Acre-foot
| Physical unit | |
|---|---|
| Unit name | Acre-foot |
| Unit symbol | |
| Physical quantity (s) | volume |
| dimension | |
| system | Anglo-American system of measurement |
| In SI units | |
| Derived from | Acre , foot |
An acre-foot (plural: acre-feet) is a unit of volume used in the United States . It is preferably used for large-scale water tanks, aqueducts, canals and reservoirs and is also used to measure groundwater abstraction and water consumption in agriculture.
The acre-foot is defined as the volume required to flood an area of 1 acre to a depth of 1 foot with water. One acre is exactly 43,560 ft² ( square feet ). Thus, one acre-foot has a volume of exactly 43,560 ft³ ( cubic feet ).
The peculiarity is that one usually expects a cube with three equal edge lengths for a volume measure. For the acre-foot, that would be a cube with an edge length of around 35 feet (the number 35.1854 is more precise). In the metric system this is a cube with an edge length of about 10.72 m.
According to the US definition, however, it is a cuboid with three different edge lengths:
1 furlong × 1 chain × 1 foot = 660 ft × 66 ft × 1 ft (or 1 acre × 1 foot)
Conversions
1 acre-foot = 43560 cubic foot = 75,271,680 cubic inch = 1233.48183754752 cubic meters ≈ 1,233,482 liters
3 acre feet = 4840 cubic yards
7 acre-feet = 2,280,960 US gallons
168,133 acre-feet = 45,619,200,000 Imp.gallons = 54,786,378,240 US gallons
1 acre-foot ≈ 271,328 imp.gallon ≈ 325,851 US gallon
Application example
Water is scarce in hot New Mexico . The water rights are regulated by the authorities. A well has z. B. an approved water quota of 0.7 acre-foot per year. That is 863 m³ per year or 2.3 m³ daily. The average water consumption of a German household is (for comparison) 100 m³ / year.
As a rule of thumb, the US water authorities estimate an annual water consumption of one acre-foot for a family of four. Many historical water management contracts use the acre-foot / year unit. For example, the water of the Colorado River is divided between seven states under a contract - it's 15 million acre-feet / year. The river sometimes has less water.