Side channel spillway
SIDE CHANNEL SPILLWAY

Side channel spillway

SIDE CHANNEL SPILLWAY This spillway is suitable for earth or rock fill dams, in narrow canyons and other situations.  This spillway is also the best choice where a long overflow crest is require so as to limit the surcharge head and also under the situation where abutments are steep and precipitous. In this spillway the control weir is kept along the side. The flow after passing over the crest turns at approximately 90°. Flow may enter the side channel from one side only or from both the sides and one end also. Discharge characteristics are similar to ordinary overflow weir, except that at high discharge its crest may be partly submerged. Generally a trough is formed on D/S side of the crest and water enters it before taking a turn to flow in the side channel.

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Chute and Tunnel spillway
Chute and Tunnel spillway

Chute and Tunnel spillway

CHUTE SPILLWAY It is also call an open channel or trough spillway. It consists of a steep-sloped open channel which is call trough or chute. It is place in the dam abutment, or in a saddle. The discharge flown over the chute, is carrie to the D/S of the dam through a natural channel which may be meeting the river on D/S side. The channel may be forme artificially or by excavating the trench, if natural channel does not exist. This spillway is provid for earth or rock fill dams and is always isolated from the main dam. This spillway has following advantages. (i) It is simple in design and construction. (ii) It is adoptable to almost any foundation condition. (iii) It is economical. TUNNEL SPILLWAY In this spillway a close channel is used to convey surplus water from U/S to D/S of the dam. When the close channel is…

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Siphon spillway

SIPHON SPILLWAY This spillway consists of one or a number of units of conduits formed by inverted U-tubes. The initial discharge through the conduits is similar to that of a weir. when air is drawn away from above the end over the crest, the discharge starts flowing by siphonic action. The inside of the bend of inverted U-tube is at normal reservoir level. When water level in the reservoir rises, the water first flows as for the weir spillway. when air inlet is block by rising water, siphonic action starts and spillway starts discharging with full capacity.   Spillway continues to discharge with full capacity unless the reservoir level drops below the air inlet pipe, when air enters the conduit and breaks the siphonic action. Siphon spillway can be classified into two categories. (i) Saddle siphon spillway. (ii) Volute siphon spillway.   1. Saddle Siphon Spillway. Saddle siphon spillway can…

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Free overfall or straight drop spillway
FREE OVERFALL OR STRAIGHT DROP SPILLWAY

Free overfall or straight drop spillway

FREE OVERFALL OR STRAIGHT DROP SPILLWAY It is a low height weir, whose D/S face is either vertical or nearly vertical. In this spillway the flow drops freely from the crest. The under side of the falling nappe is sufficiently ventilat to prevent a pulsating jet. The crest is also sometimes extend in the form of an over hanging slab on D/S side so as to keep the nappe of falling water away, from coming in contact with the D/S surface of the spillway. The falling jet of water hits the D/S floor almost vertically and thus lot of energy is generat due to impact. This energy can be dissipat by adopting any of the following measures. Provide concrete apron for some length on the D/S side. Develop a small pool of water, below the falling jet of water, by constructing a small secondary dam at some distance on the…

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Overflow or ogee type spillway
OVERFLOW OR OGEE TYPE SPILLWAY

Overflow or ogee type spillway

OVERFLOW OR OGEE TYPE SPILLWAY This spillway consists of a control weir whose shape is ogee or S-shape. The shape of the ogee spillway conforms to the profile of lower nappe of water, falling from a sharp crested weir. The profile of the spillway is so shape that the overflowing water remains in touch with the spillway surface throughout the fall, when the rate of overflow corresponds to the maximum designe capacity. When head on the spillway crest is less than the maximum designe head, the falling nappe would remain adhering to the profile of the spillway. This causes positive hydrostatic pressure and thus reduces the discharging capacity of the spillway. On the contrary, when head on the crest exceeds the maximum design head during unexpected large floods, the lower nappe of falling water may not remain in touch with the spillway surface. This phenomenon causes negative pressure and cavitation.…

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Type of spillways
TYPES OF SPILLWAYS

Type of spillways

TYPES OF SPILLWAYS The spillways may be broadly classified as: Emergency spillways, and Main spillways. EMERGENCY SPILLWAYS Main spillway is the spillway which is called upon to work under normal conditions of flood. Emergency spillway is provid to deal with abnormal conditions of flood. Under normal flood conditions, the emergency spillways are not required to work. They may be called upon to work under following abnormal conditions. Rise is water level in the reservoir is continuing above the maximum permitt level even when main spillway and other outlet works are working at their full capacity. This happens when flood greater than design flood has occurred. When, due to certain reasons, enforced shut down of the outlet works have to be applied and flood water is entering the reservoir with full vigour. If spillway gates have got struck down and cannot be opened immediately. In all the above three conditions the…

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Introduction Spillways

INTRODUCTION Spillway is a structure, use to pass surplus flood water from reservoir to the downstream side of the dam. It is sometimes also know surplussing work, as its main job is to handle the surplus water. It is a sort of safety valve for a dam. During floods, the reservoir level goes on increasing, as more and more water enters the reservoir. If spillways had not been there, the level in the reservoir will go on rising even beyond the maximum reservoir level. This may lead to over topping of the dams. Additional stresses may be induced in the dam and this may cause failure of the dam. More rise in water level beyond the maximum flood level will cause submergence of vast additional areas and may cause suffering to the people living on the U/S side. Spillways act as safety valve for the safety of the dam and…

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Supply sluices in gravity dams
SUPPLY SLUICES IN GRAVITY DAMS

Supply sluices in gravity dams

SUPPLY SLUICES IN GRAVITY DAMS Some openings in the dam have to be provid so as to pass the excess flow D/S of the dam. These openings are know outlet sluices or supply sluices. If water from the reservoir is to be release for irrigation purpose at a controll rate, it is done with the help of these supply sluices. All the supply sluices are fitted with gates which can be raise or lowere. The control on the gates is exercise from the top of the dam. The gates are fitted in the grooves form at the sides of the openings in the dam. When gates are lowere they stop flow of water and when raised they again start discharging water D/S. Sluices may be provided at more than one depth. By this, water can be drawn from different elevations or depths. Supply sluices are also sometimes used to scour…

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Concrete dam and Gravity dam
ADVANTAGES OF CONCRETE DAMS and DISADVANTAGES OF GRAVITY DAMS

Concrete dam and Gravity dam

ADVANTAGES OF CONCRETE DAMS There are some advantages of concrete dams described as following: The maintenance cost of gravity dams is very small. Spill ways can be installed in the dam itself and no separate site for them is required. They can be constructed for very large heights. Ice and other outer effects do not affect the stability of the dam. Water is not lost by seepage. Outlet sluices may be installed in the dam. At valleys where side slopes are very steep, only this dam is found as the most suitable choice. This dam gives pre-warning before failure. If timely measures are taken, the dam may even be made safe. DISADVANTAGES OF GRAVITY DAMS There are some disadvantages of concrete dams as below: 1. They are very costly. 2. They require very skilled labor for construction. 3. They have to be continuously cured during construction. 4. Large calculation work…

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foundation treatment of gravity dam
FOUNDATION TREATMENT OF THE GRAVITY DAMS

foundation treatment of gravity dam

FOUNDATION TREATMENT OF THE GRAVITY DAMS The foundation of the gravity dam should be hard, strong, durable and impervious. The imperviousness of the foundation is very important as uplift pressure depends greatly upon the seepage. Uplift pressure is increase when seepage is more. Hence to render the foundation water proof or impervious, it has to be suitably treat. All the loose overlying soil from the site is removed and solid rocky foundation is reach. The rocky foundation should also be excavated for some depth so that the proposed dam fits in the rock. This aspect will prevent the sliding of the dam over its foundation. A 3 cm thick layer of rich cement mortar should be laid on the excavated rocky foundation before concreting is done over it. All the faults, seams, cavernous rocks, crushed zones etc., should be either made good or removed from the foundation site. In order…

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