JOHNSTOWN FLOOD OF 1889 – DESTRUCTION AND REBIRTH

This year is the 120^th anniversary of the flood that caused the greatest loss of life from dam breach in U.S. history. The Johnstown flood of 1889 is well-known for its devastation of Johnstown and surrounding mining and milling communities of the Conemaugh Valley. More than 2200 lives were lost. Although the catastrophe is well documented in the popular literature and cinema, little scientific work has been done on this flood. Based on new surveys at the site and along the Conemaugh River, and review of contemporary photographs and historical documents, we are reexamining this event to reconstruct the peak discharge and flood hydrograph. Our presentations (see companion abstract) will include an outline of our research approach, 1889 images of the South Fork dam breach and flood damage, present-day views of dam remnants, and a hydrologic analysis of the reservoir geometry and dam breach. One of our efforts is to reconcile 1889 elevation data and flood levels with modern-day GIS and GPS reference frames. An early result of our research is that the peak discharge rate for the flood appears to be controlled less by the release rate from the South Fork Reservoir and more by the sudden collapse of the massive Conemaugh viaduct bridge, 6 km downstream from the dam. A debris dam blocked the arch beneath this stone masonry bridge, causing water to build up in a river meander gorge until the bridge was overtopped and collapsed, releasing a flood wave that obliterated almost everything in its path. The peak discharge likely exceeded 12,000 m³/s. Economic and material assistance from across the nation soon reached the Conemaugh Valley. The survivors rebuilt the communities, which once again thrived given the region’s importance in coal production.