Desilting stormwater wetlands

A project to more efficiently remove and manage sediment build-up in stormwater treatment wetlands is reducing the amount of prescribed waste sent to landfill, saving significant costs. Read this case study to learn more.

Sustainable Develop Goals:
Goal 15: Life on land
 

Background

Stormwater is a growing concern across Melbourne. As urban development increases and climate change brings more extreme weather events, it is critical we continue improving the quality of stormwater discharged to Port Philip and Western Port bays. One of the ways we’ve been doing this is by building and managing stormwater wetlands.

Our stormwater wetlands network includes sediment ponds. These ponds ensure contaminants carried by stormwater can settle out, after which they are processed for disposal. In 2014 a survey of these ponds showed that 55 per cent of the ponds had accumulated sediment to such an extent it was impairing their ability to trap sediment.

Sediment is made up of waste material classified as ‘prescribed’ (higher risk) and ‘non-prescribed’ (lower risk), with the prescribed waste material being more costly to dispose of. Investigation of the sediment indicated that over 60 per cent of these ponds were producing sediment in the higher-risk, prescribed waste category, or otherwise known as Category C.

Research focus

In response to the growing problem, we initiated the Dredging and Sediment Separation System Project. The project uses equipment that more efficiently removes and manages sediment, separating it into prescribed and non-prescribed material.

During field trials we identified that equipment modifications were needed to effectively isolate small particles (less than 0.3 to 5mm in diameter) from the larger particles. Once this was achieved, we confirmed that metals linked to these smaller particles were largely responsible for the contamination of wetland sediment.

Outcomes

The trial project has resulted in a reduction of the amount of prescribed waste sent to landfill, representing significant cost savings.

We are currently implementing the project outcomes in our sediment management program and will continue to work to ensure we manage stormwater in line with State Environment Protection Policy guidelines.