The earliest attempts in Europe to solve the problems of water-supply
were made by the Greeks, who perhaps derived their ideas from the
Phoenicians. It has generally been held, partly on the strength of a
passage in Strabo (v. 3. 8, p. 235), and partly owing to the comparative
unimportance of the remains discovered, that the Greek works were
altogether inferior to the Roman. Research in the Greek towns of Asia
Minor, together with a juster appreciation of the remains as a whole,
must be held to modify this view. Among the earliest examples of Greek
work are the tunnels or _emissaria_ which drained Lake Copais in
Boeotia; these, though not strictly aqueducts, were undoubtedly the
precursors of such works, consisting as they did of subterranean tunnels
([Greek: hyponomoi]) with vertical shafts ([Greek: phreatiai]), sixteen
of which are still recognizable, the deepest being about 150 ft. They
may be compared with that described by Polybius as conveying water from
Taurus to Hecatompylos, and with numerous other remains in Asia Minor,
Syria, Phoenicia and Palmyra. Popular legend ascribed them to Cadmus,
just as Argos referred the irrigation of its lands to Danaus. They are
undoubtedly of great antiquity.
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 Samos and Peisistratus of Athens
were distinguished for their wisdom and enterprise in this respect. The
former obtained the services of Eupalinus, an engineer celebrated for
the skill with which he had carried out the works for the water-supply
of Megara (see _Athen. Mittheil._ xxv., 1900, 23) under the direction of
the Tyrant Theagenes (c. 625 B.C.). At Samos the difficulty lay in a
hill which rose between the town and the water source. Through this hill
Eupalinus cut a tunnel 8 ft. broad, 8 ft. high and 4200 ft. long,
building within the tunnel a channel 3 ft. 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,
cloacae, &c., and ultimately passed into the harbour (Herod, iii. 60).
In Athens, under the rule of the Peisistratids (c. 560-510 B.C.), a
similarly extensive, if less difficult, series of works was completed to
bring water from the neighbouring hills to supplement the inadequate
supply from the springs. From Hymettus were two conduits passing under
the bed of the Ilissus, most of the course being 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 130-160 ft.;
the diameter of these shafts is 4-5 ft., 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 is
sufficiently large for two men to pass in it. The precise location of
the reservoir depends on the value of Dr Wilhelm Dorpfeld's theory as to
the site of the Enneacrunus of Thucydides and Pausanias (see ATHENS:
_Topography and Antiquity_). Dorpfeld places it south-west of the
Acropolis, where there is a cistern connected with an aqueduct which
passed under the theatre of Dionysus and on towards the Ilissus (see map
under ATHENS). Others have placed it south of the Olympieum in the
Ilissus bed. Beside these works water was brought from Pentelicus in an
underground conduit begun by the emperor Hadrian and completed by
Antoninus Pius. This aqueduct is still in use, having been repaired in
1869.
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 the ground. Syracuse was supplied by two aqueducts, one
of which the Athenians destroyed (Thuc. vi. 100). One was fed by an
affluent (the mod. Buttigliara) of the Anapus (mod. Anapo); it carried
the water up to the top of Epipolae, where the channel was open, and
thence down to the city and finally into the harbour. The other also
ascends to the top of Epipolae, skirts the city on the north, and then
proceeds along the coast. Its course is marked by rectangular shafts
(_spiragli_) at the bottom of which water is still visible.
An example of what appears to have been the earliest form of aqueduct in
Greece was discovered in the island of Cos beside the fountain Burinna
(mod. Fountain of Hippocrates) 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 from the top of the
chamber supplied fresh air. From this reservoir the water was led by a
subterranean channel, 114 ft. long and 6-1/2 ft. high. (J. M. M.)
Roman.
In comparing Greek and Roman aqueducts, many writers have enlarged on
the greatness of the latter as an example of Roman contempt for natural
obstacles, or even of Roman ignorance of the laws of nature. Now, in the
first place, the Romans were not unacquainted with the law that water
finds its own level (see Pliny, _Hist. Nat._ xxxi. 57, "subit
altitudinem exortus sui"), and took full advantage of it in the
construction of lofty fountains and the supplying of the upper floors of
houses. That they built aqueducts across valleys in preference to
carrying pipes underground was due simply to economy. Pipes had to be
made of lead which was weak, or of bronze which was expensive; and the
Romans were not sufficiently expert in the casting of large pipes which
would stand a very great pressure to employ them for the whole course of
a great aqueduct. Secondly, the water was so extremely hard that it was
important that the channels should be readily accessible for repair as
well as for the detection of leakage.[1] Moreover, as we shall see, the
Roman aqueducts did not, in fact, preserve a straight line regardless of
the configuration of the country. A striking example is the aqueduct of
Nemausus (Nimes), the springs of which are some 10 m. from the town,
though the actual distance traversed is about 25. Other devices, such as
changing the level and then modifying the slope, and siphon arrangements
of various kinds, were adopted (as in the aqueduct at Aspendus).
Sextus Julius Frontinus, appointed _curator aquarum_ in A.D. 97,
mentions in his treatise _de aquaeductibus urbis Romae_ (on the
aqueducts of the city of Rome) nine aqueducts as being in use in his
time (the lengths of the aqueducts as given here follow his
measurements). These are: (1) AQUA APPIA, which took its rise between
the 6th and 7th milestones of the Via Collatina, and measured from its
source to the Porta Trigemina 11 Roman miles, of which all but about 300
ft. were below ground. It appears to have been the first important
enterprise of the kind at Rome, and was the work of the censor Appius
Claudius Caecus, from whom it derived its name. The date of its
construction was 312 B.C. (2) ANIO VETUS, constructed in 272-269 B.C. by
the censor Manius Curius Dentatus. From its source near Tivoli, on the
left side of the Anio, it flowed some 43 m.,[2] of which only 1100 ft.
was above ground. At the distance of 2 m. 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 Porta Esquilina. (3) AQUA MARCIA, reconstructed in
1869-1870 under the name of Acqua Pia or Marcia-Pia after Pius IX.
(though from Tivoli to Rome the modern aqueduct takes an entirely
different course), rising on the left side of the Via Valeria near the
36th milestone. It traversed 61-3/4 m., of which 54-1/4 were
underground, and for the remaining distance was carried partly on
substructions and partly on arches. It was the work of the praetor
Quintus Marcius Rex (144-140 B.C.), not of Ancus Marcius, 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. Its volume was largely increased by Augustus, who
added to it the Aqua Augusta; and it was repaired and restored by Titus,
Septimus Severus, Caracalla and Diocletian. (4) AQUA TEPULA, from its
source (now known as Sorgente Preziosa) in the district of Tusculum, to
Rome, was some 11 m. in length. The first portion of its course must
have been almost entirely subterranean and is not now traceable. For the
last 6-1/2 m. it ran on the same series of arches that carried the Aqua
Marcia, but at a higher level. It was the work of the censors Cn.
Servilius Caepio and L. Cassius Longinus, and was completed in the year
125 B.C. Its water is warm (about 63 deg. Fahr.) and not of the best
quality. (5) The AQUA JULIA, from a source 2 m. from that of the Tepula,
joined its course at the 10th milestone of the Via Latina. The combined
stream, after a distance of 4 m., was received in a reservoir, and then
once more divided into two channels. The entire length of the Julia was
15-1/2 m. It was constructed in the year 33 B.C. by M. Vipsanius
Agrippa, who also built the (6) AQUA VIRGO which, from its origin at a
copious spring in a marsh on the Via Collatina, measured 14 m. in
length; it was conveyed in a channel, partly under and partly above
ground. It was begun in the year 33 B.C. and was celebrated for the
excellence of its waters. It was restored to use by Pius V. in 1570. (7)
AQUA ALSIETINA or AUGUSTA, the source of which is the Lacus Alsietinus
(mod. Lago di Martignano), to the north of Rome, was over 22 m. in
length, of which 358 paces were on arches. It was the work of Augustus,
probably with the object of furnishing water for his _naumachia_ (a
basin for sham sea-fights), and not for drinking purposes. Its course is
unknown, as no remains of it exist, but an inscription relating to it
is given in _Notizie d. Scant_ (1887), p. 182. (8, 9) The AQUA CLAUDIA
and ANIO NOVUS were two aqueducts begun by Caligula in A.D. 38 and
completed by Claudius in A.D. 52. The springs of the former belonged to
the same group as those of the Marcia, and were situated near the 38th
milestone of the Via Sublacensis, not far from its divergence from the
Via Valeria, while the original intake of the latter from the river Anio
was 4 m. farther along the same road. As the water was thick it was
collected in a purifying tank, and 4 m. below, a branch stream, the
Rivus Herculaneus, was added to it. According to Frontinus, over 10 m.
of the course of the Claudia and nearly 9-1/2 of that of the Anio Novus
were above ground. Seven miles out of Rome they united and ran from that
point into Rome, following a natural isthmus formed by a lava stream
from the Alban volcano, upon a line of arches, which still forms one of
the most conspicuous features of the Campagna. The original inscription
of Claudius (A.D. 52) on the Porta Maggiore, by which the Aqua Claudia
and Anio Novus crossed the Via Praenestina and the Via Labicana, gives
the length of the Aqua Claudia as 45 m., and that of the Anio Novus as
62 m. Frontinus, on the other hand, gives 46.406 m. (i.e. about 43
English miles) and 58.700 m. (i.e. about 54 English miles). Albertini
(_Melanges de l'Ecole Francaise_, 1906, 305) explains the difference as
due to the fact that Frontinus was calculating the length of the Claudia
from the farthest spring, the Fons Albudinus, and that of the Anio Novus
from the new intake constructed by Trajan in one of the three lakes
constructed by Nero for the adornment of his villa above Subiaco. Two
other inscriptions on the Porta Maggiore record restorations by
Vespasian in A.D. 70, and by Titus in A.D. 80. That the aqueducts should
be spoken of as _vetustate dilapsi_ so soon after their construction is
not a little surprising, and may be attributed either to hasty
construction in order to complete them by a fixed date, or to jobbery by
the imperial freedmen who under Claudius were especially powerful, or to
the fact that a line of arches intended originally in all probability
for the Aqua Claudia alone was made to carry the Anio Novus as well.
The size of the channels (_specus_) of the principal aqueducts varies
considerably at different points of their course. The Anio Novus has the
largest of them all, measuring 3 to 4 ft. wide and 9 ft. high to the top
of the roof, which is pointed. They are lined with hard cement (_opus
signinum_) containing fragments of broken brick. Those aqueducts of
which the most conspicuous remains exist in the neighbourhood of Rome
are the four from the upper valley of the Anio, the two which took their
supply and their name from the river itself, and the Marcia and the
Claudia, which originated from the same group of springs, in the floor
of the Anio valley 6 m. below Subiaco. Those of the Anio Vetus, which
travelled at a considerably lower level than the other three, are the
least conspicuous, while the Claudia and Anio Novus as a rule kept close
together, the latter at the highest level of all. The ruins of bridges
and substructions in the Anio valley down to Tivoli, though
comparatively little known, are of great importance. In all the
aqueducts the original construction of the bridges was in _opus
quadratum_ (masonry), while the substructions are in brick-faced
concrete; but the bridges are as a rule strengthened (and often several
times) with reinforcing walls of concrete faced with _opus reticulatum_
or brickwork. Below Tivoli, where the Anio leaves its narrow valley, the
aqueducts sweep round towards the Alban hills, and pass through some
very difficult country between Tivoli and Gallicano, alternately
crossing ravines, some of which are as much as 300 ft. deep, and
tunnelling through hills.[3]
The engineering skill displayed is remarkable, and one wonders what
instruments were employed--probably the so-called _chorobates_, an
improvement upon the ordinary water-level (Vitruvius viii. 6), though
this would be slow and complicated. The optical properties of glass
lenses were, however, unknown to the ancients, and the _dioptra_, or
angle measure, was considered by Vitruvius less trustworthy than the
_chorobates_ for the planning of aqueducts (cf. E. Hultsch, _s.v_. in
Pauly-Wissowa, _Real-encyclopadie_). The aqueducts as a rule were
carried on separate bridges, though all four united at the Ponte Lupo, a
huge structure, which after the addition of all the four, and with the
inclusion of all the later strengthening walls that were found necessary
in course of time, measures 105 ft. in height, 508 in length, and 46 in
thickness at the bottom, without including the buttresses. From
Gallicano onwards the course of these four aqueducts follows the lower
slopes of the Alban Hills. Previous writers on the subject have been
unable to determine their course, which is largely subterranean; but it
can be followed step by step with the indications given by the presence
of the calcareous deposit which was thrown out at the _putei_ or shafts
(which were, as a rule, placed at intervals of 240 ft., as were the
_cippi_) when the _specus_ was cleaned; and remains of bridges, though
less important, owing to the less difficult character of the country,
are not entirely absent (cf. the works by T. Ashby cited in
bibliography).[4] Near the 7th milestone of the Via Latina at Le
Capanelle, the Aqua Claudia and Anio Novus emerge from their underground
course, and run into Rome upon the long series of arches already
mentioned, passing over the Porta Maggiore. The Claudia sent off an
important branch from the Porta Maggiore over the Caclian to the
Palatine, but the main aqueduct soon reached its termination. A mile
farther on the Aqua Marcia also, owing to the gradual slope of the
ground towards Rome, begins to be supported on arches, which were also
used to carry the Aqua Tepula and the Aqua Julia (of the two latter,
before their junction with the Marcia, no remains exist above ground,
but inscribed _cippi_ of the last named and its underground channel have
been found at Le Capanelle, and _cippi_ also close to its springs, which
are a little way above Grottaferrata at Gli Squarciarelli). The Anio
Vetus followed the same line, but kept underground (as was natural at
the early period at which it was constructed) until the immediate
neighbourhood of Rome, near the locality known as "ad Spem veterem"
(from a temple of Spes, of which no remains are known) close to the
Porta Maggiore. At this point, besides the aqueducts named, the Aqua
Appia, as we are told by Frontinus, entered the city, and received an
important branch, the Appia Augusta. No remains of either have been
discovered outside the city.
The Aqua Alexandrina must also have entered the city here, though its
channel, which lay at some depth below ground, has not been discovered.
Considerable remains of its brick aqueducts exist in the district
between the Via Praenestina and the Via Labicana.
Of the two aqueducts on the right bank of the Tiber, the Alsietina, as
we have said, has no remains at all, while those of the Traiana are not
of great importance. The line of the aqueducts was marked by _cippi_,
inscribed (in the case of the Anio Vetus, Marcia, Tepula, Julia and
Virgo--those of the Claudia and Anio Novus are uninscribed, and those of
the Traiana are differently worded) with the name of the aqueduct, the
distance from the next _cippus_ (generally 240 ft.) and the number,
counting from Rome (not from the springs). These boundary stones were
erected in pairs, to mark off the strip of land 30 ft. in width reserved
for the aqueduct, and for the road or path which generally followed it.
The shafts (_putei_) often stood, but not necessarily, at the same
points as the _cippi_.
To these nine must be added the two following, constructed after
Frontinus's time: (10) AQUA TRAIANA, from springs to the north-west of
the Lacus Sabatinus (Lago di Bracciano), constructed by Trajan in A.D.
109, about 36-1/2 English miles in length. It was restored by Paul V. in
1611, who made use of and largely transformed the remains of the ancient
aqueduct; he allowed some of the inferior water of the lake to flow into
the channel, and it is thus no longer used for drinking. (11) AQUA
ALEXANDRINA, rising about 14 English miles from Rome, between the Via
Praenestina and the Via Labicana, the work of Alexander Severus (A.D.
226). The springs now supply the modern Acqua Felice, constructed by
Sixtus V. in 1585, but the course of the latter is mainly subterranean
and not identical with that of the former.
[Illustration: PLATE I.
_Photo, Altnari._
AQUA CLAUDIA, ROME.
_Photo, Neurdein._
PONT DU CARD, NIMES (NEMAUSUS).]
[Illustration: PLATE II.
_Photo, Laureat y Cia._
ROMAN AQUEDUCT AT SEGOVIA.
AQUEDUCT OF ROQUEFAVOUR, MARSEILLES.
Early nineteenth century.
_Photo, Brogi._
PISCINA MIRABILIS AT BAIAE.
_Photo, Dr T. Ashby._
AQUA MARCIA, ROME.]
It is agreed that these eleven are all that were constructed. Procopius
speaks of fourteen (and the Regionary catalogues mention others), but
this number includes branch conduits. All the aqueducts ended in the
city in huge _castella_ or reservoirs for the purpose of distribution.
Vitruvius recommends the division of these into three parts--one for the
supply of fountains, &c., one for the public baths and one for private
consumers. In the Piazza Vittorio Emmanuele at Rome there are still to
be seen the remains of a large ornamental fountain built probably for
the Aqua Julia by Domitian or Alexander Severus (Jordan-Hulsen,
_Topographie_, i. 3350). Besides these main _castella_ there were also
many minor _castella_ in various parts of the city for sub-distribution.
To allow the water to purify itself before being distributed in the
city, filtering and settling tanks (_piscinae limariae_) were built
outside the walls. These _piscinae_ were covered in with a vaulted roof,
and were sometimes on a very large 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 Mirabilis 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, who were not, however, the constructors of them; of
the four aqueducts built during this period, three are the work of
censors, one (the Marcia) of a praetor. Under the empire this task
devolved on special officials styled _Curatores Aquarum_, instituted by
Augustus, who, as he himself says, "rivos aquarum omnium refecit"
(inscription on the arch by which the Aqua Marcia crossed the Via
Tiburtina). (T. As.)
Among the aqueducts outside Italy, constructed in Roman times and
existing still, the most remarkable are: (1) the aqueduct at Nimes
(Nemausus), erected probably by Vipsanius Agrippa in the time of
Augustus, which rose to 160 ft. The Pont du Card, as this aqueduct is
now called, consists of three tiers of arches across the valley of the
river Gardon. In the lowest tier are six arches, of which one has a span
of 75 ft., the others each 60 ft. In the second tier are eleven arches,
each with a span of 75 ft. In the third tier are thirty-five smaller
arches which carried the _specus_. 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. (2) The aqueduct bridges
at Segovia (Merckel, _Ingenieurtechnik_, pp. 566-568), Tarragona
(_ibid._ 565-566), and Merida in Spain, the former being 2400 ft. long,
with 109 arches of fine masonry, in two tiers, and reaching the height
of 102 ft. The bridge at Tarragona is 876 ft. long and 83 ft. high. (3)
At Mainz are the ruins of an aqueduct 7000 yds. long, about half of
which is carried on from 500 to 600 pillars (_Archaeological Journal_,
xlvii., 1890, pp. 211-214). This aqueduct was built by the XIVth legion
and was for the use of the camp, not for the townspeople. For the
similar aqueduct at Luynes see _Arch. Journ._ xlv. (1888), pp. 235-237.
Similar witnesses of Roman occupation are to be seen in Dacia, Africa
(see especially under CARTHAGE), Greece and Asia Minor. (4) The aqueduct
at Jouy-aux-Arches, near Metz, which originally extended across the
Moselle, here very broad, conveyed to the city an abundance of excellent
water from Gorze. 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 m. from Metz, and conveyed it to the
city. The bridge consisted of only one row of arches nearly 60 ft. high.
The middle arches have given way under the force of the water, but the
others are still perfectly solid. This aqueduct is probably to be
attributed to the latter half of the 4th century A.D. It is for the use
of the town; hence its size. (5) One of the principal bridges of the
aqueduct of Antioch in Syria is 700 ft. long, and at the deepest point
200 ft. 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 Beit el-Ma (anc. Daphne) about 4 or 5 m. 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. (6) At the village of Moris,
about an hour's distance north-west from the town of Mytilene, is the
bridge of an aqueduct, carried by 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 ft. in
length, and at the deepest point was from 70 to 80 ft. 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 Moris, and at St Demetri, two hours
and a half from Ayasos, on the road to Vasilika.
Asia Minor.
The whole subject of the ancient and medieval aqueducts of Asia Minor
has been considered in great detail by G. Weber ("Wasserleitungen in
kleinasiatischen Stadten," in the _Jahrbuch des kaiserl. deutsch.
archaolog. Instit._ xix., 1904; see also earlier articles in _Jahrbuch_,
1892, 1899). The aqueducts examined are those at Pergamum, Laodicea and
Smyrna (in the earlier articles), and those at Metropolis (Ionia),
Tralles (Aidin), Antioch-on-Maeander, Aphrodisias, Trapezopolis,
Hierapolis, Apamea Cibotus and Antioch in Pisidia. In most of these
cases it is difficult or even impossible to decide whether the work is
Hellenistic or Roman; to the Romans Weber inclines to attribute, e.g.
those at Metropolis, Tralles (perhaps), Aphrodisias; to the Greeks, e.g.
those at Antioch-on-Maeander and Antioch in Pisidia. Since, therefore, a
detailed description of these remains does not provide material for any
satisfactory generalizations as to the distinctive features of
Hellenistic and Roman work, it will be sufficient here to mention a few
of the more interesting discoveries.
In the case of Metropolis, the aqueduct in the valley of the Astraeus
consisted of an arcade about 13 to 16 ft. high. Nearer to the town in
the hills there are distinct traces of a canal with brick walls. It is
clear that the water could not have served more than the lower parts of
the town, the acropolis of which is nearly 200 ft. above the level of
the conduit. In the case of Tralles the water was supplied by a high
pressure conduit and distributed from the acropolis, where there are the
remains of a basin (13 ft. by 10) arched over with brick. The ancient
aqueduct is to be distinguished from a later, probably Byzantine, canal
conduit, the course of which avoids the deeper depressions, crossed by
the old aqueduct. Of the Antioch-on-Maeander aqueduct only a few
clay-pipes remain, and the same is true of the aqueduct which was built
by Carminius in the 2nd century A.D. to supply the community when
reinforced by the amalgamation of Plarasa and Tauropolis; two of its
basins are still distinguishable, but the two water-towers which are
still standing belong to a later Byzantine structure. Trapezopolis was
supplied from Mt. Salbacus (Baba Dagh): some twenty stone-pipes have
been found built into a low wall which varies from 3-1/4 to about 5 ft.
wide. Of the pillars which carried the conduit-pipe to Antioch in
Pisidia, nineteen are still standing. Each arch consists of eleven
keystones; no cement was used. The conduit, which was high-pressure,
ends in a distributing tower and reservoir. (J. M. M.)
II. _Medieval._--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 ft. in span, and about 300
ft. in height.
Constantinople.
The aqueduct of Pyrgos, near Constantinople, is a remarkable example of
works of this class carried out in the later times of the Roman empire,
and consisted of two branches. From this circumstance it was called Egri
Kemer ("the Crooked Aqueduct"), to distinguish it from the Long
Aqueduct, situated near the source of the waters. One of the branches
extends 670 ft. in length, and is 106 ft. in height at the deepest part.
It is composed of three tiers 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 leads to
the belief that the date of the structure is about the 10th century. The
breadth of the building at the base was 21 ft., and it diminished with a
regular batter on each side to the top, where it was only 11 ft. The
base also was protected by strong buttresses or counterforts, erected
against each of the pillars. The other branch of the aqueduct was 300
ft. long, and consisted of twelve semicircular arches. This aqueduct
serves to convey to Constantinople the waters of the valley of Belgrad,
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 m.
from the city, and between 3 and 4 m. west of the village of Belgrad, 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 m. below the Aqueduct of Justinian, by means of
an aqueduct, with two tiers of arches of a very beautiful construction.
The conduit then proceeds onward in a circuitous route, till it reaches
the reservoir of Egri Kapu, 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 (Usun Kemer) 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 tiers of arches, the lower being
forty-eight in number, and the upper fifty. The whole length was about
2200 ft., and the height 80 ft. The aqueduct of Justinian (Muallak Kemer
or "Hanging Aqueduct") is without doubt one of the finest monuments
which remain to us of the middle ages. It consists of two tiers of large
pointed arches, pierced transversely. Those of the lower story have 55
ft. of span, the upper ones 40 ft. The piers are supported by strong
buttresses, and at different heights they have little arches passing
through them laterally, which relieve the deadness of the solid pillar.
The length of this aqueduct is 720 ft. and the height 108 ft. This
aqueduct has been attributed both to Constantine I. and to Justinian,
the latter being perhaps the more probable.
Besides the waters of Belgrad, Constantinople was supplied from several
other principal sources, one of which took its rise on the heights of
the same mountains, 3 or 4 m. east of Belgrad. 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 (on his voyage to the
Black Sea, the account of the Thracian Bosporus), 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 underground, 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 siphons 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 (see also works quoted under
CONSTANTINOPLE). The other principal source from which Constantinople is
supplied, is from the high grounds 6 or 8 m. 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 ft. per day.
(A. S. M.; J. M. M.)
Aqueducts and water supply.
III. _Modern Construction._--Where towns are favourably situated the
aqueduct may be very short and its cost bear a relatively small
proportion to the total outlay upon a scheme of water supply, but where
distant sources have to be relied upon the cost of the aqueduct becomes
one of the most important features in the scheme, and the quantity of
water obtainable must be considerable to justify the outlay. Hence it is
that only very large towns can undertake the responsibility for this
expenditure. In Great Britain it has in all large schemes become a
condition that, when a town is permitted to go outside its own
watershed, it shall, subject to a priority of a certain number of
gallons per day per head of its own inhabitants, allow local
authorities, any part of whose district is within a certain number of
miles of the aqueduct, to take a supply on reasonable terms. The first
case in which this principle was adopted on a large scale was the
Thirlmere scheme sanctioned by parliament in 1879, for augmenting the
supply of Manchester. The previous supply was derived from a source only
about 15 m. distant, and the cost of the aqueduct, chiefly cast-iron
pipes, was insignificant compared with the cost of the impounding
reservoirs. But Thirlmere is 96 m. distant from the service reservoir
near Manchester, and the cost of the aqueduct was more than 90% of the
total cost. As a supply of about 50,000,000 gallons a day is available
the outlay was justifiable, and the water is in fact very cheaply
obtained. Liverpool derives a supply of about 40,000,000 gallons a day
from the river Vyrnwy in North Wales, 68 m. distant, and Birmingham has
constructed works for impounding water in Radnorshire, and conveying it
a distance of 74 m., the supply being about 75,000,000 gallons a day. In
the year 1899 an act of parliament was passed authorizing the towns of
Derby, Leicester, Sheffield and Nottingham, jointly to obtain a supply
of water from the head waters of the river Derwent in Derbyshire.
Leicester is 60 m. distant from this source, and its share of the supply
is about 10,000,000 gallons a day. For more than half the distance,
however, the aqueduct is common to Derby and Nottingham, which together
are entitled to about 16,000,000 gallons a day, and the expense to
Leicester is correspondingly reduced. These are the most important cases
of long aqueducts in England, and all are subsequent to 1879. It is
obvious, therefore, how greatly the design and construction of the
aqueduct have grown in importance, and what care must be Exercised in
order that the supply upon which such large populations depend may not
be interrupted, and that the country through which such large volumes of
water are conveyed may not be flooded in consequence of the failure of
any of the works.
Construction.
Practically only two types of aqueduct are used in England. The one is
built of concrete, brickwork, &c., the other of cast-iron (or, in
special circumstances, steel) pipes. In the former type the water
surface coincides with the hydraulic gradient, and the conditions are
those of an artificial river; the aqueduct must therefore be carefully
graded throughout, so that the fall available between source and
termination may be economically distributed. This condition requires
that the ground in which the work is built shall be at the proper
elevation; if at any point this is not the case, the aqueduct must be
carried on a substructure built up to the required level. Such large
structures are, however, extremely expensive, and require elaborate
devices for maintaining water-tightness against the expansion and
contraction of the masonry due to changes of temperature. They are now
only used where their length is very short, as in cases where mountain
streams have to be crossed, and even these short lengths are avoided by
some engineers, who arrange that the aqueduct shall pass, wherever
practicable, under the streams. Where wide valleys interrupt the course
of the built aqueduct, or where the absence of high ground prevents the
adoption of that type at any part of the route, the cast-iron pipes
hereafter referred to are used.
Masonry aqueducts.
The built aqueduct may be either in tunnel, or cut-and-cover, the latter
term denoting the process of cutting the trench, building the floor,
side-walls, and roof, and covering with earth, the surface of the ground
being restored as before. For works conveying water for domestic supply,
the aqueduct is in these days, in England, always covered. Where, as is
usually the case, the water is derived from a tract of mountainous
country, the tunnel work is sometimes very heavy. In the case of the
Thirlmere aqueduct, out of the first 13 m. the length of the tunnelled
portions is 8 m., the longest tunnel being 3 m. in length. Conditions of
time, and the character of the rock, usually require the use of
machinery for driving, at any rate in the case of the longer tunnels.
For the comparatively small tunnels required for aqueducts, two
percussion drilling machines are usually mounted on a carriage, the
motive power being derived from compressed air sent up the tunnel in
pipes. The holes when driven are charged with explosives and fired. In
the Thirlmere tunnels, driven through very hard Lower Silurian strata,
the progress was about 13 yds. a week at each face, work being carried
on continuously day and night for six days a week. Where the character
of the country through which the aqueduct passes is much the same as
that from which the supply is derived, the tunnels need not be lined
with concrete, &c., more than is absolutely necessary for retaining the
water and supporting weak places in the rock; the floor, however, is
nearly always so treated. The lining, whether in tunnel or
cut-and-cover, may be either of concrete, or brickwork, or of concrete
faced with brickwork. To ensure the impermeability of work constructed
with these materials is in practice somewhat difficult, and no matter
how much care is taken by those supervising the workmen, and even by the
workmen themselves, it is impossible to guarantee entire freedom from
trouble in this respect. With a wall only about 15 in. thick, any
neglect is certain to make the work permeable; frequently the labourers
do not distribute the broken stone and fine material of the concrete
uniformly, and no matter how excellent the design, the quality of
materials, &c., a leak is sure to occur at such places (unless, indeed,
the pressure of the outside water is superior and an inflow occurs). A
further cause of trouble lies in the water which flows from the strata
on to the concrete, and washes away some of the cement upon which the
work depends for its watertightness, before it has time to set. For this
reason it is advisable to put in the floor before, and not after, the
sidewalls and arch have been built, otherwise the only outlet for the
water in the strata is through the ground on which the floor has to be
laid. Each length of about 20 ft. should be completely constructed
before the next is begun, the water then having an easy exit at the
leading end. Manholes, by which the aqueduct can be entered, are usually
placed in the roof at convenient intervals; thus, in the case of the
Thirlmere aqueduct, they occur at every quarter of a mile.
Timber aqueducts.
In some parts of America aqueducts are frequently constructed of wood,
being then termed flumes. These are probably more extensively used in
California than in any other part of the world, for conveying large
quantities of water which is required for hydraulic mining, for
irrigation, for the supply of towns and for transporting timber. The
flumes are frequently carried along precipitous mountain slopes, and
across valleys, supported on trestles. In Fresno county, California,
there is a flume 52 m. in length for transporting timber from the Sierra
Nevada Mountains to the plain below; it has a rectangular V-shaped
section, 3 ft. 7 in. wide at the top, and 21 in. deep vertically. The
boards which form the sides are 1-1/4 in. thick, and some of the
trestlework is 130 ft. high. The steepest grade occurs where there is a
fall of 730 ft. in a length of 3000 ft. About 9,000,000 ft. of timber
were used in the construction. At San Diego there is a flume 35 m. long
for irrigation and domestic supply, the capacity being 50 ft. per
second; it has 315 trestle bridges (the longest of which is that across
Los Coches Creek, 1794 ft. in length and 65 ft. in height) and 8
tunnels, and the cost was $900,000. The great bench flume of the
Highline canal, Colorado, is 2640 ft. in length, 28 ft. wide, and 7 ft.
deep; the gradient is 5.28 ft. per mile, and the discharge 1184 ft. per
second.
Aqueduct in iron piping.
As previously stated, the type of aqueduct built of concrete, &c., can
only be adopted where the ground is sufficiently elevated to carry it,
and where the quantity of water to be conveyed makes it more economical
than piping. Where the falling contour is interrupted by valleys too
wide for a masonry structure above the surface of the ground, the
detached portions of the built aqueduct must be connected by rows of
pipes laid beneath, and following the main undulations of, the surface.
In such cases the built aqueduct terminates in a chamber of sufficient
size to enclose the mouths of the several pipes, which, thus charged,
carry the water under the valley up to a corresponding chamber on the
farther hillside from which the built aqueduct again carries on the
supply. These connecting pipes are sometimes called siphons, although
they have nothing whatever to do with the principle of a siphon, the
water simply flowing into the pipe at one end and out at the other under
the influence of gravity, and the pressure of the atmosphere being no
element in the case. The pipes are almost always made of cast-iron,
except in such cases as the lower part of some siphons, where the
pressure is very great, or where they are for use abroad, when
considerations of weight are of importance, and when they are made of
rolled steel with riveted or welded seams. It is frequently necessary to
lay them in deep cuttings, in which case cast-iron is much better
adapted for sustaining a heavy weight of earth than the thinner steel,
though the latter is more adapted to resist internal pressure. Mr D.
Clarke (_Trans. Am. Soc. C.E._ vol. xxxviii. p. 93) gives some
particulars of a riveted steel pipe 24 m. long, 33 to 42 in. diameter,
varying in thickness from 0.22 in. to 0.375 in. After a length of 9 m.
had been laid, and the trench refilled, it was found that the crown of
the pipe had been flattened by an amount varying from 1/2 in. to 4 in.
Steel pipes suffer more from corrosion than those made of cast-iron, and
as the metal attacked is much thinner the strength is more seriously
reduced. These considerations have prevented any general change from
cast-iron to steel.
Mr. Clemens Herschel has made some interesting remarks (_Proc. Inst.
C.E._ vol. cxv. p. 162) as to the circumstances in which steel pipes
have been found preferable to cast-iron. He says that it had been
demonstrated by practice that cast-iron cannot compete with
wrought-iron or steel pipes in the states west of the Rocky Mountains,
on the Pacific slope. This is due to the absence of coal and iron ore
in these states, and to the weight of the imported cast-iron pipes
compared with steel pipes of equal capacity and strength. The works of
the East Jersey Water Company for the supply of Newark, N.J., include
a riveted steel conduit 48 in. in diameter and 21 m. long. This
conduit is designed to resist only the pressure due to the hydraulic
gradient, in contradistinction to that which would be due to the
hydrostatic head, this arrangement saving 40% in the weight and cost
of the pipes. For the supply of Rochester, N.Y., there is a riveted
steel conduit 36 in. in diameter and 20 m. long; and for Allegheny
City, Pennsylvania, there is a steel conduit 5 ft. in diameter and
nearly 10 m. long. The works for bringing the water from La Vigne and
Verneuil to Paris include a steel main 5 ft. in diameter between St.
Cloud and Paris.
Cast-iron pipes rarely exceed 48 in. in diameter, and even this
diameter is only practicable where the pressure of the water is low.
In the Thirlmere aqueduct the greatest pressure is nearly 180 lb. on
the square inch, the pipes where this occurs being 40 in. in diameter
and 1-3/4 in. thick. These large pipes, which are usually made in
lengths of 12 ft., are generally cast with a socket at one end for
receiving the spigot end of the next pipe, the annular space being run
with lead, which is prevented from flowing into the interior of the
pipe by a spring ring subsequently removed; the surface of the lead is
then caulked all round the outside of the pipe. A wrought-iron ring is
sometimes shrunk on the outer rim of the socket, previously turned to
receive it, in order to strengthen it against the wedging action of
the caulking tool. Sometimes the pipes are cast as plain tubes and
joined with double collars, which are run with lead as in the last
case. The reason for adopting the latter type is that the stresses set
up in the thicker metal of the socket by unequal cooling are thereby
avoided, a very usual place for pipes to crack under pressure being at
the back of the socket. The method of turning and boring a portion,
slightly tapered, of spigot and socket so as to ensure a watertight
junction by close annular metallic contact, is not suitable for large
pipes, though very convenient for smaller diameters in even ground.
Spherical joints are sometimes used where a line of main has to be
laid under a large river or estuary, and where, therefore, the pipes
must be jointed before being lowered into the previously dredged
trench. This was the case at the Willamette river, Portland, Oregon,
where a length of 2000 ft. was required. The pipes are of cast-iron 28
in. in diameter, 1-1/2 in. thick, and 17 ft. long. The spigots were
turned to a spherical surface of 20 in. radius outside, the inside of
the sockets being of a radius 3/8 in. greater. After the insertion of
the spigot into the socket, a ring, 3 in. deep, turned inside to
correspond with the socket, was bolted to the latter, the annular
space then being run with lead. These pipes were laid on an inclined
cradle, one end of which rested on the bed of the river and the other
on a barge where the jointing was done; as the pipes were jointed the
barge was carefully advanced, thus trailing the pipes into the trench
(_Trans. Am. Soc. C.E._ vol. xxxiii. p. 257). As may be conjectured
from the pressure which they have to stand, very great care has to be
taken in the manufacture and handling of cast-iron pipes of large
diameter, a care which must be unfailing from the time of casting
until they are jointed in their final position in the ground. They are
cast vertically, socket downwards, so that the densest metal may be at
the weakest part, and it is advisable to allow an extra head of metal
of about 12 in., which is subsequently cut off in a lathe. An
inspector representing the purchaser watches every detail of the
manufacture, and if, after being measured in every part and weighed,
they are found satisfactory they are proved with internal fluid
pressure, oil being preferable to water for this purpose. While under
pressure, they are rapped from end to end with a hand hammer of about
5 lb. in weight, in order to discover defects. The wrought-iron rings
are then, if required, shrunk on to the sockets, and the pipes, after
being made hot in a stove, are dipped vertically in a composition of
pitch and oil, in order to preserve them from corrosion. All these
operations are performed under cover. A record should be kept of the
history of the pipe from the time it is cast to the time it is laid
and jointed in the ground, giving the date, number, diameter, length,
thickness, and proof pressure, with the name of the pipe-jointer whose
work closes the record. Such a history sometimes enables the cause
(which is often very obscure) of a burst in a pipe to be ascertained,
the position of every pipe being recorded.
Cast-iron pipes, even when dipped in the composition referred to,
suffer considerably from corrosion caused by the water, especially
soft water, flowing through them. One pipe may be found in as good a
condition as when made, while the next may be covered with nodules of
rust. The effect of the rust is twofold; it reduces the area of the
pipe, and also, in consequence of the resistance offered by the rough
surface, retards the velocity of the water. These two results,
expecially the latter, may seriously diminish the capability of
discharge, and they should always be allowed for in deciding the
diameter. Automatic scrapers are sometimes used with good results, but
it is better to be independent of them as long as possible. In one
case the discharge of pipes, 40 in. in diameter, was found after a
period of about twelve years to have diminished at the rate of about
1% per year; in another case, where the water was soft and where the
pipes were 40 in. in diameter, the discharge was diminished by 7% in
ten years. An account of the state of two cast-iron mains supplying
Boston with water is given in the _Trans. Am. Soc. C.E._ vol. xxxv. p.
241. These pipes, which were laid in 1877, are 48 in. in diameter and
1800 ft. long. When they were examined in 1894-1895, it was estimated
that the tubercles of rust covered nearly one-third of the interior
surfaces, the bottom of the pipe being more encrusted than the sides
and top. They had central points of attachment to the iron, at which
no doubt the coating was defective, and from them the tubercles spread
over the surface of the surrounding coating. In this case they were
removed by hand, and the coating of the pipes was not injured in the
process. Cast-iron pipes must not be laid in contact with cinders from
a blast furnace with which roads are sometimes made, because these
corrode the metal. Mr Russell Aitken (_Proc. Inst. C.E._ vol. cxv. p.
93) found in India that cast-iron pipes buried in the soil rapidly
corroded, owing to the presence of nitric acid secreted by bacteria
which attacked the iron. The large cast-iron pipes conveying the water
from the Tansa reservoir to Bombay are laid above the surface of the
ground. Cast-iron pipes of these large diameters have not been in
existence sufficiently long to enable their life to be predicted. A
main, 40 in. in diameter, conveying soft water, after being in
existence fifty years at Manchester, was apparently as good as ever.
In 1867 Mr J.B. Francis found that no apparent deterioration had taken
place in a cast-iron main, 8 in. diameter, which was laid in the year
1828, a period of thirty-nine years (_Trans. Soc. Am. C.E._ vol. i. p.
26). These two instances are probably not exceptional.
Methods of laying.
Pipes in England are usually laid with not less than 2 ft. 6 in. of
cover, in order that the water may not be frozen in a severe winter.
Where they are laid in deep cutting they should be partly surrounded
with concrete, so that they may not be fractured by the weight of earth
above them. Angles are turned by means of special bend pipes, the curves
being made of as large a radius as convenient. In the case of the
Thirlmere aqueduct, double socketed castings about 12 in. long
(exclusive of the sockets) were used, the sockets being inclined to each
other at the required angle. They were made to various angles, and for
any particular curve several would be used connected by straight pipes 3
ft. long. As special castings are nearly double the price of the regular
pipes, the cost was much diminished by making them as short as possible,
while a curve, made up of the slight angles used, offered practically no
more impediment to the flow of water in consequence of its polygonal
form, than would be the case had special bend pipes been used. In all
cases of curves on a line of pipes under internal fluid pressure, there
exists a resultant force tending to displace the pipes. When the curve
is in a horizontal plane and the pipes are buried in the ground, the
side of the pipe trench offers sufficient resistance to this force.
Where, however, the pipes are above ground, or when the curve is in a
vertical plane, it is necessary to anchor them in position. In the case
of the Tansa aqueduct to Bombay, there is a curve of 500 ft. radius near
Bassein Creek. At this point the hydrostatic head is about 250 ft., and
the engineer, Mr Clerke, mentions that a tendency to an outward movement
of the line of pipes was observed. At the siphon under Kurla Creek the
curves on the approaches as originally laid down were sharp, the
hydrostatic head being there about 210 ft.; here the outward movement
was so marked that it was considered advisable to realign the approaches
with easier curves (_Proc. Inst. C.E._ vol. cxv. p. 34). In the case of
the Thirlmere aqueduct the greatest hydrostatic pressure, 410 ft.,
occurs at the bridge over the river Lune, where the pipes are 40 in. in
diameter, and in descending from the bridge make reverse angles of
31-1/2 deg. The displacing force at each of these angles amounts to 54
tons, and as the design includes five lines of pipes, it is obvious that
the anchoring arrangements must be very efficient. The steel straps used
for anchoring these and all other bends were curved to fit as closely as
possible the castings to be anchored. Naturally the metal was not in
perfect contact, but when the pipes were charged the disappearance of
all the slight inequalities showed that the straps were fulfilling their
intended purpose. At every summit on a line of pipes one or more valves
must be placed in order to allow the escape of air, and they must also
be provided on long level stretches, and at changes of gradient where
the depth of the point of change below the hydraulic gradient is less
than that at both sides, causing what may be called a virtual summit.
It is better to have too many than too few, as accumulations of air may
cause an enormous diminution in the quantity of water delivered. In all
depressions discharge valves should be placed for emptying the pipes
when desired, and for letting off the sediment which accumulates at such
points. Automatic valves are frequently placed at suitable distances for
cutting off the supply in case of a burst. At the inlet mouth of the
pipe they may depend for their action on the sudden lowering of the
water (due to a burst in the pipe) in the chamber from which they draw
their supply, causing a float to sink and set the closing arrangement in
motion. Those on the line of main are started by the increased velocity
in the water, caused by the burst on the pipe at a lower level. The
water, when thus accelerated, is able to move a disk hung in the pipe at
the end of a lever and weighted so as to resist the normal velocity;
this lever releases a catch, and a door is then gradually revolved by
weights until it entirely closes the pipe. Reflux valves on the
ascending leg of a siphon prevent water from flowing back in case of a
burst below them; they have doors hung on hinges, opening only in the
normal direction of flow. Due allowance must be made, in the amount of
head allotted to a pipe, for any head which may be absorbed by such
mechanical arrangements as those described where they offer opposition
to the flow of the water. These large mains require most careful and
gradual filling with water, and constant attention must be given to the
air-valves to see that the gutta-percha balls do not wedge themselves in
the openings. A large mass of water, having a considerable velocity, may
cause a great many bursts by water-ramming, due to the admission of the
water at too great a speed. In places where iron is absent and timber
plentiful, as in some parts of America, pipes, even of large diameter
and in the most important cases, are sometimes made of wooden staves
hooped with iron. A description of two of these will be found below.
Thirlmere.
The _Thirlmere Aqueduct_ is capable of conveying 50,000,000 gallons a
day from Thirlmere, in the English lake district, to Manchester. The
total length of 96 m. is made up of 14 m. of tunnels, 37 m. of
cut-and-cover, and 45 m. of cast-iron pipes, five rows of the latter
being required. The tunnels where lined, and the cut-and-cover, are
formed of concrete, and are 7 ft. in height and width, the usual
thickness of the concrete being 15 in. The inclination is 20 in. per
mile. The floor is flat from side to side, and the side-walls are 5
ft. high to the springing of the arch, which has a rise of 2 ft. The
water from the lake is received in a circular well 65 ft. deep and 40
ft. in diameter, at the bottom of which there is a ring of wire-gauze
strainers. Wherever the concrete aqueduct is intersected by valleys,
cast-iron pipes are laid; in the first instance only two of the five
rows 40 in. in diameter were laid, the city not requiring its supply
to be augmented by more than 20,000,000 gallons a day, but in 1907 it
was decided to lay a third line. All the elaborate arrangements
described above for stopping the water in case of a burst have been
employed, and have perfectly fulfilled their duties in the few cases
in which they have been called into action. The water is received in a
service reservoir at Prestwich, near Manchester, from which it is
supplied to the city. The supply from this source was begun in 1894.
The total cost of the complete scheme may be taken at about
L5,000,000, of which rather under L3,000,000 had been spent up to the
date of the opening, at which time only one line of pipes had been
laid.
Vyrnwy.
The _Vyrnwy Aqueduct_ was sanctioned by parliament in 1880 for the
supply of Liverpool from North Wales, the quantity of water obtainable
being at least 40,000,000 gallons a day. A tower built in the
artificial lake from which the supply is derived, contains the inlet
and arrangements for straining the water. The aqueduct is 68 m. in
length, and for nearly the whole distance will consist of three lines
of cast-iron pipes, two of which, varying in diameter from 42 in. to
39 in., are now in use. As the total fall between Vyrnwy and the
termination at Prescot reservoirs is about 550 ft., arrangements had
to be made to ensure that no part of the aqueduct be subjected to a
greater pressure than is required for the actual discharge. Balancing
reservoirs have therefore been constructed at five points on the line,
advantage being taken of high ground where available, so that the
total pressure is broken up into sections. At one of these points,
where the ground level is 110 ft. below the hydraulic gradient, a
circular tower is built, making a most imposing architectural feature
in the landscape. At the crossing of the river Weaver, 100 ft. wide
and 15 ft. deep, the three pipes, here made of steel, were connected
together laterally, floated into position, and sunk into a dredged
trench prepared to receive them. Under the river Mersey the pipes are
carried in a tunnel, from which, during construction, the water was
excluded by compressed air.
Denver.
_Denver Aqueduct._--The supply to Denver City, initiated by the
Citizens Water Company in 1889, is derived from the Platte river,
rising in the Rocky Mountains. The first aqueduct constructed is
rather over 20 m. in length, of which a length of 16-1/2 m. is made of
wooden stave pipe, 30 in. in diameter. The maximum pressure is that
due to 185 ft. of water; the average cost of the wooden pipe was
$1.36-1/2 per foot, and the capability of discharge 8,400,000 gallons
a day. Within a year of the completion of the first conduit, it became
evident that another of still greater capacity was required. This was
completed in April 1893; it is 34 in. in diameter and will deliver
16,000,000 gallons a day. By increasing the head upon the first pipe,
the combined discharge is 30,000,000 gallons a day. An incident in
obtaining a temporary supply, without waiting for the completion of
the second pipe, was the construction of two wooden pipes, 13 in. in
diameter, crossing a stream with a span of 104 ft., and having no
support other than that derived from their arched form. One end of the
arch is 24-1/2 ft. above the other end, and, when filled with water,
the deflection with eight men on it was only 7/8 of an inch. A
somewhat similar arch, 60 ft. span, occurs on the 34-in. pipe where it
crosses a canal. Schuyler points out (_Trans. Am. Soc. C.E._ vol.
xxxi. p. 148) that the fact that the entire water supply of a city of
150,000 inhabitants is conveyed in wooden mains, is so radical a
departure from all precedents, that it is deserving of more than a
passing notice. He says that it is manifestly and unreservedly
successful, and has achieved an enormous saving in cost. The sum saved
by the use of wooden, in preference to cast-iron pipes, is estimated
at $1,100,000. It is perhaps necessary to state that the pipe is
buried in the ground in the same way as metal pipes. The edges of the
staves are dressed to the radius with a minute tongue 1/16 in. high on
one edge of each stave, but with no corresponding groove in the next
stave; its object is to ensure a close joint when the bands are
tightened up. Leaks seldom or never occur along the longitudinal
seams, but the end shrinkage caused troublesome joint leaks. The
shrinkage in California redwood, which had seasoned 60 to 90 days
before milling, was frequently as much as 3 in. in the 20 staves that
formed the 34-in. pipe, and the space so formed had to be filled by a
special closing stave. Metallic tongues, 3/4 in. deep, are inserted at
the ends of abutting staves, in a straight saw cut. The bands, which
are of mild steel, have a head at one end and a nut and washer at the
other; the ends are brought together on a wrought-iron shoe, against
which the nut and washer set. The staves forming the lower half of the
pipe are placed on an outside, and the top staves on an inside, mould.
While the bands are being adjusted the pipe is rounded out to bring
the staves out full, and the staves are carefully driven home on to
the abutting staves. The spacing of the bands depends on
circumstances, but is about 150 bands per 100 ft. With low heads the
limit of spacing was fixed at 17 in. The outer surface of the pipe,
when charged, shows moisture oozing slightly over the entire surface.
This condition Schuyler considers an ideal one for perfect
preservation, and the staves were kept as thin as possible to ensure
its occurrence. Samples taken from pipes in use from three to nine
years are quite sound, and it is concluded that the wood will last as
long as cast-iron if the pipe is kept constantly charged. The bands
are the only perishable portion, and their life is taken at from
fifteen to twenty years. Other portions of the second conduit for a
length of nearly 3 m. were formed of concrete piping, 38 in. diameter,
formed on a mould in the trench, the thickness being 2-1/2 to 3 in. So
successful an instance of the use of wooden piping on a large scale is
sure to lead to a large development of this type of aqueduct in
districts where timber is plentiful and iron absent.
Pioneer, Utah.
_Pioneer Aqueduct, Utah._--The construction of the Pioneer Aqueduct,
Utah, was begun in 1896 by the Pioneer Electric Power Company, near
the city of Ogden, 35 m. north of Salt Lake City. The storage
reservoir, from which it draws its water, will coyer an area of 2000
acres, and contain about 15,000 million gallons of water. The aqueduct
is a pipe 6 ft. in diameter, and of a total length of 6 m.; for a
distance of rather more than 5 m. it is formed of wooden staves, the
remainder, where the head exceeds 117 ft., being of steel. It is laid
in a trench and covered to a depth of 3 ft. The greatest pressure on
the steel pipe is 200 lb. per sq. in., and the thickness varies from
3/8 to 11/16 in. The pipe was constructed according to the usual
practice of marine boiler-work for high pressures, and each section,
about 9 ft. long, was dipped in asphalt for an hour. These sections
were supported on timber blocking, placed from 5 to 9 ft. apart, and
consisting of three to six pieces of 6 X 6 in. timbers laid one on the
top of the other; they were then riveted together in the ordinary way.
The wooden stave-pipe is of the type successfully used in the Western
States for many years, but its diameter is believed to be unequalled
for any but short lengths. There were thirty-two staves in the circle,
2 in. in thickness, and about 20 ft. long, hooped with round steel
rods 5/8 in. in diameter, each hoop being in two pieces. The pipe is
supported at intervals of 8 ft. by sills 6 X 8 in. and 8 ft. long. The
flow through it is 250 cubic ft. per second.
Santa Ana.
The _Santa Ana Canal_ was constructed for irrigation purposes in
California, and is designed to carry 240 cub. ft. of water per second
(_Trans. Am. Soc. C.E._ vol. xxxiii. p. 99). The cross section of the
flumes shows an elliptical bottom and straight sides consisting of
wooden staves held together by iron and steel ribs. The width and
depth are each 5 ft. 6 in., the intended depth of water being 5 ft.
The staves are held by T-iron supports resting on wooden sills spaced
8 ft. apart, and are compressed together by a framework. They were
caulked with oakum, on the top of which, to a third of the total
depth, hot asphalt was run. The use of nails was altogether avoided
except in parts of the framework, it being noticed that decay usually
starts at nail-holes. It was found possible to make the flume
absolutely watertight, and in case of repair being necessary at any
part the framework is easily taken to pieces so that new staves can be
inserted. The water in the flume has a velocity of 9.6 ft. per second.
The Warm Springs, Deep, and Morton canons on the line are crossed by
wooden stave pipes 52 in. in diameter, bound with round steel rods,
and laid above the surface of the ground. The work is planned for two
rows of pipes, each capable of carrying 123 cub. ft. per second; of
these one so far has been laid. The lengths of the pipes at each of
the three canons are 551, 964 and 756 ft. respectively, and the
maximum head at any place is 160 ft. The pipes are not painted, and it
has been suggested that they would suffer in their exposed position in
case of a bush fire, a contingency to which, of course, flumes are
also liable.
New York.
_Aqueducts of New York._--There are three aqueducts in New York--the
Old Croton Aqueduct (1837-1843), the Bronx River Conduit (1880-1885),
and the New Croton Aqueduct (1884-1893), discharging respectively 95,
28, and 302 million U.S. gallons a day; their combined delivery is
therefore 425 million gallons a day. The Old Croton Aqueduct is about
41 m. in length, and was constructed as a masonry conduit, except at
the Harlem and Manhattan valleys, where two lines of 36-in. pipe were
used. The inclination of the former is at the rate of about 13 in. per
mile. The area of the cross-section is 53.34 sq. ft., the height is
8-1/2 ft., and the greatest width 7 ft. 5 in.; the roof is
semicircular, the floor segmental, and the sides have a batter on the
face of 1/2 in. per foot. The sides and invert are of concrete, faced
with 4 in. of brickwork, the roof being entirely of brickwork. There
is a bridge over the Harlem river 1450 ft. in length, consisting of
fifteen semicircular arches; its soffit is 100 ft. above high water,
and its cost was $963,427. The construction of the New Croton Aqueduct
was begun in 1885, and the works were sufficiently advanced by the
15th of July 1890 to allow the supply to be begun. The lengths of the
various parts of the aqueduct are as follows:--
Miles.
Tunnel 29.75
Cut-and-cover 1.12
Cast-iron pipes, 48 in. diameter, 8 rows. 2.38
-----
Croton Inlet to Central Park. 33.25
=====
The length of tunnel under pressure (circular form) is 7.17 m., and
that not under pressure (horse-shoe form) 23.70 m. The maximum
pressure in the former is 55 lb. per sq. in. The width and height of
the horse-shoe form are each 13 ft. 7 in., and the diameter of the
circular form (with the exception of two short lengths) is 12 ft. 3
in. The reason for constructing the aqueduct in tunnel for so long a
distance was the enhanced value of the low-lying ground near the old
aqueduct. The tunnel deviates from a straight line only for the
purpose of intersecting a few transverse valleys at which it could be
emptied. For 25 m. the gradient is 0.7 foot per mile; the tunnel is
then depressed below the hydraulic gradient, the maximum depth being
at the Harlem river, where it is 300 ft. below high water. The depth
of the tunnel varies from 50 to 500 ft. from the surface of the
ground. Forty-two shafts were sunk to facilitate driving, and in four
cases where the surface of the ground is below the hydraulic gradient
these are closed by watertight covers. The whole of the tunnel is
lined with brickwork from 1 to 2 ft. in thickness, the voids behind
the lining being filled with rubble-in-mortar. The entry to the old
and new aqueducts is controlled by a gatehouse of elaborate and
massive design, and the pipes which take up the supply at the end of
the tunnel are also commanded by a gate-house. The aqueduct, where it
passes under the Harlem river, is worthy of special notice. As it
approaches the river it has a considerable fall, and eventually ends
in a vertical shaft 12 ft. 3 in. in diameter (where the water has a
fall of 174 ft.), from the bottom of which, at a depth of 300 ft.
below high-water level, the tunnel under the river starts. The latter
is circular in form, the diameter being 10 ft. 6 in., and the length
is 1300 ft.; it terminates at the bottom of another vertical shaft
also 12 ft. 3 in. in diameter. The depth of this shaft, measured from
the floor of the lower tunnel to that of the upper tunnel leading away
from it, is 321 ft.; it is continued up to the surface of the ground,
though closed by double watertight covers a little above the level of
the upper tunnel. Adjoining this shaft is another shaft of equal
diameter, by means of which the water can be pumped out, and there is
also a communication with the river above high-water level, so that
the higher parts can be emptied by gravitation. The cost of the Old
Croton Aqueduct was $11,500,000; that of the new aqueduct is not far
short of $20,000,000.
Nadrai.
The _Nadrai Aqueduct Bridge_, in India, opened at the end of 1889, is
the largest structure of its kind in existence. It was built to carry
the water of the Lower Ganges canal over the Kali Naddi, in connexion
with the irrigation canals of the north-west provinces. In the year
1888-1889 this canal had 564 m. of main line, with 2050 m. of minor
distributaries, and irrigated 519,022 acres of crops. The new bridge
replaces one of much smaller size (five spans of 35 ft.), which was
completely destroyed by a high flood in July 1885. It gives the river
a waterway of 21,000 sq. ft., and the canal a waterway of 1040 sq.
ft., the latter representing a discharge of 4100 cub. ft. per second.
Its length is 1310 ft., and it is carried on fifteen arches having a
span of 60 ft. The width between the faces of the arches is 149 ft.
The foundations below the river-bed have a depth of 52 ft., and the
total height of the structure is 88 ft. It cost 44-1/2 lakhs of
rupees, and occupied four years in building. The foundations consist
of 268 circular brick cylinders, and the fifteen spans are arranged in
three groups, divided by abutment piers; the latter are founded on a
double row of 12-ft. cylinders, and the intermediate piers on a single
row of 20-ft. cylinders, all the cylinders being hearted with
hydraulic lime concrete filled in with skips. This aqueduct-bridge has
a very fine appearance, owing to its massive proportions and design.
(E. P. H.*)
AUTHORITIES.--For ancient aqueducts in general: Curt Merckel, _Die
Ingenieurtechnik im Alterthum_ (Berlin, 1899); ch. vi. contains a very
full account from the earliest Assyrian aqueducts onwards, with
illustrations, measurements and an excellent bibliography. For Greek
aqueducts see E. Curtius, "Uber stadtische Wasserbauten der Hellenen,"
in _Archaeologische Zeitung_ (1847); G. Weber (as above); papers in
_Athen. Mittheil._ (Samos), 1877, (Enneacrunus) 1892, 1893, 1894,
1905, and articles on ATHENS, PERGAMUM, &c. For Roman aqueducts: R.
Lanciani, "I Commentari di Frontino intorno le acque e gli
acquedotti," in _Memorie dei Lincei_, serie iii. vol. iv. (Rome,
1880), 215 sqq., and separately; C. Herschel, _The Two Books on the
Water Supply of the City of Rome of Sextus Julius Frontinus_ (Boston,
1899); T. Ashby in _Classical Review_ (1902), 336, and articles in
_The Builder_; cf. also the maps to T. Ashby's "Classical Topography
of the Roman Campagna," in _Papers of the British School at Rome_, i.,
in., iv. (in progress).
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; Report of
the Aqueduct Commissioners_ (1887-1895), and _The Water Supply of the
City of New York_ (1896), by Wegmann; _Memoires sur les eaux de
Paris_, presentes par le Prefet de la Seine au Conseil Municipal (1854
and 1858); _Recherches statistiques sur les sources du bassin de la
Seine_, par M. Belgrand, Ingenieur en chef des ponts et chaussees
(1854); "Descriptions of Mechanical Arrangements of the Manchester
Waterworks," by John Frederic Bateman, F.R.S., Engineer-in-chief, from
the _Minutes of Proceedings of the Institution of Mechanical
Engineers_ (1866); _The Glasgow Waterworks_, by James M. 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). For
accounts of other aqueducts, see the Transactions of the Societies of
Engineers in the different countries, and the Engineering Journals.