The design of hydraulic structures from small culverts to large dams requires engineers to calculate the amount of water that will flow through the channel along which the structure is built. The rate of flow through a stream channel, or discharge, is measured using units of cubic feet per second for engineering

Engineers are often challenged when attempting to calculate how much drainage a particular area will need. Nature, however, has proven difficult to predict. AP/Wide World. Reproduced by permission.

projects in the United States, and in units of cubic meters per second in other countries.

In many cases, knowledge of the maximum rate of flow that is likely to occur in a channel is required. For example, an engineer may wish to ensure that a bridge will be built high enough to allow passage of the largest flood likely to...