A Discussion on the Current Practice of Risk-Informed Decision Making in Canada C. Richard Donnelly and M. O’Mara, Hatch – Canada K. Ponnambalam, University of Waterloo – Canada K. Cain, Ontasrio Ministry of Natural resources and Forestry - Canada

Introduction The public’s perception of dams is complex Appreciation of their benefits Remove at any cost due to environmental and safety concerns

Are Environmental Concerns Real? Hydro is the cleanest of all renewable energy sources Fish ladders can address fish passage issues

Safety Concerns are Real Dam Safety Management reduces the risk

Dam Safety - A Historial Concern “ Section 53 – If somebody is too lazy to maintain his dam in adequate conditions and does not do it, if the dam fails and the fields are flooded, then that who caused the failure shall be sold for money, and the collected money shall replace the wheat that was ruined because of him.” King Hammurabi Code, 1800 BC

The Importance of Dam Safety Management currently over 67,000 large dams worldwide more than 50% in excess of 50 years in age However, properly engineered and maintained useful life of dams easily exceeds 100 years With a robust dam safety Management program, the actual life span can be much longer

Dam Safety Management in Canada In Canada practice of dam safety is somewhat variable unlike many jurisdictions around the world the regulation of dam safety a provincial responsibility. While some differences in the practice of Dam Safety exist across the country General philosophy consistent. Dam Safety Management based on the hazards that a dam failure would create.

The Probability of Dam Failure Many researchers have shown that the probability of dam failure is in the order of 10-4 Area Reference No. of Failures Total Dam Years (x10-3) Failure Rate USA Gruner (1963, 1967) 33 71.0 5 x 10-4 Babb & Mermel (1968) 12 43.0 3 x 10-4 USCOLD (1975) 74 113.0 7 x 10-4 Mark & Stuart-Alexander (1977) 1 4.5 2 x 10-4 World 125 300.0 4 x 10-4 Middlebrooks (1953) and 9 47.0 Japan Takase (1967) 1046 30 000.0 4 x 10-5 Spain Gruner (1967) 150 235.0 6 x 10-4 Overall Average Dam Failure Rate

Reducing the Probability of Failure a well-structured dam safety management program helps reduce the frequency of dam failure. In the US, following the introduction of formal dam safety programs failure rates have fallen from an average of about 39 dam safety incidents per year between 1995 and 2000 to about nine after the benefits dam safety programs began to take effect.

Risk Informed Dam Safety Management To move to the next level of dam safety, risk informed approaches are rapidly evolving complementary tool for identifying all of the risks a dam presents to the public; allows for a rational prioritization of expenditures of finite resources to reduce risks to “As Low As Reasonably Practicable”

Status of Risk Informed Dam Safety in Canada Two provinces advancing in the are of risk informed Dam Safety British Columbia Introduction of the term “reasonably safe” - indicates owner has implemented all accepted dam safety management measures The province recommends that a dam owner’s risk informed approach following the CDA guidelines no guidance as to the limits of tolerability for risk. Ontario Ministry considering a Technical Bulletin that will outline what would constitute acceptable risk assessment methodologies Compliance is achieved when the owner can demonstrate that residual risks conform with the ALARP principle A unique risk assessment tool developed to assist in the performance of quantitative risk screening.

Quantitative Risk Assessment Assessment of an Ageing Dam in Ontario, Canada

Assessing the Real Hazards Assessment performed to establish risks associated with a concrete dam with known sliding stability issues and insufficient discharge capacity Tool demonstrated that the overtopping risk was within the tolerable risk zone identified the risks associated with sliding failure as unacceptable showed that internal erosion, that had not been quantified using Standards Based approaches was another intolerable risk. .

The Advantage of Quantitative Risk Assessment Rectifying the deficiencies identified as a result of the Standards Based review would cost five time more and the risk would remain intolerable The risk assessment process better reduced the risk at a fraction of the cost Methodology Cost Residual risk Description Risk Assessment < 1 million 2 x 10-5 Tolerable Standards Based Review > 5 million 4 x 10-4 Intolerable

Thank You C. Richard Donnelly and M. O’Mara, Hatch – Canada K. Ponnambalam, University of Waterloo – Canada K. Cain, Ontasrio Ministry of Natural resources and Forestry - Canada