The information contained on this web page has been provided to assist the community in understanding how Redland City Council's storm tide mapping was developed, how it is to be interpreted and how it will be used.
The coastline of Redland City is vulnerable to impacts from coastal hazards such as storm tide inundation, which presents risks to people, property and infrastructure. Accordingly, Council has an obligation to make the community aware of these risks (e.g. by producing storm tide mapping) and ensure planning and development decision-making accounts for these risks.
On this web page there are two storm tide maps. The first is the statutory Flood and Storm Tide Hazard Overlay and the second is the non-statutory 2070 Storm Tide Map. These maps each serve different purposes, as outlined below.
- Flood and Storm Tide Hazard Overlay Map
- 2070 Storm Tide Hazard Map
- Frequently Asked Questions (FAQ's)
Note: The Flood and Storm Tide Hazard Overlay map is broken into two parts. One covers the mainland and the other covers the Southern Moreton Bay and North Stradbroke Islands.
The Flood and Storm Tide Hazard Overlay (FSTHO) is a statutory map that forms part of the new Redland City Plan. It has been developed in accordance with the requirements of the State Planning Policy (SPP). Within the FSTHO there are two storm tide 'layers'; the 2016 Storm Tide Inundation Area (non-statutory) and the 2100 Storm Tide Inundation Area (statutory). The 2016 Storm Tide Inundation Area depicts the area predicted to be impacted during a 1% Annual Exceedance Probability (AEP) Storm Tide Event in the year 2016. It enables the community to understand the areas that may be subject to impacts from a 1% AEP storm tide event under current climatic conditions. When determining the 2016 Storm Tide Inundation Area, the future effects of climate change have not been considered.
The 2100 Storm Tide Inundation Area depicts the area predicted to be inundated during a 1% AEP Storm Tide Event in the year 2100. It enables the community to understand the areas that may be subject to impacts from a 1% AEP storm tide event under future climatic conditions (i.e. in the year 2100). It may have implications for certain types of development that are proposed in a storm tide inundation area. For example, residential development proposed in a storm tide inundation area may be required to construct habitable floor levels above the peak level reached during a defined storm tide event. The peak storm tide levels can be obtained by performing a 'property enquiry' on Council's website, via Developmenti. It is noted that the maximum storm tide levels vary along the Redland City coastline.
When determining the 2100 Storm Tide Inundation Area, the effects of climate change have been considered. This includes an assumption of the following impacts at 2100:
- A rise in sea level of 0.8m
- An increase in cyclone maximum potential intensity of 10%
Note: The 2070 Storm Tide Map is broken into two parts. One covers the mainland and the other covers the Southern Moreton Bay and North Stradbroke Islands.
The 2070 Storm Tide Map is a non-statutory map. It has been developed to assist the community in understanding the storm tide impacts that may be experienced in Redland City over the next 50 years, as this reflects the approximate design life of a newly constructed dwelling house.
The 2070 Storm Tide Map depicts the area predicted to be inundated during a 1% AEP Storm Tide Event in the year 2070. When determining the 2070 Storm Tide Inundation Area, the effects of climate change have been considered. This includes an assumption of a 0.41m sea level rise by the year 2070.
2011:Council commissioned a consultant firm (Cardno) to produce a 1% AEP Storm Tide Map for the year 2100. The mapping factored in the predicted impacts of climate change, including a 10% increase in storm intensity and a 0.8m sea level rise by 2100. Furthermore, a 0.3m freeboard was incorporated as a contingency.
2014: Council provided direction to remove the 0.3m freeboard. The revised mapping was subsequently utilised to develop the Flood and Storm Tide Hazard Overlay (FSTHO) that formed part of the draft Redland City Plan (public consultation version).
2015: The revised storm tide hazard mapping was made available to the community during the public consultation period for the draft Redland City Plan, which took place between 14 September 2015 and 27 November 2015. In response to public submissions and interest, Council resolved on 18 November 2015:
- To conduct a desktop review of all Storm Tide studies, assumptions and methodologies prepared for Redland City Council in consultation with the technical working groups of Raby Bay Ratepayers Association and Aquatic Paradise Ratepayers Association, with the State Government; and
- That the findings to be presented to Council for its consideration prior to the draft Redland City Plan being resubmitted to the Planning Minister.
2016: In accordance with the resolution by Council, an independent consultant (Water Technology Pty Ltd) was engaged to undertake the review. The review was coordinated by Council planning officers and prepared in consultation with the technical working groups from the Raby Bay Ratepayers Association and Aquatic Paradise Residents Association and representatives from the State Government. The review culminated in the development of the consultant report titled 'Independent Technical Review of Storm Tide Hazard Studies'. The report noted that while the methodology used to undertake the storm tide hazard studies was appropriate, the methodology used to generate the mapping could be improved.
2016-2017: Further meetings and discussions were held with nominated representatives from the technical working groups to develop a refined FSTHO. As requested by the technical working groups, the refined FSTHO incorporated amendments that will enable users to differentiate between the 2016 (non-statutory) and 2100 (statutory) 1% AEP storm tide event, as well as explanatory notes. The refined mapping was prepared by Water Technology Pty Ltd in early 2017.
2017: Following further discussions with Council officers, a representative from the Aquatic Paradise Residents Association wrote to the Mayor and each of the Councillors requesting the production of a 2070 storm tide map. The rationale provided was as follows:
- As there is an increasing degree of uncertainty associated with predicting the impacts of climate change into the future, using a shorter timeframe reduces the potential margin of error in those predictions;
- Empirical evidence from nearby tidal gauges has not aligned with Sea Level Rise predictions made to date; and
- The mapping could have an adverse impact on property values, as prospective property purchasers may not understand what the mapping is seeking to portray.
Given that newly constructed houses have an approximate engineering life of 50 years, Council officers agreed that preparing a non-statutory 2070 Storm Tide Hazard Map would have merit and assist landowners in gaining a better understanding of storm tide impacts over time. Water Technology Pty Ltd was engaged to undertake this further body of work.
What is a storm tide?
A storm tide is a type of flooding. It occurs when abnormally high ocean levels are caused by cyclones and severe storms, resulting in the inundation of low lying coastal areas.
Why does Council produce storm tide mapping?
State legislation, namely the State Planning Policy 2017, requires Councils to take appropriate account of the potential impacts of natural hazards in order to make effective land use planning and development decisions. Storm tide mapping is produced to assist in this process.
How are the maps used?
The Flood and Storm Tide Hazard Overlay (FSTHO) forms part of the draft Redland City Plan. It will be used in conjunction with the associated Flood and Storm Tide Hazard Overlay Code to assess and decide certain development applications. For example, the FSTHO is used to establish the habitable floor levels of new residential development proposed in a Storm Tide Inundation Area.
The 2070 map is for information purposes only. Its primary function is to convey the area predicted to be inundated during a 1%AEP storm tide event in the year 2070. It assists the community to understand how the risks associated with storm tide are likely to change over time, as the predicted impacts of climate change unfold (e.g. when the sea level rises).
Why are there two different storm tide maps?
The Flood and Storm Tide Hazard Overlay contains statutory storm tide hazard mapping that is used to inform land use planning and development decisions. It was produced in accordance with State Planning Policy requirements.
The 2070 Storm Tide Hazard Map is a non-statutory map that was produced at the request of the community. It assists the community in understanding how the impacts of storm tide are likely to change over time, as the predicted impacts of climate change unfold. It is based on a 50 year planning horizon, which approximately corresponds with the design life of a dwelling house constructed today.
Why is the Flood and Storm Tide Hazard Overlay map based on the year 2100?
The State Planning Policy requires local government to account for the projected impacts of climate change by the year 2100 in its statutory storm tide mapping. This includes:
- A sea level rise factor of 0.8 metres; and
- An increase in the maximum cyclone intensity by 10%.
Why was a 0.8m SLR assumption used?
The State Planning Policy requires that a sea level rise of 0.8m by the year 2100 be used. This projection is based on the best available science that has been prepared by the Intergovernmental Panel on Climate Change.
What is meant by climate change?
Climate change refers to the changes to the present day climate associated with the effects of global warming. Climate change is projected to have a significant impact on the coastal zone especially through sea-level rise and intensification of cyclones. Pre-eminent information about the impact of climate change is provided in the Fifth Assessment Report of the United Nation's Intergovernmental Panel on Climate Change (IPCC).
Annual Exceedance Probability (AEP): means the probability, expressed as a percentage, of an event exceeding a particular level or magnitude in any 1 year (Source: Coastal Protection and Management Act 1995)
Defined Storm Tide Event (DSTE): means the event, measured in terms of likelihood of reoccurrence, and associated inundation level adopted to manage the development of a particular area. The DSTE is equivalent to a one in 100 year average recurrence interval storm event incorporating: (a) sea level rise; and (b) an increase in cyclone intensity by 10 per cent relative to maximum potential intensity (Source: State Planning Policy 2017).
Storm Tide Inundation: means temporary inundation of land by abnormally high ocean levels caused by cyclones and severe storms (Source: State Planning Policy 2017).
Storm Tide Inundation Area: means the area of land determined to be inundated during a defined storm tide event that is identified by a local government in a local planning instrument as a storm tide inundation area, based on a localised storm tide study prepared by a suitably qualified person (Source: State Planning Policy 2017).
For further information, please contact Council on (07) 3829 8999.