Analysis of the South Fork Dam and the Former Lake Conemaugh

Abstract

Key objectives are outlined for the hydrologic calculations of the former Lake Conemaugh and the dam breach flood. Dam remnant survey data collected in 1889 were compared with the modern GPS reference frame. They differ by ~6.2 ft. (1.9 m), the 1889 data being systematically lower. At the moment the dam breached in 1889, the surface of Lake Conemaugh had an elevation in the range of ~492.5 to 492.6 m. Using LiDAR data and this lake stage, a storage-elevation curve was developed for the lake. The impoundment held about 1.455 × 107 m3 of water. The equivalent tonnage (14.3 million) is less than the usually cited figure of 20 million tons. Analysis of the South Fork watershed indicates that the time of concentration for runoff from the major rain event should have been in the range ~3.6 to 7.3 h, and the time to peak discharge less than 7.3 h. Observations of local streams suggest that rivers had peaked between 12 noon and 1:00 p.m. on the day of the flood, several hours before the dam breach.