CS6C - Concurrent Session 06C: Dam Failure Case Studies from the 2015 South Carolina Flood

Abstract Description: In October 2015, South Carolina experienced historic rainfall and flooding leading to the failures of 50 state-regulated, 1 federally-regulated, and an untold number of unregulated dams throughout the state. The rainfall from Hurricane Joaquin was estimated to be more severe than the 0.1 percent annual-exceedance-probability storm, or greater than the 1,000-year event, caused widespread damage, and resulted in loss of life. In response to the flooding, dam safety officials in South Carolina issued 76 emergency orders to dam owners, responded to dam failures, inspected all 652 high and significant hazard potential dams statewide with the assistance of the Army Corps of Engineers, identified additional low hazard potential dams, evaluated dams for hazard reclassification, and supported recovery efforts in dam safety.

This paper and presentation will focus on a select number of dam failure case studies to illustrate the story of the 2015 South Carolina Flood, including its impacts on the performance of many dams throughout the state and the rehabilitation efforts for affected structures.

Lexington Old Mill Pond Dam, Gibsons Pond Dam, and Barr Lake Dam: These three failed dams are located in series in the Twelve Mile Creek watershed. Dam safety concerns were noted in inspection reports for the Lexington Old Mill Pond Dam prior to the 2015 flood. Subsequently, each dam has been rehabilitated.

Carys Lake Dam: This dam had a unique configuration with two auxiliary spillways, but this did not provide enough spillway capacity during the flood and the dam failed, releasing its pool into the downstream lakes. The dam was ultimately rehabilitated with a spillway constructed in the breach location and reusing elements of the remaining dam and spillways.

These case studies will spotlight the immediate flood impacts, long-term recovery from the flood, and challenges following a major flood.