Councils in New South Wales have responsibility for identifying and managing flooding, and informing the community. Councils follow the NSW Flood Prone Land Policy, which outlines how Councils should manage flooding to reduce the risk of flooding to people and properties.

It also sets consistent guidelines such as using the 1% AEP flood as the industry standard for design and planning purposes. One of the most important steps in this process is increasing our community's awareness of flooding so that people are better able to understand and plan for the flood risks they face.

The study area comprises parts of Belrose, Davidson, Frenchs Forest, Forestville and Killarney Heights.

The Middle Harbour Catchments Flood Study will identify flood behaviour in the study area.

The Frenchs Creek Flood Study was completed for the northern part of this study area in 2010. Since then, technology has improved and computer modelling has become more accurate. The Frenchs Creek Flood Study is one of Council’s oldest current flood studies, and will be superseded by the Middle Harbour Catchments Flood Study. There has not previously been a formal flood study undertaken elsewhere in the study area.

If it is a life threatening situation call 000.

During a flood, storm or tsunami, please contact the State Emergency Service (SES) on 132 500 or visit their website at www.ses.nsw.gov.au.

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 flood has a 1% chance (that is a one-in-100 chance) of occurring in any one year.

This does not mean that if a location floods one year, that it will be flood free for the next 99 years. Also, if it has not flooded for 99 years, it does not mean there will definitely be a flood the next year.

Some parts of Australia have received a couple of 1% AEP floods within a decade of each other, and flood events much larger than the 1% AEP flood can, and do, occur (such as the January 2011 flood in Toowoomba).

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

It is used for planning purposes, and land below the FPL is considered to be flood affected and therefore subject to flood related development controls. The FPL can be calculated as:

FPL = 1% AEP flood level + freeboard (typically 0.5m).

Freeboard is included in the Flood Planning Level as a buffer, to account for factors such as wind, waves, unforeseen blockages, other localised hydraulic effects and uncertainties in the modelling and determination of flood levels. Freeboard is usually 0.5m above a flood level.

Council prepares Flood Studies and Plans according to the NSW Government's Flood Risk Management Manual (2023), and implements associated recommendations with the financial and technical assistance of NSW Government through its Flood Prone Land Policy.

Development controls on buildings in a flood zone are an effective way of protecting life and properties from flood risk.

Additional ways that Council manages flooding in the area include installing and monitoring a flood warning network, raising flood awareness in the community, and opening of lagoon entrances to lower water levels.

The State Emergency Service has a useful website providing advice on how to manage flood risk. Visit www.floodsafe.com.au for more information.

Flood related development controls in this area can be found in the Warringah Local Environment Plan (Clauses 5.21 and 5.22) and the Warringah Development Control Plan (Part E11), which can be viewed at https://www.northernbeaches.nsw.gov.au/planning-and-development/building-and-renovations/planning-controls