The majority of people know that Johnstown has been decimated by some historical floods, as it has even been nicknamed the Flood City.
Some don’t realize that the area was devastated by not just one, but three disastrous floods. All three floods were sparked by weather, though only the widespread flood of 1936 was by weather alone. That flood was caused by the combination of heavy rainfall and a rapidly melting snowpack, and did not only affect the Johnstown area, but still holds the high-water mark for many spots in Pennsylvania.
Both the deadly Great Flood of 1889 and the Flood of 1977 were sparked not only by rounds of heavy rainfall, but were enhanced by the failure of manmade dams.
Since we are now coming up on the 40th anniversary of the 1977 flood, I thought I would go into details on why the flood happened and whether it could happen again.
July of 1977 was a hot month. Temperatures reached 90 degrees or above on 12 days between July 6 and July 22. This heat wave was thanks to a massive ridge of high pressure that dominated the eastern United States.
The Bermuda high nosed its way into the southeastern United States and helped fuel our area with plenty of not only hot air, but extremely humid air.
An upper-level disturbance formed a complex of thunderstorms along the top of this ridge. This disturbance and its showers and thunderstorms moved southeastward through the western into the south-central part of the state.
Just on its own this can bring flooding rain, but in this case, we developed what is known as a training situation with the thunderstorms over the Johnstown region.
Training thunderstorms are when multiple thunderstorms form in a line parallel to the flow of the storms. They follow each other much like the cars of a freight train.
Storm after storm bring rounds of heavy rainfall, and in this case, the thunderstorms were back-building.
This means a new thunderstorm would form on the backside of the line, which prolonged the rainfall for this event.
Eventually, the rainfall total exceeded 10 inches in less than a day near the Johnstown area.
You take that amount of rainfall over higher terrain and the water rushes down to the lowest elevations, overloading the local rivers and streams. This alone would have created disastrous flooding, but the amount of water also caused the failure of six dams in the region, most of which were built to prevent a repeat of the 1936 flood.
These dam failures helped to send more than 100 million gallons of water into the valley on top of what was coming from the heavy rain event.
According to NOAA and the Army Corps of Engineers, the previous channel improvements to move water through Johnstown were built to handle more than 81,000 cubic feet of water per second, but the combination of runoff and the dam bursts sent 115,000 cubic feet of water per second. This backup inundated Johnstown.
The flood caused 85 deaths and more than $200 million in damage. While this pales in comparison to the loss of more than 2,000 people in the 1889 flood, it was the last straw for many in the city. The population shrank by more than
15 percent in the decade between 1970 and 1980, and while there were some other economic factors involved, the Flood of 1977 shared a large blunt of the blame.
Could this happen again?
Yes. The sharp terrain around the region makes the region prone to flash flooding. And as long as there are dams that lead into the surrounding rivers, the potential will always be there for a dam burst. Though with modern inspections and engineering, the potential is there to minimize the risk.
All week, WTAJ News and the Tribune Democrat will share memories from survivors of the 1977 Johnstown Flood and you will hear from those who worked to rebuild the region.
New ’77 Flood Photo Gallery on Display (WTAJ)
Survivor Stories in communities hardest hit (Tribune Democrat)
Steelworkers Trapped by Flood (WTAJ)
River Walls: Past & Future (Tribune Democrat)
Recovery Effort & President Carter (WTAJ)
Family vacation ends in Tragedy (WTAJ)
How we remember: Preserving the ’77 Flood for future generations (Tribune Democrat)
Firefighter Rescue (WTAJ)
Remembering Tanneryville (WTAJ)
Through the Lens: Photographers reflect on what they saw the night of the flood (Tribune Democrat)