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Urban Geological Mapping

Urban Image Auckland

Understanding the geology beneath New Zealand’s towns and cities (urban areas) enables better informed approaches to planning, development and urban management. Geological knowledge aids in the mitigation of geological hazards such as landslides and the effects of earthquake shaking, as well as the utilisation and management of geological resources such as aggregate and groundwater. Geological maps are an important way of conveying knowledge of urban geology.

Geological mapping of urban areas requires a different approach to regional-scale geological mapping. Urban areas need to be mapped at a more detailed scale to be of benefit to the people who need to understand the geological foundations of their properties, buildings and infrastructure. This detail includes needing to know geological variation below the surface. Earthworks in cities will typically involve excavations of many metres depth and the challenge for urban geological maps is to provide information on what materials may be encountered below the surface.

QMAP graphic

All of New Zealand is covered at 1:250 000 by the QMAP geological map series. While for most of New Zealand, QMAP is the most up-to-date digital geological map information available, the maps are generalised and show broad geological context, rather than details relevant at the scale of urban areas. Many New Zealand cities, and some larger towns, have print-published geological maps at more detailed scales, with or without explanatory notes or books. Most of these are more than 20 years old.

GNS Science is providing improved and more detailed geological information for New Zealand urban areas. The new geological map datasets include information on the surface geological materials, landform characteristics (geomorphology) and interpretations of subsurface geology. The new datasets contain a mix of conventional 2D surface mapping and its integration with subsurface information obtained from drill holes, geotechnical probes and interpretation of geophysical data to create 3D geological models.

Geological maps are only one element of our understanding of the geology of New Zealand urban areas. In addition to published geological maps, GNS Science holds a lot of unpublished map compilations and reports, for example. Other geological information is commonly held and made available by city and regional councils and Quotable Value (QV). Drillhole information, particularly from public land, is commonly archived by territorial authorities. The New Zealand Geotechnical Database is a national repository of drillhole and geotechnical information, with substantial holdings from Christchurch, Auckland and Wellington.

In addition Consultancy services are offered, commonly with specialist geotechnical or other components.