[Illustration: American Falls from Below.]
Before work on the main tunnel was begun, a shaft was sunk on the river bank just opposite the crest of Horseshoe Falls. From this shaft a tunnel was dug to the point where the lower end of the main tunnel would terminate. No difficulties were experienced in the driving of this opening until near the face of the cliff behind Horseshoe Falls. Here, with only fifteen feet to go, water began to rush into the cavern through a fissure in the rocks. The engineers fought against the water for several days but could not stop its flow. Finally eighteen holes were drilled into the cliff between the end of the tunnel and where the final opening was to be made; these holes were loaded with dynamite, which, together with a large charge placed against the end of the passage, was exploded, after the tunnel had been flooded. This only accomplished a part of what was desired. An opening was made in the cliff but too near the roof of the tunnel to allow of any work. What to do now was a difficult problem, but American daring accomplished the work. Volunteers were called for to crawl along the ledge of rock running along the cliff behind the Falls to where the opening had been made. Several men offered to make this almost impossible trip. Lashed together with cords, with the thunder of the Falls in their ears, blinded by spray which was driven into their faces with cyclonic fury, the men at last reached the opening and placed a heavy charge of dynamite against the opposing wall. This was discharged, making a sufficiently large opening for the water to run out, and the work was continued.
In the design of the main tunnel, ingenious provision was made for recession of the Falls. From the opening in the cliff for three hundred feet the lining will be put in in rings six feet long; this arrangement will allow a joint to drop out whenever the Falls recede so that it is exposed, thus leaving a smooth section always at the end of the tunnel. Through this main tunnel and through the branch races, the water, after having left the turbines, will whirl along at the rate of twenty-six feet per second, having generated a total of 125,000 electric horse-power. In engineering problems connected with the tunnel and the construction of the plant, the work of this company far surpasses that of any of the others. In order to secure a place for the wheel-pit and gathering dam, an area of about twelve acres in the bed of the river was converted into dry land. To do this a coffer dam was constructed 2153 feet in length and from twenty feet to forty-six feet wide in water varying in depth from seven feet to twenty-four feet, besides being very swift in most places. About two thousand feet above the Falls, in the space thus deprived of its water, an immense wheel-pit was sunk into the solid rock. On the bottom of this pit, 150 feet below the surface rest the monster turbines, from which two tail-races conduct the water to the main tunnel. A large gathering dam sufficient to supply the maximum capacity of this plant runs obliquely across the river for a distance of 750 feet. The height of this dam varies from ten to twenty-three feet; it is constructed of concrete, the top being protected by a course of cut granite. The power plant is located on the original shore line and parallel to it in Queen Victoria Park. In the power room are to be found eleven monster generators capable of developing 12,500 horse-power each.