Extension of Potential Failure Modes Analyses to Significant and Low Downstream Hazard Potential Dams
For the last 6 years, the FERC dam safety program has been conducting Potential Failure Mode Analyses (PFMAs) for all high and significant downstream hazard potential dams that require Part 12D Inspections. A PFMA is conducted by thoroughly reviewing the available information on the dam and then analyzing the ways in which the dam could potentially fail through a facilitated discussion among representatives of the owner, including their consultant(s) if applicable, and the FERC inspector.
This process, part of the Dam Safety Performance Monitoring Program (DSPMP), has been highly successful in providing an improved understanding by all parties of the design and construction, project history, and operation of the project and how each of these aspects influences potential failure modes for a particular structure. In addition, the PFMA process results in a focusing of operations and maintenance, surveillance and monitoring activities, investigations, and engineering evaluations on those areas that are deemed critical based on the results of the PFMA.
In spring of 2008, the FERC proposed to extend the PFMA process to significant hazard potential dams that do not require Part 12D Inspections (SIGNIs) and low hazard potential dams greater than 9 feet high or that impound more than 25 acre-feet (Low Hazard Dams). This proposal was coordinated with the dam safety community and we received significant comments and suggestions. Of the 13 responses we received, including comments from the Hydraulic Power Committee (HPC) of the National Hydropower Association (NHA), 7 dam owners supported the proposal, with suggestions and 4 dam owners did not agree that PFMAs were necessary for Low Hazard Potential dams.
The majority of dam owners responding supported the initiative. The comments and suggestions offered by dam owners were:
PFMAs at Low Hazard Potential dams should be voluntary
Revise Low Hazard Potential Dam criteria to 25 feet high and 50-250 acre-feet of storage volume
The default should be the owner providing the facilitator. The FERC engineer is available when necessary
Delay proposal so owners can focus on the work required at high and significant dam - don't divert limited resources
Even at low hazard potential dams, PFMAs provide a better understanding of a facilities' potential vulnerabilities and are a worthwhile exercise for risk management purposes.
The comments and suggestions by NHA-HPC were:
Some dam owners thought it was a good idea
Some dam owners can not afford to divert limited resources to low hazard potential dams
Costs involved may not commensurate with project revenues
- Some dam owners did not believe it was worth the effort and expense
Description of New Initiative to Conduct PFMAs at Significant Hazard Potential Dams Without Part 12D Reports (SIGNIs) and Low Hazard Potential Dams
The comments and suggestions were carefully considered in finalizing the proposed extension of the PFMA process to SIGNIs and low hazard potential dams.
Given that significant hazard potential dams can cause substantial property damage in the event of a dam failure, a PFMA is warranted and appropriate. Accordingly, a PFMA will be required for all significant hazard potential dams.
- All Significant Hazard Potential dams subject to PFMA shall be performed in accordance with Chapter 14. Flexible schedules will be set to avoid deferring available resources from required ongoing work at high hazard potential dams.
- Dam owners of Significant Hazard Potential dams that need a PFMA will be contacted by the Regional Office and requested to propose a plan and schedule for completing the PFMA.
- For low hazard potential dams, while FERC strongly encourages the owners to conduct PFMAs on their projects, at this time it will be voluntary. Prior to the inspection season, the D2SI regional office will contact Low Hazard Potential Dam owners to propose conducting a PFMA during the dam safety inspection. The dam owner will have the choice of voluntarily including the PFMA in the inspection.
As a practical matter, conducting PFMAs at SIGNIs affects 67 dams nationwide. For most dam owners, this will result in only one or two additional PMFAs. The dam owners who have a larger number of SIGNIs in their inventory should propose a schedule to conduct the PFMAs. FERC will consider available resources and current commitments at high hazard potential projects in considering the proposed schedule.
- The PFMA for a SIGNI can be accomplished as part of the FERC dam safety inspection.
- The D2SI regional office will contact SIGNI owners to develop a schedule for conducting PMFAs
Dam owners will take the lead in PFMAs and follow the guidance provided in Chapter 14 of the FERC Engineering Guidelines for the Evaluation of Hydropower Projects, a copy of which can be found at:
- Dam owners can perform this program with their in-house dam safety knowledge, experience, and expertise, if available, or by retaining a consultant.
- The facilitator should be a civil engineer with a broad background and experience in dam safety.
- The FERC inspector will participate in the PFMA as described in Chapter 14.
- The PFMA for a Low Hazard Dam can be accomplished as part of the FERC dam safety inspection.
- Dam owners who prefer to take the lead and conduct the PFMA are encouraged to do so.
- The FERC inspector may serve as the facilitator if requested by the owner.
The general sequence to accomplish the PFMA for a Low Hazard Potential Dam is as follows:
- Prior to the inspection season, the D2SI regional office will contact Low Hazard Potential Dam owners to propose conducting a PFMA during the dam safety inspection. The dam owner will have the choice of including the PFMA in the inspection.
- The FERC inspector initiates coordination with the dam owner to discuss the effort and explain the PFMA process.
- The dam owner will review project files, assemble the information needed to understand the design, construction, and operation of the dam, compile this information into a single document, and provide the information document to all PFMA participants a minimum of 60 days prior to the session.
- Prior to the PFMA, each participant will review the compiled information and develop a list of Potential Failure Modes (PFM) for use during the field inspection and PFMA session.
- The PFMA participants (the owner, in-house engineers, project operator(s), field personnel, etc) conduct the dam safety inspection guided by the PFMs identified during the review of the background information, and note any additional PFMs identified during the field inspection.
- Following the inspection, the PFMA participants assemble at a convenient location to review the information previously complied and discuss the PFMs
- The owner or the owner's consultant, with assistance from the FERC inspector, records the PFMA session.
- Generally, the owner will write the PFMA report. PFMA reports for Low Hazard Dams at a minimum should include:
- Major Findings and Understandings;
- PFMs identified - corresponding categories, adverse and non adverse points, likelihood of occurrence, and dam owners ability to detect and/or mitigate the PFMs;
- Risk reduction measures; and
- Assumptions made to fill in information gaps.
- The FERC inspector will review the PFMA report and provide comments prior to finalizing the report.
- The final PFMA report will be attached to the current dam safety inspection report and subsequent inspection reports. Any necessary follow up engineering studies or risk reductions measures will be addressed in the inspection follow up letter issued by the Regional Engineer after considering input from the dam owner and (if applicable) consultant and undertaking the appropriate review by the inspecting staff and Regional Office Management Team.