of the Aqueduct, where the masonry of the side wall is enlarged for
its base; we can descend from the door and gain an entrance to the
channel-way by an opening in the side of the roofing arch. The sill of
the door is about 12 feet above the bottom of the channel-way.
[Illustration: VI
_F. B. Tower._ _Gimber._
ENTRANCE VENTILATOR]
Those not intended for an entrance stand directly over the top of the
Aqueduct and are groined into the roofing arch.
Besides these Ventilators, there are openings 2 feet square in the top
of the roofing arch, every quarter of a mile: they are covered with a
flag stone and the place is marked by a small stone monument projecting
above the surface of the ground. These may be useful to obtain entrance
to the Aqueduct, or to afford increased ventilation should it ever
become necessary.
CULVERTS.
Where streams intersect the line of Aqueduct, culverts are built to
allow them to pass under it. They are simply a stone channel-way built
under the Aqueduct of such form and dimensions as will allow the stream
to pursue its natural direction without causing injury to the work. The
foundation of these culverts is formed by laying down concrete, upon
which an inverted arch of cut stone is laid forming the bottom of the
water-way: side walls of stone are built and surmounted by an arch of
stone. The span, or width of water way, of the culverts built, varies
from 1½ foot to 25 feet. Those of 1½ foot span have a square form for
the water-way, and are constructed by making a foundation of concrete,
upon which a flooring of well dressed stone is laid forming the bottom
of the water-way, and from this, side walls are built and covered by a
course of thick stone flagging well dressed and closely fitted. At each
end of the culvert a deep wall is built underneath so as to prevent
the water from doing injury by undermining it. Buttresses and wing
walls are built at each end of the culvert to guide the water to and
from the channel-way, and a parapet wall is built over the top of the
channel-way at each end to sustain the embankment of earth over the
culvert. These wing walls and parapets have various forms; sometimes
the parapet is built across the top of the culvert, and the wing walls
built at right angles to it, and sloping down to the buttresses, and
sometimes the wing walls and parapet form one continuous wall of a
semi-circular form, the top sloping up from the buttresses in a plane
parallel with the slope of the embankment covering the Aqueduct above.
These culverts are permanently constructed, and in preparing the plans
for them much skill has been displayed in adapting the form and size
which the circumstances required, and much taste displayed in the
design for their construction.
Plate VII. is an isometrical drawing of one of the culverts with
rectangular wings and parapets; the body of the culvert is cut in two
in the drawing, showing that it may be of any length, according to the
width of the embankment through which it is constructed. The length is
generally arranged so that the slope of the embankment may intersect
the rear of the top of the parapet and pursue a direction down,
parallel with the slope of the top of the wing walls.
[Illustration: VII
Scale of 4 feet to one inch
_F. B. Tower._ _Gimber._
]
_Gate Chamber at the Head of the Aqueduct and Grade of the Water-way of
the Aqueduct._
Plate VIII. is a longitudinal section through the _tunnel_ and _gate
chamber_ at the head of the Aqueduct showing its connection with the
_Fountain Reservoir_. This gate chamber is not in any way connected
with the dam itself, but stands some distance from it, and the water
reaches it by means of the tunnel which leaves the Reservoir above the
dam and passes through the solid rock of the hill against which the
masonry of the dam is built, a distance of over 200 feet. This tunnel
descends into the Reservoir, so that the centre of it at the mouth is
about 12 feet below the surface of the water; any floating substance
cannot enter it, and during the winter season when the water is frozen
over no obstruction can take place to the flow into the Aqueduct, and
during the summer season the water will be drawn from a level where it
is cooler than at the surface.
The gate chamber has two ranges, or sets of gates; one called
_regulating gates_, and the other _guard gates_: the regulating gates
are made of gun metal, and work in frames of the same material which
are fitted to stone jambs and lintels: the guard gates are made of
cast iron, and work in cast iron frames also attached to stone jambs
and lintels. The gates are all managed by means of wrought iron rods
attached to them, having a screw formed on the upper part on which a
brass nut works, being set in a cast iron socket-cap.
The bottom of the water way, of the Aqueduct, where it leaves the gate
chamber is 11.40 feet below the surface of the Fountain Reservoir, and
154.77 feet above the level of mean tide at the city of New-York. The
following table shows the length of the Aqueduct as it is divided into
different planes of descent, from the gate chamber at the Croton dam to
the gate chamber at the Receiving Reservoir on the Island of New-York.
Commencing at the south side of the gate chamber at the Croton dam,
and the
ft. miles, descent
The 1st plane of Aqueduct extends 26099.72 = 4.943, 2.94 ft.
The 2d plane of Aqueduct extends 148121.25 = 28.053, 30.69 ft.
Length of pipes across Har. River, 1377.33 = 0.261.
Diff. of level betw’n extremes of pipes 2.29 ft.
The 3d plane of Aqueduct extends 10733.14 = 2.033, 2.25 ft.
Length of pipes across Manhat. valley, 4105.09 = 0.777.
Diff. of level betw’n extremes of pipes 3.86 ft.
The 4th plane of Aqueduct extends 10680.89 = 2.023 1.60 ft.
--------- ------ ---------
201117.42 = 38.090 43.63 ft.
Making the whole distance from the gate chamber at the Croton dam to
the gate chamber at the Receiving Reservoir 201117.42 feet, or 38.09
miles, and the whole descent 43.63 feet.
The descent on the first plane is about 7⅛ inches per mile.
The descent on the second and third plane is about 13¼ inches per mile.
The descent on the fourth plane is about 9½ inches per mile.
In crossing Harlem River there is a fall of 2 feet more than there
would have been had the Aqueduct continued across with its regular
inclination: this _extra_ fall will afford an opportunity to adjust the
number and capacity of the pipes (which descend below the level of the
Aqueduct and rise again) to discharge the full quantity of water as
freely as the Aqueduct, or channel-way of masonry, would have done had
it continued its regular inclination across the valley.
In crossing Manhattan Valley there is an _extra_ fall of 3 feet for the
same reasons as before stated for that at Harlem River. In both cases,
by using the pipes, there is a loss of the head of water for the City
Reservoirs, equal to the amount of this _extra_ fall; but this small
loss of head was not considered of such importance as to induce the
building of structures across these valleys up to the plane of Aqueduct
grade.
[Illustration: VIII
_F. B. Tower._ _Gimber._
]
The bottom of the water-way of the Aqueduct at the gate chamber where
it enters the Receiving Reservoir, is 7.86 feet below the level of
top water line in the Reservoir, thus when the Reservoir is full the
water will rise to within 7¼ inches of the top of the interior of
the Aqueduct at that place, and the height from top water to the
top of the interior will increase, going northward according to the
inclination of the plane of Aqueduct grade, until it reach the surface
level of the flow of water in the Aqueduct.
The height of the interior of the Aqueduct is 8 feet 5½ inches, and the
greatest width is 7 feet 5 inches. The sectional area of the interior
is 53.34 square feet. On the _first plane_, the Aqueduct is larger;
being 2.05 feet higher at the gate chamber, 2.31 feet higher at 2244.
feet from the chamber, and then diminishing, to the head of the second
plane, where it assumes the size above mentioned and continues of that
size throughout the remainder except in tunnels, where it assumes the
forms before described. Where the Aqueduct on the _first plane_ is
larger, the width across the interior at the spring line of the roofing
arch is the same as the general width, but the increase takes place
only in the height of the side walls, and the slope of the inner face
of the walls being the same, the width across at the spring line of the
inverted arch will be less according to the increased height of walls.
The original design was to continue the inclination which the _second
plane_ has, up to the _Fountain Reservoir_; but it was considered
desirable to draw from this Reservoir at a lower level, and the head
of the Aqueduct was depressed for that purpose, and a less inclination
adopted for the length of the _first plane_. The roofing arch was left
on the same inclination as was originally designed, except for the
distance of 2244. feet from the gate chamber, where it was built on a
level.
The curves which are used to change the direction of the line of the
Aqueduct are generally formed with a radius of 500 feet; some have a
radius of 1000 feet, and in a few instances larger ones are adopted,
but the majority of them are of 500 feet radius.
The velocity of the water in the Aqueduct has been ascertained to be
about one mile and a half an hour when it is 2 feet deep; this was
determined by floating _billets_ of wood from the Croton Dam to Harlem
River and noting the time of their passage. Such an experiment would
express the surface velocity and would give a greater velocity than
it would be proper to attribute to the _whole body_ of water in the
Aqueduct; but the depth of water in the Aqueduct will be probably 4
feet as soon as it is brought into general use, and then there will be
a corresponding increase in the velocity of the _body_ of water. This
velocity of a _mile and a half an hour_ may be taken in general terms
as the _velocity of the water in the Aqueduct_.
[Illustration: IX
_F. B. Tower._ _W. Bennett._
VIEW ABOVE THE CROTON DAM.]
DESCRIPTION OF THE LINE OF AQUEDUCT.
The dam, built to form the Fountain Reservoir, is about six miles above
the mouth of the Croton River. The reservoir forms a beautiful sheet of
water in the lap of the hills in the wild region of the Croton, and has
received the name of the “Croton Lake.”
Pine’s Bridge over the Croton River, which is mentioned in the early
history of the country, occupied a position which is now about the
middle of this Reservoir, and there is at that place a bridge over the
Reservoir resting upon piers and abutments.
The hills which bound the Croton Valley where the Reservoir is formed
are so bold as to confine it within narrow limits: for about two miles
above the dam the average width is about one eighth of a mile; at this
distance from the dam the valley opens so that for the length of two
miles more the width is about a quarter of a mile; here the valley
contracts again and diminishes the width until the flow line reaches
the natural width of the River at the head of the lake. The country
immediately contiguous to the shore has been cleared up, and all that
would be liable to impart any impurity to the water has been removed.
This gives a pleasing aspect to the lake, showing where the hand of
art has swept along the shores leaving a clean margin. Retiring from
the water are the richly cultivated slopes with the neat farm houses
overlooking the lake, or the hills crowned with forest trees, while at
intervals a valley or ravine opens and empties in its tributary stream.
Plate IX. is a view taken above the dam showing the position of the
entrance to the tunnel which leads from the Reservoir to the gate
chamber at the head of the Aqueduct. The entablature which is seen on
the left against the rock, is built directly over the mouth of the
tunnel, and from this the tunnel extends through the rock to the gate
house, which is seen on the right of the picture and some distance from
the dam. The structure which is seen in the centre of the picture and
on the ridge of the dam is a gate house over a culvert which extends
through the body of the dam; this culvert is 30 feet below the surface
of water when the Reservoir is full, and has gates which are operated
by means of rods which rise to the interior of the house. During low
stages of the River the water which is not drawn off by the Aqueduct
may pass through this culvert and allow none to pass over the dam.
The entrance to the tunnel is protected by a screen of timber work.
Plate X. is a representation of the entablature over the mouth of the
tunnel, showing the inscriptions upon it, relating to the date of
the commencement of the dam and its completion, the persons who had
contracts for building it, and those having charge of the work during
the time.
[Illustration: X
ENTRANCE TO THE CROTON AQUEDUCT
COMMENCED 1837
COMPLETED 1842
]
Plate XI. is a view taken from a point below the dam and shows the
relative positions of the dam and the gate chamber at the head of the
Aqueduct.
The original channel of the River where the dam is built, was about
120 feet wide; the average depth of water at this place was about 4
feet; and the greatest depth 10 feet.
The left bank of the river arose abruptly with rock, the channel was
gravelly, and on the right bank a sandy table land about 3 feet above
the ordinary surface of water extended about 80 feet; then a sandy hill
arose on a slope of about forty-five degrees.
In making the plan for a dam at this place it was determined to
fill the main channel and the table land on the right bank with an
embankment of earth; and on the left bank where rock was found, to
build a body of masonry against the slope to the requisite height for
the surface of the Reservoir and connect it with the embankment in
the channel; this masonry formed the overfall for the water, and the
rock in the side of the hill adjacent to it was excavated down to the
level of the overfall, thereby extending it into the hill, making the
space for the water to pass over partly of masonry and partly of rock.
The embankment extended with a slope on the upstream side giving it a
broad base, and the lower or downstream side was faced with a heavy
wall of stone. There was a timber pier constructed in the embankment
extending across the channel and faced with plank on the upstream side.
The overfall was made of such length as was thought sufficient to pass
all the water of the river during its highest stages, and with the view
of adapting it to such purpose, examinations were made to find the
highest marks of floods on the banks of the river; and those who were
engaged in determining these marks were guided also by the observations
of the inhabitants of the vicinity who had long known the river in its
various stages. High freshets were witnessed during the construction
of the work, for in the course of two years that the work was going up,
all the various changes and freshets of rainy seasons were experienced,
and those in charge of it did not neglect to note the quantity of water
flowing on such occasions.
[Illustration: XI
_F. B. Tower._ _Gimbrede. sc._
VIEW BELOW THE CROTON DAM.]
With such opportunities to become acquainted with the changes of the
stream they could not fail to know the quantity of water flowing at
periods of the highest freshets, and knowing it, to adapt an overfall
of sufficient capacity for its discharge. For this purpose it was
thought ample provision was made; yet at the time when the work
was nearly completed such a flood occurred as could not have been
anticipated from previous knowledge of the River; the water filling the
entire passage at the overfall, flowed over the top of the embankment
where it was not supposed it could ever reach. The lower slope of this
embankment was covered with a wall not calculated to resist the action
of the water and it gave way; the water broke through the embankment
and rushed along the valley with most disastrous consequences. The
breach occurred at an early hour in the morning; and many persons were
suddenly aroused from their sleep to escape before the approaching
waters. Dwelling-houses and mills were carried away and three lives
were lost. Two of those who were drowned had taken refuge in the tops
of trees, but these being swept away they were drowned; while others
who were not able to reach the main land, but had also taken refuge in
trees, were saved. The change wrought by the flood, in the appearance
of the country, was truly wonderful and the destruction was complete.
Night had closed over that valley where all was happiness and quiet,
but day opened upon a scene of desolation. The fertile fields were torn
up and covered with masses of stone and gravel, and the flood left
marks of its fury far up on the hill sides.
At the commencement of the rain which caused this flood, the ground was
covered with snow to the depth of eighteen inches: the weather became
warm and the powerful rain storm continued incessantly for forty-eight
hours. Notwithstanding the immense volume discharged at the overfall
of the dam, the water was rising, during the night previous to this
disaster, at the rate of fourteen inches per hour over the Reservoir,
covering an area of four hundred acres.
It occurred on the 8th of January, 1841.
In repairing the breach it was decided to build an extension of solid
hydraulic masonry in the place of the portion of embankment which was
carried away.
The gate house and wing wall, which is seen on the ridge of the dam,
shows where the masonry of the original structure connected with the
embankment which extended across the river. The whole length of the
overfall is 251 feet. Access to the house over the culvert, is gained
by a foot bridge which is seen in the picture. The masonry of the
original structure has a rock foundation, and the extension of the
overfall which is seen on the left of the house extending across to the
embankment has an artificial foundation of concrete.
The masonry of the dam is about 8 feet thick at the top and 65 feet at
the base; it is built in a vertical form on the upstream side, with
occasional offsets, and the lower face has a curved form such as to
pass the water over without giving it a direct fall upon the apron at
the foot; this apron is formed of timber, stone, and concrete; and
extends some distance from the toe of the masonry, giving security at
the point where the water has the greatest action. A secondary dam has
been built at a distance of 300 feet from the masonry in order to form
a basin of water setting back over the apron at the toe of the main dam
so as to break the force of the water falling upon it. This secondary
dam is formed of round timber, brush wood, and gravel; it may be seen
in the picture directly under the bridge which extends across below the
main structure.
On the upstream side of the masonry of the dam, an embankment of earth
is filled in, extending 275 feet from the masonry at the base, and
extending from the masonry with a slope of 1 foot in 5 on the top.
[Illustration: XII
_F. B. Tower._ _W. Bennett._
CROTON AQUEDUCT AT SING SING.]
The whole work about the dam possesses great interest, and though it
be distant from the city and somewhat difficult of access, will not
fail to please those who may take time to visit it. Just above the
place where the dam is constructed the River had a bold turn and flowed
along at the foot of a steep and rugged bank. A road passed along at
the base of this hill leading to a mill which was situated at the turn
of the River, before mentioned; a substitute for this road, which was
submerged, has been made along the hill side passing on the right of
the gate house. Enough of the forest has been cleared away to admit of
the construction of the work, but the place still possesses much of its
original wildness, and to see such beautiful mechanical work standing
against the rude rocks,--to observe what changes have been wrought
in the form of this rock to render it subservient to the purposes of
the work, makes us feel that there has been a strife there; but it all
shows that _art_ has gained the ascendency.
The form which has been adopted for the face of the extension of the
overfall is a reversed or double curve which would be easily recognized
as _Hogarth’s line of beauty_: the overfall for the original dam has a
plane face with a curve at the base.
Walks are formed about the work bordered with grass, giving a neatness
and finished appearance to the whole; and every thing in connection
seems to indicate that the vicinity of the _Croton Dam_ will be one of
the resorts in summer seasons for the citizens of New-York. From the
Croton Dam the Aqueduct passes along the left side of the valley of the
Croton River until at the mouth of this river it reaches the left bank
of the Hudson, which it pursues, keeping at a distance of nearly half
a mile from the River, until it arrives at the village of Sing-Sing,
which is eight miles from the dam. In the course of this distance the
Aqueduct passes through four tunnels and encounters many valleys and
ravines where high foundation walls were required, and culverts for the
passage of the streams.
At the village of Sing-Sing there are two Aqueduct bridges; one over a
public road-way, and the other over the Sing-Sing Kill. These bridges
and the adjacent work form a very interesting point on the line of
Aqueduct.
Plate XII. is a view of the Aqueduct at this place: at the left of the
picture may be seen the bridge over the road, and on the right that
over the Kill. The bridge over the road has a span of 20 feet, and the
direction of the road-way being not at right angles with the line of
Aqueduct required the arch to be built askew; the arch lies in the
direction of the road-way, having the ends in planes parallel with the
direction of the Aqueduct. This bridge is worthy of notice, but public
attention is more generally directed to the larger one: _that_ has an
arch of 88 feet span and a rise of 33 feet; the form of the arch is
elliptical, being a compound curve drawn from five different centres,
or radius points. The Kill, or valley over which this arch stands, is a
deep narrow gorge worn by a small stream which empties into the Hudson
River.
The bottom of the ravine is about 70 feet below the soffit or under
side of the arch. Plate XIII. is another view of the large arch taken
from the bottom of the valley near it, and shows the bridge which has
been constructed for a public road passing under it, and the mill near
by.
[Illustration: XIII
F. B. Tower. Napoleon Gimbrede. sc.
AQUEDUCT BRIDGE AT SING SING.]
This arch presents a singularly bold appearance, vaulting over the
roadway and rising high up above the old mill, and what adds much to
this boldness, is the narrowness of the arch, or small distance from
one end of it to the other; being only 23⅓ feet long at the springing
line while the span is nearly four times this length. The length of
the arch diminishes towards the crown, the ends being in planes not
vertical, but inclining towards each other at the top. Each end has
a batter or inclination of one twenty fourth of its height, or half
an inch to the foot. The arch is built of granite, is 3 feet thick
at the crown and 4 feet at the spring or base. The abutments have a
foundation of solid rock which was excavated in proper form to give
them firm footing. The whole structure presents a degree of stability
which seems to defy the effects of time. The Aqueduct has a cast
iron lining over this bridge (as it has over all of this character): it
is formed of plates five eighths of an inch thick, put together with
screw-bolts and nuts and the joints closely filled with iron cement.
This lining is within the brick work of the bottom and sides of the
channel-way, having four inches of brick outside of it and four inside.
The object of it is to prevent any water dripping through the work,
lest by any means it should fill the exterior masonry of the bridge
with moisture and thus render it liable to injury from frost. Other
precautions are taken in forming the masonry about the channel-way, to
prevent this exuding, and the whole plan of the work shows foresight
and precaution worthy of the highest praise.