Point Lonsdale Groyne Investigations Long term options to maintain a sandy beach Point Lonsdale Groyne Investigations Long term options to maintain a sandy beach 59918185 Prepared for The Department of Environment, Land, Water and Planning 22 August 2018 22 August 2018 Cardno i Point Lonsdale Groyne Investigations Long term options to maintain a sandy beach Contact Information Document Information Cardno Victoria Pty Ltd Prepared for The Department of ABN 47 106 610 913 Environment, Land, Water and Planning Level 4 Project Name Long term options to 501 Swanston Street maintain a sandy beach Melbourne 3000 Australia File Reference 59918185_PtLonsdale_Groy neIvestigation_Rev0.docx www.cardno.com Phone +61 3 8415 7777 Job Reference 59918185 Fax +61 3 8415 7788 Date 22 August 2018 Version Number Rev 0 Author(s): Phebe Bicknell Effective Date 20/08/2018 Senior Engineer Approved By: Chris Scraggs Date Approved 20/08/2018 Principal Coastal Engineer Document History Version Effective Date Description of Revision Prepared by Reviewed by V1 Internal Draft Phebe Bicknell David Provis Rev A Draft for Client Review Phebe Bicknell Chris Scraggs Rev B Draft for Client Review Phebe Bicknell Chris Scraggs Rev 0 Final Phebe Bicknell Chris Scraggs © Cardno. Copyright in the whole and every part of this document belongs to Cardno and may not be used, sold, transferred, copied or reproduced in whole or in part in any manner or form or in or on any media to any person other than by agreement with Cardno. This document is produced by Cardno solely for the benefit and use by the client in accordance with the terms of the engagement. Cardno does not and shall not assume any responsibility or liability whatsoever to any third party arising out of any use or reliance by any third party on the content of this document. 59918185 | 22 August 2018 ii Point Lonsdale Groyne Investigations Long term options to maintain a sandy beach Table of Contents 1 Introduction 6 1.1 Overview 6 1.2 Scope of Work 7 1.3 Methodology 8 2 Study Area 9 2.1 Background 9 2.2 Site Inspection 12 2.3 How groynes work 14 3 Existing Conditions 15 3.1 Currents 15 3.2 Waves 15 3.3 Sediment Transport 17 4 Concept Option Development 20 4.1 Preliminary Options 20 4.2 Concept Options 22 4.3 Options Summary – Layout, Efficacy & Considerations 23 5 Option Evaluation 30 5.1 Evaluation Criteria 30 5.2 Evaluation of options 31 6 Conclusions & Recommendations 38 7 References 39 Tables Table 3-1 Mean wave conditions 16 Table 3-2 Summary of wave model cases 16 Table 4-1 Summary of Groyne Variables 20 Table 4-2 Groyne material options for Point Lonsdale 21 Table 4-3 Option: Maintain existing rock groynes 24 Table 4-4 Option: Extend existing groynes - Rock 25 Table 4-5 Option: Add additional groynes – Rock 26 Table 4-6 Option: Add additional groynes – Timber/Polymer 27 Table 4-7 Option: Combination – Rock & Timber Groynes 28 Table 4-8 Option: Combination – Rock & Timber Groynes with Small Breakwater 29 Table 5-1 Criteria Definitions 30 Table 5-2 Evaluation of Options – Summary 31 Table 5-3 Evaluation of Options – Detailed analysis 32 59918185 | 22 August 2018 iii Point Lonsdale Groyne Investigations Long term options to maintain a sandy beach Figures Figure 1-1 Study Area (Nov 2017, Nearmap image) 6 Figure 1-2 Methodology Flow Chart 8 Figure 2-1 Annotated site map (Nearmap Image, Nov 2017) 13 Figure 2-2 Diagram of sediment movement along a beach and trapping by a barrier such as a groyne. 14 Figure 3-1 Distribution of wave direction and significant wave height (Hs) for waves approaching the Entrance from Bass Strait (data from PoMC buoys south east of Pt. Nepean) 16 Figure 3-2 Average wave energy vectors, with arrow length representing energy level; and direction of the arrow the direction of the wave energy at the origin of each arrow. (Nearmap Nov 2017) 17 Figure 3-3 Modelled shoreline at site of interest with existing groyne structures from an average 1-year wave time series. (Nearmap Nov 2017) 19 59918185 | 22 August 2018 iv Point Lonsdale Groyne Investigations Long term options to maintain a sandy beach Glossary Symbol Name Definition AHD Australian Height The Australian Height Datum is a geodetic datum for altitude measurement Datum in Australia, "In 1971 the mean sea level for 1966-1968 was assigned the value of zero on the Australian Height Datum at thirty tide gauges around the coast of the Australian continent” BoM Bureau of Meteorology CD Chart Datum The datum to which soundings on a chart are referenced. It is usually taken to correspond to a low-water elevation, typically the lowest astronomical tide. Crest Height The height of the crest of the structure Ebb tide Outgoing or receding tidal current, (that is, when water is flowing away from the shore line) leading to low tide. Fetch The maximum distance over water that winds of a given direction can generate waves. Areas such as Western Port Bay are defined as fetch- limited meaning that wave heights will always be restricted by the area over which wind can blow. Groyne A rigid structure on a shoreline that interrupts water flow and limits the movement of sediment. These structures are effective at trapping material as it is moved along the coast by longshore drift, creating beaches or preventing them being washed away. Hs Significant wave height The significant wave height is originally defined as the average height of the largest one third of the waves in a given record. With the advent of digital processing techniques and spectral analysis of wave records, the significant wave height is now commonly defined as Hs=4 √m0, where m0 is the variance of the wave spectrum or the “zero order moment”. For the purposes of this study the definition based on variance is used. Wave heights referred to in this report are the significant wave height. For practical purposes, the significant wave height is close to the value reported by an experienced observer making visual observations of the wave height. Tp Spectral peak wave The period associated with the peak of the wave energy spectrum period Pdir Peak wave direction The wave direction associated with the peak of the wave energy spectrum. Directions are given as the direction the waves are coming from. SLR Sea-level rise Swell Waves which have travelled away from the area where they were generated such as a remote storm system. Often appearing as a series of regular spaced waves of unbroken appearance. The waves may have travelled many 100’s of kilometres from their point of origin. Tidal current Movement of water associated with the rise and fall of the tides Wave Direction from which the waves are coming from and are given as the direction bearing, in degrees, clockwise from true north. 59918185 | 22 August 2018 v Point Lonsdale Groyne Investigations Long term options to maintain a sandy beach 1 Introduction 1.1 Overview The Department of Environment, Land, Water and Planning (DELWP) has commissioned Cardno to investigate long-term beach management options in the form of groynes to maintain sand at the Point Lonsdale Front Beach, starting from in front of the shops, up to the commencement of the rock revetment. This investigation looks to build on the existing efforts towards maintaining a long-term sandy beach. Figure 1-1 Study Area (Nov 2017, Nearmap image) The natural processes for this dynamic section of coast at Point Lonsdale have been significantly changed through intervention from manmade infrastructure including masonry seawalls, rock revetments and timber and rock groynes. The state of the beach fluctuates following exposure to certain storm events and at various times of the year. 59918185 | 22 August 2018 6 Point Lonsdale Groyne Investigations Long term options to maintain a sandy beach Modelling and analyses are required to understand the effectiveness the existing and alternate configuration opportunities for using groynes to capture and hold a beach at this location. This project aims to undertake a technical investigation to explore and present possible options, providing a scientifically informed analysis. The potential solutions from this assessment are to be presented in an Open House Community session to inform an outcome that reflects the feedback and opinions of this community. 1.2 Scope of Work DELWP’s key objectives as part of this project are to: > Understand the coastal processes at Point Lonsdale Front Beach and existing groyne configurations actions in influencing sand supply; > Identify and model options with the objective of maintaining a sandy beach > Compare options > Present technical report to major stakeholders Deliverables: Report – Presenting long-term options to maintain a sandy beach Posters – “butcher paper” style poster for each option conveying both the technical aspects and development criteria of each option. Intended to promote discussion and feedback from the community. 59918185 | 22 August 2018 7 Point Lonsdale Groyne Investigations Long term options to maintain a sandy beach 1.3 Methodology Cardno’s methodology was designed to align with DELWP’s scope of works (Figure 1-2). This method was informed by our experience and knowledge of the Port Phillip Heads (PPH) and Point Lonsdale foreshore and similar groyne investigations within Port Phillip Bay. Each of the components to be undertaken as part of the Project is presented in more detail the sections below. Figure 1-2 Methodology Flow Chart > Data Inputs – Site data (survey, wave measurements, available site literature) was combined with experience and knowledge from Cardno’s previous work was used as the basis of the project’s analytical approach.