May 31, 1889 was a day that brought terror to the small town of Johnstown Pennsylvania. The small town was established in 1794 as a steel town and had a population on 30,000. The cause of the flood actually starts not at the town but 14 upstream at the South Fork Dam were the Little Conemaugh and Stony Creeks rivers meet as you can see in the image below. At this place is Lake Conemaugh, a 3-mile long lake located up against the side of a mountain, 450 feet higher than Johnstown PA. The construction started in 1840 under the supervision of engineer William E. Morris but wasn't completed till 1852 due to financial difficulties. (Johnstown Historical Society)
The dam itself spanned a gap of 918 feet across the valley and was 72 feet high. The primary materials used for the dam were rock and other earth. The dam started as 10 feet thick at the top of the structure and expanded to 220 feet at the base (NPS). As you can see in the image below of the dam there is a culvert that runs under the dam that was used to discharge water in the South Fork Creek that was then sent to a local canal. The flow of water was controlled by five 2ft diameter cast iron valves that were located in the tower to the left of the structure. In the event of an emergency were the culvert couldn't handle a large quantity of water an 85 ft wide spill-way was cut through the solid rock of the hillside near the eastern end of the dam (Jackson, Donald Dale).
The dam failed for a number of reasons, the primary reason was because of the failure of the dam that dumped over 20 million gallons of water onto the small town. But there were other contributing factors that caused the dam to break. On May 28, 1889 a storm traveling east from Kansas dumped almost 10 inches onto the flood plains of central PA. Overnight gallons of water rushed into streams everywhere and water started to form gather in the streets of Johnstown. It didn't take long for the South Fork dam to...
Cited: "A Roar like thunder" Historic Information. Oct, 26 2006
Johannson, Shelley "History of Johnstown Flood"Johnstown Area Heritage Society Oct. 29, 2006
"park history" National Park Service Nov. 1 2006
Haddock, Vikki "Deadly 1889 flood near crash gives birth to Red Cross". Sept, 2001.
Jackson, Donald Dale. "20 Million tons of water floods Johnstown"Smithsonian. Volume 20, Issue 2 pg. 50
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