Long term monitoring of estuarine water quality: Brisbane River turbidity

A project at the CRC for Coastal Zone, Estuary and Waterway Management is providing information on the variability of water quality at different locations in the Brisbane River. Data is being used to help: (1) determine the effectiveness of waterway management measures designed to reduce turbidity (eg stormwater control devices, changes to dredging, sewage treatment plant upgrades); (2) optimise existing water quality models used for waterway management for providing accurate field data for remote sensing projects, and (3) to enhance understanding of significant river/estuary processes. By obtaining a continuous record of these water quality parameters over a range of seasons, tides and rainfall, stakeholders will be better equipped to assess the ecosystem health of the Brisbane River and Moreton Bay. Turbidity, salinity and temperature measurements were taken every fifteen minutes at a single site in the Brisbane River estuary over a period of thirteen-months. Wide variations in turbidity were observed over both short and long time scales, highlighting the difficulty in the satisfactory interpretation of monthly (or less frequent) snapshots of estuarine water quality. A fit of average turbidity versus tidal range was made during a period of minimal sediment input into the estuary from freshwater inflows, with the best fit found to be T = -93.7 + 123 G^0.7463, where T is the average turbidity (NTU) and G the tidal range (m). The data also assists in determining the underlying processes occurring with regard to estuarine turbidity.