Tidal inlet configuration and bathymetric changes resulting from active sedimentation, Buffalo Bay, New Zealand.

Abstract

The Whitianga tidal inlet lies within Mercury Bay, on the northeast coast of New Zealand. The Whitianga Estuary harbours many recreational and commercial vessels. Terrestrial sediment inputs into the Whitianga Estuary catchment are high, due to the erodible tertiary sediments and the steep nature of the catchment, which suffers intense rainfall that results in high sediment influxes, much of which becomes deposited within the estuary. In recent years active shoals have appeared in Buffalo Bay and the inlet channel has noticeably shallowed, both of which inhibit the use of the inlet by boat traffic. The past and present bathymetry of Buffalo Bay is compared to establish changes in morphology and zones of accretion and erosion within Buffalo Bay. The outcomes of this research contribute to a larger research programme which aims to use numerical model simulations to identify sediment transport pathways and patterns within Buffalo Bay. This research will particularly provide information which can be used to calibrate a sediment transport model. Comparison of the Buffalo Bay bathymetries over the 38 year period from 1938 to 1979 and Whitianga inlet bathymetries between 1979 and 1995, show extensive accretion in the ebb discharge channel which is predominantly associated with the migration of the tidal inlet channel and growth of the ebb delta, and within the inner inlet area which are attributed to the growth of the flood delta system.