2019 Dataset

The 2019 liquefaction susceptibility dataset, prepared by GNS Science under contract to Otago Regional Council (ORC), covers the entire extent of the Central Otago District, Clutha District, Queenstown Lakes District, and that part of the Waitaki District lying in the Otago Region. The dataset comprises a four-fold classification of liquefaction susceptibility classes, called 'domains', that identifies areas that are assessed as being underlain by sediments which may have some liquefaction susceptibility. In making the assessment, consideration has been given to whether groundwater levels are likely to be sufficiently close to the ground surface to make liquefaction possible.

This dataset does not define hazard zones, but rather identifies liquefaction-susceptibility domains. In terms of the MBIE (2017) guidelines, the mapping approach used to produce this dataset equates to a “Level A” basic desktop assessment, that is aimed at distinguishing between areas where liquefaction damage is unlikely to occur (Domain A) versus areas where liquefaction damage is possible (domains B, B1 and C).

The liquefaction-susceptibility domains in this dataset, with reference to MBIE (2017) guidelines, are defined as follows:

• Domain A. The ground is predominantly underlain by rock or firm sediments. There is little or no likelihood of damaging liquefaction occurring. In MBIE (2017) terms, liquefaction damage is unlikely;

• Domain B. The ground is predominantly underlain by poorly consolidated river or stream sediments with a shallow groundwater table. There is considered to be a low to moderate likelihood of liquefaction-susceptible materials being present in some parts of the areas classified as Domain B. In MBIE (2017) terms, liquefaction damage is possible;

• Domain B1. As for Domain B, but there is geotechnical evidence for the presence of liquefaction-susceptible materials at least in some locations in the subsurface;

• Domain C. The ground is predominantly underlain by poorly consolidated marine or estuarine sediments with a shallow groundwater table. There is considered to be a moderate to high likelihood of liquefaction-susceptible materials being present in some parts of the areas classified as Domain C. In MBIE (2017) terms, liquefaction damage is possible.

Reference: MBIE (2017). Planning and engineering guidance for liquefaction-prone land. Wellington (NZ): Ministry of Business, Innovation and Employment (MBIE). 134 p. Technical report; ISBN (online) 978-1-98-851770-4.

Accuracy: The positioning of boundaries between domain polygons is based largely on landform features. The main topographic and photographic basemaps used to aid the mapping were the 1:50,000-scale LINZ Topo 50 map series, and high-resolution colour aerial photos, accessed digitally through the ArcGIS software. Unless stated otherwise in the companion report (see Credits), the mapping scale was 1:50 000, and the boundary between each domain polygon should be regarded as being a 100 m wide zone, rather than a line. In areas where lidar coverage was available for the mapping, the mapping scale is 1:10 000, and domain boundaries should be regarded as 20 m wide zones. In towns and villages, where Google Earth Street View was available at the time of mapping, Google Earth ground photography was accessed to help in positioning domain boundaries. In those areas, the assigned mapping scale is 1:1 000, and boundaries are considered accurate at the scale of property parcels and buildings. The commentary in Appendix 2 of the companion report indicates where these more detailed scales apply.

2014 Dunedin dataset

The 2014 liquefaction susceptibility dataset, prepared by GNS Science under contract to Otago Regional Council (ORC), shows Liquefaction susceptibility of mapped geological units in the Dunedin district area.