Hydropower plants and dams represent a huge investment by most nations around the world and are essential for long term energy supply. Decision makers are adopting better risk-informed approaches to help rationalize and support decisions on necessary ongoing investments to maintain optimal operations and public safety. Civil works and dam safety will be one of several tracks offered at HydroVision International; risk considerations is a feature of the track.
In most countries, dams are a central element of the infrastructure. However, dams are aging and the emphasis is now on maintaining safety, rehabilitation, and extending the operational life of these valuable assets.
Some new dams are still being constructed to suit particular needs, and some of these are very large. Also, some aging and redundant dams that are no longer viable or have outlived their purpose are being decommissioned or removed.
Traditionally, dam safety assessments have been based on analyses of stability, hydrology and other identifiable elements of the projects and decisions made using deterministic loadings, including extremes such as "Maximum Credible Earthquakes" or "Probable Maximum Floods."
In reality, dam safety decision making frequently requires that decisions be made in the absence of complete and perfect information and it has become increasingly apparent that failures continue to occur and that many of these are due to "non-standard" causes, such as piping, loss of operability or human factors. The industry's response to this has been to move into a broader approach that considers many more factors, many of which are not presently amenable to quantitative analysis. This move has embraced the tools of "Risk Assessment." The risk assessment process provides a framework for capturing what we do and don't know in a way that can help decision makers determine the next most reasonable step to take in evaluating, analyzing, or reducing risk and incorporate a much wider range of factors that previously have not been systematically considered.
At HydroVision International 2010, the Civil Works and Dam Safety track will address the following "hot topics" in which "risk informed decision making" is a common thread:
- What Precautionary Measures Should a Dam Owner Take in case of Climate Change?
What are the potential effects of climate change on historical trends of precipitation and runoff?
- Effectiveness of Dam Safety Programs
What comprises a good and effective dam safety program? How is effectiveness measured? How do you make continual improvement to the program? Speakers share advice and lessons learned for creating and maintaining dam safety programs in which owners/operators can identify dam safety problems before they become incidents or failures.
- Dam Safety Criteria – Current and Future Thinking
Dam safety programs historically have been based on a set of defined criteria. As risk-based approaches to dam safety evaluation gain acceptance, what should be the role of criteria that has been developed based on knowledge of past events and expert judgment. Such criteria are very useful where the condition being investigated can be numerically analyzed. However, the dam industry struggles with failures of structures that appeared to meet applicable criteria or that could not be remediated to meet criteria at a practicable level of effort. As risk-informed decision-making becomes an accepted complement to traditional analyses in assessing the safety of dams, how do traditional standards-based analyses and criteria fit within this framework?
- Risk-Informed Decision-Making
For years, engineers have informally considered and performed risk assessments in investigations, analyses, design, construction, and inspection of dams without addressing specifically the concept of "risk" in the thinking process. Today, it is becoming more common to formally address the concept of risk in making better informed dam safety decisions. This session will address the value and role of "risk thinking process" in making good dam safety decisions to protect life and property that dam owners are responsible for.
- How Reliable Are Your Discharge Facilities?
This session will focus on the importance of the reliability and capability of discharge facilities and how to adequately assess performance of various components. Overall discharge system reliability, including control systems, gates, valves, redundancies, and existing performance will be discussed. Discharge systems include both those used to pass major flood events and those used to reduce the water level in the event of an emergency.
- Sediment Management: Current Practices for Reservoir Sustainability
Sediments cause severe interruption in power generation and water supply due to damage to hydro-machinery, blocking of intakes, and reduction of live reservoir storage. It is estimated that about one third of original storage in U.S. reservoirs has been lost to sedimentation. This panel discussion focuses on how sediment can be effectively managed and the selection of appropriate sediment-management techniques.
- How Are We Transferring Dam Safety Knowledge? Learning from Experiences
The panel will present several progressive in-house dam safety training programs that focus on learning from previous experiences and incidents. The panelists will discuss their innovative practices and the benefits achieved.
Risk-informed techniques gaining acceptance
When implementing risk assessment approaches, it is important to note that risk assessment is not a new topic. In 1977, after the Teton dam failure, U.S. President Jimmy Carter issued an executive order to the federal agencies involved with dam safety.
The order called for the investigation of several aspects of dam safety, including the means of inclusion of new technological methods into existing structures and procedures and the degree to which probabilistic or risk-based analysis is incorporated into the process of site selection, design, construction, and operation. In response to the president's executive order, the federal agencies, working with the Federal Emergency Management Agency, prepared the Federal Guidelines for Dam Safety.
In 1979, they wrote: "Risk-based analytical techniques and methodologies are a relatively recent addition to the tools available for assessing dam safety. With further refinement and improvement, risk-based analyses will probably gain wider acceptance in the engineering profession and realize potential as a major aid to decision-making in the interest of public safety. However, even when fully developed, risk analyses cannot be used as a substitute for sound professional judgment of engineers, contractors, or review boards."
In the years since the federal guidelines were written, risk-based techniques have undergone much refinement and improvement and gained wider acceptance in the engineering profession. Fundamental differences among dam owners such as the U.S. Bureau of Reclamation, the U.S. Army Corps of Engineers, non-Federal dam owners and utilities, dam regulating agencies such as the U.S. Federal Energy Regulatory Commission, and the states result in each group taking different approaches to risk-informed dam safety assessments and decisions.
Use of risk-based techniques
As the nation's largest wholesaler of water, Reclamation owns, operates and maintains approximately 350 high or significant hazard dams throughout the 17 western states. These multi-purpose dams are used for irrigation, flood control, water supply, hydro-electric generation and recreation.
Reclamation uses risk-based techniques to assess its dams and to prioritize dam safety studies and modifications with the goal that the greatest risk reduction over the whole portfolio is achieved in the shortest period of time within the funds available.
The U.S. Army Corps of Engineers owns, operates and maintains a diverse inventory of over 600 dams based on the most recent data from the National Inventory of Dams. Project purposes for these dams include navigation, flood control, water supply, irrigation, hydropower, recreation, environmental, and various combinations of these purposes.
The Corps of Engineers is working to incorporate risk concepts into dam safety management, routine activities, and programming decisions. A number of initiatives are ongoing to achieve this objective. These include developing new policy based on risk concepts, a more detailed methodology, and a plan to communicate these strategies.
The FERC Division of Dam Safety and Inspections regulates over 2,600 dams owned by more than 800 owners for the purpose of generating hydro-electricity. The dams include 788 classified as high hazard potential and 194 classified as significant hazard potential. In many cases, FERC-regulated dams also are subject to state regulation.
FERC works with each of its 800 owners individually. Although FERC has an overarching responsibility to protect the public from dam safety hazards, the responsibility for the safety of each dam rests with the specific owner and so the potential use of risk assessment to prioritize dam safety remediation is different for FERC than for Reclamation or the Corps of Engineers.
How much risk is tolerable?
Dams can pose threats to people, the economy, the environment, societal structure and the survival of a private or governmental dam-owning organization. Even factors such as the financial implications of dam failure for the dam owner can have important societal implications if the cost and continuity of water or electricity supply or the value of shareholders investments would be affected.
Therefore, it is generally agreed that tolerable or acceptable risk criteria that address protection of the interests of the community should be determined through the political process based on societal values. However, the Netherlands is the only known example of legislatively approved risk criteria. In the U.S., Reclamation has taken the lead in establishing and applying risk evaluation guidelines but no national criteria have been established.
It is recognized that there is no such thing as zero risk in dam safety or any other human endeavor. When we undertake activities such as dam building for the benefit of society, we must accept some level of residual risk associated with dam failure. Dam safety organizations, including the U.S. Society on Dams and the International Commission on Large Dams should play an important role in this public debate.
Understanding of risk-informed approaches improves
There is no doubt that risk assessment techniques are improving our understanding and the results are being used to improve the actual safety of dams.
When properly conducted, risk assessment allows the appraisal of failure modes that are not amenable to analysis by "traditional" analyses such as piping, spillway plugging, mis-operation, controls failure, the assessment of uncertainty in analyses, the evaluation of risks against tolerable risk guidelines, and the evaluation of the effectiveness of risk reduction measures whether they be physical modifications to the structure or "soft" solutions such as enhanced emergency action plans and warning systems.
The USSD Working Group's commentary on the current practice of risk assessment is considered a cautious approach, which provides for flexibility in recognition of different decision contexts and information needs across the business. The commentary emphasizes that limitations must be fully considered and that risk assessment approaches should be used only as a supplement and not as a replacement for the traditional approach.
In the five-years since the working group completed its work on the USSD White Paper, the practical application of risk-informed approaches to solving practical dam safety problems in the United States has increased.
While the topic continues to be heavily discussed in the U.S., the nature of the discussion has shifted from one of resistance and discomfort, to a desire to understand it better, the sharing of practical experiences and insights from real-world projects, and seeking ways to realize its potential as a major aid to the improved management of dam safety and better decision-making in the interest of public safety.
Robin Charlwood is principal of Robin Charlwood & Associates and chairman of the ICOLD Committee on Concrete Dams. He is the track chair for the Civil Works & Dam Safety track at HydroVision International 2010, to be held July 27-30 in Charlotte, N.C.
A Focus on Civil Works and Dam Safety