FAQs for Liquefaction Mapping
What is liquefaction?
Liquefaction is a natural process where earthquake shaking increases the water pressure in soft, sandy or silty soils, resulting in loss of soil strength. It can cause significant damage and disruption, as we saw with the Christchurch earthquakes.
Why do we have liquefaction layer mapping?
An update to the Building Code’s ‘Good Ground’ definition in November 2019 required all councils to identify liquefaction prone areas in their district.
Why has the building code changed?
The change in the Building Code arose from the experience of the Canterbury earthquakes, which caused widespread liquefaction, and subsequent recommendations by the Royal Commission of Inquiry.
Who will be using liquefaction mapping?
Mapping of liquefaction prone areas helps to manage risk for anyone looking to buy property in the Waipā district. This includes developers, real estate agents and the public looking to purchase a new home or a section.
How will Waipā District Council be using this information?
Primarily to manage liquefaction-related risk when assessing building and consent applications. The council will alsoliquefaction mapping to assess risk levels for resource consent applications. The Level A maps may trigger further information requests.
Where can I find the mapping tool?
Liquefaction Maps can be found on Waikato Regional Council’s online Regional Hazards Portal under Earthquakes and Landslides here.
How is the assessment made?
Ministry of Business Innovation and Employment has published guidance 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.
What level of assessment is available for Waipā District?
Currently there is a Level A assessment available for Waipā and the Waikato Region. This identifies a scale of three risk levels: possible, unlikely and undetermined. In many cases, site specific investigation may still be needed.
How was the Level A assessment determined?
The level A, desktop assessment of liquefaction was made using available data on geology, water tables and land stability. That is looking at how hard or soft the earth is; how much water is there is the ground, and how prone land is to shaking.
When will more detailed B-D assessments be available for Waipā?
Waipā District Council is looking to join a tender for region-wide Level B assessment which is calibrated desktop mapping. Level B maps would be at a scale and level of detail that will enable the Council to update the District Plan. The council will decide on whether to proceed following the tender evaluation. Level C and D are site specific assessments and are typically undertaken by applicants.
I’m a property owner in Waipā and the maps show a possible liquefaction risk on my land. What do I do?
Further risk assessments will only be needed if you are planning on building or developing. These will be assessed as part of the building and/or resource consent process.
