The quantity of water that will escape from an aperture 1 inch (2.54 centimeter) square through a 2-inch-thick (5.08- centimeter) plank, with a steady flow of water standing 6 inches (15.24 centimeters) above the top of the escape aperture, the quantity so discharged amounting to 2274 cubic feet (64.39 cubic meters) in 24 hours.