Land use planning and development suitability in Queenstown, New Zealand

Abstract

The demand for residential properties in Queenstown is high, but the demand is not matched by the availability of subdivided land and hence there is pressure to develop land which is less geotechnically suitable. It is therefore important that land use planners have an understanding of geological processes and conditions that impose physical constraints to development. The Wakatipu Basin lies within the Otago Schist belt. It is underlain by pelitic and psammitic greyschist with minor greenschist and mafic schists. The structure and texture of the greyschists control many of the geomorphic features in the Basin, the most notable being the extensive foliation-controlled slope failures. Glacigenic deposits dating from the Waimean and Otiran Glaciations are preserved in parts of the Basin. Post-glacial geology is dominated by lacustrine and fluvio-deltaic sediments deposited when Lake Wakatipu was more extensive and at a higher level than it is at present. Foundation materials in the Queenstown urban area consist mainly of greyschist bedrock, Otiranaged tills, and fan-delta complexes, with minor deposits of beach gravels, lacustrine silts and sands, and alluvial gravels. An engineering geological investigation was undertaken to determine the nature and distribution of the geological material in the Wakatipu Basin. The Basin was mapped at a scale of 1:25,000, and the urban area of Queenstown was mapped in more detail at 1:10,000. The maps produced show bedrock and surficial geology, and geomorphology, and as such they are a guide to expected foundation conditions in the area. Limited laboratory testing was undertaken to determine the grainsize distributions of various surficial deposits. On the basis of the engineering geological investigation, seven geological conditions and processes affecting or potentially affecting the area have been identified. They are stream bank and lake shore erosion, debris deposition, slope movement, weak foundation materials (silts, cohesionless gravels, schist crush zones), topography, flooding, and seismicity. The identification and evaluation of the physical constraints forms the basis for the compilation of a Development Suitability Map for the Queenstown urban area (1:10,000). By showing the type of constraint present, and the degree of geotechnical limitation it places on development in that area, the map effectively subdivides the map into parcels delineating areas that are more, or less, suitable for residential development.