Westport has partnered with the Western Australian Marine Science Institution (WAMSI) to deliver the $13.5 million WAMSI-Westport Marine Science Program. This 3-year program is developing the latest data, information and modelling on the complex environmental systems and community values associated with Cockburn Sound.
Project 3.1.3 Water Quality and Sediment Deposition – December 2022 to December 2023
Theme: Water and Sediment Quality
Researchers: C. Wilson, K. Wienczugowt, Murdoch University (2025)
Developing an updated baseline for water quality and sediment disposition in Cockburn Sound.
The water quality of Cockburn Sound has been a key environmental focus since the 1970s, when it was identified that nutrient enrichment largely driven by nitrogen runoff and effluent discharge was destroying seagrass beds in Cockburn Sound.
A water quality monitoring program, running for the past 30 years during summer, has identified significant reductions in nitrogen and phosphorous.
With Westport proposing the development of the new container port in the Kwinana Industrial Area, more robust data was required to inform environmental management strategies for dredging and vessel movement.
This study set out to create an up-to-date baseline for water quality and sediment deposition, the process by which sediment is laid down through the movement of water or wind
From December 2022 to December 2023, nephelometers were placed at four sites in Cockburn Sound and two sites in Owen Anchorage. These measure turbidity, water depth, light (photosynthetically active radiation (PAR)), sediment deposition and water temperature, Wind data was obtained from the Garden Island Bureau of Meteorology weather station.
What the report found
- The average annual wind speed was 23.3 km/hr. Seasonal average wind speeds were the highest in summer at 27.5 km/hr and lowest in winter at 21.1 km/hr.
- Elevated turbidity occurred more frequently in winter in Owen Anchorage, but peaks were observed year round in Cockburn Sound. Increases in turbidity were generally wind induced.
- Water temperatures in Owen Anchorage and Cockburn Sound were lowest in winter (late June or early July) and highest in summer (February). Generally, the temperature was higher in Owen Anchorage during winter compared to Cockburn Sound.
- Daily sediment deposition tended to peak when turbidity peaked, influenced by wave action or currents depending on site location, water depth and sediment type.
How Westport will use the report
This study was part of a series intended to establish baseline metrics on water and sediment quality that Westport can use for its environmental management strategies. It will inform our dredge management plan and provide data for water quality modelling and seagrass rehabilitation programs.
