Council is working on a design to replace the causeway on Otford Road after it was damaged beyond repair during flooding in February 2023.
During significant rainfall, huge slabs of concrete lifted off the causeway and moved along the road and Hacking River. The culverts under the road surface were also moved and broken.
Our current work involves a number of steps and considerations. Since the causeway was damaged, we have:
- Progressed work on a design to replace the culvert. As part of this work, we have met with NSW Fisheries – as a key stakeholder who will need to approve the project design – to discuss their needs and expectations for a replacement culvert over the waterway.
- Spoken with suppliers about what materials are needed to deliver this project, so that we can fast-track the start of works. We are still facing supply chain challenges on building materials and products.
- Had conversations with the NSW Rural Fire Service and other key agencies to consider the risk to our community due to the road closure. A particular focus of these conversations has been what steps need to be considered if the road is not reopened by summer 2023-2024.
- Started work on a plan to remove the debris of the old causeway from the waterway. This removal work is complicated because the river environment is sensitive, and there are overhead powerlines at the site. A crane would be needed to lift the concrete slabs out of the waterway. We are developing a plan to do this work safely and with minimum disruption to local electrical supply. The first stage of the cleanup started on Friday 10 March 2023 in the road corridor. We are waiting on approvals for work within the watercourse.
- Created temporary pedestrian access across the former causeway, so people can move from one side to the other more safely.
Throughout this process we’ve been focused on making sure the new causeway will be more resilient to future floods.
The previous causeway was constructed in the 1970s. The replacement causeway will be built to current engineering standards, and we will consider the latest flood and debris movement data and information when preparing the new design. This is expected to make it more robust in rain events.
We have also made a commitment to local residents to continue looking into designing flood gates on either side of the causeway to manage risk to drivers in time of flood.
A section of Otford Road either side of the causeway is closed. We appreciate that this is challenging for many residents and people going about their daily routines. We are working to replace the causeway and get the road reopened as soon as possible.
We will keep residents updated about the steps Council is taking and any further updates for this important project.
Why a causeway and not a bridge?
We know there have been questions about why Council will not build a bridge at this point in Otford Road.
Council did investigate a bridge option in 2020. However, the geology, topology and landscape at this location, as well as the impact on residents and private property, means a bridge would not be feasible at this location.
The 2020 investigation considered a detailed survey of the area, flood modelling which used confirmed historical flood data, and the Australian Standards for bridge design. This work showed that a bridge span of approximately 90m would be required at this location to provide safe access in major flood events. This is because a combination of flood modelling, historical information, rainfall records and observation show that floodwaters can reach a depth greater than 5m at this location. This is 2.8m higher than the flood levels of the February 2023 event, according to photos shared with Council by local residents.
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