Page:The Canal System of England.djvu/47

 There are three chief methods of overcoming changes of level on a waterway.

I. The first, and by far the most common, is by means of the lock, which has been in use for so many centuries. This method is so cheap as regards first cost and so easily worked, that for moderate falls of 15 to 18 feet, where water is plentiful, it is undoubtedly the most advantageous.

But the great disadvantages of the lock system are:—

The latter is a most important factor where water is not abundant.

At the Fourth International Congress on Inland Navigation a scheme was submitted for a lock of French standard size but having a 66 ft. fall, the total cost of which was estimated at £65,000. The difficulty of the rush of the water was overcome by side chambers at different levels storing most of the water, but the depth used at each operation was over 25 ft., and this would require a very copious supply, where there was much traffic.