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Gross pollutant traps capture debris at Perth urban wetland

Water Corporation will be overseeing a two year investigation of gross pollutant traps (GPT) at Herdsman Lake, one of Perth’s most popular urban wetlands, with the potential the water waste traps will be rolled out across the capital and other parts of the state.

Designed to capture plastic, debris and floating litter bigger than 5 mm and remove it from the waterbody, the GPT trial follows a study commissioned by the utility, Water Corporation Manager of Drainage and Liveable Communities Suzanne Brown said.

“In 2019, Water Corporation commissioned an external study which looked at different litter trap designs and locations where they might deliver best value. We’ve since appointed a contractor to install three traps at drainage inlets and outlets around Herdsman Lake, which is one of Perth’s largest urban wetlands,” she said.

“Moving forward, we’ll conduct a monitoring and a maintenance program which broadly looks at the traps’ effectiveness and any ongoing operational costs. The results will be used to inform the potential future use of gross pollutants traps on other arterial drains in Perth and Western Australia.

“We’ll monitor the traps over the next two years to examine things like how much litter they collect, their overall effectiveness, any operational and maintenance considerations and their cost-effectiveness.”

Brown said GPTs can take many different forms depending on their location and the type of litter they’re designed to capture.

“After reviewing our options, we settled on two designs – a floating litter boom and two floating litter traps,” she said.

“The litter boom sits on the outlet of a branch drain into Herdsman Lake. It’s made of polyethylene pipe that floats on the water surface and acts as a barrier to prevent litter escaping downstream.

“A mesh skirt is attached to the pipe to capture submerged rubbish but still allow fish and other fauna to pass safely underneath.

“At two other points around the lake we’ve installed litter traps. These are essentially floating rubbish bins fitted with polyethylene booms to direct litter to a retention chamber. The rubbish is collected and recycled where possible.”

Understanding floating pollutant levels

Brown said the investigation will help the utility ensure cleaner stormwater, provide better understanding of floating pollutant levels within the network and protect the environment.

“While it’s not a huge amount of rubbish typically found within drains, we’re always looking at new and innovative ways to ensure cleaner stormwater across our network,” she said.

“Herdsman Lake was chosen because, as a monitoring location, it’s really quite unique. Multiple stormwater drains flow into and away from the lake, which means we can capture data on the amount of litter at both inlet and outlet points.

“But perhaps the biggest driver for choosing this site is the potential environmental benefits. Herdsman Lake is one of Perth’s largest and most important urban wetlands and is a habitat for many native animals.

Plastic pollution is a blight on the area’s natural aesthetic, so it’s important we explore new ways of reducing its impacts.

“GPTs are by no means the answer to eliminating plastic pollution, however, they may have an important role to play in supporting government efforts to reduce waste.”