Scientists are using Earth observation imagery and in situ water quality measurements to map, monitor and understand coastal outflows.

Outflows, particularly those following heavy rain, are plumes of freshwater that flow down rivers to the sea, often carrying substances that can either be beneficial (nutrients) or harmful (fertilisers and pollutants).

The researchers are investigating the size, frequency and distribution of outflows at certain locations along the NSW coast.

The project is being led by the NSW Department of Climate Change, Energy, the Environment and Water (NSW DCCEEW), in partnership with the CSIRO and the Coastal and Marine Research Centre at Griffith University.

The aim is to better understand outflows and the effects they have on coastal environments, such as reefs.

It is hoped the use of satellite sensing will revolutionise water quality monitoring, which, for the past 30 years, has relied upon field-based investigative methods.

One recent step has been the installation of a real-time sensor station at the mouth of the Clarence River estuary at Iluka on the NSW north coast.

The station has instruments that physically measure water quality, plus a ‘Hydraspectra,’ which is an array of light sensors developed by the CSIRO.

The system collects water quality data every 15 minutes with the aim of bridging the gap between satellite images, which are captured every 14 days.

“This work is a vital step in ensuring the satellite data accurately reflects what’s happening in our estuaries,” explained Mapping coastal outflows project lead, Dr Tim Ingleton, from the Department of Climate Change, Energy, Environment and Water (DCCEEW).

The sensor station has been established as a collaboration between the CSIRO, Aquawatch, and the Mapping Coastal Outflows team in the Water Wetlands and Coastal Science Branch.

One big change is that with the satellite monitoring system, the researchers only need to collect occasional physical water quality samples to ensure their algorithms are accurate.

Those algorithms are used to gauge the levels of chlorophyll, suspended solids (sediments) and organic matter (carbon levels), without the need to physically visit the site to collect samples.

“By simultaneously measuring characteristics of light via the satellite sensors, and biogeochemistry through water quality sampling, we’ve developed algorithms that can map water quality across previously unsampled areas of estuaries and offshore waters,” Dr Ingleton said.

“To enhance our algorithms, we need a deeper understanding of how the relationship between light and water chemistry varies over time.”

“The sensor station at Illuka is supplying additional data on how water quality changes at the estuary entrance, from hour to hour, day to day, and month to month,” Dr Ingleton said.

The sensor station will operate until late 2026. It is one of many projects being tackled by the Mapping Coastal Outflows program, which is funded through the NSW Government’s Marine Estate Management Strategy under the Water Quality Initiative.