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.
|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|
|≈ 271,328.072596 imp gal|
|≈ 325,851 3⁄7 US gal|
|1 U.S. survey acre-foot||= 43,560 U.S. survey cubic feet|
|≈ 1233.4892384681 m3|
|≈ 271,329.700571 imp gal|
|≈ 325,853.383688 U.S. gal[nb 1]|
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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