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Page:Popular Science Monthly Volume 73.djvu/300

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296
THE POPULAR SCIENCE MONTHLY

adjust itself in the general averages, as on previous occasions, so that we must consider the effects of power diversion under normal conditions. As stated before, when the corrections are made in the discharge calculations prior to 1891, they fall into harmony with those of more recent date. These corrections do not appear in the work of any other writer, but I find them necessary, in order to explain incongruities, and to arrive at a satisfactory understanding of the effects of power diversion on Niagara Falls and the Great Lakes. Under these conditions, let us examine the physics of Niagara River.

10. Basin above the Rapids.—Above Niagara Falls are the Upper Rapids, descending fifty-five feet to the brink of the cataract. These begin as the water passes over a rim of rock (see figures 2, 3, 5) which crosses the river at the head of Goat Island. This is the "critical point," not merely in the distribution of water over the falls, but also in the level of Lake Erie, and indirectly of Lakes Huron and Michigan. Except at one small part near the Canadian side, the rock rim is from two to five feet higher than the rock-floor of the shallowest part of the river, about seventeen miles above the head of the Upper Rapids, and two miles below the outlet of Lake Erie. Throughout this distance the river crosses a depression, refilled with drift, so that here the channel itself was easily excavated to a much greater depth than across the two rock barriers mentioned, thus forming, de facto, a basin beginning with the narrows at the Buffalo Water Works, which are only 1,850 feet across, soon widening out into the broad stretches of the river on either side of Grand Island, below which they unite into another basin, over a mile wide, above Goat Island and its associated rock rim. This from its greater height than at the Water Works, constitutes the true rim of the Erie basin. The slope of the river between these points is due to the narrowness of the outlet of the lake, where the waters are so piled up that they have a velocity reaching to eight miles an hour, while in the basin above Goat Island the current is reduced, and is there from two to four miles an hour. The descent of the river from the lake to the rock rim at the Upper Rapids is about twelve feet.

11. Depth of Water on the Rim of Upper Rapids.—At mean stages, the average depth of the water in the American channel, as it begins to flow past Goat Island, is less than three feet, with a maximum of 4.5 feet. In the Canadian channel, for some 400 or 500 feet from Goat Island, under present ordinary conditions, the water is only from half a foot to one foot in depth, then for another stretch it increases to between two and three feet, beyond which the river shoals, so that in ordinary stages the water is seen to descend, not only in almost broken streams, but it is so shallow that the floats which have been sent down the river do not pass over the rock ledges, but are carried by the