Geomorphological and environmental studies of karst, Northwest Nelson, New Zealand
Degree GrantorUniversity of Canterbury
Degree NameMaster of Science
This study describes the characteristics of the karst terrains and evaluates the surface and subsurface processes operating on the karst systems located between the Takaka and Riwaka Valleys, northwest Nelson, New Zealand. The purpose of this study is to differentiate between natural environmental and human induced changes in the karst system, and where possible, quantify human impacts. Detailed geomorphological mapping at 1:7500 scale was used to compile an inventory of the karst geomorphology. Geomorphological classification of the surface karst features and an assessment of the lithological and geological variations resulted in the identification of eight karst land systems or zones, in which a similar pattern of topography, hydrology, surface features and soils are recognised. Based on the predominant landforming processes, the karst zones: Kairuru, Takaka Plateau, Canaan South, Canaan North, Pikikiruna, Takaka Walkway, East Takaka and Pohara, are categorised into three groups. Solution is the dominant process in the first group (Takaka Plateau and Takaka Walkway) which is characterised by internal drainage and a lack of surface streams, rolling topography, numerous, well-formed dolines and karren, and exposed rock surfaces. In the second group (Canaan South, Canaan North, and Pikikiruna), wide karst valleys, numerous alluvial dolines, covered rock surfaces and focused allogenic recharge occur in response to combined fluvial and solutional processes operating on low slope angles. Fluvio-karst processes are also active in the third group, comprising the Kairuru, East Takaka and Pohara zones. This group is characterised by incised karst valleys, mixed drainage systems, steep slopes, and limited doline development. It varies from the low slope - fluviokarst group in that overland flow and lateral solution are common because of the steeper slope gradients. The eight karst zones are useful management units and the vulnerabilities of the karst to human activities has been evaluated using these zones. The primary impact in the zones of the first group is soil erosion. The presently exposed marble surfaces in these karst zones reflect the loss of 10 - 30cm of soil following land clearance c.100 years ago. The impacts of stream and subsurface sedimentation and water quality degradation dominate in the other zones because of focused runoff, allochthonous soils and higher intensity of land use.