Imagine a city where every drop of rain is accounted for. That is the vision of the SMAF Stormwater Rules. This article is an orientation to what the framework is and what it is for. It is not a substitute for the Auckland Unitary Plan, which is where the rules themselves live.
What SMAF stands for and where the rules sit
SMAF stands for Stormwater Management Area Flow. The rules are a component of The Auckland Unitary Plan, which is where their force comes from and where the detail is set out. That matters for anyone reading a page like this one: the Unitary Plan is the authority on what the rules require and where they apply, and a general article can only describe the shape of the framework. The SMAF rules were crafted to safeguard and improve Auckland's streams and rivers, which are vital to the region's freshwater biodiversity. Everything else in the framework follows from that purpose.
Why Auckland's streams are the focus
The framework starts from the condition of Auckland's streams and rivers rather than from the convenience of any single development, because those waterways are vital to the region's freshwater biodiversity. Urban development changes how rain moves across a catchment, and SMAF is the Unitary Plan's response to that change. Understanding the purpose makes the two area classifications much easier to read, because each one is describing a different kind of receiving stream and a different level of exposure to changes in stormwater flow. The classification is about what is downstream as much as it is about the site itself.
SMAF 1 areas
The SMAF framework categorises stormwater management into two distinct areas: SMAF 1 and SMAF 2. SMAF 1 areas are critical for catchments that lead to sensitive or high-value streams with low levels of impervious surfaces, hence more susceptible to stormwater flow changes. The primary aim is to preserve these fragile ecosystems from the impacts of urban development. In other words, the classification is driven by what the catchment drains into and how much that receiving environment can absorb. Whether a given site falls inside a SMAF 1 area is a question for the Unitary Plan and your consent, not for an article.
SMAF 2 areas
SMAF 2 areas, on the other hand, are concerned with catchments that lead to streams with moderate to high sensitivity to stormwater. These areas typically have a higher presence of impervious surfaces, which makes them more vulnerable to stormwater flow variations. Read side by side, the two categories show what the framework is tracking: the sensitivity of the stream a catchment leads to, and how much of the surface above that catchment already sheds water rather than absorbing it. If impervious surface is the constraint you are working against, managing impermeable surface issues is a useful companion piece.
The measures new developments must address
The SMAF rules are comprehensive, outlining specific measures that new developments must adhere to for effective stormwater management. These measures include:
- Runoff control: implementing strategies such as permeable surfaces, green roofs, and stormwater retention areas to manage runoff.
- Pollution prevention: installing natural filtration systems like bioswales and rain gardens to maintain water quality.
- Flood mitigation: creating natural solutions like floodplains and wetlands to manage excess water during heavy rains.
- Maintenance and monitoring: ensuring regular upkeep and functional checks of stormwater management systems.
The last of those is the easiest to skip at design stage and the one that decides whether the rest keeps working, because a system nobody maintains stops doing the job it was sized to do.
Sizing the solution: the Promax SMAF Calculator
Promax's SMAF Calculator is a tool designed to aid in complying with these SMAF regulations. It simplifies the process of meeting Auckland's stormwater detention and retention requirements, so projects align with environmental standards and promote sustainable practices. SMAF calculators help estimate the amount of stormwater that needs to be mitigated, and provide an estimate of the correct minimum sizing for solutions designed to mitigate those stormwater volumes. Note the word estimate. It is a sizing aid that gets you to a defensible starting number, and the requirement itself still comes from the plan and your consent. You can request access to the Promax SMAF Calculator.
Working out what applies to your site
For those involved in urban development, it is imperative to understand and implement the SMAF guidelines to not only comply with regulations but also contribute to the ecological well-being of our waterways. Because SMAF sits inside the Auckland Unitary Plan, the plan and your consent are what determine whether the rules reach your site and what they ask of it. This article explains the shape of the framework; the sizing is where the calculator helps. Before you start, it is worth understanding the difference between a detention tank and a retention tank, and sizing up your stormwater tank covers the sizing question more generally.