No discharge for up to 5mm rainfall

The criterion requires no run-off to leave the developed site into the local watercourse(s) for a storm event that results in rainfall depths up to 5mm.  It is not acceptable to collect the rainfall within an attenuation tank and allow the runoff to be released from the site at a restricted rate. This simply slows the rate at which it is released to the watercourse(s).

The 5mm rainfall event is considered one of the most common rainfall events and, therefore, a system should be designed to prevent this run-off leaving the site thus protecting a receiving watercourse from pollution.