Peak flow and volume control

Peak flow control

For greenfield developments, the peak runoff rate to any highway drain, sewer or surface water body up to the 1 in 100 year rainfall event + 40% for climate change should never exceed the peak greenfield runoff rate for the same event.

For developments which were previously developed, the peak runoff rate from the development to any drain, sewer or surface water body up to the 1 in 100 year rainfall event + 40% for climate change should reduce the surface water discharge by 40% of that existing or be as close as is reasonably practicable to the greenfield runoff rate from the development for the same rainfall event, but in any event should never exceed the rate of discharge from the development prior to redevelopment for that event.

Volume control

Where reasonably practicable, for greenfield development, the runoff volume from the development to any highway drain, sewer or surface water body in the 1 in 100 year, 6 hour rainfall event + 40% for climate change should never exceed the greenfield runoff volume for the same event.

Where reasonably practicable, for developments which have been previously developed, the runoff volume from the development to any highway drain, sewer or surface water body in the 1 in 100 year, 6 hour rainfall event + 40% for climate change should reduce the surface water discharge by 40% of that existing or must be constrained to a value as close as is reasonably practicable to the greenfield runoff volume for the same event, but should never exceed the runoff volume from the development site prior to redevelopment for that event.