A dam is a barrier across flowing water that obstructs, directs or slows down the flow, often creating a reservoir or lake. Most dams have a section called a spillway or weir over or through which water flows, either intermittently or continuously. Dam failure is sudden, rapid, and uncontrolled release of impounded water. One of the main course for dam failure is natural hazards such as high intense rainfall, earthquakes etc. It is recognized that there are lesser degrees of failure and that any malfunction or abnormality outside the design assumptions and parameters which adversely affect a dam's primary function of impounding water could be considered a failure. Such lesser degrees of failure can progressively lead to or heighten the risk of a terrible failure.
High and significant hazard dams should be designed to pass an appropriate design flood. Dams constructed prior to the availability of extreme rainfall data should be assessed to make sure they have adequate spillway capacity.
The ability to quickly and safely perform reservoir drawdown can be crucial to the protection and preservation of a dam. A reservoir low level outlet works and/or drain system with adequate capacity should be provided in all dams to provide a method of lowering the reservoir level in an emergency within a reasonable period.