Flooding and your property

Flooding is unpredictable. There may be many years between floods or multiple events can occur in a single year.

Mainstream and overland flooding occurs during and following heavy rainfall in a catchment.

The size of a flood depends on several factors. These include the intensity and duration of rainfall, the area, surface shape and fall of the affected catchment, and the area of hard surfaces - such as roads and roofs - within the catchment.

For example, a large flat area at the bottom of a catchment is more likely to have a larger flood area.

Large floods are less frequent than small floods.

Council’s stormwater drainage network comprises stormwater pits, pipes and open channels.

Like all drainage networks, it is primarily designed to manage minor, more frequent rainfall.

In major storm events, excess runoff may flow overland. Roads and valleys are usually the primary flow paths.

Flood risk is a combination of the likelihood and impact of a flood.

Flood risk maps show whether flood-prone properties have a high, medium or low risk.

Generally, the lower the land and/or the closer to a creek, river, overland flow path or coast, the greater the flood risk.

A 1% annual exceedance probability (AEP) flood represents a 1% chance of occurring in any year. This is a large but rare flood. It was previously known as the 100-year recurrence flood. The 1% AEP flood defines a medium flood.

A probable maximum flood (PMF) is the largest possible flood. While extremely rare, a few floods in Australia have approached the magnitude of a PMF.

The PMF defines the maximum extent of a floodplain.

Areas that flood in a PMF, but do not flood in the 1% AEP flood are generally considered low-risk. Some situations, such as underground carparks, are always high-risk in any flooding event.

Under the NSW Government’s Flood-Prone Land policy, local councils have the primary responsibility for managing flood risk.

This risk management process includes studying floods and identifying and implementing measures to reduce the risk.

A flood study is the first stage in the floodplain risk management process. It involves a technical investigation of flood behaviour in a defined catchment.

Flood studies reveal the extent, levels and velocity of floodwaters across the floodplain for different flood events.

1. Visit Shire Maps
2. Expand 'Layers' and select ‘Flood Prone Land’
3. Search your property address
4. Select ‘I want to’ at the top-left corner of the map, then 'show legend' to identify the flood risk on your property.

For more information about high, medium and low flood risk, see Sutherland Shire Development Control Plan (DCP) 2015.

This is a document that identifies, assesses and recommends cost-effective measures to reduce flood risk. Issues addressed include measures to alter flood behaviour, modify property and improve our response.

Our management of flood risk is ongoing.

When we review and update flood maps, we take into account new rainfall data, updated asset data, updated ground levels and more up-to-date modelling.

This includes taking account of the latest information and methodologies that assess locations as flood-affected.

A recent example was the 2020 review of the Woolooware Bay catchment floodplain, which identified additional lots as flood-affected in the PMF. These lots are all in a low-risk precinct.

Council cannot advise on this. Property values are based on a range of factors, of which potential flooding is only one.

Chapter 40 of the Sutherland Shire Development Control Plan (DCP) 2015 lists controls to minimise the impact of flooding on proposed developments, as well as the impact of the proposed development on flooding.

These controls relate to floor levels, building components, structural soundness, flood effects, car parking, evacuation, and management and design.

Different controls may apply depending on the nature of the proposed development and the nature of flooding.

Prospective purchasers will request a Section 10.7 certificate from Council.

This will inform them of Council policies (including those related to flooding) that apply to the property, including any that restrict the use or development of the land, or which places obligations on the owner.

Detailed information regarding flood-affected properties is available for purchase from Council.

Before requesting this information, you should contact our Stormwater and Waterway Assets Unit on  9710 0333 to confirm it is available for your property. (Fees apply).

Submit an Application for Flood Information