Acre foot

An 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, and river flows. It defined by the volume of water necessary to cover one acre of surface area to a depth of one foot. It is equal to exactly 43,560 cubic feet, or to 325,851 U.S. gallons, or equivalently to approximately 1233.5 cubic meters. As a rule of thumb in U.S. water management, one acre foot is taken to be roughly the amount of water used annually by a family of four. 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 per year among seven western U.S. states. Reservoir capacities in the U.S. are typically given in acre feet.