A part of BMT in Energy and Environment Lonsdale Bight Investigations Review and Options Overview Reference: R.B22316.001.03.docx Date: January 2017 Draft Lonsdale Bight Investigations Review and Options Overview Lonsdale Bight Investigations Review and Recommendations Lonsdale Bight Investigations Review and Recommendations Prepared for: Department of Environment, Land, Water and Planning Prepared by: BMT WBM Pty Ltd (Member of the BMT group of companies) Offices Brisbane Denver London Mackay Melbourne Newcastle Perth Sydney Vancouver J:\Anglesea\Environmental Planning\CEP\2016-2017\Planning\Project Briefs\Point Lonsdale coastal processes\Coastal Processes Review\Reports\R.B22316.001.03.1.docx Document Control Sheet Document: R.B22316.001.03.docx BMT WBM Pty Ltd Level 8, 200 Creek Street Title: Lonsdale Bight Investigations Review and Brisbane Qld 4000 Options Overview Australia PO Box 203, Spring Hill 4004 Project Manager: Craig Witt Tel: +61 7 3831 6744 Author: Craig Witt Fax: + 61 7 3832 3627 Client: Department of Environment, Land, Water ABN 54 010 830 421 and Planning www.bmtwbm.com.au Client Contact: Louise Hanigan Client Reference: Contract No: 332261 Synopsis: An independent review of reports and investigations of coastal processes and management strategies for Lonsdale Bight with an overview of suitable options for short and long term sand management (retention). REVISION/CHECKING HISTORY Revision Number Date Checked by Issued by 0 24th Oct 2016 IAT CLW 1 7th Nov 2016 IAT CLW 2 25th Nov 2016 IAT CLW 3 5th Jan 2017 IAT CLW DISTRIBUTION Destination Revision 0 1 2 3 4 5 6 7 8 Department of Word Word Word Word Environment, Land, Water & pdf & pdf & pdf & pdf and Planning BMT WBM File Word Word Word Word BMT WBM Library & pdf & pdf & pdf & pdf J:\Anglesea\Environmental Planning\CEP\2016-2017\Planning\Project Briefs\Point Lonsdale coastal processes\Coastal Processes Review\Reports\R.B22316.001.03.1.docx Lonsdale Bight Investigations Review and Options Overview i Summary Report Summary Report Background The Lonsdale Bight foreshore is an important recreational asset for the region. It is also partly within the Port Phillip Heads Marine National Park which extends to High Water Mark and is recognised for its state-wide environmental, cultural and recreational values. The embayment is at the entrance to Port Phillip Bay and is therefore exposed to complex and varying coastal processes which cause shoreline erosion and fluctuations in beach levels. Seawalls and groynes of different types have been constructed over many years aimed at protecting the foreshore and as an attempt to retain a sandy beach with varying degrees of success. There have also been numerous investigations and reports associated with the processes and works. Community concerns about the low beach level in front of the shopping precinct at Point Lonsdale Front Beach have amplified in recent months. There are also other sections of the foreshore which have experienced erosion and concerns have been raised about potential future risks, particularly in response to climate change influences including sea level rise. The Department of Environment, Land, Water and Planning (DELWP), the Borough of Queenscliffe (BoQ) and Parks Victoria (PV), all of whom have responsibilities in management of the area, recognise the importance of understanding the coastal hazards and associated risks as well as the consideration of future strategies and actions to manage and mitigate those risks where needed. Given the considerable body of knowledge already gained through the previous investigations and reports, DELWP has commissioned this independent review of those reports since 1997 as the next step in moving forward. Review of those reports together with project stakeholder liaison and site inspections has allowed a broad understanding to be gained of the processes, values and key issues. Gaps in knowledge important to inform future coastal management decisions have been identified and an overview provided of options which may be considered to address specific issues. An overall approach to coastal zone management based on a risk management framework is also presented for consideration. Review of Reports A total of 29 reports have been reviewed and summarised together with other readily available information including historical photographs as uploaded on community Facebook pages and Nearmap aerial imagery over recent years. These reports date back to 1997 and generally cover one or more of the following broad topics: Geomorphology and historical changes Coastal processes and related hazards Environmental values Cliff stability and management Coastal management options and works J:\Anglesea\Environmental Planning\CEP\2016-2017\Planning\Project Briefs\Point Lonsdale coastal processes\Coastal Processes Review\Reports\R.B22316.001.03.1.docx Lonsdale Bight Investigations Review and Options Overview ii Summary Report Seawall and groyne condition and structural stability. The extensive document list provides a good overview of the processes, values and issues at hand with respect to management of the Lonsdale Bight foreshore. There is general agreement throughout the reports with respect to the broad coastal processes although there are some gaps in knowledge of relevance to future coastal management decisions. Overview of Coastal Processes Beaches are subject to natural fluctuations in level and alignment in response to how sand moves along and across the foreshore. This movement is driven by the changing forces of waves, currents and water levels that the foreshore is exposed to particularly during storm events with elevated water levels and high waves. Natural controlling features such as rocky headlands and reefs as well as man-made structures such as seawalls and groynes can also affect the processes. The driving forces and shoreline response are subject to variability seasonally throughout the year and over longer annual and decadal cycles associated with meteorological phases as well as over geological time scales and with future climate change. Knowledge and understanding of contemporary and longer term processes are essential in developing appropriate coastal management strategies to address hazards associated with the processes. Dealing with natural variability and uncertainty with respect to the nature, timing and extent of future changes are key considerations. There is a broad understanding and agreement of the coastal processes influencing Lonsdale Bight as interpreted from the documents reviewed. Sand is transported along the Bass Straight foreshore from west to east to Point Lonsdale under the influence of the dominant SSW – SW waves. At Point Lonsdale, it has been estimated that about half of this sand is transported offshore or into deeper parts of the entrance during the ebb tide. The remainder is transported around the headland and into Port Phillip Bay under the combined and complex interactions of waves and flood tide currents. This supply of sand is noted as being intermittent and dependent on weather conditions typically occurring in pulses predominantly during storms and varying from year to year. There are strong tidal currents in the entrance to Port Phillip Bay and along parts of the foreshore. Ocean waves also penetrate in through the entrance and gradually reduce in height as they propagate further into Lonsdale Bight and approach the shoreline. The waves are also influenced by the strong tidal currents. About half of the sand that enters around Point Lonsdale continues to be moved into the Bay across the seabed of Lonsdale Bight under the influence of the waves and tidal currents. The presence of exposed reefs and a thin veneer of sand indicate that the potential to transport the sand exceeds the supply. The remainder of the sand is moved along the coast from south-west to north-east in a narrow band primarily under the influence of the waves approaching the shoreline at an angle. At Point Lonsdale Front Beach, the waves approach at a steep angle and therefore the potential to move the sand along the coast is high. The key coastal processes of relevance to ongoing management of the Lonsdale Bight foreshore is this dominant wave induced longshore transport of sand along the coast coupled with offshore transport during storm events, both of which are subject to seasonal, inter-annual and decadal J:\Anglesea\Environmental Planning\CEP\2016-2017\Planning\Project Briefs\Point Lonsdale coastal processes\Coastal Processes Review\Reports\R.B22316.001.03.1.docx Lonsdale Bight Investigations Review and Options Overview iii Summary Report variations. These variations lead to fluctuations in the volumes of sand, levels of the beaches and alignment of the foreshore. In addition to this, the intermittent and potentially reducing supply of sand around Point Lonsdale and into the compartment adds further variability and uncertainty with respect to fluctuations in the volumes of sand along the foreshore. With future climate change influences including a rise in mean sea level and increased storminess, it can be expected that enhanced wave energy will impact on the beaches and structures at a higher level. This will have associated implications for beach erosion, overtopping and potential damage to structures. Such processes will be gradual and necessitate ongoing and potentially increased maintenance of structures and associated adaptation strategies. Summary of Historical Changes and Works Numerous works have been undertaken over many decades including the