[Illustration: PLACING THE 9¹⁄₂ FOOT STEEL PIPES.]
[Illustration: A HUGE UNDERGROUND RIVER
The water is conducted from Ashokan reservoir as a huge, underground,
artificial river. The aqueduct is ninety-two miles in length from
Ashokan to the northern city line, and it should be explained that it
is built on a gentle grade, and that the water flows through this at
a slow and fairly constant speed. The aqueduct contains four distinct
types: the cut-and-cover, the grade tunnel, the pressure tunnel,
and the steel-pipe siphon. The cut-and-cover type, which is used on
fifty-five miles of the aqueduct, is of a horseshoe shape and measures
17 feet high by 17 feet 6 inches wide, inside measurements. It is
built of concrete, and on completion it is covered in with an earth
embankment. This type is used wherever the nature of the ground and
the elevation allow. Where the aqueduct intersects hills or mountains,
it is driven through them in tunnel at the standard grade. There are
twenty-four of these tunnels, aggregating fourteen miles in length.
They are horseshoe in shape, 17 feet high by 16 feet 4 inches wide, and
they are lined with concrete. When the line of the aqueduct encountered
deep and broad valleys, they were crossed by two methods: if suitable
rock were present, circular tunnels were driven deep within this rock
and lined with concrete. There are seven of these pressure tunnels
of a total length of seventeen miles. Their internal diameter is 14
feet, and at each end of each tunnel a vertical shaft connects the
tunnel with the grade tunnel above. If the bottom of the valley did
not offer suitable rock for a rock tunnel, or if there were other
prohibitive reasons, steel siphons were used. These are 9 feet and 11
feet in diameter. They are lined with two inches of cement mortar and
are imbedded in concrete and covered with an earth embankment. There
are fourteen of these pipe siphons of a total length of six miles. At
present one pipe suffices to carry the water. Ultimately three will be
required for each siphon.]
Our water-works man sees how earnest you are in seeing just where the
water comes from, so he proposes that we go find out. We go outside and
there is an automobile all ready to go and we jump in and the machine
starts off along quite one of the nicest roads you were ever on. Soon
you exclaim, “Why, this is the aqueduct road,” and so it is. The great
pipe through which the water comes to the city is an aqueduct and they
have built the road right over the place where the aqueduct runs. Away
we go as fast as the car can carry us, sometimes ten, or twenty or
perhaps fifty miles, according to what city you are in. The city goes
as far as it must to find a supply of pure water and plenty of it and
spends millions upon millions of dollars to make its supply of water
good and certain. Occasionally we come to a little stone house along
the way where we can go down and see the sides of the great stone pipe.
After a while, however, we find our aqueduct road comes to an abrupt
stop before another great stone wall. It is the great dam which has
been built out there in the country to form one end of a great tank
that catches and holds the waters from the creeks and rivers that flow
into it. Usually the dam is built up right across a river. They simply
build the dam strong enough to stop the river from going any further.
Then, of course, the water piles up on the other side of the dam and
occasionally this tank, which is simply another huge reservoir, gets so
full that the water flows over. It does not really overflow the top of
the dam, because underneath the top the engineers have left openings
here and there for the water to get through. If it were not for these
loopholes, so to speak, the great wall of water within the reservoir,
piled against the dam, would break down the wall no matter how well
built, by the great pressure it exerts.
[Illustration: THROUGH THIS CHAMBER THE FLOW OF WATER TO THE AQUEDUCT
IS REGULATED.]
~THE REAL SOURCE OF THE WATER~
We are now near to the real source of the water. We take a trip around
the top of the great reservoir. Around at the other end we find what
looks like a river, excepting that there isn’t any current to speak of.
It is a river, but a much deeper one than it would have been but for
the dam which has been built across it, and originally its surface was
quite far down in a valley. Sometimes man makes his water dam at one
end of a lake, which has been formed by streams flowing into a valley
which has no opening for the water to run out of. In these cases the
lake will be high up in the hills and man simply builds his dam at one
end, lets the end of his aqueduct into the bottom of the lake and the
water flows. In other cases he picks out a valley where there is no
lake at all, builds his dam and then drains the water which he finds in
small lakes higher up in the hills into the one big valley and makes a
very large lake. But the water in the lakes comes originally from the
creeks, rivers or springs which run into it, and so we will follow our
original river back into the hills. Here and there along its course we
find a little stream flowing into our river and, as we go up higher and
higher into the hills, we find our river getting smaller and smaller.
Now it is only a creek and, if we go far enough, we find its source but
the tiniest kind of a tinkling brook with the water dripping almost
noiselessly between the rocks as it makes its path down the side of
the hill. There is the source of the water in the glass you have just
enjoyed.
[Illustration: DIGGING A HOLE UNDER A RIVER
DIAMOND DRILL BORING A HORIZONTAL HOLE 1100 FEET BELOW THE HUDSON
RIVER.]
[Illustration: HUDSON RIVER SIPHON, 1100 FEET BELOW THE RIVER.
Of the many siphons constructed, by far the most interesting and
difficult is that which has been completed beneath the Hudson River.
The preliminary borings made from scows in the river showed that great
depths would have to be reached before rock sufficiently solid and
free from seams was encountered to withstand the enormous hydraulic
pressure of the water in the tunnel. After failing to reach rock by the
scow drills, two series of inclined borings were made from each shore,
one pair intercepting at about 900 feet depth and the other at about
1500 feet. Both showed satisfactory rock, and accordingly a shaft was
sunk on each shore, to a depth of approximately 1100 feet, and then a
horizontal tunnel was driven connecting the two. It is of interest to
note that because of the enormous head, which must be measured from the
flow line far above the river surface, the pressure in the horizontal
tunnel reaches over forty tons per square foot.]
[Illustration: THE HIGHEST BUILDING IN THE WORLD UPSIDE DOWN