For this purpose, a spillway is constructed. Spillways act as safety valves by releasing excess waters that the reservoir cannot contain. A spillway may be a channel apart from the dam or a section of the dam over which water can flow freely. The excess water flows from the reservoir through the spillway and back to the downstream river or drainage channel. A spillway must be large enough to handle the water from a major flood.
Dams can create serious safety hazards.
If a dam collapses, it can cause enormous property damage, injury, and sometimes death. A dam can collapse because of faulty construction or an earthquake. Erosion can also lead to a dam's collapse. A dam can be eroded from the inside by water leaking into the embankment, the foundation, or structures attached to the dam. If the spillway is too small, water may flow over the top of the dam and cause erosion.