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Natural Hazards

 
This page contains information about Natural hazards as defined in the Building Act 2004 and acid sulphate soils and Council's requirements when building in areas affected them.
Updated: 15/10/2018 12:02 p.m.

Natural hazards are addressed by a range of regulatory processes, some of which arise under the Building Act 2004.

The Building Act defines a 'natural hazard' as:

  • Erosion including coastal erosion, bank erosion, and sheet erosion
  • Falling debris including soil, rock, snow, and ice
  • Subsidence
  • Inundation including flooding, overland flow, storm surge, tidal effects and ponding
  • Slippage.

The Whangarei District experiences natural hazards in many different forms. The main areas of effect are slippage and flooding.

There are several means of identifying natural hazards.

The Regional Council identifies hazard areas such as Coastal hazard, indicative areas of flooding and erosion.

There is GIS mapping which identifies hazards, suspect ground and known events.

Whangarei District Council, as the Building Consent Authority (BCA), must refuse to grant a building consent for the construction of a building, or major alterations to a building, under Section 71(1)(a) and (b) of the Building Act if:

  • the land is subject to one or more natural hazards or
  • the building work is likely to accelerate, worsen, or result in a natural hazard on that land, or any other property.

However, under Section 71(2) the restriction on the BCA's ability to grant a building consent does not apply if:

The BCA is satisfied that 'adequate provision' has been made, or will be made, to:

  • protect the land, building work, or other property from the natural hazard(s); or
  • restore any damage to that land or other property as a result of the building work.

Section 71 of the Building Act 2004 (New Zealand Legislation website)

What does adequate provision mean?

In order to demonstrate that 'adequate provision' has been made for the purposes of Section 71(2)(a) or (b), applicants are required to provide a site specific report from a Chartered Professional Engineer in support of their building consent application.

Council will take that report into account when deciding whether Sections 71(2)(a) or (b) apply.

The report must address Sections 71(2)(a) and/or (b) (as the case may be) and confirm that the applicable statutory requirements will be satisfied, including:

  • Confirmation that suitable mitigation of the relevant natural hazard has been or will be achieved on site;
  • Confirmation that the proposed design incorporates appropriate protection of the land, the building work, or other property and/or that any damage to the land or other property will be restored;
  • Producer Statement (PS1) certification of the design;
  • Assessment of compliance with the NZ Building Code.

Are there any other alternatives?

Despite the requirements of Section 71, there are instances when the BCA must grant a building consent for building work on land subject to natural hazards.

The criteria are set out in section 72 of the Building Act. They are:

  • The proposed building work will not accelerate, worsen, or result in a natural hazard on the land on which the building work is to be carried out or on any other property; and
  • The land is subject to, or is likely to be subject to, one or more natural hazards; and
  • It is reasonable to grant a waiver or modification of the building code in respect of the natural hazard (if required).

Section 72 of the Building Act 2004 (New Zealand Legislation website)

These criteria must be satisfied before section 72 will operate to avoid the restriction on a BCA's ability to grant a building consent that arises under section 71(1).

Criteria must be satisfied before section 72 will operate to avoid the restriction on a BCA's ability to grant a building consent that arises under section 71(1).

The building consent will be issued with a condition as required under section 73 of the Building Act 2004 and also notify the Registrar-General of Land of the consent.

The Registrar-General of Land will place an entry on the title of the land, confirming that the building consent has been granted under section 72 and identifying the natural hazard concerned (see Section 74 of the Building Act for more details).

Please note that an entry on a title under Section 74 of the Building Act directly relates to the proposed building work or any existing building or land to which it relates.

Acid Sulphate Soils

These are feature of some parts of our region and are identified, where known, on various GIS maps provided by Whangarei District Council. 

There is some debate over whether these constitute a Natural Hazard as defined in the Building Act 2004, however, it is known that they can have a devastating effect on buildings if the right materials or methods are not used.

If your proposed building work is in an area affected by these soils you will have to show in your application how you are going to mitigate this feature.

If officers cannot be satisfied on reasonable grounds that this mitigation is in place consent will not be issued.

The Building Code Clause F1 Hazardous agents on site, sets out the minimum performance criteria when dealing with this type of site and  details investigation methods and possible remedial actions that may be required.

F1 Hazardous Agents on Site (Ministry of Business, Innovation and Employment website)

Mine Zones

The Whangarei district has a history of mining and has known mining hazard areas of land that are subject to subsidence due to past mining activities.

These areas have been incorporated into the District Plan rules and require, at least, a site specific geotechnical survey of the ground under and in the immediate vicinity of any proposed building work.

Council will, in these cases, on application for building consent, have the required geotechnical report peer reviewed by another competent geotechnical engineer to ensure that suitable consideration and conclusions are present.

This will incur an extra cost for the application. This is necessary to ensure satisfaction on reasonable grounds that building work will not be affected by previous mining activities or subsidence.

Please refer to Section 56.2.4 within Chapter 56 Natural Hazards Resource Area Rules, under Part F - Resource Areas of the District Plan.  You can view the District Plan by following the link below.

Resources

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