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GODFREY LOWELL CABOT SCIENCE LIBRARY
of the Harvard College Library
This book is
FRAGILE
and circulates only with permission.
Please handle with care
and consult a staff member
before photocopying.
Thanks for your help in preserving
Harvard's library collections.
Digitized by
34.163
Enc
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Jerris
DESCRIPTION
OF THE
CROTON AQUEDUCT;
BY
JOHN B. JERVIS,
CHIEF ENGINEER.
NEW-YORK:
PUBLISHED BY SLAMM AND GUION,
CORNER OF NASSAU AND SPRUCE STREETS.
1842.
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DESCRIPTION
OF THE
CROTON AQUEDUCT;
BY
JOHN B. JERVIS,
CHIEF ENGINEER.
I
NEW-YORK:
PUBLISHED BY SLAMM AND GUION,
CORNER OF NASSAU AND SPRUCE STREETS.
1842.
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Eng1078.42
1051 beely
Proj Longfellors
ENTERED according to Act of Congress, in the year 1842, by
SLAMM & GUION,
in the Clerk's Office of the Southern District of New-York.
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PREFACE.
IT is seventy years ago since the subject of procuring a sup-
ply of pure and wholesome water for this city was first agitated
in our Common Council. The population of the city was then
only twenty-two thousand, and notwithstanding it was at that
time considered a matter of the highest importance, yet it was
reserved for this late day to plan and execute the Croton aque-
duct.
Comparatively few of the inhabitants of this city are aware
of the magnitude of the works erected, or the character of the
obstacles overcome, in bringing a river forty miles, over moun-
tains, streams and valleys, to pour its blessings in the midst of
a populous city. It has occurred to the publishers that they
could not perform a more gratifying or acceptable service to
the public than to present them a'full and complete description
of the aqueduct from the pen of John B. Jervis, Esq. To the
eminent ability and devotion of this distinguished engineer are
the public mainly indebted for the successful accomplishment
of this great enterprise. Although he has been connected with
almost all the great public works of this state, it will be the
Croton Aqueduct that will transmit his name to all future gen-
erations with enviable distinction.
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This pamphlet contains a minute, full and accurate descrip-
tion of the whole work, from the Craton river to the distribu-
ting reservoir, from Mr. Jervis's pen, and the publishers do not
hesitate in making the assurance, that while it cannot fail to
satisfy the popular curiosity, it will be everywhere regarded as
an acquisition in hydraulic science.
THE PUBLISHERS.
October 14, 1842.
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GENERAL DESCRIPTION OF THE LINE.
THE Croton Aqueduct was designed to supply the city of
New-York with an abundance of pure and wholesome water.
It commences about six miles above the mouth of the Croton
river, where a dam has been constructed to elevate the water
of the river 40 feet, to the level of the head of the aqueduct,
or 166 feet above mean tide. The course of the aqueduct passes
along the valley of the Croton to near its mouth, and thence
passes into the valley of the Hudson. At 8 miles from the
Croton dam it reaches the village of Sing Sing, and continues
south through the villages of Tarrytown, Dobbs' Ferry, Has-
tings, and Yonkers.
At the latter place it leaves the bank of the Hudson,
crosses the valleys of Saw-mill river and Tibbits' brook,
thence along the side of the ridge that bounds the southerly
side of Tibbits' brook valley, to within 3½ miles of the Harlem
river, where the high grounds of the Hudson fall away so
much as to require the aqueduct to occupy the summit of the
country lying between the Hudson and East rivers.
This formation of country continues to, and is terminated
by the Harlem river, at the point where the aqueduct intersects
it; which is one mile northwesterly from McCombs' dam.
The length of the aqueduct from the Croton dam to Har-
Iem river, is 32.88 miles, for which distance it is an uninter-
rupted conduit of hydraulic stone and brick masonry. The
high ground that bounds the northerly side of the Harlem river
valley, is very near the level of the aqueduct at that place; and
the width of the valley at the aqueduct level is about 1450 feet,
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or a little over one quarter of a mile ; over which a bridge is
designed to be constructed (and is now in progress) at an ele-
vation of 114 feet above the level of high tide in the Harlem
river, on which iron pipes are to be laid to convey the water
across the valley.
The shore on the southerly side of the river is a bold, pre-
cipitous rock, rising at an angle of about 30 degrees, to a
height of 220 feet, or about 100 feet above the level of the bot-
tom of the aqueduct.
After crossing this valley, the aqueduct of masonry is re-
sumed, and continued 2.015 miles, to the termination of the
high ground on the north side of Manhattan valley.
This valley is 0.792 mile wide at the level of the aque-
duct; below which it descends 102 feet. The conduit of ma-
sonry here gives place to iron pipes, which descend into the
bottom of the valley, and rise again to the proper level on the
opposite side; from which point the masonry. conduit is again
resumed, and crossing the Asylum ridge, and Clendinning val-
ley, is continued 2.173 miles, to the receiving reservoir at York
hill.
This reservoir is bounded by 86th street on the north, 79th
street on the south, 7th Avenue on the west, and 6th Avenue
on the east. It is 1826 feet long and 836 feet wide on the out-
side angle of the embankment; containing an area of 35 acres,
divided into two divisions, and is (a little over) 5 miles from
the City Hall. From the receiving reservoir, a double line of
iron pipes three feet in diameter, are laid down in 80th street
and 5th Avenue, to convey the water 2.176 miles to the dis-
tributing reservoir at Murray hill. The location of this reser-
voir is on the 5th Avenue, between 40th and 42d streets, and is
three miles from the City Hall; it is 420 feet square on the
cornice of the exterior wall, and contains an area of 4.05 acres,
divided into two equal divisions, and has an average elevation
of 44.5 feet above the level of the streets around it.
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The length of aqueduct from the Croton dam to the dis-
tributing reservoir is 40.562 miles-to wit :
Masonry conduit in Westchester county
32.880
Do.
do. on New-York Island
4.187
Total length
37.067
Receiving reservoir from end of aqueduct to south-
eastern effluent gate house
0.172
Distributing reservoir.
0.080
Iron pipes on bridge over Harlem valley
0.275
Do. do. across Manhattan valley
0.792
Do. do. between reservoirs
2.176
40.562
It is proper to add to the above, the length of the Croton
reservoir, which has been formed by the erection of the Croton
dam and other work necessary to obtain the water, at a suita-
ble level on the Croton river, as without this dam and reservoir,
the aqueduct would have required an extension of five miles to
reach the proper level on the river; which is now attained by
means of the dam. The entire length, therefore, from the point
on the Croton which has the requisite elevation, to the distribu-
ting reservoir, is 45.562 miles. The large mains running from
the distributing reservoir through the central part of the city,
would add about four miles, making. the total length of the
main conduit nearly fifty miles.
DESCRIPTION OF THE COUNTRY THROUGH WHICH THE AQUEDUCT
IS LOCATED.
The soil, earth and rock, of the country from the banks of
the Croton to the city of New-York, is of one general charac-
ter. The line cuts a small section of marble of inferior quality,
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about two miles below the Croton dam. In running through
the State farm at Sing Sing, it passes a few hundred feet
(mostly by a tunnel) in a marble of pretty fair quality for
building ; and again at Dobbs' Ferry and at Hastings it lightly
cuts a similar rock ; at the latter place marble has been got
out to some extent for market. No more marble was discov-
ered by constructing the aqueduct until it reached Harlem
river, where in excavating two of the coffer dams to obtain
foundation for the piers, marble rock was found in the bed of
the river. This is supposed to be a continuation of the stratum
that appears in Harlem valley at the Kingsbridge road, near
the Hudson river. With these limited exceptions, the prevail-
ing rock of this district is gneiss, of great variety in quality. In
many places it affords excellent building stone for ordinary
purposes, and to some extent good blocks of hewn stone have
been obtained. A very large proportion, however, of this rock
is totally unfit for building purposes.
The surface soil is generally a sandy loam, containing a
very small proportion of argillaceous earth. Below the surface
soil, gravel, sand, boulders, or detached rock, have in most
cases been found, and also hard pan to a considerable extent.
A large proportion of the open cutting, and nearly the whole
tunnel cutting, has been through rock. More than 400,000
cubic yards of rock have been excavated.
The general formation of the country is extremely irregular,
and unfavorable for the economical construction of such a work.
Commencing at the Croton dam, on a level 40 feet above
the river, which descends from this point to tide-water, at the
average rate of 25 feet to the mile, the grade of the aqueduct
was compelled to encounter great irregularities of surface.
Very little regular table-land could be found for its location.
While the main ridge of high land, that lay on the left of the
line in Westchester county, controlled the general location,
numerous spurs of ridges, of various forms and extent, bounded
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by deep ravines, rendered it impossible to avoid deep cutting
and frequent tunnelling, through ridges, and heavy filling in
the valleys ; leaving a very limited proportion of the line in fa-
vorable cutting. On the island of New-York, with the excep-
tion of about one mile from Harlem river, there was no leading
ridge to control or guide the location; which rendered it more
difficult to decide on the conflicting claims of different routes.
There are on the line sixteen tunnels, varying in length from
160 to 1263 feet, making an aggregate length of 6841 feet.
The height of the ridges above the grade level at the tunnels
ranges from 25 to 75 feet.
There are in Westchester county twenty-five streams cross-
ing the line of aqueduct, that are from 12 to 70 feet below the
grade line, and from 25 to 83 feet below the top covering of
the aqueduct. The most prominent of the valleys, are Louns-
berry's, Indian brook, Sing Sing kill, Mill river, Jewell's
brook, and Saw-mill river; the foundations of which are in no
case less than 40 feet below the grade line, or 53 feet below
the top covering of the aqueduct. Besides those above-men-
tioned, there are numerous brooks and valleys of less depth, re-
quiring culverts, and artificial foundations to support the aque-
duct. The level of mean tide at Harlem river is 120.66 feet
below the grade line of the aqueduct, of which a more particu-
lar description will be given hereafter.
On New-York island there are several deep and abrupt
valleys, along the precipitous rocky hill, that bounds the south-
erly shore of Harlem river. But the most important valleys on
the island are Manhattan valley, Clendinning valley, and
Bowne's valley. A more particular notice of Manhattan and
Clendinning valleys will be given when describing the plan
of work; the manner of construction for the others being
similar to that for the valleys in Westchester county.
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DESCRIPTION OF THE PLAN OF WORK FOR THE AQUEDUCT AND
ITS APPURTENANCES.
Aqueduct.
The form and dimensions of the interior of the aqueduct are
as follows : The bottom is an inverted arch ; the chord or
span line is 6 feet and 9 inches, and the versed sine 9 inches.
The masonry of the side walls rises four feet above the spring-
ing line of the inverted arch, with a bevel of one inch to a foot
rise, or four inches on each side, which brings the width at the
top of the side walls 7 feet and 5 inches ; forming the abut-
ments of the roofing arch, which is a semicircle, having a radius
of 3 feet 8½ inches, or a chord line of 7 feet 5 inches. It will
therefore be perceived, the greatest interior width is 7 feet 5
inches, and greatest height 8 feet 51/2 inches. The area of the
interior is 53.34 square feet. In rock tunnels the roofing arch
is generally dispensed with, but the bottom and sides are formed
with masonry similar to that above described. There is an
exception to this form in the first 4.949 miles of the upper end
of the aqueduct, where the side walls have an extra height, on
account of the bottom being depressed, to draw the water at a
lower level from the Croton reservoir. The plan, dimensions,
and character of masonry are as follows : In excavation, a bed
of concrete masonry is laid down as a foundation. It is laid
level across the bottom, three inches thick at the centre of the
inverted arch, and curved on its upper surface, to form a bed
for the arch, which brings it 12 inches thick at the spring line,
and is carried three inches thick under the side walls, or abut-
ments. The abutments are 2 feet 8 inches thick at the spring
line of the inverted arch, and 2 feet at the top, or spring line of
the roofing arch. The inverted arch is of brick, 4 inches thick.
The roofing arch is also of brick 8 inches thick. The abut-
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11
ments, or side walls, are of rubble stone, with a brick facing 4
inches thick. Spandrels of stone are carried up solid from the
exterior angle of side wall, on a line that is tangent to the arch.
When. the bed of concrete is formed for the inverted arch, a
beavy course of plastering is laid over it, on which the arch is
laid. When the stone work of the side walls was up, the face
that received the brick lining had its irregularities filled with
successive courses of plastering, and finally a uniform course of
1/4 of an inch in thickness over the whole, in front of which the
brick facing was laid up. A course of plastering was also put
over the roofing arch. The concrete masonry was formed by
mixing one part hydraulic cement, three parts clean sand, and
three parts fine broken stone ; in some cases fine pebbles were
in part substituted for broken stone. The masonry was all
laid up in hydraulic cement, obtained mostly from the hydraulic
lime of Ulster county. The mortar for the stone work was
composed of one measure of cement to three of clean sharp
sand, and for the brick masonry and plastering, one of cement
to two of sand. It may be proper to remark, that every cargo
of cement was tested by actual experiment, after it was brought
on the ground, before any was allowed to be used. This pre-
caution has had a very salutary influence on the character of
the work ; the cement in all cases where it is exposed to view,
in its exterior, or broken up for examination, or otherwise, has
appeared highly satisfactory. In the commencement of the
work, there was much difficulty in getting the workmen to lay
their stone and brick in a thorough, full bed of mortar, which
is obviously very important in hydraulic masonry. But a rigid
system of inspection, requiring all imperfect work to be taken
down and relaid, was successful in obtaining work of great
compactness and solidity.
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The area of a cross-section of masonry in the aqueduct is :
Concrete masonry
4.605
Stone in side walls
21.572
Do. in spandrels
2.690
28.867.
Brick in arches and side facing
13.658.
Total
42,525 sqr. feet.
A limited departure from the above area has been made where
peculiar circumstances seemed to justify or require it ; the most
important in extent is, where the aqueduct passes over low
grounds or valleys, and a dry wall of stone is raised to the
proper level to support the conduit masonry ; and generally for
the depressed bottom on the 4.949 miles at the upper end of
the aqueduct, and in a few other cases in the first contracts,
where the bottom arch and brick facing is 8 inches thick. On
the foundation walls, the concrete masonry is laid one foot
extra thickness, and three feet extra width ; the base of the
side walls is also increased, and the proportion of cement to
sand in concrete and mortar for stone work is 1 to 21. In
other respects the masonry in conduit, is similar on foundation
walls to that in excavation. The proportion of lime of aque-
duct masonry on foundation walls over valleys, to that in
excavation is about as 1 to 8. The masonry of the aqueduct
is covered with earth to a sufficient depth to protect it from
frost.
Culverts.
To pass the streams that intersect the line, and the land
floods, there has been constructed under the aqueduct 114 cul-
verts, whose aggregate length is 7959 feet. The span varies
from 1½ foot to 25 feet. Those of 1½ foot span are of a square
form, and are constructed by laying down a foundation of con-
crete masonry ; on which a course of well jointed stone, not
less than 9 inches thick is laid, forming a stone platform on
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which well dressed stone is laid, one or two courses high, for
the abutments or side walls, and finished by a second course of
well dressed flagging, not less than 9 inches thick ; all the
work laid in hydraulic mortar. The culverts over 1½ foot span,
with the exception of three of 25 feet span, are constructed as
follows :
A foundation of concrete masonry is formed, and in a few
instances some timber and plank is used with it ; on this an
inverted arch of well dressed stone is laid in regular courses,
to form the bottom channel of the culvert ; side walls or abut-
ments are thence raised to such height as required, the face
being well dressed stone, laid up in courses, and backed with
rough dressed work. An arch is then turned from the abut-
ments, with well dressed stone in regular courses. Wing walls
at the ends are constructed in different forms as circumstances
required.
The character of masonry in the large 25 feet culverts is
similar to that above described, except they have no inverted
arch.
There are five road culverts of from 14 to 20 feet span,
constructed of masonry of the same character. All the culverts
are of stone laid in hydraulic cement.
Ventilators.
There are 33 ventilators constructed to give free circulation
of air through the aqueduct. Eleven of them are constructed
with doors that admit an easy entrance into the aqueduct.
They rise 14 feet above the surface of the ground over the
aqueduct, and are constructed with well dressed stone, circular
in their form, slightly beveling or tapering towards the top,
where the opening is 15 inches in diameter. They are placed
at a uniform distance of one mile, except where they are ren-
dered unnecessary by a waste weir, which serves all the pur-
poses of a ventilator. At this distance apart, they are found to
afford a free and sufficient ventilation.
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Waste Weirs.
There are six waste weirs constructed on the line of aque-
duct, SO arranged as to allow the water to pass off when it rises
to the proper height ; with gates to draw the water from the
aqueduct when necessary. They are constructed with well
dressed stone ; the gates and gate frames are of cast iron, fitted
to stone jambs and lintels ; the frames are faced with brass for
the gates to work against, and the gates are operated by a
wrought iron screw rod and brass nut, working in a cast iron
socket. The water from the weir or gates, falls into a well,
and is then carried off through a culvert to the outside channel.
A stone building with a brick arched roof is erected, so as to
inclose the waste weir and its appurtenances.
Croton Dam.
The southern shore of the Croton river at the point where
the dam is located, is a gneiss rock ; moderately sloping up
the hill from the water's edge, but not appearing to extend far
into the river. The dam required to be raised 40 feet above
low water in the river ; and it was an important object to
arrange the plan so as to obtain a rock foundation for the
masonry.
To effect this, the northern abutment was located as far in
the river as the rock was supposed to extend, and from this to
build up the dam to the level where the top line intersected
the natural slope of the hill, and then to cut the hill away ;
making an opening sufficient for the waste weir of the dam.
In prosecuting the work, it was found the rock descended
more rapidly into the river than was supposed, which induced
the moving of the abutment further towards the hill than at
first located ; and finally, an artificial foundation had to be
made for a small portion of it. It was intended to make the
waste of the dam 100 feet, with abutments of eight feet high ;
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but in consequence of the disappointment in regard to the ex-
tent of the rock in the river, it was found difficult to obtain the
desired length of water way, and it was concluded to raise the
abutment to 12 feet at the lower end, and 15 feet at the upper
end, and allow the water way to remain an average length of
90 feet for this height. The natural rock formed the southern
abutment, and the aqueduct being on this side, the water was
conducted to the gateway at its head, by a tunnel, cut 180 feet
through the rock ; this allowed the gateway to be located on
solid rock, in a situation not exposed to the floods of the river.
The water enters the gate chamber by an archway through
the second bulk-head. The gate chamber is provided with a
double set of gates ; one set of guard gates, of cast iron set in
cast iron frames, and one set of regulating gates, made of gun
metal, set in frames of the same material ; the gates are all 18
by 40 inches, and there are nine gates in each set. They are
all operated by means of wrought iron screw rods.
The gate chamber and bulk-heads are constructed of well
dressed masonry, laid up in hydraulic cement.
In the north abutment a waste culvert has been constructed,
with suitable gates of cast iron, to draw the water down in the
reservoir at such times as it may be necessary, to facilitate the
making of any repairs that may be required, and to discharge
the river at ordinary times during the construction of the work.
From this abutment the old channel of the river was filled by
an embankment, with a heavy protection wall on the lower
side, which was raised 15 feet above the waste weir of the
dam, and designed to be 50 feet wide on the top, but was not
completed the full width, when the unprecedented flood of
January, 1841, carried it away. The embankment stood well,
and gave no indications of failure, until the water rose to near
the surface, and passed through between the frozen and un-
frozen earth about 20 inches below the top. After the breach
was made in the embankment, large masses of heavy ice came
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down from the reservoir, which soon broke down the unfinished
protection wall, and carried off nearly the whole embankment.
The masonry of the dam and abutment sustained but little
injury. Such a flood had not been anticipated, and the water
way proved insufficient to pass it off. Had the embankment
been completed the full width, and the protection wall carried
up to the full height it was intended to carry them, the work
might have proved adequate to the emergency. It was deter-
mined to fill the gap made by this breach, (about 200 feet
long,) by a structure of hydraulic stone masonry, adapting 180
feet as waste weir. This work presented all the difficulties it
was originally intended to avoid, by carrying the work par-
tially into the hill. It was necessary to form an artificial
foundation, and carry up a heavy body of masonry, in the
channel of the river, which in some parts had 15 feet in depth
below its ordinary level; subject in ordinary seasons to frequent
and sudden floods, and affording no means to form another
channel for it to pass, until the work could be accomplished.
Had it been admissible to construct the dam with timber,
the difficulties would have been far less. But the importance
of the object it was designed to secure, and its great height, de-
manded the most permanent and durable structure that could
be made.
The greatest height of the weir of the dam is 40 feet above
the low-water level, and 55 feet above the bed of the river.
The width of masonry, at low-water line of river, is 61 feet.
The form on the lower face commences on a curve, described
by a radius of 55 feet, and continues to within about 10 feet of
the top, when a reversed curve, on a radius of 10 feet, carries
the face over and meets the back line of the wall. The back
line is carried up vertically, with occasional offsets. The main
body of the work is laid up of rough stone ; the curved face of
large and closely cut stone, with four heavy courses at the
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bottom dovetailed together, the joints cut to the line of radius
of curve.
Above the masonry an embankment of earth is filled in, and
extends to 275 feet in width on the bottom, with a slope of one
to five on the up-stream face. The north end of the new weir
is terminated by an abutment that rises 12 feet above it. From
the toe of the masonry an apron is extended 35 feet, composed
of hewn timber secured by ties, bolts, and treenails, in a very
substantial manner, and filled for 16 feet from the stone work,
with concrete masonry, and the remainder with loose stone, and
covered with a course of 6 inch white elm plank. A second
apron is partly made which is to extend 30 feet further.
At 300 feet below the main dam, a second dam is in pro-
gress, which is to be 9 feet high, constructed of timber, stone
and gravel, which will set the water back over the apron of
the main dam, and form a pool to check the water as it falls
on it.
A coffer-dam was constructed in the river to inclose about
120 feet of the work, from which the water was pumped by a
steam-engine, and a concrete foundation laid down on a very
firm hard pan. The remainder of the foundation was made by
sinking timber piers at suitable distances, running parallel with
the dam, and filling the spaces between them with concrete
masonry. In preparing the specifications for this work, the
method and order of prosecuting it, was particularly designed,
and from which no material departure has been found neces-
sary ; the structure is now nearly completed.
The contractors, Messrs. McCullough, Black, McManus,
and Hepburn, have evinced a highly commendable energy and
ability in its prosecution.
This dam sets the water of the river back five miles, and
forms a reservoir of about four hundred acres, and has rendered
it necessary to construct several new roads and bridges as a
substitute for those covered by the flow ; the principal of which
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is the Somerstown turnpike. The grounds lightly flowed on
the margin, have been excavated so as to give dd feet for the
least depth of water. From this reservoir the water flows into
the bulk-head, at the upper end of the tunnel, from a level ave-
raging 10 feet below the surface.
AQUEDUCT BRIDGE AT SING SING.
The Sing Sing kill, where it crosses the line of aqueduct,
runs in a deep and narrow gulf, the bottom of which is 63 feet
below the grade line, or 76 feet below the top covering of the
masonry. Over this gulf an aqueduct bridge has been con-
structed. Near the north end of the valley that spreads out
from this gulf, a road culvert, or arched viaduct has been con-
structed under the conduit. The principal work here is the
large arch directly over the gulf. It is 88 feet span, and 33
feet rise ; the form is an oval drawn from five centres; the
abutments are commenced on the solid rock, near the bottom of
the gulf. The work is constructed of well-dressed stone ma-
sonry, laid in hydraulic cement. Open hance walls are carried
up over the interior and above the solid spandrels, and united
at the top by brick arches. The spaces between the hance
walls are carried entirely across the crown of the arch, to afford
as much facility as possible for any water that might leak from
the conduit to pass off. The depth of arch stone at the spring
line is four feet, and at the crown three feet. The parapets
and walls of the conduit are carried up with an opening of six
inches between them, more effectually to guard against the ef-
fects of frost, and to carry off any water that might leak from
the conduit, and prevent its being absorbed by the outer or
parapet wall. The conduit over this bridge is constructed of
stone and brick masonry, so arranged as to receive a lining of
cast-iron ; the iron being set back so as to receive a facing of
brick over the bottom and sides, which is further secured by
three courses of hydraulic cement plastering.
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It is not probable that any considerable quantity of water
would have escaped, if there had been no other security than
the stone and brick masonry but it is hardly possible to make
masonry SO perfectly impervious, that it will not show wet, or a
sweating appearance on the exterior wall, and the action of
frost in this climate, will produce in such cases a deterioration,
that may be slow, but will eventually destroy the work : hence
the importance of using every precaution to guard against the
smallest leakage. This bridge was erected under the contract
of Young and Scott of Philadelphia, and the work conducted by
Andrew Young (of the firm), who was the first contractor to
commence work on the aqueduct. It is due to Mr. Young to
say, this work was thoroughly executed ; the arch proved this,
when on striking the centres, it did not settle over + of an inch,
and has not changed since. This I consider a very small set-
tlement for so large an arch.
HARLEM RIVER BRIDGE.
The width of the river at the place where the aqueduet
line crosses it, is 620 feet at ordinary high water mark ; as has
been before stated, the shore on the southern side is a bold rock
rising from the water's edge, at an angle of about 30 degrees,
to a height of 220 feet : on the northern side, a strip of table-
land forms the shore, and extends back from the river 400 feet
to the foot of a rocky hill, which rises at an angle of about 20
degrees to a few feet above the level of the aqueduct: the ta-
ble-land is elevated about 30 feet above the river: the channel
of the river to which the water is reduced at very low ebb
tides, is 300 feet wide, and the greatest depth 16 feet : each
side of the channel the bed is a deep mud, covered from three
to four feet at ordinary flood tide : next below the mud there is
a thin stratum of sand, and this is followed by a stratum of sand
and large boulders intermixed ; below the stratum of boulders,
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or detached rock, there has been found in the coffer dams for
two piers, Nos. 8 and 9, a compact marble rock, and in the
coffers for Nos. 7 and 10, a stratum of clay and sand, that is
quite impervious to water, and affords a good medium for piling.
The general plan of the bridge now in progress of construc-
tion, is as follows : Across the river there are 8 arches, each of
80 feet span, resting on piers that are at each extremity and in
the centre 20 feet wide at the spring line of the arches; with
intermediate piers that are 14 feet wide at the spring line ; on
the south of this range of large arches there is one arch, and on
the north 6 arches, each of 50 feet span, resting on piers 7 feet
wide at the spring line, and two abutments that terminate the
arch work of the bridge. From the abutments a continuous
foundation wall of dry stone work is extended to the gate
chambers on each side.
The whole length of the bridge is 1450 feet ; the height of
the river piers above high water line is 60 feet to the spring of
the arches, and 95 feet above the lowest foundation that has
been put down; the arches are semicircular, and the height
100 feet to the soffit, or under side, at crown ;-to the top of
the parapets 114 feet above the ordinary high water line of the
river, and 149 feet above the lowest foundation of the piers
that have been commenced. The width across, on the top of
the parapets, is 21 feet ; the exterior of piers, spandrels and
parapets has a bevel of 1 in 48, and have openings in the inte-
rior walls.
The space between the parapets is arranged to receive and
protect from frost two cast iron pipes, each four feet in diame-
ter, which are to lie 12 feet below the grade line of the aque-
duct, to which they will descend from the gate chambers at the
ends of the bridge. The object of using pipes in this case, is,
more effectually to secure the conduit from leakage, that might
eventually injure the masonry of the bridge, and it incidentally
allows the bridge to be constructed of less height.
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To make the capacity of the pipes for conveying water,
equal to that of the aqueduct, an extra fall of two feet has been
given across the bridge, and the aqueduct on the southern side
of the river is constructed two feet lower than the regular
grade, to accommodate this arrangement. It is intended in the
first place to put down pipes 3 feet in diameter, and to increase
the size as the wants of the city may require.
The foundations of all the land piers but two have been
put down, with bearing piles to support them ; they are placed
below high water line ; and 5 to 6 of the base courses of ma-
sonry have been laid on each ; the remaining land pier and
both abutments will have a rock foundation. There are seven
piers in the river, the foundations of four of which have been
laid ; for two of them solid rock has been obtained at a depth
below high water line of 17 feet for one, and 35 feet for the
other. The pier next the northern shore has a piled founda-
tion ; to prepare it, an excavation of 16 feet was made, passing
through the strata of mud, sand and detached rock, whence the
piles could be properly driven.
The piles were of oak, from 16 to 35 feet long, and driven
at 21, feet apart from centre to centre. The other pier (called
No. 10 in the general series) for which a piled foundation has
been prepared, is near the centre of the river channel. The
stratum of boulders lies much lower at this place, and required
an excavation to be carried 30 feet below common high water
line, before a suitable stratum for driving piles could be reached.
When the excavation was carried to this depth, boring was
made to ascertain if rock could be found for the foundation ;
but after going down without success to a depth of 70 feet be-
low high water, the effort was abandoned, and the driving of
piles commenced, as the only means of securing the foundation.
The piles were driven at three feet apart from centre to centre,
to the depth of 30 to 35 feet.
It may be remarked, that all the piling for the bridge has
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" come home" with great regularity and firmness, and gives
great confidence that it will afford an unyielding support to the
structure. The foundations for the water piers are yet to be put
down ; two of them will probably require bearing piles to sup-
port them, and rock is expected to be found for the other. The
coffer dams are all put down and embanked, and the work of
emptying them is soon to commence.
A temporary pipe 3 feet in diameter is laid down, (partly on
the embankment of the coffer dams) which now conveys the
water across this valley.
Gate chambers are arranged at each end of the bridge,
with gates to regulate the water, and the one on the north end
has a waste weir to discharge the surplus water that at any
time the pipes might not be able to carry.
The bridge is to be constructed of well-dressed granite.
It may very properly be inquired, if the water can be car-
ried temporarily across this valley by iron pipes, why construct
this expensive bridge? The reply is, that a plan was prepared,
and the work put under contract, to construct a low bridge
with one arch for water way ; but a supposed value which was
attached to the future navigation of the river, was so pressed
upon the legislature, as to induce them to pass a law, requiring
that the under side of the arches should be 100 feet above or-
dinary high tide in the river. The law, therefore, and not the
otherwise necessity of the case, has controlled the plan for
crossing this valley.
MANHATTAN VALLEY.
The water is conveyed across this valley by means of iron
pipes. A gate chamber is placed on each side, by which a
connection is formed between the conduit of masonry and the
iron pipes ; and gates prepared for regulating the flow of water
in the same manner as before described for Harlem river. The
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width of the valley is 0.7917 miles from gate chamber to gate
chamber, and the depth at which the pipes are laid in the cen-
tre, is 102 feet. Two cast iron pipes, each three feet in diam-
eter are laid down, and provision made for two more, to be laid
when they shall be required for the wahts of the city. In order
to give the pipes sufficient capacity to discharge the quantity
of water required, an extra head of three feet is given in cross-
ing the valley.
CLENDINNING BRIDGE.
This bridge is constructed over a valley of the same name,
that is situated about equally distant between Manhattan valley
and the receiving reservoir. The greatest depression is 50 feet,
below top of aqueduct, and the valley is 1900 feet across.
The line of aqueduct runs 100 feet westerly of, and parallel
to, the 9th Avenue.
In the plan of the city, streets are laid out, but not yet
opened, that cross the aqueduct at right angles. For three of
the streets archways are constructed under the aqueduct for
their accommodation when they may be opened for use. The
archways for each street are, one for carriage-way of 30 feet
span, and an arch on each side for side walks of 10ₜ feet
span. The style of masonry is similar to that before described
for the Sing Sing bridge, and the same method of open walls
and cast iron lining is also adopted. That part of the bridge
which has no provision for street arches, is composed of a con-
tinuous wall of masonry, carried up on a bevel of 1/2 its rise.
to the grade line of the aqueduct, where it is 30 feet wide the
outside or face of this wall for one foot in breadth, is laid in
hydraulic mortar, and the remainder is laid dry. The method
of laying up this dry masonry was to lay a course of large stone
in such a manner as to give them the greatest solidity, and with-
in a few inches of each other ; after the course was laid over
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the work, the interstices were thoroughly filled with small
broken stone, well pounded in, and levelled up to receive the
succeeding course. (The'same plan was adopted in all the dry
foundations which were laid up to support the conduit over low
grounds.) After the foundation was carried up to the proper
height for the conduit masonry, parapets of hydraulic masonry
were carried up to the level of the roofing arch of conduit, be-
tween which the conduit masonry of the usual form (excepting
the side walls, which were 12 inches extra thickness) has been
constructed, and covered with earth to protect the sides and top
from frost ; the earth covering being secured by turfing carried
over from parapet to parapet. The work presents a very sub-
stantial and finished appearance.
RECEIVING RESERVOIR.
This reservoir is 1826 feet long and 836 feet wide, and in-
cluding its embankments contains 35.05 acres, and its area at
top water line, 31 acres, divided into two divisions : the north-
ern division is designed to contain 20 feet depth of water, and
the southern 30 feet in depth. But they are not fully excavated
in some parts, where rock occurs, it not being deemed suffi-
ciently important to incur the expense of excavation in rock for
the increased capacity that would be obtained. The reservoir
has a capacity for 150,000,000 imperial gallons, as it now
stands. The reservoir is formed with earth banks, the interior
having regular puddled walls to render them impervious to wa-
ter ; the outside protected by a stone wall, laid up on a slope
of one horizontal to three vertical, the face laid in cement mor-
tar and the inside dry : the inside is protected by a dry slope
wall, laid on the face of the embankment which slopes 1½
horizontal to one vertical. The embankments are raised four
feet above the top of water line, and are 18 feet wide on the
top, excepting the high banks on the southern division and the
western bank on the northern division, which are 21 feet wide.
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The greater part of the embankments for the northern division
are of moderate height ; but a portion of the eastern and west-
tern banks of the southern division are 38 feet high above their
base. Vaults or brick archways are constructed, in which iron
pipes are laid, so arranged that the pipes from the northern di-
vision connect with those from the southern division, and thence
pass off to the distributing reservoir, and to supply the adjacent
districts. The main vault is on the eastern side ; it is 540 feet
long and is 16 feet span ; that on the western side is 400 feet
in length, and 8 feet span designed for supplying at a future
day the district on the North river side above 42d street. The
pipes are all provided with stop cocks, and SO arranged that
they can receive the water from either division ; except one
pipe from each division, that leads to the distributing reservoir.
It is intended to carry three lines of pipes, each three feet diam-
eter to the distributing reservoir, (at present only two lines are
put down,) and the arrangement will allow two pipes to be
drawn from either division, so that in the event of emptying one
division for repairs, the other would supply two pipes for the
distributing reservoir, and all other pipes having a connection
with each division would be in full supply, notwithstanding the
suspension of one division, A pipe is put through the division
bank, with a stop cock, to allow the water or not, as may be
desired, to pass from one division to the other.
The aqueduct intersects the reservoir at right angles with
its westerly line, and 252 feet south of the north-westerly
corner.
At this point a gate chamber is constructed, with one set of
gates to pass the water into the northern division, and another
set to pass it into a continued conduit of masonry constructed
within the embankment of the reservoir to the angle of the
southern division, where it enters by a brick sluice into this di-
vision. This arrangement gives the power of directing the
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water into either division, or both, at the same time, as may be
desired.
In the division bank, a waste weir is constructed to carry
off the surplus water from either division, when it rises to the
proper height.
DISTRIBUTING RESERVOIR.
This reservoir occupies the highest ground in the vicinity,
and higher than any part of the city south of it ; the site is
generally known as Murray Hill.
In order to maintain the elevation of the water, it was ne-
cessary to raise the walls of the reservoir to an average height
of 451 feet above the grade of the streets that bounded it on
three sides ; the greatest height being, 49 feet, and the least
39 feet ; the foundations were sunk five feet below the grade
of the streets. The walls are of hydraulic stone masonry, con-
structed with openings, to reduce the quantity of masonry and
give a more enlarged base.
The openings are made by an exterior and interior wall,
connected at every ten feet by cross walls ; which are carried
up to within 17 feet of the top, and there connected by a brick
arch thrown from one to the other, and the spandrels between
them levelled up solid, and a course of concrete put over the
whole, 6 inches thick, which reaches a level 10 feet below the
top ; whence the exterior wall is carried up single to the top
The exterior wall has a bevel of one to six, and is uniformly
four feet thick from the bottom to the top of the connecting
arches; the inner wall is carried up plumb, with offsets, the
lower section six feet thick, the middle section five feet,
and the upper section four feet thick. The space between the
exterior and interior walls, at 41 feet below the top, is 14 feet,
or 24 feet from the outside of exterior to inside of interior
walls ; and the space between them at the spring of connect-
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ing arches, in consequence of the bevel of the exterior wall, is
reduced to 9 feet and 9 inches, and from outside of exterior to
inside of interior walls, 17.75 feet.
The cross walls are four feet thick at bottom, and have one
offset of six inches on each side, at 8 feet below the spring line
of connecting arches ; they have an opening 6 feet high, and 11,
feet wide, at a suitable level near the bottom, to allow a drain
to be formed, to collect any water that may leak through the
work, and carry it off in sewers provided for that purpose, and
also to allow persons to go in and examine the work.
Some modifications in the cross walls are made to accom-
modate the gate chambers, and connect the corners of the work.
On each corner of the reservoir pilasters 40 feet in width are
raised, projecting four feet from the main wall, and in the cen-
tre, on the streets and 5th Avenue, there are pilasters 60 feet
wide and projecting 6 feet from the wall. The pilaster in the
centre, on the 5th Avenue, rises 7 feet above the main wall,
and all the others 4 feet above. Doors are placed in the cen-
tral pilasters on 40th and 42d streets, which give access to the
pipe chambers, to work the influent and effluent stop-cocks,
from which chambers, an entrance is made to the openings in
the walls.
In the central pilaster on the 5th Avenue, an entrance is
made by a door to a stairway that leads up to the top of the
walls. On the outside walls an Egyptian cornice is laid, which
accords with the general style of the work. The pilasters are
laid in courses, and well dressed ashlar face, and the main wall
with coursed rubble work, rough hammer-dressed. Inside of
the walls of masonry, a thorough puddled embankment of suit-
able earth is formed, 58 1₃ feet wide at the line of reservoir bot-
tom, and sloping on the inside face one and a half to one for 24
feet high, and one to one for the remaining 16 feet high, and
making with the walls on top a width of 17 feet; the faces of
the banks are lined with a course of rubble hydraulic masonry
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15 inches thick, and coped with dressed stone. The bottom is a
very impervious hard-pan, on which two feet of puddled earth
is laid, and this covered by 12 inches of hydraulic concrete.
The reservoir is divided into two divisions by a wall of hy-
draulic masonry, at the toe of which a sloping bank of puddled
earth is raised 18 feet high and covered with rubble ma-onry ;
this wall is 19 feet thick at the bottom, 6², feet thick at top
water line, and four feet at top. In this wall a waste weir is
placed, with a well of-two falls, together 52 feet, from which
the 'waste water enters a sewer in 42d street, and passes off
about one mile to the Hudson river. In each division there is
a waste cock to draw the water from the bottom.
The reservoir is designed for 36 feet of water, and when full
will stand 115 feet above mean tide. The walls rise 4 feet
above the water line. An iron railing is to be p'aced around
the walls on top of the cornice. The capacity of this reservoir
is 20,000,000 imperial gallons.
GRADE LINE OF AQUEDUCT.
The general declivity of the aqueduct in Westchester
county is 0.021 foot per hundred, or a fraction over 13 inches
per mile.
The top of the conduit pursuing this grade, corresponds with
the top of the dam on the Croton ; but in order to adapt the
aqueduct to draw at a lower level from the Croton reservoir,
the bottom grade was depressed at the head 2.93 feet, and a
declivity of 0.0113 foot per 100 feet, or 0.59664 foot per mile
for 4.949 miles, where it intersects the regular grade. The top
of the aqueduct was depressed only 0.583 foot, and carried level
2276 feet, where it intersected the regular grade line of the top.
This gave an extra height of side walls, enlarging the capacity
of the aqueduct, more than equivalent to the diminution of de-
clivity, and provides for drawing from the reservoir to a depth
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of 6 feet, and still leave the capacity of the conduit 35,000,000
of imperial gallons.
The grade of the aqueduct from Harlem river to Manhattan
valley, is the same as the general declivity in Westchester
county; but that from Manhattan valley to the receiving reser-
voir 2.1727 miles, is 9 inches per mile. It has been stated, the
extra fall given for the pipes at Harlem river, is 2 feet, and
at Manhattan valley 3 feet ; between the reservoirs there
is a fall of 4 feet, when both are full but it is expected
something more than this will be required at times, to furnish
the full quantity that will be wanted. The pipes are provided
with waste cocks at the depressions, and air cocks at the summit
bends.
The first contracts for work on the aqueduct were made in
April, 1837 ; at which time about ten miles of the upper end
was advertised but in consequence of the proposals being
considered too high, only about half of it was contracted for.
About the middle of May, the contractors generally entered on
the work contracted for. In September following, about 16
miles more was put under contract ; in May, 1838, the balance
of the line to Harlem river was put under contract ; and the
work on the Island, except the grading of the 5th Avenue for
pipes, in October following. In consequence of legislative
interposition, the Harlem river work was re-let in August,
1839.
The work was so far completed, as to permit the water to
be let in from the Croton dam on the 22d day of June, 1842 ;
and it was admitted into the distributing reservoir on the 4th
of July following. There is yet considerable work to be done
at the Croton dam, the receiving and distributing reservoirs,
which will probably all be completed in September or early in
October. The Harlem river bridge will require at least two
years to complete it. At the latter place, a temporary pipe
conveys the water across the valley.
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The following extract is taken from my report of the 12th
inst. to the Board of Water Commissioners :-
" Since the water was introduced into the aqueduct, the
velocity has several times been ascertained ; though not in so
perfect a manner as I intend to have it done, as soon as other
duties will allow the time necessary. Sufficient data, however,
have been obtained to show, that the capacity of the aqueduct
for delivering water will be at least 15 per cent. greater than
the calculated flow. I have not been much disappointed in
finding the flow of water in the aqueduct to exceed the calcu-
lation, as all my observations on the currents in canal feeders,
have led me to believe, the formulas laid down give rather less
than the actual result. The flow of water through the pipes
across Manhattan valley, and also the temporary pipe across
Harlem river, being attended with circumstances somewhat
different, has led some very intelligent persons to predict, that
our expectations would not be realized in these cases ; it there-
fore may be proper to observe, the trial has proved such pre-
dictions to have been not well founded ; as the flow through
the pipes has in a very exact manner corroborated the antici-
pated capacity, as compared with that in the aqueduct.
The Croton reservoir, (which has received the name of
Croton lake,) covers about 400 acres of land, and is available
as a reservoir for 500,000,000 imperial gallons of water, above
the level that would allow the aqueduct to discharge 35,000,000
gallons per day. The flow of the Croton is about 27,000,000
gallons in twenty-four hours at the lowest stages, which con-
tinues, with moderate rises by occasional rains, from two to
three months in the year. This may be considered the minimum
capacity of the river. When the wants of the city shall require
a daily supply of 35,000,000 gallons, it will be necessary,
during the season of lowest water, to draw daily from this
reservoir 8,000,000 gallons, to make up the deficiency in the
natural flow of the river. This amount the reservoir would
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supply for 62 days, without any aid from occasional rains ;
which may safely be relied upon, to keep up the required supply
from the reservoir, beyond any drought we have ground to
apprehend. The supply of the Croton, from its daily flow,
aided by this reservoir, may therefore be taken with great con-
fidence at 35,000,000 gallons; which will be very ample for
the wants of the city for a long time to come; and when the
day arrives that it will require a larger quantity, it may be ob-
tained by constructing other reservoirs further up the stream,
where there are abundant facilities for such purposes."
The total cost of the aqueduct, from the Croton dam to the
distributing reservoir inclusive, will be nearly 9,000,000 of
dollars.
New-York, 27th July, 1842.
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