Key points
- A new flood planning level for the local government area was determined using freeboard and climate change projections.
- Flood mitigation infrastructure could be used to protect the suburb while long-term adaptation measures are implemented.
Davistown is a low-lying suburb within the Brisbane Water catchment in the Central Coast local government area. The properties within Davistown are at risk of coastal inundation, flooding by overland flows and tidal inundation exacerbated by sea level rise.
Davistown will face difficulty maintaining normal urban residential area functions under climate change projections.
The Davistown and Empire Bay Climate Change Adaptation Study (commissioned by Central Coast Council and authored by Rhelm, 2020) describes the development of a draft landform and drainage master plan to manage the impacts of sea level rise and local drainage. The plan will fill and raise the entire local government area (private and public assets) in a staged process to reduce the damage associated with the hazards and improve drainage.
To provide interim protection up to the 1% annual exceedance probability flood level set in 2015, a levee would be developed between 2025 and 2030. This levee, shown in Davistown GD706 interim landform scenario map (PDF, 1.4 MB) will comprise the berm, retaining wall and shared path and will be set at 1.5 m above the Australian Height Datum. Sea level rise is expected to increase this by 7 cm by 2030.
Associated with the filling and redevelopment of properties, the new properties would have floor levels that comply with the council’s development controls. The analysis for the adopted maximum floor level included:
- a flood planning level equal to the 1% annual exceedance probability flood level plus 0.5 m freeboard plus 0.3 m climate change increase, as per the base case or
- a level 0.3 m above ground level, given that the master plan ground levels exceed the flood planning level in some locations to achieve the overall raised surface.
This case study shows how sea level rise can impact local hazards such as overland flooding and tidal and coastal inundation. Using this information, the council has planned to raise the area to increase its future resilience and it’s short term resilience through a mitigation structure.
