A spillway is a structure used to provide the controlled release of water downstream from a
dam or
levee
A levee (), dike (American English), dyke (Commonwealth English), embankment, floodbank, or stop bank is a structure that is usually earthen and that often runs parallel to the course of a river in its floodplain or along low-lying coastl ...
, typically into the riverbed of the dammed river itself. In the United Kingdom, they may be known as overflow channels. Spillways ensure that water does not damage parts of the structure not designed to convey water.
Spillways can include
floodgate
Floodgates, also called stop gates, are adjustable gates used to control water flow in flood barriers, reservoir, river, stream, or levee systems. They may be designed to set spillway crest heights in dams, to adjust flow rates in sluices and c ...
s and
fuse plugs to regulate water flow and reservoir level. Such features enable a spillway to regulate downstream flow—by releasing water in a controlled manner before the reservoir is full, operators can prevent an unacceptably large release later.
Other uses of the term "spillway" include bypasses of dams and outlets of channels used during high water, and outlet channels carved through
natural dams such as
moraine
A moraine is any accumulation of unconsolidated debris ( regolith and rock), sometimes referred to as glacial till, that occurs in both currently and formerly glaciated regions, and that has been previously carried along by a glacier or ice sh ...
s.
Water normally flows over a spillway only during flood periods, when the reservoir has reached its capacity and water continues entering faster than it can be released. In contrast, an
intake tower
An intake tower or outlet tower is a vertical tubular structure with one or more openings used for capturing water from reservoirs and conveying it further to a hydroelectric or water-treatment plant.
Unlike spillways, intake towers are intende ...
is a structure used to control water release on a routine basis for purposes such as water supply and
hydroelectricity
Hydroelectricity, or hydroelectric power, is electricity generated from hydropower (water power). Hydropower supplies one sixth of the world's electricity, almost 4500 TWh in 2020, which is more than all other renewable sources combined a ...
generation.
Types
A spillway is located at the top of the
reservoir
A reservoir (; from French ''réservoir'' ) is an enlarged lake behind a dam. Such a dam may be either artificial, built to store fresh water or it may be a natural formation.
Reservoirs can be created in a number of ways, including control ...
pool. Dams may also have bottom outlets with valves or gates which may be operated to release flood flow, and a few dams la