What is the Catchment Remediation Rate (CRR)

The 1970s and 1980s saw the increasing urbanisation of Hornsby’s sensitive bushland catchments and an influx of tens of thousands of new residents. Sediment runoff from developing and newly developed residential areas and nutrient pollution from sewage treatment plants contributed to the deteriorating quality of local creeks and estuaries.

Unsavoury smells from the natural waterways became more potent and more common; algal blooms were becoming more substantial and more frequent; run off and sewage overflows in wet seasons became more difficult to manage; frog watchers noted the loss of familiar species; recreational fishermen caught fish with black livers; bush walkers watched weeds intrude into relatively pristine natural reserves; indigenous plants died or were depleted by theft; and locals watched the sea grass retreat under increasingly muddy water.

Source: A New Legend – The Story of the Berowra Creek Community Contract(PDF, 10MB)

By the 1990s it was clear that Hornsby Shire’s waterways were under severe stress. Berowra Creek was being despoiled by instances of fish kills and algal blooms. Urgent action was needed.

To force the State Government to see how desperate the situation was Hornsby Shire Council placed a moratorium on the processing of any development application located within the West Hornsby Sewage Treatment Plant’s catchment area until action was taken.

The strategy worked and in April 1994 a Statement of Joint Intent (SoJI) was signed between Hornsby Shire Council, NSW Government, Environment Protection Authority, (Sydney) Water Board and the Hawkesbury-Nepean Catchment Management Trust. The principal intent behind this “community contract” was the ecologically sustainable development of Berowra Creek catchment and recovery of the environmental health of the Creek.

• Original Signed Statement of Joint Intent (SoJI) 1994(PDF, 611KB)

The SoJI not only acknowledged the significant impacts of polluted urban stormwater run-off but instigated the upgrading of the West Hornsby and Hornsby Heights Sewage Treatment Plants (reducing nutrients through increased levels of wastewater treatment) and the creation of the CRR.

• Water quality / biological treatment of stormwater pollution
• Reduction of pollution loads impacting the terrestrial environment and waterways
• Enhancement and protection of indigenous habitat
• Reduction of wastewater flows and flooding impacts
• Reduction of the dependency of potable water and cost savings from reusing water
• Engagement of WSUD, ecological sustainability and water conservation practices.

Biofiltration basins (a.k.a. Bio-basins)

Bio-basins are landscaped vegetated basins used to slow and treat stormwater runoff. Stormwater is directed into the basin where the stormwater percolates downwards through almost a metre of loamy sand, removing pollutants (e.g. nutrients and heavy metals) through physical, chemical and biological processes, including filtration, plant uptake and microbial activity.

Gross Pollutant Traps

Gross pollutant traps can be nets, screens, racks or underground vaults that capture gross pollutants such as litter, organic matter and coarse sediment from stormwater runoff.

Stormwater harvesting

Harvested stormwater is treated and stored for reuse in sports field irrigation. Stormwater harvesting collects runoff water from pipes and surface drains whereas rainwater harvesting collects water directly from roofs.

• Maintenance of stormwater quality improvement devices
• Water quality monitoring and research
• Environmental education
• Street sweeping
• Industrial auditing
• Emergency spill response
• Environmental compliance and management.

Cleaner Water Starts Here: New Gross Pollutant Traps in Hornsby Shire

Council is installing two new high-performance vortex-style Gross Pollutant Traps (GPTs) to help protect our waterways by capturing pollution before it reaches our creeks and rivers. These smart devices are designed to trap litter, sediment, vegetation, and nutrients—making a big difference to the health of our catchments.

Projects scheduled for Construction in 2024/2025

Bridge Road, Hornsby, Gross Pollutant Trap

A new GPT is being installed along the open channel at Bridge Road, targeting pollution from a 43-hectare urban catchment. Once operational, it will:

• Capture pollutants larger than 1mm
• Remove up to 40 tonnes of pollution each year
• Help reduce the amount of waste entering Berowra Creek, making it a cleaner, more enjoyable place for everyone

Pecan Close, Cherrybrook Gross Pollutant Trap (GPT)

• A gross pollutant trap (GPT) is planned for construction at Pecan Close to improve the performance of the existing biofilter.
• The GPT is expected to annually remove around 17 tonnes of pollutants captured from the surrounding 17-hectare catchment area.
• It will be an underground vortex style GPT.
• The addition of this GPT will allow the bio-basin to better remove the dissolved pollutants in the stormwater.

Derribong Place, Thornleigh Gross Pollutant Trap

• A gross pollutant trap (GPT) has been designed for Derribong Place. This device will complement the other gross pollutant traps within Larool Creek catchment.
• The GPT is expected to annually remove around 100 tonnes of pollutants captured from the surrounding 130-hectare catchment area.
• It will be an underground vortex style GPT.

Edward Bennett, Cherrybrook, Gross Pollutant Trap

Another GPT is being installed at the end of Pecan Close, Cherrybrook. This device will:

• Remove up to 20 tonnes of pollution annually
• Connect to the existing stormwater harvesting system, increasing the amount of water we can reuse for irrigating the sports field
• Support our goal of smarter, more sustainable water management

Projects Planned for Design in 2024/2025

All designs will be advertised for public consultation.

The Lakes of Cherrybrook

• The Lakes of Cherrybrook will have 2 GPT’s designed during the 2024/25 financial year, one for each inlet.
• They will both be underground vortex style GPT’s. Together they are forecast to capture up to 32 tonnes of pollution each year.
• The goal will be to improve the amenity of the Lakes of Cherrybrook.

Wetland investigations and design

• Council will undertake investigations and design at 3 wetland locations.
• The designs will improve the performance of the wetlands for pollution capture, habitat values, urban cooling and amenity.
• If the investigations are favourable, Council will proceed to detailed design.
• Possible locations include Lakes of Cherrybrook, Clarinda Wetlands and Walumeda Wetlands.

The CRR assets are maintained through a regular and proactive maintenance program which ensures the stormwater quality improvement devices are operating to their full potential thereby resulting in a better environmental outcome.

Maintenance activities are provided by external qualified and experienced contractors and are selected through a competitive tendering process.

Stormwater harvesting is a sustainable water reuse initiative that captures, treats, stores, and reuses stormwater — primarily for irrigating Council parks and sports fields. This approach supports greener parks while conserving valuable drinking water supplies.

Over time, Hornsby Shire Council has progressively installed stormwater harvesting systems across a number of key community sites, including:

• Pennant Hills Nursery
• Greenway Park
• Orara Park footpath(JPG, 223KB) (Mark Taylor Oval)
• Berowra Oval
• Foxglove Oval
• Epping Oval(JPG, 428KB)
• North Epping Oval(JPG, 454KB)
• Thornleigh Oval
• James Henty Oval
• Pennant Hills Park Synthetic Soccer Field(JPG, 258KB)
• Asquith Oval(JPG, 227KB)
• Rofe Park
• Storey Park
• Normanhurst Park
• Edward Bennett Oval

These systems typically include a gross pollutant trap, biofiltration process, storage tanks, and in many cases, UV treatment, ensuring the water meets safety and quality standards for reuse.

Key Benefits of Stormwater Harvesting:

• Reduces demand on potable (drinking) water supplies, especially during dry periods
• Reduces volume of polluted stormwater runoff, helping to protect local creeks and waterways
• Improves the quality of stormwater through on-site treatment processes such as pollutant screening, biofiltration and ultraviolet (UV) disinfection
• Promotes a water-wise culture, supporting Council’s sustainability goals and encouraging the community to adopt responsible water use practices

Stormwater harvesting forms part of Council’s broader commitment to integrated water management and environmental stewardship. By turning a once-overlooked resource into a valuable asset, we are improving liveability, resilience, and the health of our local environment.