6. Improve overflows


Sydney’s sewer system is over 100 years old, and built for a smaller city. So, when it rains, stormwater can flow into the sewer system, causing it to overflow into our creeks and rivers. Understanding where, when and how this happens and putting measures in place to stop it are an essential part of making our river swimmable again.


Improve water quality outcomes through targeted wet weather overflow management, focused on those overflows impacting existing and proposed swimming sites.



Lead Agency

NSW Environment Protection Authority and Sydney Water.

Current measure

Overflows in the Parramatta River catchment meet all EPA licencing conditions.

Status Update

Sydney Water is working closely with the EPA to prioritise wet weather overflow abatement works in the Parramatta River catchment. Planned works are prioritised following a risk-based approach that considers multiple factors such as the frequency and volumes of Wet Weather Overflow discharges, the sensitivity value and use of the receiving environment and the cumulative impacts of multiple discharges.

The current priority is the Upper Parramatta Stage 1, which is a Source Control project. The assets are mainly Emergency Relief Structures (to manage and avoid heavy wet weather overflows discharging into customer properties or public areas). The design and delivery solutions included repairs of existing relief structures and new constructions, including concrete chambers, headwalls, pipes, duckbill valves, and in-line check valves.

Progress Timeline

March – June 2020

  • Delivery in Upper Parramatta River catchment to be completed by 1 June. On 5 May, 43 sites have been completed, two are in construction and two have not started (all of these in Baulkham Hills). Balance structures are expected to be completed by 30 June 2020. Once completed modelling and gauging will be undertaken to measure the reduction in frequency and overflow volumes.
  • Middle Parramatta River overflows in planning phase with initiation expected in July 2020.
January – March 2020

  • Delivery in progress.
  • 30 out of 47 overflow structures have been repaired/constructed in the Upper Parramatta catchment. Balance structures are expected to be completed by 30 June 2020.
October – December 2019

  • Delivery commenced.
  • 17 out of 47 overflow structures have been repaired in the Upper Parramatta catchment.
July – September 2019

  • Planning for Upper Parramatta River source control works program (inflow reduction) finalised and business case has been approved. Delivery is due to commence.

Useful Links

Review of Sydney Water Corporation’s sewage treatment Environment Protection Licences.