The Bennington banner. [volume] (Bennington, Vt.) 1858-1894, 1889-06-13
The Banner.
BENNINGTON. VERMONT
Thursday Afternoon, June ID, 1889.
THE CoNEMAUGH DAM.


THE CONEMAUGH DAM.
We give herewith an abstract of the
views of Prof. ID. NJ. Greene of the Rens
salear Polytechnic Institute, an engi-
neer well known in this vicinity, on the
cause of the failure of the Conemaugh
dam, as reported in a recent issue OF the
Troy Times. The same conclusions had
been arrived at by one of our own citi
zens, a person we'll versed in hydraulics
and of practical experience in their ap-
plication, and the BANNER had engaged
HIM to prepare an article on the subject.
He, however, prefers to let Prof, Greene
talk. The views of Engineer Greene, we
see, are beginning to be accepted quite
generally, now that the facts are better
understood. Mr.. Ward, the contractor
of the monument, we understand, &C
cepts them. The chief engineer of the
Croton water works in New York City,
says ~ am far from condemning earth
work reservoirs. If the YOUNGSTOWN dam
had been provided with proper outlet
it would probably be standing to-day"
Prof, Greene, in the Times, says that
"All sorts of sensational reports as to the
breaking away of the dam have been
published, evidently written by persons
utterly incompetent to judge the case on
its merits"
He continues, ~ have read the &C
counts in the newspapers, but have moi
found an intelligent description Of thai
dam. II is only by taking little here
and a little there from the different re-
ports that l have finally got together q
pretty clear idea of the dam as it existed
before the disaster occurred.
Dams may be divided for the purpose
OF this interview into two classes
FirSt-Dams constructed across stream'
to make water power.
Second-Dams built for the purpose Of
storing water, as reservoir.
The Conemaugh dam was OF the latter
kind. The dam was built across the
valley, holding back the water and stor
ing it.
There are three essential requisites fol
a reservoir dam, or any dam of this
second class:
FirSt-The volume, mass and forma
ton of the dam should be such as to eff
fectually resist the pressure of the water
Second-The dam should be imperyi'
Gus to water.
Third-There should be at one end OF
the dam a waste, or spillway, of suffi'
cient capacity to discharge the largest
volume Of water which can by any pos
sibility reach it.
The dam was twenty feet wide on top
Its slope on the waterside was two t.
one-two feet horizontal to one foot YER
tical. On the other side, one and half
to one. Its height was about seventy
two feet,
The dam, if even entirely of earth, had
ample ability to resist the pressure OF
the water upon it.
The first requirement is satisfied.
A further evidence Of Its satisfaction is
the fact that the dam had existed a
great many years and had never broken
away.
Was it tight?
II the dam leaked and the leaks had
not been stopped the dam would have
long since been destroyed. The fact that
1t stood till the date of it's final yielding
shows that if it ever had leaked serious
ly the leaks must have been etfectually
stopped by using the proper means
Hay, straw and horse stable manure are
proper materials for stopping leaks in
such dams, and if covered with ground
and clay they constitute tight dam.
Was the third condition satisfactory
was there ample spilway?
Originally spillway was cut throu gh
the solid rock at such dept that water
could waste through it to depth Of
three feet before rising to level with
the top of the dam,
The sporting club-the organization
that owned the lake-raised the top OF
the dam four feet above its original
height, so that water could flow through
the waste 10 the rock to depth of seven
feet before reaching the top of the dam.
Tie raising of the dam was in the direc-
ton of safety.
The dam did not yield to the pressure
Of water against it. but to the erosion or
wash Of the water passing over low
place at the top oil the dam. The CEN
ter of the dam was foot and half
lower than at the ends, so that when
the water had risen to depth of five
and one half feet in the spiIlway it be-
gan to pour over this spot, From the
instant that the water began to pour
over the top of that dam at the low part,
the structure was doomed: no human
power could have saved it, Once the
washout began the water made quick
work OF it.
Had the dam been level on the top, or
had there been no sinking of foot and
half or 30 in the centre, it is barely
possible that the additional depth of a
foot and a half in the spilway might
have carried off the flow of the lake and
averted the disaster. Had there been no
low point in the dam a foot and half
Of water over its entire surface could
have still been stored IN the lake after it
had reached the five aud half-foot level
OF the spillway. The lake had an srea
Of 800 acres, it 10 stated. That would
have provided storage for 52.272, 900
cubic feet of water above the five-and a.
half-foot level before the water would
have begun to go over the top OF the
dam.
The fact, however, that the water
rose to depth of five and one half feet
in the spillway shows almost beyond
question that the capacity OF the spill
way through the rock around the end Of
the dam was too small, and it seems clear
to me that the responsibility for that ma
turally rests upon the designer OF the
structure. unless he was overruled by
higher authority.
Prof. Green, in speaking Of the wash.
out in the low point at the Conemaugh
dam, alluded to break in the FEEDER
dam of the Erie canal for the ifty-mile
level in 1853. 81 saw the water as it be
gan to go over the top of the dam at
low point" he said. "At first the stream
was tiny rivulet not bigger than my
little finger. In another second it was
as large as my arm then 1t was of the
dimensions of hogshead, and in very
few minites it was rushing torrent that
could not be checked. The force of the
water in such case is wonderful. AT
first email particles of earth give away,
but as the washout continues to open
a way for the water the current becomes
Irresistible"