2 Principles for Planning Approaches
The information in this guide is based on the four over-arching principles below. However, past planning decisions have not always taken this approach. The principles recognise that a different planning approach is needed for an area that has not been developed (a greenfield site) and an area that has been developed or subdivided, or where there exists an expectation to build. Defining a greenfield site is something that each council needs to do. It may be an area where there is currently no expectation to build (eg, no zoning for intensive development) or may be an undeveloped area of a certain defined size (eg, < 20 acres).
2.1 Principle 1: Gather accurate active fault hazard information
Identifying and accurately locating hazards on planning maps is an essential step towards communicating hazard risk and mitigating hazards. Collecting information will often require specialised scientific knowledge and surveys. Maps showing the location of hazards around property boundaries must be developed at the right scale. Because the existence of a particular hazard may have a major effect on a decision to purchase or build on a property, all information on hazards should be as accurate as technology and resources permit.
2.2 Principle 2: Plan to avoid fault rupture hazard before development and subdivision
Building away from areas of fault rupture can avoid, or certainly mitigate, the fault hazard risk. For example, a new subdivision can be required to avoid building in an area of fault rupture (a fault avoidance zone in the district plan). This is the safest and most satisfactory long-term solution for current and later landowners and for the territorial authority. It can also be achieved for little or no extra cost (although it is recognised that loss of development opportunities are a cost to the developer).
2.3 Principle 3: Take a risk-based approach in areas already developed or subdivided
If land has already been subdivided and sites have been purchased, there is an expectation that building on these sites will be allowed. Planning for land use in a fault avoidance zone helps to avoid or mitigate the hazard risks caused by land-use intensification (such as urban infill) and inappropriate building.
These guidelines propose a risk-based approach, based on risk management standard AS/NZS 4360:1999. This standard takes into account the fault recurrence interval and fault complexity, and the Building Importance Category of the building proposed for the site.
This approach does not guarantee that a building will not suffer damage from fault rupture in an earthquake. It does establish that the risk of damage is sufficiently low to be generally accepted.
2.4 Principle 4: Communicate risk in built up areas subject to fault rupture
One of the most difficult problems concerning fault rupture hazard is dealing with urban areas where buildings have already been constructed on or close to an active fault. One of the clearest examples of this situation is the suburb of Thorndon in Wellington. Although the risk posed by building in such a location is obvious to us now, it was not clear when urban subdivision started in New Zealand in the 19th century.
The ideal approach in this situation would be to avoid further development in high-risk areas, to limit existing use rights to rebuild, and to limit the use of buildings.
The most realistic approach, however, is to accept the status quo whilst ensuring that:
- any further development and use of buildings is consistent with the level of risk posed
- district plan maps clearly show fault rupture hazard zones.
Non-regulatory approaches, such as hazard education programmes and incentives to retire at-risk land, would also ensure that landowners and building occupiers are made aware of the hazard, and the probability of future fault rupture.
