[Illustration: FIG. 16.--Power-house on White River, Oregon.]
Another interesting example of conditions that require a power-house to be located some distance from the point where water is diverted from its natural course may be seen at the falls on the Apple River, whence energy is transmitted to St. Paul, Minn. By means of a natural fall of 30 feet, a dam 47 feet high some distance up-stream, and some rapids in the river, it was there possible to obtain a total fall of 82 feet. To utilize this entire fall a timber flume, 1,550 feet in length, was built from the dam to a point near the power-house on the river bank and below the falls and rapids. The flume was connected with the wheels, 82 feet below, by a steel penstock 313 feet long and 12 feet in diameter.
As the St. Mary’s River leaves Lake Superior it passes over a series of rapids about half a mile in length, falling twenty feet in that distance. To make the power of this great volume of water available, a canal 13,000 feet long was excavated from the lake to a point on the river bank below the rapids. Between the end of the canal and the river sits the power-station, acting as a dam, and the water passes down through it and the wheels under a head of twenty feet.
[Illustration: FIG. 17.--Power-house Across Canal at Sault Ste. Marie, Mich.]
By means of a canal 16,200 feet long from the St. Lawrence River a head of water amounting to fifty feet has been made available at a point on the bank of Grass River near Massena, N. Y. There again the power-station acts as a dam, and the canal water passes down through it to reach the river.
[Illustration: FIG. 18.--Canal and Station on Payette River, Idaho.]
From these illustrations it may be seen that in many cases, in comparatively level country, a water-power can be fully developed only by means of canals or pipe lines, and the generating stations cannot be located at the points where the water is diverted.
Thus far the cases considered have been only those with moderate heads and rather large volumes of water. In mountainous country, where rivers are comparatively small and their courses are marked by numerous falls and rapids, it is generally necessary to utilize the fall of a stream through some miles of its length in order to effect a satisfactory development of power. To reach this result, rather long canals, flumes, or pipe lines must be utilized to convey the water to power-stations and deliver it at high pressures.