October 11 meeting, 2022
The Davistown and Empire Bay Floodplain Risk Management Study and Plan (FRMS and FRMP) is expected to be adopted at the October 11 meeting of Council-under-administration.
The study includes recommendations for a Davistown foreshore barrier, an Empire Bay foreshore barrier, a review of evacuation centres, and sea wall construction guidelines.
Another high priority is to advance to the next stages of the Davistown and Empire Bay Climate Change adaptation planning process which includes a drainage masterplan.
“The effects of climate change will potentially aggravate the flood conditions in Davistown and Empire Bay over time and significantly compromise the liveability of some portions of the suburbs through flooding of roads, services, and private properties,” the study says.
“The timely preparation and implementation of a Climate Change Adaptation Masterplan will be crucial to guarantee that the flood mitigation measures are ready for implementation when sea level rise triggers are reached.
“Therefore, it is recommended that Council proceed with the next stages of the development of a Climate Change Adaptation Masterplan.
“This will include assessment of the constructability of the proposed adaptation strategy and the implementation planning.”
Council said aspects of the infrastructure associated with proposed climate change adaptation (e.g. foreshore barriers and drainage easements) have been considered and assessed in the FRMS and FRMP as options for managing existing flood risk.
“It was found that not only are these works critical to the future development of climate change adaptation landforms; they also provide immediate management of flood risk through protection against Brisbane Water flooding and improved drainage.
These works included:
- A drainage easement between Myrtle Road and Kendall Road
- A foreshore barrier at Davistown.
The report said the community and other stakeholders provided valuable insights about the flooding issues experienced in Davistown and Empire Bay and how they could be addressed.
“The potential flood risk management measures identified and assessed as part of this study attempt to address the reported issues as far as reasonably possible, considering potential impacts, technical constraints, and the current understanding of the local flood behaviour,” the report states.
Once the FRMSP has been adopted by the administrator, the Council becomes eligible for NSW Government grant funding to implement the recommendations.
The projects would be listed and ranked on Council’s future capital works program; funding options for each would be considered at the time of listing on the 4-year Delivery Program.
“It should be noted that the FRMSP commits Council to implementing the Master Plan (including the foreshore barriers and land raising) in principle; however, the final decision on how to proceed will be informed by detailed feasibility analysis,” the report to the administrator stated.
“The concept level economic analysis undertaken in this FRMSP does not include the following unquantified benefits such as mitigating the loss of public infrastructure (beyond parks and roads), loss of environmental values (e.g. wetland preservation through tidal management), and loss of recreational values (foreshore reserves etc.).
“Detailed economic feasibility analysis would be undertaken; this would involve the inclusion of the unquantified benefits and would also typically involve a more detailed understanding of design, costs and community input.”
Sensitivity analysis undertaken as part of the FRMSP shows that for the structural options such as Empire Bay Foreshore Barrier, the Benefit Cost Ratio (BCR) improves significantly (>1) with a 20% increase in the rate of sea level rise.
Similarly, BCR increases (>1) if the actual discounted rate used in Net Present Value (NPV) calculations are less than the conservatively assumed 7%.
The full report is on the council website, included in the October 11 agenda and attachments.
