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| {{about|physical floodgates|the venture capital fund|Floodgate Fund}}
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| [[Image:Floodgate Tokyo.jpg|thumb|right|300px|[[Tokyo]] floodgates created to protect from [[typhoon]] surges]]
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| '''Floodgates''' are adjustable gates used to control water flow in [[flood barrier]]s, [[lake|reservoir]], [[river]], [[stream]], or [[levee]] systems. They may be designed to set [[spillway]] crest heights in [[dam]]s, to adjust flow rates in [[sluice]]s 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.
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| ==Types==
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| {| class="wikitable"
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| |'''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|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 [[coupure]]s 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 [[Canal lock|locks]] and usually close at an 18° angle to approximate an arch.
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| | [[Image:Harran canal-GAP.jpg|thumb|under|200px|A sluice gate on the [[Southeastern Anatolia Project|Harran canal]]]]
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| | [[Image:Floodgate floodwall.jpg|thumb|under|200px|A [[flood wall]] gate at Harlan, Kentucky]]
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| |'''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 machinery|hydraulic power]], although some are passive and are powered by the water being impounded. Variations:
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| * flap gate
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| * fish-belly flap gates
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| * Bascule gates
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| * Pelican gates
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| | [[Image:Floodgate crest bascule.jpg|thumb|under|200px|A hinged crest gate during installation]]
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| | [[File:Scrivener Dam.jpg|thumb|under|200px|Fish belly flap gates at the [[Scrivener Dam]], Canberra]]
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| |'''Radial gates''' are rotary gates consisting of cylindrical sections. They may rotate vertically or horizontally. [[Tainter gate]]s are a vertical design that rotates up to allow water to pass underneath. Low friction [[trunnion]] [[Bearing (mechanical)|bearings]], along with a face shape that balances [[Fluid pressure|hydrostatic forces]], allow this design to close under its own weight as a safety feature.
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| |[[Image:LgRadialGatefigc4-6.jpg|thumb|under|200px|[[Tainter gate]] diagram]]
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| |[[Image:Tainter gates.jpg|thumb|under|200px|Tainter gates and spillway]]
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| |'''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.
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| |[[Image:Drumgate.png|thumb|under|200px|Drum gates are controlled with valves.]]
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| |[[Image:Floodgate drum.JPG|thumb|under|200px|Drum gates on a [[diversion dam]]]]
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| *'''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.
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| *'''Clamshell gates''' have an external clamshell leaf design.
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| |[[Image:Floodgate roller.jpg|thumb|under|200px|A roller gate on the [[Mississippi River|Mississippi]]. ]]
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| |[[Image:Floodgate clamshell.JPG|thumb|under|200px|Clamshell floodgates at the [[Arrowrock Dam]].]]
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| |'''Fusegates''' are a mechanism designed to provide the controlled release of water in the event of exceptionally large floods. The design 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, but in excessive flood conditions they are designed to topple forward, allowing the controlled discharge of water. Multiple fusegates are generally set up side by side, with each fusegate designed to release under progressively extreme flooding, thus minimizing the impact of the floodwater on the river downstream.<ref>{{cite web|url=http://www.hydroplus.com/hydroplus/site.nsf/web/fusegate-operation.htm |title=Fusegate Operation|publisher=www.Hydroplus.com ||accessdate=2013-11-21}}</ref> 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.
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| |[[Image:Typical fusegate.jpg|thumb|under|200px|Typical fusegate sketch]]
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| |[[Image:Terminus Hydroplus.JPG|thumb|under|200px|Fusegate in [[Terminus Dam]] - [[Lake Kaweah]]]]
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| |'''Mitre gates'''
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| |}
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| ==Valves==
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| {{Clarify|date=March 2008}}
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| [[Image:Howell-Bunger valve.jpg|thumb|right|300px|Discharge from a Howell-Bunger valve]]
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| 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.
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| Other design requirements include taking into account [[head (hydraulic)|pressure head]] operation, the flow rate, whether the valve operates above or below water, and the regulation of precision and cost.{{Citation needed|date=March 2008}}
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| *'''Fixed cone 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 [[Head (hydraulic)|heads]] up to 300 m.
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| *'''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.
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| *'''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.
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| *'''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.
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| ==Physics==
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| In order to do a simple calculation of the force on a rectangular flood gate one can use the following [[equation]]:
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| :<math>\ F = pA</math>
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| where:
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| :''F'' = force measured in the [[SI]] units kg·m·s<sup>–2</sup> which is called the [[Newton (unit)|newton]] (N)
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| :''p'' = pressure <math>= \rho g h\,</math> measured in N/m<sup>2</sup>, which is called the [[pascal (unit)|pascal]] (Pa)
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| :::where:
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| :::*''ρ'' ([[rho]]) is the [[density]] of fresh water (1000 kg/m<sup>3</sup>);
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| :::*''g'' is the [[Gravitational acceleration|acceleration due to gravity]] on Earth (9.8 m/s<sup>2</sup> );
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| :::*''h'' is the height of the water column in meters.
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| :''A'' = area = [[rectangle]] : [[length]] × [[height]] measured in m<sup>2</sup>
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| :::where:
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| :::length = the horizontal length of a rectangular floodgate measured in meters
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| :::height = the height of a non-submerged flood gate from the bottom of the [[water column]] to the water surface measured in meters
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| 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.
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| ==See also==
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| {{Portal|UK Waterways}}
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| {{commons|Floodgate}}
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| * [[Tidal barrage]]
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| * [[Canal lock]]
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| * [[Thames Barrier]]
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| * [[Delta Works]]
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| ** [[Oosterscheldekering]]
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| ==References==
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| {{reflist}}
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| ===Sources===
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| * US Army Corps of Engineers. (31 July 1995). Engineering manual 1110-2-2607, [http://140.194.76.129/publications/eng-manuals/em1110-2-2607/toc.htm Planning and Design of Navigation Dams], [http://140.194.76.129/publications/eng-manuals/em1110-2-2607/c-5.pdf Chapter 5, Overview of gate types]. Retrieved 2008-04-14.
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| ==External links==
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| * [http://www.deltaworks.org DeltaWorks.Org] – project in the Netherlands on floodgates
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| {{coastal management}}
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| [[Category:Dams]]
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| [[Category:Hydrology]]
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| [[Category:Water transport infrastructure]]
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| [[Category:Flood barriers]]
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Hi there, I am Alyson Boon even though it is not the title on my beginning certificate. Invoicing is my profession. North Carolina is exactly where we've been living for many years and will never move. She is truly fond of caving but she doesn't have the time recently.
Feel free to surf to my website ... accurate psychic readings