Aqueduct

While modern water pipes are much wider (20–30 ft or 6.1–9.1 m in diameter) and significantly longer (hundreds of miles long) than the first aqueducts, the hydraulic principles governing water carriage remain essentially the same. Water flows along gradients, and its velocity depends on a number of factors. Water flows more quickly along steeper gradients, but wear and tear on such pipes is greater, resulting in the need for more frequent repair. More gradual sloping pipes result in slower-flowing water with greater sludge deposits; hence, these pipes require more cleaning with less repair.

Water velocity along conduits is also greater in larger, smoother pipes. Pipes or canals that have rough surfaces disrupt water flow, slowing it down. In addition, larger diameter passageways provide less resistance, because a smaller percentage of the flowing water is retarded by the surface friction of the conduit. Thus, smaller diameter pipes slow the flow of water compared to larger diameter pipes.

The use of water to generate other forms of power is not new at all. The ancient Greeks and Romans both used water mills for work in such places as flour factories. In such mills, aqueducts were used to supply water on a relatively continuous basis. A modern application of water power is hydroelectric power.