Vortex flow control devices are used to restrict the outflow volume (litres/sec) from a stormwater detention storage to a regulated allowable discharge whilst maximising the outlet orifice size in comparison to the largest standard pipe outlet diameter with a maximum discharge below the allowable discharge. This not only minimises the potential for outlet blockages, but greater discharge (litres/sec) from the flow control devices at lower storage water heads (m) will reduce the required storage volume (and cost for the installation) as the outlet is operating more efficiently than a fixed diameter pipe outlet.