Draft Floodplain Risk Management Study and Plan 2025

A Flood Study offers technical insights into the likelihood and characteristics of flooding within an area of land where water collects when it rains (catchment area). It provides comprehensive details on flood risk, including the distribution, extent, depth, levels, and velocity of floodwaters across various storm events, such as the 1% AEP flood and PMF.

A Floodplain Risk Management Study and Plan analyses flood behaviour and identifies and prioritises flood mitigation options to protect people and properties through improved planning, emergency management, and infrastructure works.

There are three main measures of managing flood risk:

• Flood modification – This approach aims to alter flood behaviour, including depth and velocity, by implementing drainage structures such as detention basins or improvements to the drainage system. Flood modification measures that have been assessed in the Study and Plan include: levees, temporary defences, channel construction and modification, major structure modification, drainage network modification, drainage maintenance and retarding basins. 
  
  
• Property modification – this approach includes modification to existing properties and aims to better manage future development through effective land use planning. Property modifications that have been assessed in the Study and Plan include: flood proofing, land use zoning, flood planning levels and areas, planning policy changes, S10.7 certificates and flood insurance.
  
  
• Response modification – this approach focuses on increasing the community flood resilience through better preparedness, improved warning, and recovery planning. Response modification measures that have been assessed in the Study and Plan include: flood warning, flood emergency management, community awareness and flood plan/recovery plans.

The PMF is the largest flood that could conceivably occur at a particular location, usually estimated from probable maximum rainfall. Generally, it is not physically or economically possible to provide complete protection against this event. The PMF defines the extent of flood prone land, that is, the floodplain.

Annual Exceedance Probability (AEP) is a term used to the express the percentage of likelihood of a flood of a given size or larger occurring in a given year. AEP is an alternative to ARI (Average Recurrence Interval) to express the likelihood of occurrence of a flood event. For example, a 1-in-100-year ARI flood or a 1% AEP flood is a flood event that has the probability of occurring on average once every 100 years, i.e. there is a 1% chance of a flood of this size occurring at a particular location in any given year. This does not mean that if a location floods one year that it will not flood for the next 99 years. Nor, if it has not flooded for 99 years that it will necessarily flood the next year.

NSW councils are responsible for identifying and managing the impacts of flooding, as well as informing their communities. They adhere to the NSW Government’s Flood Prone Land Policy, which outlines strategies for managing flooding to reduce risks to people and properties. Councils prepare Flood Studies and Floodplain Risk Management Studies and Plans in accordance with the NSW Flood Risk Management Manual (2023) and implement the associated recommendations with technical and financial support from the NSW Government and key stakeholders.

Council's drainage infrastructure is designed to manage frequent minor storms, aiming to reduce day-to-day nuisance flooding. For major storms, overland flow paths are utilised to protect life and property during significant events. It is not feasible to provide piped drainage systems for major storm events due to the high costs involved, geographic limitations, climate change, and other restrictive factors.

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. Freeboard acts as a safety margin, typically applied when designing floor levels, levee crests, and similar elevations.

Property owners must maintain the stormwater pipes, gutters, downpipes, gully pits and any other components of the approved stormwater system on a private property in good condition and in compliance with any Council requirements. If your property contains a stormwater easement it must be maintained and kept clear of obstructions to allow the natural flow of stormwater.

Property owners are responsible for maintaining the stormwater system on their property to the kerb and gutter and if maintenance is needed within the footpath area an application to carry out work within the road reserve is required. Applications are available at Council’s Customer Service Centre or on Council’s website.

If the situation is life threatening you should call 000.

For other assistance during an emergency such as flood, storm or tsunami, please contact the NSW State Emergency Service (SES) on 132 500 or visit their website at www.ses.nsw.gov.au.