Flooding is caused by heavy rainfall. During heavy rainfall, flooding events can occur in two ways: 

• Mainstream flooding, where creeks and rivers can overflow, break their banks and flood nearby low-lying areas and properties. These flows may be several metres deep and relatively fast moving. This is also known as riverine or fluvial flooding. 

• Local overland flooding, occurs during rainfall events where the drainage system reaches capacity and stormwater then flows aboveground, following the low areas of the landscape. This type of flooding usually subsides quickly but can still be fast flowing and dangerous. This type of flooding will always occur to some extent as it is not practical or possible to provide piped systems to cater for every conceivable storm event. This is also known as flash or pluvial flooding. 

Flooding cannot be completely prevented. Flooding is a natural part of how rivers work and will always be a possibility when we experience large amounts of rain in a catchment. However, infrastructure and development can be designed to reduce the impacts and risks of flooding by slowing the water down, stopping it reaching certain areas, or by making space for the water to move. 

If the situation is life threatening you should call 000. 

For other assistance during an emergency such as flooding or storm damage, please contact the NSW State Emergency Service (SES) on 132 500 or visit their website. 

The State Emergency Service also provides advice on how to manage your flood risk on their website. 

The Flood Planning Level (FPL) is a height used to set floor levels for property development in flood prone areas. It is generally defined as the 1% AEP flood level plus an appropriate freeboard (see explanation of ‘freeboard’ below). This level may be higher for vulnerable land uses (e.g. hospitals or schools). 

The Flood Prone Land Policy and Flood Risk Management Manual guide local government in their approach to managing flood risk in their communities. Flood studies identify flood behaviour including the areas flooded, water depth, hazard categories and the likelihood of flooding within the catchment. Floodplain Risk Management Studies and Plans assess potential management approaches to reduce the impact of flooding, such as drainage upgrades, development controls, community awareness and emergency response arrangements. 

The term probable maximum flood (PMF) refers to the largest possible flood. While extremely rare, there have been a few floods in Australia that have approached the magnitude of a PMF. The recent flood at Wilsons River at Lismore on February 2022 reached a level at 14.4m Australian Height Datum (AHD) and was higher than the 1 in 100 year flood level of 12.38m AHD. The PMF defines the maximum extent of a floodplain. It is calculated to aid in the design of critical facilities such as hospitals, nursing homes, schools and emergency service facilities. 

NSW Councils have responsibility for identifying and managing flooding and informing the community. Councils follow the NSW Flood Prone Land Policy, which outlines how Councils should manage flooding to reduce the risk to people and properties. 

Councils prepare Flood Studies and Flood Risk Management Plans in accordance with the NSW Government’s Flood Risk Management Manual (2023). The recommendations are implemented with the technical and financial assistance of the NSW Government and key stakeholders through the Flood Prone Land Policy. 

Council’s piped stormwater system is designed to convey water from frequent minor storms with the aim of reducing day-to-day nuisance flooding, while major storms are conveyed via overland flow paths with the aim of protecting life and property in major events. It is impractical and cost prohibitive to provide piped drainage systems for major storm events. 

Council’s stormwater drainage network comprises of stormwater pits, pipes and open channels. Like all drainage networks, it is designed to manage minor, more frequent storm events. In major storm events, runoff that is not captured by the drainage network must flow overland. Our roads and valleys are usually the primary overland flow paths. 

Council is required under State Government legislation to advise impacted property owners that their property has been identified as potentially flood affected. Any property which is identified as being flood prone has a notation placed on the property’s Section 10.7 Planning Certificate. This is the same process for any other identified potential hazards, such as bushfire, landslip, coastal hazards or contamination. This notation indicates that flood related development controls apply to the land. This simply means that a development proposal on the land, such as a new house would need to consider the flood risk so that the future occupants can live safely on the land. 

The Duck river, Duck creek and A’Becketts Creek catchment covers an area of 42 km2 and includes the suburb of Granville South, Granville, parts of Regents Park, Auburn, Merrylands etc. Refer to the map on Council’s website found Have Your Say Flood Area Map

A 1% annual exceedance probability (AEP) flood represents a 1% chance of flooding occurring in any year. This is a large but rare flood. It was previously known as the 1 in 100-year recurrence flood. 

A 1 in 100 year or 1% AEP flood is a flood event that has the probability of occurring on average once every 100 years. This does not mean that if a location floods one year that it will not flood for the next 99 years, or if it hasn’t flooded for 99 years then it will flood the next year. Some parts of Australia have experienced more than one 1 in 100-year floods within a single decade. 

Council’s flood modelling will determine the extent of flooding throughout the catchment and the identification of properties partially or fully impacted by flooding. 

Floods do not occur in a regular pattern. There may be a period of no floods and a period of several floods. For example, the last time the Brisbane River flooded before the 2011 event was in 1974. Residents who moved there in more recent times may never have experienced flooding as an issue until the floods in January 2011. 

A freeboard is a height above the 1% AEP flood level that is included in the Flood Planning Level to account for factors such as wind, waves, unforeseen blockages, other localised hydraulic effects. Freeboard is usually 0.5m above a flood level. 

The flood planning area is the area within which developments may be conditioned with flood related development controls. The flood planning area is calculated as the area below the Flood Planning Level. 

The current study will not have any impact on your rates. Council collects rates from residents and business based on property values set by the Valuer General. 

Council’s DCP lists controls to minimise the impact of flooding on proposed developments, as well as the impact of the proposed development on flooding. These controls relate to floor levels, building components, structural soundness, flood effects, car parking, evacuation requirements, management and design. Different controls may apply depending on the nature of the proposed development and nature of flooding. 

House prices vary with changes in the real estate market and are based on a large range of criteria such as location, size, age, inflation and interest rates. These factors are outside of Council’s control. Ultimately, it is the market that determines the value. 

Flood studies or floodplain risk management plans are not prepared by councils for, or on behalf of insurance companies. Flood studies are a legal requirement for Council to complete and part of our responsibility to help manage flood risk in the community. These studies do not prevent the sale or purchase of property but may impact how the land can be developed in the future. 

Insurance companies rely on their own assessment of risk and use their own methods to identify flood risk. 

The Insurance Council of Australia have indicated that insurers already have extensive data on flood risk that is priced into premiums. Further information on flood insurance is available from Flood Management Australia Flood Insurance Fact Sheets. 

Properties can be identified as being flood affected, in accordance with Council’s policy, regardless of the current floor levels in the building. This is to ensure any future developments on the property are built appropriately for the flood planning area and not built below the flood levels. 

Development over many years has left many areas with a legacy of undersized infrastructure which cannot adequately carry water from storms. It has also removed many natural creek or open water surface bodies in the catchment areas that would have previously accommodated stormwater. This can result in flooding in some properties. Council undertakes upgrades of its piped stormwater system on a priority basis across the local government area as funding allows. 

Members of the public can make a written submission to Council to raise any concerns related to flood related issues. You can provide your valuable feedback and comments by emailing Council at council@cumberland.nsw.gov.au 

Climate change will be considered in the Flood Study. Rainfall data is used to develop the flood study model. The model will be reviewed periodically as changes occur to rainfall patterns and guidelines are established. 

Consultation is open to anyone who is interested in flood risk management in the study catchment area.

Residents, property owners and business operators affected by flooding in the areas of the Duck River, Duck Creek and A'Becketts Creek catchment areas, including Granville South, Granville, Regents Park, Guildford, Auburn, Merrylands and Chester Hill, are particularly encouraged to provide feedback. 

As a local resident or business owner, you have probably witnessed first-hand the impact of minor or major storm events in your local streets, parks and on your property. Community feedback and input into Council strategies and plans during public exhibition periods helps Council ensure they meet the needs of the community. 

Community consultation is also an important part of the process for the development of Flood Risk Management Studies and Plans as outlined in the NSW Flood Risk Management Manual. 

Feedback will be considered and incorporated where appropriate in the overland flood study. The document will then be presented to the Cumberland City Council Floodplain Management Committee for endorsement, and then to the Council for adoption. Once adopted, Council officers will begin seeking grant funding and working to implement the Plan.