Developing in Stormwater Overlays- what’s required?

The Auckland Unitary Plan- Operative in Part (AUP(OP)) introduced a new management regime for stormwater- the Stormwater Management Area Overlay or “SMAF”. If your property is subject to the Stormwater Management Area Overlay- Flow 1 or Flow 2 (SMAF) then additional stormwater requirements are triggered. You can determine if your site is subject to the SMAF overlay via the AUP on-line mapping system.


Why SMAF?

The SMAF is applied to various sites throughout Auckland to protect and enhance Auckland's rivers, streams and aquatic biodiversity in urban areas. Auckland has numerous small and narrow urban rivers and streams whose values are threatened by the effects of ongoing urban development. The SMAF overlay seeks to manage these effects, as expanded below:


  • Stormwater management area control – Flow 1 (SMAF-1) are those catchments which discharge to sensitive or high value streams that have relatively low levels of existing impervious area.

  • Stormwater management area control – Flow 2 (SMAF-2) areas typically discharge to streams with moderate to high values and sensitivity to stormwater, but generally with higher levels of existing impervious area within the catchment.


Generally speaking, future development and redevelopment is still provided for in the SMAF1 and SMAF-2, but it is subject to standards and provisions which seek to reduce stormwater runoff.


What are the SMAF requirements?

The SMAF overlay has introduced new stormwater management regulations including new retention and detention flow controls for sites subject to the SMAF. Sites within SMAF areas should provide;

  • Retention (volume reduction) of at least 5mm runoff depth for the related impervious area; and

  • Detention (temporary storage) and a drain down period of 24 hours for the difference between the pre-development and post-development runoff volumes from the 90-95th percentile, 24 hour rainfall event minus the 5 mm retention volume or any greater retention volume, that is achieved over the related impervious area.


Resource consent triggers

If your property is subject to the SMAF overlay, then additional resource consent requirements may be triggered. Generally speaking, if you’re developing new or redeveloping impervious areas over 50m2 then a resource consent will be required, and hydrology retention or detention will be essential. A technical hydrology report will also be required when you lodge an application with council.


When designing development there are a number of ways you can approach the SMAF requirements:

  • Reduce the proposed impervious area on your site to meet the SMAF-1 or SMAF-2 flow requirements,

  • Reduce runoff volumes, and hence peak flow rates, by water reuse and harvesting schemes,

  • Retain and detain stormwater on the same site such as:

  1. If your proposing retention then you can utilise rainwater tanks (with reuse), bioretention devices (unlined), living roofs, pervious paving (unlined) or other Infiltration devices.

  2. If you’re proposing detention then you could utilise pervious pavements, bioretention devices, wetlands, ponds (dry and wet) and rainwater tanks.

When council are assessing a SMAF resource consent, a processing officer will generally consider the potential cumulative effects of increased stormwater flows on freshwater systems and will also consider the best practicable options for reducing adverse environmental effects. Council will also consider what’s proposed for the management of stormwater flows onsite and the practicality and limitations of applying stormwater flow management to the site.


Need help?

In Auckland, many sites are now affected by a Stormwater Management Area Overlay (SMAF), where resource consent is needed for redevelopment and development over certain thresholds. Contact us if you’d like advice on getting resource consent in overlays, including the SMAF overlay; hello@planningplus.co.nz.

Disclaimer

As with all our blogs, the information detailed here is general in nature and meant as a preliminary guide only. This should not be substituted for your own investigations or use of your own professional’s.

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