Types of spillway pdf

In this case, the downstream face of the weir is constructed corresponding to the shape of lower nappe of freely falling water jet which is in ogee shape. The ogee shape of the downstream face is designed on the basis of the principle of a projectile. In general, the shape of lower nappe of the water jet is not constant for all water heads hence, the shape obtained for the maximum head is taken into account while designing ogee spillway.

Whenever there is surplus water, it will be freely disposed of through ogee spillway along its ogee shaped crest hence it can also be called as an overflow spillway. Ogee spillways are most commonly used in case of gravity dams, arch dams, buttress dams, etc. For gravity dams, it is generally located within the dam body.

A Shaft spillway is a type of spillway which consists of a vertical shaft followed by a horizontal conduit. The surplus water enters into the vertical shaft and then to the horizontal conduit and finally reaches the downstream of the channel. The shaft constructed is either artificial or natural. Excavation for the natural shaft is possible only when the hard rocky layer is present on the upstream side. The horizontal conduit either passes through the dam body or through the foundation of the dam.

In the case of large projects, the inlet hole of the vertical shaft is specially shaped which is called as morning glory or glory hole of the spillway. Hence, shaft spillway is also called as Morning glory spillway or Bell Mouth spillway.

Shaft spillway is recommended when there is no space to provide for other types of spillways such as ogee spillway, straight drop spillway, etc. Chute spillway is a type of spillway in which surplus water from upstream is disposed to the downstream through a steeply sloped open channel.

It is generally constructed at one end of the dam or separately away from the dam in a natural saddle in a bank of the river. Chute spillway is suitable for gravity dams, earthen dams, rockfill dams, etc.

But it is preferred when the width of the river valley is very narrow. The water flows along the steeply sloped chute or trough or open channel and reaches the downstream of the river.

Chute spillway is also called as trough spillway or open channel spillway. The slope of chute spillway is designed in such a way that the flow should be always in supercritical condition. To dissipate energy from the falling water, energy dissipators can be provided on the bed of chute spillway. Side channel spillway is similar to chute spillway but the only difference is the crest of side channel spillway is located on one of its sides whereas crest of chute spillway is located between the side walls.

In other words, the water spilling from the crest is turned to 90 degrees and flows parallel to the crest of side channel spillway unlike in chute spillway. Side channel spillways are preferred over chute spillways when flanks of sufficient width are not available, usually to avoid heavy cutting. The angle of turn of water flow after passing weir crest can also be kept between 0 0 and 90 0. Most forms of control structures, including overflow crests, vertical or inclined orifice entrances, drop inlet entrances, and side channel crests, can be used with conduit and tunnel spillways.

Tunnel spillways may present advantages for dam sited in narrow canyons with steep abutments or at sites where there is danger to open channels from snow or rockslides. Conduit spillways may be appropriate at dam sites in wide valleys, where the abutments rise gradually and are at a considerable distance from the stream channel.

Use of a conduit will permit the spillway to be located under the dam near the streambed. The structure may be considered as being made up of three elements; namely, an overflow control weir, a vertical transition, and a closed discharge channel. The control will shift according to the relative discharge capacities of the weir, the transition, and the conduit or tunnel.

For example, as the heads increase on a glory hole spillway, the control will shift from weir flow over the crest to orifice flow in the transition and then to full pipe flow in the downstream portion. A drop inlet spillway can be used advantageously at dam sites in narrow canyons where the abutments rise steeply or where a diversion tunnel or conduit is available for use as the downstream leg. This characteristic also may be considered disadvantageous, in that there is little increase in capacity beyond the designed heads, should a flood occur.

This would not be a disadvantage if this type of spillway were used as a service spillway in conjunction with an auxiliary or emergency spillway. It is distinguished from the drop inlet and other conduit types in that its inlet opening is placed either vertically or inclined upstream or downstream, and its profile grade is made uniform or near uniform and of any slopes. The spillway inlet opening might be sharp edged or rounded, and the approach to the conduit might have flared or tapered sidewalls with a level or sloping floor.

If it is desired that the conduit flow partly full for all conditions of discharges, special precautions are taken to prevent the conduit from flowing full. Culvert spillways should not be used for high-head installations where large negative pressures can develop. The initial discharges of the spillway as the reservoir level rises above normal are similar to flow over a weir. Siphon action takes place after the air in the bend over the crest has been exhausted.

Continuous flow is maintained by the suction effect due to the gravity pull of the water in the lower leg of the siphon. Siphon spillway is composed of five component parts.. These include an inlet, an upper leg, a throat or control section, a lower leg, and an outlet. A siphon-breaker air vent is also provided to control the siphon action of the spillway so that it will cease operation when the reservoir water surface is drawn down to normal level.

Otherwise the siphon would continue to operate until air entered the inlet. The inlet is generally placed well below the normal reservoir water surface to prevent entrance of ice and drift and to avoid the formation of vortices and draw downs, which might break the siphon action. The upper leg is formed as a bending convergent transition to join the inlet to a vertical throat section. The throat or control section is generally rectangular in cross section and is located at the crest of the upper bend of the siphon.

The upper bend then continues to join a vertical or inclined tube, which forms the lower leg of the siphon. A further advantage is its positive and automatic operation without mechanical devices or moving parts. In addition to its higher cost, as compared with other types, the siphon spillway has a number of disadvantages, including the following: a The inability of the siphon spillway to pass ice and debris.

Closer regulation which will more nearly balance outflow and inflow can be obtained by providing a series of smaller siphons, with their siphon breaker vents set to prime at gradually increasing reservoir heads. The flow in the side channel is at right angle to the direction of the incoming flow from the reservoir.

Is this content inappropriate? Report this Document. Flag for inappropriate content. Download now. Related titles. Carousel Previous Carousel Next. Jump to Page. Search inside document. Chute Spillway The chute or trough spillway is the commonest type of water conductor used for the conveyance of flow between the control section and the downstream. Chute spillways are commonly adopted for earth and rock-fill dams.

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