Spillway

A spillway is a structure used to provide for the controlled release of flows from a dam or levee into a downstream area, typically being the river that was dammed
– Spillways release floods so that the water does not overtop and damage or even destroy the dam. Except during flood periods, water does not normally flow over a spillway
– In contrast, an intake is a structure used to release water on a regular basis for water supply, hydroelectricity generation, etc.
– Floodgates and fuse plugs may be designed into spillways to regulate water flow and dam height
– Other uses of the term “spillway” include bypasses of dams or outlets of a channels used during highwater, and outlet channels carved through natural dams such as moraines