Acceptable flood capacity of referable dams
A key cause of dam failure is dam overtopping resulting from inadequate flood-carrying capacity.
The required spillway capacity of a referable dam is called the acceptable flood capacity.
The design standards for referable dams and the magnitude of the required flood capacity are determined primarily by the consequences of dam failure. Their aim is to limit the overall risk of failure from all causes, based on the consequences of dam failure and the probability of occurrence, to tolerable levels.
Dams that have higher consequences of failure need to be designed and constructed to higher standards. The resulting risk needs to be reduced as low as reasonably possible, using accepted risk management standards.
The guideline also details the maximum timelines for spillway upgrades. However, dam owners are encouraged to perform any upgrades sooner, if possible.