International Commission on Irrigation & Drainage Commission Interationale des Irrigation et du Drainage

Multilingual Technical Dictionary (MTD)
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Term No.Term Name/Term DescriptionAction
2735
Spillway
1 - A passage or water way for spilling surplus water. 2 - A surplusing work over the dam or upstream of the dam in the side ridge, in the form of an open or closed conduit......
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2736
Main spillway
The spillway designed to pass the design flood which usually comes into operation. The main spillway can be assisted by an emergency spillway in passing the design flood......
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2737
Spillway design flood
1 - The flood that has been decided to be carried past the dam, without failure of that structure during a stipulated time period after a thorough study of the hydrology of the drainage area. 2 - The flood used in the design of a dam for sizing the spillway and for determining the flood storage or the flood subcharge during a determined time period.....
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2738
Service spillway
Any spillway that may be utilized whenever desired, without significant damage to the structure or downstream channel. As a general rule service spillways have paved channels and if necessary, to reduce velocities of outflow to non-eroding velocities through appropriate stilling basins......
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2739
Limited-service spillway
Any spillway that may be utilized infrequently for operation of the reservoir without incurring excessive damage to the spillway structure by erosion or to downstream areas from deposition of eroded material. .....
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2740
Emergency spillway, or Auxiliary spillway
An excavated or natural channel usually located some distance from a dam to permit the release of extraordinary flood flows or flood discharge beyond the capacity of the service spillway. .....
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2743
Automatic spillway
A spillway that operates through the rise of water in the reservoir or canal, generally by lowering the spillway crest or increasing the area of the outlet orifices......
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2744
Controlled spillway, or Gated spillway
A spillway having any type of control, e.g. crest control or crest gate at the crest to control the reservoir water surface......
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2745
Uncontrolled spillway, or Ungated spillway
A spillway the crest of which permits water to discharge, whenever the reservoir surface is higher than the crest.
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2746
Overflow spillway, Overfall spillway, or Ogee type spillway
It is a section of a dam designed to permit water to pass over its crest, widely used on gravity, arch, buttress and hollow dams......
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2750
Separate spillway
A spillway built separately as an appurtenant work and not as a section of the dam.
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2751
Circular drop inlet spillway, Shaft spillway, Morning glory spillway, or Glory hole spillway
Spillway consisting of entrance structures shaped like a vertical flared funnel with its top as the lip of the spillway, with central, vertical or inclined shaft that carries discharge downward to tunnels leading to a river channel below the dam (illustrated)......
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2752
Glory hole
The vertical part of the shaft of a glory hole spillway.
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2753
Standard-crested morning glory spillway
A circular spillway, having its shape at the top confirming to the `standard crest`. The water begins its free fall immediately upon leaving the crest (illustrated)......
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2754
Flat-crested morning glory spillway
A circular spillway composed of three parts (i) sloping weir section, (ii) free falling section, and (iii) the vertical shaft section. The water is allowed to approach the crest of the free falling section, on a flat slope before beginning its free fall (illustrated)......
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2756
Trough spillway, or Chute spillway
A spillway isolated from the dam, having its crest normal to its centre line with an open discharge channel to the river in an excavated trench that is usually paved with concrete in whole or in part. The crest or spillway proper is usually of an insignificant height or may even be actually flat (illustrated)......
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2757
Side channel spillway, or Lateral flow spillway
A type of spillway where the flow after passing over a weir or ogee crest is carried away by a channel running essentially parallel to the spillway crest (illustrated)......
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2758
Inclined tunnel spillway
A spillway comprising a steeply inclined tunnel connected to the reservoir and having control devices (gates) at its inlet end......
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2760
Stepped spillway, or Cascade spillway
A spillway having a series of steps on the downstream face of the spillway for dissipation of energy by contact with successive steps or cascades......
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2761
Box-inlet drop spillway
A rectangular box open at the top and at the downstream end with an outlet structure attached to the open end of the box inlet......
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2762
Spillway elements, or Spillway components
Components of a spillway that convey, control, carry away discharge, destroy excess energy and finally lead water to an outlet channel and may comprise all or some of the following : (i) entrance channel, (ii) control structure, (iii) discharge carrier, (iv) energy dissipator, (v) spillway outlet channel......
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2766
Discharge carrier, or Face of the spillway
It is that portion of a spillway that extends from the control structure to the energy dissipator or to the downstream end of the spillway......
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2768
Spillway outlet channel
A channel connecting the stilling basin or the downstream end of the spillway or the stilling basin of the spillway either to the parent stream or another drainage......
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2769
Siphon spillway
A spillway operating on the siphon principle.
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2859
Spillway splitter
A horizontal block fixed on the downstream face of the spillway to split the stream (illustrated).
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