Acre-foot: the amount of water needed to cover one acre of land by one-foot (about 325,850 gallons).
Beneficial consumptive use: the amount of water diverted from a river, less the quantity not consumed, which returns to the river for further use.
Equitable apportionment: the label which the Court has applied to the body of federal interstate common law based on the settlements of prior interstate suits over the use of interstate rivers. It is based on the priority of appropriation modified by equitable considerations.
Present perfected rights: valid rights under state law measured by the water put to use as of June 25, 1929, the effective date of the Boulder Canyon Project Act.
Priority of appropriation: In the West, this law developed for the first users of an area’s water supply. It is based on the principle of “first-in-time is first-in-right.” It established that late-comers could never appropriate water to the injury of other projects. Sometimes called the “Colorado Doctrine.”
Upper and Lower Basins: The division of the Colorado River and its tributaries into two basins for the purposes of allocating water. The dividing point is at Lee’s Ferry, Arizona. The Upper Basin states include Colorado, Wyoming, Utah, New Mexico, and part of Arizona. The Lower Basin states include California, Arizona, Nevada, and part of New Mexico.