A spillway is a structure used to provide the controlled release of water from a dam or levee, typically downstream into the dammed river. In the United Kingdom, it may be known as an overflow channel. A spillway ensures that water does not damage parts of the structure not designed to convey water.
Spillways can include floodgates and fuse plugs to regulate water flow and reservoir level. Such features enable a spillway to regulate downstream flow, allowing dam operators to release water in a controlled manner before the reservoir is full, thereby preventing an unacceptably large release later.