What is liquefaction?
Liquefaction can occur when some saturated soils (typically silts and sands) lose strength and stiffness (temporarily behaving as a liquid rather than a solid) in response to earthquake shaking. Only some soil types are prone to liquefaction and only some earthquakes are strong enough to cause liquefaction.
Important Update 29/11/21
Recent changes to the Building Code require that ground subject to liquefaction can no longer be considered “good ground”. Council has new liquefaction maps to assist with implementing these new changes. Please see below for more information.
Where are liquefaction areas identified?
The District Plan maps do not currently identify any liquefaction areas.
Council does however hold reports which map liquefaction.
New Reports (2021, 2020)
Bay of Plenty Regional Council commissioned two reports which map liquefaction hazards within the Western Bay of Plenty District. Council is now using these new maps when processing subdivision and building consents.
- Region-wide study (2021) (PDF, 7MB)
- Omokoroa Stage 3 Structure Plan Area study (2020) (PDF, 36MB)
Both reports were prepared in accordance with the MfE and MBIE “Planning and Engineering Guidance for Potentially Liquefaction Prone Land” (2017).
The region-wide study was prepared to a Level A (basic desktop assessment) level of detail. The Omokoroa Stage 3 Structure Plan Area study was prepared to a Level B (calibrated desktop assessment) level of detail. This level B assessment included consideration of data collected from geotechnical investigations and groundwater monitoring undertaken within the study area boundary as defined in the T+T report.
The liquefaction vulnerability categories recommended for use in the “Planning and Engineering Guidance for Potentially Liquefaction Prone Land” (2017) are shown below.
You can view Council's liquefaction maps below.
Search your property - current natural hazard maps
To show the natural hazard map for your property please enter a valid Address or Parcel ID below and click the launch button. Or you can browse the natural hazard maps.
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
Here are the technical reports supporting the liquefaction maps:
Tonkin + Taylor Bay of Plenty Regional Liquefaction Vulnerability Assessment 2021 (PDF 7MB)
Tonkin + Taylor Omokoroa 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 Building code and as referenced in NZS3604:2011 ALL STRUCTURES must have a Liquefaction assessment; however council adopted a risk based policy to allow some minor works 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 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.
- For basic unlined Garages over 40m2 a Liquefaction report will be required.
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:
Assessment shall also consider the MFE and MBIE “Planning and Engineering Guidance for Potentially Liquefaction Prone Land” (2017).
Note: Buildings carried out under schedule one (Exempt Building Work) will still need to consider if Liquefaction needs to be considered in the foundation design as required under Section 17 of the Building act 2004.
Noteany site-specific natural hazards are still applicable to all Projects regardless of size or type.
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 email@example.com.