The Tidal Influence on the Turbidity Maximum in a Tide-dominated Estuary: The Brisbane River Estuary, Australia

Abstract

Studies have shown that the tides play an important role on the turbidity distribution in an estuary, particularly in the turbidity maximum zone in the tide-dominated estuary. In this project, a one dimensional hydrodynamic numerical model, which was calibrated and verified in terms of water levels, salinity and turbidity, was applied to investigate the tidal influence on the turbidity maximum in the Brisbane River estuary, Queensland, Australia. The simulated results show that the turbidity maximum zone always occurred in the upstream reach of the Brisbane River estuary, with a maximum value of approximately 160 NTU, during the wet season under non-significant flood conditions. It was also found that the upstream turbidity distribution was relatively less impacted by the tide and the turbidity remained at a high level during the tidal cycle. In contrast, the turbidity in the middle reach of the estuary was significantly influenced by the tidal condition. At downstream reach during the tidal cycle, the combined effects of relatively clean coastal water and asymmetry of tidal currents during the flood and ebb tides resulted in small changes in turbidity. Significantly, the outcomes of this work revealed that the tidal influences mainly impact the turbidity distribution in the middle reach of the river estuary. In contrast, the turbidity distributions are relatively stable at upstream and downstream reach during the tide cycle. This fundamental study will be helpful to estimate the estuary's turbidity distribution and ecosystem status and also useful for the further sediment transport study.