Reducing stormwater in the sewer


We are working towards sustainable solutions for reducing stormwater in the sewerage system (inflow and infiltration) in Mullumbimby.

Ideas and input are sought from anyone with an interest or view on stormwater, sewerage or inflow and infiltration reduction in Mullumbimby.

Council is committed to providing a sanitary sewerage system for the safety, health and well being of our community and conservation of our natural environment.

An improved sewerage and stormwater network is needed to better accommodate the area’s growing population and more extreme weather in the future.

A good sewerage network requires a combined approach from Council and community.

This process will help Council better understand the scope of inflow and infiltration in the Mullumbimby area, assist with providing the most sustainable solutions and help to better plan for future infrastructure.

Water sensitive urban design is being considered as one sustainable mode of reducing the amount of stormwater that ends up in the sewer as well as complimenting street aesthetics and potentially lowering the air temperature of public spaces.


Stormwater that incorrectly enters the sewer system rather than the stormwater system is called inflow or infiltration.

Inflow is caused by runoff from hard surfaces, such as roofs and driveways, which enters the sewer system through incorrectly installed downpipes, drains or low lying gully traps(External link) that overflow when it rains.

The gully trap prevents smells and overflows from entering buildings. They are usually located outside your house, generally in the area outside your kitchen, and should be above ground level to ensure stormwater does not enter it.

Infiltration is groundwater, or stormwater that seeps into the ground, then incorrectly enters the sewer system through defects or leaks in sewer pipes or joints.

The cause is generally cracked sewer pipes that have deteriorated from age, been placed under pressure from local development and heavy traffic, suffered damage from tree roots or have been poorly installed or maintained. Groundwater then enters or infiltrates through the cracks in the sewer pipes.

Infiltration usually occurs where the groundwater is higher than the sewer pipe or where soil above the sewer system becomes saturated. Leakage increases over time.





Stormwater can cause problems, such as erosion, and transports nutrients, chemical pollutants, litter and sediments to waterways.

When stormwater or groundwater incorrectly enters the sewer system it can cause problems and increase costs for the community as:

  • Private residences and businesses can experience property damage from flooding as sewage pipes become overloaded and stormwater does not drain away quickly enough;

  • The health of our waterways and its users can be compromised by overflow from the sewerage system when it enters our rivers and creeks;

  • Roads and surfaces deteriorate with surface flooding and poor drainage, increasing maintenance costs for Council and ratepayers; and

  • Electricity and treatment costs at the sewage treatment plant increase to process the extra water in the system.


What is the Reducing Stormwater in the Sewer project?

Byron Shire Council has embarked on the Reducing Stormwater in the Sewer project which is looking at improvement to both the stormwater and sewerage networks. The aim is to achieve a controlled level of stormwater that enters the sewer system yet does not exceed the capacity of the sewerage network.

Council has conducted flow monitoring of the sewerage network to better understand how it operates during rainfall events. Inspection of Council’s sewer and stormwater mains and residential sideline connections, sewer and stormwater pipes will also occur to assist in identifying problem areas.

Additionally, Council is looking at implementing Water Sensitive Urban Design(External link) to reduce the amount of stormwater that enters the sewerage system.

The program has received funding of $5 million over five years, with $2.5 million allocated towards the worst affected area (Mullumbimby). The program will be initially implemented at Mullumbimby.


  • The efficiency of the sewerage network will be improved as the identification of defected pipes will prompt urgent repairs. 

  • Costs of damage to personal property and homes will be reduced as efficient plumbing systems and sideline connections reduce the risk of stormwater overflow and localised flooding.

  • The risk of wastewater overflow into residential properties and street frontages will be reduced. 

  • Electricity and maintenance costs of sewage pumping stations will reduce.

  • Risk of pollution to local rivers and creeks will reduce and the biodiversity and health of the waterways and its users will be protected. 

  • Street aesthetics and stormwater drainage in Mullumbimby will be maintained or improved. 

  • Reducing water waste and using water more efficiently will help protect Mullumbimby’s water source for the future.


Why has Mullumbimby been chosen for the Reducing Stormwater in the Sewer project when other areas in the Shire also flood?

Mullumbimby is the worst affected area in the Byron Shire and experiences a significantly high level of stormwater infiltration and inflow into the sewer during rainfall events. The CBD area in Mullumbimby in particular is affected by inflow.

Mullumbimby is a low lying, flood prone area that is adjacent to a river and receives a high annual rainfall.

In a storm or rain event, the intensity of water is high and quick. In low lying areas, the stormwater gathers on the surface and can enter the sewer system rather than draining into the stormwater system. Inflow and infiltration has been a recurring problem for Mullumbimby since the 1960s, when the sewerage network was first constructed.

Other areas of the Byron Shire will also receive assistance with the reduction of stormwater into the sewer. The investigation stage has commenced in these areas.


Inspections of Council’s stormwater and sewer mains in the Mullumbimby CBD area were done in 2019 by authorised specialist contractor, Interflow.

Interflow advised residents via letter prior to inspection and door knock at time of inspection.

Property inspections by Council may also occur in the future.  Further information will be available to residents should this occur.

Council and specialist contractor, Interflow used a variety of inspection methods to identify sources of stormwater inflow and infiltration into the sewer in Mullumbimby.

Standard inspection methods included camera and visual inspection, and non-toxic smoke testing.


Smoke testing involves the pumping of non-toxic, non-staining coloured smoke into a public or private sewer or manhole during dry weather.

Possible sources of stormwater inflow, infiltration or cracked pipes are identified at points where the smoke becomes visible, such as from yards, roof gutters or pipes.


Camera inspection will be limited to Council mains and connections only. At this stage, there are no planned camera inspections of private connections, however, if this becomes necessary, Council will advise affected homeowners by letter prior to inspection.

Camera inspection is carried out by specialist contractors, Interflow. It enables a detailed visual inspection of sewer and stormwater pipes without the need for manned entry.

A camera is placed inside Council pipes and any obstructions, defects or cracks can be seen. Camera inspection is below ground or inside pipes only.


Pumping station systems for Mullumbimby were upgraded in 2009-2010, which have contributed to resolving the majority of sewage overflow or septic backup in residential areas, however significant stormwater overflow issues (from inflow and infiltration) still occur.

Flow monitoring: Flow meters were installed into the sewer network with drawdown tests and ultrasonic level sensors, as well as rain gauges and weather stations, which recorded and provided data on rates of stormwater flow and levels of sewerage inflow and infiltration.

Inspections: Inspections of Council mains have commenced with specialist contractor, Interflow, conducting smoke testing and camera inspections in the Mullumbimby CBD area. 

Pump system trials: A pilot project is underway with different pump systems being trialled on connection points to Council mains. Both Vacuum Sewer and Low Pressure Pump Systems are being tested to ensure sustainable solutions are found for the wet silty, clay soil areas which can present high risks for cracks and leaks, while also considering electricity and maintenance costs of such systems.

Water Sensitive Urban Design: Concepts are in development for the use of Water Sensitive Urban Design to help drain areas of Mullumbimby’s CBD that are at high risk of stormwater overflow. Council is working with contractor, Australian Wetlands Consulting (AWC), to identify opportunities and design a customised range of solutions to be implemented in the Mullumbimby area. Projects will be implemented in consultation with community. The project is at draft concept stage and pilot projects will be announced for community feedback soon.


Water Sensitive Urban Design uses raingardens, raised garden beds, rainwater tanks and planted swales (gutters) to capture stormwater, slow the flow and either hold it, or repurpose it from being released into the sewer network.

Intercepting stormwater and redirecting it towards garden beds of native Australian plants, either on private lots or street gardens, benefits the treatment plant downstream as well as low lying areas that traditionally flood.

The staggered or slowed release of captured stormwater reduces the impact on the sewerage network and the environment. 

There is opportunity for raingardens to incorporate onsite treatment systems to reduce nitrogen and phosphorus levels in stormwater to safe environmental levels so that it can be released back into the Brunswick River. 

Australian Wetlands Consulting (AWC) is an industry leader in ecological consulting, stormwater, wastewater and catchment management and has been contracted by Council to design a custom solution to reduce stormwater inflow and infiltration into the sewer in Mullumbimby.

The suite of devices will aim to capture the maximum volume of water required to reduce the pooling of stormwater in Mullumbimby’s back lanes and street swales.




The stormwater drainage problems in Mullumbimby are diverse. There are a number of narrow rear laneways with only one drainage point and swales adjacent to roads that are in poor condition and do not drain adequately. 

AWC will be proposing a number of street-based garden and landscape projects which aim to maintain the character of Mullumbimby while improving stormwater drainage.

The projects are currently at concept stage and will be presented for community feedback. The concepts are based on data received from flow meters and rainfall gauges. 

Three pilot projects are planned for three target locations based on flow data. Locations include a laneway and Council Chambers. There will be opportunity for the community to have creative input.

The laneway pilot project proposes a formalised planted swale on one side of the lane and a planter bed on the other side to absorb surface water. A raised raingarden will soften the laneway aesthetic and capture rainwater before it reaches the swale.

The Council Chambers pilot project proposes to demonstrate how raingardens reduce surface flooding from downpipes and divert stormwater from the sewerage system. A planter bed raingarden at street level (half metre wide tank filled with plants and drainage system on the bottom) will capture stormwater as it is released from the downpipes and intercept it from the footpath.

Further street-based edible and Australian native raingarden projects will be investigated once community has provided feedback. Council will also provide information to residents on how to install DIY rainwater gardens on private properties. 

There is no significant increase in Council maintenance costs of Water Sensitive Urban Design. This will be a consideration in the design process.



In response to community concern about flooding and overflow incidents in the community, Council will use Water Sensitive Urban Design to help absorb excess stormwater as a low impact and long term, sustainable solution.

Mullumbimby’s leafy wide streets currently have grassy nature strips with mature trees offering valued shade. Some have edible street gardens, pockets of parking sealed with permeable, functional materials. All lend to a relaxed, walkable and spacious feel.

The town’s rear lanes, although narrow, are highly valued as they maintain a connection with the service and industrial architecture of the past, but deliver a more pedestrian and cycle friendly space.

The Water Sensitive Urban Design projects aim to enhance Mullumbimby’s low scale, 'country town' feel and landscape character with further street-based garden projects.

The use of greening techniques to create cooler microclimates, capture stormwater and continue to combat the urban heat island effects in the town centre are all important to the delivery of a high-quality, attractive environment. Well blended planting of local indigenous trees and vegetation will create a connection to the caldera as well as provide shade, shelter and ecological benefits.

Mullumbimby’s ‘heritage’ look and feel will not only be maintained through Water Sensitive Urban Design projects, but will benefit from better stormwater drainage in private residences and street frontages. Flooding will be reduced, street aesthetics will improve, public spaces will be greener and cooler.