SQRAs require more effort than Level 1 risk analyses because more detail and effort are put into several aspects of the analysis.
First, there is more detail in identifying the PFMs. For example, a general PFM identified during Level 1, such as “internal erosion through the embankment,” should be enhanced to provide the location and specific internal erosion mechanism, such as “concentrated leak erosion at the embankment to foundation contact.”
Next, more effort is required to understand the hazards. Probabilistic loading data for flood and seismic hazards provide a starting point to estimate the likelihood of failure. Finally, participants need a better understanding of the consequences to quantify an order of magnitude risk of failure.
The scale of the effort varies greatly depending on the size of the facilities being evaluated, the number of PFMs, and specific issues with the project that need to be addressed. Unlike a Level 1 screening level risk analysis, an SQRA can be used to support dam safety decision-making.
Performing an SQRA gives the owner a better understanding of the baseline risk and helps determine if PFMs require additional analyses, remediation, or other dam safety management actions.
Level 2 and Level 3 risk analyses are both SQRAs. The key difference between them is that Level 2 risk analyses are performed periodically as part of FERC’s 10-year comprehensive assessment, the comprehensive review performed by the Bureau of Reclamation, or the U.S. Army Corps of Engineers’ periodic assessment.
For unregulated dam owners, this may be a periodic review of safety evaluated on a term determined by an adopted dam safety program. The Level 2 risk analysis is comprehensive and leverages the project review information being performed for the periodic assessment.
A Level 3 risk analysis is an SQRA not performed during a periodic review cycle and may be performed for a specific concern. It may focus on a subset of PFMs, such as a spillway or seismic risk analysis. A trained facilitator should lead both types of risk analyses.