Inner Shelf Dynamics on a Storm-Dominated Coast, East Coromandel, New Zealand

Abstract

Initial observations of the coastal oceanography on the east Coromandel inner shelf, northeast New Zealand, were examined using the combined results of sea-bed drifter experiments and Aanderaa continuous recording current meter records. The inner shelf at this location is fairly narrow, ranging from 20-30 km out to the 200 m bathymetric contour. Near bottom currents in the study area are characterized by two shore-parallel flows. During calm weather, a relatively weak current flows to the south at speeds of between 0.10-0.20 ms^-1. This appears to be a remotely forced bottom current possibly associated with the southward directed East Auckland Current. Episodic storm events associated with cyclonic depressions result in the generation of a strong northerly flowing current, with speeds of up to 0.40 ms^-1 recorded. This is a local wind-generated bottom current, and probably represents part of a more complex 3-dimensional circulation associated with downwelling conditions. From consideration of current and combined wave-current dynamics, potential long-shelf sediment transport pathways were found to be directed to the north during episodic storm events. Such high magnitude wind events are concentrated during winter and spring each year and occurred relatively infrequently (0.5%-6% p.a.) during the study.