Concrete or masonry overflow spillway can be built in the river section where rock foundations are suitable even though adjacent section of the dam may be embankment type. Separate spillways are required for all types of embankment dams. Major components of spillways are as follows Entrance channel: It admits reservoir water to the spillway and controls the discharge. An outlet structure to dissipate the energy of the high velocity flow from the conduit and conveys the water to the channel downstream Type of spillways: Spillways are classified according to their most prominent feature either as it pertains to the discharge carrier or some other component.
These may be gated or ungated. Common types, which are generally constructed in MIW, are as below: Free overfall or straight drop spillways broad crested Overflow or ogee spillways. Chute spillways Saddle spillway Bye wash spillway Free overfall or straight drop spillway In this type, water drops freely from the crest. Occasionally the crest is extended in the form of overhanging lip to direct small discharges away from the face of overfall section. Ordinarily the use of this structure for hydraulic drops head pool to tail water in excess of 20 meters should not be considered.
Ogee or overflow spillway This type comprises a control weir, which is ogee or 'S' shaped. The ogee shape conforms closely to the profile of aerated lower nappe and falling from a sharp crested weir. The upper curve at the crest may be made either broader or sharper than the nappe. A broader curve will support the sheet and hydrostatic pressures will occur along the contact surface. Support sheet thus creates a backwater effect and reduces the coefficient of discharge.
The sharper crest on the other hand creates negative pressure, increases the effective head and thereby discharge. This type of spillway should be constructed in the Nalla itself as far as possible. Chute spillway In this type water is conveyed from the reservoir to the river or to nalla below the dam through an excavated open channel, through fairly steep slope and placed either along the abutment or through a saddle in the rim of reservoir.
Chute spillway ordinarily consist of an entrance channel either straight or curved in alignment, a control structure, a terminal structure, and an outlet channel. The main design consideration would be to fix the longitudinal bed profile of the channel and its sectional dimensions.
The energy of the flow has to be suitably dissipated at the outlet, before the flow enters the downstream channel.
These are mostly used with earth dams and have the following merit. It can be provided on any type of foundations. The two main types of spillways are controlled and uncontrolled. Controlled spillways use mechanical structures or gates to control the flow of water on command, allowing for the full height of the dam to be used to store water.
Uncontrolled spillways are designed to allow water to flow down a ramp or similar structure whenever the water level rises to the crest of the spillway, typically down a ramp or similar structure. When designing spillways, there are a few important factors to consider. First and foremost, any uncontrolled discharge of surplus water needs to be automatic and not require any manual activation.
They are located just upstream and to the side of the dam. The water flows over the spillway, into a side channel. Then it flows down a chute and joins the river downstream of the dam.
Sometimes, a tunnel is used which may divert the water elsewhere. A shaft spillway is sometimes called a "morning glory" spillway. It is a hollow tower or shaft, usually circular, which has a funnel at its top.
The tower sits in the reservoir near the dam. When the reservoir level rises above the top of the spillway, the water flows over its sides and down into the shaft. At the bottom of the shaft, it enters a tunnel. The tunnel usually runs under the dam, and diverts the water to join the river downstream.
The outlet tower is the one on the left. The tunnel leading away from the two towers houses the outlet pipe.
Outlet towers are found in reservoirs, usually near to the dam. Volume 97, Number 2. Previous Article Next Article. Article Navigation. Research Article February 01, Google Scholar. MARK L. GSA Bulletin 97 2 : — Article history first online:. Abstract Deglaciation of the northern Great Plains produced two basic types of fluvial systems: 1 depositional regimes produced by the action of glacial melt water that formed outwash plains and 2 highly erosive systems produced by the sudden, rapid drainage of glacial lakes that formed spillways.
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