Frequently asked questions

Under the NSW Government's Flood Prone Land Policy as outlined in the NSW Government's Floodplain Risk Management Manual, Council has a duty of care to manage lands subject to flooding within its Local Government Area.

In line with the Manual, the process includes gathering flood data, developing a flood model, and preparing flood maps. The model helps assess flood risk within a catchment, and community engagement is undertaken to ensure the information is as accurate as possible.

Existing flood studies did not cover entirety of the study area and are due for a review as per the requirement set out in Floodplain Risk Management Manual.

Heavy rainfall can sometimes overwhelm our stormwater drains, causing water to flow across roads and properties. This is called "overland flooding" and is different from river flooding.  

Stormwater drainage is typically adequate for the frequent storms (e.g. 20% AEP event).

An overland flood study is a comprehensive technical investigation of flood behaviour. it defines the nature and extent of overland flooding across a study area by providing information on flood extents, discharges, levels, and velocities for different flood events.

Overland flooding (also referred as flash flooding) occurs during rainfall events where drainage systems reach capacity and excess water will flow over land.

This type of flooding is generally quick to occur and subside.

This might be observed as water trapped within low points, flow travelling along roads, surcharging pits, local parks/basins filling up or water travelling through private and public properties. 

The outcomes of this study are intended to fulfill the requirements of a flood study within the NSW

Floodplain Management Process. The study objectives are as follows:

• Outline the flood behaviour within the catchment to aid in Council’s management of flood risks, and
• Form the basis for a subsequent floodplain risk management study where detailed assessment of flood mitigation options and floodplain risk management measures will be undertaken.

The information presented in the study will assess the impact of flooding on urban development and assist in planning works for managing flood risk across study area.

The State Government defines the guidelines on how to conduct Flood Studies. To prepare the study, Council has engaged an independent consultant and will draw upon the advice of the NSW Department of Climate Change, Energy, the Environment and Water.

The preparation of a flood study involves the collection and review of all available flood-related information for the study area, followed by the development of computer flood models to simulate the runoff resulting from excess rainfall and its distribution across the catchment.

The computer model is calibrated against collected information to reproduce historic floods, then utilised to simulate a range of hypothetical floods ranging in low to extreme severity.

A draft Flood Study report and mapping is then produced, summarising the outcomes of all phases of the investigation.

This study is being undertaken based on the latest guidelines, legislation, and industry best practice, including climate change. It includes latest rainfall database, ground elevation, building footprint and drainage infrastructure database.

We have used up-to-date modelling techniques, as well as expert assistance from consultants and the NSW Government, to determine mapping and analysis of risk. We believe our flood level estimates are as accurate as possible at this point in time. The study was peer reviewed to ensure they accurately reflect the views of experienced professionals.

The flood maps developed as part of this process are used to show where flood affected areas are located.

The stages of a flood study are generally divided into the following:

• Stage 1: Data Collection, gap analysis and Community Survey 
• Stage 2: Hydrological and Hydraulic Model Development and Validation.
• Stage 4: Design event modelling, model simulations and mapping.
• Stage 4: Draft Flood Study Report including flood tagging.
• Stage 5: Community Consultation - we are here
• Stage 6: Finalise Flood Study Report.

For most people, there's no immediate change. If you're planning development, you may need to consider flood-related design requirements like building heights or locations on your land to reduce property damage during a major storm event. 

This study looked at whether water flows over ground. The study has not identified if water is likely to flow into buildings. However, in a rare storm event such as 1% AEP flood event, water may enter the building.

The probability (or chance) of flooding hasn't changed as a result of this study, so your property is no more ‘flood prone’ than it was previously. The study is simply the first step in developing a solution to the problem of flooding.

Recent studies were undertaken using sophisticated, modern modelling computational techniques that capture a more detailed flood pattern and allow us to look at flood behaviour closely.

Flood events don't follow regular patterns. Properties may not flood for many years, then experience several floods. The study models rare events that may not have been experienced in living memory.  

If you believe your property has been incorrectly included:

1. Write to the council referencing the flood study.
2. Provide evidence (such as ground survey of the site) to prove inaccuracy of flood extent and flood level
3. Request Council staff and the consultant to review the mapping.

A Section 10.7 Planning Certificate provides information on any controls, requirements and restrictions that may impact how a property is used, such as land zoning, permissible and prohibited land uses, and controls for development or hazards such as flooding. Under NSW legislation, a contract for sale of a property must include a current s10.7 certificate from the relevant local Council.

Under the regulation, answers to the following questions are provided in a planning certificate for flood risk to a site:

1. If the land or part of the land is within the flood planning area and subject to flood related development controls.
2. If the land or part of the land is between the flood planning area and the probable maximum flood (PMF) and subject to flood related development controls.

Note: PMF Flood related development controls are dependent on the type of development being proposed. Sensitive and hazardous development or critical infrastructure development and land uses, such as hospitals, early education and care facilities, group homes, seniors housing, and emergency service facilities may need to be consider the PMF Flood Risk and Evacuation constraints.

The Flood Planning level (FPL) is the height used to set floor levels for houses in flood prone areas. It is generally defined as the "1% AEP flood level" plus and appropriate freeboard (see explanation of 'freeboard' below).

The FPL can be calculated as:

FPL = 1% AEP flood level + freeboard

It's unlikely that development controls will prohibit all development on flood prone land. However, some factors may need to be taken into consideration in any future development to alleviate risk to life and property. For example, you may be asked to build on a certain part of your land or elevate your building to a certain height or avoid building in a section where flood risk is high. Council's Development Services team can help you understand these considerations.

Insurance companies already hold extensive flood data, which they use to set premiums. This study simply identifies an existing risk rather than creating new risks.

Premiums are influenced by many factors, including property type, value, location, and claims history, and insurers conduct their own risk assessments regardless of this study. 

Adoption of overland flow information is not expected to affect premiums, as each provider applies its own pricing process. It is always recommended to compare policies, since prices and inclusions vary between insurers.

No. The study will not impact your rates. Council collects rates based on land values determined by the Valuer General.

Access to modelled overland flow data helps Council plan infrastructure upgrades and guide development within the LGA, while also supporting residents in managing their own risk. Property values are shaped by many factors—such as location, size, age, and interest rates—that are outside Council’s control. There is no evidence to suggest that adopting overland flow information alone would cause a lasting impact on property values.

Council's network of stormwater pits, pipes, and open channels are designed to manage minor, more frequent storm events (e.g. 20% AEP or 1 in 5 chances in any given year). Excess runoff during major storms is conveyed via overland flow paths, such as roads and valleys. This aims to maximise the protection of life and property in major events.

The next stage of flood study will focus on risk reduction measures.

Council’s stormwater pipes are designed to manage smaller, more frequent storms, which helps reduce localised flooding in everyday conditions. For larger storms, it would not be practical or affordable to build pipes big enough to carry all the water. Instead, overland flow paths are used to safely move stormwater during major events—this is the standard approach across the industry.

Much of Council’s drainage system was built many years ago, before the understanding of flood risks in the area. As a result, when heavy rain exceeds the system’s capacity, water can flow across roads and into properties where ground is lower than the surrounding area. This study will help identify where that excess water goes, so Council can better plan for managing flood risks in the future.

Yes, but flood-related development controls may apply. These ensure new buildings are safe and don't make flooding worse. Council's Development Services team can help you understand any requirements.

A 1% annual exceedance probability (AEP) flood represents a flood which has a 1% chance of occurring within any year. This is a large and rare flood. It was previously referred to as the 1-in-100-year flood. 

A probable maximum flood (PMF) is the largest possible flood that could conceivably occur at a particular location and is therefore extremely rare. The PMF defines the maximum extent of flood prone land, that is, the floodplan. While extremely rare, a few floods in Australia have approached the magnitude of a PMF. It is calculated to aid in the design of critical facilities such as hospitals, nursing homes, schools and emergency service facilities. the PMF is also modelled so that emergency managers can understand the maximum possible extent of flooding that could ever occur in a location and plan accordingly.

During significant rainfall, water from higher areas flows downhill, following natural paths such as gullies, channels, and surface depressions. The steep slope of the hill can cause water to travel quickly, increasing its velocity. Where this flow encounters obstructions—such as fences, buildings, or landscape changes—it can lead to increased flood depths and concentrated flows. This can result in serious flood damage and significant erosion, even on properties located on a hill.

During the public exhibition of the Flood Study, a draft note is added in the 10.7 planning certificate to warn any potential buyer that a draft flood study is currently underway and this site might be affected by future flood related development controls.

After the completion of the community consultation, subject to the final endorsement of Council, a final note is added to the planning certificate confirming whether the site is located within flood planning area, PMF and whether a flood related development control is applicable for a site.

This simply means that if there is a development proposal on the land, then it would need to consider the flood risk so that the occupants can live safely on the land, minimising the flooding risk to this property and adjacent neighbouring properties.

Freeboard is included in the Flood Planning level as a buffer, to account for factors such as unexpected blockages, waves from vehicles (such as cars, SES rescue tracks), other localised hydraulic effects and uncertainties in the modelling and determination of flood levels. Freeboard is typically 0.5m above a flood level.

Our website provides more information on flood management for the Georges River area. You can view this page at Georges River Council - Flood management . 

 Additional information on emergency plans and flood preparation can be found on the following websites:

•           NSW State Emergency Service https://www.ses.nsw.gov.au 

•           Bureau of Meteorology http://www.bom.gov.au

•           NSW Office of Emergency Management Rescue and emergency management | NSW Government 

We have used up-to-date modelling techniques, as well as expert assistance from consultants and the NSW Government, to determine mapping and analysis of risk. The study is on exhibition and can be viewed on our project page.  

You can request a flood advice letter from us. This will provide you with detailed information and maps for your specific property, showing flood levels and associated flood hazard conditions, where this information is available. There is a processing fee for this service.

You can lodge a flood advice application via:

• Online: you can lodge your application using Georges River Councils Log It/Fix It page. Select the Stormwater Flood Level Enquiry. Customer service centre will then contact you for the payment.
• In person: at Council’s Customer Service Centres. Corner MacMahon and Dora Streets, Hurstville. (Monday to Friday 8.30am - 5.00pm).
• Contact us: visit our contact us page, call (02) 9330 6400 or send your enquiry via email: mail@georgesriver.nsw.gov.au.

We believe our flood level estimates are as accurate as possible at this point in time. However, the studies are undertaken at a broad level, rather than for individual properties. If you believe that these are not accurate for your property, you can seek professional advice relating to your property and request our review. 

The SES’s ‘Be prepared for a flood’ gives you all the information you need to prepare for flooding. 

This includes signing up for flood warnings, preparing a flood plan and a flood kit.

Everyone’s situation is slightly different so a big part of being prepared is taking time to think about what is the safest thing for you to do if a flood happens.

Floods can cause enormous damage very quickly. They can cut off communication and transport options and they can happen anywhere in Australia.

In an emergency, the situation can change rapidly. So, before a flood arrives, it's important to plan and prepare.

For emergency assistance during a flood, storm or tsunami, call NSW SES on 132 500. In a life-threatening emergency, call Triple Zero (000). Visit the Contact page for more information.
 

For help with sandbags: 

Using sandbags to protect your home or business can help reduce damage.  

If a storm or flood warning has been issued, your local council and/or SES unit may announce where sandbagging stations may be set up in your area. Check your local information page for information.  

Visit the Using sandbags to protect your home page to learn more about how to make and use sandbags.