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Almost every water resources project has a reservoir or diversion work for the control of floods or to store water for irrigation or power generation, domestic or industrial water supply. A spillway with control mechanism is almost invariably provided for release of waters during excess flood inflows. Releases of water may also be carried out by control devices provided in conduits in the body of the dam and tunnels. In order to achieve flow control, a gate or a shutter is provided in which a leaf or a closure member is placed across the waterway from an external position to control the flow of water.

Gates are installed at the barrages, dams, intakes, spillways, sluice etc. where water pressure may be high, medium or low, so as to permit flow of water either into or out of a water passage. Gates are used for regulation of flow or for throttling the flow so as to vary the rate of discharge across the gate. Another distinct use of gate is to unwater the fluid ways for inspection or maintenance. Gates also finds their application for control of elevation of pond water or reservoir level. The gates installed at the spillway crest provide additional temporary storage, which is permissible in periods of lean inflows, and in flood periods full spillway capacity is made available by opening of these gates.

Different types of hydraulic gates and hoists, working on different principles and mechanism are in use for controlled release of water through spillways, sluices, intakes, regulators, ducts, tunnels, etc. Right selection of gates and their hoisting arrangement is very important to ensure safety of the structure and effective control. The choice for the gates and hoists depends on several factors, primarily safety, ease in operation as well as maintenance and economy are the governing requirements in the same order.

However, among all types of hydraulic gates, Radial Gates are popularly preferred to control the water flow through dams, spillways and canal locks.

The radial gates or the tainter gates as they are often termed, are raised and lowered by radial arms located on either side of the gate. The design of the Radial Gate consists of a suitably reinforced rolled steel skin plate that has two structurally designed radial arms located on either side. The pivoting radial arms are individually located at the ends by a steel mounted 'trunnion' located on the adjacent concrete walls to enable circular rotation of the gate to be achieved during the 'opening/closing' operations.

When closed, the outer curved surface of the skin plate is loaded against the water pressure with the radial arms and associated pivoting system located on the dry side. The Radial Gate can also operate in a partially open position to allow restricted downstream water flow. In special applications, the Radial Gate can operate in submerged conditions as a bottom outlet. In this event a special sealing system in the upper side of the gate is provided.

The skin plate of the radial gate is bent to an arc with convex surface of the arc on the upstream side. The centre of the arc is at the centre of the trunnion pins, about which the gate rotates. The skin plate is supported by suitably spaced stiffeners either horizontal or vertical or both. If horizontal stiffeners are used, these are supported by suitably spaced vertical diaphragms which are connected together by horizontal girders transferring the load to the two end vertical diaphragms. If vertical stiffeners are used, these are supported by suitably spaced horizontal girders which are supported by radial arms. The arms transmit the water load to the trunnion/yoke girder. 

Suitable seals are provided along the curved ends of the gate and along the bottom. If used as a regulating gate in tunnels or conduits, a horizontal seal fixed to the civil structure, seals with the top horizontal edge of the gate, in the closed position. The upstream face of the gate rubs against the top seal as the gate is raised or lowered. Guide rollers are also provided to limit the sway of the gate during raising or lowering. 

The hoisting arrangement for radial gates is generally arranged on the road way or on the piers or on an under deck below the road way. The hoisting or lowering is usually done by means of a suspension chains or ropes or links connected to the gate and controlled manually or by power operated winches. Links for hoisting are usually used in case of submerged radial gates, where the downward closing force may be necessary or advantageous. The hoisting gear for radial gate is so arranged that, as far as possible, hoisting force is applied to the gate at the largest possible radius (thereby taking advantage of the lever arm) and the hoisting angle does not change much during the travel of the gate. In case the reservoir water is of corrosive nature, the hoisting is preferred to be done from the downstream side of the gate to prevent deterioration of hoisting cable.

The rather wide use of radial gates in dams and canal locks can be explained by the numerous advantages which these gates have compared to other types of gates, including over such common ones as sliding gates and fixed wheel type vertical lift gates. The advantages include:

1. Simplicity of construction, requiring no precision finish, except at bearing.

2. Easily accessible for maintenance.

3. Absence of groove in the piers which are unfavorable for the smooth hydraulic flow conditions. 

4. Absence of wheels and wheel assembly.

5. Considerably smaller forces during maneuvering compared to the vertical lift gates, hence reduction in the hoist capacity.

6. More reliable seating on the sill