Convert of water per year.<ref>Santa Fe, New Mexico rate averages 0.25 acre-foot per year per household. See {{#invoke:citation/CS1|citation |CitationClass=web }}</ref> One acre-foot per year is approximately Template:Convert.

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 Template:Convert 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 Template:Convert. Large bodies of water may be measured in cubic kilometers (Template:Val equals Template:Convert); Template:Convert.

A volumetric change of 10 acre-feet per hour is equivalent to exactly 121 cubic feet per second. Dividing by 120, this reduces to 1 acre-inch per hour is approximately Template:Val. This can be visualized as such: suppose a 1-acre field is receiving a sustained rainfall of 1 inch per hour. In order prevent the field from flooding or overflowing, the drainage system must be able to handle a discharge of at least 1 cubic foot per second.

See also

• Cubic meter per second
• Cubic foot per second
• List of unusual units of measurement
• United States customary units
• Unit of measurement