Seismic Risk Assessment for a State-Regulated Dam

ABSTRACT ONLY - Dam safety and dam engineering design practices have traditionally employed a standards-based approach in which deterministic methods are used to inform decision making as it relates to dam safety and design criteria. However, a transition to a risk-informed decision-making framework has ensued due to the inherent limitations associated with the traditional standards-based approach, most notably the inability to explicitly account for downstream consequences and thus life safety risk. While this transition has been led by federal dam owners and regulatory agencies, the majority of dams in the United States are regulated under state dam safety programs. For these state-level jurisdictions, the transition away from a standards-based approach in favor of a risk-informed decision-making framework remains largely in its incipient stages.
To help facilitate this transition, funding was made available by the Georgia Environmental Protection Division’s (EPD) Georgia Safe Dams Program (GSDP) through the Federal Emergency Management Agency’s (FEMA) High Hazard Potential Dams (HHPD) grant program to conduct a risk-informed seismic evaluation of Sequoyah Lake Dam. Sequoyah Lake Dam, a 60-foot-tall earthen embankment dam classified as a Category I (High Hazard) dam, is owned and operated by a local property owner’s association (POA) and is regulated under the GSDP. The Georgia EPD issued a regulatory notice to the POA identifying deficiencies in the Dam related to seismic slope stability and requested that an engineer be engaged to conduct engineering analysis to address the deficiencies. The first phase of the HHPD grant was to conduct a limited scope seismic risk-informed evaluation of the existing dam in support of the design addressing the seismic deficiencies identified by GSDP.
The scope of the seismic risk assessment was tailored to the needs and resources of the POA and included a seismic failure modes analysis, engineering analyses (seismic hazard analysis, pseudostatic slope stability and deformation analysis, conduit strength analysis), and a seismic risk model. The results of the seismic risk assessment provided increased confidence in the proposed remedial design to address the seismic deficiencies of Sequoyah Lake Dam. This project demonstrates how risk-informed decision making can be used to enhance dam safety assessments under the auspices of state dam safety programs.