Sediment Dynamics in the Lower Section of a Mixed Sand and Shell-Lagged Tidal Estuary, New Zealand

Abstract

A series of field investigations and a numerical hydrodynamic model were applied to determine the sediment transport characteristics in the lower section of a large tidally-dominated estuary at Whangarei Harbour, northeast New Zealand. The results show a consistent pattern in this unusual case where shell lag and shell/sand mixes have a dominant influence on the net sediment transport even though the estuary is subjected to a wide range of competent flows well above the sandy sediment threshold. A description of the estuary's sediment transport capacity, the influence of lagged beds, the relationship of morphology and sediments to tidal dynamics, especially tidal -cycle velocity residuals, and the implications for a proposed marine terminal in the study region are presented and discussed.