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Final Report Point Lonsdale Groyne Feasibility Study DELWP Final Report Point Lonsdale Groyne Feasibility Study DELWP 22 September 2020 Document Status Version Doc type Reviewed by Approved by Date issued V01 Interim GXC GXC 04/06/2020 V02 DRAFT GXC GXC 1/09/2020 V03 FINAL GXC GXC 11/09/2020 V04 FINAL GXC GXC 22/09/2020 V05 FINAL GXC GXC 22/09/2020 Project Details Project Name Point Lonsdale Groyne Feasibility Study Client DELWP Client Project Manager Dianne Moore Water Technology Project Manager Michael Miloshis Water Technology Project Director Gildas Colleter Authors Michael Miloshis, John Gater Document Number 19010148_R01_V05_FINAL.docx COPYRIGHT Water Technology Pty Ltd has produced this document in accordance with instructions from DELWP for their use only. The concepts and information contained in this document are the copyright of Water Technology Pty Ltd. Use or copying of this document in whole or in part without written permission of Water Technology Pty Ltd constitutes an infringement of copyright. Water Technology Pty Ltd does not warrant this document is definitive nor free from error and does not accept liability for any loss caused, or arising from, reliance upon the information provided herein. 15 Business Park Drive Notting Hill VIC 3168 Telephone (03) 8526 0800 Fax (03) 9558 9365 ACN 093 377 283 ABN 60 093 377 283 19010148_R01_V05_FINAL.docx DELWP | 22 September 2020 Point Lonsdale Groyne Feasibility Study Page 1 CONTENTS EXECUTIVE SUMMARY 4 1 INTRODUCTION 5 1.1 Community Design Proposal 5 2 BACKGROUND 7 2.1 History of Shoreline Management 7 2.2 Local Coastal processes 10 2.3 Previous studies 11 3 METHODOLOGY 13 3.1 Numerical Modelling 13 3.2 Model Development 13 3.2.1 Bathymetry and Model Mesh 14 3.2.2 Water Level Boundary 14 3.2.3 Wave Boundary 14 3.3 Wave and tide data 16 3.4 Model Calibration 17 3.4.1 Water Level 17 3.4.2 Waves 18 3.5 Model Simulations 20 3.5.1 Design wave parameters 20 3.5.2 Beach morphology 20 3.6 Groyne field effectiveness 21 4 CONSTRUCTABILITY 23 4.1 Concept design standard and process 23 4.2 Concept design 24 4.2.1 Armour sizing 24 4.2.2 Geometry 24 4.2.3 Construction access 27 4.2.4 Construction Sequence 28 4.2.5 Construction program 28 4.2.6 Safety 28 4.2.7 Material Quantities and Cost Estimate 29 5 COMMUNITY DESIGN OPTION REVIEW 30 5.1 Stakeholder engagement 30 5.2 Multicriteria assessment 30 5.3 Limitations – model and groyne design limitations 31 6 CONCLUSION 32 19010148_R01_V05_FINAL.docx DELWP | 22 September 2020 Point Lonsdale Groyne Feasibility Study Page 2 LIST OF FIGURES Figure 1-1 Existing and proposed groyne plan 5 Figure 2-1 Point Lonsdale Foreshore, 1920s 7 Figure 2-2 Point Lonsdale Point, 1962 9 Figure 2-3 Point Lonsdale front beach before and after rock groyne A installation, 1990-2019 9 Figure 2-4 Existing groyne locations with moderate wave action, 14 January 2014 10 Figure 2-5 Groyne designs and likely accretion zones, BMT WBM Study, 2017 11 Figure 2-6 Existing and modelled groyne designs, Cardno, 2018 12 Figure 3-1 Port Phillip Bay model mesh with high resolution around Port Phillip Heads 15 Figure 3-2 Proposed groyne field as captured by the model mesh 15 Figure 3-3 Wave and tide data recorded at Point Lonsdale and at the Point Nepean wave buoy 16 Figure 3-4 Tide calibration – Point Lonsdale tide gauge 17 Figure 3-5 Tide calibration – Queenscliff tide gauge 17 Figure 3-6 Tide calibration – Point Lonsdale Bight 18 Figure 3-7 Wave calibration – offshore, Point Nepean wave buoy 18 Figure 3-8 Wave calibration – Point Lonsdale Bight 19 Figure 4-1 Beach Groyne typical section 24 Figure 4-2 Point Groyne 1 and 2 typical section 25 Figure 4-3 Point Groyne 4 26 Figure 4-4 Point Groyne 1, 2 and 3 26 Figure 4-5 Construction site plan 27 LIST OF TABLES Table 3-1 Storm events wave during deployment 16 Table 3-2 Offshore wave height and water level at Point Lonsdale Bight 20 Table 3-3 2014 to 2015 storm waves 20 Table 4-1 Project Standards and Guidelines 23 Table 4-2 Groyne armour mass 24 Table 4-3 Cost estimate of each group of groynes 29 19010148_R01_V05_FINAL.docx DELWP | 22 September 2020 Point Lonsdale Groyne Feasibility Study Page 3 EXECUTIVE SUMMARY The Department of environment, Land, Water and Planning engaged Water Technology to review a “Community Design Option” (CDO) for Point Lonsdale Front Beach to improve the beach amenity. The Community Design Option, prepared by three members of the Point Lonsdale community, proposes a denser groyne field. The aim is to improve the volume and consistency of sand on the Point Lonsdale Front Beach. The CDO Groyne field incorporates eight additional groynes along the Front Beach. Four Point Groyne structures are spread around the southern rocky headland, in the same location as historic timber barriers. Four additional Beach Groynes are added north of the existing Cheshunt Street groyne. Three existing groynes (rock type) and a seawall have been built to manage coastal erosion along the Front Beach. These groynes improve beach amenity for beach users and protect the seawall from beach scour. The beach evolution at Point Lonsdale Front Beach is influenced by transient natural processes as well as the seawall and the groynes. The existing groynes increase the longevity of intermittent sand build-up and widen the beach profile. A range of numerical modelling and engineering techniques were used to investigate the performance, functionality, feasibility and construction of the CDO, including of: ◼ Collection of local wave and tide data, including storm waves ◼ Coastal processes assessment for the existing and proposed groyne fields ◼ Extreme value analysis to understand the likely design conditions affecting the groynes ◼ Numerical modelling of tide, currents and waves at the site for a range of scenario ◼ Conceptual engineering design review of the CDO groynes and high-level cost estimation ◼ Engagement and consultation, including 3 meetings, prepared in association with the CDO stakeholders, Victoria Parks and Borough of Queenscliff ◼ Multi-criteria analysis and ranking of groynes The CDO Beach Groynes are likely to increase the average beach width at the Front Beach, however the last groyne may exacerbate beach erosion to the north. The CDO Point Groynes would require significant strengthening to meet the necessary level of performance required for structural safety. On balance, Beach Groyne 5 provides the most effective outcome for improving beach amenity. Point Groyne 4 and Beach Groyne 6 would also be good at improving beach amenity. Point Groynes 1 & 2 are not suitably located for a consistent improvement to sand volume. They generally pose challenging construction and maintenance issues as well as a significant impact to visual amenities. The estimated budget required for the resulting CDO groyne field modification is approximately $4.5 million. Construction may take 5 months considering the tidal limitation, particularly for the Point Groynes, which would need to be constructed during spring and summer to maximise the most suitable weather conditions for construction. 19010148_R01_V05_FINAL.docx DELWP | 22 September 2020 Point Lonsdale Groyne Feasibility Study Page 4 1 INTRODUCTION The Department of environment, Land, Water and Planning engaged Water Technology to assess a proposed community-based groyne field modification in terms of technical functionality, feasibility, and construction. Members of the CDO aim to increase the volume and consistency of sand on the Point Lonsdale Front Beach. Additional rock groynes are proposed at locations of historic timber barriers, along the point, and at foreshore beach locations that have a typically low volume of sand. 1.1 Community Design Proposal Figure 1-1 shows the layout proposed by the CDO with the 3-existing groynes (A, B and C). 8 7 6 5 4 3 2 1 Figure 1-1 Existing and proposed groyne plan A denser groyne field of eight additional groynes is proposed. It is suggested that the existing groynes may be spaced too far for sand build-up to overlap, which reduces the available beach surface for beach goers. 19010148_R01_V05_FINAL.docx DELWP | 22 September 2020 Point Lonsdale Groyne Feasibility Study Page 5 There are four additional groynes proposed north of the existing groyne at Cheshunt Street, along the beach. These four new Beach Groynes would be typically 50 to 60m long and start 1m below the level of the seawall, sloping 1:30 down towards the sea - over 30m, with the remaining length 2m below the seawall crest. The seawall crest is located at 2.6m AHD. Four additional rock groyne structures would be positioned at the southern rocky headland, in the same location as historic timber barriers. The rock groyne structure would be typically shorter, about 30m long and would be built as low as possible. The Department of Environment, Land, Water and Planning (DELWP) conducted a community-centred process, with direct consultation and involvement of the CDO representatives to study the Point Lonsdale Front Beach Groyne field modification. The current coastal management arrangements originate from practical knowledge and site experience with more recently scientific and engineering design used to manage the site amenities. The current investigation aims to identify if the CDO proposal is technically feasible and can achieve increased sand on the Point Lonsdale Front Beach. 19010148_R01_V05_FINAL.docx DELWP | 22 September 2020 Point Lonsdale Groyne Feasibility Study Page 6 2 BACKGROUND 2.1 History of Shoreline Management The coastline at Point Lonsdale Front Beach is exposed to strong currents due to its proximity to Port Phillip Heads and to moderate waves refracting in “The Rip” from Bass Straight.
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