Risk-based or risk-informed reservoir safety management? Reflections on current practice

Current practice in risk analysis and assessment of dams in the UK, including historical development and current practice, is summarised. This includes comments on current features and areas for improvement in estimation of both consequences of failure and annual likelihood of failure. It is noted that a condition of implementation of the Reservoirs Act in 1985 was that a wide spectrum of safety criteria should be introduced to account for the wide variation of risk between individual reservoirs, a fact which appears to have been overlooked in current regulatory requirements in UK. The differences between risk-based and risk-informed approaches in dam safety management are covered; risk-based is a narrow interpretation based largely on the outcome from a risk assessment, while risk-informed considers the outcome from a risk assessment with many other factors, always including considerations such as cost to save a life of any candidate upgrades and benefits of the reservoir to society. The paper suggests features that should be considered in a risk-informed approach. The paper finally reflects on how reservoir engineers can use risk assessments to improve the safety of dams in the UK, with suggestions to improve both the regulatory regime and how to assess when the cost of candidate risk reduction measures is proportionate to the reduction in risk to the public.