A resource consent may be required for the diversion and discharge of stormwater.
The attenuation and treatment of stormwater discharge may also be required in order to comply with permitted activity rules or as a condition of consent. Consent may be required for a discharge even when it is not a direct discharge to land or receiving water, such as where the discharge is to an existing network.
Stormwater devices may be required to avoid any potential adverse water quality effects on receiving land or waters. The type of contaminants that could become entrained in the stormwater shall be identified during the stormwater system design phase and then a suitable treatment device(s) shall be considered to address the particular issues.
Guidance and criteria for the design of stormwater devices is provided in the Auckland Regional Council technical publication TP10 (Stormwater Management Devices: Design Guidelines Manual) which is based on the requirements of the Auckland Council Regional Plan: Air, Land and Water rather than on those of the Proposed Auckland Unitary Plan (PAUP). The volume-based design methodology in TP10 is equivalent to treating the runoff from 90% of the annual rainfall. Flow-based devices treat an equivalent proportion of the annual runoff by sizing to a design rainfall intensity of 10mm/hr, as detailed in Auckland Council technical report TR2013/035 (Unitary Plan Stormwater Management Provisions: Technical Basis of Contaminant and Volume Management Requirements).