Johnstown Flood Disaster

Johnstown Flood

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 become so overwhelmed that it broke and dumped water onto the town causing the deaths of 2,200 people. This was not the first problem they had with the dam though; structural problems with the dam were not a new development. Only two years after the finishing of the dam 2 leaks were discovered before the dam was even put into its full usage. They were forced to empty the dam so they could repair it. The dam suffered a major break on June 10, 1862, when the up-stream portion of the stone culvert running under the dam collapsed (Haddock, Vikki). There was little damage to property downstream, but a large section of the dam over the damaged portion of the culvert collapsed and was washed away. They dam was then closed and left with the large gap in it because of financial reasons until 1875 when the Pennsylvania Railroad sold the dam and also 500 acres to Benjamin Ruff who wanted to turn the area into a summer resort. Ruff’s plan was to fill in the gap left in the dam and allow the lake behind it to refill to make a resort and the remaining water would run-off he had decided to sell the valves used to control the run-off for scrap metal (Johannson, Shelley). Ruff had hired a man to fill the gap who had some experience building railway embankments but no experience with dams. The plan was to add a double thickness of hemlock pilings was placed across the culvert entrance as you can see below. Earth and large stone were dumped into the downstream part of the gap. This embankment was built up until it was high enough to enable a road to be graded out to it. Then rock, clay, shale and earth were hauled out and dumped. Because the discharge system had been removed and sold for scrap, the water rising in the lake found its way to the stone embankment and started washing away any earth that was mixed with the stone. Hay, straw and cut brush were placed across the upstream face to stop the seepage. Then, earth and clay were dumped over the hay and straw to create the watertight section of the dam. Another failed design was causing a risk with the lake (NPS). A large bridge was put in across the lake which looked innocent but the bridge supports had iron screens attached to them that ran to the bottom of the lake and reduced the discharge of water by 40%. Another leak appeared in the dam but because it was not cost effective