Mapping the morphology of a dredged ebb tidal, Tauranga Harbour, New Zealand

Abstract

The morphological units of an ebb tidal delta were mapped and results used to evaluate the relationship between morphology and hydrodynamics, as part of an investigation into the sedimentation at the Entrance Channel at Tauranga Harbour, New Zealand. Four end-member map units (shell lag, coarse sand, medium sand, and fine sand) were identified from the sidescan sonar imagery, which was verified using seabed sediment samples and SCUBA diver observations. These four units were used in a classification scheme that consisted of 10 composite map units. The use of standardized map units helped to reduce the subjectivity involved in sidescan sonar image interpretation. The mapping scheme was used to assist in the understanding of the impact of capital dredging on the morphological evolution of an ebb tidal delta. Observed morphological changes over the ebb tidal delta were attributed to possible changes in the asymmetry of the vertical tide and residual eddy currents.