Flood planning

In NSW, there is a state-wide initiative to improve flood resilience.

The NSW Government released the Flood Risk Management Manual in 2023, with an accompanying toolkit. Together these documents guide how Councils state-wide should address flood risks at a local level, and how the state may financially support Councils to make Local Government Areas (LGA) more flood resilient.

Aside from being a hilly, coastal area, Waverley LGA is heavily developed which means few of the natural stormwater runoff paths exist. Combined with increasingly intense rainfall events linked to climate change, incidents of short-term flooding and ponding are becoming more frequent.

The stormwater networks around inner-city suburbs in Sydney are fairly similar and are only designed to cope with more common rain events. In Waverley, the main cause of flooding is called ‘overland flow’ which is essentially rainwater flowing downhill, overwhelming or bypassing the stormwater network during heavy rain. That is why properties on hills may also be considered a flood risk, due to rainwater making its way from the land peak down to a watercourse/waterbody.

Floodplain Risk Management

The primary contribution of local Sydney Councils to flood mitigation is in two areas:

  1. Management of the stormwater network (with the exception of larger stormwater infrastructure under Sydney Water control)
  2. Ensuring planning controls factor in the flood risk to property and people

To that end, considerable work has been done locally in Waverley to fulfil the requirements of the NSW Government Floodplain Risk Management Process:

  • In 2021 a four-year process of flood modelling the local area was completed. The resulting report is the Waverley LGA Flood Study prepared by BMT which was endorsed by Council in April 2021, with a record of the public consultation available on Have Your Say.
  • In May 2024 the Waverley Development Control Plan (DCP) - Flood Amendment was adopted. Together with the Local Environmental Plan, this section of the DCP provides for controls relating to Flood Planning including defining flood risk precincts. A record of the public consultation regarding the amendment is available on Have Your Say.
  • In early 2024 Waverley Council started the next step in the NSW Government's Flood Risk Management Framework, which is preparing a Flood Risk Management Study and Plan for the Waverley LGA. The objective of this project is to refine the model across the LGA and explore and recommend flood mitigation options to reduce or alleviate detrimental impacts of flooding where possible. The proposed Flood Risk Management Study and Plan will be exhibited in 2025 for public feedback. View progress on Have Your Say.

Measuring the regularity of flood events

Residents reading flood planning documentation will encounter a measurement called ‘AEP’ which is the standard for most government organisations in Australia.

Annual Exceedance Probability (AEP) is the chance of a flood of a specific size occurring in any one year, expressed as a percentage. For example, a 1% AEP flood has a 1% or 1 in 100 chance of being reached or exceeded in any given year, meaning if it did occur, it would likely be a severe weather event.

For comparison, most suburban Sydney stormwater networks are designed to cope with a 20% AEP event, although in some areas of Waverley the infrastructure is designed to cater for larger storm events up to a 10% AEP.

Flood Risk Precincts

In Waverley, land is categorised into three Flood Risk Precincts:

  • High: In this precinct there would be a significant risk of flood damages without compliance with flood related building and planning controls.
  • Medium: In this precinct there would still be significant risk of flood damage, but these damages can be minimised by the application of appropriate development controls.
  • Low: The risk of damages is low for most land uses.

Many parts of the LGA are unaffected by flood, so do not have a precinct.

   
 

For the AEP and technical definitions of the precincts, please refer to the Water Management (Flood Planning) section of the DCP.

 


Flood risk is based on what is statistically expected to occur on the best available information today. It is not a representation of what has occurred in the past, although Waverley has experienced major rainfall events in the past, such as a 1%AEP flood event in November 1984 which impacted much of the LGA.

The flood risk rating is not fixed and is intended to be reviewed over time.

Obtaining flood risk information

  • Flood Risk Precincts are included on the Discovery Waverley Planning Map (turn on the ‘Flood Planning Area’ layer). Many parts of the LGA are unaffected by flood, so do not have a precinct marked on the map. Use the ‘Environment’ map and turn on the ‘Stormwater Pit & Pipe’ layer to view the public stormwater network.
  • A Planning Certificate provides basic flood information for a small fee.
  • For more detailed information, residents can submit an Request For Flood Level Information form. This level of detail is likely to be required by residents looking to develop a property.

Development and flood risk

The Flood Risk Precincts ratings are representative of the flood risk that already existed.

Flood planning controls are focussed on common sense approaches to development in relation to the risk level. For instance, in an area at high risk of flood, any development would need to be conscious of floor level heights, structural soundness, safety of car parking and driveway access, fencing and the ability to safely evacuate during an extreme weather event.

The implication for residents wanting to development their property will vary. For instance, a first-floor addition to an existing home with no footprint change would be unlikely to trigger any flood planning controls, regardless of the precinct risk level. Conversely, a complete knock-down/re-build of a home in a high flood risk precinct would likely require all the flood controls to be considered.

Research undertaken by HillPDA on behalf of Council found “the identification of land as being potentially flood (stormwater) affected is on its own unlikely to have a material impact on property prices in Waverley over time.” (read the report)

Insurance and flood

The Waverley LGA Flood Study outlined that most of the water where inundation could occur in the LGA (aside from Bronte Gully and Tamarama Gully), should be considered as ‘stormwater’ for the purposes of insurance. In Australia, all insurers have adopted a consistent definition of a flood as:

“The covering of normally dry land by water that has escaped or been released from the normal confines of any lake, river, creek or other natural watercourse, whether or not altered or modified; or any reservoir, canal or dam.” That is, stormwater is not considered a ‘flood’ for insurance purposes.

Council undertook research which  concluded that there was no clear correlation between flood risk related planning controls and mapping and increased insurance premiums and that a variety of factors influence insurance premiums provided by insurers.

The Insurance Council of Australia recommends that if a flood premium has been incorrectly charged, that the resident raise this directly with their insurer, most of whom have dedicated flood premium review processes. The ICA can also assist in reviewing information if an insurer cannot.

Stormwater

For more information on the local stormwater network: