Dams are complex structures with many technical uncertainties, and they involve risk just as they provide benefits. Safety can be threatened by the processes of ageing, natural events and new threats, even if the dam was built using accepted good practices of the day.
What is a Dam?
A dam is a barrier constructed for the retention of water, water containing any other substance, fluid waste, or tailings, provided the barrier is capable of impounding at least 30,000 m3 of liquid and is at least 2.5 m high. Height is measured vertically to the top of the barrier (i) from the natural bed of the stream or watercourse at the downstream toe of the barrier, in the case of a barrier across a stream or watercourse; or (ii) from the lowest elevation at the outside limit of the barrier, in the case of a barrier that is not across a stream or watercourse.
Generally CDA uses the term dam to include appurtenances and systems incidental to, necessary for, or connected with the barrier. Furthermore, the definition may be expanded to include dams less than 2.5 m high or with an impoundment capacity of less than 30,000 m3 if the consequences of dam operation or failure are likely to be unacceptable to the public, such as dams that create hydraulic conditions posing a danger to the public; dams with erodible foundations that, if breached, could lower the reservoir by more than 2.5 m; or dams retaining contaminated substances.
Dam safety typically refers to the protection of the public and environment from the effects of dam failure, as well as release of any or all of the retained fluids behind a dam. Public safety addresses hazards to the public, created by the presence or operation of a dam, but not associated with structural failure of the dam or with passage of floods.