Semaphore South dune restoration
- Why is the area to the north of the Semaphore South breakwater an erosion hot spot?
- What has been done to restore the dunes?
- How is the sand being stabilised?
- What do I need to do when I visit this area?
- What community engagement has occurred?
Why is the area to the north of the Semaphore South breakwater an erosion hot spot?
The area immediately north of the Semaphore South breakwater (from approximately Noonies Cafe to Hart Street) is prone to erosion.
A severe storm in May 2016 caused widespread coastal erosion throughout South Australia. At Semaphore South, much of the dune and its vegetation was lost.
Major replenishment works to restore the dunes and protect the area from further damage by storms was undertaken in 2020.
What was done to restore the dunes?
Sand was moved from north of the Largs Bay jetty, where there is a large accumulation to rebuild the eroded dunes at Semaphore South between Arthur Street and Hart Street.
More than 8000 plants were planted and drift net fencing was installed to stabilise the dunes. Sprinkler irrigation was installed to help the plants establish and grow and also help to reduce wind-blown sand.
When was the work done?
Dune restoration works commenced in late April 2020 and were completed in August 2020.
- Sand was moved from the beach between the Largs Bay jetty and Strathfield Tce, Largs North to rebuild the sand dunes at Semaphore South. (Stage 1 – completed end May 2020)
- Drift net fencing, revegetation and sprinkler irrigation was installed to help stabilise the dunes. (Stage 2 – fencing and irrigation completed July 2020 / revegetation (planting) completed August 2020)
- The City of Port Adelaide Enfield replaced the boundary fence and upgraded the turf and irrigation in the area.
This timing ensured that a buffer was in place to protect the area for winter when storms causing further erosion are more likely.
How is the sand being stabilised?
The sand was shaped to match the normal dune profile along Adelaide’s metropolitan coast (i.e. a raised fore dune area and lower rear dune / swale behind).
Stabilisation has followed well established methods using drift net fencing and revegetation (refer for example to the Tasmanian Coastal Works Manual for further information).
- Standard drift net fences, as used extensively in other council areas, has been erected along the dune, parallel to the beach. The drift fences help to trap windblown sand coming from the beach and dune face and provide a more stable environment for establishment of vegetation.
- During Stage 1 of the project (moving sand to rebuild the dune) beach-cast seagrass wrack, left on the beach by tides and waves in the vicinity of the works, was incorporated into the replenished dune at Semaphore South. The seagrass wrack provides some organic nutrients, assisting plant growth and it also helps to bind the sand.
- Extensive revegetation followed, in accord with a species list and planting plan provided by independent ecologists who completed a comprehensive vegetation survey of the Largs Bay coast.
- Ongoing weed control and further planting will occur in subsequent years to increase the biodiversity and resilience of this area.
These techniques have been used with great success to re-establish dunes on Adelaide’s southern beaches, such as at Seacliff and South Brighton (example pictured below).
| Replenishment of the dunes at Semaphore South is required periodically to keep the dunes topped up and the area protected. This was last undertaken in August 2021. |
What do I need to do when I visit this area?
The community and beach users are asked to:
- Take extra care on the beaches and adhere to safety signs and directions.
- Stay off the dunes. This is important so that the sand remains stable and there is no damage to plants.
See: Why have some of the beach access tracks been raised in height?
What community engagement has occurred?
The department worked closely with the City of Port Adelaide Enfield and community representatives on the project. Community input was sought in March 2020 on the proposal, and the majority of feedback received supported the work to restore the dunes at Semaphore South.
ADDITIONAL INFORMATION
Why have some of the beach access tracks been raised in height?
Some of the beach access tracks at Semaphore South were raised with sand to match the shape of the newly placed dunes. This was done to ensure that all of this stretch of foreshore is protected from flooding and erosion. The department and council regularly monitor the area.
The beach access path nearest to Noonies Café has not been raised in height.
We apologise for any inconvenience caused.
How do you know that the sand to the north of the Largs Bay jetty is suitable?
Historically, sand at the northern end of Largs Bay has proven to be unsuitable for replenishing beaches further south on the Adelaide coast as it is finer and would wash away more quickly. The most recent sand sampling analysis (2019) indicated that sand in the area immediately north of Largs Bay jetty has become coarser over time and is now suitable for replenishing the dunes at Semaphore South.
Large volumes of coarse sand from external sources were added to the southern beaches in the 1990s. It is possible that this sand has now moved northwards into this section of the coast.
How much sand was moved from Largs Bay to restore Semaphore South?
An estimated 34,000 cubic metres (m³) of sand was moved to Semaphore South to rebuild the Semaphore South dunes in 2020. This includes approximately 30,000 m³ from the beach north of the Largs Bay jetty to Strathfield Tce, Largs North and approximately 4,000 m³ moved from around the Largs Bay jetty. The new sand dunes were built to resemble the wider dunes to the north of Hart Street in size and width.
What impact will moving sand have to the dunes north of the Largs Bay jetty?
The approach for managing Adelaide’s beaches is based on expert advice underpinned by decades of collected data, including current and historical survey information on beach profiles and independent technical reports. A team of environmental specialists monitor and assess Adelaide’s beaches regularly. Annual beach surveys are undertaken along the coast to measure the beach profiles and assess if there is a sufficient dune volume buffer in the area.
- The government has assessed that any environmental impacts on the coastline north of Largs Bay jetty as a result of the proposed removal of the volume of sand required to rebuild the Semaphore South dunes would be minor.
- The stabilisation and revegetation of the Semaphore South dunes will create significant environmental benefits associated with improved biodiversity outcomes.
- At the location north of the Largs Bay jetty, the government’s beach profile data indicates that there is sufficient dune volume buffer to allow removal of the sand required to rebuild the Semaphore South dunes.
- Based on previous experience and monitoring of areas where sand has been collected, the impact on the dunes of removing sand from the intertidal zone as part of the trial is expected to be minimal.
- The area will steadily build up again through natural processes.
- The department engaged independent ecologists to undertake a vegetation survey in March 2020 to assess and map the flora communities along the 5km length of coast between Semaphore Surf Life Saving Club and Strathfield Terrace.
- This baseline information has informed species selection for the planting of the restored Semaphore South dunes, will enable any impacts of the trial to be monitored, and will inform future works.
- The field assessment includes gathering information about native species present, weed species present and their cover category, native plant life forms, native/exotic understory biomass, tree health, etc. Incidental fauna observations were also recorded.
An independent review has also been undertaken to assess the impacts of moving sand from the northern beaches.
More information
Image gallery
