174. How much is a Stream Worth? The work which a stream can perform may be easily calculated. Suppose, for example, that 50,000 pounds of water fall over a 22-foot dam every second; the power of such a stream would be 1,100,000 foot pounds per second or 2000 H.P. Naturally, a part of this power would be lost to use by friction within the machinery and by leakage, so that the power of a turbine run by a 2000 H.P. stream would be less than that value. Of course, the horse power to be obtained from a stream determines the size of the paddle wheel or turbine which can be run by it. It would be possible to construct a turbine so large that the stream would not suffice to turn the wheel; for this reason, the power of a stream is carefully determined before machine construction is begun, and the size of the machinery depends upon the estimates of the water power furnished by expert engineers. A rough estimate of the volume of a stream may be made by the method described below:-- Suppose we allow a stream of water to flow through a rectangular trough; the speed with which the water flows through the trough can be determined by noting the time required for a chip to float the length of the trough; if the trough is 10 feet long and the time required is 5 seconds, the water has a velocity of 2 feet per second. [Illustration: FIG. 123.--Estimating the quantity of water which flows through the trough each second.] The quantity of water which flows through the trough each second depends upon the dimensions of the trough and the velocity of the water. Suppose the trough is 5 feet wide and 3 feet high, or has a cross section of 15 square feet. If the velocity of the water were 1 foot per second, then 15 cubic feet of water would pass any given point each second, but since the velocity of the water is 2 feet per second, 30 cubic feet will represent the amount of water which will flow by a given point in one second. 175. Quantity of Water Furnished by a River. Drive stakes in the river at various places and note the time required for a chip to float from one stake to another. If we know the distance between the stakes and the time required for the chip to float from one stake to another, the velocity of the water can be readily determined.