[269] ‘Transactions of the American Philosophical Society,’ vol. iv. p. 303.
[270] These particulars are abstracted, through the “Minutes of Proceedings of the Institution of Civil Engineers,” from the ‘Zeitschrift für technische Hochschulen’ for 1881.
[271] Paper read before the Manchester Association of Engineers.
[CHAPTER XXIX.]
LOCKS, PLANES, SLUICE-GATES AND LIFTS.
The main difference between rivers and canals, is that the former are usually capable of being navigated without any artificial provision for overcoming differences of level, whereas canals are so constructed that differences of level are overcome by locks or lifts. There are, of course, many cases in which the navigation of a river is suddenly and effectually obstructed by differences of level which are unsurmountable. This is notably the case on the Niagara river, where the falls of that name interpose a bar to the further navigation of a stream which would otherwise be the natural connection between lakes Erie and Ontario. The same sort of obstruction is interposed to the navigation of the Gotha river in Sweden, by the Falls of Trolhätta. There are many cataracts on the Mississippi river and its tributaries which render navigation all but impossible. These natural barriers have in many cases been got over by the risky and difficult operation of “shooting the rapids”—a feat in which the red Indian navigators have long excelled. But while it may be possible with a canoe to overcome such obstructions without absolute disaster, it is manifest that such risks could never be run in the everyday business of commercial transport.
For these reasons, it has, in not a few cases, been found expedient to overcome the obstructions to river navigation that are interposed by rapids or cataracts, by constructing an artificial waterway parallel to the falls, on which the rise or fall of the natural waterway is surmounted by locks or lifts. The Welland Canal performs this function in Canada, and the Gotha Canal in Sweden. There is practically no limit to the differences of level that may be met by this arrangement, always assuming that water supply can be commanded at the summit.
VIEW FROM THE NIAGARA ESCARPMENT, LOOKING DOWN
THE WELLAND CANAL TOWARDS LAKE ONTARIO.