Bellows Falls times. [volume] (Bellows Falls, Vt.) 1856-1965, 1889-06-27
THE J0HNST0WN DAM.
TESTIMONY BY AN EXPERIENCED
ENGINEER.

How the Dam was UOnstructed-the Dimen-
sions Ofthe Embankment Three Miles of
Water Drained Out In Forty five Minutes.
So much has been said about the great
pennsylvania horror that an investiga-
ton into the condition of the dam which
held in check until the fatal day the
mighty agent of destruction, will be of
interest. practical engineer named II.
Nj. Brinkerhoff of the editorial staff of
the Engineering and Building Record of
New York city, has made such an inves-
LEGATION and has given some interesting
facts. This gentleman says that the
earthen embankment crossed the valley
on straight line and was about 900 feet
long on its crest Its central portion had
been completely washed out down to,
and even below, the original bed of the
stream, the rush of the released water
having scooped out quite basin Just be-
low the dam. He says:
| The width of the break at the crest was $50
| feet, narrowing to perhaps less than one
fourth of that amount at the bottom. The
| structure of the remaining portions thus eX-
posed in section showed a tolerably homoge-
| neous mass of stiff gravelly clay, well covered
| with rip-rap, on both slopes, the lower slope
| having quite growth of trees and bushes ON
| 1t. MY first look was for the heart wall of
| puddle or masonry that is usual in large earth
EN- dams, but a closer examination of the ma
terial left no doubt in my mind that the omis-
sion was due to the fact that the dam was
| practically all puddle of very good quality.
The embellishments on either side of the
| break were left standing with very steep
and IN some cases perpendicular slopes,
| showing the compactness and strength
of the material with which it was built.
The height of the dam was so feet width
at top 20 feet; width at bottom 300
feet; inner slope, two to one, length 100
feet; outer slope, one and half to one,
length l2O feet. The slopes were rip
raped with irregular quarry stones, such
as one or two men could handle From
this it will be seen that the bank of earth
had abundant strength, being very flat,
regardless of its height.
The dam crossed the stream from north
to south, and around the north end of it
a slulceway or waste weir had been cut
through the solid rock, of which both
SIDES OF the valley at that point is COM
| posed, but more or less covered with soil
| The sluiceway was 65 feet wide at its
| lower extremity and enough wider at it's
inlet to offset the obstruction occasioned
by fish screen three feet high. 1t would
| seem that three feet of water was the ut
most volume expected to be reached in
the sluiceway. The bottom of this waste
Weir was ten feet below either end of the
dam, and of the centre of it as construct
| ed. But the dam had settled three feet
IN the centre, leaving only seven feet in
the weir, instead of ten, before the water
should reach the crest. The iron waste
pipes mentioned by newspaper CORE
| SDOO6pptS wore of ba hot+or, 90 +I,o L.,
AMI as leaks had sprung around them,
and as they were no longer needed to
supply the canal, for which purpose they
were built, were permanently stopped as
means of safety.
A gentleman who was on the spot
three hours before the break writes as
follows
At about O'Clock walked over the dam :
! 1T that time the water was three inches deep
Oh it and was gradually eating away the earth
| on the outer face. As the stream rolled down
the outer face it kept wearing down the edge
OF the embankment and saw it was merely
| question of time. l then went up to the
club house and got dinner, and when 1 re-
turned saw that good deal more of the
outer edge of the dam had crumbled away.
The dam did not give way. At rough guess
| should say that there were sixty million tons
of water i'll that lake and the pressure of that
mass of water was increased by floods from
| TWO streams pouring into it, but the dam
would have stood it could the level of the lake
have been kept below the top of the dam.
But the friction of the water pouring over the
dam gradually wore it away from the outer
| face until the top became so thin that it gave
way. The break was about ten feet wide at
first and shallow, but now that the flood had
| made gap, it grew wider with increasing
rapidity, and the lake went roaring down the
valley. That three miles of water was drained
out in forty-fve minutes.