Hornsby Creek Catchment is one of many small creek sub-catchments located within the larger Cowan Creek Catchment.
The Cowan Catchment is one of the four major catchment areas within the Hornsby Shire LGA, alongside the Berowra Creek, Hawkesbury River, and Lane Cove River Catchments (refer to Map of the 4 Catchments of Hornsby Shire). The catchment includes three Local Government Areas (namely Hornsby Shire, Ku-ring-gai and Northern Beaches Councils).
The Cowan Catchment covers an area of approximately 16,430 hectares in an area bounded by the Hawkesbury River, the Pacific Highway, Telegraph Road Pymble, Mona Vale Road, McCarrs Creek Road, and West Head Road. Approximately 80% of the catchment is protected within the Ku-ring-gai Chase National Park, the second oldest national park in Australia.
The Pacific Highway ridgetop marks its western boundary in Hornsby Shire, while Cockle and Cowan Creeks form the southern and eastern local government boundaries. Land-uses in the southern part of the Catchment include extensive light industrial areas, large commercial shopping centres and developed urban areas.
Understanding the Hornsby Creek Catchment
Hornsby Creek Catchment (HCC) forms part of the larger Cowan Catchment. Covering an area of 334 hectares, HCC includes urban, commercial, and industrial zones and stretches from Waitara to its confluence with Cockle Creek. (refer to the Hornsby Creek Catchment Maps)
Hornsby Creek flows for 2.2 km in a north-easterly direction from around Waitara Station to where it converges with Cockle Creek next to the M2 motorway. Hornsby Creek and Cockle Creek are tributaries of the Cowan Creek estuary.
The catchment is characterised by rapid urbanisation and industrial activities, with growing populations and land-use changes placing significant pressure on its natural resources. Despite these challenges, riparian vegetation and bushland is present along the main creekline with varying degrees of weed infestation and waste accumulation.
The majority of the small tributary feeder creeks flowing into Hornsby Creek have been piped and developed. Several small sections of creekline still remain unpiped and open to the sunlight (e.g. within Edgeworth David Reserve between Burdett Street and Northcote Road, and between Denison Street and Bridge Road).
The land around Leighton Place and Salisbury Road, located adjacent to Hornsby Creek, is essentially an industrial area comprising industrial units suspended on concrete slabs constructed on very steep hills of Hawkesbury Sandstone. The southern section of the catchment, towards Waitara Station, the Pacific Highway and Alexander Parade, is primarily zoned residential and commercial.
Challenges facing Hornsby Creek
Urbanisation has caused "urban stream syndrome," which impacts creeks by altering water flow, increasing pollution, and harming ecosystems.
Stormwater runoff is the main issue, carrying pollutants like litter, oils, sediments, bacteria, and heavy metals into the creek. These pollutants come from various sources:
- Point sources: Specific discharge locations, like stormwater pipes or industrial sites.
- Diffuse sources: Pollutants washed from large areas, such as shopping malls, roads, parks and yards.
Traditionally, urban stormwater management has focused on channelling stormwater into local waterways to reduce localised flooding, often with little regard for its environmental impact. This approach has contributed to the decline in water quality. However, newer design strategies, such as Water Sensitive Urban Design (WSUD), are being implemented to better protect urban waterways by integrating stormwater management with natural systems.
Specific sources of pollution in Hornsby Creek are not always certain, but the activities and infrastructure within the catchment suggest possible contributors. Monitoring has shown that pollutants from residential areas, commercial zones, and industrial activities are all potential contributors to water quality issues.
Human behaviours also play a significant role in the health of local waterways. Improper disposal of waste, use of chemicals, and poor work practices can exacerbate pollution levels. Even small individual actions, such as littering or washing cars in driveways or on streets, can collectively have a major impact when pollutants are carried by stormwater into the local creek.
A key part of preventing stormwater pollution relies on responsible choices by residents and businesses. For example, using a commercial car wash or washing cars on a permeable surface helps reduce runoff. Similarly, managing the use of herbicides, pesticides, and fertilisers in gardens can prevent excess nutrients from entering the stormwater system.
Water quality monitoring has demonstrated that these stormwater impacts can make urban waterways unhealthy for primary human contact, harmful to sensitive aquatic life, and less able to support ecological balance. The interplay of land use, human activities, and stormwater runoff continues to shape the state of Hornsby Creek and its water quality.
To address these issues, Hornsby Council has implemented a number of waterway remediation projects, including stormwater management infrastructure, community education programs, and sustainable urban design practices. Funding for these initiatives is supported by the Catchments Remediation Rate (CRR), an environmental levy applied across the Shire.
Key features of Hornsby Creek Catchment
The Hornsby Creek Catchment has distinct physical and land-use characteristics:
Topography and geography
HCC generally encompasses the valley running northwards from Waitara Station and the Pacific Highway and situated between Peats Ferry Road (Pacific Highway) to the west and Hornsby Hospital to the east.
The catchment has been extensively cleared and is characterised by gentle undulating crests on sandstone plateau surface slopes with less than 10% vegetation cover. The catchment appears to have been overdeveloped with little consideration of topographic limitations.
The catchment slopes 70 metres from the ridgetop at Waitara to its confluence with Cockle Creek. Many smaller tributaries have been piped and developed. Cockle Creek continues downstream flowing under the M2, through Ku-Ring-Gai Chase National Park before entering the Cowan Creek estuary at Bobbin Head.
Land Use
- 57% of the catchment is residential
- 23% is commercial or industrial, including light manufacturing and service industries
- 4% is open space, which is very low for an urban area.
The southwest portion of the catchment includes retail and auto service industries, while the northeast has general industrial businesses on steep terrain. Hornsby Hospital and other health services dominate the eastern areas. The northwestern section includes a rail depot and high school and there is a significant concrete plant at the centre of the catchment near the creek.
Infrastructure
26.4 km of stormwater drainage and 47 km of sewerage mains.
Over 100 Stormwater Quality Improvement Devices (SQIDs) such as stormwater pit inserts, trash racks, gross pollutant traps, sediment basins and biofilters help reduce stormwater pollution.
Monitoring water quality in Hornsby Creek
Hornsby Shire Council has monitored water quality within Hornsby Creek for more than 30 years. Regular sampling and data collection has been carried out at Sampling Site 012 - located near where Leighton Place crosses Hornsby Creek (Sampling Site Location - Site 012 Hornsby Creek)
This data has provided valuable insights into the challenges facing the creek and guided efforts to improve its condition.
10-year Water Quality Datasets – Site 012 Hornsby Creek and Site 036 Murray Anderson Creek
- The accompanying datasets were collected at Sampling Sites 012 and 036 by Council’s Water Quality Officer from 2014 - 2024 and are presented here for your interpretation and analysis of the results.
- Please note there are some data gaps present due to issues such as water quality monitoring instrument malfunction and COVID lockdowns.
- In order to compare and contrast water quality results from the urbanised Hornsby Creek dataset with a more natural National Park creekline we have provided the dataset for Freshwater (Reference) Sampling Site 036 - Murray Anderson Creek, Ku-ring-gai Chase National Park. Both these sites are located within the Cowan Creek Catchment.
- Sampling Site Location - Site 036 - Murray Anderson Creek
Sources of pollution in Hornsby Creek
Stormwater runoff is a major source of pollution in Hornsby Creek, carrying both visible and dissolved contaminants into the water. During rainfall, gross pollutants such as litter, sediment, and organic matter are washed into the creek. Less obvious but equally harmful pollutants include nutrients (like nitrogen and phosphorus) and toxic chemicals, which degrade water quality.
Everyday activities contribute significantly to pollution. Overusing fertilisers, washing cars on the street (allowing detergents to enter stormwater drains), decomposing lawn clippings, and pet waste all add excess nutrients to the water.
FUN FACT: A medium-sized dog produces around 180 kg of dog poo each year!
Other potential sources of pollution include failures in sewerage infrastructure or blockages that cause dry-weather sewer overflows, further introducing contaminants into the creek.
Efforts to improve waterway health
Hornsby Shire Council’s Catchments Remediation Rate (CRR) program supports several initiatives:
- Water quality monitoring
- Installing and maintaining SQIDs like gross pollutant traps and biofiltration basins
- Stream restoration and bushland regeneration
- Street sweeping and responding to spills
- Community education and enforcing environmental regulations.
Over 400 SQIDs have been installed across the Shire to reduce stormwater pollution. These devices capture litter, sediment, and smaller pollutants before they enter waterways.
Further reading and resources
Hornsby Shire Council
Web Map CRR - Map of Hornsby SQIDs (Check out locations of Hornsby’s stormwater quality improvement devices)
Maps