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.
Environmental Geosurveys Pty Ltd (1997) - Lonsdale Bay Analysis of Beach, Dune and Offshore Sand Analysis of sand samples to in inform the Vantree (1998) report Five samples from the seafloor in Lonsdale Bay, two from a beach and one from a cliffed dune along The Narrows Various analytical methods used Conclusions Similarity of texture, composition and grain size characteristics point to a common origin Shape and texture consistent with an aeolian history – derived from dunes but subject to wave transport and worked in shallow environment Carbonate/quartz consistent with other beach and dune surveys Broad similarities between onshore and offshore material suggests an exchange and reworking of material between the environments Sufficient differences to suggest episodes of different nourishment and transport occur Repeated sampling combined with profiling would reveal actual rate of exchange and mobility of sand bodies Limited samples but confirms likely origins and history of sand movement Lawson and Treloar Pty Ltd (1998) - Lonsdale Bight Coastal Processes Investigation Wave and Current Measurements This report details the wave and current measurements carried out to inform the modelling and assessment of coastal processes undertaken for the Vantree (1998) report. Extensive field measurements to support modelling and investigations as part of Vantree (1998) report. Aim to measure transformation of waves as they propagate from Bass Staright into Lonsdale Bight and to determine the strength and spatial distribution of currents within Lonsdale Bight and the entrance region. Data included waves and currents for 2 months at a number of sites including 2 in Lonsdale Bay. Spatial variations in currents were measured via ADCP transects over 3 days but the quality was compromised by adverse conditions. Waves Marked reduction in wave height between Bass Straight and the beaches of Lonsdale Wave heights are modified by strong currents Wave periods indicate swell from the Southern Ocean and from a steady direction Currents Flood tide currents in Lonsdale Bight approx. parallel to the coast and stronger than ebb near the beach Provides information on broad processes Limited time frame for measurement of waves but suitable to assess transormations No apparent data near Point Lonsdale Front Beach
Geotechnical advice on appropriate to batter cliff Detailed design of new groyne could be progressed in parallel and make use of wave studies and survey rubble mound 50m long with a crest elevation of 1.5m CD Atkins Maritime Engineering Pty Ltd (2013b) - Dog Beach Adaption Concepts Concepts for possible works at Dog Beach Concept drawings for 3 options works at Dog Beach Periodic Renourishment Geotextile sandbag toe protection buried under renourished beach to provide last line of defence Renourish beach using mid-scale dredging plant with opportunity to integrate with Queenscliff sand bypassing Periodic renourishment required as part of management of embayment Gabion Revetment Dune protected by teatree brush filled gabions at toe of dune Shallow slope and low reflectivity selected to minimise erosion Height dependent on maximum wave run-up tbc Offshore Breakwaters Height location and dimensions designed to prevent tombolo formation and enable bypassing of longshore drift Concept could initially impact on down drift beaches until equilibrium of salient formation reached No supporting report provided and apparently rejected in DEPI assessment Presumably this is meant to mean prevention of a shore connected tombolo Victorian Coastal Council (2014) - Victorian Coastal Strategy A long term vision and framework for planning and management of the Victorian coastline Ensure that development or protective works seeking to respond to coastal hazard risks avoids detrimental impacts on coastal processes to lessen the effects of coastal processes on public and private land are avoided, particularly along the open coastline. Investment in new and existing coastal infrastructure is based on a life cycle planning approach that takes account of: projected future erosion and inundation patterns – this planning incorporates scope for the removal and replacement of structures as may be necessary and the use of trigger points to initiate adaptation responses (including an assessment of acceptable level of risk and behaviour change) cost benefit analysis that takes into account social, environmental and economic values future operating and maintenance costs and accountabilities any statutory requirements to maintain coastal infrastructure Background policy considerations for planning coastal works
Some capping blocks need replacing but compromise structural integrity More evidence of mortar joint loss but no evidence of blocks falling out. Should be addressed issues include corroded handrails and blocked path drainage Conclusion no sign of instability apart from crack at southern end. Not sufficient to suggest the wall is unstable but should be repaired and monitored. Indicates masonry wall is basically stable with substantial sand build in some sections resulting in no load. Cardno (2015) - Inundation Report Bellarine Peninsula – Corio Bay Local Coastal Hazard Assessment Provides an understanding of the extent of coastal hazards and impacts on the coastal environment Intended to provide comprehensive understanding of coastal hazards and impacts on coastal environments through addressing coastal, estuarine/riverine and climate change challenges by defining the possible magnitudes and extents in a considered and robust manner. Provides info and basis for to identify additional studies so Councils and land managers are prepared for future hazard and climate change related challenges and to inform strategic planning and decision making. Intended to inform subsequent risk and mitigation assessments to guide and prioritise implementation of management actions. Entrance area is a complex environment dominated by swells and strong currents with the influence of swells diminishing with distance from the entrance. Lonsdale Bight section consists of high cliffs, long sections of protection structures and dunes Key hazards are erosion, overtopping of the protection structures and inundation of low areas Methodology initially involved modelling of and water levels throughout to provide design conditions for inundation modelling Key findings for Lonsdale Bight: Subject to overtopping and inundation hazards with assessment undertaken of the overtopping of the shore protection structures Quite a significant hazard for the present day and in future with sea level rise Seawall is regularly repaired due to the effects of direct wave impact Incidence of damage likely to increase over time therefore continued maintenance is Overtopping hazard decreases further around Lonsdale Bight due to change in seawall type , increasing height and general decrease in wave energy Area wide recommendations at reducing uncertainty and to aid future management decisions: Establish a thorough and consistent monitoring program – beach profiling will be a key aspect While an overview of coastal processes is provided, focus is on inundation and overtopping rather than direct erosion related hazards Is there a similar separate document that focusses on erosion covering Lonsdale Bight? on inundation modelling rather than erosion