Tokyo floodgates created to protect from typhoon surges

Floodgates 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 canals, or they may be designed to stop water flow entirely as part of a levee or storm surge system. Since most of these devices operate by controlling the water surface elevation being stored or routed, they are also known as crest gates. In the case of flood bypass systems, floodgates sometimes are also used to lower the water levels in a main river or canal channels by allowing more water to flow into a flood bypass or detention basin when the main river or canal is approaching a flood stage.



A sluice gate on the Harran canal
A flood wall gate at Harlan, Kentucky
  • Bulkhead gates are vertical walls with movable, or re-movable, sections. Movable sections can be lifted to allow water to pass underneath (as in a sluice gate) and over the top of the structure. Historically, these gates used stacked timbers known as stoplogs or wooden panels known as flashboards to set the dam's crest height. Some floodgates known as coupures in large levee systems slide sideways to open for various traffic. Bulkhead gates can also be made of other materials and used as a single bulkhead unit. Miter gates are used in ship locks and usually close at an 18° angle to approximate an arch.

A hinged crest gate during installation
Fish belly flap gates at the Scrivener Dam, Canberra
  • Hinged crest gates, are wall sections that rotate from vertical to horizontal, thereby varying the height of the dam. They are generally controlled with hydraulic power, although some are passive and are powered by the water being impounded.
  • flap gate
  • fish-belly flap gates
  • Bascule gates
  • Pelican gates

Tainter gate diagram
Tainter gates and spillway
  • Radial gates are rotary gates consisting of cylindrical sections. They may rotate vertically or horizontally. Tainter gates are a vertical design that rotates up to allow water to pass underneath. Low friction trunnion bearings, along with a face shape that balances hydrostatic forces, allow this design to close under its own weight as a safety feature.

Drum gates are controlled with valves.
Drum gates on a diversion dam
  • Drum gates are hollow gate sections that float on water. They are pinned to rotate up or down. Water is allowed into or out of the flotation chamber to adjust the dam's crest height.

A roller gate on the Mississippi.
Clamshell floodgates at the Arrowrock Dam.
  • Roller gates are large cylinders that move in an angled slot. They are hoisted with a chain and have a cogged design that interfaces with their slot.
  • Clamshell gates have an external clamshell leaf design.

  • Fusegates are an innovative spillway control technology, which consists of free standing blocks (the Fusegates) set side by side on a flattened spillway sill. The Fusegate blocks act as a fixed weir most of the time and operate independently without any remote control or energy source only in case of excessive flood conditions. The System is developed and patented by Hydroplus from Paris, France. It has been installed on more than 50 dams around the world with sizes ranging from 1m to more than 9m in height. Fusegate are typically used to increase the storage capacity of existing dams or to maximize the discharge potential of undersized spillways.

Typical fusegate sketch
Fusegate in Terminus Dam - Lake Kaweah


[clarification needed]

Discharge from a Howell-Bunger valve

Valves used in floodgate applications have a variety of design requirements and are usually located at the base of dams. Often, the most important requirement (besides regulating flow) is energy dissipation. Since water is very heavy, it exits the base of a dam with the enormous force of water pushing from above. Unless this energy is dissipated, the flow can erode nearby rock and soil and damage structures.

Other design requirements include taking into account pressure head operation, the flow rate, whether the valve operates above or below water, and the regulation of precision and cost.[citation needed]

  • Fixed cone valves, also known as Howell-Bunger valves, are designed to dissipate the energy from a water flow during reservoir discharge. They are a round pipe section with an adjustable sleeve gate and cone at the discharge end. Flow is varied by moving the sleeve away or towards its cone seat. The design allows high pressure water from the base of a dam to be released without causing erosion to the surrounding environment. Fixed cone valves are able to handle heads up to 300 m.
  • Hollow jet valves are a type of needle valve used for floodgate discharge. A cone and seat are inside a pipe. Water flows through an annular gap between the pipe and cone when it is moved downstream, away from the seat. Ribs support the bulb assembly and supply air for water jet stabilization.
  • Ring jet valves are similar to fixed cone valves, but have an integral collar that discharges water in a narrow stream. They are suitable for heads up to 50 m.
  • Jet flow gate, similar to a gate valve but with a conical restriction prior to the gate leaf that focuses the water into a jet. They were developed in the 1940s by the United States Bureau of Reclamation to allow fine control of discharge flow without the cavitation seen in regular gate valves. Jet flow gates are able to handle heads up to 150 m.


In order to do a simple calculation of the force on a rectangular flood gate one can use the following equation:

\ F = pA


F = force measured in the SI units kg·m·s–2 which is called the newton (N)
p = pressure = \rho g h\, measured in N/m2, which is called the pascal (Pa)
A = area = rectangle : length × height measured in m2
length = the horizontal length of a rectangular floodgate measured in meters
height = the height of a non-submerged flood gate from the bottom of the water column to the water surface measured in meters

If the rectangular flood gate is submerged below the surface the same equation can be used but only the height from the water surface to the middle of the gate must be used to calculate the force on the flood gate.

See also

Moore Bridge.jpg UK Waterways portal



External links

Wikimedia Foundation. 2010.

Look at other dictionaries:

  • floodgate — flood·gate n: something serving to restrain an outburst (as of litigation) usu. used in pl. a decision that will open the floodgates for other claims Merriam Webster’s Dictionary of Law. Merriam Webster. 1996 …   Law dictionary

  • floodgate — early 13c. in the figurative sense (especially with reference to tears or rain); literal sense is mid 15c.; from FLOOD (Cf. flood) + GATE (Cf. gate) …   Etymology dictionary

  • floodgate — ► NOUN 1) a gate that can be opened or closed to admit or exclude water, especially the lower gate of a lock. 2) (the floodgates) last restraints holding back a powerful outpouring …   English terms dictionary

  • floodgate — [flud′gāt΄] n. 1. a gate in a stream or canal, to control the height and flow of the water; sluice 2. anything like this in controlling a flow or an outburst …   English World dictionary

  • Floodgate — This interesting and unusual surname is of Anglo Saxon origin, and was originally given either as a metonymic occupational name to a keeper of the floodgate, or a topographical name to one resident by such a gate. The derivation is from the Olde… …   Surnames reference

  • floodgate — UK [ˈflʌdˌɡeɪt] / US noun [countable] Word forms floodgate : singular floodgate plural floodgates a gate that controls a flow of water in a river or lake • open the floodgates …   English dictionary

  • floodgate — noun Etymology: Middle English flodgate Date: 13th century 1. a gate for shutting out, admitting, or releasing a body of water ; sluice 2. something serving to restrain an outburst < opened the floodgates of criticism > …   New Collegiate Dictionary

  • floodgate — /flud gayt /, n. 1. Civ. Engin. a gate designed to regulate the flow of water. 2. anything serving to control the indiscriminate flow or passage of something. [1175 1225; ME; see FLOOD, GATE] * * * ▪ engineering  gate for shutting out or… …   Universalium

  • floodgate — noun a) An adjustable gate or valve used to control the flow of water through a sluice. b) Anything that controls or limits an outpouring of people, emotion etc …   Wiktionary

  • floodgate — Synonyms and related words: aboideau, air lock, avenue, blowhole, channel, chute, debouch, dock gate, door, egress, emunctory, escape, estuary, exhaust, exit, flood hatch, flume, gate, head gate, lock, lock gate, loophole, opening, out, outcome,… …   Moby Thesaurus