The radial or Tainter gate.

Where a river is used for navigation there is a need to maintain the levels in the river despite variations of flow. At one time, control devices were continually supervised by lock-keepers who lived nearby, but there is an obvious advantage in devising control gates which work automatically. Such devices have evolved over the years and modern designs are based on the drum gate. This is part of a cylinder mounted on a lever that is pivoted on a horizontal axis as shown in figure 10-23. The attraction of the radial gate is that, if the pivot is also the centre of the arc of the drum, the forces exerted by the water on the gate have a resultant force that always acts through the pivot and this minimises the force needed to move the gate. The depth upstream can be sensed with floats and these may be very large and provide sufficient force to alter continuously the position of the gate in response to changes in depth. In other circumstances electrically powered control systems, that may form part of a sophisticated system the whole river, may be used to move the gate.

 

 The gate is really just a curved sluice gate and when it is half open the flow pattern is very like that of a sluice gate. When it is nearly closed it is more like a convergent nozzle of rectangular cross section producing a high velocity jet.  The radial gate is followed by energy dissipating devices like those used with a sluice gate.

 

The radial gate is a device that can be designed quite satisfactorily using the physics of this chapter and the mechanics of floats and levers. Data for the flow under a radial gate is stored in the same way as that for the sluice gate.