CHAPTER XXXIII.

THE MAKING OF ARTIFICIAL WATERWAYS. “When, with sounds of smother’d thunder, On some night of rain, Lake and river break asunder Winter’s weakened chain; Down the wild March flood shall bear them, To the saw mill’s wheel, Or where steam, the slave, shall tear them, With his teeth of steel.” —_Whittier._ There is no direction in which the triumph of man over the material forces with which he has to deal may be studied with greater advantage, even by the casual reader and the unscientific observer, than in that of the making of railways, the deepening or widening of rivers, the construction of artificial waterways, and the maintenance of ports and harbours. Each of these operations involves the employment of machinery and appliances that were quite unknown to our forefathers. The modern processes of excavation of the soil, in order to form or deepen the bed of a waterway, or of the construction of an embankment, in order that a railway or a canal may be carried above the level of the surrounding country, are now so familiar and commonplace, that we are accustomed to think but little of the slow and laborious steps whereby the means of carrying them out have been evolved from the necessities, the experience, and the scientific acquirements of modern times. Had the engineers of the present day been limited to the rude and imperfect appliances that they had alone at command a hundred years ago, such works as the making of the Suez, the Panama, and the Manchester canals; the deepening of the harbours that are now scattered up and down our extensive coast-line; and the adaptation to the requirements of modern shipping of the navigable rivers that have done so much for our maritime supremacy would have been all but impossible. Let us take only a single instance, by way of illustration, and it shall be one that is very familiar, and easily capable of verification. On the works of the Manchester Ship Canal, in a length of only 35½miles, and over a comparatively level country, 45 million cubic yards of excavation are necessary. More than one-half of this vast quantity had been accomplished up to the end of 1889, by the employment, of 95 steam navvies or dredgers, 180 cranes, 160 locomotives, using 205 miles of temporary railway, 5500 waggons, and 220 portable and other steam engines, the number of employés being about 4000. To have executed this amount of work by any other system would have involved, perhaps, twenty times the amount of labour and more than twenty times the amount of time, if we are to judge by the accounts that have been handed down to us from ancient records as to the period over which the great works of antiquity extended. It is not, however, in the mere work of excavation, that economy and progress have been effected. Another notable economy has resulted from the employment of large hopper barges, whereby 1000 tons or more of the dredged or excavated material may at once be removed to sea. The economy resulting from this source is stated to have enabled a saving of 40,000_l._ per annum to be effected in the works connected with the port of Dublin, without which economy the improvements actually carried out there would have been impossible.[299] In larger spheres of operations the economy must, of course, have been correspondingly greater. Ralph Dodd appears to have contrived a machine to be worked by men, by means of levers, for excavating canals, which was tried in the year 1792, in the deep cutting at Dawley, near Hayes, on the Grand Junction Canal. Carne’s machine, for the same purpose, but worked by a horse at length, appears to have been used in 1794, in the deep cutting near Cofton Hacket, on the Worcester and Birmingham Canal. In the ‘Monthly Magazine’ (vol. ii., page 594) we have the following account of the operation of E. Haskew’s patent excavator:— “This machine takes the soil from the bottom of the canal at 40 feet deep with equal facility as at six feet from the surface. One of them is at work upon the Gloucester and Berkeley Canal; by the assistance of two men only it removes 1400 loaded barrows from the bottom of the canal, to the distance of 40 feet, in twelve hours, and is so contrived as to take up the loaded barrows, leave them at the top, bring down the empty ones in regular rotation, and leave them at the bottom; it can be moved along the canal to the distance of 26 yards in ten minutes by the two men that work it.” In October 1793 Joseph Sparrow took out a patent for a machine, consisting of a box, with its bottom opening on hinges, suspended by a sort of universal gib or crane, the whole moving upon wheels, which he strongly recommended for elevating and discharging the soil dug out of the canal. Among the most considerable deep cuttings in England up to the end of the last century were those at Ashton, on the Lancaster; Tring, on the Grand Junction; Coston Hacket, on the Worcester and Birmingham; Burbage, on the Kennet and Avon; Littleborough, on the Rochdale; and Smethwick, on the old Birmingham canals. As the development of the processes of excavation and embankment forms one of the fullest chapters in the history of both civil and mechanical engineering, we shall not here presume to enter upon it at any length. A history of dredgers would be almost as serious an undertaking as a history of steamboats or locomotive engines. Their actual number is legion; but the dredgers that are now used on a large scale are comparatively few. Of course, everything depends upon the amount of work to be done, its locality, and other surrounding circumstances; but for operations on a scale of magnitude, few dredgers appear to have a better reputation than that which bears the name of Couvreux. In the case of the improvement works undertaken on the Belgian Ship Canal, the Couvreux excavator removed, in 1875, 218,400 cubic yards of material in 166 days, being at the rate of 1316 cubic yards per day. Notwithstanding this, hand labour was very largely employed upon the work, a large quantity of water having to be dealt with at a depth of about 10 feet. The earth excavated was carried to spoil, and in many cases was employed to form dykes enclosing large areas, which served as receptacles for the semi-liquid material excavated by the dredging machines with the long conductors; the Couvreux excavator used had already done service on the Danube regulation works. The material with which it had to deal in this case was, however, of a more difficult nature, being a fine sand, charged with water, and very adherent. The length of track laid for the excavator was about three miles along the side of the old canal, which had been previously lowered to the level of the water. The floating dredgers employed were 88 feet 7 inches long, 19 feet 8 inches wide, and 7 feet 9 inches deep; the arm was 39 feet 4 inches long, and passed through the hull. The form of the buckets was the same as that used at the Vienna regulation works, but the staging was higher, the axis of the driving-wheel of the bucket-chain being 26 feet 3 inches above the water-level. This increased elevation was necessary on account of the different methods employed for transporting the dredged material. To a large extent the same method of transport that was adopted on the Suez Canal was repeated in the case of the Belgian Canal Works. The conductor used allowed the sand and mud excavated to be delivered at a point 140 feet and 150 feet from the dredge, and at a height of 13 feet from the water-line. The excavated materials fell into the concave conductor 6 feet below the point of their discharge, and on falling they encountered the action of a stream of water which was constantly pumped along the conductor, and by which they were converted into semi-liquid mud. The slope of the conductors was generally 1 in 2000; it was supported by cables attached to a staging connected with the framing of the dredge, and the base of which rests on the deck of the vessel. The conductor is counterbalanced by a platform, on which was placed the portable engine and pump used for lifting the water into the conductor. This platform was suspended to the dredge in the same manner as the conductor itself. The general arrangement is shown on the engraving at p. 453. The supply and the maximum incline depend on the facility of disintegrating the ground, and on the quantity of water contained in the mixture. The proportions generally used were three parts of water to one of sand. When the excavators met with compact clay which disintegrates slowly, or not at all, under the action of the water, the fragments raised were carried along in the current running through the conductor, but, of course, at a slower rate than the sand. Stones even of large size were also easily dealt with in the same manner. These materials were, however, only occasionally met with, the ground being chiefly composed of the fine sand, already referred to, mixed with a little clay, which was easily reduced to the required consistency. Deposits were formed for the reception of the excavated material, which constitute filtering basins enclosed within vaults formed by the solid materials previously removed. Where it was not possible to discharge direct into their depots by the long conductor, barges received the mud and carried it to a convenient destination. [Illustration: SYSTEM OF EXCAVATOR ADOPTED ON THE GHENT AND TERNEUZEN CANAL.] The floating excavators were placed on two hulls carrying an iron framework, on which the staging supporting the bucket wheel was mounted. The engines and boiler were installed in one of the hulls, and in the other was placed the pump and engine for driving it. The upper level of the conductor was 78 inches below the bucket wheel. The conductor, 100 feet in length, was of the section corresponding to that of the buckets, 17¾ inches in diameter. It was supported by three cables attached to a staging, resting on the boat and secured to the bucket-wheel frame. The slope was 1 in 400, which allowed the material to be deposited at a level 22 feet 3 inches above that of the water. These excavators performed excellent duty; they could be easily transported from place to place, and were not affected by changes in the water level. The position of the depots often involved the necessity of transporting the dredged material distances of 1200 or 1500 feet from the excavator. In such cases supplementary conductors were added. These were open, and were laid on the ground with a slope of 1 in 1000. Not unfrequently large blocks of old masonry, which formed the _revetment_ of the sides of the canal, were raised by the excavator. These were generally carried down with the rest of the material, but occasionally they stopped, choking the channel, and requiring hand labour to remove them. When this mode of transport could not be adopted, barges were employed to receive the dredged material and remove it to convenient points of discharge. These boats were built of iron, with double sides; they were 82 feet long and 15 feet 8 inches wide. Barges of similar dimensions were employed in the formation of earthworks under water, which were required at various parts of the canal. In these boats, holes 12 inches in diameter were placed 13 feet apart, iron tubes connecting the inner and outer shells. These holes were closed by means of valves while the boat was being loaded, and they were opened when it was brought over the place where it was desired to discharge. [Illustration: EXCAVATOR ON THE GHENT AND TERNEUZEN CANAL.] One of the most remarkable and successful dredgers of the present day is employed on the Montreal harbour and ship channel improvements, and is known as the Canadian dredger. This machine, instead of being like the ordinary St. Lawrence dredgers, attended by a tug and scows, has an internal mud-hopper, and is self-propelling, thus being in fact dredger, tug, and scows combined, and requiring a proportionately large hull. In a recent comparison of this dredger with one employed at Otago, it was stated that the Otago dredger cuts to 35 feet deep, as do those of the St. Lawrence, but the latter have buckets a third larger, and arranged so as to be very nearly twice as effective. The Otago dredger is reported to have raised at the rate of 400 tons an hour, while filling her hopper, but the improved St. Lawrence dredgers easily fill their scows at the rate of 750 tons per hour, or nearly double the working rate of the “largest dredger in the world.” For the hourly capacity for consecutive hours, something must be deducted for time lost in going to dump or to change scows, and in the case of the St. Lawrence dredgers this reduces the hourly rate to about 650 tons, still, leaving them, however, better than the best rate of the Otago dredger. Average rates for a day, or longer periods, are further reduced, for both kinds of dredgers, by detentions for shifting anchors, moving out of the channel for passing vessels, and other contingencies, not present in a mere trial of speed. The St. Lawrence dredgers, however, often raise 4800 cubic yards in twelve hours, or an average of 500 tons per hour, while, according to the published reports for a recent month, two of them raised an aggregate of 117,525 cubic yards of clay, giving an hourly average of 336 tons per dredge for 69 hours of duty per week. As a combined steamship and dredger which can be turned out complete on the Clyde for export, the Otago dredger is said to be the largest and the best thing yet built, but as a machine to dig a channel, one of these St. Lawrence dredgers is better still.[300] Another comparatively modern machine is known as the La Châtre dredger, 92 feet long, and 20 feet width of hull. It has an engine of 50 H.P., which works the chain of buckets. The material falls 2⅔ feet from the buckets into a long steel shoot 2¼ feet in width and depth, and semi-circular at the bottom, extending out 15⅓ feet from the axis of the dredger, and supported by twenty-four steel cables from shear-legs 80 feet high, standing on two iron pontoons fastened to the dredger; a pontoon on the opposite side, weighted with 32 tons of ballast, counterweights the shoot. The material is drawn along the shoot (which has a general inclination of 1 in 20, increasing close to the dredger) by water pumped into the shoot, at least double in volume the amount of material. The dredger, shortly after starting work, lifted and transported 183 cubic yards of excavation per hour. It cost about 10,800_l._ Another dredger deposited the material from the buckets on a divisor formed of two sets of revolving sharp blades, turning in opposite directions, which cut up the large pieces and discharge the material on gratings of sharp blades, through which it falls, mixed with about 85 per cent. of water, on a sheet-iron inclined plane, along which it is conveyed to the pipe of a suction pump. This Dumont 1-foot pump, specially designed for silt, stands with its engine on a pontoon alongside the dredger. Another similar pump draws along the silt discharged by the first, and discharges it into a 1-foot iron pipe. The silt is deposited from 650 to 1000 feet away, at a height of 16 to 20 feet, with a velocity of about 13 feet per second. The mound formed at the outlet of the pipe has a very flat slope, but the settlement is rapid and complete. The dredger was able at once to lift and transport 130 cubic yards per hour, and this amount will probably be eventually raised to 160 cubic yards. This dredger is said to have cost 12,800_l._, with its accessories. In the construction of the Amsterdam Ship Canal, the excavations had to be deposited on the banks some distance away from the dredgers; and after being raised by the ordinary bucket dredger, instead of being discharged into barges, they were led into a vertical chamber on the top side of a sand-pump, suitable arrangements being made for regulating the delivery. The pump known as Burt and Freeman’s was 3½ feet in diameter, and made about 230 revolutions per minute; it drew up the water on the bottom side, and mixing with the descending mud on the top side, the two were discharged into a pipe 15 inches in diameter. The discharge-pipe was a special feature in this work, and consisted of a series of wooden pipes jointed together with leathern hinges, and floated on buoys from the dredger to the bank. In some cases the pipe was 300 yards long, and discharged the material 8 feet above the water-level. Each dredger and pump was capable of discharging an average of 1500 cubic yards per day of twelve hours. A centrifugal sand-pump, designed by Mr. Hutton, was also used on those works. At Hull, the cost of dredging on the Humber, including everything except interest on capital and depreciation, is stated to be 2·1_d._ per ton. The material is mud, varying in consistency, and it is discharged about 1½ miles from the docks by steam hoppers, and by ordinary mud-barges and tugs. On the Clyde, the average cost, including everything—depreciation, interest, and carrying in hopper barges 27 miles—is as follows:—Very hard clay, boulders, and sand, 30·15_d._ per cubic yard; hard silt, gravel, and sand, 24·17_d._; silt, clay and sand, 8·49_d._; silt, gravel, sand, clay, and mud, 8·08_d._; and silt and sand, 7·94_d._ per cubic yard. On the Tyne, the cost varies from 2_d._ to 6½_d._ per ton, according to the nature of the material. One dredger has dredged over 1,000,000 tons in one year, and, including discharging a distance of 17 or 18 miles, the cost per ton was a little over 3½_d._ The cost of removing the bar at Carlingford Lough, including everything—Parliamentary expenses and insurance of plant—was about 1_s._ 9_d._ per ton. Taking the cost for one season, it was 1_s._ 4_d._ to 1_s._ 5_d._ per ton, or 2_s._ to 2_s._ 3_d._ per cubic yard. The material was hard clay and boulders. At Aberdeen, the cost of dredging and transporting about 2 miles beyond the bar, including insurance, but not depreciation and interest, is 1_s._ 2_d._ per ton for dredging, and 2·9_d._ for discharging, giving a total of 4_s._ 1_d._ per ton. On the Wear, at Sunderland, the total cost of dredging, including every item of depreciation and interest, is 2·37_d._ per ton. The material consists of sand, gravel, and clay. On the Tees, at Stockton and Middlesbrough, the cost of dredging sand, gravel, and occasionally boulders, including the conveyance of deposits out to sea, a distance of about 12 miles, is 4·96_d._ per cubic yard or about 2½_d._ per ton. This amount includes everything except interest on capital expended on dredging plant. On the Birmingham Canal., when there has been any slipping of the sides, or a discharge into it of water laden with silt and detritus from cuttings and high lands, the material, if soft, costs 5_d._ to 9_d._ per ton to dredge; and if hard, from 10_d._ to 14_d._ per ton. With a “spoon dredger” the cost is about 8_d._ per ton, and with a grab dredger it is about 5_d._ where the circumstances are favourable.[301] Where hard material has to be dealt with, the water is taken out of the canal, and the material is excavated by pick and shovel. On narrow canals dredging costs more, owing to the necessity of having a narrow beam, to enable the dredger to enter the canal. The beam is, however, sometimes increased when the machine is working by attaching baulks of timber or iron pontoons to the sides, to prevent its capsizing.[302] The dredging machines that were chiefly employed on the Danube regulation works were, on an average, from 25 to 30 H.P., and had one inclined arm, which could be depressed to work in a depth of 22 feet of water or more. They were high enough to load direct into the waggons, by means either of a distributing table or an elevating endless chain bucket. The dimensions of the machine, which was found to be very economical, were: ft. in. Length of boat 88 7 Breadth ” 19 8 Height ” 7 9 Draught of water 3 11 The working steam pressure was six atmospheres, and the power consisted of a vertical engine of 15¾ inches cylinders and 35-7/16 inches stroke; the main shaft was 7-1/16 inches in diameter, and the ratio of the pinion to the driving-wheel was 1 to 7. The buckets were of steel, having a capacity of 8·75 cubic feet. The links of the chain were 31½ inches long, 1¾ inch by 3½ inches for those to which the buckets were attached, and 15/16 inch by 3½ inches for the others. These machines were employed in several different ways on the Danube works. They load direct into waggons, running upon a side track, either by means of a transporting apparatus or of an elevating wheel and buckets. The transporting apparatus was attached to the dredge, and consisted of a girder about 46 feet long, guiding and carrying an endless band formed of steel plates mounted on chains, which were driven by wheels at each end of the girder. The buckets of the dredging machine discharged their contents upon this band, to which a forward motion was imparted by an independent six-horse power engine, and the forward movement thus given discharged the ballast in the waggons alongside. The whole of this system rested at one end on the deck of the drag, and at the other on trestles, secured in a small auxiliary boat fastened alongside the machine. It was afterwards considered that a useful alteration might be made in the means of transferring the ballast, and with this object a large wheel, fitted with buckets, was mounted on the dredge, and driven by an independent engine. The wheel was of wrought iron, 19 feet 8 inches in diameter, and furnished with buckets which received the ballast from those of the dredging machine, and, after raising, discharged it into an open channel, whence it fell into the waggons. The buckets of this wheel were fixed to the periphery, and were so arranged as to discharge automatically into the channel. It was found that this mode of loading produced excellent results, but the full capacity of the dredgers could not be developed, both on account of the loss of time incurred, and because the material dredged was not always easily transferred into the waggons. A large quantity of the material excavated was also loaded into barges and taken by them to suitable points of discharge. The amount of work performed by the dredging machines depended greatly on the means available of removing the earth excavated, and to do this with regularity, and without loss of time, was one of the most difficult portions of the work of excavation. During 1870 and 1871 the dredging machines loaded almost exclusively into the waggons by means of the endless bands already described. Two of them were worked exclusively in this manner; other two began to load into boats in 1872, and the following year this method was entirely adopted with them, and their production was remarkably large. Another machine loaded the waggons by means of the large wheel. The dredging machines employed on the first and third sections of the works, and which also loaded into boats, gave remarkable results. The Condreux excavating machine consists essentially of a carriage carried upon three lines of rails. A lateral projecting arm carries an endless chain with buckets, passing around a wheel at the lower end of the arm. This chain is driven by a 20 horse-power engine, mounted on the frame of the carriage, and the whole machine is caused to traverse on the rails by means of a small four-horse locomotive. The buckets, which become filled in succession in traversing the face of the slope, being excavated, are of steel plate or of wrought iron mounted with steel edges. The buckets are mounted on two pitched chains, which, in rising, pass over a loose pulley placed at the level of the road, and serve as a support to the loaded buckets. This arrangement largely reduces the friction, and prevents excessive torsion of the chain. The loaded buckets are discharged automatically, by means of flap openings in their bottoms, and their contents fall either into the waggons alongside, or into inclined conducting channels. These machines run alongside, and at the top of, the excavations they make, and the earth which they raise can be either deposited alongside so as to form a continuous embankment, or be loaded into waggons. On the Mersey Dock Estate, which extends over a total water area of 520 acres, the dredgers used up to 1875 were of the ladder type, five of them having double, and one single ladders. A double set of hopper barges was attached to each dredger. The barges were 50 feet long by 20 feet beam, and contained 82 cubic yards. The expense of towing the barges out to the Seacombe Narrows, where they deposited their silt, rendered the operations costly, and in 1874 a steam hopper barge was brought into use, 144 feet long, 23 feet beam, 11 feet 9 inches depth of hold, and with a hopper capacity of 285 cubic yards. In 1876 two other hopper barges of the same size were brought into use. Subsequently, larger barges, with a hopper capacity of 414 cubic yards, were introduced. These have been found much more economical than the old system. FOOTNOTES: [299] Paper on ‘Recent Improvements in the port of Dublin,’ read in 1878 before Section G of the British Association. [300] Mr. Kennedy, chief engineer of Montreal, in _Engineering_, September, 1881. [301] Paper by Mr. G. R. Jebb on “The Maintenance of Canals,” &c., in the ‘Journal of the Society of Arts’ for 1888. [302] On the Birmingham Canal, which has an average top width of 36 feet, and an average depth of 5 feet, this has to be done with a Priestman Grab Dredger, but it causes very little trouble.