- Flood extent – how far the water spreads
- An indication of flood depth – how deep the water is across the flooded area
- An indication of flood velocity – how fast and in which direction the water is travelling
- Flood hazard – low, medium, high and extreme areas of hazard based on factors including the velocity of the water and whether this poses a threat
- Improvements to flood warning and emergency management
- Structural works (e.g. levees or detention basins) to protect existing development
- Planning and building controls to ensure future development is compatible with the flood risks
- Measures to raise the community’s awareness of flooding so that they are better able to deal with the flood risks they face
- New rainfall or ground topography information becomes available;
- New floods occur which provide additional data from which to fine-tune the models;
- Better computer models become available as the science of flood modelling improves and computer capabilities increase; or
- Flood mitigation works may have been carried out, or development within the catchment may have occurred, that was not previously represented in the models
- 1%AEP – is a one-in-100-year flood. This means it occurs on average once every 100 years.
- 2%AEP – is a one-in-50-year flood which occurs on average once every 50 years.
- 5%AEP – is a one-in-20-year flood which occurs on average once every 20 years.
What is the North Byron Floodplain Risk Management Study?
The North Byron Shire Floodplain Risk Management Study (FRMS) is a detailed look at current flood management measures for the Simpson's Creek, Marshall's Creek and Brunswick River catchments and includes the towns of Mullumbimby, South Golden Beach, Billinudgel, Ocean Shores and Brunswick Heads.
The FRMS is a technical investigation of flood behaviour in the north of the Byron Shire. It looks at the way floods have impacted the area, particularly the flood in 2017, taking into account depths of flood water, extent of flooding and velocity.
Using the most up-to-date information on rainfall, run-off and topography, along with extensive work Council has done on mapping the floor levels of properties in flood zones in the Shire, the FRMS will be used to help Council determine the impact of future floods and put measures in place to mitigate these impacts through planning practices, capital works and building community awareness.
The FRMS takes into account the economic impact of flooding and future management measures such as flood zonings for properties, levees, hydraulic structures, channel maintenance and evacuation routes and centres.
An important part of the FRMS is the production of a series of flood maps which shows the impact of previous floods as well as the predicted behaviour/impact of a number of flood scenarios. For example a one in 10-year flood, a one in 20-year flood, or a one in 100-year flood.
For each town and locality in the North Byron Shire the flood maps in the Study show the following:
These maps are a good way for people to understand the potential impact of flooding on their property.
What is the North Byron Floodplain Risk Management Plan?
Using information from the FRMS the North Byron Floodplain Risk Management Plan (FRMP) sets out how to manage flood risk in the foreseeable future.
The FRMP sets out a range of priorities including capital works and measures to manage the flood risk such as:
Is flood planning a new thing for Council?
Under NSW legislation, Councils have the primary responsibility for management of floodplains. To appropriately manage development, Councils need a strategic plan which considers the potential flood risks and balances these against the beneficial use of the floodplain for development. To do this, Councils have to consider a range of environmental, social, economic, financial and engineering issues. This is what happens in a floodplain risk management study.
All Councils are required by the NSW State Government to undertake studies to determine what land has the potential to be affected by flooding. This is to ensure that new developments are adequately protected and do not make flooding worse.
Why does Council have to do a new floodplain study and plan or update plans every couple of years?
Flood levels change over time and aretypically estimated using computer models. Computer models are the preferred method for establishing flood levels as they can be used to simulate a range of floods including floods well in excess of those that have been experienced since settlement of the area. Given the importance of estimating flood levels accurately, Councils engage experts (consultants) to establish and operate the computer models.
From time to time the computer models are revised and predicted flood levels can change. The resultant change in flood levels however is normally very small. The reasons why the computer models are revised can include:
What does AEP mean?
AEP stands for Annual Exceedance Probability. It means how likely a flood is to occur in a given year.
10%AEP – is a one-in-10-year flood which occurs on average once every 10 years
My property is in flood zone – what does this mean?
The FRMS identifies properties in the north Byron Shire that are at risk of flooding according to the size of the weather event. Some people may find that with the new scientific data used as part of the study that their properties are now in a flood zone, whereas previously they were not.
Council now has information on the floor levels of all properties in flood zones and the level of predicted inundation during floods.
If your property is in an identified flood zoning this could have an impact on rates and possible future development.
Will the flood study affect my rates?
Rates are determined according to the land value of a property. The land value is set by the NSW Valuer General and Council then calculates the rates accordingly.
For more information visit the NSW Valuer General website www.valuergeneral.nsw.gov.au
Will the flood study affect my insurance?
Council is not responsible for, or able to influence, insurance premiums. Insurers do their own flood risk assessments and risk mapping independent of Local Government. Insurance companies assign risk estimates to different areas based on a wide range of things including bushfire and flood risk.
Flood Studies are a legal requirement for Council to complete 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.
More information about flood insurance is available from the Floodplain Management Australia website -www.floods.org.au/site/flood-insurance-fact-sheets.
My property has never flooded so why has it been identified in a flood risk area?
Although you have never been flooded before there is no guarantee it won’t happen in the future. 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 after 1974 may never considered flooding an issue until the floods in January 2011. Following extensive rain every water course will flood.
Flood studies have been done over many years, showing a range of scenarios and therefore providing an estimate of areas that may be affected during different types of flood events according to the most up-to-date modelling and scientific data available.
Will being in a flood zone restrict/influence the future development of my property?
The aim of the FRMS is to look at ways we can live with flooding to lessen risk to property and people’s lives.
The FRMS will influence land use planning. Council will use this information to ensure flood risk is considered as part of assessment for future development, including development applications.
The information from the FRMS provides greater clarity around the type of development that is best suited to different areas, and it could also influence the level and form of future buildings.
What does it mean if I have a current DA with Council?
Your DA is assessed according to the rules at the time of assessment.
When I built my home it complied with all of Council’s requirements. Now I find it is in a flood-risk area. What do I do?
Property owners should check to see if their property is in a flood risk area and use this information to ensure they are prepared for future flooding events.
Will the value of my property be affected if it is in a flood risk area?
The value of properties in the Byron Shire is driven by a range of factors but ultimately the market determines property values. As at June 2018 Byron Shire had a median house valuation of $1,019,082, $279,358 higher than the median house valuation for NSW.
The fact a property is identified as being in a flood risk area allows owners and residents the opportunity to ensure they are prepared for significant weather events, in terms of personal safety and preservation of property.