The Use of A Geotechnical Constraint Map to Inform Subdivision Development: A Case Study

One of the biggest challenges faced by geo-professionals is how to convey complex information to non-technical end users. One method of conveying information in a straightforward manner is the use of geotechnical constraints mapping. A case study is presented for a site in the Maymorn Region of Wellington, New Zealand, where several geotechnical limitations for future subdivision were identified. The geomorphology of the site comprises level ground across the western side of the site, incised by a stream channel in the north; with hills present across the eastern side of the site. The flat area of the site has experienced historical filling of the stream channel and settling ponds associated with farming. The hill areas of the site have been extensively modified by forestry works. The geomorphology and past site works suggest a large number of geological hazards may affect future land use. These comprise liquefaction, lateral spreading and static settlements across the flat areas of the site; with landsliding (both shallow and deep seated), debris flows and rockfall across the sloping areas of the site. For each area of the site, we considered the risk posed by each hazard to the development and assigned it a rating class, from 1 (lowest) through 5 (highest). This was presented in a geotechnical constraints map with coloured zones reflecting each of the rating classes. The end result provided an easy and concise means of conveying extensive technical information to the end user who was readily able to apply it to their decision-making.