Impacts of dredging on dry season suspended sediment concentration in the Brisbane River estuary, Queensland, Australia

Abstract

Extensive dredging in the Brisbane River estuary since European settlement has significantly altered estuarine hydrological and sediment transport processes. A large tidal ingress resulting from extensive dredging in the lower Brisbane River estuary and gravel extraction including point and non-point inputs in the upper estuary are currently maintaining two distinct turbidity maximum zones within the estuary: at the mouth (100–150 mg/L) and at about 60 km upstream (>300 mg/L). In addition, extensive dredging has also increased Brisbane estuary dry season flushing time significantly (>300 days) and as a consequence the estuary is currently unable to flush any point and non-point inputs beyond 35 km upstream from its mouth during the entire dry season resulting in a very high suspended sediment (SS) concentration all along the estuary except an area between two turbidity zones. In general, this work shows strong ramifications of dredging estuaries in other parts of the world, which are currently facing increased pressure from urbanisation and navigation requirements in conjunction with industrial developments.