Suspended Sediment Distribution within a Partially Mixed Subtropical Estuary

Changes in volume concentration and grain size were recorded in the microtidal Coomera River Estuary, Queensland, Australia, using a Laser In Situ Scattering and Transmissiometry instrument. By sampling along the length of the River, it was possible to compare results from areas of saline to fresher water, and at differing depths. Results showed that the particulate concentration and composition vary along the estuary. At the mouth of the estuary, which was vertically homogenous in salinity, bottom currents were resuspending material. In the upper reaches of the estuary, there is a stratified flow of low salinity water over more saline estuarine water. This upper layer was characterised by a low suspended sediment volumetric concentration. A persistant turbidity maximum exists around the 5 parts per thousand salinity isohaline. This turbidity maximum moved according to the amount of river discharge and tidal movement. A conceptual model of the river was developed.