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 Twenty million 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 rainfall and the dam
failures created the Great Flood of 1977.
Weather Service said a once-in-a-1,000 year flood
in the valley could have resulted from 7.32
inches of rainfall in a 10 hour period. But an
11.82 Inch rainfall would be a once-in -a- 5,000
to 10,000 year occurrence.
The dams failed
because of overtopping. The dams that burst were:
Laurel Run Dam on
Laurel Run. The 10 year old earthen dam held 101
million gallons of water. It had a 42 foot high
spillway. The dam Is owned by the Johnstown Water
Authority. When it failed the water enveloped
Tanneryville and caused deaths and heavy property
Sandy Run Dam on
Sandy Run. The dam held 18 million gallons of
water. It Is 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
Peggys 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.
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
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).
Col. Max Janairo
Jr., district engineer for the Army Corps of
Engineers - Pittsburgh office, said sufficient
resources to control the amount of water that
Johnstown received in rainfall July 19th and 20th
are not available. No dams are constructed to
contain such a quantity of water received in such
a short period of time."