Engineering Discoveries A spillway is a structure constructed at a dam site, for effectively disposing of the surplus water from upstream to downstream. Just after the reservoir gets filled up, up to the normal pool level, water starts flowing over the top of the spillway crest which is generally kept at normal pool level. Hence, a spillway is essentially a safety valve for a dam. Location of a Spillway A spillway can be located either within the body of the dam, or at one end of it or entirely away from it, independently in a saddle. If a deep narrow gorge with steep banks, separated from a flank by a hillock with its level above the top of the dam such as-shown in Fig.
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Engineering Discoveries A spillway is a structure constructed at a dam site, for effectively disposing of the surplus water from upstream to downstream. Just after the reservoir gets filled up, up to the normal pool level, water starts flowing over the top of the spillway crest which is generally kept at normal pool level. Hence, a spillway is essentially a safety valve for a dam. Location of a Spillway A spillway can be located either within the body of the dam, or at one end of it or entirely away from it, independently in a saddle.
If a deep narrow gorge with steep banks, separated from a flank by a hillock with its level above the top of the dam such as-shown in Fig. Parameters considered in Designing Spillways Thus controlled spillways allow more storage for the same height of the dam.
Many parameters need consideration in designing a spillway. These include: 1- The inflow design flood hydro-graph. The topography, hydrology, hydraulics, geology and economic considerations all have a bearing on these decisions. This type of Spillway is suitable for arch dam.
Several Earth and Rock fill dams are also provided with this type of spillway as a superstructure. The crest of the spillway is shaped to conform to the lower nappe of a water sheet flowing over an aerated sharp crested weir. The control structure is generally normal to the conveyance channel.
The channel is constructed in excavation with stable side slopes and invariably lined. The flow through the channel is super-critical. The spillway can be provided close to the dam or at a suitable saddle away from the dam where site conditions permit.
A chute spillway is sometimes known as a waste weir. If it is constructed in continuation to the dam at one end, it may be called a flank weir. If it is constructed in a natural saddle in a bank of the river separated from the main dam by a high ridge, it is called a saddle weir.
The water after flowing over a crest enters a side channel which is nearly parallel to the crest. This is then carried by a chute to the downstream side. Sometimes a tunnel may be used instead of a chute.
The diversion tunnels constructed during the dam construction can be used as the horizontal conduit in many cases. When the valley is very narrow and no space is available for constructing a separate spillway, the siphon pipes can be installed within the dam body An air vent may be connected with the siphon pipe 2- Hooded Type of a Siphon Spillway The construction of a Hooded type of Siphon spillway is more commonly adopted.
In this case a reinforced concrete hood is constructed over an ordinary overflow section of a gravity dam. The inlet of this hood is kept submerged so as to prevent the entry of debris, ice, etc.
It is constructed in the abutment or under the dam.
Different Types Of Spillways
There are different channel type spillways in use. The function of Chute Spillway is to prevent damage to the valley walls that could endanger the dams. It consists of steeply sloping open channel which is made up of reinforced concrete slab. The Spillway is sometimes of constant width, but is usually narrowed for economy and then widened near the end to reduce the discharging velocity. Side Channel Spillway: It is similar to the chute spillway but the only difference between it and chute spillway is that in a chute spillway, the water flows at right angles to the weir crest after spilling over it whereas in a side channel spillway the flow of water is turned by 90 degrees such that it flows to the weir crest. Shaft Spillway: In the shaft spillway, the water from the reservoir enters into a vertical shaft which conveys the water into a horizontal tunnel. The horizontal or the conduit may be taken either through the body of dam or through the underground.
8 Most Common Types of Spillways (With Diagram)
Stepped channels and spillways have been used for over 3, years. Roller-compacted concrete , gabions and design techniques e. A bell-mouth spillway  is designed like an inverted bell where water can enter around the entire perimeter. These uncontrolled spillways are also called morning glory,  after the flower or glory hole  spillways. In areas where the surface of the reservoir may freeze, this type of spillway is normally fitted with ice-breaking arrangements to prevent the spillway from becoming ice-bound.
DESIGN OF OGEE SPILLWAY PDF
Gotaxe Chapter 2: Design of Overflow Structures For the larger design flood, a return period of years is considered, for example As such an extra oc event can be extrapolated from the limited data available only as a rough estimation, other conventions are used. If the curvature is sufficiently large, the internal pressure may drop below the atmospheric pressure and even attain values below the vapor pressure for large structures. However, the coefficients and ex- successfully to spillways with a free drop. First assume an overall coefficient of discharge, say The discharge per unit length, q, is then equal to: As an alternative, numerical reevaluating a dam for higher flows or improved hydrologic methods may offer accurate solutions, within given param- event flood calculations. The force diagram for this condition desigb shown on figure 8. The effect of end contractions may be taken into account by reducing the net crest length as follows: Log In Ohee Up.