See also:water course used for the drainage of low lands, for irrigation (q.v.), or more especially for the purpose of navigation by boats,
See also:barges or
See also:ships . Probably the first canals were made for irrigation, but in very early times they came also to be used for navigation, as in
See also:Assyria and
See also:Egypt . The Romans constructed various
See also:works of the kind, and Charlemagne projected a
See also:system of waterways connecting the
See also:Main and the Rhine with the
See also:Danube, while in
See also:China the
See also:Grand Canal, joining the Pei-ho and Yang-tse-Kiang and constructed in the 13th century, formed an important artery of commerce, serving also for irrigation . But although it appears from Marco Polo that inclines were used on the Grand Canal, these early waterways suffered in general from the defect that no method being known of conveniently transferring boats from one level to another they were only practicable between points that
See also:lay on nearly the same level; and inland navigation could not become generally useful and applicable until this defect had been remedied by the employment of locks .
See also:Great doubts exist as to the
See also:person, and even the nation, that first introduced locks . Some writers attribute their invention to the Dutch, holding that nearly a century earlier than in Italy locks were used in
See also:Holland where canals are very numerous, owing to the favourable
See also:physical conditions . On the other
See also:hand, the contrivance has been claimed for
See also:engineers of the
See also:Italian school, and it is said that two
See also:brothers Domenico of
See also:Viterbo constructed a
See also:lock-chamber enclosed bya pair of
See also:gates in 1481, and that in 1487 Leonardo da
See also:Vinci completed six locks uniting the canals of Milan . Be that as it may, however, the introduction of locks in the 14th or 15th century gave a new character to inland navigation and laid the basis of its successful extension . The
See also:Languedoc Canal (Canal du Midi) may be regarded as the
See also:pioneer of the canals of
See also:Europe . Joining the
See also:Bay of Biscay and the Mediterranean it is 148 M. long and rises 62o ft. above
See also:sea-level with 119 locks, its
See also:depth being about 61 ft . It was designed by Baron Paul Riquet de Bonrepos (1604-1680) and was finished in 1681 . With it and the still earlier
See also:Briare canal (1605-1642) France began that policy of canal construction which has provided her with over 3000 M. of canals, in addition to over 4600 m. of navigable
See also:rivers .
See also:Peter the Great undertook the construction of a system of canals about the beginning of the 18th century, and in Sweden a canal with locks, connecting
See also:Eskilstuna with Lake
See also:Malar, was finished in ,6o6 . In England the
See also:oldest artificial canal is the
See also:Foss Dyke, a relic of the
See also:Roman occupation . It extends from Lincoln to the
See also:river Trent near Torksey (ii m.), and formed a continuation of the Caer Dyke, also of Roman origin but now filled up, which ran from Lincoln to
See also:Peterborough (40 m.) .
See also:Camden in his Britannia says. that the Foss Dyke was deepened and to some extent rendered navigable in 1121 . Little, however, was done in making canals in Great Britain until the
See also:middle of the ,8th century, though before that date some progress had been made in rendering some of the larger rivers navigable . In 1759 the duke of Bridgewater obtained
See also:powers to construct a canal between Manchester and his collieries at Worsley, and this
See also:work, of which
See also:Brindley was the engineer, and which was opened for
See also:traffic in 1761,was followed by a
See also:period of great activity in canal construction, which, however, came to an end with the introduction of
See also:railways . According to evidence given before the royal commission on canals in 1906 the
See also:total mileage of existing canals in the
See also:Kingdom was 3901 . In the United States the first canal was made in 1792-1796 at South Hadley, Massachusetts, and the canal-system, though its expansion was checked by the growth of railways, has attained a length of 4200 m., most of the mileage being in New
See also:Ohio, and Pennsylvania . The splendid inland navigation system of
See also:Canada mainly consists of natural lakes and rivers, and the artificial waterways are largely " lateral " canals, cut in
See also:order to enable vessels to avoid rapids in the rivers . (See the articles on the various countries for accounts of the canal-systems they possess.) The canals that were made in the early days of canal-construction were mostly of the class known as
See also:barge or
See also:boat canals, and owing to their limited depth and breadth were only available for vessels of small
See also:size . But with the growth of commerce the
See also:advantage was seen of cutting canals of such dimensions as to enable them to accommodate sea-going ships . Such
See also:ship-canals, which from an
See also:engineering point of view chiefly differ from barge-canals in the magnitude of the works they involve, have mostly been constructed either to shorten the voyage between two seas by cutting through an intervening
See also:isthmus, or to convert important inland places into sea-ports .
An early example of the first class is afforded by the Caledonian Canal (q.v.), while among later ones may be mentioned the
See also:Suez Canal (q.v.), the Kaiser Wilhelm,
See also:Nord-Ostsee or
See also:Kiel Canal, connecting Brunsbiittel at the mouth of the Elbe with Kiel, (q.v.) on the Baltic, and the various canals that have been proposed across the isthmus that joins
See also:North and South
See also:America (see
See also:PANAMA CANAL) . Examples of the second class are the Manchester Ship Canal and the canal that runs from Zeebrugge on the North Sea to,Bruges (q.v.) . Construction.—In laying out a
See also:line of canal the engineer is more restricted than in forming the route of a road or a railway, Since water runs downhill, gradients are inadmissibLe, and the canal must either be made on one
See also:uniform level or must be adapted to the general rise or fall of the
See also:country through which it passes by being constructed in a series of level reaches at varying heights above a chosen datum line. each dos ed by a lock or some
See also:device to enable vessels to be transferred from one to another . To avoid unduly heavy earthwork, the reaches must closely follow the bases of hills and the windings of valleys, but from
See also:time to time it will become necessary to
See also:cross a sudden depression by the aid of an
See also:embankment or aqueduct, while a piece of rising ground or a
See also:hill may involve a cutting or a tunnel . Brindley took the Bridgewater canal over the Irwell at
See also:Barton by means of an aqueduct of three
See also:arches, the centre one having a span of 63 ft., and T .
See also:Telford arranged that the
See also:Ellesmere canal should cross the Dee valley at Pont-y-Cysyllte partly by embankment and partly by aqueduct . The embankment was continued till it was 75 ft. above the ground, when it was succeeded by an aqueduct,
See also:food ft. long and 127 ft. above the river, consisting of a
See also:cast iron trough supported on iron arches with stone piers . Occasionally when a navigable stream has to be crossed, a
See also:swing viaduct is necessary to allow
See also:shipping to pass . The first was that built by
See also:Sir E .
See also:Williams to replace Brindley's aqueduct at Barton, which was only-high enough to give
See also:room for barges (see MAN-CHESTER SHIP CANAL) . One of the earliest canal tunnels was made in 1766–1777 by Brindley at Harecastle on the Trent and
See also:Mersey canal; it is 288o yds. long, 12 ft. high and 9 ft. wide, and has no
See also:tow-path, the boats being propelled by men lying on their backs and pushing with their feet against the tunnel walls (" leggers ") . A•second tunnel, parallel to this but 16 ft. high and 14 ft. wide, with a tow-path, was finished by Telford in 1827 .
Standedge tunnel, on the
See also:Huddersfield canal, is over 3 M. long, and is also worked by leggers . The dimensions of a canal, apart from considerations of water-supply, are regulated by the size of the vessels which are to be used on it . According to J . M . Rankine, the depth of water and sectional
See also:area of waterway should be such as not to cause any material increase of the resistance to the motion of the boats beyond what would be encountered in open water, and he gives the following rules as fulfilling these conditions: Least breadth of bottom =2X greatest breadth of boat . Least depth of water =1z ft.+greatest
See also:draught of boat . Least area of waterway =6Xgreatest midship section of boat . The ordinary inland canal is commonly from 25 to 30 ft. wide at the bottom, which is
See also:flat, and from 40 to 50 ft. at the water level, with a depth of 4 or 5 ft., the
See also:angle of slope of the sides varying with the nature of the
See also:soil . To retain the water in porous ground, and especially on embankments, a strong watertight lining of puddle or tempered
See also:clay must be provided on the
See also:bed and sides of the channel . Puddle is made of clay which has been finely chopped up with narrow spades, water being supplied until it is in a semi-plastic state . It is used in thin layers, each of which is worked so as to be firmly united with the
See also:lower stratum . The full thickness varies from 2 to 3 ft .
To prevent the erosion of the sides at the water-line by the
See also:wash from the boats, it may be necessary to pitch them with stones or
See also:face them with brushwood . In some of the old canals the slopes have been cut away and vertical walls built to retain the towing-paths, with the result of adding materially to the sectional area of the waterway . A canal cannot be properly worked without a supply of water calculated to last over the driest
See also:season of the
See also:year . If there be no natural lake available in the
See also:district for supper supply . 'storage and supply, or if the engineer cannot draw upon some stream of sufficient size, he must
See also:form artificial reservoirs in suitable situations, and the conditions which must be attended to in selecting the positions of these and in constructing them are the same as those for drinking-water supply, except that the purity of the water is not a
See also:matter of moment . They must be situated at such an
See also:elevation that the water from them may flow to the
See also:summit-level of the canal, and if the expense of pumping is to be avoided, they must command a sufficient catchment area to supply the loss of water from the canal by evaporation from the
See also:surface, percolation through the bed, and lockage . If the supply be inadequate, the draught of the boats plying on the canal may have to be reduced in a dryseason, and the consequent decrease in the size of their cargoes will both lessen the carrying capacity of the canal and increase the working expenses in relation to the
See also:tonnage handled . Again, since the
See also:consumption of water in lockage increases both with. the size of the locks and the frequency with which they are used, the difficulty of finding a sufficient water supply may put a limit to the
See also:density of traffic possible on a canal or may prohibit its locks from being enlarged so as to accommodate boats of the size necessary for the economical handling of the traffic under modern conditions . It may be pointed out that the up consumes more water than the down traffic . An ascending boat on entering a lock displaces a
See also:volume of water equal to its submerged capacity . The water so displaced flows into the lower reach of the canal, and as the boat passes through the lock is replaced by water flowing from the upper reach . A descending boat in the same way displaces a volume of water equal to its submerged capacity, but in this case the water flows back into the higher reach where it is retained when the gates are closed .
An essentialadjunct to a canal is a sufficient number of waste-weirs to
See also:discharge surplus water accumulating during floods, which, if not provided with an exit, may waste. overflow the.tow-path, and cause a
See also:breach in the
See also:banks, weirs and stoppage of the traffic, and damage to adjoining Stto s lands . The number and positions of these waste-weirs must depend on the nature of the country through which the canal passes . Wherever the canal crosses a stream a waste-
See also:weir should be formed in the aqueduct; but independently of this the engineer must consider at what points large influxes of water may be apprehended, and must at such places form not only waste-weirs of sufficient size to carry off the surplus, but also artificial courses for its discharge into the nearest streams . These waste-weirs are placed at the top water-level of the canal, so that when a
See also:flood occurs the water flows over them and thus relieves the banks . Stop-gates are necessary at
See also:short intervals of a few
See also:miles for the purpose of dividing the canal into isolated reaches, so that in the event of a breach the gates may be shut, and the discharge of water confined to the small reach intercepted between two of them, instead of extending throughout the whole line of canal . In broad canals these stop-gates may be formed like the gates of locks, two pairs of gates being made to shut in opposite directions . In small works they may be made of thick planks slipped into grooves formed at the narrow points of the canal under road bridges, or at contractions made at intermediate points to receive them . Self-acting stop-gates have been tried, but have not proved trustworthy . When repairs have to be made stop-gates allow of the water being run off by " off-lets " from a short reach, and afterwards restored with but little interruption of the traffic . These off-lets are pipes placed at the level of the bottom of the canal and provided with valves which can be opened when required . They are generally formed at aqueducts or bridges
See also:crossing rivers, where the contents of the canal between the stop-gates can be run off into the stream . Locks are
See also:chambers, constructed of
See also:masonry or concrete, and provided with gates at each end, by the aid of which vessels are transferred from one reach of Locks. the canal to another .
To enable a boat to ascend, the upper gates and the sluices which command the flow of water from the upper reach are closed . The sluices at the lower end of the lock are then opened, and when the level of the water in the lock has fallen to that of the lower reach, the boat passes in to the lock . The lower gates and sluices being then closed, the upper sluices are opened, and when the water rising in the lock has floated the boat up the level of the upper reach the upper gates are opened and it passes out . For a descending boat theprocedure is reversed . The sluices by which the lock is filled or emptied are carried through the walls in large locks, or consist of openings in the gates in small ones . The gates are generally of
See also:oak, fitting into recesses of the walls when open, and closing against sills in the lock bottom when shut . Dimensions . In small narrow locks single gates only are necessary; in large locks pairs of gates are required, fitting together at the
See also:head or " mitre-
See also:post " when closed . The vertical
See also:timber at the end of the
See also:gate is known as the "
See also:heel-post," and at its
See also:foot is a casting that admits an iron
See also:pivot which is fixed in the lock bottom, and on which the gate turns . Iron straps
See also:round the head of the heel-post are let into the lock-
See also:coping to support the gate . The gates are opened and closed by
See also:balance beams projecting over the lock side, by gearing or in cases where they are very large and heavy by the
See also:action of a
See also:hydraulic ram . In order to economize water canal locks are made only a few inches wider than the vessels they have to accommodate .
See also:English canal boat is about 70 or 75 ft. long and 7 or 8 ft. in
See also:beam; canal barges are the same length but 14 or 15 ft. in width, so that locks which will hold one of them will admit two of the narrower canal boats side by side . In general canal locks are just long enough to accommodate the longest vessels using the navigation . In some cases, however,
See also:provision is made for admitting a
See also:train of barges; such long locks have sometimes intermediate gates by which the effective length is reduced when a single vessel is passing . The lift of canal locks, that is, the difference between the level of adjoining reaches, is in general about 8 or ro ft., but sometimes is as little as
See also:r2 ft . On the Canal du Centre (Belgium) there are locks with a lift of 17 ft., and on the St Denis canal near La Villette basins in
See also:Paris there is one with a lift of 322 ft . In cases where a considerable difference of level has to be surmounted the locks are placed close together in a series or "
See also:flight," so that the lower gates of one serve also as the upper gates of the next below . To save water, expecially where the lift is considerable, side ponds are sometimes employed; they are reservoirs into which a portion of the water in a lock-chamber is run, instead of being discharged into the lower reach, and is afterwards used for partially filling the chamber again .
See also:Double locks, that is, two locks placed side by side and communicating by a passage which can be opened or closed at will, also tend to save water, since each serves as a side pond to the other . The same advantage is gained with double flights of locks, and time also is saved since vessels can pass up and down simultaneously . A still greater
See also:economy of water can be effected by the use of inclined planes or vertical lifts in place of locks . In China Inclines.
See also:rude inclines appear to have been used at an early date, vessels being carried down a sloping
See also:plane of stonework by the aid of a flush of water or hauled up it by capstans . On the
See also:Bude canal (England) this plan was adopted in an improved form, the small flat-bottomed boats employed being fitted with wheels to facilitate their course over the inclines .
Another variant, often adopted as an adjunct to locks where many smallpleasure .boats have to be dealt with, is to
See also:fit the incline itself with rollers, upon which the boats travel . In some cases the boats are conveyed on a wheeled trolley or
See also:running on rails; this plan was adopted on the
See also:Morris canal, built in 1825-1831, in the case of 23 inclines having gradients of about i in ro, the rise of each varying from 44 to
See also:loo ft . Between the Ourcq canal and the
See also:Marne, near
See also:Meaux, the difference of level is about 40 ft., and barges weighing about 70 tons are taken from the one to the other on a wheeled cradle weighing 35 tons by a
See also:wire rope over an incline nearly Soo yards long . But heavy barges are
See also:apt to be strained by being supported on cradles in this way, and to avoid this objection they are sometimes
See also:drawn up the inclines floating In a tank or
See also:caisson filled with water and running on wheels . This arrangement was utilized about 1840 on the Chard canal (England), and 10 years later it was adapted at Blackhill on the Monkland canal (Scotland) to replace a double flight of locks, in consequence of the traffic having been interrupted by insufficiency of water . There the height to be overcome was 66 ft . Two pairs of rails, of 7 ft.
See also:gauge, were laid down on a gradient of r in ro, and on these ran two carriages having wrought iron, water-tight caissons with lifting gates at each end, in which the barges floated partially but not wholly sup-ported by water . The carriages, with the barge and water,weighed about 8o tons each, and were arranged to countess balance each other, one going up as the other was going down . The power required was provided by two high pressure steam engines of 25 h.p.,
See also:driving two large drums round which was coiled, in opposite directions, the 2-inch wire rope that hauled the caissons . An incline constructed on the Union canal at Foxton (England) to replace ro locks giving a total rise of 75 ft., accommodates barges of 70 tons, or two canal boats of 33 tons . It is in some respects like the Monkland canal incline, but the movable caissons work on four pairs of rails on an incline of 1 in 14,
See also:broadside on, and the boats are entirely waterborne . Steam power is employed, with an hydraulic
See also:accumulator which enables hydraulic power to be used in keeping the caisson in position at the top of the incline while the boats are being moved in or out, a water-tight joint being . maintained with the final portion of the canal during the operation .
The gates in the caisson and canal are also worked by hydraulic power . The incline is capable of passing 200 canal boats in 12
See also:hours, and the whole plant is worked by three men . Vertical lifts can only be used instead of locks with advantage at places where the difference in level occurs in a short length of canal, since otherwise long embankments or Lifts . aqueducts would be necessary to obtain sites for their construction . An early example was built in 1809 at Tardebigge on the
See also:Worcester and
See also:Birmingham canal . It consisted of a timber caisson, weighing 64 tons when full of water, counterpoised by heavy weights carried on timber platforms . The lift of 12 ft. was effected in about three minutes by two men working winches . Seven lifts, erected on the Grand Western canal between Wellington and
See also:Tiverton about 1835, consisted of two chambers with a masonry
See also:pier between them . In each chamber there worked a timber caisson, suspended at either end of a chain hung over large pulleys above . As one caisson descended the other
See also:rose, and the apparatus was worked by putting about a ton more water in the descending caisson than in the ascending one . At Anderton a lift was erected in 1875 to connect the
See also:Weaver navigation with the Trent and Mersey canal, which at that point is 5o ft. higher than the river . The lift is a double one, and can
See also:deal with barges up to 100 tons .
See also:change is made while the vessels are floating in 5 ft. of water contained in a wrought iron caisson, 75 ft. long and 151 ft. wide . An hydraulic ram 3 ft. in diameter supports each caisson, the bottom of which is strengthened so as to transfer the
See also:weight to the side girders . The descending caisson falls owing to being filled with 6 in. greater depth of water than the ascending one, the weight on the rams (240 tons) being otherwise
See also:constant, since the barge displaces its awn weight of water; an hydraulic accumulator is used to over-come the Ioss of weight in the descending caisson when it begins to be immersed in the lower level of the river . The two presses in which the rams work are connected by a 5-in.
See also:pipe, so that the descent of one caisson effects the raising of the other . A similar lift, completed in 1888 at Fontinettes on the Neuffosse canal in France, can accommodate vessels of 250 tons, a total weight of 785 tons being lifted 43 ft.; and a still larger example on the Canal du Centre at La Louviere in Belgium has a rise of 5o ft., with caissons that will admit vessels up to 400 tons, the total weight lifted amounting to over r000 tons . This lift, with three others of the same character, overcomes the rise of 217 ft., which occurs in this canal in the course of 41 M . Haulage.—The
See also:horse or
See also:mule walking along a tow-path and
See also:drawing or " tracking " a boat or barge by means of a towing rope, still remains the typical method of Animal conducting traffic on the smaller canals; on ship- Power canals vessels proceed under their own steam or are aided by tugs . Horse
See also:traction is very slow . The maximum
See also:speed on a narrow canal is about 32 M. an
See also:hour, and the
See also:average speed, which, of course, depends largely on the number of locks to be passed through, very much less . It has been calculated that in England on the average one horse hauls one narrow canal boat about 2 M. an hour loaded or 3 m. empty, or two narrow canal boats 11 m. loaded and 21m . Steam towage was first employed on the Forth and
See also:Clyde canal in 1802, when a tug-boat fitted with steam engines by W . Symington drew two barges for a distance of 191 m. in 6 hours in the teeth of a strong headwind .
As a result of this successful experiment it was proposed to employ steam tugs on the Bridgewater canal; but the projectfell through owing to the
See also:death of the duke of
See also:Bridge-water, and the
See also:directors of the Forth and Clyde canal also decided against this method because they feared damage to the banks . Steam tugs are only practicable on navigations on which there are either no locks or they are large enough to admit the tug and its train of barges simultaneously; otherwise the advantages are more than counterbalanced by the delays at locks . On the Bridgewater canal, which has an average width of 50 ft. with a depth of 51 ft., is provided with vertical stone walls in place of sloping banks, and has no locks for its entire length of 40 M. except at
See also:Runcorn, where it joins the Mersey, tugs of 50 i. h. p., with a draught of 4 ft., tow four barges, each weighing 6o tons, at a
See also:rate of nearly 3 M. an hour . On the
See also:Aire and Calder navigation, where the locks have a minimum length of 215 ft., a large
See also:coal traffic is carried in trains of boat-compartments on a system designed by W . H . Bartholomew . The boats are nearly square in shape, except the leading one which has an ordinary
See also:bow; they are coupled together by knuckle-
See also:joints fitted into hollow stern-posts, so that they can move both laterally and vertically, and a wire rope in tension on each side enables the train to be steered . No boat crews are required, the
See also:crew of the steamer regulating the train . If the number of boats does not exceed 11 they can be pushed, but beyond that number they are towed . Each compartment ' carries 35 tons, and the total weight in a train varies from 700 to 900 tons . On the arrival of a train at
See also:Goole the boats are detached and are taken over submerged cradles under hydraulic hoists which lift the boat with the cradle sufficiently high to enable it to be turned over and discharge the whole cargo at once into a shoot and thence into sea-going steamers. j Another method of utilizing steam-power, which was also first tried on the Forth and Clyde canal by Symington in 1789, is to provide each vessel with a
See also:separate steam engine, and many barges are now running fitted in this way . Experiments have also been made with
See also:internal combustion engines in place of steam engines .
In some cases, chiefly on rivers having a strong current, recourse has been had to a submerged chain passed round a
See also:drum on a tug: this drum is rotated by steam power and thus the tug is hauled up against the current .
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