Floodgate

For other uses, seeFloodgate (disambiguation).

Tokyofloodgates created to protect fromtyphoonsurges

Floodgates,also calledstop gates,are adjustable gates used to control water flow inflood barriers,reservoir,river,stream,orleveesystems. They may be designed to setspillwaycrest heights indams,to adjust flow rates insluicesandcanals,or they may be designed to stop water flow entirely as part of a levee orstorm surgesystem. Since most of these devices operate by controlling the water surface elevation being stored or routed, they are also known ascrest 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 ordetention basinwhen the main river or canal is approaching a flood stage.

Types

Bulkhead gatesare vertical walls with movable, or re-movable, sections. Movable sections can be lifted to allow water to pass underneath (as in asluice gate) and over the top of the structure. Historically, these gates used stacked timbers known asstoplogsor wooden panels known asflashboardsto set the dam's crest height. Some floodgates known ascoupuresin 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 shiplocksand usually close at an 18° angle to approximate an arch.	A sluice gate on theHarran canal	Aflood wallgate at Harlan, Kentucky
Hinged crest gates,are wall sections that rotate from vertical to horizontal, thereby varying the height of the dam. They are generally controlled withhydraulic power,although some are passive and are powered by the water being impounded. Variations: flap gate fish-belly flap gates Bascule gates Pelican gates	AUS Army Corps of Engineershinged bascule crest gate during installation	Fish belly flap gates at theScrivener Dam,Canberra
Radial gatesare rotary gates consisting of cylindrical sections. They may rotate vertically or horizontally.Tainter gatesare a vertical design that rotates up to allow water to pass underneath. Low frictiontrunnionbearings,along with a face shape that balanceshydrostatic forces,allow this design to close under its own weight as a safety feature.	Tainter gatediagram	Tainter gates and spillway
Drum gatesare 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.	Drum gates are controlled with valves.	Drum gates on adiversion dam
Roller gatesare 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 gateshave an external clamshell leaf design.	A roller gate on theMississippi.	Clamshell floodgates at theArrowrock Dam.
Fusegatesare 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.The System was invented and patented byFrançois Lempérièrefor Hydroplus (Paris, France), subsidiary of GTM Entrepose. It has been installed on more than 50 dams around the world with sizes ranging from 1 m to more than 9 m 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 inTerminus Dam-Lake Kaweah
Mitre gates

Valves

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 accountpressure headoperation, the flow rate, whether the valve operates above or below water, and the regulation of precision and cost.

• Fixed cone valvesare 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 adamto be released without causingerosionto the surrounding environment. Fixed cone valves are able to handleheadsup to 300 m.
• Hollow jet valvesare a type ofneedle valveused 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 valvesare 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 agate valvebut with a conical restriction prior to the gate leaf that focuses the water into a jet. They were developed in the 1940s by theUnited States Bureau of Reclamationto allow fine control of discharge flow without thecavitationseen in regular gate valves. Jet flow gates are able to handle heads up to 150 m.

Physics

Opened floodgates at theMerikoski Power PlantinOulu,Finland

The force on a rectangular flood gate can be calculated by the followingequation:

$\ F=pA$

where:

F= force measured innewtons(N)

p= pressure$=\rho gh\,$measured inpascal(Pa)

where:

• ρis thedensityof fresh water (1000 kg/m³);
• gis theacceleration due to gravityon Earth (9.8 m/s²);
• his the height of the water column in metres.

A= area =rectangle:length×heightmeasured in m²

where:

length = the horizontal length of a rectangular floodgate measured in metres

height = the height of a non-submerged flood gate from the bottom of thewater columnto the water surface measured in metres

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

• Flood barrier
• Tidal barrage
• Canal lock
• Thames Barrier
• Delta Works
  • Oosterscheldekering

References

Sources

• US Army Corps of Engineers. (31 July 1995). Engineering manual 1110-2-2607,Planning and Design of Navigation Dams,Chapter 5, Overview of gate types.Retrieved 2008-04-14.

External links

• DeltaWorks.Org– project in the Netherlands on floodgates