Flood risk FAQs

Under the NSW Flood Prone Land Policy the management of flood prone land is primarily the responsibility of councils. Although Ku-ring-gai’s primarily ridge-top development means we do not have extensive floodplains, localised flooding from overland flow and the overflowing of creeks does occur.

We need to identify areas subject to mainstream and overland flow so we can put in appropriate planning controls, emergency management plans and mitigation works.

Our floodplain risk management process aims to:

• Minimise risk to life, health and safety.
• Reduce flood damage to property and infrastructure.
• Ensure future development is controlled in a manner which is compatible with a catchment’s flood risk.
• Protect and enhance the floodplain environment and be consistent with State Government policies.
• Ensure the flood study and/or floodplain risk management study and plan has the support of the local community.

Ku-ring-gai Council follows the process outlined in the NSW Flood Risk Management Manual (2023). The process is broken down into series of key stages to:

• understand the nature and extent of the flood problem,
• identify the consequences of flooding on the community,
• identify options to reduce the impact of flooding and,
• finally develop a plan to help protect people and property.

This process is overseen by the Flood Risk Management Committee which includes councillors, community members and state agency representatives. Community consultation is also a major component which is undertaken at each stage of the process. 

A flood study is a comprehensive technical investigation of flood behaviour within a catchment or study area. A flood study provides information on extent, level and velocity of flood waters which is used to understand and define flood hazard within a study area.

A flood study forms the initial stage towards a comprehensive flood risk management study and plan, in accordance with the NSW Flood Risk Management Manual (2023).

A flood risk management study uses the information from the preceding flood study to identify risks to the community and assess and compare various flood risk management options. These options consider are assessed for a range of performance criteria including effectiveness, practicality, and community and environmental impacts.

A flood risk management plan offers preferred options to mitigate flood risk within a study area, balancing the social, economic, environmental and cultural interests in the floodplain with the resultant flood hazard.

Council’s major studies and reports receive funding assistance and technical support through the NSW Government’s Floodplain Management Program.

Council is investigating and managing the natural flooding caused by significant catchment rainfall resulting in either overland flow or mainstream flooding. 

Flooding from overland flow occurs when runoff after rain exceeds the capacity of the drainage system including the creeks, rivers, built pipes and channels. Local overland flows after heavy rains which take the ‘path of least resistance’ on the way to drains or watercourses can also cause localised flooding.  

Mainstream flooding occurs when creeks overflow, spilling over their banks and flooding nearby areas. 

Flooding that is sudden and unexpected is referred to as flash flooding. It is usually caused by intense thunderstorms which deposit a large amount of rainfall in a short period of time. Flash flooding is the main type of flood which impacts the Ku-ring-gai local government area.

A map showing the status of our flood risk management process can be viewed on council’s online map viewer.

Currently only two catchments have completed flood studies and flood risk management studies and plans: 

Blackbutt Creek Catchment includes several watercourses and overland flow paths within the suburbs of Pymble, West Pymble, Gordon and Killara.

The catchment is bounded by the Pacific Highway to the east and Fiddens Wharf Road to the south, and is traversed by Ryde Road, Pymble Avenue and Livingstone Avenue on its western boundary. A flood study and flood risk management study and plan have been completed for this catchment.

Lovers Jump Creek Catchment includes Lovers Jump Creek and several tributaries in the suburbs of Turramurra, North Turramurra, Warrawee, Wahroonga and North Wahroonga.

The catchment is approximately bounded by the Pacific Highway to the south, Bobbin Head Road to the east and Grosvenor Road to the west. Burns Road crosses east-west through the southern half of the catchment, while the North Shore railway line traverses the far southern portion of the catchment. Eastern Road passes north-south through the centre of the study area. A flood study and flood risk management study and plan have been completed for this catchment.

The Middle Harbour – Southern Catchments flood study was completed in 2023. This area includes Echo point Catchment, Moores Creek Catchment, Gordon Creek Catchment and Northern and Southern Creeks in Killara.

These catchments cover the area between the Pacific Highway and Middle Harbour including the suburbs (or parts of) Roseville Chase, Roseville, Lindfield, East Lindfield, Killara and East Killara.

Current and completed studies can be found on our Flooding page.

Middle Harbour – Northern Catchments

The Middle Harbour – Northern Catchments flood study report draft was placed on public exhibition in 2023.

Following the consideration of submissions, in July 2025 Council resolved to undertake further investigation to refine the report.

Lane Cove – Northern Catchments

Ku-ring-gai Council received funding for the Lane Cove Northern Catchments Flood Study through the NSW Government Floodplain Management Program grants 2020 – 21

The draft report has been received and will go on formal public exhibition following finalisation of the Norman Griffiths Oval upgrade design. Following the exhibition submissions will be considered in the development of the final report.

Some preliminary information on the Lane Cove Northern Catchments Flood Study has been made available on the Norman Griffiths Oval upgrade page Norman Griffiths Oval flood studies Ku-ring-gai. 

Lane Cove – Southern Catchments - update on project

The Lane Cove – Southern Catchments flood study received funding through the NSW Government Floodplain Management Program grants 2020 – 21.

The flood study is underway, we expect to receive a draft report in late 2025. Public exhibition will take place in 2026. 

The Annual Exceedance Probability (AEP) is the chance of a flood of a given size occurring in any one year, expressed as a percentage. The 1% AEP has a 1% chance of occurring in any one year. This event was previously known as a “1 in 100-year flood”, however, this doesn’t mean that if a location experiences a 1% AEP flood one year it won’t happen again for another 99 years, there would still be a 1% chance of similar sized event the following year.

The 1% AEP is typically used to set flood planning levels for future residential development; one of the tools used in effective floodplain management. 

The flood planning area (FPA) incorporates land impacted by the 1% AEP flood event with the addition of a designated freeboard, this is known as the flood planning level (FPL).

Freeboard is a specified height above a 1% AEP flood level which is included in the flood planning level to account for a range of factors such as wind, unforeseen blockages and other localised effects that can influence flood levels.

In Ku-ring-gai the freeboard is usually set at 500mm for areas of mainstream flow and 300mm for overland flow. It usually represents the area of land where careful consideration of floor levels will need to be made. The flood planning level mapping represents this information as a level (usually AHD) which indicates what the floor level will need to be above to ensure a structure is flood free.

The Probable Maximum Flood (PMF) is the largest flood that could possibly occur in a catchment. The PMF should be considered extremely rare and is developed to support critical design of critical facilities and infrastructure, and for emergency management planning.

In Ku-ring-gai, development types that may need to consider flooding above the FPA and up to the PMF include sensitive and hazardous development such as:

1. Early education and care facilities
2. Educational establishments
3. Emergency services facilities
4. Group homes
5. Hospitals
6. Respite day care centres
7. Seniors housing
8. Hazardous storage establishments

Certain types development – even those undertaken under State Environmental Planning Policy (Exempt and Complying Development Codes) 2008 need to consider flood risk.

Having flood mapping or the Flood Planning Area identified on your property does not mean you will be prevented from undertaking development; you may just need to carefully consider the location and type of development on your property or the floor level of certain structures.

Please refer to part 24D.2 of Council's Development Control Plan - Flood Studies and the Design Flood Standard.

Having Flood Planning Area mapping or Probable Maximum Flood mapping on part of your property will result in a notation on the Section 10.7 planning certificate.

There are two key notations a section 10.7 planning certificate, required information provided under 10.7(2) and additional information provided under 10.7(5) of the NSW Environmental Planning and Assessment Act 1979.

These notations are not an indication that a property may be severely impacted by flood, they provide clarity that a property, or part of the property, may be subject to flood related development controls.

The section issued under section 10.7(2) of the NSW Environmental Planning and Assessment Act 1979 includes notations under the heading “Flood related development controls information”. The two questions and potential responses are:

Is the land or part of the land within the flood planning area and subject to flood related development controls?

• Yes.

  A Flood study has been completed and Flood Planning Areas applies to part of the lot – refer to Council's online map viewer for mapping details. Any development in the mapped areas is potentially subject to flood related development controls.

• No.

  A Flood study has been completed and there is no part of the property subject to Flood Planning Area

• No. (Unknown)

  The flood risk of this land has not yet been mapped. Unmapped locations may also be subject to flood related development controls.

  Where No. (unknown) is noted in the planning certificate, an appropriately qualified stormwater engineering consultant should be engaged to provide advice on whether flooding and overland flows are required to be considered, particularly where drainage features such as easements (usually noted on the Deposited Plan (DP)), depressions, drainage swales or Riparian Land (available on council’s Online map viewer) are present on or immediately adjacent to the site.

  Is the land or part of the land between the flood planning area and the probable maximum flood and subject to flood related development controls?

• Yes.

  A Flood study has been completed and part of the lot is subject to flooding between the Flood Planning Area Map and Probable Maximum Flood Tagging Map. Flood controls will need to be considered where a Sensitive and Hazardous development is proposed (as listed in 24D.2(4) of the Ku-ring-gai DCP and the NSW Guideline Considering Flooding in Land Use Planning July 2021).

• No.

A Flood study has been completed and there is no part of the property subject to Probable Maximum Flood Tagging Area Map. This does not mean the property is completely flood free – it may be subject to shallow flows up to the Probable Maximum Flood event.

• No. (Unknown)

The flood risk of this land has not yet been mapped. Unmapped locations may also be subject to flood related development controls.

Where No. (unknown) is noted in the planning certificate, and consideration of flooding between the FPA and PMF is required, an appropriately qualified stormwater engineering consultant should be engaged to provide advice on whether flooding and overland flows are required to be considered, particularly where drainage features such as easements (usually noted on the Deposited Plan (DP)), depressions, drainage swales or Riparian Land (can be viewed on council’s Online map viewer) are present on or immediately adjacent to the site.

Further information is provided in the additional section of the planning certificate (that issued under section 10.7(5) of the NSW Environmental Planning and Assessment Act 1979). This may include details for any flood study that has been commenced in the area, or a notation that due to Ku-ring-gai’s steep topography it is always important to carefully consider overland flows.

Where the Flood Planning Area or Probable Maximum Flood on a property is entirely within the front or rear setback, or the building floor height is significantly above the Flood Planning Area or Probable Maximum Flood, a note may also be included to provide more context to the notation.

Insurance companies use many different sources of information to assess risk. Much of the information they use is internally generated, however in some cases it appears they also consider Council flood studies and related plans.

Often important details, such as where a dwelling is on a property in comparison to mapped flood flows is overlooked. The flood studies and flood risk management studies and plans can provide important information for individual property owners to decide whether flood insurance is the right product for them, if they should change insurers or if they should provide more information to the insurance company to re-evaluate a quoted premium.

Flood planning area mapping, which has been endorsed by Council, is also available to view under the hydrology layers on Council's online map viewer.

If site specific details for including levels are required (such as to aid the preparation plans) a flood certificate report can be purchased, please email floodriskmanagement@krg.nsw.gov.au

Flood information is also provided through the Climate Wise Communities website.

Additional drainage information can also be purchased separately, please contact Customer Service and complete the Search of Records – Operations Department Application Form.

Council is unlikely to have any specific information if a flood study has not yet been completed in your area.

If you are concerned as your property is near an easement or open watercourse often a specialist drainage engineer will need to be engaged to provide expert advice which is particularly important if you need information to prepare plans.

If you are required to submit a flood study as part of your Development Application, please refer Part 24R.7 of Council's DCP - Flood Study Requirements.

Climate change is projected to increase both rainfall intensity and sea level which will influence flood behaviour such as flood depth. Each flood study assesses how changes in rainfall intensity may increase peak flood levels.  In some catchment studies, the impact of sea level rise is also assessed. The incorporation of climate change into flood studies has changed over time. For example, our earlier studies used the NSW Government’s Practical Consideration of Climate Change. In more recent studies, our approach to incorporate climate change risks follows the Australian Rainfall and Runoff 2019 Guidelines.