Wianamatta South Creek – Cumulative Impacts on Flooding Policy

The Wianamatta South Creek Catchment Flood Study Cumulative Impact Assessment (2023) highlighted that new development in some parts of Wianamatta South Creek could affect the height and extent of flooding upstream and downstream of the development.  

The policy has been created to support ongoing development in the catchment while limiting cumulative impacts from flooding.    

If these cumulative flood impacts are not managed, the studies show that the height and extent of floods in the catchment would likely increase above those previously anticipated.

The policy applies to identified critical flood areas and controlled vegetation densification areas in the Wianamatta South Creek floodplain between the M4 motorway to the north and Bringelly Road to the south.  

The policy generally only applies to land currently located within the existing flood planning area. Most of the affected land is currently used for recreation, conservation or special purposes. For further details, please refer to the maps identified in the policy. 

The policy is intended to apply to all levels of planning from local to strategic – including regional planning, strategic land use planning and development assessment.

Any new development within the policy application area needs to consider the policy. The policy outlines the considerations and information required.

Critical Flood Areas are where any development can impact flood behaviour (flood heights and flows). These areas are identified as the floodways, high level floodways and critical flood storage in the Wianamatta South Creek Catchment Flood Study Cumulative Impact Assessment released by the NSW Government in 2023.  

The extent of the Critical Flood Areas in Wianamatta South Creek is based on flood modelling completed in the Wianamatta South Creek Catchment Flood Study Cumulative Impact Assessment.

Critical Flood Areas are vulnerable to change, and if altered may impact flood flows and heights in other parts of the catchment.  

This is different to simply identifying the 1% Annual Exceedance Probability (AEP) flood level. The government identified key areas that are generally within the 1% AEP flood level where development could negatively impact existing residents and businesses.  

This information was published in the Wianamatta South Creek Catchment Flood Study Cumulative Impact Assessment.

The NSW Government supports the benefits to the community and our environment from urban greening. The policy identifies areas – Controlled Vegetation Densification Areas – where increased vegetation should balance ecological and flood considerations by encouraging the appropriate selection of vegetation types and planting arrangements.

This policy has been developed to address planning related recommendations from the Wianamatta South Creek Flood Study: Cumulative Impact Assessment (Advisian, 2023) prepared by Infrastructure NSW.      

The Wianamatta South Creek Catchment Flood Study Cumulative Impact Assessment (2023) recommended that no cut, fill, increased vegetation densification or physical structures that could impede the path of floodwaters occur in the identified floodways, high level floodways and critical flood storage areas. Allowing these activities could result in significant increases to flood levels for existing and future development in the catchment.    

The policy was exhibited for public feedback from 21 July to 29 August 2025. The information received helped shape the final Wianamatta South Creek Cumulative Impacts on Flooding Policy.