Western Bay of Plenty District Council: New liquefaction maps available online

Liquefaction and flooding to streets and houses in Christchurch following the December 23, 2011 aftershocks. Photo / Geoff Sloan

All Western Bay of Plenty residents can now access new liquefaction maps online.

The maps are available on the Western Bay of Plenty District Council's website and show where ground damage from liquefaction is possible, unlikely or yet to be determined.

Liquefaction can occur during an earthquake and causes soils (such as sand and silt) to act more like a liquid than a solid. Earthquake shaking moves the sand and silt in wet soil underground and forces water to the surface taking the silt and sand with it.

In this process, the ground loses strength and stiffness. It can tilt and sink and cause damage to property, buildings and infrastructure such as roads, pipes and tanks.

"These maps help us to build a picture of what places, properties and infrastructure could be affected by liquefaction in the event of a large (one in-500-year) earthquake," the council's group manager for policy, planning and regulatory services Rachael Davie said.

"Council will use this data when considering subdivision and building consents, ensuring that the risk to people and buildings are assessed. The District Plan will also be updated to include this information in due course.

"This report will also help council to implement changes to the Building Code, that see the liquefaction rules currently in place for Canterbury applied across New Zealand. These changes will ensure robust foundations are included when building on liquefaction-prone ground."

The new information is freely available on the council's website and will be included in property files and land information memoranda (LIMs) requested for properties.

The new liquefaction maps, along with other natural hazards which have already been identified, can be viewed on the council's natural hazards webpage with an interactive online map. Anyone can browse the map or search for a specific property by address.

Council's newest data comes from a region-wide report carried out by the Bay of Plenty Regional Council. The study was done according to Ministry for Business Innovation and Employment / Ministry for the Environment Liquefaction Guidelines (2017).

The updating of the council's hazard maps is a multi-year project undertaken with the Bay of Plenty Regional Council. The remaining natural hazard maps for the district such as coastal erosion, coastal inundation, tsunami, and landslide will be completed over the coming years.

For more information visit the council's natural hazards webpage or call the council's customer services team on 0800 926 732.