A floodplain map shows the depth of floodwater in a given flood event. For the purposes of planning, a 1-in-100-year flood event is used as a standard measure. The 1-in-100-year floodplain map shows the extent of inundation and provides the City of Burnside with a guide for planning urban development. It also provides a base for development of strategies to reduce and manage flood risk. Another way of describing a 1 in 100 year flood, is to say that it has a 1% (1/100) chance of happening in any one year.
Floodplain Mapping
A flood of the magnitude of 1-in-100 years would be expected to occur, on average, once every 100 years. That means there is a one percent, or 1-in-100, chance of a flood of this magnitude in any one year.
Of course, floods do not occur on a regular basis and a 1-in-100 year flood may not occur in every 100 year period. Conversely there could be several floods that exceed the 1-in-100 year flood levels within any period of 100 years.
For planning purposes, the 1-in-100 year rainfall event is used as a standard measure.
The map was generated by computer modelling to predict how water from a series of 1-in-100 year storm events in both rural and urban catchments would affect the local creek systems. This is based on our knowledge of the likely volume of runoff water generated and the topography the across the catchment.
The floodplain study and map will help Councils and the Government with planning decisions for safe and orderly development. Importantly, it will also help with the development of flood management, prevention and reduction initiatives. It also allows residents, Councils and emergency services to be prepared and to know where water is likely to flow, in the event of a flood.
Council's Development Plans already contain policies which require that new development in the City of Burnside is located and designed so as not to increase flooding risk or expose occupants to avoidable risk. Where older, outdated maps and policies are contained in Council's Development Plan, the Development Plan is amended through a Development Plan Amendment (DPA) process to ensure that the best available technical advice on the floodplain is included.
As part of the development assessment process, Council planning staff will determine whether the proposed development is likely to be affected by flooding. Applicants will be required to provide evidence as part of the development application indicating how they have mitigated any threat of inundation and this may be by raising floor levels above the flood level.
Council will use the mapping study to inform its decisions on development applications. Decisions are made on the basis of the best available information at the time and on safe and orderly development. You should speak to Council's planning department.
There is no provision for such compensation. The floodplain mapping study does not increase the risk of flooding, it merely identifies areas of risk.
A UK study into the impact of flooding on residential property (2004) showed that recent flooding (water entering the home) can adversely affect the value. Average drop in value was found to be 12%. The study also found that the value of flooded properties experience a progressive recovery over several years, providing there was no recurrence.
An Australian study into the consequences of the release of floodplain maps, was undertaken by the Natural Hazards Research Centre based at Macquarie University in 2003. The report concludes that there is no long-term impact on property values. It identifies that different studies (conducted in a number of different countries) show different results, some have negative impact, whilst others do not. The study resolved that whether there was an impact or not, Councils have a duty of care to disclose the information It also concluded (as noted above) that there is a bigger impact on property values from actual floods rather than identifying that a property is at risk of flooding.
A study undertaken by the Bureau of Meteorology in Adelaide's western suburbs showed that the cost of damage due to flooding could be reduced by 30 - 60% by simple 'flood proofing' measures such as: provision of temporary flood barriers across windows and doors and; elevating at-risk articles above flood level. A brochure and checklist to assist residents to prepare an Emergency Flood Plan, with information about how to safeguard your home, is available on the City of Burnside website (www.burnside.sa.gov.au). They can also be obtained from the Civic Centre or by calling 8366 4200.
Insurance cover varies and you should check with your insurer. It should be noted that generally, house and contents insurance does not cover flooding.
Flooding is a natural event. Virtually the entire eastern suburbs are on a natural floodplain. Understanding the risk and the likely behaviour of floodwaters is the first step towards managing the situation. Councils, the Adelaide & Mount Lofty Ranges NRM Board and the State Government are working together to develop strategies to better prepare for and manage flood events. The solutions could cost many millions of dollars and take many years to implement. A range of options needs to be thoroughly assessed and the community consulted. The risk of flooding cannot be completely removed.
The City of Burnside has prepared a brochure providing information to assist residents to prepare an Emergency Flood Plan. A checklist has also been prepared. Copies can be obtained from Council's Customer Service Centre or by phoning 8366 4200.
The Adelaide and Mount Lofty Ranges Natural Resources Management Board acts as a facilitator to ensure that these issues are examined and acted upon on a catchment-wide basis, rather than just at the local Council level. Floodplain management responsibilities are shared by State and Local Governments and their various agencies.
Council has the primary responsibility for management of development within floodplains. Council will use the up-to-date floodplain maps to guide its planning and development decisions to ensure that any development does not adversely affect flood risk in other areas and that new developments are not at risk of flood damage in a 1-in-100 year flood. Council is also working with neighboring Councils, the Adelaide and Mount Lofty Ranges Natural Resources Management Board and the State Government to develop and implement strategies to better prepare for and manage flood events.
These maps have only just been finalised, so the latest information has not been available to Council or the public until now. Council makes decisions based on the best information it has available at any given time. We now have a better understanding and knowledge of rainfall patterns throughout the catchment, so we can better predict where water will flow.
The fact that you have never been flooded before is no guarantee that it won't happen in the future. The flood shown on this map is a relatively rare event that may not occur in a lifetime. We now have a better understanding and knowledge of rainfall patterns and topography throughout the catchment so we can better predict where water will flow.
By planning for a 1-in-100 year flood, we're also reducing the impact of lesser floods. When Councils undertake floodplain mapping studies they look at all possible floods from the fairly regular 1-in-5 year flood through to the unlikely 1-in-500 year and probable maximum floods. Councils, the State Government and emergency services use all of this information to plan for and assess flood risk. The 1-in-100 year flood is the accepted standard for development planning and is the level that Councils in South Australia generally take into consideration when making planning and development decisions. Some Councils also have policies based on other recurrence intervals.
When Councils undertake floodplain mapping studies they look at all likely floods from the fairly regular 1-in-5 year flood through to the unlikely 1-in-500 year flood and the probable maximum flood. Councils, the State Government and emergency services use this information to plan for and assess flood risk. The 1-in-100 year flood is the internationally accepted standard for development planning and is the level that Councils in South Australia generally take into consideration when making planning and development decisions.
The cost of physical works required to prevent flooding in the case of larger floods (i.e. a 1-in-500 year flood) would be prohibitive and unreasonable given the likelihood of this magnitude of flood occurring. The environmental and visual impacts of such infrastructure would also be considerable.
The limit of flooding shown on the map is not a boundary between flood-prone and flood-free land. The floodplain mapping only dealt with water flowing down the creeks and did not model the capacity of local drainage systems to cope with such storm events.
Land outside the flood extent shown on this map could be affected by:
- larger storms
- flooding from local drainage systems, which can occur as a result of localised heavy rainfall or drain blockage
Council is working with neighbouring Councils, the Adelaide and Mount Lofty Ranges Natural Resources Management Board and the State Government to develop an Urban Stormwater Management Plan. The Management Plan will, among other things, identify options, priorities and costs for reducing the risk of flooding in vulnerable areas.
Our aim is to better prepare for and manage flood events for the majority of properties. No property can be made entirely free from risk.
Council is working with neighboring Councils, the Adelaide and Mount Lofty Ranges Natural Resources Management Board and the State Government to develop an Urban Stormwater Management Plan. The Management Plan will, among other things, identify options, priorities and costs for reducing the risk of flooding in vulnerable areas.
With the sale of a property, real estate agents are obliged to provide potential purchasers with the Section 7 statement. The Section 7 statement is a statement of encumbrances on the property and will include an advisory note highlighting that some properties may be subject to inundation.