Effects of dredging and reclamation on the sediments of Botany Bay

Abstract

Bottom sediments in Botany Bay were surveyed and analysed for particle size using a wet-sieving volumetric determination. Sediments are predominantly clean sands. although substantial changes in sediment type have occurred in the northern region of the bay since 1968. Large areas which were formerly clean sand, now contain significant amounts of mud. This increase in fine sediments is particularly marked in the dredged areas protected by the Port Botany revetment and the Kingsford-Smith Airport runway extension. These changes have not been the result of exposure by dredging of silt and clay lenses within the underlying sediments, but have probably been caused by the combined effects of deposition of fine material discharged during dredging and reclamation, and increased deposition of fluvial suspended matter due to changes in tidal circulation following the development of port and airport facilities. Sediments in the Port Botany harbour area are expected to become progressively more muddy. Water turbidity in turn may increase as a result of resuspension of fine material by shipping movements.