CANAL of Communication, an artificial cut in the ground, supplied with water from rivers, springs, &c., in order to make a navigable communication betwixt one place and another.
The particular operations necessary for making artificial navigations depend upon a number of circumstances. The situation of the ground; the vicinity or connection with rivers; the ease or difficulty with which a proper quantity of water can be obtained; these and many other circumstances necessarily produce great variety in the structure of artificial navigations, and augment or diminish the labour and expense of executing them. When the ground is naturally level, and unconnected with rivers, the execution is easy, and the navigation is not liable to be disturbed by floods; but, when the ground rises and falls, and cannot be reduced to a level, artificial methods of raising and lowering vessels must be employed; which likewise vary according to circumstances.
A kind of temporary sluices are sometimes employed for raising boats over falls or shoals in rivers by a very simple operation. Two polls or pillars of mason-work, with grooves, are fixed, one on each bank of the river, at some distance below the shoal. The boat having passed these polls, planks are let down across the river by pulleys into the grooves, by which the water is dammed up to a proper height for allowing the boat to pass up the river over the shoal.
The Dutch and Flemings at this day, sometimes when obstructed by cascades, form an inclined plane or rolling-bridge upon dry land, along which their vessels are drawn from the river below the cascade into the river above it. This, it is said, was the only method employed by the ancients, and is still used by the Chinese, who are said to be entirely ignorant of the nature and utility of locks. These rolling-bridges consist of a number of cylindrical rollers which turn easily on pivots, and a mill is commonly built near by, so that the same machinery may serve the double purpose of working the mill and drawing up vessels.
A Lock is a basin placed lengthwise in a river or canal, lined with walls of masonry on each side, and terminated by two gates, placed where there is a cascade or natural fall of the country; and so constructed, that the basin being filled with water by an upper sluice to the level of the waters above, a vessel may ascend thro' the upper gate; or the water in the lock being reduced to the level of the water at the bottom of the cascade, the vessel may descend through the lower gate; for when the waters are brought to a level on either side, the gate on that side may be easily opened. But as the lower gate is strained in proportion to the depth of water it supports, when the perpendicular height of the water exceeds 12 or 13 feet, more locks than one become necessary. Thus, if the fall be 17 feet, two locks are required, each having 8½ feet fall; and if the fall be 26 feet, three locks are necessary, each having 8 feet 8 inches fall. The side-walls of a lock ought to be very strong. Where the natural foundation is bad, they should be founded on piles and platforms of wood; they should likewise slope outwards, in order to resist the pressure of the earth from behind.
Plate LXIX. fig. 1. A perspective view of part of a canal: the vessel L, within the lock A C.—Fig. 2. Section of an open lock: the vessel L about to enter.—Fig. 3. Section of a lock full of water; the vessel L raised to a level with the water in the superior canal.—Fig. 4. Ground section of a lock. L, a vessel in the inferior canal. C, the under gate. A, the upper gate. G H, a subterraneous passage for letting water from the superior canal run into the lock. K F, a subterraneous passage for water from the lock, to the inferior X and Y (fig. 1.) are the two flood-gates, each of which consists of two leaves, resting upon one another, so as to form an obtuse angle, in order the better to resist the pressure of the water. The first (X) prevents the water of the superior canal from falling into the lock; and the second (Y) dams up and sustains the water in the lock. These flood-gates ought to be very strong, and to turn freely upon their hinges. In order to make them open and shut with ease, each leaf is furnished with a long lever A b, A b; C b, C b. They should be made very tight and close, that as little water as possible may be lost.
By the subterraneous passage G H (fig. 2, 3, &c.) which descends obliquely, by opening the sluice G, the water is let down from the superior canal D, into the lock, where it is flopped and retained by the gate C when shut; till the water in the lock comes to be on a level with the water in the superior canal D; as represented, fig. 3. When, on the other hand, the water contained by the lock is to be let out, the passage G H must be shut by letting down the sluice G, the gate A must also be shut, and the passage K F opened by raising the sluice K; a free passage being thus given to the water, it descends through K F, into the inferior canal, until the water in the lock is on a level with the water in the inferior canal B; as represented, fig. 2.
Now, let it be required to raise the vessel L (fig. 2) from the inferior canal B, to the superior one D; if the lock happens to be full of water, the sluice G must be shut, and also the gate A, and the sluice K opened, so that the water in the lock may run out till it is on a level with the water in the inferior canal B. When the water in the lock comes to be on a level with the water at B, the leaves of the gate C are opened by the levers C b, which is easily performed, the water on each side of the gate being in equilibrium; the vessel then falls into the lock. After this the gate C and the sluice K are shut, and the sluice G opened, in order to fill the lock, till the water in the lock, and consequently the vessel, be upon a level with the water in the superior canal D; as is represented in fig. 3. The gate A is then opened, and the vessel passes into the canal D.
Again, let it be required to make a vessel descend from the canal D, into the inferior canal B. If the lock is empty, as in fig. 2, the gate C and sluice K must be shut, and the upper sluice G opened, so that the water in the lock may rise to a level with the water in the upper canal D. Then open the gate A, and let the vessel pass thro' into the lock. Shut the gate A and the sluice G; then open the sluice K, till the water in the lock be on a level with the water in the inferior canal; then the gate C is opened, and the vessel passes along into the canal B, as was required.
It is almost needless to spend time in enumerating the many advantages which necessarily result from artificial navigations. Their utility is now so apparent, that most nations in Europe give the highest encouragement to undertakings of this kind wherever they are practicable. The advantages of navigable canals did not escape the observation of the ancients. From the most early accounts of society we read of attempts to cut through large isthmuses, in order to make a communication by water, either betwixt different nations, or distant parts of the same nation, where land-carriage was long and expensive. Herodotus relates, that the Cnidians, a people of Caria in Asia Minor, designed to cut the isthmus which joins that peninsula to the continent; but were superstitious enough to give up the undertaking, because they were interdicted by an oracle. Several kings of Egypt attempted to join the Red-Sea to the Mediterranean. Cleopatra was exceedingly fond of this project. Soliman II., emperor of the Turks, employed 50,000 men in this great work. This canal was completed under the caliphate of Omar, but was afterwards allowed to fall into disrepair; so that it is now difficult to discover any traces of it. Both the Greeks and Romans intended to make a canal across the Isthmus of Corinth, which joins the Morea and Achaea, in order to make a navigable passage by the Ionian sea into the Archipelago. Demetrius, Julius Caesar, Caligula, and Nero, made several unsuccessful efforts to open this passage. But, as the ancients were entirely ignorant of the use of water-locks, their whole attention was employed in making level cuts, which is probably the principal reason why they so often failed in their attempts. Charlemagne formed a design of joining the Rhine and the Danube, in order to make a communication between the ocean and the Black Sea, by a canal from the river Almutz which discharges itself into the Danube, to the Reditz, which falls into the Maine, and this last falls into the Rhine near Mayence: for this purpose he employed a prodigious number of workmen; but he met with so many obstacles from different quarters, that he was obliged to give up the attempt.
The French at present have many fine canals: that of Briare was begun under Henry IV., and finished under the direction of cardinal Richelieu in the reign of Lewis XIII. This canal makes a communication betwixt the Loire and the Seine by the river Loing. It extends 11 French great leagues from Briare to Montargis. It enters the Loire a little above Briare, and terminates in the Loing at Cepoi. There are 42 locks on this canal.
The canal of Orleans, for making another communication between the Seine and the Loire, was begun in 1675, and finished by Philip of Orleans, regent of France, during the minority of Lewis XV. and is furnished with 20 locks. It goes by the name of the canal of Orleans; but it begins at the village of Combleux, which is a short French league from the town of Orleans.
But the greatest and most useful work of this kind is the junction of the ocean with the Mediterranean by the canal of Languedoc. It was proposed in the reigns of Francis I. and Henry IV., and was undertaken and finished under Lewis XIV. It begins with a large reservoir 4000 paces in circumference, and 24 feet deep, which receives many springs from the mountain Noire. This canal is about 64 leagues in length, is supplied by a number of rivulets, and is furnished with 104 locks, of about eight feet rise each. In some places it passes over bridges of vast height; and in others it cuts thro' solid rocks for 1000 paces. At one end it joins the river Garonne near Thoulouse, and terminates at the other in the lake Tau, which extends to the port of Cette. It was planned by Francis Riquet in the 1666, and finished... ed before his death, which happened in the 1680.
In the Dutch, Austrian, and French Netherlands, there is a very great number of canals; that from Bruges to Ostend carries vessels of 200 tons.
The Chinese have also a great number of canals; that which runs from Canton to Pekin, extends about 825 miles in length, and was executed about 800 years ago.
It would be an endless talk to describe the numberless canals in Holland, Russia, Germany, &c. We shall therefore confine ourselves to those that are either already finished, or at present executing, in our own country.
As the promoting of commerce is the principal intention of making canals, it is natural to expect that their frequency in any nation should bear some proportion to the trade carried on in it, providing the situation of the country will admit of them. The present state of England and Scotland confirms this observation. Though the Romans made a canal between the Nyne, a little below Peterborough, and the Witham, three miles below Lincoln, which is now almost entirely filled up, yet it is not long since canals were revived in England. They are now however become very numerous, particularly in the counties of York, Lincoln, and Cheshire. Most of the counties between the mouth of the Thames and the Bristol channel are connected together either by natural or artificial navigations; those upon the Thames and Isis reaching within about 20 miles of those upon the Severn. The duke of Bridgewater's canal in Cheshire runs 27 miles on a perfect level; but at Barton it is carried by a very high aqueduct bridge over the Irwell, a navigable river; so that it is common for vessels to be passing at the same time both under and above the bridge. It is likewise cut some miles into the hills, where the Duke's coal-mines are wrought.
A communication between the Forth and Clyde in Scotland, by a navigable canal, was projected as far back as the year 1722; and on a survey was reported to be practicable. No further notice, however, was taken of this project till the 3rd of December 1761, when the right honourable Francis lord Napier, at his own expense, employed Mr Mackell to make a survey, plan, and estimate thereof, on a very small scale; only capable of carrying lighters or barges, of about 10 or 12 tons burden.
In 1764, the trustees for fisheries, &c. in Scotland, employed Mr John Smeaton to make a survey, plan, and estimate of a canal of five feet depth of water. The expense of this canal was estimated at £7,970.
In 1766, Mr Mackell was employed to make another survey, plan, and estimate, of the abovementioned small canal. A number of the most respectable merchants in Glasgow joined in the subscription for it, which was soon filled up: an application was made to parliament; and after the bill was nearly obtained, an opposition was made by the east of Scotland, on account of the smallness of the scale; being only 24 feet medium breadth, by 4 feet depth of water. Upon this, the bill was given up; and a new subscription was set on foot for a canal of 7 feet deep, estimated at £47,337.
Mr Smeaton being appointed principal engineer, and Mr Mackell resident engineer, the work was begun in June 1768; but with some deviation from the original plan, as to its origin and course. It begins at Grangeburn foot, near the mouth of Carron, where they have a very good harbour called Green Brae, for large ships; there being 18 feet of water at the sea-lock, and at very high stream-tides 21 feet. It then proceeds westward three miles, till it comes abreast with the town of Falkirk, the ground rising so little that there are only six locks in that space; though in the fourth mile, which cost about £18,000, there are no less than ten locks, and a very fine aqueduct bridge; under which the great road leading from Edinburgh, by Falkirk, to Glasgow and Stirling, passes: from the fourth mile, or 16th lock, to the east end of Dollator-bog, is six miles; and in that space there are only four locks and seven aqueduct bridges, two of which are considerable, besides small tunnels: at the east end of Dollator-bog, or tenth mile stone, is the 20th lock placed, which begins the canal of partition on the summit between the east and west sea; and which canal of partition continues no less than 18 miles on a level, passing by the south side of Kirkintulloch, and terminates at Hamilton-hill, about a measured mile from Glasgow.
The carrying the canal through the Kerlie below Falkirk was attended with little trouble in the digging, though the foundations of the six locks in that track were very troublesome; being in a quick soft mud: the carrying it through Dollator-bog, a soft moss of two miles in length, was attended with more difficulty, and was two years in executing, tho' drained as much as possible a year before the work began; and notwithstanding all this, a part had to be dragged to the depth, after the water was let in to hold down the bottom and prevent it from rising: however, that space is now one of the best parts of the whole canal. Round the point of the Stronhill, opposite to Kilflyth, the canal is banked on the north side for a considerable space above the surface of the ground about 20 feet high, and the water in that place is about 16 feet deep.
There were several places from that to Kirkintulloch to cut through free-stone rock a considerable depth; and at Kirkintulloch the canal is carried over the water of Logie on an aqueduct bridge, whose arch is 90 feet broad; which arch was thrown over in three different stretches, of 30 feet each, having only 30 feet of a centre, which was shifted on small rollers from one stretch to another. Though this was a thing new, and never attempted before with an arch of this size, yet the joinings are as fairly equal as any other part of the arch. This bridge is thought to be a very fine piece of masonry of its kind: on each side there is a very considerable banking over the valley in which the water runs, and which is made up with the soil taken out of a deep cut immediately adjoining thereto on the west side; which cut is not less than 250 yards long, and 42 feet deep.
About two miles west of this the canal goes for near half a mile thro' an open gravel, where it was thought impracticable to make it hold water, as the ground declines suddenly to the north at that place, facing the water of Kelvin; but from the precautions taken to secure that part after the canal was cut through, it proves remarkably tight.
About three miles west from that, the canal goes through the east verge of Poilie Loch; and to the westward is cut for a considerable length through a free-stone rock, gray ribs, blaes, and soil on the top, about 20 feet deep. About a mile and a half west of that, at a place called Stockingfield, the canal turns right to the south; and terminates at Hamilton-hill, within about a mile of Glasgow, where there is a commodious basin or harbour fit to hold 20 sloops at a time. The natural situation of this basin or harbour, in point of convenience for building warehouses, loading and unloading goods, is acknowledged by every person who has seen it to be exceedingly commodious.
To supply this canal with water, is itself a very great work. The first supply is from a large reservoir formed a mile east of Killyth, and supplied with water from three of the feeders of the river Kelvin; which reservoir contains about 50 acres, and is upwards of 24 feet deep. The Killyth-burn is carried into this reservoir by an expensive aqueduct of about a mile in length, and the water from the reservoir is also conducted into the canal by an aqueduct cut for that purpose. The next supply is brought by a cut made from the water of Logie, about five miles above Kirkintulloch, to carry off the spare water therefrom, and which falls into the Shirva-burn, and is carried off from that by an aqueduct of about ½ of a mile in length. The third supply is from the lakes that discharge themselves by the Muthland-burn; the water of all which is carried off by an aqueduct of about two miles in length, cut through a hill on the south-west side of Kirkintulloch, and carried into the canal at that place. The fourth supply is from Auchinloch and Loch Grog, carried into the canal by an aqueduct of about two miles in length, cut from near the mouth of the mine which drains Auchinloch, and falls into the canal at Park-burn, west of Kirkintulloch about a mile. There are several other supplies of less consequence; and were more thought necessary, or should become so when the canal is lock'd down to Clyde, a thing much wished for, there can be very great additional supplies got at a moderate expense.
In order to repay the river Kelvin for the feeders which are taken from it into the canal, a large reservoir is formed in Kilmanan muir, about seven miles north of Glasgow; consisting of 70 acres and banked up at the sluice 22 feet deep. This is thought to be the finest artificial reservoir in Britain; and amply repays the Kelvin for any feeders that can be taken from it. The water of this reservoir is conveyed down the tract of the water of Allinder, which joins the river Kelvin above the uppermost mills built thereon, and supplies the whole in time of drought.
The surface of the water in the canal of partition on the summit between the two seas, is 155 feet above the medium full-sea mark. There are 20 locks on the east side, 20 feet wide by 75 feet long, about 8 feet of rise of the summit; but 19 locks are sufficient on the west side, as the tide does not ebb below in Clyde as in the Forth by about 9 feet; which make in all 39 locks. There are no less than 18 draw-bridges and 15 aqueduct-bridges of note; besides small ones and tunnels.
It is supposed there is now £150,000 laid out upon this work. If the canal is continued from Stockingfield (where it now turns south to Glasgow), over the river Kelvin, where a great aqueduct bridge is required, and down to Clyde at or near Dalmuir-burn-foot, it is supposed the expense will be above £40,000.
The trade has increased greatly since the canal was opened to Glasgow, and vessels from 30 to 60 tons burden have found their way up it from all parts of the coasts of England and Scotland, in so much that it is thought that the revenues already amount to about £6000, and that they will still increase greatly.