A Discussion on the Current Practice of Risk Informed Decision Making in Canada
There are currently over 67,000 large dams worldwide listed in ICOLD’s registry, with more than 50% in excess of 50 years in age [ASCE, 1975]. While the expected useful life of a properly engineered and maintained dam can easily exceed 100 years [ASCE, 1975, ICOLD Bulletin No. 99, 1995], this exceptional life span is dependent on the level of care a dam owner provides. Following a robust dam safety management program, the actual life span can be much longer than 100 years. For this reason, dam safety management is a fundamental concern of responsible dam owners and regulators alike.
The Safety of the world’s dams has been well served through the use of the traditional Standards Based assessment approaches, coupled with evolving dam safety management practices. For example, ICOLD Bulletin 99 reported that the percentage of failures of large dams have shown a remarkable decrease, from 2.2% of dams built before 1950 to less than 0.5 % since 1950. Currently, the accepted average annual likelihood of failure rate for dams of all types has leveled out at about 10-4 failures per dam year. While UK guidelines indicate that this may be a broadly acceptable individual risk, perceptions on acceptable risk are evolving leading to a desire to continually lower risks of all kinds, including risks associated with dams.
In Canada, the practice of dam safety is not consistent due to the fact that, unlike many jurisdictions around the world, the regulation of dams and dam safety is a provincial responsibility. This results in some differences in the practice of Dam Safety across Canada but the general philosophy adopted by the various provinces is more or less consistent. That is, the requirements for Dam Safety Management should consider the incremental hazards of consequences that a dam failure would create.