The acre-foot is a non-
SI unit of
volume
Volume is a measure of occupied three-dimensional space. It is often quantified numerically using SI derived units (such as the cubic metre and litre) or by various imperial or US customary units (such as the gallon, quart, cubic inch). Th ...
equal to about commonly used in the
United States
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., federal district, five ma ...
in reference to large-scale water resources, such as
reservoir
A reservoir (; from French ''réservoir'' ) is an enlarged lake behind a dam. Such a dam may be either artificial, built to store fresh water or it may be a natural formation.
Reservoirs can be created in a number of ways, including control ...
s,
aqueducts,
canal
Canals or artificial waterways are waterways or engineered channels built for drainage management (e.g. flood control and irrigation) or for conveyancing water transport vehicles (e.g. water taxi). They carry free, calm surface fl ...
s,
sewer flow capacity, irrigation water, and river flows.
An acre-foot equals approximately an eight-lane
swimming pool, long, wide and deep.
Definitions
As the name suggests, an acre-foot is defined as the volume of one
acre
The acre is a unit of land area used in the imperial and US customary systems. It is traditionally defined as the area of one chain by one furlong (66 by 660 feet), which is exactly equal to 10 square chains, of a square mile, 4,840 square ...
of surface area to a depth of one
foot.
Since an acre is defined as a
chain
A chain is a wikt:series#Noun, serial assembly of connected pieces, called links, typically made of metal, with an overall character similar to that of a rope in that it is flexible and curved in compression (physics), compression but line (g ...
by a
furlong
A furlong is a measure of distance in imperial units and United States customary units equal to one eighth of a mile, equivalent to 660 feet, 220 yards, 40 rods, 10 chains or approximately 201 metres. It is now mostly confined to use i ...
(i.e. ), an acre-foot is .
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".
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. 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 of water per year.
Santa Fe, New Mexico
Santa Fe ( ; , Spanish for 'Holy Faith'; tew, Oghá P'o'oge, Tewa for 'white shell water place'; tiw, Hulp'ó'ona, label= Northern Tiwa; nv, Yootó, Navajo for 'bead + water place') is the capital of the U.S. state of New Mexico. The name “S ...
rate averages 0.25 acre-foot per year per household. See One acre-foot/year is approximately .
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 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
The metric system is a system of measurement that succeeded the decimalised system based on the metre that had been introduced in France in the 1790s. The historical development of these systems culminated in the definition of the Intern ...
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 m, or 1000 gigaliter), with 1 million acre-feet approximately equalling 1.233 km.
See also
*
Cubic meter per second
*
Cubic foot per second
*
List of unusual units of measurement
*
United States customary units
*
Unit of measurement
A unit of measurement is a definite magnitude of a quantity, defined and adopted by convention or by law, that is used as a standard for measurement of the same kind of quantity. Any other quantity of that kind can be expressed as a mult ...
Explanatory notes
Citations
Customary units of measurement in the United States
Units of volume
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