Risk comprises the following three elements: the likelihood that natural events will take place, the performance of the infrastructure during these events, and the consequences of poor performance or failure. Risk allows USACE to look at the project in terms of its purposes; ecosystems; constrained budgets; the uncertainty of future events and current knowledge; past design decisions; and combinations of these factors and make sense of it all.
USACE takes a multi-faceted approach to managing risk of the dams it operates and maintains. Risk-informed decisions integrate traditional engineering analyses with estimations of risk through experience-based engineering judgment. Dam safety risk-informed program is managed with three main components: risk assessment, risk management, and risk communication.
A risk assessment is a systematic approach to quantify and describe the hazard, likelihood of something going wrong, and consequences if something goes wrong. It is used to define safety issues, evaluate remediation options, and measure effectiveness of repairs. It enhances decision-making for setting short and long-term priorities for studies, investigations, and repairs. Risk assessments are performed on a continuous basis because risk can change over time.
A national screening-level risk assessment process began in 2005 in which USACE categorized dams among five Dam Safety Action Classifications (DSAC) based on relative risks. This allowed USACE to identify dam safety issues and prioritize actions and funding according to those risks.
Risk management is the process of problem finding and initiating action to identify, evaluate, select, implement, monitor and modify actions taken to alter levels of risk, as compared to taking no action. The purpose of risk management is to choose and prioritize work required to reduce risk.
USACE uses routine and non-routine activities to make risk-informed management decisions.
Routine: Routine activities include monitoring of instrumentation, inspections and assessments. Instrumentation monitors critical components of the dam. Engineers regularly inspect projects for structural and operational integrity and identify potential problems and issues.
Non-Routine: An incident or special event at a dam or a safety concern during routine activities triggers non-routine activities. This may include an issue evaluation study to determine the extent of the dam safety issue. Concurrently, interim risk reduction measures (IRRM) to lower risk are used until permanent measures can be put in place and may include lowering reservoir pools, stockpiling emergency material, updating emergency action plans and inundation maps, and increasing instrumentation and monitoring. If permanent action is needed, a modification study determines options and aids prioritization.
Dam Safety Modifications: Many dam safety issues can be addressed through normal maintenance. Some, however, require extensive and expensive modifications. A risk-informed alternative analysis determines the most cost-effective measures to reduce the project risk as low as practicable. Modifications can take several years and include such actions as foundation cutoff walls, anchoring dams, and placing seepage berms.
Risk communication is the open, two-way exchange of information and opinion about hazards and risks leading to a better understanding of the risks and better risk management decisions. USACE provides risk information on a project basis to affected stakeholders and the public. An informed and engaged public that better understands risk can contribute to the evaluation of risk reduction options, and take appropriate action for their safety.