In 1992 the entrance channel through the tidal inlet to Tauranga Harbour, which is located along the Bay of Plenty littoral drift system, was deepened from 10 m to 14 m. The deepened channel has become a sediment trap for littoral drift bypassing and tidal current driven sediment transport through the inlet. Since 1992, there has been an increase in maintenance dredging requirements at the inlet, because of sand accumulation along the southeastern border of the entrance channel. Previous studies have identified an ebb tide–induced eddy operating on the eastern side of the ebb-jet as it exits the tidal gorge. In this article, the eddy system has been simulated with a validated two-dimensional hydrodynamic model, detailing time-varying current patterns over the ebb-tidal delta. Particular emphasis is placed on defining the trajectory of the eddy and evaluating its influence on the observed sedimentation patterns. The model results indicate the formation of opposing eddies on either side of the entrance channel, both of which are transient in nature. The centre of the eastern eddy propagates seaward along the downdrift margin of the entrance channel as the ebb-jet lengthens. Bathymetric survey residuals between 2004 and 2006 confirm significant accumulations of sediment along this downdrift margin. The evidence is consistent that the eddy system exerts a directional control over transport of sediments entrained by waves over the ebb-tidal delta.
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Vol. 2009 • No. 251