Liquefaction

Tips for finding your property:

• Type the address in full such as 10 Example Road or 10 Example Street, instead of using street name abbreviations (Rd or St etc)
• If there are identical addresses in other parts of the District, you'll need to type in community abbreviations e.g. Beach Road (KK), Beach Road (MAK) or Beach Road (WB). Help with identical addresses
• If searching by Parcel ID, recent letters from us about natural hazards show your Parcel ID number.

How is the mapping done?

To generate liquefaction maps, the following things are taken into account:

• Soil type
• Groundwater levels
• Strength of earthquake

Technical Reports

Here are the technical reports supporting the liquefaction maps:

Tonkin + Taylor Bay of Plenty Regional Liquefaction Vulnerability Assessment 2021 (PDF 7MB)

Tonkin + Taylor Ōmokoroa Stage 3 Structure Plan Area – Supplementary Level B Liquefaction Assessment 2020 (PDF 36.4 MB)

Frequently asked questions about liquefaction

What are the requirements if I am constructing a habitable building?

Under the New Zealand Building Code and as referenced in NZS3604:2011 ALL STRUCTURES must have a Liquefaction assessment. However, council has adopted a risk-based policy to allow some low-risk structures to be carried out without a Liquefaction assessment, see below:

A liquefaction assessment will be required where land is identified as “liquefaction damage is possible” or “liquefaction category is undetermined” in the following situations:

• All dwellings, IL2 buildings or greater, and additions that have a total floor area over 30m2.
• All Garages that contain a habitable space (sleep out, office, studio) that have a total floor area over 30m2.

A liquefaction assessment may not be required in certain low risk buildings

• Uninhabited detached garages (ie, that are not constructed as an integral part of a house)
• IL 1 buildings (As defined in NZS1170)
• A Deck, Carport, or other minor structure such as a Fence/Landscape Wall

All other building not specifically noted in this guidance will be assessed on a case-by-case basis.

The noted structures above not requiring a liquefaction assessment are considered as having a low risk of loss of human life, and/or small or moderate economic, social, or environmental consequences. It covers minor structures where their failure is not likely to endanger human life.

Where foundations have been noted as reliant on Good Ground as per NZS3604:2011 (even for the buildings listed above) these will also still require a Liquefaction assessment to confirm the design is within the scope of NZS3604:2011

Please see the following MBIE website links 'Ensuring new buildings can withstand liquefaction effects' and 'Garage classification guidance''Garage classification guidance' for more information on liquefaction and the testing requirements:

Any assessment shall also consider the MFE and MBIE “Planning and Engineering Guidance for Potentially Liquefaction Prone Land” (2017).

Note: Buildings carried out under BA Schedule 1 (Exempt Building Work) will also still need to consider Liquefaction in the foundation design as required under Section 17 of the Building act 2004.

Note any site-specific natural hazards are still applicable to all Projects regardless of size or type or whether they require consent.

What are the requirements if I am constructing a Small Shed, Deck, Carport, or a Minor Structure such as a Fence/Wall?

No liquefaction assessment is required.

*Pole sheds with dirt floor and no foundations supporting walls, No Liquefaction report required. All other Poles sheds constructed with a floor slab and/or internal wall partitioning larger than 40m2 will required a Liquefaction report.

*This will apply to any site that is identified as Liquefaction damage is possible or Liquefaction Damage is Undetermined. Both Categories will need to have the foundation design take Liquefaction into account.

If I have a building site approved from a previous subdivision can I go ahead and build?

Yes, but only if the subdivision has addressed all identified natural hazards (including liquefaction), and building works are in accordance with the requirements of the subdivision. If new natural hazard information has become available since the subdivision, this will need to be addressed when you go to build.

Is new subdivision allowed?

Yes it is, but you'll need to provide a geotechnical report with the resource consent. This will help identify suitable building sites and will explain what foundations are required. If there are no suitable building sites, a subdivision can be declined.

What will the subdivision need to address?

This is provided within the requirements of WBOPDC Development Code.

In 2018, WBOPDC advised practitioners to utilise the DS-10 Natural Hazards and Earthworks chapter of the Tauranga City Council (TCC) Infrastructure Development Code (IDC) in tandem with the special feature areas noted within the WBOPDC Development Code (e.g., Minden). The TCC IDC contains the most up to date requirements for this area of practice. It also acknowledges the joint Geo-professional accreditation system applicable to both Councils.

Assessment shall also consider the MfE and MBIE “Planning and Engineering Guidance for Potentially Liquefaction Prone Land” (2017).

Who can carry out a liquefaction assessment report?

If “liquefaction damage is possible” on our new maps, then you will need to engage a Category 1 Geo-professional to carry out a liquefaction assessment report.

If the “liquefaction category is undetermined”, then a Category 2 Geo-professional can carry out the assessment. (Note: If this assessment concludes that “liquefaction damage is possible”, the report shall be reviewed and certified by a Category 1 Geo-professional).

The liquefaction report may still need to address the sites ground bearing capacity and any other relevant site requirements, such as stability, soakage requirements etc.

Who can I ask to prepare a geotechnical report?

The list of approved geotechnical engineers can be found here.

Got a different question?

If you have any further questions, please contact Council on 0800 926 732 or at customerservice@westernbay.govt.nz.