OANAI 



OAHAL. 



only one vane U and, and 0-648 when two vanes re u*ed ; 8= the 

 sectional area of the opening of the TUMI; and H= the head above 



When the navigation upon a OHM! U active.it may become advis- 

 able to place two lock* ride by ride, eo that one should be able to lock 

 an. and the other down, simultaneously. In this manner it is easy to 

 feat a oooridenble Having el water, by meant of a culvert between 

 the two chambers ; and in aome other caaea, as in the Canal d'Antoing, 

 the same object of economising water is effected by means of side 

 . On this Canal d'Antoing, a system waa also adopted for 



Ride-pond on the Canal d'Antolng. 



pumping the water, which had served to pass boats through^ chain of 

 fire locks, back again into the upper reach of the canal ; and in countries 

 where water is scarce, this system may be recommended for imitation. 

 There are, it may be added, an almost infinite number of inventions 

 for the purpose of saving time in the passage of boats through locks, 

 and for saving water during that operation, a description of which 

 would extend this article to inconvenient limits. The reader is there- 

 fore referred for further details to Telford's Life, to Sgauzin's ' Cours 

 de Construction,' Minard's ' Navigation des Canauz et des Rivieres.' 



The proportion of locks per mile of canal is necessarily very variable ; 

 for it depends upon . the longitudinal section of the country to be tra- 

 versed. In England, the average upon the more important canals 

 ranges from 1 lock in 0'33 mile to 1 in 1 '43 ; in France, the average 

 varies from 1 in 0-66 to 1 in 1'89 ; and in America, there is upon the 

 Erie Canal on the average 1 lock in every 4'36 miles. Occasionally, 

 in very hilly countries, locks are dispensed with altogether, and the 

 boat* are raised by means of machinery upon inclined planes, from one 

 level to the other. Thus, in the Duke of Bridgewater's subterranean 

 canals, there U one inclined plane 151 yards long, by means of which n 

 difference of level of 854 yards is at once overcome. On the Shropshire 

 Canal there are three inclined planes, respectively of 126, 120, and 207 

 feet rise, executed about the year 1792 ; and Tel ford executed an 

 inclined plane of the same description on the Shrewsbury Canal, of 

 228 yards in length and 25 yards rise. On the Canal du Centre similar 

 inclined plane* are used, on account of the want of water ; and on the 

 Morris Canal, Pennsylvania, there are no less than fourteen such planes, 

 each of which has a rise of about 100 or 102 feet In the latter case, 

 the barges are run into a species of lock, which is carried upon rollers, 

 an that the barges are kept constantly afloat. It is said that the 

 economical result* of these inclined planes are very satisfactory ; but 

 evidently they can only be applicable upon canals of small section, for 

 even in the case of the Morris Canal, the weight of the boat, lock, and 

 carriage is about 85 tons, and in a canal of larger dimensions the weight 

 would increase in so marked a proportion as to increase the cost of 

 lifting the load to a very serious extent. The vertical lift used upon 

 the Bridgewater Canal seems to be the best for large canals. 



8. A'/*td*rU. .SipAoiu, and Cutvcrtt.ln traversing a great length of 

 country, especially in a hilly or mountainous region, it may often 

 happen that the canal would meet in its course streams holding much 

 foreign matters in suspension, or (abject to floods or drought*, of a 

 capricion* and dangerous character ; and these streams may occur at 

 dlBaeul level* with respect to the water-line of the canal, requiring 

 consequently a different treatment in each case. If the natural level 

 of the stream should be above that of the canal, of course, it must be 

 carried over it at once by an aqueduct; but this is a case which rarely 

 occurs, and it i* far more common to find that it is necessary to pas* the 

 water under the canal by means of a culvert, or of a siphon aqueduct. 

 The construction of the culvert* is simple enough, for all that is 

 required of them is, that their water-way should be sufficiently large 

 to carry off any flood which may occur in the upper jmrU nf the valley 

 they serve to discharge, and that they should be executed of imper- 

 meable materials, both fur the purposes of resulting leakage from the 

 canal above them and from their own bed. Greater difficulties, how- 

 ever, attend the execution of the siphons, for they are at all time* 

 dimoult to repair; there U moreover great danger of their leaking, in 



consequence of the hydrostatic*! preaiure acting upon their lower sur- 

 faces; and there is a tendency to choke up the passage, from the 

 accumulation of silt or alluvial matter. So great, indeed, is the danger 

 from the latter cause, that siphons should only be used for the moat 

 limpid waters, and under any circumstances settling reservoirs should 

 be formed at their entrances. 



If the lateral stream thus encountered should attain considerable 

 dimension*, it will become necessary to carry the canal over it by 

 means of a bridge aqueduct, whose form, mode of construction, and 

 dimensions must depend upon the particular circumstances of the caw. 

 It is very rarely that the width of the channel is made more than 

 8 inches on each side beyond the extreme width of the barges using 

 the canal. Only one towing-path is absolutely necessary, though it U 

 usual to execute two, and these paths are made 8 feet wide when the 

 haulage is effected by men, or 6 feet wide when it in effected by hones. 

 When, as it is usually the case, the aqueduct is executed in masonry, 

 the actual bed of the canal ought not to be commenced until the 

 centres have been struck, and the settlement* of the materials have 

 taken their full effect upon the piers and arches of the substructure. 

 In the beet modern works of this description, the bed itself is formed 

 of hydraulic concrete ; and under those circumstances, a strong timber 

 guard is required to protect the concrete from the jars or shocks of 

 the barges ; as also an earthwork lining if the bargemen are likely to 

 use their gaffe. The primary object to be borne in mind in executing 

 an aqueduct being, in fact, that it must be water-tight, it is impossible 

 to attach too much importance to the mechanical execution of the bed, 

 and in some cases the engineers have even gone so far as to line the 

 trough with lead. This was a needlessly expensive method of securing 

 the desired end; but it is impossible to exaggerate the neces- 

 observing the minutest precautions to insure the impermeability of the 

 channel, or the immediate removal of any water which may force its 

 way through, without its being allowed in any way to compromise 

 the solidity of the structure. For this purpose it is advisable to form 

 small aqueduct* in the haunches of the arches ; and the warm air-flues, 

 which are occasionally formed in these structures, may likewise be 

 made to contribute to the same end. The water should be introduced 

 as soon after the execution of the bed as possible, in order to prevent 

 any fissures from the sudden drying of the lining. 



Great difficulties are at times encountered in executing the founda- 

 tions of canal aqueduct*, from the fact of their being necessarily con- 

 structed in the befls of rivers, which are composed of loose alluvial 

 matters of a great depth. This was the case with the aqueduct* of 

 Digoin and the Allier, erected over some of the torrential affluents of 

 the Loire ; and still more markedly with the great Solani and Oodavery 

 aqueducts recently executed in India. In the former cases, the founda- 

 tions were protected by establishing a floor, over the whole of the 

 water-way, between an upper and lower face-wall, and a close i 

 sheet piling was driven in front of each of the latter. In the case* of 

 the Indian aqueducts, the native system of founding upon wells was 

 adopted ; for brick wells were mink to a considerable depth, and sub- 

 sequently filled in with coin-rote, forming, as it were, masonry piles, 

 on which the superstructure was erected. Local consideration!! nm-i 

 determine the choice of the system to be adopted in any particular 

 case, the object to be effected being to effectually guard against any 

 tendency in the waters of the stream traversed to undermine the 

 foundations. 



Amongst the most remarkable canal aqueduct* hitherto executed, it 

 may be worth while to mention those upon the line of the Ellesmere 

 and Chester Canal, by Telford, on account of the novel application in 

 them of cast iron to building purposes. In the Chirk Aque.ln 

 bed only of the canal was formed of that material ; but in the Pont y 

 Cysslte Aqueduct, the whole of the upper structure was execi i 

 oast iron. The Lune Aqueduct, by Mr. Kennie, is a very bold and 



Lnne Aqueduct. 



elegant structure ; and there are some very remarkable works of this 

 description near Leeds, executed by Mr. Leather, in which cast iron 

 has again been employed on a very large scale. In France there are 

 some remarkable aqueduct* of masonry, such as the one* before men- 

 tioned at Digoin ami liuetin, the fomn-r of which is 810 feet long, and 

 the latter is 1298 feet long; and in the United States there is a great 

 work of this description, of wood, 1077 feet long. The aqueduct nf the 

 Ganges Irrigation Canal \ however the largest construction of this 

 nature yet erected, for its actual water-way is not less than 170 I 

 \vi.lth f.y in feet in depth; the Godavery Aqueduct is of a smaller 



i.ut its total length is not less than 2248 feet. 



I '/,,,/,/,. -The bridges to be erected over a canal being 

 designed to accommodate the local traffic, it must be evident that the 

 most important gum-mi Condition to be observed in their construction 

 is, that they should be kept ax low as possible, consistently with (In 

 service of the navigation. It ha* been tuuud, practically, that upon 



