CANALS. Canals are waterways, wholly or partially artificial, used for conveying water or for providing navigation. Those used for irrigation, drainage and water-power develop ment are of the first class and, being closely related to the subjects of their purpose, are not considered here.
Navigation canals have been designated according to the size or kind of boats that can navigate them, as boat, barge or ship canals; according to the nature of the channel, whether purely artificial or in ' natural streams, they have been known as artificial canals or canalized rivers; and according to geographical location they have been called isthmian canals, penin sular canals, canals around falls or rapids, arti ficial seaport canals or canals connecting water way systems. Also there are sea-level canals— built at sea level — and tidal canals, which are sea-level canals subject to tidal flow.
The term ship canal is applied to those canals intended for ocean-going ves sels, but the other terms — boat and barge— are not so generally used, probably because they fail to convey any definite idea as to size. However, the term thousand-ton barge canal, which was used to designate one particular canal, gives a fairly close idea of the boats that can be accommodated. As no standard of size has ever been or is likely to be established, the size of canal is truly defined only by stating the maximum dimensions of the boats that can be accommodated. These are usually given in terms of draft, beam and length, but sometimes the form of bow and stern must also be considered.
Until a few years ago the great majority of canals were of small size, and before the advent of the lock, unless a canal could be built at one level, the boats used were limited to a size which could be transferred from one level to another by some mechanical device. After locks came into use, France, in the 17th century, undertook considerable canal construction. England followed next, but did little until the latter half of the 18th century. Early in the 19th century the beginning of canal construc tion was witnessed in America. This was all prior to the coming of railroads and at a time when canals furnished the only cheap means of transportation. The sizes of the canals up to
this time seem, in the light of present dimen sions, but very small. During the latter part of the 19th century several of the European countries began enlarging and improving their more important canals, making some radical changes in size and in manner of construction and operation. These changes were worked out by careful study, made in accordance with modern scientific methods rather than by the rtile-of-thumb procedure of former years. American waterway improvement along mod em lines did not become very active until the beginning of the present-20th—century, but now various Federal projects, also the Panama Canal and New York State Barge Canal have caused a reawakening of canal construction in America.
The artificial channel, which among engi neers is now known as a land-line, was the prevailing type of construction for many years, even where the route was parallel and in close proximity to a natural stream, as was often the case. To control a river sufficiently for naviga tion by small boats was often considered im practicable and the cost, prohibitive. The liabil ity of damage to canal structures by floods and the damage to adjacent territory resulting from backwater caused by canal structures at flood time argued against the use of the natural channels. Later, when larger canals were built and methods for the control of rivers were improved, it became more economical to utilize the natural channels, where available.
Isthmian and peninsular canals, so called from the neck of land crossed, provide shorter and safer routes between certain ports. Canals around falls or rapids connect navigable por tions of a river above and below the fall. There are several of these on the Saint Law rence River. Artificial seaport canals extend from the coast inland and are designed to perthit sea-going vessels to reach inland ports. Canals connecting waterway systems enable boats to pass from one system to another, thereby increasing the utility of both systems, and often also they possess other features of much importance.