WATER POWER. A term used by en gineers to define the power obtained or capable of being obtained from water by its fall from a higher to a lower level: also, more specifically, the term applied to a fall in a stream which is used or is capable of being employed to develop power. Water power is, perhaps, after wind power, the most natural and at the same time the most truly economic source of energy. The term water power is something of a misnomer. The real agent is gravity, the fluid itself being the medium through which the action of gravity is transmitted to the prime motor. In order that water may be available for the purpose of doing work, it must lie in such a position that it can fall from a higher to a lower level, or must be under pressure produced by some ex ternal force. such as that of a weight or spring acting on the surface of the fluid through a pis ton or plunger. Under the former condition its utmost capacity for doing work—potential energy or energy of position—is the product of the height through which it can fall into the weight of the water falling, so that if h denote the avail able height of the fall and G denote the weight of the water falling per second, then h X equals the energy or power available per second. If the fluid is allowed to fall without resistance under the action of gravity, either free or confined in pipes. the power available is expended in impart ing velocity to the water. and the potential energy of position is converted into kinetic energy or energy of motion, and in this form is available for performing work. It is, however, not neees sary that the potential energy of water should be transformed into Idnetie energy in order that it may be employed for motive power. The weight of the fluid can also he allowed to act directly on the prime motor in a manner similar to that in which the weight of a body attached to one a passed over a pulley for in stance, may be made to raise another body sus pended at the opposite end. A third way of using water power for doing work is by means of its pressure. hut the difference between this method and the preceding method is more ap parent than real. The so-palled pressure of water is the result or its equivalent. For practical purposes it may. nevertheless, be said that there are three ways in which water power eau be applied to the performance of work: (1) As kinetic energy. or through the velocity of the fluid; (2) by weight and (3) by Each of these three methods requires a different type of motor for its application, denoted respectively as (1) turbine (q.v.), (2) water wheel (q.v.), and (3) hydraulic pressure engine (q.v.).
The most usual source of water power in nature is a river or stream, but to make this available for practical purposes sonic form of work such as dams (q.v.), canals (q.v.), and
aqueducts (q.v.) is almost invariably neces sary. A river has always a certain fall or gradient, but to be able to take advantage of this fall for doing work, the portion of it utilized must be applied in one or several nearly perpen dicular steps. One common way of accomplish ing this object is to build a dam across the stream. The effect of this dam is to raise the level of the water above it a height equal to the difference between the original level and the level of the top of the dam, while the level of the stream below the dam remains as it was. To illustrate, let us assume that the stream had originally a fall of 1 foot in 100 feet. and that a dam 6 feet high is built across it. The head which was previously expended almost entirely in overcoming the resistance of the river bed over a distance of 600 feet, while the water grad ually descended 6 feet down a gentle incline, will now be available for doing a corresponding amount of useful work by a sudden drop through the same height as before. In other words, the energy originally wasted in useless friction in the gradual descent of the stream is accumulated in the form of head immediately behind the dam before the plunge of the water. To apply this energy the water flowing over the dam is taken into the chamber or reservoir containing the motor through which it passes to the tail race. In other eases, where it is not admissible or pos sible to eonstrnct a dam. or where only a por tion of the water of a stream is required, the necessary quantity is drawn off by a separate channel at a sufficient disitance above the point where the power is required to obtain the de sired fall. Occasionally water power is avail able in the form of a natural waterfall, ;trel then it is simply necessary to guide the water in a tube or ehannel to the motor. Sometimes the velocity only of the flowing stream is employed for working the motor, the head in that ease be ing already converted into kinetie energy.
The preeeding table gives the water powers which have notably enhaneed the industrial de velopment of the country, In this table the hiatus from 1 Sfi 1 to 1 806 is accounted for by the stagnation of industrial en terprise due to the Civil War. In recent years the possibility of transforming water power into electrical energy and its transmission to dis tant points has aided greatly in promoting the development of water-power enterprises of great magnitude. The Great Falls, the Sault Ste. Marie, the Niagara, the Ogden, and t he Mechanics ville developments are notable examples of such water-power electric plants. In each of these eases the water power operates turbines or water wheels which drive dynamos.