Local councils, building consent authorities, engineers and developers now have more clarity on ‘good ground’ thanks to
new liquefaction hazard mapping of the Waikato region.
Co-Lab (formerly Waikato Local Authority Shared Services) commissioned the development of the liquefaction hazard
mapping layer, which can be found on Waikato Regional Council’s online Regional Hazards Portal
under the ‘earthquakes and landslides’ tab.
Senior Regional Hazards Advisor Dr Phil Mourot, who developed the layer on behalf of the 12 councils that make up
Co-Lab, said an update to the Building Code’s ‘Good Ground’ definition in November 2019 required all councils to
identify liquefaction prone areas in their district so they could manage any liquefaction-related risk when reviewing
district plans and assessing building and resource consent applications.
Dr Mourot said the change in the Building Code arose from the experience of the Canterbury earthquakes, which caused
widespread liquefaction, and subsequent recommendations made by the Royal Commission of Inquiry.
“Liquefaction is a natural process where earthquake shaking increases the water pressure in soft, sandy or silty soils,
resulting in loss of soil strength,” said Dr Mourot.
“It can cause significant damage and disruption, as we saw with the Christchurch earthquakes, and because of what
happened there it is now a requirement across New Zealand to ensure buildings can stand up to the effects of
“This mapping of liquefaction prone areas will help councils plan for growth in a resilient way, and the layer is
available for use by anyone who is looking to buy property, or develop or build on property, in the Waikato region.”
To provide national consistency on liquefaction mapping, the Ministry of Business, Innovation and Employment has
on how councils should be identifying liquefaction prone areas. The guidance uses levels of assessment, starting with
regional scale, Level A, to very detailed, site specific scale Level D.
The level A assessment of liquefaction for the Waikato region was made using available data on geology, ground water and
“So that’s looking at how hard or soft the earth is; how much water is there is the ground, and how prone is the land to
“It’s important to note that this is broad mapping to identify at-risk areas, where more detailed assessments (Levels B
to D) will be required for building and resource consent purposes.”
The Level A mapping does not include Hamilton city, as Hamilton City Council has already undertaken a Level B assessment
that provides more accuracy regarding the possible risks of liquefaction. Other local councils will be considering their
own Level B assessments in due course.Waikato Regional Hazards Portal
The Waikato Regional Hazards Portal contains all the spatial natural hazard information available from Waikato Regional
Council and some data from other organisations. It’s basically an interactive map, and for some natural hazards a user
can zoom right down to individual property level, for example, for flood hazard and coastal inundation information. The
Waikato Regional Hazards Portal also incorporates the Waikato Coastal Inundation Tool.
The Waikato Regional Hazards Portal was launched in 2018 and is continuously updated with new information and data.
Other new features recently added to the portal include:tsunami inundation zones (under the coastal hazards tab) and areas which are safe to evacuate to in the event of a
tsunamihistoric shoreline data (under the coastal hazards tab), which shows how the position of the shoreline has changed over
timea new emergency management tab with the Waikato Civil Defence and Emergency Management Group Public Information Map
showing COVID-19 locations of interest, latest earthquakes over magnitude 3, state highway information, severe weather
alerts, etca new district councils’ data tab.