FAQs

The flood risk management process is a series of studies undertaken to understand and manage the risks of flooding to the community.

The first stage in this process is a Flood Study. Flood Studies help us understand how flooding behaves across an area. To achieve this, information about how past floods have behaved is collected and computer models are developed to replicate the flood behaviour. From this, maps of flood extents, depths, velocities and flood hazard are used to increase our understanding of flooding across the community. 

This is followed by a Floodplain Risk Management Study & Plan (FRMSP) which investigates and assesses the different ways that flood risk can be mitigated for a community. These options are assessed against a range of criteria including effectiveness, practicality, and environmental impacts. The options that provide the most benefit to the community then form the plan for Council to implement, with financial support from NSW Government.  

More information can be found in the NSW Government’s flood risk management manual and toolkit.

A flood study helps Council understand how a flood behaves in a particular area so we can manage existing development and plan for future growth. It uses computer modelling to show where floodwaters go during heavy rain, how deep they can get, and how fast they might flow.

A flood study looks not only at current flood behaviour but also considers future changes, such as those caused by climate change, to help us understand how flooding might evolve over time.

As flood modelling techniques have improved, new technology allows us to more accurately understand flood behaviour within a catchment area. Flood models now map flooding from rivers and creeks, as well as local flooding from stormwater drains and overland flow.

Flood studies also help emergency services, such as the NSW State Emergency Service (SES) and Police, to better understand how flooding affects people’s safety. They also help landowners understand their own flood risk so they can be better prepared for future floods.

A Floodplain Risk Management Study is a technical and strategic assessment that looks at how flooding behaves across a catchment or floodplain, and what risks that flooding poses now and in the future.

The study builds on flood modelling to examine the consequences of flooding, not just where water goes. It considers things such as:

• how often different areas flood and how deep and fast floodwaters can be
• risks to people, homes, businesses, infrastructure and the environment
• how flood risk may change over time due to climate change, population growth or development
• how existing flood controls, drainage systems and planning rules perform during flood events

Importantly, the study does not recommend actions on its own. Instead, it identifies the nature and scale of flood risk, outlines constraints and opportunities, and sets a shared evidence base for decision-making.

Floodplain Risk Management Studies are prepared in line with NSW Government guidelines and are used to support informed, transparent discussions with the community, councils, emergency services and other stakeholders about flood risk.

A Floodplain Risk Management Plan takes the findings of the Floodplain Risk Management Study and turns them into a coordinated set of actions to manage flood risk over time.

This includes a set of rules for future development, to ensure they are prepared for floods.

The plan focuses on reducing flood impacts where possible and helping people better understand and live with flood risk where it cannot be fully removed. Actions may include a mix of:

• land use planning and development controls
• infrastructure works or changes to existing drainage systems
• property-level measures, such as raising floor levels or improving building resilience
• emergency response and evacuation planning
• community awareness, education and preparedness initiatives

Not all actions of the plan are physical works. Many relate to planning, policy, behaviour and communication, recognising that flood risk management is not just an engineering issue.

The plan also considers feasibility, cost, benefits, environmental impacts and community values. Actions are usually prioritised and staged, acknowledging that flood risk management is a long-term process rather than a single solution.

Once adopted, the Floodplain Risk Management Plan guides Council decisions, investment and engagement with the community, helping ensure flood risk is managed consistently and responsibly over time.

In NSW, Councils are responsible for local planning in their Local Government Area (LGA) including the management of flood risk.

The NSW Government provides councils with technical and financial support to manage the flood risk through the Floodplain Management Program provided by DCCEEW (Department of Climate Change, Energy, the Environment and Water). The Program exists to understand and reduce the impacts of flooding and flood liability on communities, as well as individual owners and occupiers of flood prone property.

You can find more details about flood study requirements on the NSW Government’s website.

The study area also incorporates adjoining land to the south along Captain Cook Drive including Green Hills estate. These local catchments comprise an additional area of about 5 square kilometres. 

This study will investigate flooding driven by heavy rainfall over the local catchments. This includes flooding along minor watercourses and drainage paths, overland flows along roads and through properties, and ponding of water on low-lying land.

A Floodplain Risk Management Study and Floodplain Risk Management Plan for this area was prepared in 2013 and progressed through technical review and consultation at the time. Final draft versions of both documents were completed and endorsed at a technical level, however they were never formally adopted by Council.

This means the documents were not endorsed by Council as an official policy or planning instrument, and they were not implemented as a formal Floodplain Risk Management Plan.

While the 2013 study and plan provide useful background information and technical analysis, they do not reflect current flood modelling standards, updated guidelines, changes in land use, or more recent data and guidance on climate and rainfall. As a result, Council does not rely on the 2013 documents as an adopted or current basis for decision making.

The final draft versions remain publicly available for transparency and historical reference and can be accessed on Council’s website:

• 2013 Floodplain Risk Management Study – Final Draft 
• 2013 Floodplain Risk Management Plan – Final Draft

These documents are provided for information only. Council is now progressing updated flood studies and floodplain risk management work to ensure flood risk planning is based on current data, standards and best practice.

Overland flooding happens when intense, short duration rainfall overwhelms stormwater systems, causing water to flow across land making its way to creeks and rivers.

Riverine flooding is typically caused by prolonged or widespread rainfall that leads to rivers rising above their banks, though shorter events can still create the right conditions for riverine flooding.

Flood prone land is defined in the NSW Floodplain Development Manual as all land below the level of the Probable Maximum Flood.'

A probable maximum flood (PMF) is the largest flood which can possibly occur in a given area. While extremely rare, a few floods in Australia have approached the magnitude of a PMF.  

The mapping which shows the PMF extent shows the full extent of a floodplain and is mainly used to plan for emergency access and to guide the location of critical infrastructure like hospitals and evacuation routes.  Its purpose is to help ensure community safety in the most extreme scenarios — not to define everyday flood risk.

Probable Maximum Precipitation is the greatest depth of rainfall considered meteorologically possible in a given area based on its climate and terrain, and assuming that the atmosphere is fully saturated with moisture.

A 1% annual exceedance probability (AEP) flood represents a 1% chance of occurring in any year based on a long-term average. This is a large but rare flood. It was previously known as the 100-year recurrence flood. Many parts of Australia have experienced 1% AEP floods in the past few years and some areas such as Lismore experienced even rarer floods. Just because you have had a 1% AEP flood in the past does not mean that one cannot occur again or that it will not happen for another 100 years. 1% AEP floods could even happen in the same year.

It is sometimes easier to think of this as rolling a dice with 100 sides during each major storm event - the chance of landing on the number 1 is always 1 in 100, no matter what happened in the previous events. Even if a 1% AEP event occurred recently, the odds remain the same for the next storm. 

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