Stormwater and hazards Print

Design Outcome

Subdivisions manage stormwater and hazards by carefully locating structures, building-platforms, and density away from vulnerable land.

​​​​​​​​​​​​​​​​​​​​​​​​Auckland is subject to a number of hazards. Some are natural and some are strongly influenced by human activity. 

Hazards include landslides, erosion, contaminated land, tsunami and tidal or storm surges, flooding, volcanic activity, earthquakes, sea-level rise and subsidence. All of these can create serious human health and safety risks that must be managed. As Auckland continues to urbanise, the risk of impervious surface-based flash flooding (where water cannot soak into the​​ ground and is channelled by constructed barriers) is also likely to increase.​​​​​​​​​​​​​​

Better Design Practice

  • Locate building platforms away from 100-year flood plains and overland water-flow paths.
  • Avoid areas that are susceptible to natural hazards, even if this means creating higher building densities and smaller lots in other places on the development site.
  • Use engineering tools, such as rain gardens, tree pits, swales, detention tanks and piped networks, to manage the speed and amount of stormwater.
  • Slow down the flow of stormwater and clean it on site, rather than piping it away at high speed, which can cause big disruption to stream habitats and coastal erosion.
  • Use water-sensitive design and 'soft' engineering (i.e. minimise large-scale engineering structures). Where large structures are necessary, they should add amenity to the subdivision and be cost effective. Such infrastructure must be supported by education and communication regarding their ongoing maintenance needs and must be able to be maintained in a straightforward manner that does not place an inappropriate burden on future residents. 
  • Use hazard-prone and other environmentally sensitive areas to add value and outlook space to the development, rather than fencing it off, which can lower the value of adjoining sections.
  • Land that has a high tsunami risk should be subdivided to allow for a clear and straightforward evacuation route to high ground, with risks made clear to purchasers by the developer or sales representative.​

Rules of Thumb

1. Base your decisions on life-cycle costs, not just short-term capital costs, particularly when planning infrastructure and considering stormwater management.

2. Consider evacuation or escape needs if undertaking development on flood plains, overland flow paths, or tsunami-risk land.

3. Consider all hazards on the basis of a once-per-100-year occurrance, notably for flood plains and overland flows, erosion, tsunami, and sea-level rise.

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