However, there are potential significant implications for the Marine National Park, surfing values and visual intrusion associated with offshore breakwaters that would need to be assessed. The advantages and disadvantages are summarised below. Advantages potentially provide long term benefits subject to detailed investigation and design Use of nourishment in conjunction will enhance the benefits and minimise potential impacts Structures and semi-permanent sand will add other environmental and social values Others as determined by stakeholders Disadvantages Potential implications of works in the Marine National Park Visual intrusion into the vista along the shoreline and across the Bay Implications for surfing would need to be investigated Potential for downdrift erosion although this is likely to be negligible given the presence of seawalls and previous works and can be mitigated with beach nourishment but at an additional cost Detailed investigations would be required into the likely success given the importance of tidal currents Risk that offshore breakwaters would not successfully retain a stable beach Very high capital cost and potentially high maintenance cost Difficult to adapt to address the influences of future climate change including sea level rise and does not fully address overtopping of the existing seawall Others as determined by stakeholders Material Sources and Costing Considerations The implementation of coastal protection is dependent on suitable material being able to be obtained and placed in a practical, economical and environmentally acceptable manner. General considerations associated with sourcing, cost and applicability of different material types are discussed below, including preliminary estimates in terms of unit costs for capital and ongoing maintenance works provided on the basis of available information. Cost estimates for the various options can be developed based on these unit rates for comparison purposes. This will be dependent on the extent and combination of hybrid options. Specific recommended works would be subject to detailed design, impact assessment and tendering processes that may influence the final cost. There will also be on costs associated with the design, impact assessment and approval processes for the recommended options.
However, there are potential significant implications for the Marine National Park, surfing values and visual intrusion associated with offshore breakwaters that would need to be assessed. The advantages and disadvantages are summarised below. Advantages potentially provide long term benefits subject to detailed investigation and design Use of nourishment in conjunction will enhance the benefits and minimise potential impacts Structures and semi-permanent sand will add other environmental and social values Others as determined by stakeholders Disadvantages Potential implications of works in the Marine National Park Visual intrusion into the vista along the shoreline and across the Bay Implications for surfing would need to be investigated Potential for downdrift erosion although this is likely to be negligible given the presence of seawalls and previous works and can be mitigated with beach nourishment but at an additional cost Detailed investigations would be required into the likely success given the importance of tidal currents Risk that offshore breakwaters would not successfully retain a stable beach Very high capital cost and potentially high maintenance cost Difficult to adapt to address the influences of future climate change including sea level rise and does not fully address overtopping of the existing seawall Others as determined by stakeholders Material Sources and Costing Considerations The implementation of coastal protection is dependent on suitable material being able to be obtained and placed in a practical, economical and environmentally acceptable manner. General considerations associated with sourcing, cost and applicability of different material types are discussed below, including preliminary estimates in terms of unit costs for capital and ongoing maintenance works provided on the basis of available information. Cost estimates for the various options can be developed based on these unit rates for comparison purposes. This will be dependent on the extent and combination of hybrid options. Specific recommended works would be subject to detailed design, impact assessment and tendering processes that may influence the final cost. There will also be on costs associated with the design, impact assessment and approval processes for the recommended options.
R.B22316.001.03.2.docx