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Natural Hazards Waimakariri District Council

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Natural Hazards Waimakariri District Council Waimakariri District Plan Review -Natural Hazards Waimakariri District Council Coastal Erosion and Sea Water Inundation Assessment Technical Report IZ105900-005-NC-RPT-002 | 1 21 June 2018 Client Reference Coastal Er osion and Sea Water Inundation Assessment T echnical R eport Waimakariri District C ouncil Document history and status Revision Date Description By Review Approved 1 19/6/2018 Draft Derek Todd Joris Jorissen 2 21/6/2018 Final Draft Derek Todd Distribution of copies Revision Issue Date issued Issued to Comments approved 2 22/6/2018 Waimakariri District Council Coastal Erosion and Sea Water Inundation Assessment Technical Report Waimakariri District Plan Review -Natural Hazards Project No: IZ105900 Document Title: Coastal Erosion and Sea Water Inundation Assessment Technical Report Document No.: IZ105900-005-NC-RPT-002 Revision: 2 Date: 21 June 2018 Client Name: Waimakariri District Council Client No: Client Reference Project Manager: Ian Wiseman Author: Derek Todd File Name: J:\IE\Projects\02_New Zealand\IZ105900\21 Deliverables\Coastal hazards assessment V2 Jacobs New Zealand Limited Level 2, Wynn Williams Building 47 Hereford Street Christchurch Central PO Box 1147, Christchurch 8140 New Zealand T +64 3 940 4900 F +64 3 940 4901 www.jacobs.com © Copyright 2018 Jacobs New Zealand Limited. The concepts and information contained in this document are the property of Jacobs. Use or copying of this document in whole or in part without the written permission of Jacobs constitutes an infringement of copyright. Limitation: This document has been prepared on behalf of, and for the exclusive use of Jacobs’ client, and is subject to, and issued in accordance with, the provisions of the contract between Jacobs and the client. Jacobs accepts no liability or responsibility whatsoever for, or in respect of, any use of, or reliance upon, this document by any third party. IZ105900-005-NC-RPT-002 i Coastal Erosion and Sea Water Inundation Assessment Technical Report Contents Executive Summary ...................................................................................................................................... 4 1. Introduction ....................................................................................................................................... 5 1.1 Project Background ............................................................................................................................ 5 1.2 Pegasus Bay Coast ............................................................................................................................ 5 1.2.1 Shoreline Accretion ............................................................................................................................ 5 1.2.2 Waimakariri District Coastal Characteristics ...................................................................................... 8 2. Methodology ................................................................................................................................... 10 2.1 Coastal Erosion Hazard Mapping ..................................................................................................... 10 2.1.1 Long-term Historical Shoreline Movements ..................................................................................... 11 2.1.2 Sea Level Rise Impacts .................................................................................................................... 12 2.1.3 Short-term Storm Erosion. ................................................................................................................ 14 2.1.4 Dune Stability Factor ........................................................................................................................ 15 2.2 Coastal Inundation Hazard Mapping ................................................................................................ 15 3. Coastal Process Inputs .................................................................................................................. 17 3.1 Storm Tide Levels ............................................................................................................................. 17 3.1.1 Sea level Rise ................................................................................................................................... 17 3.2 Waves ............................................................................................................................................... 17 3.2.1 Wave Set-up and run-up components of water levels ..................................................................... 18 3.3 River Flood Levels and Bank Heights .............................................................................................. 19 3.4 Historical Shoreline Movements ....................................................................................................... 19 3.5 Dune Parameters ............................................................................................................................. 21 3.6 Sediment Budget .............................................................................................................................. 21 4. Coastal Erosion Hazard Results ................................................................................................... 23 4.1 Historical Long-Term Shoreline Movements .................................................................................... 23 4.2 Sea Level Rise Effects ..................................................................................................................... 23 4.3 Short-term Storm Effects .................................................................................................................. 25 4.4 Dune Stability Factor ........................................................................................................................ 25 4.5 Coastal Hazard Erosion Zones ........................................................................................................ 25 4.5.1 50-year CEHZ Widths to 2070 ......................................................................................................... 26 4.5.2 100-year CEHZ Widths to 2120 ....................................................................................................... 27 4.5.3 130-year CEHZ Widths to 2150 ....................................................................................................... 27 4.5.4 Sediment Budget Check ................................................................................................................... 28 4.5.5 Dune Width Approach to Land Use Zone......................................................................................... 28 5. Coastal Inundation Hazard Results .............................................................................................. 29 5.1 2070 Sea Level Rise Results ........................................................................................................... 29 5.2 2120 Sea Level Rise Results ........................................................................................................... 30 5.3 2150 Sea Level Rise Results ........................................................................................................... 30 5.4 Further Modelling Recommendations .............................................................................................. 30 6. Conclusions .................................................................................................................................... 31 6.1 Coastal Erosion ................................................................................................................................ 31 IZ105900-005-NC-RPT-002 ii Coastal Erosion and Sea Water Inundation Assessment Technical Report 6.2 Coastal Inundation ............................................................................................................................ 31 References ................................................................................................................................................... 31 Appendicies Appendix A: Beach and dune profiles from ECan monitoring sites .............................................................. 34 Appendix B: Historical shoreline and DSAS transect locations .................................................................... 41 Appendix C: River Cross-section Locations ................................................................................................ 45 Appendix D: 50-year (2070) Coastal Erosion Hazard Zone Positions ........................................................ 46 Appendix E: 100-year (2120) Coastal Erosion Hazard Zone Positions ...................................................... 50 Appendix F: 100-year (2120) Coastal Erosion Hazard Zone Positions ....................................................... 54 Appendix G: 50-year Coastal Inundation Maps ........................................................................................... 59 Appendix H: 100-year Coastal Inundation Maps ......................................................................................... 60 Appendix I: 130-year Coastal Inundation Maps .......................................................................................... 61 IZ105900-005-NC-RPT-002 iii Coastal Erosion and Sea Water Inundation Assessment Technical Report Executive Summary Waimakariri District Council (WDC) as part of its review of the 2005
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