Key Flood Terminology & FAQs

For this study, this term refers to areas within the Mosman area where new developments may be subject to flood-related planning controls to minimise flood risks. 

Details of the process used to develop FPA is provided in the Draft Flood Study Report.

The preliminary FPA has been determined as part of the current study and this will be finalised in the next stages of the Flood Risk Management process.

Whilst no immediate action is required by an owner, should your property 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.

Planning controls contained within Council’s Local Environmental Plan (LEP) and Development Control Plans (DCP) relating to flood risk management.

For this study, this term describes how likely it is for a rainfall or a flood event to occur.

For example, a 20% AEP event means there is a 20% chance (or 1 in 5 chance) of this event occurring or being exceeded in any given year.

A 1% AEP event means there is a 1% chance (or 1 in 100 chance) of this event occurring or being exceeded in any given year.

Just because a 1% AEP event occurred last year does not mean that it won’t happen for another 100 years.

The largest flood that could conceivably occur at a particular location.

The PMF supports emergency management planning and considers the ease of evacuation during an extreme flood.

NSW Flood Risk Management Manual outlines the State supported pathway to understand flood behaviour and effectively manage flood risk. The key stages of the Flood Risk Management (FRM) process include data collection, flood study, flood risk management study and flood risk management plan.

Floods do not have regular patterns and can be affected by a range of factors. There also may be long periods when there are no floods and short 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 in the 80’s and 90’s 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.

There are many factors that can affect the value of any property including economic and financial conditions, supply and demand, aircraft noise or nearby significant construction works. 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 and note that impact on property values is outside the scope of a flood study.

The Insurance Council of Australia states that insurers already have extensive data on flood risk. The general insurance industry has developed the National Flood Insurance Database (NIFD) for use by insurers to determine flood risk. Insurers use the NFID and other criteria including building type, location and claims history to calculate insurance premiums. Further information on flood insurance is available from the Insurance Council of Australia:

Flood insurance explained - Insurance Council of Australia https://insurancecouncil.com.au/resource/flood-insurance-explained/

Councils complete flood studies to understand flood risk to their communities. These studies inform Council, government, and the community about flood risk so it can be considered in decisions in response to floods and managing flood risk. The impact on property insurance is outside the scope of all flood studies.