How Does An Attenuation System Work?
When the peak inflow rate in a storm exceeds the allowed discharge into the watercourse, the excess flow has to be ‘attenuated’ on the site for the duration of the storm. This is then released at, or less than, the allowed discharge rate after the storm. To store the excess volume and allow the correct discharge rate to go to the watercourse, a flow regulator is installed to ‘bleed off’ the correct maximum flow rate. The flow regulator can be a vortex type system or a simple orifice plate system. The remainder of the water is stored either in-line or off-line, depending on the design. In-Line Attenuation Tanks In-line systems allow the water to back up through the tank and drain by gravity through the flow regulator. This system is normally used for installations where a fall through the system of 2.5-2.6 metres (on a sloped site) can be accommodated. In-line Orifice Tank System V.1 An orifice plate system works on the principle that the pressure created at a particular head will resul
