What Is a Spillway?
To control the release of water from a dam or levee downstream, A spillway is a structure used to provide, generally into the riverbed of the dammed river itself.
The spillway may be known as overflow channels in the United Kingdom. Not designed to convey water and water does not damage parts of the structure, the spillway is constructed to use it. To regulate reservoir level and water flow, the Spillways can include fuse plugs and floodgates.
Before the reservoir is full, the spillway has features that enable a spillway to regulate downstream flow in a controlled manner by releasing water. When the water continues entering faster, and the reservoir has reached its capacity, Water normally flows over a spillway only during flood periods than it can be released.
Types of Spillway
There are different types of spillways depending on their parameters and the suitability of the site. Generally, a spillway consists of a conveyance channel, control structure, and terminal structure. The common types of the spillway are described below-
- Drop Spillway
- Ogee Spillway
- Siphon Spillway
- Chute or Trough Spillway
- Shaft Spillway
- Side Channel Spillway
1. Drop Spillway
- In a drop spillway from the hydraulic structure, the overflowing waterfalls almost vertically and freely and on the downstream side.
- This type of spillway is suitable for low dams or weirs.
- The water jet does not strike the downstream base. For this, the spillway crest is provided with the nose.
- On the downstream side, an impervious apron should be provided to protect the structure from the effect of scouring horizontally.
- Which is known as on the downstream side Sometimes a basin is constructed to form a small artificial pool called a water cushion.
- For energy dissipater, this cushion serves.
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2. Ogee Spillway
- The Ogee spillway is mainly provided to forms a part of the main dam and in a rigid barrier itself if sufficient length is available.
- The lower nappe of a water sheet is flowing over the crest of the spillway is shaped to conform to an aerated sharp-crested weir.
- With the lower nappe’s shape, the spillway’s downstream profile is made to coincide with the free-falling water jet from a sharp-crested weir.
- Where “0” is the origin of the parabola, the ogee spillway will follow the parabolic path. Hence downstream surface and the lower nappe are similar to a projectile.
- This “T” point is known as the point of tangency. Of the letter “S” thus the spillway takes shape. Hence, this spillway is called the ogee spillway.
- The weir is not the same over the crest for all the heads of water. With the head of water, it differs.
- The maximum head is considered for the design of the ogee spillway.
- The curved profile of the spillway is the overflowing water that just follows If the spillway runs with the maximum head.
- And there is no gap between the spillway surface and the water, and the discharge is maximum.
- From the designed head, when the actual head becomes more than, the lower nappe gets separated from the spillway surface and does not follow the ogee profile. Thus at the point of separation, a negative pressure develops.
- Due to the negative pressure for the frictional force, These air bubbles are responsible, which causes much damage to the spillway surface.
3 Siphon Spillway
- The principle of the spillway is works on siphon, as the name indicates. To forms a conduit over a conventional spillway a hood is provided.
- The crest of an “ogee” spillway starts flowing over with the rise in reservoir level.
- The discharge is larger head Under this condition. Although this type of spillway has a larger discharging capacity.
- From entering the conduit to prevent floating debris, generally, the inlet end of the hood is kept below the reservoir level.
- Before the siphon action breaks below the normal level to be drawn down, this may cause the reservoir.
- At the normal reservoir, the level is provided, therefore, arrangement for de-priming the siphon.
4. Chute or Trough Spillway
- In trough type of spillway, the water, after flowing over another kind of control structure or a short crest, to the downstream side of the river, is carried by an open channel.
- To the conveyance channel, the control structure is generally normal.
- The conveyance channel is constructed in excavation with invariably lined and stable side slopes. The flow through the conveyance channel is super-critical.
- Where site conditions permit, The spillway can be provided at a suitable saddle away from the dam or close to the dam.
5. Shaft Spillway
- This type of spillway has a circular crest plan, and the flow is carried by a vertical or sloping tunnel onto a horizontal tunnel nearly at the bed level and the downstream side.
- The diversion tunnels are constructed during the dam construction can be used as the horizontal conduit.
6 Side Channel Spillway
- Side-channel spillways are located to the side of the dam and upstream of the dam.
- Enters a side-channel The water, after flowing over a crest which is nearly parallel to the crest.
- To the downstream side, This is then carried by a chute.
- For instead of a chute, sometimes a tunnel may be used.
The definition of the spillway is for the controlled release of water from a dam or levee downstream. A spillway is a structure used to provide the riverbed of the dammed river itself generally. The spillway may be known as overflow channels in the United Kingdom.
Not designed to convey water and water does not damage parts of the structure, the spillway is constructed to ensure it. To regulate reservoir level and water flow, the Spillways can include fuse plugs and floodgates.
Before the reservoir is complete, the spillway has features that enable a spillway to regulate downstream flow in a controlled manner by releasing water. When the water continues entering faster, and the reservoir has reached its capacity, Water normally flows over a spillway only during flood periods than it can be released.
- Spillways are provided for detention dams and storage to release surplus or flood water that cannot be contained in diversion dams and the allotted storage space to by-pass flows exceeding those which are turned into the diversion dam.
- To prevent possible failure and overtop the dam, the spillway is constructed to release surplus waters from the reservoir.
- Due to its static head, the water discharged over the spillway of a dam attains a very high velocity.
- The safe non-eroding velocity in the downstream, which is generally much higher than.
- This high-velocity flow may cause erosion and serious scour of river bed downstream.
(B). Inflow Design Flood
- “Guidelines for fixing spillway capacity” the criteria for inflow design flood is given in IS:11223-1985.
- The dams are classified according to the gross storage size and the hydraulic head behind the dam.
- Of the following two parameters of the overall size classification for the dam would be greater.