Frequently Asked Questions

Flooding is a natural phenomenon that occurs when water covers land which would normally be dry. Floods generally are a result of prolonged or heavy rainfall over catchments, coastal inundation, or a combination of these.

If the situation is life threatening you should call 000.

For assistance during an emergency such as flood, storm, or tsunami you should contact the NSW State Emergency Service (SES) on 132 500 or visit their website at www.ses.nsw.gov.au. 

It is best to be prepared for any flood and the State Emergency Service provides advice on how to manage your flood risk at www.ses.nsw.gov.au/floodsafe/prepare-your-home/before-a-flood/

The management of flood prone land is primarily the responsibility of local councils. Flooding can cause significant damage to property and risk to life. All councils are required by the NSW State Government to undertake studies to determine what land has the potential to be affected by flooding.

It will help ensure that new developments are adequately protected and do not make flooding worse. Successful completion of the Flood Study and preparation of subsequent plans may be used to attract grant funding including for physical improvements to existing drainage infrastructure to reduce flooding. 

Council has a programme for routine inspection and auditing of storm water infrastructure for repair and maintenance to minimise drainage issues. This also includes street sweeping and pit cleaning to reduce the amount of litter/leaves entering the drains. Council has received grant funding from the NSW Government for this flood study and hopes to receive more support for infrastructure improvements as a result of the study.

The Flood Study is the first step in planning for flood risk management and will help Council to understand the flood risk in the Mosman LGA. Maps showing potentially affected areas of Mosman LGA will be produced. The next steps will be to develop a Flood Risk Management Study and Plan for Council to implement.  Funding will be sought from the NSW government for infrastructure upgrades to reduce flooding.

Flood modelling will be undertaken by specialist consultants Manly Hydraulics Laboratory (MHL), who have worked with multiple councils. The modelling will determine the extent of flooding throughout the LGA, including identifying the properties impacted. When Council has reliable information regarding flooding, it is obliged to provide that information when asked. Council is also required to provide this information on S10.7 Planning Certificates, which cover planning controls and other relevant property matters that affect a specific piece of land.

Being classified as ‘flood affected’ means the property has a risk of being affected in a specific rainfall event. Whilst no immediate action is required by an owner, should you be affected and wish to develop the land in the future, this may result in flood-related development controls being applied to the development consent e.g. there may be a requirement to raise floor levels or use flood resistant materials.

Floods do not have regular patterns and can be affected by a range of factors. There also may be periods when there are no floods and periods when there are several floods. For example, the last time the Brisbane River flooded before the most recent 2011 disaster was in 1974.  Residents who moved there more recently may have not considered flooding an issue until January 2011. Any water course experiencing extensive rain will flood. Flood modelling simulates severe rainfall events that on average might be infrequent, but this flooding risk needs to be understood for a property.

A property will be designated as flood affected based on inundation of the land rather than the floor level of a property. For development applications, the floor level is considered where appropriate. Any future developments of the property need to address the flood risk and controls.

This will depend on the type and scale of the development. New proposed developments which affect flood behaviour and have the potential to negatively impact the flood affectation to neighbouring properties will need to submit with a development application a flood study and a flood impact assessment. The Flood Study for the Mosman LGA (if available at the time of the application) may lead to reduced requirements for a specific flood study and flood impact assessment for the property.

There are many factors that can affect the value of any property including economic and financial conditions, supply and demand, increased aircraft noise or construction of a nearby road or shopping centre. The extent to which a property’s value might be affected if it is identified as at risk of flooding is impossible to determine. While learning of this may affect one potential buyer’s decision to purchase a property it may have no impact for another. Ultimately, it will be the market that will determine the value of the property.

Flood studies or floodplain risk management plans are not created for, or on behalf of insurance companies. Flood studies are a legal requirement for Council and part of Council’s responsibilities to help manage flood risk and the impact on people and property. Insurance companies may rely on their own assessment of risk and their own methods to identify flood risk.

The Draft Flood Study will be publicly exhibited and at that time individuals are invited to comment and make representations. Council is in the process of developing a dispute mechanism in the case of there being disputes related to properties identified as flood affected.

Climate change impacts will be considered in the Flood Study by assessment of the significance of increases in rainfall and sea level on flood levels

By following the prescribed Flood Risk Management process, Council will be in a position to request grant funding from the NSW Government for work that is identified by the Flood Risk Management Study and Plan (the development of these documents follows completion of the Flood Study)

Annual exceedance probability (AEP) is now the preferred terminology and that which will be used in the study as opposed to the previously used ‘annual recurrence interval’ terminology. For example, a 1% AEP flood has a 1% or 1 in 100 chance of being reached or exceeded in any given year.

This is the largest flood that could conceivably occur at a particular location, usually estimated from probable maximum precipitation (PMP), coupled with the worst flood-producing catchment conditions.

The greatest depth of precipitation for a given duration meteorologically possible over a given size storm area at a particular location at a particular time of the year, with no allowance made for long- term climatic trends (World Meteorological Organisation 1986)