Flooding

If the situation is life threatening you should call 000.

For other assistance during an emergency such as flood or storm, please contact the NSW State Emergency Service (SES) on 132 500 or visit their website.

It is best to be prepared for any flood. The State Emergency Service also provides advice on how to manage your flood risk, on their website.

Development over many years, stretching right back to the initial subdivisions that created the suburbs we live in today, has left many areas with a legacy of undersized infrastructure which cannot adequately carry water from minor storms. It has also removed many natural creek or open water surface bodies in the catchment areas to accommodate stormwater. This results in flooding of some properties. Council undertakes upgrades of its piped stormwater system on a priority basis across the local government area as funding allows. When a new development is proposed, Council reviews the potential impacts to ensure the current flooding situation is not worsen by the proposed development. 

Council’s piped stormwater system is designed to convey frequent minor storms with the aim of reducing day-to-day nuisance flooding, while major storms are conveyed via overland flow paths with the aim of protecting life and property in major events. It is impractical to provide piped drainage systems for major storm events as this is cost prohibitive. Overland flows are also part of our natural environment and are an important part of a sustainable catchment management approach.  

Flood Studies identify flood behaviour including the areas flooded, water depth, hazard categories and the likelihood of flooding within the catchment. Floodplain Risk Management Studies and Plans assess potential management approaches to reduce the impact of flooding (e.g. drainage upgrades, development controls, community awareness and emergency response arrangements). Council’s Floodplain Risk Management Studies and Plans can be found here. 

Flood Planning Levels are the combinations of flood levels (estimated heights of floodwater from defined flood events) and freeboards selected for floodplain risk management purposes, as determined in management studies and incorporated in management plans.

Annual Exceedance Probability (AEP, measured as a percentage) is a term used to describe flood size. It is a means of describing how likely a flood is to occur in a given year. For example, a 1% AEP flood is a flood that has a 1% chance of occurring, or being exceeded, in any one year. 

The Flood Planning Area is the area of land below the Flood Planning Level and thus subject to flood related development controls.

Freeboard is a height included in the Flood Planning Level and provides reasonable certainty that the risk exposure selected in deciding on a particular flood chosen as the basis for the Flood Planning Level is actually provided. It is a factor of safety typically used in relation to the setting of floor levels, levee crest levels, etc, to account for factors such as wind, waves and any other localised hydraulic effects. Freeboard can vary but is usually 0.5m above a flood level for habitable areas.

A 1 in 100 year ARI (Average Recurrence Interval) flood is a flood event that has the probability of occurring on average once every 100 years, i.e. there is a 1% chance of a flood of this size occurring at a particular location in any given year. This does not mean that if a location floods one year that it will not flood for the next 99 years. Nor, if it has not flooded for 99 years that it will necessarily flood the next year. Some parts of Australia have experienced more than one ‘1 in 100 year’ floods within a decade of each other.

The Probable Maximum Flood (PMF) is the largest flood that could conceivably occur at a particular location, usually estimated from probable maximum precipitation, and where applicable, snow melt, coupled with the worst flood producing catchment conditions. Generally, it is not physically or economically possible to provide complete protection against this event. The PMF defines the extent of flood prone land, that is, the floodplain.

It depends on the type and scale of the development. New developments which affects the flood behaviour and has potential to negatively impact the flood affectation to the neighbouring properties will require flood study with development application lodgement. In any case, specific requirements of a development proposal will be determined in the assessment of a development application. 

There are many factors that can affect the value of any property including inflation, a change in interest rates, construction of a new development nearby, etc. The extent to which a property’s value is affected once it has been identified as flood affected is impossible to determine. While the notification may affect one potential buyer’s decision to purchase a property it may have no impact for another. Ultimately, it is the market that determines the value.

Flood Studies are a legal requirement for Council to complete and are part of our responsibilities to help manage flood risk in the community. Insurance companies may rely on their own assessment of risk and can use their own methods to identify flood risk. Council doesn’t put together Flood Studies or Floodplain Risk Management Plans for, or on behalf of insurance companies.

Floods do not occur in a regular pattern. There may be a period of no floods and a period of several floods. For example, the last time the Brisbane River flooded before the 2011 disaster was in 1974. Residents who moved there in more recent times may never considered flooding an issue until the floods in January 2011.

Members of the public can request a Flood Levels Certificate for their property, by calling Council's Customer Service Centre on 9952 8222. This certificate will provide detailed information about the flooding situation of a particular lot.  

The flood related development controls are within clause 6.3 of the Ryde Local Environmental Plan 2014 and Section 8.2 of the Ryde Development Control Plan 2014.

Council has answered ‘unknown’ to questions on Section 10.7 Certificates for certain land where the extent of the FPA was not known at the time that the certificate was issued. In the absence of the FPA information, Council provided information on Section 10.7(2) and (5) Certificates as to whether a property is within the PMF to provide a better understanding of flood affectation until FPA maps were updated. These changes affected Section 10.7 Certificates issued between 14 July 2021 and 14 January 2022.

As of 14 January 2022, Council implemented the FPA maps which changes ‘unknown’ values to either ‘Yes’ and ‘No’ depending on if the lot is located inside or outside the Flood Planning Area.

Please note: Section 10.7 Certificates are reviewed and released with the correct controls and information at the time of issue. Therefore, there may be past certificates ordered for the same property with different answers under Clause 9 (formerly Clause 7A). Generally, the older the certificate, the more likely it is that the controls and/or restrictions affecting the development potential of the land have changed since its time of issue. It is the responsibility of the certificate user to determine whether they consider the certificate to be recent enough to be deemed reliable for their given purpose.

Prior to the availability of FPA maps, Council provided additional flood information on planning certificates. This information related to whether a property is within the PMF.

If a property is within the PMF, a flood study may be required as part of any development application to determine if a proposed development could affect flood behaviour and have the potential to negatively impact the flood affectation to the neighbouring properties. The need for a flood study will be determined at development application stage.