THE State Government is calling on the community to provide feedback on the Silverleaves Coastal Processes Study and have their say on future management of the local coastal environment.
The draft study outlines the current state of the Silverleaves coastline, identifies areas at risk from coastal processes and explores potential responses – including natural solutions to mitigate the risk of erosion and protect natural habitats.
The project has developed detailed modelling, analysis and hazard maps to offer a regional perspective on coastal processes and the potential exposure of locations, values, and assets to coastal hazards.
Member for Bass Jordan Crugnale has encouraged those with an interest in Silverleaves to provide some feedback or attend one of the information sessions.
“Silverleaves is a cherished part of our local community and it’s important that we do what we can to protect its character and environment,” Ms Crugnale said.
“We encourage everyone to get involved in the consultation.”
In addition to online information sessions, in person information sessions will be held on Friday, August 30 from 10am to 12pm at Berninneit Cultural Centre in Cowes – giving attendees the opportunity to learn more about the study’s scientific coastal processes, ask questions and share their priorities.
Community members, local organisations, and stakeholders are invited to review the draft study and provide share their thoughts on the study from Thursday, August 29 to Friday, September 27, 2024.
According to Ms Crugnale, since 2014, the State Government has invested $140 million into marine and coastal projects to respond and adapt to coastal hazards, building the resilience of local communities and Victoria’s iconic natural environments.
From the Silverleaves Coastal Processes Study
Executive summary: This study focuses on the approximately 2km stretch of the Silverleaves coastline, west of Coghlan Road, encompassing a broader geomorphological unit that includes East Cowes Beach and the sandy spit extending to Observation Point.
The objectives of this project were to assess the impacts and effectiveness of existing coastal protection structures along the East Cowes foreshore adjacent to Silverleaves, evaluate the coastal dynamics and processes affecting the East Cowes and Silverleaves shoreline, assess coastal hazards, and determine the likelihood of erosion leading to breaches as well as temporary inundation during regular and extreme events.
Key findings indicate that the shoreline position along East Cowes and Silverleaves is influenced by various anthropogenic interventions as well as naturally occurring and locally modified coastal processes. This dynamic shoreline was formed by sand supplied from Bass Strait into Western Port and along Northern Phillip Island over geological timescales.
This sand supply, which varies seasonally and temporally, continues to provide sediment to many beaches on Phillip Island, including East Cowes and the Cowes Bank.
East Cowes is heavily modified by coastal protection structures, such as groynes and revetments, which shape much of this shoreline and influence both sediment transport and shoreline dynamics.
Terminal erosion at the eastern most revetment (near Silverleaves) that was constructed in 1977 has led in the decades since its construction to erosion, scouring, and reorientation of the shoreline at Silverleaves. Aerial imagery analysis indicates that the shoreline has eroded at an accelerated rate especially in recent years (since 2022), where shoreline setback of up to 8m/year has been observed.
Numerical model results suggest that the altered shoreline orientation at Silverleaves that has resulted from this long-term erosion may now be enhancing sand scour during strong tidal circulations or wave activity, contributing to the increased local erosion rate recently observed.
Current patterns and survey data analysis indicate that upstream revetments and previous timber seawalls have contributed to scour in the nearshore area, likely due to wave reflection, pushing sediment to the outer bank, where it is possibly carried east.
This appears to result in some sediment bypassing Silverleaves, likely due to the combined effects of shoreline orientation and flow separation. The analysis suggests that the sediment pathway reattaches to the Silverleaves shoreline further downstream at central and eastern Silverleaves, where both historic and recent shoreline accretion is observed.
We note that historic sand scraping may also be a contributing factor. Recent beach nourishment efforts have proven to be sacrificial and are not considered a sustainable long-term solution for mitigating this erosion. Further analysis indicates that existing interventions like groynes, while preserving beach amenity and retaining sand locally at East Cowes, impedes natural sediment supply to downstream areas such as Silverleaves.
This is particularly relevant directly in front of the recently constructed pattern placed rock revetment where the newly upgrade/installed groynes are relatively inefficient. Substantial erosion of the Silverleaves shoreline can be expected within the immediate planning horizon.
It is important to note that Silverleaves is also subject to inundation hazards within the current planning horizon. Inundation from Rhyll Inlet is beyond the scope of this assessment but has been shown in past assessments to be a critical hazard and thus it will be a key consideration for adaption planning at Silverleaves.
The key recommendation from this study is that there is a critical need to develop sustainable, long-term adaptation pathway and coastal protection strategies for Silverleaves encompassing inundation hazards from Rhyll Inlet.
A key gap identified in this study is the lack of comprehensive time-series validation of current patterns. Numerical models used in such shallow, complex environments may produce erroneous results. Therefore, we recommend collecting both current and wave data on Cowes Bank to confirm these results, particularly along the shoreline to validate the predicted flow separations.
Such validation data could be obtained once the an endorsed adaptation pathway has been identified (if required).
From the Silverleaves Coastal Processes Study summary:
“Silverleaves has changed significantly over geological timescales and has been formed by successive spits and the natural filling in of the Silverleaves Bight. In recent history, the eastern shoreline has experienced accretion while the western shoreline has faced ongoing erosion, receding about 77 metres since 1953. This is mainly due to terminal erosion from a nearby revetment and reduced sand supply caused by natural factors and upstream human activities like groynes and revetments. Since 2022, terminal erosion has locally accelerated, with the shoreline retreating up to 16 metres in just two years.”
For more details on the Silverleaves Coastal Processes Study click HERE
