AQUEDUCT
A QUEDUCT, a conduit or channel for the conveyance of water (Lat. aquaeductus), but commonly a structure of masonry erected to conduct water across a valley at a high level, though structures of this kind would be more properly termed aqueduct bridges. This distinction it is necessary to bear in mind, more particularly when dealing with the undertakings of this class carried out by the Greeks and Romans respectively, because, from the fact of the former having apparently seldom if ever constructed aqueduct bridges, it has been usual to institute a very unfavourable comparison between them and the Romans, who, with imperial disdain of obstacles, furnished the cities of their immense empire with a series of constructions of this kind for the supply of water, which still in their ruins excite our astonishment. True to the difference in national genius the Greeks, following the analogy of nature, in which in their own country they saw the water collected in the hills passing for miles along subterranean courses, and issuing in cool fountains at the coast, adapted their system of conduits to the physical formation of a district, cutting tunnels and canals, rather than bridging over valleys, and as a consequence no conspicuous monument of their system now remains. But even if what they did was so little as to justify Strabo (v. p. 235) in charging them with neglect in this matter as compared with the carefulness of the Romans, it is still clear from the records that they accomplished much, and that in this, as in other respects, they were the instructors of the Romans. It is here to be premised that the term aqueduct applies only to the conveyance of such water as was used for drinking or other useful purposes, and not to the draining of marshes, though in both cases the works may often have been of the same kind. The insufficiency of water, supplied by natural springs and cisterns hewn in the rock, which in an early age had satisfied the small communities of Greece, had become a pressing public question by the time of the Tyrants, of whom Polycrates of Samus and Pisistratus of Athens distinguished their rule by extensive works to meet the exigencies of their states. For this purpose the former obtained the services of Eupalinus, an engineer celebrated for the skill with which he had earned out the works for the water supply of Megara, under the direction of the Tyrant Theagenes (circa 625 b.c. ) At Samus the difficulty lay in a hill which rose between the town and the water source. Through this hill Eupalinus cut a tunnel 8 feet broad, 8 feet high, and 4200 feet long, building within the tunnel a channel 3 feet broad and 11 ells deep. The water, flowing by an accurately reckoned declivity, and all along open to the fresh air, was received at the lower end by a conduit of masonry, and so led into the town, where it supplied fountains, pipes, baths, eloaeae, <fcc., and ultimately passed into the harbour. In Athens, under the rule of Pisistratus (b.c. 560), a similarly extensive, if less difficult, series of works was completed to bring water from the hills Hymettus, Pentelicus, and Parnes. From Hymettus were two conduits passing under the bed of the Uιssus, and most part of the course cut in the rock. Pentelicus, richer in water, supplied another conduit, which can still be traced from the modern village of Chalandri by the air shafts built several feet above the ground, and at a distance apart of 40-50 metres; the diameter of these shafts is 4-5 feet, and the number of them still preserved is about sixty. Tributary channels conveyed into the main stream the waters of the district through which it passed. Outside Athens, those two conduits met in a large reservoir, from which the water was distributed by a ramification of underground channels throughout the city. These latter channels vary in form, being partly round, partly square, and generally walled with stone; the chief one, that under the bazaar, is sufficiently high and broad to allow two men to pass in it. Sometimes pipes of baked clay were laid within them. The conduit from Mount Parnes appears to have been reconstructed in later times. Some of these aqueducts continue to supply Athens to this day, and are described as marvels of enterprise and skill (E. Curtius, über die Wasserbauten der Hellenen, in the Archäol. Zeit. 1847, p. 19). In Sicily, the works by which Empedocles, it is said, brought the water into the town of Selinus, are no longer visible; but it is probable that, like those of Syracuse, they consisted chiefly of tunnels and pipes laid under ground. The system of conduits in Syracuse which Thucydides says (vi. 100) the Athenians partly destroyed on the Sicilian expedition, still supplies the town with an abundance of drinkable water; and at one point, where the tunnel passes under the sea to the island of Ortygia, presents what has long been regarded as a remarkable achievement for early times. An example of what appears to have been the earliest form of aqueduct in Greece has been discovered in the island of Cos (Ross, Inselreise, iii. p. 131), beside the fountain Burinna on Mount Oromedon. It consists of a bell-shaped chamber, built underground in the hill side, to receive the water of the spring and keep it cool; a shaft rising from the top of the chamber supplied fresh air. From this reservoir the water was led by a subterranean channel, 35 metres long and 2 metres high.
Of the constructions for the conveyance of water in Italy in early times, there is an example at Tusculum, consisting of an oblong basin, divided into several chambers, which received the water of a spring, and then distributed it by pipes (tubi, fistuloe) or canals. The basin is built of blocks of stone, which, along the sides, overlap each other, till they meet and form a roof—a principle of building which was afterwards supplanted by vaulting, and which occurs also in the earliest Greek masonry. The pipes were either of lead or baked clay. When the course lay in soil, gullies were cut and conduits of masonry built within them. When rocky ground intervened, tunnels were pierced, and in both cases shafts (spiramen, lumen) were made at intervals of about 240 feet, to admit light and fresh air. The inside of the walls of these channels received a coating impervious to water, composed of chalk and erushed fragments of tile. Where the course was interrupted by an inequality in the ground, a vertical pipe (venter) was placed reaching to the surface or above it. The water rushing up this pipe was freshened by contact with the air, and again fell back to the new course which it had to take. Works of this kind, undertaken for the public convenience, were paid for out of the public purse, a tax being levied for the use of the water.
If, to obtain a proper incline, the water-course had to be carried above ground, the simple plan was to support it on a stone wall, and in this case the conduit itself was also built of blocks of stone, coated with a stucco impervious to water. But since a solid wall across a valley would have cut off the usual traffic, it was found necessary to break up the wall, by means of arches, into a series of pillars, and with this commenced the system of aqueduct bridges, which have proved to be the most striking monuments of the Roman empire. As perhaps the best known instance of this double purpose, of an archway under which traffic might pass, and over which water might be conveyed, there is the Porta Maggiore at Rome (Plate III.) The waters conveyed over it in two separate channels, are the Aqua Claudia and the Anio Novus, and from the three inscriptions above the arches it appears (1.)—that the Emperor Claudius had constructed the so-called Aqua Claudia Aqueduct from the springs Caeruleus and Curtius, 45 miles from Rome; (2.) that the same emperor had constructed the so-called Anio Novus Aqueduct from the 6 2d milestone from Rome; (3.) that the Emperors Vespasian and Titus had restored these splendid undertakings of Claudius. Both aqueducts had been begun by Caligula, 38 a.d., and were completed ten years after by Claudius. The two springs from which the Aqua Claudia took its rise were in the Sabine hills near the 35th milestone, on the Via Sub-lacensis. It was augmented by part of the Aqua Martia, famous for the goodness of its water, and, owing to bends in the course, reached the length of 45 miles, as stated in the inscription, 35 miles of it being under and 10 above ground. The Anio Novus, so called to distinguish it from an older aqueduct, the Anio Vetus, took its rise in the river Anio at the 62d milestone, on the road just named, the water being first collected in a large basin, where it was allowed to purify itself. At the 32d milestone it was augmented by the clearer water of the spring, rivus Herculaneus. The entire length of 62 miles was partly above and partly below ground. About 6 miles from Rome it approached the Aqua Claudia, and from that point the two waters travelled together to the city in two distinct channels, one above the other, and supported by a chain of arches, which at one place reached the height of 109 feet. But in height these arches must yield to those of the aqueduct at Nismes, the ancient Nemausus, erected in the time of Augustus, which rose to 180 feet. *Γhe Pont du Gard, as the aqueduct at Nismes is now called, consists, as will be seen from Plate IV., of three rows of arches striding acrose the valley of the river Gardon. In the lowermost row are six arches, of which one has a span of 75 feet, the others each 60 feet. In the second row are twelve arches, each with a span of 75 feet. In the third row are thirty-six smaller arches, immediately above which was the water-course. As a bridge, the Pont du Gard has no rival for lightness and boldness of design among the existing remains of works of this class carried out in Roman times.
Besides the two principal aqueducts at Rome already described, there remain to be noticed twelve more which assisted in the supply of water for the city. These are (1.) Aqua Appia, which took its rise at the foot of the Alban mountains on the Praeneste road, between the 7th and 8th milestones, and measured from its source to the Porta Trigemina 11,180 paces, of which 11,130 were below ground. It appears to have been the first important enterprise of the kind at Rome, and was the work of the old Censor Appius Claudius, from whom ‘it derived its name. The date of its construction was the year of Rome 442, according to Frontinus, an overseer of aqueducts (curator aquarum) under the empire, whose work De Aquoeduct. urb. Rornae we still possess. (2.) Anio Vetus, constructed forty years after the last-mentioned aqueduct, by the Censor Manlius Curius Dentatus, with the help of L. Papirius Censor, who finishedit. From its source near Tivoli, on the left side of the Anio, it flowed 43,000 paces, of which 42,779 were below ground, and 221 above. At the distance of 2 miles from Rome (Frontinus, i. 21) it parted into two courses, one of which led to the horti asiniani, and was thence distributed; while the other (rectus ductus) led by the temple of Spes to the Esquiline gate, the site of which was near the modern Villa Negroni, where, in 1861, was found a subterranean conduit and an inscribed stone, which left no doubt as to its having been one of the stones set up to mark the distances of the Anio Vetus. (3.) Aqua Martia, rising on the left side of the Via Valeria, traversed 61,710 paces, of which 54,247 were underground, and the remaining distance carried partly on solid wall and partly on arches. It was the work of Quintus Martius Rex, not of Ancus Martius the fourth king of Rome, as Pliny (N.H., xxxi. 3) fancied, and took its name from its constructor. Its waters were celebrated for their coolness and excellent quality. (4.) Aqua Tepula, from its source in the district of Tusculum, flowed 10,000 paces, mostly above ground, and on the 4 same series of arches as carried the Aqua Martia, but at a higher level. It was the work of the Censors Cn. Servilius Caepio and L. Crassus Longinus, and was completed in the year 126 b.c. Again, partly on the same structure of arches, and with a still higher channel, flowed—(5.) Aqua Julia, from a source near that of the last-mentioned aqueduct to within 7000 paces of the walls of Rome, where the joint waters were received in a reservoir, and thence distributed in various channels to the city. Its entire length was 15,426 paces. It was constructed in the year 34 b.c. by Marcus Agrippa, to whose zeal to meet public wants in this direction were due the two other aqueducts— (6.) Aqua Virgo, and (7.) Aqua Crabra or Damnata, the former as well known for the goodness of its water as was the latter for the inferiority which procured it the designation of Damnata. The Aqua Virgo, from its origin at a copious spring in a marsh on the Collatine way, not far from the ancient Gabii, measured 14,105 paces, along which it was conveyed in pipes, partly under and partly above ground, on a solid substructure or on arches. It was completed in the year 48 b.c. (8.) Aqua Alsie-tina or Augusta rose in Etruria, on the Via Claudia, and travelled 22,172 paces, of which 358 were on arches. It was the work of Augustus, whose object was to furnish by it water for gardens and other than drinking purposes. (9.) AquaTrajana, rising in Lake Sabatinus (Bracciano), was constructed by Trajan. (10.) Aqua Alexandrina, rising in the district of Tusculum, was the work of Alexander Severus. (11.) Aqua Septimi ana seems to have been only a branch led from the Aqua Julia to supply the baths of the emperor from whom it takes its name, Septimius Severus. (12.) Aqua Argentina rose on Mount Algidus; at whose instance it was made is unknown. Of the fourteen aqueducts which supplied ancient Rome, three remain in use at the present time, furnishing the modern city with abundance of water. The first of the three is the Aqua Virgo, now known as Fontana di Trevi, supplying the best water in Rome. It was restored by Pope Pius IV. The next is the Aqua Claudia, known as the Aqua Felice or di Termini, which was restored by Sixtus V. The third is the Aqua Trajana, called, from the Pope who restored it, viz., Paul V., Aqua Paole.
At regular intervals along the course of an aqueduct were built reservoirs (castella), to enable repairs to be made at any point, and also to let off water for the population of the district through which it passed. It was the law that material necessary for repairs should be supplied from the private property nearest to where the damage was, and should be conveyed at the cost of the owner of such property. Castella of smaller dimension were also required in many parts of the city. Of these, it was said, there were 247 in Rome. To allow the water to purify itself before being distributed in the city, large basins (piscinae limariae), were built outside the walls. For the process of purification salt was used (Vitruvius, viii.) These piscinae were covered in with a vaulted roof, and were usually on a colossal scale, as in the example still preserved at Fermo, which consists of two stories, each having three oblong basins communicating with each other; or the Piscina Mirabile at Baiae, which is covered in by a vaulted roof, supported on forty-eight pillars, and perforated to permit the escape of foul air. Two stairs lead by forty steps to the bottom of the reservoir. In the middle of the basin is a sinking to collect the deposit of the water. The walls and pillars are coated with a stucco so hard as to .resist a tool. The oversight of aqueducts was placed, in the times of the republic, under the aediles and censors, though the latter appear to have taken part in work of this kind rather from their financial interest in the matter. Under the empire this task devolved on special officials styled Curatores Aquarum.
Among aqueducts outside of Italy, constructed in Roman times and existing still, the most remarkable, next to the Pont du Gard at Nismes already described, are—(1.) The aqueduct bridges at Segovia and Tarragona in Spain, the former being 2400 feet long, with 159 arches of greatly admired masonry, in two tiers, and reaching the height of 102 feet. The bridge at Tarragona is 876 feet long, and 83 feet high. (2.) At Mayence are the ruins of an aqueduct 16,000 feet long, and carried on from 500 to 600 pillars. Similar witnesses of Roman occupation are to be seen in Dacia, Africa, and Greece. (3.) The aqueduct at Metz (figured on Plate IV.), which originally extended across the Moselle, here very broad, conveyed to the city an abundance of excellent water from Gorsa. From a large reservoir at the source of the aqueduct the water passed along subterranean channels built of hewn stone, and sufficiently spacious for a man to walk in them upright. Similar channels received the water after it had crossed the Moselle by this bridge, at the distance of about 6 miles from Metz, and conveyed it to the city. The bridge consisted of only one row of arches. The middle arches have given way under the force of the river, but the others are still perfectly solid. (4.) On Plate III. is figured one of the principal bridges of the aqueduct of Antioch, 700 feet long, and at the deepest point 200 feet high. The lower part consists almost entirely of solid wall, and the upper part of a series of arches with very massive pillars. The masonry and design are rude. The water supply was drawn from several springs at a place called Battelma, about 4 or 5 miles from Antioch. From these separate springs the water was conducted by channels of hewn stone into a main channel, similarly constructed, which traversed the rest of the distance, being carried across streams and valleys by means of arches or bridges. (5.) At the village of Morea, about an hour’s distance N.W. from the town of Mytilene, is the bridge of an aqueduct, figured on Plate III. The water-course is carried above massive pillars built of large hewn blocks of grey marble, and connected by means of three rows of arches, of which the uppermost is of brick. The bridge extended about 500 feet in length, and at the deepest was from 70 to 80 feet high. Judged by the masonry and the graceful design, it has been thought to be a work of the age of Augustus. Remains of this aqueduct are to be seen at Larisson Lamarousia, an hour’s distance from Morea, and at St Demetri, two hours and a half from Ayasso, on the road to Vasilika.
The aqueduct near Spoleto, which now serves also as a bridge, is deserving of notice as an early instance of the use of the pointed arch, belonging as it does to the 7th or 8th century. It has ten arches, remarkable for the elegance of their design and the airy lightness of their proportions, each over 66 feet in span, and about 300 feet in height. (See Plate IV.)
The aqueduct of Pyrgos, near Constantinople (figured on Plate III.), is a remarkable example of works of this class carried out in the later times of the Roman empire. It consists of two branches, of which only one is seen in elevation on the plate. The other branch stood nearly ^,t right angles to this, and is seen partly on the plan. From this circumstance it was called the Bended or Crooked Aqueduct, to distinguish it from another termed the Long Aqueduct, situated near the source of the waters. The branch seen in elevation extends 670 feet in length, and is 106 feet in height at the deepest part. It is composed of three rows of arches, those in each row increasing in width from the bottom to the top—an arrangement very properly introduced with the view of saving materials without diminishing the strength of the work. The two upper rows consisted of arches of semicircles, the lower of Gothic arches; and this circumstance serves to fix the date of the structure, as these last were not introduced until the 10th century. The breadth of the building at the base was 21 feet, and it diminished with a regular batter on each side to the top, where it was only 11 feet. The base also was protected by strong buttresses or counterforts, erected against each of the pülars. The other branch of the aqueduct was 300 feet long, and consisted of twelve semicircular arches.
This aqueduct serves to convey to Constantinople the waters of the valley of Belgrade, one of the principal sources from which the city is supplied. These are situated on the heights of Mount Haemus, the extremity of the Balkan Mountains, which overhangs the Black Sea. The water rises about 15 miles from the city, and between 3 and 4 miles west of the village of Belgrade, in three sources, which run in three deep and very confined valleys. These unite a little below the village, and then are collected into a large reservoir. After flowing a mile or two from this reservoir, the waters are augmented by two other streams, and conveyed by a channel of stone to the Crooked Aqueduct. From this they are conveyed to another which is the Long Aqueduct; and then, with various accessions, into a third, termed the Aqueduct of Justinian. From this they enter a vaulted conduit, which skirts the hills on the left side, of the valley, and crosses a broad valley 2 miles below the Aqueduct of Justinian, by means of an aqueduct, with a double row of arcades of a very beautiful construction. The conduit then proceeds onward in a circuitous route, till it reaches the reservoir of Egri Kapan, situated just without and on the walls of the city. From this the water is conducted to the various quarters of the city, and also to the reservoir of St Sophia, which supplies the seraglio of the grand signior. The Long Aqueduct is more imposing by its extent than the Crooked one, but is far inferior in the regularity of design and disposition of the materials. It is evidently a work of the Turks. It consists of two rows of arcades, the lower being forty-eight in number, and the upper fifty. The whole length was about 2200 feet, and the height 80 feet. The Aqueduct of Justinian is a very excellent work, and without doubt one of the finest monuments which remain to us of the Middle Ages. It consists of two rows of large arcades in the pointed style, with four arches in each. Those of the lower story have 52 feet of span, the upper ones 40 feet. The piers are supported by strong buttresses, and at different heights they have little arches passing through them, which relieve the deadness of the solid pillar. The length of this aqueduct is 720 feet, and the height 109 feet. This aqueduct, though it bears the name of Justinian, was probably erected in the time of Constantine.
Besides the waters of Belgrade, Constantinople was supplied from several other principal sources, one of which took its rise on the heights of the same mountains, 3 or 4 miles east of Belgrade. This was conveyed in a similar manner by an arched channel, elevated, when it was necessary, on aqueduct bridges, till it reached the northern parts of the city. It was in the course of this aqueduct that the contrivance of the souterasi or hydraulic obelisks, described by Andreossy (in his voyage to the Black Sea and account of the Thracian Bosphorus) was constructed, which excited some attention, as being an improvement on the method of conducting water by aqueduct bridges. “The souterasi,” says Andreossy, “are masses of masonry, having generally the form of a truncated pyramid or an Egyptian obelisk. To form a conduit with souterasi, we choose sources of water, the level of which is several feet higher than the reservoir by which it is to be distributed over the city. We bring the water from its sources in subterranean canals, slightly declining until we come to the borders of a valley or broken ground. We there raise on each side a souterasi, to which we adapt vertically leaden pipes of determinate diameters, placed parallel to the two opposite sides of the building. These pipes are disjoined at the upper part of the obelisk, which forms a sort of basin, with which the pipes are connected. The one permits the water to rise to the level from whence it had descended; by the other, the water descends from this level to the foot of the souterasi, where it enters another canal under ground, which conducts it to a second and to a third souterasi, where it rises and again descends, as at the last station. Here a reservoir receives it and distributes it in different directions by orifices of which the discharge is known.” Again he says, “it requires but little attention to perceive that this system of conducting tubes is nothing but a series of syphons open at their upper part, and communicating with each other. The expense of a conduit by souterasi is estimated at only one-fifth of that of an aqueduct with arcades.” There seems to be really no advantage in these pyramids, further than as they serve the purpose of discharging the air which collects in the pipes. They are in themselves an evident obstruction, and the water would flow more freely without any interruption of the kind. In regard to the leaden pipes, again, they would have required, with so little head pressure as is stated, to be used of very extraordinary dimensions to pass the same quantity of water as was discharged along the arched conduits. There is something, therefore, which would require explanation in the account Andreossy gives of these pyramids, if, indeed, he did not misunderstand the nature of them.
The other principal source from which Constantinople is supplied, is from the high grounds 6 or 8 miles west of the town, from which it is conducted by conduits and arches, in the same manner as the others. The supply drawn from all these sources, as detailed by Andreossy, amounted to 400,000 cubic feet per day. The charge of the water-works at Constantinople belongs to a body of 300 Turks and 100 Albanese Greeks, who form almost an hereditary profession.
In ancient Egypt and Babylonia a different problem of water supply was presented, both countries being flat and traversed by great rivers, from which they were subject to regular inundations. Hence canals with large basins took the place of the aqueducts of Greece and Rome, and the stupendous scale on which in Egypt the waters of the Nile, and in Babylonia the waters of the Tigris and Euphrates, were utilised, was a marvel to ancient travellers.
In France various aqueducts have been formed after the manner of the Romans. The most remarkable are those constructed in the reign of Louis XIV., at vast expense, for conducting water from Marly to Versailles. The famous aqueduct bridge of Maintenon, which was erected for conveying the waters of the river Eure to Versailles, is without doubt, in point of magnitude and height, the most magnificent structure of the kind in the world. In Plate IV. a view is given of a portion of this work, on the same scale as the others there represented. Had the whole been delineated on the same scale, it would have extended to four times the breadth of the plate. It extends about 4400 feet in length, that is, about five-sixths of a mile, is upwards of 200 feet in height, and contains 242 arcades, each divided into three rows, forming in all 726 arches about 50 feet span. Of the subterranean aqueducts in France the finest is that of Arcueil, which serves to conduct water to that village. It is 44,300 feet in length, or upwards of 8 nailes, extending from the valley of Arcueil to the castle at the gate of St Jaques, all built of hewn stone. It is about 6 feet in height, and has on each side a foot-path 18 inches wide; it has a declivity of 1 foot in 1300. Another aqueduct of this kind is that of Rocquancourt, part of the system which brings water to Versailles; it is 11,760 feet in length, or upwards of 2 miles, and has a declivity in its whole course of only 3 feet. In some parts of its course it was necessary to make excavations 80 or 90 feet deep, which rendered the execution very difficult.
The great waterworks that supply the city of Marseilles with the water of the Durance, by a canal about 60 miles in length, are among the boldest undertakings of the kind in modern times. This canal, begun in 1839, and completed in 1847, is conveyed through three chains of limestone mountains by forty-five tunnels, forming an aggregate length of 8∣ miles, and across numerous valleys by aqueducts; the largest of which, the Aqueduct of Roquefavour, over the ravine of the River Arc, about 5 miles from Aix, surpasses in size and altitude the ancient Pont du Gard. The immense volume of water, which passes at the rate of 198,000 gallons per minute, is carried across as in the old Roman aqueducts by a channel of masonwork. The height of this aqueduct is 262 feet, and its length 1287.
One other aqueduct of modern construction is worthy of notice. In those parts of British India where the fall of rain is scanty and uncertain, recourse is had to artificial irrigation, and the waters of many of the rivers of the country have been rendered available for this purpose by means of public works constructed by the Government. Of these the most important is the Ganges Canal, which traverses the North-Western Provinces of Bengal, and distributes over their vast area nearly the whole volume of the waters of the Ganges. The canal begins at the point where the river issues from the mountains, and enters the plains of Bengal. About 20 miles from its source, the line of the canal crosses the valley of the Solani river, and the works for effecting the transit are designed on a scale worthy of the undertaking. The valley is between 2 and 3 miles in width. An earthen embankment is carried across, raised on an average between 16 and 17 feet above the surrounding country, and having a width of 350 feet at its base, and 290 feet in the upper part. This embankment forms the bed of the canal, which is protected by banks 12 feet in depth, and 30 feet wide at the top. To preserve these banks from the effects of the action of the water, lines of masonry formed into steps extend on each side throughout their entire length. The Solani river is crossed by an aqueduct 920 feet long, having side walls 8 feet thick and 12 deep, the depth of the water being 10 feet. The water of the canal passes through two separate channels. That of the River Solani flows under fifteen arches, having a span of 50 feet each, constructed in the most substantial manner, and springing from piers resting on blocks of masonry sunk into the bed of the river. The cost of the aqueduct was upwards of <£160,000. In grandeur of design, solidity of construction, and, above all, in extensive utility, it may challenge competition with any similar work in the world.
Within the last century, the invention and improvement of the manufacture of cast iron has completely changed the mode of conducting water into cities, by the introduction of cast-iron pipes instead of the stone conduits of former times. These pipes can now be formed of almost any dimensions, and united together into a continued series so closely as to prevent the escape of the water even under a violent pressure, arising from the altitude of the fountainhead. They enable us, therefore, to take advantage of and give effect to the fundamental principle of hydrostatics, that the fluid tends continually to a level, even though it be confined in the smallest or most complicated system of pipes ; so that however low it be carried in any valley, or to whatever distance, still it will rise on the opposite side to the original altitude of the fountainhead—a principle which is most important indeed in such works, seeing that by it we are not restricted, as the Romans were, almost to a perfect level in the line of the conduit. We have seen that, for the purpose of attaining this level or very gentle declivity all along the conduit, they were under the necessity of raising it by arcades continued in one unbroken series, frequently 30 or 40 miles in extent; and, in addition to this, they had often to prolong the length of the track by a circuitous route, turning and winding for miles out of its course, for the very purpose of increasing its length.
But the use of pipes enables us to dispense with these long arcades all raised nearly to the same level with the fountainhead; because the conduit may be varied in its level to any extent, and still will rise at last to its original altitude. The pipes, therefore, are merely laid all along the surface of the ground, with a cover of 2 or 3 feet of soil to place them beyond the reach of frost. To prevent, however, the frequent or abrupt alternations of rise, and fall, any sudden inequalities in the ground are equalised by cuttings and embankments, but not to anything like the extent that would be required to raise the whole to a level. This,’therefore, forms a very great improvement in the method of conducting water, the greatest indeed which has ever been made in this important branch of practical mechanics. That it was not introduced by the Romans, is not to be ascribed, as many have supposed, to their ignorance of the hydrostatic principle that the fluid would rise to a level in the opposite branches of the same train of pipes. They were well acquainted with this principle, and a portion of a leaden pipe, supposed to have been used in the baths of Caracalla, has been found, which sets this matter at rest; but, from the low state of the arts at that period, they were unable to give effect to the principle. They had not the means of fabricating pipes of such a magnitude as would have been required for the enormous quantities of water consumed in Rome, and at the same time, of strength sufficient to withstand the pressure from the fountainhead. Lead was the only material that could be used by them for the purpose; and besides the enormous thickness that so weak a material would have required, and the impracticability of their forming pipes, and uniting them together endwise, they were too well acquainted with the tendency of lead to render the water unwholesome by its poisonous impregnation. The use of cast iron was quite unknown. There remained, therefore, no resource but in the aqueducts, which, though attended no doubt with vast expense, and requiring great enterprise, skill, and patience, were yet attainable by these means, and formed when completed a simple and very perfect mode of effecting the object. Now, however, when the manufacture of cast iron has been brought to such perfection, and methods contrived for uniting perfectly together all the pipes into one connected train, this improved system has been universally adopted.
In former editions of this work (under this heading) the works of the Edinburgh Water Company, undertaken in 1819, and designed by Mr Jardine, civil engineer, were described; but as there is little which can properly come under the popular definition of Aqueduct, they will be more consistently referred to in the article Waterworks. Croton Aqueduct, New York.
The Croton Aqueduct, by which the city of New York is supplied with water, was justly regarded at the time of its execution, from 1837 to 1842, as one of the most magnificent works of the kind in modern times (figs. 1 to 5)
Its length from the Croton Lake to the receiving reservoir is 38∣ miles. The original reservoir, called Croton Lake, is formed by an embankment across the Croton Creek, a small stream of wholesome water falling into the Hudson. It covered 400 acres, and contained about 500,000,000 gallons of water. To the valley of the Harlem River, a distance of 33 miles, the aqueduct (fig. 2,) is built of stone, brick, and cement, arched over and under, 6 feet 3 inches wide at the bottom, 7 feet 8 inches at the top, and 8 feet 5 inches high, and capable of discharging 60,000,000 gallons per day. It is carried over the Harlem
Valley in iron pipes, laid upon a magnificent bridge (figs. 3 and 4) 1460 feet long, constructed of arches 114 feet above high-water mark at Yorkville. These pipes passed into a receiving reservoir capable of holding 150,000,000 gallons, and from thence the water was conducted for 2∣ miles to a distributing reservoir, containing 20,000,000 gallons, by a double line of iron pipes, 3 feet in diameter. From this reservoir the water was distributed to the city.
The Croton water was originally introduced into New York in 1842, whop the population was about 450 000 persons, and from that time to 1848, 18,000,000 gallons per day gave an abundant supply. In 1872, with a population of 1,000,000 persons, the quantity required was 88,000,000 gallons per day. Thus, between 1848 and 1872, while the population little more than doubled, the consumption of water increased nearly five times. This fact, coupled with severe droughts in 1870 and 1871, when the natural volume of the Croton River fell to 27,000,000 gallons per day, caused great anxiety, and shewed the necessity of largely extended works. It was estimated that the basin above the Croton Dam, YT~ 4 77
339 square miles in area, would give ⅛2*⅜
300,000,000 gallons per day on the average, if the water could be impounded, and that, therefore, abundant water could be obtained by increasing the number ⅜ ... *
or capacity of the impounding reservoirs. New reservoirs were therefore projected, one of which, to contain 3,000,000,000 gallons, was expected to be completed in the autumn of 1872. nm E⅜⅞⅛ With this the gross storage would be ∣ ⅛∑lLjIf rι 4,670,000,000 gallons, in addition to the daily produce of the Croton River, A- ∖ which, at its minimum as stated, is
27,000,000 gallons per day. Another Fig · 4.—Cross secreservoir to contain 3,700,000,000 gal- tl0n of bndge ∙ Ions was also projected, and will, it is presumed, be constructed when necessary (fig. 5). To meet the growing demand for water, the reservoirs were not only increased as described, but the means of distribution were largely extended, and in one part of the city six lines of pipes 4 feet in diameter were laid side by side.
Manchester Waterworks.
The works by which the city of Manchester and its suburbs are now supplied with water, and which have been in course of construction from the year 1848 to the present time (1874), are perhaps, in some respects, the most stupendous works of the kind which have ever been constructed, in which difficulties of no ordinary character have been successfully overcome. These remarks, however, relate especially to the impounding reservoirs, which are seven in number, with embankments varying from 70 to 100 feet above the level of the valley in which they are constructed, and cannot, therefore, be properly alluded to here. As the conveyance of the water to the city is, however, by aqueduct, a few words explanatory of the general scheme will be necessary.
The water is collected from the river Etherow and its tributaries, which, rising on the westerly slope of the Pennine chain of hills, flow into the river Mersey, and so into the Irish Sea. The drainage ground from which the water is collected lies nearly midway between Manchester and Sheffield. Its area is about 19,300 acres. It rises in parts to an elevation of about 1800 feet above the level of the sea, and about 1200 or 1300 feet above the deep and romantic valley of Longdendale, in which the main collecting reservoirs are situated. The district consists of the shales and sandstones which constitute the lower portion of the Coal Measure formation—the upper millstone grit forming the cap of the steep escarpments on each side of the valley, while the lower millstone grit, which may be said to separate the Coal Measure shale from the limestone shale, is found in the bottom. The waters produced by this geological formation are among the purest in the world. The spring water is especially brilliant, highly aerated, containing little or no foreign matter, and extremely soft. It is at all times very abundant, the district yielding much more spring water than the usual quantity, in proportion to the area from which the springs issue. The quantity of water flowing from the drainage ground would, if wholly stored, afford a gross supply of about 40,000,000 gallons per day, of which about 13,000,000 gallons per day have to be delivered as compensation to the mills on the stream, leaving about 27,000,000 gallons per day as the supply available for the city and its suburbs.
The water of heavy rains and wet seasons is collected in large impounding reservoirs, the gross capacity of which is 4,233,000,000 gallons. In some of these reservoirs thθ turbid and coloured water is impounded, where it is allowed to settle and purify, and is subsequently given as compensation to the stream; and in others, the pure water, when more than sufficient for the wants of the city, is collected. Here it is stored till required, and then given in addition to the spring water, when that is in itself deficient in quantity. The spring water is separately collected, and conveyed to the city by aqueducts specially constructed for the purpose. In heavy rains, which swell the streams, and especially in autumn, the water is discoloured, but by a simple and ingenious contrivance, every stream is made to separate its coloured water from its pure water—the coloured water being passed to reservoirs set apart for the storage of such water, and the pure water being sent at once to Manchester, or passed to reservoirs in which it is stored for future use.
The aqueducts by which this water is conveyed from the springs and from the reservoirs, consist for the most part of tunnel and covered conduit, 6 feet in diameter, with a fall of 5 feet in a mile, with cast-iron syphon pipes of large dimensions across one valley, which has to be passed before the highest service reservoir is reached. From this reservoir to the city, about 8 miles distant, cast-iron pipes are laid along or under the public roads, to convey the water to various other reservoirs at lower elevations, from which the city and its suburbs are conveniently supplied. .
In the main valleys in which the spring water is collected, or the flood and turbid waters conveyed by separate channels, the aqueducts are chiefly open, and are, to a great extent, formed of concrete 6 inches thick on the sides and bottom, faced with dry stone pitching 9 inches in thickness. They are cheap, easily constructed, and perfectly successful.
The area and capacities of all the reservoirs are as follows :— [table]
Loch Katrine Aqueduct, Glasgow.
The Loch Katrine Aqueduct of the Glasgow Waterworks is the modern aqueduct which has most probably’attracted the largest share of public attention.
The appropriation of the beautiful waters of Loch Katrine—rendered classical by Sir Walter Scott—the romantic, ragged, and almost impassable Highland country through which the aqueduct had to be constructed, and the distance from Loch Katrine to Glasgow, all contributed to lend a special interest to the undertaking. It is, however, a very simple work in itself, for, with but little artificial addition, Loch Katrine, Loch Venachar, and Loch Drunkie were converted into impounding reservoirs, the first for the supply of the city, and the two latter for compensation.
The area and capacity of these reservoirs are as follows ·— [table]
D≠
er*⅛
ttι‰w
The length of the aqueduct from Loch Katrine to Glasgow is about 35 miles, of which 27 may be considered as the aqueduct proper. The remaining 8 consist of two lines of cast-iron pipes, by which the water is conveyed from the large service reservoir at Mugdock to the city of Glasgow. The aqueduct is principally in tunnel or covered conduit, but there are three valleys which are crossed by iron syphon pipes of large diameter, and there are numerous aqueduct bridges of varied character, suited to the peculiarities of the districts in which they had to be constructed. The tunnels and covered conduits are 8 feet high and 8 feet wide, with an inclination of 10 inches in a mile, and are capable of conveying about 50,000,000 gallons of water in twenty-four hours. The syphon pipes across the valleys have an inclination of 1 in 1000, or about 5 feet in a mile, and it requires two pipes of 4 feet in diameter and one of 3 feet in diameter, to convey the quantity of water in a day which the aqueduct will deliver.
The work required the greatest engineering accuracy and skill, and so perfectly have the lines and levels been kept, that it was only upon the closest examination that the joinings in the tunnels could be detected.
The work was commenced in the spring of 1855, opened by her Majesty the Queen in October 1859, and finally completed in the course of 1860.
The cost of the engineering works of the aqueduct, including the conversion of the various lochs mentioned into reservoirs, and exclusive of land, and of the distribution of the water in the city of Glasgow and its neighbourhood, was <£668,000; but the gross cost of the water supply, including the purchase of two water companies, distribution, and everything, has been, to May 1873, £1,756,793.
The following description of the aqueduct was given by the engineer at a banquet given to him in Glasgow after the completion of the works :—
“It is impossible to convey to those who have not personally inspected it, an impression of the intricacy of the wild and beautiful district through which the aqueduct passes for the first 10 or 11 mües after leaving Loch Katrine. From the narrowest point at which it was found the ridge between Loch Katrine and Loch Chon could be pierced, the country consists of successive ridges of the most obdurate rock, separated by deep wild valleys, in which it was very difficult in the first instance to find a way. There were no roads, no houses, no building materials,—nothing which would ordinarily be considered essential to the successful completion of a great engineering work for the conveyance of water; but it was a consideration of the geological character of the material, which gavo all the romantic wildness to the district, that at onco determined me to adopt that particular mode of construction which has been so successfully carried out. For the first 10 miles, the rock consists of mica schist and clay slate—close, retentive material, into which no water percolates, and in which, consequently, few springs are to be found. This rock, when quarried, was unfit for building purposes; there was no stone of a suitable description to be had at any reasonable cost or distance, no lime for mortar, no clay for puddle, and no roads to convey material. Ordinary surface construction, therefore, was out of the question; but I saw that if tunnelling were boldly resorted to, there would be no difficulty, beyond the cost and time required in blasting the rocks, in making a perfectly watertight and all-enduring aqueduct; there would be no water to hamper and delay us in the shafts and tunnels, and’ little would require transporting through the country bur gunpowder and drill iron. This course was therefore determined upon, and my expectations have been realised to the very letter. The aqueduct may be considered as one continuous tunnel. As long as the work continued in the primary geological measures, we had no water; and even after it entered the Old Red Sandstone, and where it subsequently passed through trap rock, there was much less than I expected; so that our progress, at no part of the work, was ever materially interfered with by those incidents which usually render mining operations costly and uncertain.”
The rock, however, especially the mica slate, proved extremely hard and difficult to work. At several points along the side of Loch Chon the progress did not exceed 3 or 4 lineal yards in a month at each face, although the work was carried on day and night. The average progress through the mica slate was about 5 yards in a month. In drilling the holes for blasting, a fresh drill was required for every inch in depth on the average, and about sixty drills were constantly in use at each face. The cost of the gunpowder alone, consumed in the first 7} miles of the aqueduct, was £10,540, and there were about 175 miles of fuse burned in firing it. The average cost per yard of this length of the aqueduct was over £13, or £23,000 per mile. (Figs. 6 to 11, are cross sections of the aqueduct, showing the general construction in various kinds of ground.) The built and tunnelled part is all capable of passing 50,000,000 gallons per day.
The aqueduct bridges over the ravines are somewhat peculiar, varying in character according to the circumstances of the district. In the wilder and more inaccessible parts there are five extensive iron ones, varying in length from 124 to 332 yards, all of similar construction. (See fig. 12.) At the ends of these bridges, in the shallowest parts of the ravines, the aqueduct has a cast-iron trough supported on a solid dry stone embankment of the stone of the district, carefully set by hand; the stone embankment being 9 feet wide at top, with a batter of 3 inches to the foot on each side. The deeper parts of the ravines or valleys are crossed by malleable iron tubes 8 feet wide by 6⅜ feet high inside, supported by piers at intervals of 50 feet. The bottoms and sides of these tubes are f inch thick, and the tops √⅛ inch thick, strengthened by angle and T iron. Fig. 13 shows a section of these tubes. The cast-iron made for adding 2∣ feet to the height of the sides when additional water was required, and this has since been done. The bottoms of the malleable-iron tubes are 3 feet below the bottoms of the troughs, so that they should always be full of water, for the purpose of securing the same temperature both in the bottom and top of the tubes, and so pre venting unequal expansion and contraction. The aqueduct at the crossing of small mountain streams (of which there were many) was carried in cast-iron troughs similar to those already described, supported upon cast-iron beams over the space left for the stream.
The first deep valley which required to be crossed, by piping is that of the Duchray water, about 55 chains wide. The pipes first laid down were 4 feet diameter in 9 feet lengths, with spigot and faucet joints, run up with lead in the usual way. At the lowest point the pipes are under a pressure of 165 feet. The river itself is crossed by cast-iron arched girders of 60 feet span; and here, as well as at the small basins at each end of the piping, and at all other places where masonry was required, provision was made for laying two additional lines of pipes, one 4 feet and the other 3 feet in diameter. These pipes have since been laid. After passing through the ridge of Old Red Sandstone conglomerate by the Clashmore tunnel, the aqueduct for 5 miles is for the greater part in open cutting, with masonry sides, and a dry rubble arch covered with 2 feet of puddle, and then covered in.
The Endrick valley, like that of the Duchray, is crossed by cast-iron syphon pipes for 2⅛ miles in length. Where they cross the river Endrick at the bottom of the valley, the pipes are 1∣∙ inches thick, and have to sustain a pressure of 235 feet. The pipes are carried across small depressions in the valley by resting them upon stone piers, and at the crossing of two roads, and of the Forth and Clyde railway, they are further supported by cast-iron troughs (fig. 14) are 8 feet broad and 4 feet deep, and f inch thick, and were capable of passing at this depth upwards of 20,000,000 gallons a day. Provision was brackets. The pipes at these exposed places have flange joints, and they have been covered with woollen felt to prevent expansion and contraction. There is a short tunnel 110 yards long on this length of piping of dimensions sufficient to carry the three lines of pipes. The construction of the aqueduct, for the 5 miles extending from the valley of the Endrick to the valley of the Blane, presents the same general features as those already described. Good building stone was abundant in this district, and the bridges are all of masonry. Fig. 15 is an elevation of one of the aqueduct bridges near Killearn at 19 miles from Loch Katrine;
The piping across the Blane is about 54 chains long, with a depression of 125 feet. The Blane water itself is crossed by a stone bridge, and there are basins at each end of the pipes as before. The last piece of the aqueduct is a tunnel 2640 yards long, through a ridge of amygdaloidal trap, separating the valley of the Blane from the valley of the Allander. The tunnel is 250 feet below the summit of the hill.
Mr Bateman, at the banquet referred to, summarised the works along the line of aqueduct in nearly the following words :—“There are in the whole work eighty distinct tunnels, upon which forty-four vertical shafts have been sunk for facilitating and expediting the completion of the work.” Besides the tunnel at the commencement of the aqueduct, called the Loch Katrine Tunnel, 2325 yards in length, and upwards of 500 feet below the summit of the hill, and the Mugdock Tunnel at the end of the aqueduct, 2640 yards in length, there are “others, 700, 800, 1100, and 1400 yards in length. Not to speak of smaller constructions, there are twenty-five important iron and masonry aqueducts over rivers and ravines, some 60 and 80 feet in height, with arches of 30 feet, 50 feet, and 90 feet in span. The number of people employed, exclusive of iron-founders and mechanics, has generally been about 3000; and for the greater part of these, huts and roads and all other accommodation had to be provided, the country for the most part being of the wildest and most inaccessible description.”— “At the picturesque, ‘turf and timber’ village of Sebastopol, as the miners calledit, at the head of Loch Chon, several hundreds of work-people were accommodated. Provision stores, reading-rooms, a schoolhouse and church, and a resident medical man and schoolmaster were provided for them.”
The aqueduct from its commencement at Loch Katrine to the Mugdock reservoir, is 25∣ miles long, 13 of which were tunnelled, 3∣ miles are iron piping across valleys, and the remaining 9 miles consist of “cut and cover” conduit and bridges. Where the ground was cut open the conduit was covered in, and the surface restored after the aqueduct was built At the bridges the aqueduct is covered with timber to prevent its being choked by snow. Most of them are furnished with grooves in the masonry to receive stop planks, and with discharge sluices to facilitate the emptying of the aqueduct, when it is necessary to inspect or make repairs. Overflows are constructed at a number of the bridges, to discharge the water if it should be necessary to stop the flow suddenly at any point. The total cost of the aqueduct at the time the water was introduced into the city, was £468,000, or an average of £18,000 per mile.
It has been already stated that the 4-feet pipes across the valleys on the line of aqueduct were intended to deliver 20,000,000 gallons a day. By the well-known modification of Eytelwein’s formula, deduced from Du Buat’s experiments and more elaborate formulae, the computed discharge is 21,500,000 gallons a day nearly, and by Weisbach’s formulae, 21,750,000 gallons a day. These pipes, however, have discharged 24,000,000 gallons a day without their being completely gorged, and their ultimate discharge has therefore yet to be determined. The whole of the pipes used in the works were coated with coal pitch and.oil, according to the process patented by Dr R. A. Smith of Manchester, and first used by Mr Bateman in the Manchester Waterworks. This coating, when well done, imparts a smooth glassy surface to the pipes, and prevents, at least for a number of years, the usual, and it may be said, inevitable oxidation. Weisbach found that for wooden pipes 21 and 4 J inches diameter, the coefficient of resistance was 1 , 75 times as great as for “metallic pipes,” giving a discharge about 14 per cent, less; and Μ. Morin has shown, in a paper which it is believed is published in detail in the Mémoires des Savants Etrangers, the influence the state of the surface has upon the discharge of a pipe, amounting, in cast-iron pipes coated with pitch, and in glass pipes, to an increase of nearly one-third in the discharge.
It has also been pointed out by Μ. Morin, whose deductions are principally from observations by Μ. Darcy director of the waterworks of Paris, that for large sizes the diameters of the pipes seem also to exercise a more decided influence on the discharge than has been hitherto assigned to them. Late observations on the flow of gas through pipes by Μ. Arson, engineer of the Paris Gas Company, tend to confirm the views of Μ. Morin.
At the Mugdock Service Reservoir, 7 or 8 miles from Glasgow, the water is first discharged into a basin, from which it passes over cast-iron gauge plates, 40 feet wide, brought to a thin edge. The depth of water passing over these plates is regularly recorded and the discharge computed. From the basin the water falls into an upper division of the main reservoir, about 2 acres in extent, and from this it is discharged into the reservoir. The reservoir has a water surface of 60 acres, and a depth when full of 50 feet; it contains 548,000,000 gallons, and is 317 feet above ordnance datum. It admits of repairs being made upon the aqueduct without interrupting the supply of water to the city. Two earthen embankments were necessary to form the reservoir; the main embankment is 400 yards long and 68 feet high, and the easterly embankment 240 yards long and 50 feet high, each with a puddle wall in the centre, and pitching on the front slope in the usual way.
The water is drawn from the reservoir by pipes laid in a tunnel through the hill between the two embankments, there being no pipes through the embankments themselves.
At the end next the reservoir there is a stand-pipe so arranged that water can be drawn at various heights, and about 50 yards from the reservoir, the water passes into a circular well cut out of the rock, 40 feet in diameter and 63 feet deep, and is strained by passing through copper wire-cloth, 40 meshes to the inch, arranged in oak frames, forming an inner well of octagonal shape 25 feet diameter; and from this latter the water finally passes into the two lines of pipes leading to the city. Water can also be drawn direct from the gauge basin, and from the upper compartment of the reservoir into the straining well, by a line of 4-feet pipes through the bottom of the reservoir. These works, including road and stream diversions, cost about £56,000.
The two pipes leading from the straining well are each 42 inches diameter, and are intended to deliver the whole 50,000,000 gallons a day; but on emerging from the tunnel, which is 440 yards in length, they are diminished to 36 inches, and they are continued of this size to the city. Provision was made for additional pipes, which have since been laid. The different lines of pipes are laid side by side for about 3 miles, after which they diverge—one line being carried by the Great Western Road for the supply of the low districts of the city, and the other by Maryhill for the supply of the high districts. These pipes come together again, and are arranged so as to communicate -when necessary at St George’s Road near the commencement of the city, up to which point their respective lengths from the straining well are 7 miles for the low district main, and 6∣ miles for the high. Each of these lines of pipes crosses the River Kelvin and the Forth and Clyde Canal, and at these places provision was made for additional pipes. Eleven feet were added to the width of the Kelvin Bridge on the Great Western Road, by cast-iron girders, to carry the low district mains. The two middle spans are each 93 feet, and the two side arches 37 feet span.
The total cost of the works at their completion, in 1860, was as follows :—
[table]
Vienna Waterworks.
A still more recent work, consisting mainly of aqueduct construction, is the enterprise for supplying the city of Vienna with water. The water is obtained from the springs of Kaiserbrunn and Stixenstein, both situated at the foot of the Styrian Alps, which separate Austria from Styria. The Kaiserbrunn spring is situated 1146 English feet abovo the Danube at Vienna, and the Stixenstein spring 996 feet. The water is conducted by aqueduct to a receiving reservoir at Rosenhugel, 277 feet above the Danube, and distant 2 miles from Vienna. The length of the aqueduct from Kaiserbrunn to the receiving reservoir on the Rosenhugel, is 56 j English miles. A branch of 3'9 English miles conducts the Stixenstein spring to this aqueduct. The gradients of the aqueduct vary much in the upper or early parts; but towards the end they become more regular. The gradients have been thus varied for the purpose of keeping the canal as much as possible along the level of the ground, so as to avoid high embankments. In order to keep the water cool in summer, and lo secure it from freezing in winter, the water is always 6 feet below the surface; and in places where embankments were unavoidable, the aqueduct has been covered to the same extent. The size of the aqueduct varies from 4 feet 6 inches in height, by 2 feet 6 inches in width, to 6 feet 6 inches in height, by 4 feet in width. In order to facilitate the discharge, and to reduce friction, the inside of the aqueduct has been plastered with a coating 2 inches thick of Portland cement and sand, in the proportion of one of cement to two of sand. This coating was laid on in three layers, the last being a very thin layer of pure cement, which, when hardened, was rubbed with iron plates till it became perfectly smooth and polished. The work was commenced in the winter of 1869-70, and completed in the month of September 1873. The aqueduct is constructed for the purpose of supplying about 3,200,000 cubic feet per day, or 20,000,000 gallons. There are several important aqueduct bridges along the line of works. Of these the principal is the aqueduct of Baden, which consists of forty-three large arches, with spans varying from 5 klafters to 8⅛ klafters, and the greatest height 15 klafters 5 feet 5 inches, or 96 ’ 6 English feet, from the foundation of the pier to the top of the aqueduct. The arches are of brickwork, as well as the vaulting of the canal. The piers, together with the backing of arches and the sides of the canal, are faced with ashlar, and filled up with rubble masonry. The canal is covered on the top with earth, which is then covered with 9 inches of paving in rubble masonry
The Mödling Aqueduct is, although one of the shortest, perhaps the finest on the whole line of the works. It is situated in a very narrow gorge, with high rocks rising on the side. The canal or aqueduct passes through a tunnel on one side, and after crossing the aqueduct enters immediately into another tunnel on the other. This aqueduct bridge consists of spans of 9 klafters, or 55'98 English feet, in width, and is built entirely of bricks, with tho exception that the piers are pointed with ashlar. The abutments, the foundations of which are excavated in the rock, are built of rubble masonry, faced with ashlar. The other chief aqueducts are—the one at Liesing with forty-six arches, very similar to that of Baden, and that of Mauer with thirteen arches, built of bricks, and making a fine curve across the valley.
The receiving reservoir on the Rosenhugel, where the aqueduct ends, is divided into two parts, capable together of holding 80,000 cubic feet English. From this reservoir the water is taken to two other distributing reservoirs, from which the city is supplied. The cost of the work, together with the network of pipes in Vienna, has been about 25,000,000 florins or £2,000,000 sterling. The chief engineer of the work was Herr Carl Junker of Vienna, and the contractor Mr Antonio Gabrielli of London. The works were completed and opened in the autumn of 1873.
Water Supply of Paris.
The question of improving the water supply of this city was the subject of minute and careful investigations, extending over a period of four or five years, (from 1854 to 1859.)
Many projects were submitted to the Prefecture of the Seine, but the one finally adopted was that studied by Mr Belgrand and the engineers of the municipality of Paris. The scheme consisted in appropriating the waters of the Sonne and the Soude, together with the Soudon and the Dhuis, all being tributaries of the Marne, and flowing through chalk districts.
The population of Paris, for the supply of which the scheme was laid out, was taken at 2,000,000, and the waters from the sources selected were intended for the domestic supply only—the existing supplies to Paris, which have become gradually polluted and unfit for domestic use, being made available for all the other general wants of the population. The quantity of water which it wa3 estimated would be required for the domestic purposes of such a population was taken at 100,000 cubic metres per diem, or about 22,000,000 gallons per day; and the works have been laid out for conveying this quantity. Gaugings of the various streams selected, showed that in 1855, when the flow was at the lowest, the produce of the Sonne and the Soude was 1081 litres per second, the Soudon 100, the Dhuis 315; making a total of 1496 litres per second, or about 28,000,000 gallons per day. At the time of lowest water in 1857, however, the Sonne and the Soude together only yielded 880 litres per second, or 16,762,000 gallons per day, while in 1858, which was an exceptionally dry year (indeed the driest year on record in this locality), they yielded together only 285 litres per second, or 5,417,280 gallons per day; while in both these years the Soudon and tho Dhuis gave almost the same quantities as in the year 1855.
In order to meet the contingency of such a dry season as 1858, Mr Belgrand’s project contemplated sinking wells or adits in the chalk, and obtaining therefrom what he terms “the subterranean reservoirs of water therein contained,”—artificial supplies, which would supply any deficiency in the quantity yielded by the streams. The works comprised what are termed conduits of derivation, being subsidiary conduits for collecting the waters from the various streams, and conducting them to the commencement of the main aqueduct that conveys the waters of the combined sources to Paris. The main aqueduct commences at a level of about 105 metres above the sea. It is a little over 180 kilometres in length (about 110 English miles), and terminates at Paris in service reservoirs at Belleville, at a level of 83 j metres above the sea. The subsidiary conduits are about 80 kilometres in length, and upon these and the main aqueduct there are seventeen bridges, 6 kilometres of conduit constructed upon arches, 7 kilometres of syphon piping, and 28 kilometres of tunnel. The estimated cost of the ordinary works was about 19,000,000 francs, or £760,000, to which must be added about 2⅛ million francs, or £100,000, for special works, where the aqueduct had to be constructed through difficult ground, and 4⅜ million francs, or £180,000, for compensation to riparian owners on the streams which were selected as the sources of the supply, as well as to the owners of mills who might be injured by the abstraction of the water, and for the purchase of the lands through which the aqueduct had to be constructed; making a total estimated outlay on the works at the sources of the supply, and for the subsidiary mid main aqueducts up to the distributing at Belleville, of 26,000,000 francs or £1,010,000.
The commission, to whom were referred all the projects which had been suggested, in their report, considered on the 18th of March 1859, recommended that the sum to be voted for the works should be 30,000,000 francs, or £1,200,000, thus increasing the estimate by 4,000,000 francs, or £160,000, with the view of providing ample means to cover any unforeseen works or difficulties which might be encountered during the carrying out of the project. The works have since that time been carried out substantially in accordance with the ideas and designs of Mr Belgrand, and under his direction and supervision; but they are not yet (1874) completed. The water from these sources is naturally very hard, but it is bright, fresh, and well aerated.
Although the system of pipes has superseded the use of stone channels all raised to a level in the conveyance of water, there are still cases, such as those of canals, where the water must be kept on a perfect level, and where, therefore, aqueduct bridges are still necessary in conveying it over the valleys; and of these we have long had examples in France, on the Languedoc canal. The first aqueduct bridges for canals in this country were those made by the Duke of Bridgewater, under the direction of the celebrated Brindley, and which, being quite new here, excited no small degree of astonishment. The first and largest w as the aqueduct at Barton Bridge for conveying the canal across the Irwell, 39 feet above the surface of the water. It consisted of three arches, the middle one 63 feet span, and admitting under it the largest barges navigating the Irwell with sails set. It was commenced in September 1760; and in July of the following year the spectacle was first presented in this country, of vessels floating and sailing across the course of the river, while others in the river itself were passing under them. Since that period canal aqueducts have become more common; and many excellent examples are to be found both in England and Scotland. Of these are the aqueducts over the river Lune on the Lancaster canal, designed by Rennie,—a very excellent and splendid work of five arches, each 72 feet span, and rising 65 feet above the level of the river; and the Kelvin aqueduct, near Glasgow, which conveys the Forth and Clyde canal over the valley of Kelvin, consisting of four arches, each 70 feet span, and rising 70 feet above the level of the river. Plate IV. contains views of two other principal aqueducts, viz., those of Pont-y-Cysyllte and Chirk in Wales. Of these the Pon t-y-Cysylite aqueduct by Mr Telford is justly celebrated for its magnitude, simplicity of design, and skilful disposition of the parts, combining lightness with strength in a degree seldom attempted. This aqueduct serves to convey the waters of the Ellesmere canal across the Dee and the vale of Llangollen, which it traverses. The channel for the water is made of cast-iron, supported on cast-iron ribs or arches, and these resting on pillars of stone. The iron being much lighter than stone arches, this in one reason why the pillars have been reduced apparently to such slender dimensions. They are quite strong enough, however, as experience has proved. The whole length of the aqueduct is about 1000 feet, and consists of nineteen arches, each 45 feet span. The breadth of the pillars at the top is 8 feet, and the height of the four middle ones is 115 feet to the springing. The pillars have a slight taper, the breadth of the middle ones at the base being 15 feet. The height from the surface of the water in the Dee to that in the canal is 126 feet 8 inches. The channel for the water consists of cast-iron plates, cast with flanches, and these screwed together with bolts; they are represented in the drawing, between the arched ribs and the railing. The lines there show the joinings of the different plates. In order to preserve as much water-way as possible, the channel is made the full width of the canal and towing-path, and the latter projected over one side, and supported inside by posts resting on the bottom of the canal. The aqueduct of Chirk was designed by the same able engineer, and serves also to convey across a valley the waters of the same canal. This aqueduct was the first in which iron was employed. Hitherto the channel for the waters had been constructed of stone, or partly of stone and partly of clay puddle, which it was generally found very difficult to keep water-tight for a length of time. It was determined, therefore, by Mr Telford, to try the effect of castriron, and to lay it at first only on the bottom. The plates were accordingly laid directly over the sprandril walls, which they served to bind together, and united by flanches and screws. The sides of the channel were built with stone facings and brick hearting laid in water-lime mortar. This plan succeeded completely, and the quantity of masonry in the aqueduct was thereby greatly reduced. The aqueduct itself is 600 feet long, and 65 feet high above the river, consisting of ten arches, each 42 feet span. The piers are 10 feet thick.
An aqueduct near Edinburgh, conveying the waters of the Edinburgh and Glasgow Union Canal across the valley of the Water of Leith at Slateford, is an elegant structure, similar in plan to that of Chirk, only that the waterchannel is composed entirely of cast-iron, which is moreover built in with masonry. It is about 500 feet in length, and consists of eight arches, each 45 feet span; and the height of the canal is about 70 feet above the level of the river. On this canal another aqueduct of the very same construction occurs in crossing the valley of the Almond, and having several more arches. There are, in different parts of the country, various other aqueducts, but, excepting the formation of the water-way, these structures differ in no respect from bridges, particularly those undertaken not so much with the view of crossing rivers as of raising the level of the road entirely out of the valley,—an object now become of great importance, from the improvements in modem modes of conveyance. For the principles and mode of construction of these works, as well as of the aqueduct bridges, so far as the arch is concerned, see articles Arch and Bridge.
For further information on the subject of ancient aqueducts, see E. Curtius, “Ueber Städtische Wasserbauten der Hellenen,” in Archäologische Zeitung, 1847; Sextus Julius Frontinus, De Aquoeductibus Urbis Rornae Libri II. , with the Commentaries of Polenus (Patav. 1722) and Rondelet (Paris, 1820); Raphael Fabretti, De Aquis et Aquaeductibus Veteris Rornae Dissertatio; Plinii Hist. Nat. lib. xxxvi cap. XV.; Montfaucon, Antiquité Expliquée, tome iv. tab. 128; Governor Pownall’s Notes and Description of Antiquities in the Provincia Romana of Gaul; Belidor’s Architecture Hydraulique, containing a drawing of the aqueduct of Maintenon; also Mém. Acad. Par.; Andreossy, Voyage à V Embouchure de Mer Noire, ou Essai sur le Bosphore; Philosophical Transactions Abridged, vol. i.; and Link’s Travels in Portugal. And for modern aqueducts, see Rickman’s Life of Telford, 1838; Schramke’s New York Croton Aqueduct; Second Annual Report of the Department of Public Works of the City of New York in 1872; Mémoires sur les Eaux de Paris, présentés par le Préfet de la Seine au Conseil Municipal, 1854and 1858; Recherches statistiques sur les sources du Bassin de la Seine, par Μ. Belgrand, Ingénieur en chef des ponts et chaussées, 1854. “Description of Mechanical arrangements of the Manchester Waterworks,” by John Frederic Bateman, F.R.S., Engineerin-chief, from the Minutes of Proceedings of the Institution of Mechanical Engineers, 1866; The Glasgow Waterworks, by James Μ. Gale, Member Inst. C.E., 1863 and 1864; The Report of the Royal Commission on Water Supply, and the Minutes of Evidence, 1867 and 1868.
(a. s. μ. —J. F. B.)
