Sydney Water removes 300,000 kg of stormwater pollution

Sydney Water has removed over 300,000 kg of debris and rubbish from Sydney’s waterways during a week-long operation to prevent flooding, protect fish populations and maintain the health of connected waterways.

The heritage-listed stormwater basin in Sydenham, known as ‘The Pit’, holds stormwater as part of Sydney Water’s extensive network. It is a large-scale trap which prevents silt and waste from polluting connected waterways, such as Cooks River, and the surrounding biodiverse environments.

The Pit is located next to Sydenham Station and its sandstone walls and pumping station were constructed in the 1940s.

Sydney Water’s Integrated Stormwater Team Manager, Robert Allen, said emptying The Pit was crucial, taking a crew of more than 10 people armed with trucks and excavators over a week to complete.

“This project has seen the equivalent of 4100 wheelie bins’ worth of silt and debris removed from The Pit. Considering we undertake this project every two years, this is a substantial volume of debris,” Allen said. “During heavy rain events like we are currently experiencing, this proactive work at The Pit has been crucial to help protect the nearby areas and waterways from flooding due to the massive volume of water in our stormwater network.

“For example, during a heavy rain event in 2022 we saw The Pit reach nearly 40% capacity — this is the fullest it has been in recent years. Thanks to this emptying work the teams have just completed, we are just above 20% capacity despite the huge deluge that has been battering Sydney this week.”

The Pit temporarily holds water from the Marrickville West channel before slowly pumping it to the Marrickville East channel, draining into the Cooks River. The presence of silt in The Pit decreases its storage capacity, increasing the risk of flooding during heavy rain events. If the material moves further downstream, it could block other channels and impact aquatic habitats.

“Imagine every piece of rubbish, dust and dirt you see on the roads and in the gutters around your area ... all which is destined to end up in our stormwater channels eventually, as it washes down the stormwater drains you see on the side of the road,” Allen said. “Those drains ... mainline to our beautiful waterways and The Pit help us to clear some of the mess and protect our waterways as stormwater goes on the next stage of its journey.”

Emptying The Pit is a delicate operation involving a variety of pumps, a combination jet-vac truck, front-end loaders, posi tracks, excavators, and various additional trucks and trailers. It is heavily weather-dependent, as trucks risk being trapped in The Pit if there is sudden flooding.

The Pit holds 100,000,000 L of water at capacity. Creating an environment where it can hold stormwater without being impeded by silt and debris is said to be of great benefit to the surrounding area.

“The Pit has been operational for 80 years and is like a big bathtub, holding stormwater back and keeping it in the catchment so it doesn’t all flow into the channel at once and flood areas nearby,” Allen said. “It plays a big part in protecting the area and, by cleaning it out, we can increase the capacity of The Pit. This means it can hold even more stormwater if there is a big weather event.”

There are over 70 stormwater catchments managed by the Integrated Stormwater team at Sydney Water, including approximately 80 gross pollutant traps (GPTs), which catch rubbish in waterways so it can be removed from the environment.

“We see a lot of single-use plastic drink bottles and takeaway containers in the GPTs, demonstrating the personal impact of everyone’s litter disposal on our waterways,” Allen said. “The public can greatly impact the preservation of areas like the Cooks River by making little changes such as disposing litter appropriately.”

Sydney Water said that emptying The Pit is very important for the waterways which snake through Greater Sydney. Clearing these materials helps to prevent erosion and flooding downstream, and preserves the delicate ecosystems depending on the waterways to survive.

“So many people are surprised when they realise the huge structure they have been passing while on the train serves such an important role. It’s a very interesting piece of history in the area,” Allen said. “Removing this rubbish and sediment greatly impacts the creatures who call the Cooks River home, with the clarity of the Cooks River directly corresponding to the work done at The Pit.

“Too much sediment from these built-up areas can really choke up the waterways and create an uninhabitable environment where not enough sunlight is getting through, and this murkiness can directly impact fish populations.”

Image caption: ‘The Pit’ is a heritage-listed stormwater basin in Sydenham. Image supplied.