Page:Popular Science Monthly Volume 73.djvu/305

Rh rim on the Canadian side may be omitted from the present discussion. This leaves a volume of 51,200 cubic feet per second, including that of the Chicago canal, conceded under the franchises, though temporarily limited to 44,500 cubic feet. At the beginning of 1908 there were approximately only 18,000 cubic feet per second in continuous use out of the amount affecting the basin (and this quantity may have been considerably reduced from the shutting down of some works), yet this diversion, together with the scour on the river, has lowered the water in the basin, immediately above, so that its level is sixteen inches lower than what it would have been, if no such changes had been effected. Half of the amount is due to the diversion of the water. It is this lowering of the water, just before passing the rim of the basin, at the head of the Upper Rapids, which is causing the lowering of the water on the falls, as shown in figure 4.

In confirmation of the above results, let it be stated that on June 14 a power company stopped its use of 8,000 cubic feet per second, and this caused the water in the basin to rise six inches (the diversion by the other companies and that of the Chicago canal was not arrested at the time). At the edge of the American Falls the water rose 1.2 inches. At mean water much of the American Falls is scarcely more than six inches deep. With the lowering from extraordinarily high water to normal conditions, and the diversion increased in the future to 44,500 or 51,200 cubic feet per second, taken from above the Upper Rapids, the basin will be further lowered from twelve to sixteen inches or more, so that much of the rim of the basin will be exposed, and thus the flow of water will be largely cut off, not merely from the 800 feet on the eastern side of the Canadian Falls, thereby destroying that part, but also curtailing the water on the American Falls to half its present normal amount, which is only 5 per cent, of the total flow of both cataracts. This will be still further aggravated during years of low water, such as was 1901.

The preservation of the falls is now a question of inches. Under the conditions as set forth, the whole of the Horseshoe Falls will have shrunken from a crest line of 2,950 feet to 1,600 feet (including the curtailment on the Canadian side), and their diameter will have been reduced from 1,200 to 800 feet (see figure 6). They will then be