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The City of Johnstown
has been the site of three major floods each causing
millions of dollars of damage and loss of life.
Floods of Johnstown:
1889-1936 -1977
1889 FLOOD
On June 1,1889, Americans woke to the news that
Johnstown, Pennsylvania had been devastated by the worst
flood in the Nation's history. Over 2,200 were dead,
with many more homeless. When the full story of the
flood came to light, many believed that if this was a
"natural" disaster, then surely man was an accomplice.
Johnstown in 1889 was a steel company town of Germans
and Welsh. With a population of 30,000, it was a growing
and industrious community known for the quality of its
steel. Founded in 1800, Johnstown began to prosper with
the building of the Pennsylvania Mainline Canal in 1834
and the arrival of the Pennsylvania Railroad and the
Cambria Iron Company in the 1850’s.
There was one small drawback to living in the city.
Johnstown had been built on a flood plain at the fork of
the Little Conemaugh and Stony Creek rivers. Because the
growing city had narrowed the river banks to gain
building space, the heavy annual rains had caused
increased flooding in recent years.
1936 FLOOD
47 years later another disaster - Johnstown’s second
flood - struck on March 17, 1936, causing the much
greater property loss of forty five million dollars.
Melting snow and ice from the surrounding hills and a
steady rain caused a gradual rise of the Conemaugh and
Stonycreek rivers, that rose by 18" an hour. The flood
reached its peak at midnight and thereafter gradually
receded. Water was at a height of 14 feet at the public
safety building.
1977 FLOOD
The dams that surround Johnstown, stretching throughout
the Conemaugh Valley, were unsuspecting accomplices in
the Great Flood of 1977. They were duped by the
instigator - the rain.
When they failed, six dams poured more than 128 million
gallons of water into the Conemaugh Valley. In
comparison approximately 4.8 billion gallons were
unleashed on Johnstown when the South Fork Dam burst in
1889.
A phenomenal amount of rainfall - 11.82 inches in 10
hours - was too much for both the dams and the sewers in
the Conemaugh Valley. The Corps of Engineers originally
called the ’77 flood a 500 year flood, but it’s been
downgraded slightly since then. The dams failed because
of overtopping. The dams that burst were:
Laurel Run Dam on Laurel Run. The aged old earthen dam
held 101 million gallons of water. It had a 42 foot high
spillway. The dam was owned by the Johnstown Water
Authority. When it failed the water enveloped
Tanneryville and caused deaths and heavy property
losses. The Laurel Run Dam was built by Cambria or
Bethlehem Steel, then sold to the Water Authority when
it was created.
Sandy Run Dam on Sandy Run. The dam held 18 million
gallons of water. It was owned by the Highland Water and
Sewer Authority. The 63 year old dam had a spillway of
28 feet
Salix Water Dam on Otto Run. It held 2 million gallons
of water. Its spillway height was under 25 feet. It is
owned by the Adams Township Water Authority.
Cambria Slope Mine 33 on Sanders Run. It held 7 million
gallons of water. The dam leased by Bethlehem Mines
Corp. had a spillway of 32 feet
Unnamed Dam on Peggy’s Run, Franklin Borough. This dam
was leased by Bethlehem Mines Corp. and held an
undetermined amount of water at the time of the flood
because it was used as a catch basin.
An unnamed impoundment dam east of Johnstown at St.
Michael held less than 1,000 gallons. It was a reserve
dam for Bethlehem Mines Corp.
The dams were simply overwhelmed. After overtopping,
water eroded the earthen embankments. There was total
failure of five dams. The sixth, Cambria Slope Mine 33,
retained about two-thirds of its contents.
The dams had not shown any defects in past inspections
and no trouble was reported in them by the Pennsylvania
Dept. Of Environmental Resources (DER).
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