,-ld 



CANAL. 



CANAL. 



In ship canals it is desirable to form towing-paths on both sides, so 

 as to be able to keep a ship steady during the prevalence of high 

 winds ; and it is customary to leave a narrow zone of shallow water on 

 the banks of either of the towing-paths, for the purpose of destroying 

 the effect of any waves in the canal upon the banks. The towing- 

 paths themselves are finished at a minimum elevation of about 3 ft. 

 3 in. above the water line in the best canals of this description. The 

 other works upon ship canals, so far as regards the provisions to be 

 made to counteract interferences with the local drainage, or with the 

 ordinary water courses of the district, are so precisely analogous to 

 those required upon other lines of navigation, that they will be con- 

 sidered simultaneously with the latter. 



Lateral canals are established, as was before stated, in almost all 

 cases for the purpose of obviating the natural causes of disturbance in 

 the river navigation resulting from the irregularities in the flow, or in 

 the physical conditions of the bed of the stream ; but they are also 

 occasionally formed for the purposes of supplying irrigation channels, 

 and for utilising the dynamical power of the water, when the rivers with 

 which they are connected are of, comparatively speaking, insignificant 

 volume, and are but little exposed to floods. The works executed 

 upon the banks of the Lea, or of the Test and Itchin, in Hampshire, 

 may be cited as partial illustrations of the combined use of rivers for 

 navigation and industrial purposes ; and perhaps it is allowable here to 

 express the regret that the recent introduction of the railway system 

 should have so entirely diverted public attention from the subject. 

 For although the canals thus alluded to are far from being such as to 

 ensure the greatest results from the water privileges concerned, the 

 practical economical benefits to the public produced by them have, 

 nevertheless, been of a very extraordinary description, even without 

 any reference to the effect produced by the economical transport of 

 bulky articles. It is, however, upon the long rivers of continents that 

 lateral canals produce the moat remarkable results ; because in nearly 

 all such cases, there is a large agglomerated population upon the 

 banks of the river, and there is a rude species of navigation on the 

 main stream, exposed to the inconveniences which unfortunately 

 attend almost every large body of fresh water until it becomes dis- 

 tinctly under the influence of the tidal action. Such rivers are, 

 indeed, exposed to great differences of level from the effects of floods, 

 or of droughts; they are often divided into narrow and tortuous 

 channels ; at times they flow with great rapidity over shallows, and at 

 others they present long reaches of stagnant water of great depth ; 

 and, in fact, they present, in their natural state, almost insuperable 

 difficulties to the establishment of a regular system of navigation, 

 even when the average velocity of the stream is not so great as to 

 render such an operation physically impossible, in both the upward, 

 and the downward direction. Lateral canals must, therefore, be con- 

 sidered to be essentially the means of correcting the natural defects 

 of a river, or water course, for the purposes of navigation. 



One of the most complete works of this description hitherto executed 

 is, perhaps, the lateral canal of the Loire, which is made throughout 

 iU length to present a clear water way of 5 ft. 3 in. deep, by a width 

 of about 33 ft. on the water-line of the canal, and of 17 ft. in the clear 

 of the lock chambers, the latter being made about 101 ft. long, mea- 

 suring from point to point of cills. The projected works for the 

 hanrOYWHBt of the navigation of the Seine, are perhaps rather of the 

 nature of a river improvement than of an ordinary lateral canal ; but 

 they may lie cited as illustrating the dimensions it is considered in 

 Kurope advisable to adopt as the maximum in either of such cases. 

 Tin locks are made as nearly as possible 400 ft. long by 40 ft. wide, 

 with :\ fall of <J ft. 7 in., and the normal width and depth of the 

 channel are made about 75 ft. by 6 ft. 7 in. ; for the barges used upon 

 the Seme are often as much as 140 ft. long, by 23 ft. 6 in. wide, with 

 a depth of 1 3 ft. 4 in. from deck to keel, and are able to carry as much 

 an from 400 to 500 tons of merchandise. Upon many other rivers of 

 iitineiit, of our own country, and of North America, similar 

 works have been undertaken ; and, indeed, the lateral canals of the 

 Canadian rivers may be cited as being amongst the most remarkable 

 operations of the kind yet attempted. The Long Sault canal, by 

 means of which the dangerous rapids of the Ottawa are turned, has a 

 width of about 140 ft. on the water-line, with a depth of 10 ft. ; and 

 it* 1'icks are not less than 200 ft. long by 55 ft. wide, with a depth 

 of water over the cill of 8 ft. The Welland canal, which is in fact a 

 lateral canal to the St. Lawrence between the lakes Erie and Ontario, 

 h.-M IncliH ] 3fi ft. long by 22 ft. wide, and 8 ft. depth of water; so that the 

 schooners which navigate the inland seas of North America are actually 

 able to pass from them, through the lower St. Lawrence, to the Ocean. 



The details of lateral canals do not differ in any essential respect from 



>f summit level canals, except inasmuch as the difference may be 

 rendered necessary in consequence of their greater dimensions. It is, 

 for iimtance, customary to form, both on ship canals, and large lateral 

 ARTS AND SCI. DIV. VOL. II. 



canals, what are called surf beams on either side of the main channel, 

 for the purpose of destroying the effect of the waves caused either by 

 the wind, or by the passage of vessels through the canal ; but in ordi- 

 nary canals this precaution is hardly necessary. Again, in lateral 

 canals it is advisable to form towing paths on both sides, as in the case 

 of ship canals ; whilst a single towing-path will suffice for an ordinary 

 artificial navigation. But the most peculiar works required for the 

 formation of lateral canals are those connected with the passage from 

 one bank of the river to the other, and those executed for the purpose 

 of securing the uninterrupted discharge of the drainage of the cross 

 valleys, or of the affluents to the main stream. In many cases these 

 affluents are of sufficient importance to render it necessary to construct 

 large aqueduct bridges ; and at all times they require to be treated 

 with care and attention in order to avoid floods. 



In the annexed cut is represented one of the passages of the lateral 

 canal of the Loire from one bank to the other of the river, rendered 



necessary, be it observed, by the occurrence at a point lower down of 

 a large affluent on the side thus abandoned ; and as this work illustrates 

 the various conditions attending similar operations in a very striking 

 and comprehensive manner, it may be desirable to dwell a little upon 

 its consideration. The Loire is a stream of a very irregular character, 

 varying frequently and rapidly in volume; but it may be generally 

 described as a mere thread of water in summer, and as a deep, broad, 

 and rapid river in winter. Its tendency to inundate its banks has 

 been resisted by the construction, at a very remote period of history, 

 of banks insubmersible during ordinary floods, finishing at a height of 

 at least 21 ft. 3 in. above the mean summer level of the stream 

 though some of the inundations of this valley have attained the height 

 of at least 25 ft. These banks limit the course of the water during 

 floods ; but during the period when the river flows with its normal 

 volume, the water is confined in a definite channel, by banks finishing 

 at lower levels, as shown, so that moderate floods are allowed to dis- 

 charge themselves freely, whilst the deep water channel is maintained. 

 Under these circumstances the canal crosses the river by means of a 

 small basin on the left bank, in which barges may lie in case the main ' 

 stream should be in a state to render it unadvisable to attempt the 

 passage ; and from this basin there is a communication with the river 

 by means of a sluice pointing in both cases down the stream, and whose 

 axis forms an angle of 35 degrees with the bank. As the lock-chambers 

 of this sluice are required frequently to keep out the river floods, they 

 are provided with double sets of gates ; one pointing up, and the other 

 down, the stream of the canal itself ; and the walls of the lock-cham- 

 bers are finished off at the maximum height of the river banks. On 

 the right bank, the canal recommences with a lock entrance of a 

 precisely similar character to the one upon the left bank, terminating 

 in a rather wide bay of the canal ; which bay, in its turn, ends in a 

 circular basin, wherein the barges are able to change their direction. 

 It will be necessary hereafter to revert to the reasons for placing the 

 entrances as shown. 



Summit Icrel canals, or those intended to connect the existing lines 

 of navigation upon the streams which flow from the respective sides of 

 an elevated ridge of land, are forcedly made to overcome great differ- 

 ences of level, and thus give rise to the necessity for the execution of 

 peculiar and special works for that purpose ; and, as they are also 

 forcedly carried through the districts wherein the rivers are of feeble 

 volume, they frequently render necessary the execution of important 

 works for the supply of water. The questions connected with the 

 height to be overcome, and with the water supply, are indeed amongst 

 the most vital ones to a summit level canal ; and the success of such 

 an operation depends almost entirely upon the manner in which they 

 may have been solved. The general principles which must be boruo 

 in mind in tho formation of such a canal are, in fact, that their total 

 length should be the least possible under local circumstances ; and that 

 the difference of level be as small, and the number of locks as few, as 

 is consistent with the economy of the first cost ; for the evaporation 

 from the water surface, the loss by filtration through the banks, and 

 by the passage of boats through the locks, are dependent upon those 

 conditions. These remarks apply equally when the fall is both ways, 

 or when it is only in one direction, or when the canal has one or two 

 branches ; for there are instances in which summit level canals have 

 all their fall towards one river, as in the cases of the majority of the 

 Belgian canals, without descending on the other side from the highest 

 reach of the navigation. 



The precise direction of a line of artificial navigation may be, and 

 often is, diverted from that which would theoretically have been 



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