Evaluating the influence of tidal currents on the distribution of silt in Nara Inlet, central Great Barrier Reef, Australia

A simple model is developed to infer flood-tide dispersal of silt during fa ir-weather conditions from spatial grain size variation of mixed carbonate/ siliciclastic silt on the bed of Nara Inlet, a 3 km long shallow, tropical embayment on the mid-shelf of the central Great Barrier Reef region, Austra lia. The model uses settling velocities calculated for three dominant silt modes (23, 28 and 41 mu m) and measured tidal current data to predict the h eadward transport of silt by a large flood tide. Modelling was aided by the use of Wind and Currents 2000 (WC2000) freeware, a visualisation and analy sis tool for vectorial data. The model predicts the 23, 28 and 41 mu m mode s will be transported minimum headward distances of 1250, 950 and 500 m, re spectively and compares well with the observed silt distribution on the bed . The results indicate that under fair-weather conditions flood-tides contr ol the distribution of silt. Consistent grain size trends of bulk and silic iclastic silt implies that siliciclastic and carbonate silt-sized grains ma y exhibit similar hydraulic behaviour during transport by hood tides in Nar a Inlet. The model may be applied to embayments where fine sediment transpo rt is dominated by flood tides. It may also have application in identifying the controls on dispersal and accumulation of particle-associated contamin ants in embayments characterised by mixed carbonate and siliciclastic sedim ents. (C) 2000 Elsevier Science B.V. All rights reserved.