The Vermont Department of Environmental Conservation (DEC), Dam Safety Program (DSP) engaged GZA GeoEnvironmental, Inc. to perform a portfolio risk assessment of seven HIGH hazard potential, non-FERC regulated dams in the State of Vermont that had been rated in POOR condition based on periodic inspection. The assignment was partially funded via grant obtained through FEMA’s High Hazard Potential Dam Program (HHPD).
The primary objective of the risk assessment work was to better understand the vulnerabilities and consequences of these dams while also comparing the relative risk of each of the dams such that a defensible risk priority list by dam could be developed. Additionally, the results of the work were to be used in future assessment and rehabilitation design of these dams as well as aid in prioritizing dams for future HHPD funding.
The assignment was executed in three phases. The first phase consisted of existing data gathering and review, conducting visual inspections, performing hydrologic and hydraulic analyses including dam failure analyses and inundation mapping, and performing dam stability analyses.
The second phase included dam failure consequence analyses utilizing the US Army Corps of Engineers’ Life Loss Estimation software (LifeSim) to evaluate the Population at Risk (PAR) and estimated Loss of Life (LoL). Potential Failure Mode Analyses (PFMA) and Level 2 Risk Analyses (L2RA) were performed for each dam using FERC’s Engineering Guidelines for each dam (Chapters 17 and 18, respectively). The PFMs developed during each PFMA workshop were subsequently screened to identify the Risk Driver PFMs for further evaluation during each risk analysis workshop.
The third phase was the execution of the portfolio risk assessment using the Screening Level Portfolio Risk Analysis (SLPRA) approach outlined in FERC’s Risk-Informed Decision Making Guidelines. A normalized grouping of key Risk Driver PFMs for each dam were plotted on a SLPRA Risk Index Scoring Matrix and used to generate the portfolio risk scoring. The portfolio risk assessment results were then used to develop recommendations for the portfolio ranking for prioritization of HHPD funding. The process also led to the identification of the key risk reduction measures and follow up studies recommended for each dam.
