Flood risk FAQs

Why does Ku-ring-gai Council need flood mapping?

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, 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.

How are the flood studies and risk management study and plans funded?

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

What is a flood study?

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 floodplain risk management study and plan, in accordance with the NSW Floodplain Development Manual (2005).

What is a floodplain risk management study?

A floodplain risk management study uses the information from the preceding flood study to identify, assess and compare various flood risk management options and consider environmental enhancements as part of flood mitigation works.

What is a floodplain risk management plan?

The floodplain 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.

What kind of flooding is Council concerned with?

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

Flooding 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.

What parts of Ku-ring-gai Council have completed reports?

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

Blackbutt Creek Catchment includes a number of 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 a number of 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 commenced in September 2019. 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.

What is the 1% AEP flood?

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 (that is a one-in-100 chance) of occurring in any one 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. 

What is a flash flood?

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.

What is the flood planning area mapping?

The flood planning area incorporates the 1% AEP (1 in 100 year ARI) with the designated freeboard.

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.

What does flood mapping on my property mean?

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.

How does the flood mapping affect my home insurance policy?

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 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.

How can I access property specific flood information?

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.

What do I do if I need information and a flood study has not yet been completed in my area?

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 you 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 DA, please refer Part 24R.7 of Council's DCP - Flood Study Requirements.