What is the volume of 1 acre-foot in gallons?

One acre-foot is defined as the volume of water required to cover one acre of surface area to a depth of one foot. In terms of gallons, an acre-foot is equivalent to approximately 325,850 gallons. This conversion is based on the fact that one acre is equal to 43,560 square feet, and since there are 7.48 gallons in a cubic foot, the calculation for converting acre-feet to gallons is as follows:

1. Calculate the volume in cubic feet: 43,560 square feet (1 acre) multiplied by 1 foot (depth) equals 43,560 cubic feet.
2. Convert cubic feet to gallons: 43,560 cubic feet multiplied by 7.48 gallons per cubic foot equals approximately 325,850 gallons.

Thus, the correct answer reflects this standard unit of measure used in water resources and management, making B the accurate choice for the volume of 1 acre-foot in gallons.