Aque-duct.
A conduit for the conveyance of water.
More particularly applied to those of considerable magnitude intended to supply cities and towns with water derived from a distance for domestic purposes, or for conveying the water of canals across rivers or valleys.
Pocock describes one erected by Solomon for conveying water from the vicinity of
Bethlehem to
Jerusalem.
This was formed by earthen pipes about ten inches in diameter, encased with stone and sunk into the ground, and would seem to have conformed to its inequalities, indicating a more advanced state of hydraulic engineering in Solomon's time than is commonly supposed to have been possessed by the earlier
Romans, who were justly famed for their works of this kind, which have never been surpassed in strength and beauty.
The earliest account of any aqueduct for conveying water is probably that which is given by
Herodotus (who was born 484 B. C.). He describes the mode in which an ancient aqueduct was made by
Eupalinus, an architect of
Megara, to supply the city of
Samos with water.
In the course of the aqueduct a tunnel, nearly a mile in length, was pierced through a hill, and a channel three feet wide made to convey the water.
The first of the
Roman aqueducts (Aqua Appia) was built, according to
Diodorus, by
Appius Claudius, in the year of the city 441, or 312 B. C. The water which it supplied was collected from the neighborhood of Frascati, eleven miles from
Rome, and its summit was about one hundred feet above the level of the city.
The second (
Anio Vetus) was begun forty years after the last-named, by
M. Curius Dentatus, and finished by
Fulvius Flaccus: it was supplied from the country beyond
Tivoli, forty-three miles distant. Near Vicovaro it is cut through a rock upwards of a
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mile in length, in which part it is five feet high and four feet wide.
The water of this aqueduct was not good, and therefore only used for the most ordinary purposes.
The third (
Aqua Martia) was supplied from a fountain at the extremity of the mountains of the Peligni.
The water entered the city by the
Esquiline Gate.
This aqueduct was the work of
Quintus Martius, and had nearly seven thousand arches in a course of thirty-nine miles.
The fourth (Aqua Tepula) was supplied from the vicinity of Frascati.
The fifth (
Aqua Julia) was about six miles long, and entered the city near the
Porta Esquilina.
The sixth (Aqua Virginis) was constructed by
Agrippa thirteen years after the
Julia.
Its summit, in the territory of Tusculum, was about eight miles from
Rome, which it entered by the
Pincian Gate.
This water still bears its ancient appellation, being called Acqua Vergine.
The seventh (Aqua Alsietina, called also
Augusta, from the use to which Augustus intended to apply it for supplying his Naumachia) was brought from the lake whose name it bears.
The eighth (
Aqua Claudia), begun by
Caligula and completed by
Claudius, is about forty miles in length.
It enters the city at the
Porta Nevia, near the
Esquiline Mount.
The quality of the water which this aqueduct supplies is better than that of any of the others.
It was built of hewn stone and supported on arcades during seven miles of its length.
After a lapse of eighteen hundred years it still continues to furnish Modern
Rome with pure and wholesome water.
The ninth (Anio Novus, to distinguish it from the second-named water) was begun and finished by the same persons as the last-mentioned.
It is the water of the Anio, which, being exceedingly thick and muddy after the rains, is conveyed into a large reservoir at some little distance from
Rome, to allow the mud to subside.
The Acqua
Felice is modern, and was erected by Sixtus V. in 1581.
The Popes have, from time to time, been at considerable pains and expense in repairing and renewing the aqueducts; but the quantity of water delivered is constantly diminishing.
In the ancient city the sum-total of the areas of the different pipes (which were about an inch in diameter) through which the above immense quantity of water was delivered, amounted to about 14,900 superficial inches; but the supply was subsequently reduced to 1170.
The waters were collected in reservoirs called
castella, and thence were conveyed through the city in leaden pipes.
The keepers of the reservoirs were called
castellani.
Agrippa alone built thirty of these reservoirs during his aedileship.
There are five modern ones now standing in the city: one at the
Porta Maggiore,
Castello della Acqua Giulia, della Acqua
Felice, della Acqua Paolina, and that called the Fountain of Trevi.
The aim of the
Roman aqueduct-builders was to conduct the water along with an equal fall during the whole distance from its source to the point of delivery; and for this purpose, instead of allowing the conduits to follow the natural slope of the ground, they almost always erected long and massive stone arcades wherever it was necessary to cross a valley, instead of availing themselves of the wellknown property of water to find its level.
This was perhaps necessary in the then state of the mechanic arts, the art of casting iron pipes of large size being unknown.
It has been calculated that the nine earlier aqueducts of
Rome had a total length of more than 249 miles, and the supply of water to Ancient
Rome was computed by
Professor Leslie, on the authority of
Sextus Julius Frontinus, who was inspector of the aqueducts under the Emperor Nerva, and who has left a valuable treatise on the subject, at fifty million cubic feet per day for a population of one million souls.
This gives the immense average per head of fifty cubic feet, or three hundred and twelve gallons, per diem, — a consumption quite unequalled in modern times, except in the
city of New York, where it is said to have formerly amounted nearly to this quantity.
The aqueducts of
Metz,
Nismes, and
Segovia are also striking examples of the attention paid by the Romans to the subject of supplying water to their towns and cities.
It does not appear that the ancients were by any means ignorant of the applicability of pipes for conducting water, and it is difficult to conceive how it could have been distributed to the baths and fountains of
Rome without their aid. Their system appears to have been the result of calculation and design, and it is notable that in the greatest works of the kind of modern times, such as the aqueduct of
Marseilles and the
Croton Aqueduct, their leading principles have been carried out, and the use of pipes following the elevations and depressions of the hills and valleys has been in a great degree dispensed with, where the water had to be conveyed along a course of considerable length, — though, in general, without resorting to such an extensive, or indeed excessive, use of long and expensive areades as the Romans employed.
The advantages of this system seem to be, more perfect freedom from deposition of mineral substances in solution in the channel way, owing to the more uniform and regular flow of water which can be obtained; facility of constructing traps or wells along the route for the deposition of sediment; greater security from interruption and opportunity for repair in case of accident.
The aqueduct of
Nismes, or the
Pont du Gard, in France, is one of the earliest constructed by the Romans out of
Italy, and is supposed to have been built in the time of Augustus; it was intended for carrying the waters of the Eure and Airan from the vicinity of their sources to the town of
Nismes.
The commencement of this aqueduct was conducted along the sinuosities of a hill, entirely under ground, and was often cut in the rock itself.
Small bridges were thrown over the streams crossed in its course, and it passed over a series of arches, resembling those of the upper part of the great arcade of the
Pont du Gard, followed the crest of a hill to avoid unnecessary hight in the piers, and after a course of about 9 3/5 miles arrived at the
Pont du Gard, by which it is carried over the river
Gardon at a hight of more than 157 feet above the surface of the stream below.
This magnificent structure consists of three tiers of arches, on the upper one of which the water-way is carried.
The length at the level of the string course surmounting the lower tier of arches is 562 feet, and at the string course of the second tier 885 feet.
The large arch through which the river passes is 80 feet 5 inches in span, the three on the right side of this are 63 feet, and the smaller ones 51 feet. Those of the upper story are all equal, 15 feet 9 inches in span; their piers vary in width, and do not come immediately over those below.
The whole is constructed of freestone, from the foundation to the third course above the cymatium
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covering the piers of the upper story.
Rubble was employed for filling in the piers, spandrels, and haunches of the first and second stories.
The stones were laid without cement, each being raised by the lewis, the holes for the insertion of which are still to be seen exactly over the center of gravity of each stone.
The dimensions of the water-way are 4 feet in width and 4 feet 9 inches high; the fall throughout its entire length is 2.112 inches per mile, and it is estimated to have been capable of supplying from 14 to 18 millions of gallons of water per day.
The entire length of the aqueduct is over 25 1/2 miles.
The aqueduct of
Segovia, Spain, was built by the Emperor Trajan, and is of squared stone laid without mortar, and in crossing a valley has a length of more than 2,200 feet; it is in many places nearly 100 feet high.
An elevation and plan are shown in
Fig. 288.
The waters of the
Aquae Julia, Tepula, and
Martia at
Rome were conducted through a triple aqueduct, forming three channels, one above the other, as shown in the accompanying section; the
Aqua Martia being the lowest, the
Aqua Tepula the middle, and the
Aqua Julia the uppermost of the series.
Particular care was taken to prevent leakage from one into the other, so that the water of better quality might not become deteriorated by mingling with that of inferior clearness and purity; to effect this, the bottom of the channel of each was based upon thick stones passing into the sides of the aqueduct, and carefully lined with tiles and a coating of cement.
Doors from the outside admitted the persons in charge to examine the condition of the conduits at any time, and they were required to report constantly upon their efficiency and state of repair.
The accompanying illustration (
Fig. 290) shows one plan adopted by the Romans for conveying water across a valley.
The aqueduct was erected by the Emperor Claudius for supplying a palace in an elevated part of the ancient city of
Lugdunum (
Lyons).
The channel-way, both in ascending and descending, was formed by masonry, tiles, and cement.
The work was performed as follows: A level pavement was formed of brick, on which was raised a frame or caisson of timber planks; against the sides of this, squared stones were laid in regular courses, and their interior filled in with rubble in a dry state, after which a grouting of liquid cement was poured in to consolidate the whole.
Lime, fine
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gravel or sand, mixed with a due proportion of water, formed this grouting.
After a sufficient time had allowed this work to consolidate, the caisson was mounted upon another course or layer of tiles, and similar operations to the first took place.
The bricks or tiles used were 21 inches in length, 12 inches in breadth, and 1 1/2 inches in thickness.
The whole of the water conduit was coated with cement; at bottom, its thickness was 6 inches, at the sides 1 1/2 inches. 24 inches from the bottom of the canal, at distances of 30 inches apart, the side walls were stayed with iron ties to prevent their being burst apart.
In the ancient aqueduct at
Lyons, called at one part of its course
Mont de Pile and at another Champonest, the water was brought over eight bridges in the usual manner, and a siphon was employed for conducting it across the ninth.
At this point the valley is very deep, and a reservoir was built from which leaden pipes of large size, bedded in the sides of the valley, conducted the water to others laid over a bridge in an inverted curve; they were then conducted up the opposite side of the valley, and delivered the water into a reservoir at the same level as the first; from this they were conducted under ground for some distance, and thence, by a bridge of ninety arcades, to another reservoir, from whence it again descended into a valley through similar leaden pipes, crossing a river and ascending the other side of the valley, where it was delivered into a reservoir on that side.
From thence it was carried, partially over arcades, to a reservoir at one of the gates of the city, from whence again it was carried by leaden pipes, first falling and again rising until it reached the reservoir from whence it was finally distributed; in this last instance the pipes were bedded in solid masonry, and not carried over a bridge.
The total length of this remarkable piece of work, which certainly seems to combine all the known appliances for conveying water without the aid of extraneous mechanical power, was 13 leagues, and the fall in this distance upward of 350 feet.
Wherever the aqueduct was tunneled in the sides of the hills at a considerable distance below the surface, wells were sunk to carry off any vapors which might accumulate, and to admit light and air; they also afforded access to any workmen who might be employed to make repairs or remove accumulated deposits in the channel: these were at distances of 120 feet apart.
Perpendicular vent-pipes were also erected for ventilating purposes.
The walls, where the work was above ground, were two feet thick, and the arches were roofed over to shed rain.
The entrance to the aqueduct was through iron doors opening internally.
The underground portions were accessible by traps or man-holes brought up a little above the level of the soil.
Pipes, in cases where a very large supply of water is not required, undoubtedly possess many advantages, and in very broken and rugged localities their use, either alone, or in combination with masonry or brick conduits, along the more level portions of the route, is indispensable without increasing the cost of the work beyond all reasonable bounds; but it would seem, both from the experience of antiquity and that of more recent times, that the stone or brick channel into which the air is freely admitted, and to which ready access can be had for the removal of impurities or obstructions, is, when the engineering difficulties and cost are not too great, preferable to any other.
This of course does not apply to the delivery and discharge of water within cities or towns; there, metallic pipes of some kind are indispensable.
Castiron is the material now universally employed for the larger pipes of this description, called
mains, and is perfectly unobjectionable in every respect.
Leaden pipe is very extensively employed in buildings for discharging water, but, unless kept constantly filled, is a very dangerous material, its salts being active poisons.
Lining with tin is a good expedient.
In
China and
Japan, bamboos of large size are used to convey water from one point to another.
The ancient works executed under the later Roman emperors for the supply of
Constantinople combine the system of aqueducts with the collection and impounding of water by means of reservoirs at the head of the aqueduct.
The impounding reservoirs are situate about twelve miles from the city, on the slopes of a range of mountains which form the southeastern prolongation of the great Balkan chain.
There are four principal aqueducts, one of which conveys the water collected by three separate reservoirs, while the other three are each supplied by its own reservoir.
Besides these extensive provisions for securing water to the city, there are immense subterranean reservoirs, one of which, now in ruins, is called the Palace of the Thousand and One Pillars, not because this is the precise number supporting the roof, but because the number is a favorite one in the expression of Eastern hyperbole.
This great subterranean cistern is supposed to have been made by the Greek emperors for the purpose of storing water in case of a siege or similar calamity.
Although originally of great depth, it is now nearly filled up with earth and rubbish.
It is singular that in the nineteenth century we are reviving in our covered reservoirs, for the purpose of storing water in a state of freshness and uniform temperature, the practices which were followed nearly two thousand years ago by nations whose modern descendants are half barbarians.
Works of great magnitude were, according to Garcilasso, constructed for purposes of irrigation by the ancient
Peruvians, previous to the conquest of that country by the Spaniards.
On the western slopes of the Andes there are immense districts where rain never falls, and which are incapable of cultivation unless watered by artificial means.
The Incas caused numerous aqueducts to be constructed for this purpose: one of these is stated to have been 120 leagues in length and 12 feet in depth, and to have watered a tract of country more than 50 miles in width; another was 150 leagues in length, traversing an extensive province and irrigating a vast and arid district of pasture land.
The
Peruvians do not appear to have advanced so far as the use of bridges or pipes for conducting the water across valleys, — their purpose probably did not require it, — but gave their aqueducts a sinuous course, winding around the mountains and through the valleys with sufficient inclination to allow the water to flow freely.
The French aqueducts referred to in this article are most of them of great magnitude and importance, and the most stupendous work of the kind ever projected originated in
France.
This was the aqueduct of
Maintenon, which was undertaken in 1684 and abandoned in 1688, during which time 22,000,000 francs are said to have been expended upon it. It was intended to have brought water from the river
Eure at Pongoin to
Versailles, a distance of nearly 25 leagues, and embraced an arcade of masonry 16,090 feet in length, comprising three tiers of arches at its highest part.
The illustrations (
Fig. 291) exhibit to the same scale, —
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1.
The
Pont du Gard Aqueduct, at
Nismes, under which the river Gardon passes, and which was built by the Romans, possibly by
Agrippa.
The conduit is 157 feet above the river, and is referred to above.
2. The
Solani Aqueduct of the
Ganges Canal; the area of the water-way is eighty times that of the
Pont du Gard.
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Aqueducts. |
3. The
Roquefavour Aqueduct, erected by Montricher to conduct the waters of the Durance to
Marseilles.
The aqueduct for supplying
Marseilles with water extends from the river Durance, a distance of 51 miles, though a very hilly country.
It comprises 78 tunnels, having a united length of over 12 miles. It has 500 bridges, embankments, and other artificial constructions.
Marseilles lies in a large arid basin, and the aqueduct approaches the edge of the basin at a hight of 500 feet above the level of the sea. Branches extend to and irrigate the area of 25,000 acres, and also supply the city of
Marseilles.
The bridge over the
valley of the Arc is 1,287 feet in length and 262 feet in hight.
It is formed of a triple tier of arches; is said to have occupied from 700 to 800 workmen for seven years, and to have cost $750,000. The water channel is 30 feet wide at top, 10 at bottom, and is 7 feet deep.
It delivers 11 tons of water per second.
The aqueduct of Chirk on the
Ellesmere and Chester Canal in
England is noted as being the first in which iron was employed, the bottom of the water channel being of cast-iron and the walls of masonry; that of Pont-y-Cysyllte, on the same canal, has the entire channel made of cast-iron arches or ribs resting on pillars of stone.
It carries the waters of the canal across the
valley of the Dee.
It is upwards of one thousand feet in length, consisting of nineteen arches of equal span, but varying in their hight above the ground.
The three shown in elevation in
Fig. 292 are the highest, being those which cross the river
Dee itself; the surface of the canal is one hundred and twentyseven feet above the usual level of the water in the river.
The aqueduct itself is a cast-iron trough formed of plates with flanges securely bolted together.
This trough is supported upon cast-iron arches, each composed of four ribs, supported upon piers of masonry.
The towing-path overhangs the water, being supported at intervals on timber pillars.
Watt's submerged aqueduct across the bed of the
Clyde was an articulated pipe whose joints rendered it flexible, so as to accommodate itself to the shape of the river-bed.
It is stated to have been a success.
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Pont-y-cysyllte aqueduct. |
The Croton Aqueduct was commenced in 1837 and completed in 1842, costing $8,575,000.
Its length is 40 1/2 miles, 33 miles of which distance it is built of stone, brick, and cement, arched above and below.
It has a capacity for discharging 60,000,000 of gallons per day. It is carried over the
Harlem River by pipes laid upon a bridge consisting of fifteen arches, eight of 80 feet and seven
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of 50 feet span, rising to 114 feet above low-water mark.
At the spot where the
Croton dam is constructed, the surface-water of the creek was about 38 feet lower than the elevation required as a head for the delivery of the water into the
city of New York at a sufficient hight.
By going farther up stream a dam of less hight would have been sufficient, but the supply of water would of course have been smaller.
The medium flow of water at the dam is about 50,000,000 gallons daily, and the minimum in very dry seasons about 27,000,000 gallons.
The water is set back upon the course of the creek by the dam, about six miles, forming the reservoir, which has an area of about 400 acres, now called Croton Lake.
The available capacity of this reservoir down to the point where the water would cease to flow into the aqueduct is estimated at 600,000,000 gallons, in addition to which the receiving reservoir in the city is capable of containing 150,000,000 more when full, which together afford a reserve supply of 750,000,000 gallons in seasons of extreme drought.
In case of necessity other streams might be turned into the
Croton River at or above the reservoir, or into the aqueduct.
From the dam at the lower end of Croton Lake to the receiving reservoir there is no essential change made in the form of the channel-way, except that, in crossing the
Harlem River and a valley on
Manhattan Island, iron pipes are used instead of masonry; at these places the pipes fall and rise again so that they are always full.
The channel-way of masonry is never entirely filled, so as to cause a pressure on its interior surface.
To avoid this, six waste weirs were constructed at suitable places to allow the water to flow off upon attaining a certain level.
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Earth excavation. |
Fig. 293 is a section showing the kind of masonry used in earth excavations.
The foundation is of concrete, the side walls of stone, the bottom and sides of the interior faced with brick, and the top covered with an arch of brick.
After the masonry was finished the excavation was filled up around it and over the top of the coverin garch, generally to the depth of three or four feet, and in deep excavations up to the natural surface.
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Rock excavation. |
Fig. 294 shows a section in open cuttings in rock.
The rock was excavated to the requisite depth and width, and the bottom filled in with concrete to the proper hight and form for receiving an inverted arch of brick; the side walls were of brick bonded with an outer casing of stone, built up closely against the sides of the rock.
On the exterior of the roofing arch, and filling the space between it and the rock, spandrels of stone were built.
When finished, the space above the masonry was filled in with earth.
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Rock tunnel. |
Fig. 295 is a section in tunnel cuttings in solid rock.
In hard, sound rock the natural rock often served as a roof, but when soft, a brick arch was built over the channel walls and the space between its upper surface and the rock filled in with wellrammed earth.
In some cases where the rock was originally hard, it was found to become soft and insecure upon exposure to the air, rendering it necessary to arch over the channel-way to support the natural roof.
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Earth tunnel. |
Fig. 296 is a section in earth tunnel cuttings.
In dry and compact earth the excavation for the bottom and sides was made of just sufficient size to receive the masonry built closely against it; the top was made high enough to give room for turning the roofing arch, and when complete the space above it was filled with earth closely rammed.
In wet earth the excavation was made larger and the top and sides supported by props of timber and plank until the masonry was completed; the vacant space around it was then compactly filled with earth.
In crossing valleys, the aqueduct was supported on a foundation wall of stone, laid dry, and sloping embankments of earth were thrown up on each side of it.
At intervals of a mile apart, ventilating shafts of stone were erected over the aqueduct, rising about 14 feet above the surface of the ground; every third shaft was provided with a door to afford entrance to the interior of the aqueduct for the purpose of inspection or repairs.
Openings two feet square were also made in the top of the roofing arch every quarter of a mile; each of these was covered
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by a flag-stone, and its position indicated by a small monument projecting above the surface; these are for the purpose of obtaining entrance or increasing the ventilation if necessary.
Where the line of the work was intersected by streams, culverts were built to allow the water to pass under without injury to the aqueduct.
In connection with the reservoir at the dam is a tunnel and gate-chamber.
The gate-chamber is not directly connected to the dam itself, but is at a distance of upwards of 200 feet. The water is conducted from the reservoir to the gate-chamber by means of the tunnel T, which is cut through the solid rock of the hill, having its entrance above the dam, its center being about 12 feet below the surface of the water, so that the entrance of floating bodies is prevented.
In winter, when the reservoir is frozen over, there is no obstruction to the flow of water into the aqueduct, and in summer the water is drawn from a level where it is cooler and purer than at the surface.
The gate-chamber has two sets of gates, the one being called regulating gates, R, and the other guardgates, G, G. The regulating gates are made of gunmetal, and work in frames of the same material, fitted to stone jambs and lintels; the guard-gates are of cast-iron, working in cast-iron frames, also attached to stone jambs and lintels.
The gates are managed by means of wrought-iron rods, having a screw on their upper part working in a brass nut set in a cast-iron socket-cap.
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Dam and gate-chamber. |
The accompanying view (
Fig. 297) exhibits a section of the hill through which the tunnel is cut, showing its entrance into the reservoir, the gatehouse and gates, and the point of discharge into the channel-way of the aqueduct.
In the center of the dam and on its ridge is a gatehouse over a culvert passing through the dam. This culvert is 30 feet below the surface of the water when the reservoir is full, and has gates opened by rods rising up into the gate-house.
When the river is low, the water which is not carried off by the aqueduct may be allowed to pass through this culvert, preventing any from passing over the dam.
The bottom of the water-way of the aqueduct at the gate-chamber is 11.4 feet below the surface of the reservoir, and 154.77 feet above the level of mean tide at New York City.
The aqueduct is divided into different planes of descent from the gate-chamber at the dam to that of the receiving reservoir on
Manhattan Island, and is as follows: —
| Length. | Descent. |
| Feet. | Miles. | Feet. |
| First plane of aqueduct | 26.099.72 | 4.943 | 2.94 |
| Second plane of aqueduct | 148,121.25 | 28.053 | 30.69 |
| Length of pipes across the Harlem River | 1,377.33 | 0.261 |
| Difference of level between the ends of the pipes | | | 2.29 |
| Third plane of aqueduct | 10,733.14 | 2.033 | 2.25 |
| Length of pipes across the Manhattan Valley | 4,105.09 | 0.777 |
| Difference of level between the ends of the pipes | | | 3.86 |
| Fourth plane of aqueduct | 10,680.89 | 2.023 | 1.60 |
| ———— | —— | —— |
| 201,117.42 | 38.090 | 43.63 |
The hight of the interior of the aqueduct is 8 feet 5 1/2 inches, and the greatest width 7 feet 5 inches; the interior having a sectional area of 53.34 square feet.
On the first plane the aqueduct is larger, being 2.05 feet higher at the gate-chamber, 2.31 feet higher at 2,244 feet from the chamber, and diminishing to the head of the second plane, where it is of the dimensions above stated.
The curves used in changing the course of the aqueduct are generally of 500 feet radius; in some cases a radius of 1,000 feet or even more was employed.
The receiving reservoir is located between Sixth and Seventh Avenues and Seventy-ninth and Eightysixth Streets in the upper part of the
city of New York.
It is 1,826 feet long and 836 feet wide at the top of the external walls of the embankment, having a total area of 37 acres, the area of the water-surface being 31 acres. The reservoir is divided into two divisions by means of an embankment, either of which may be used independently while the water is drawn off from the other, in case of repairs, etc.
The greatest depth of water in the north division is 20 feet, in the south, 30 feet, and the total capacity of the whole 150,000,000 gallons.
The aqueduct enters a gate-chamber in the south division, where there are regulating gates for discharging the water into either division by a continuation of the aqueduct within the reservoir.
The two divisions are connected by a cast-iron pipe for equalizing the level of water in each.
There is also a waste weir for the escape of surplus water into a sewer.
The embankment is of earth, protected on the outside by a stone wall four feet thick, the face of which is laid in mortar; the inside slope has a stone facing, 15 inches thick, laid without mortar.
From the receiving reservoir the water is carried by iron pipes to the distributing reservoir, a distance of 2.17 miles, with a fall of four feet. The distributing reservoir is 436 feet square at the base and 425 feet square at the corners, having an area of rather more than four acres, and a capacity of 20.000,000 gallons.
The outside walls have openings, so that by entering a door one may walk entirely round the reservoir within the walls, giving a greater breadth with
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a given amount of material, and affording an opportunity of examining the work for the purpose of obviating leakage, and also preventing water from finding its way to the exterior and causing injury to the wall by freezing.
This open space rises to within about eight feet of the water-line.
Inside of the wall is an embankment of puddled earth faced with hydraulic masonry 15 inches thick.
From the distributing reservoir the water is distributed over the city by means of cast-iron pipes of from 36 to 4 inches diameter.
The total cost of the work was $8,575,000, including the purchase of land, etc., being within five per cent of the engineer's estimate.
In this the cost of the distributing pipes within the city is not included.
The Washington Aqueduct was built at the expense of the United States government, for the purpose of supplying the cities of
Washington and
Georgetown with water, and is distinguished by some bold features of engineering.
The most remarkable of these is the bridge over
Cabin John Creek, near the upper termination of the work, the widest spanned stone arch at the time of its construction; it has a span of 220 feet and a rise of 57 feet 3 inches.
The bridge over
Rock Creek is also a peculiar and noteworthy application of the results of modern science and mechanical skill.
The water is carried across this stream (which divides the cities of
Washington and
Georgetown) by means of two arches of cast-iron pipes of 3 feet 6 inches interior diameter, formed of sections with flanges firmly screwed to each other and braced; upon these are laid a bridge over which the street cars pass, and which serves as a public avenue of communication between the two cities.
The span is 200 feet, and the rise 20 feet.
The aqueduct which supplies
Madrid with water, and has a large surplus for irrigation, is fed from the river
Lozoya, where it emerges from the
Guardarama Mountains.
This work was constructed under the superintendence of Don Lucio del
Valle, between 1851 and 1858, and is 47 miles in length.
The river gorge is crossed by a cut-stone dam, 98 feet in hight, its wings abutting upon the solid rock of the hillsides.
The artificial lake thus formed contains 100,000,000 cubic feet of water.
The cost of the whole work was 57,897,368 francs.
The “canal,” as it is termed, has seven miles of subterranean galleries, 4,600 feet of aqueducts, and 8,600 feet of inverted siphons at the crossings of three valleys.
The siphon of Bedonal is 4,600 feet in length.
The transverse section of the waterway has an area of about 20 square feet, and it discharges 6,600,000 cubic feet of water per day; one fifth is required for town service, the remainder being used in irrigating a tract of nearly 5,000 acres.
The town service has 45 miles of brick culverts about six feet high, and 60 miles of cast-iron pipes.
It supplies 35 public fountains, and has 3,000 plugs for fire and irrigating purposes.
A novel expedient for the support of an aqueduct across a densely wooded ravine was suggested by
Mr. McTaggart, the resident engineer for the
Rideau Canal in
Canada.
In a part of the country traversed by the canal, materials for forming an embankment, or stone for building the piers of an aqueduct, could not be obtained but at a great expense.
The plan consisted of cutting across the large trees in the line of the works, at the level of the bottom of the canal, so as to render them fit for supporting a platform on their trunks, and on this platform the trough containing the water of the canal was intended to rest.
