Viaduct Harbour Bridge Coastal Effects Assessment
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Viaduct Harbour Bridge Coastal Effects Assessment Prepared for Panuku Development Auckland Prepared by Beca Limited 12 June 2019 Viaduct Harbour Bridge Coastal Effects Assessment | 3911594 | NZ1-16166731-13 0.13 | 12 June 2019 | Rev C Creative people together transforming our world | Viaduct Harbour Bridge Coastal Effects Assessment | Contents Executive Summary ................................................................................................ 1 1 Introduction ........................................................................................................ 1 2 Wynyard Crossing Bridges ............................................................................... 2 2.1 Existing Wynyard Crossing Bridge .................................................................................................. 2 2.2 Proposed Wynyard Crossing Bridge ............................................................................................... 3 2.3 Temporary Access ........................................................................................................................... 3 2.4 Spatial Extent of Works ................................................................................................................... 3 3 Existing Environment ........................................................................................ 4 3.1 Harbour Setting ................................................................................................................................ 4 3.2 Tides, Currents and Flushing........................................................................................................... 4 3.3 Wind ................................................................................................................................................. 7 3.4 Waves and Wakes ........................................................................................................................... 8 3.5 Sediment Processes and Sedimentation ......................................................................................... 9 3.6 Coastal Hazards and Climate Change .......................................................................................... 10 4 Effects of Construction ................................................................................... 12 4.1 Methodology for Marine Based Works .......................................................................................... 12 4.2 Water and Sediment Quality .......................................................................................................... 12 5 Effects on Coastal Processes ........................................................................ 13 5.1 Approach for the Assessment of Coastal Processes .................................................................... 13 5.2 Cumulative Effects ......................................................................................................................... 13 5.3 Tidal Flows, Current and Flushing ................................................................................................. 14 5.4 Waves and Wakes ......................................................................................................................... 14 5.5 Sediment Processes, Sedimentation and Erosion ........................................................................ 14 5.6 Coastal Hazards and Climate Change Adaptation ........................................................................ 15 6 Mitigation and Monitoring ............................................................................... 16 7 Conclusions ..................................................................................................... 16 8 References ....................................................................................................... 17 Appendices Appendix A – Tidal Modal Study Viaduct Harbour Bridge Coastal Effects Assessment | 3911594 | NZ1-16166731-13 0.13 | 12 June 2019 | i | Viaduct Harbour Bridge Coastal Effects Assessment | Revision History Revision Nº Prepared By Description Date A Stephen Priestley Draft report for client comment 14/05/19 B Stephen Priestley Final Draft 31/05/19 C Stephen Priestley Resource Consent Application 12/06/19 Document Acceptance Action Name Signed Date Prepared by Stephen Priestley 12/06/19 Reviewed by Niksa Sardelic 12/06/19 Approved by Stephen Priestley 12/06/19 on behalf of Beca Limited © Beca 2019 (unless Beca has expressly agreed otherwise with the Client in writing). This report has been prepared by Beca on the specific instructions of our Client. It is solely for our Client’s use for the purpose for which it is intended in accordance with the agreed scope of work. Any use or reliance by any person contrary to the above, to which Beca has not given its prior written consent, is at that person's own risk. Viaduct Harbour Bridge Coastal Effects Assessment | 3911594 | NZ1-16166731-13 0.13 | 12 June 2019 | Rev C | Executive Summary | Executive Summary Overview 1. This resource consent application involves the removal of the existing Wynyard Crossing bridge which has reached the end of its design life. The existing bridge was designed and consented as a temporary bridge. The existing bridge will be replaced by the proposed Wynyard Crossing bridge, which is to be a double-leaf bascule bridge along the same alignment as the existing bridge. 2. Bridge approaches will connect the proposed bridge (the Proposal ) to land (Te Wero Island and Wynyard Precinct), either side of the double leaf bascule. It is expected that the construction will take approximately 9 months. During this period a temporary crossing will be established to the south of the existing bridge 3. Piles associated will the Proposal will occupy approximately 29m2 of seabed. The elevated footprint of the bridge is about 954 m 2. Piles will be bored and installed within steel casings. 4. Pontoons associated with the temporary crossing have a footprint of 480m2 and the associated temporary piles will occupy less than 5m2 of the seabed. 5. No reclamation or dredging of the Project Area is proposed . Assessment Methodology 6. The proposal does not involve breakwaters (e.g. wave panels) or other structures which could have a large scale influence on the flow or velocity of water movement. Structures which are to be located below mean sea level are limited to piles and bulkhead structures which occupy a limited area of the Coastal Marine Area (CMA) within the Viaduct Harbour. As a result only numerical modelling of the tidal currents and basin flushing is considered appropriate to determine the actual and potential effects of the proposal on coastal processes. That modelling report is contained in Appendix A. 7. Unless otherwise stated, all other assessments in this report are based on the author’s experience with coastal structures in the Waitemata Harbour waterfront. 8. The existing environment is undergoing change. The infrastructure associated with Americas Cup 36 will alter the tidal and wave conditions within the Project Area. Relative effects on the environment are therefore described in this context, with references to Pre-Americas Cup and to Post-Americas Cup. Existing Environment 9. Referred to as the Project Area, the affected CMA is in the lower Waitematā Harbour and within a narrow corridor (about a 10m width) between Karanga Plaza and Te Wero Island. 10. Tidal velocities within the Project Area are low and less than 0.1 m/s. 11. The natural, relatively high tidal range of 2.5m (median) results in good to fair flushing of Viaduct Harbour, including the post Americas Cup project. 12. The Project Area is sheltered from wind waves and external wakes, with the annual significant wave height less than 100mm. Viaduct Harbour Bridge Coastal Effects Assessment | 3911594 | NZ1-16166731-13 0.13 | 12 June 2019 | Rev C | Executive Summary | 13. Relevant coastal hazards include storm surge (extreme storm tides) and tsunami. The effects of sea level rise are a relevant component to these coastal hazards. 14. The coastal edge of the Viaduct Harbour contains hard engineering structures which are resistance to erosion and scour. Potential Environmental Effects 15. From the author’s experience with waterfront projects, the effects during construction are expected to be less than minor. Some resuspension of sediment could be expected but will be localised and temporary. Any disturbed material will be deposited in the vicinity of the Project Area. 16. The Proposal will not change tidal currents within the harbour wide context and any changes will be local and of a low magnitude. Flushing of the Viaduct Basin will remain unchanged. 17. Any potential adverse effects related to wave/wake changes, sedimentation and scour will be negligible. 18. Coastal hazards (including the projected effects of climate change) have been considered for the Proposal as a whole. The lifting section of the proposed Wynyard Crossing bridge can be functional over a 100 year period, and the fixed sections of the bridge can be regraded to accommodate sea level rise. 19. As the overall adverse effects associated with this project are less than minor and probably negligible, no physical monitoring of water or sediment quality is proposed. Viaduct Harbour Bridge Coastal Effects Assessment | 3911594 | NZ1-16166731-13 0.13 | 12 June 2019 | Rev C | Introduction | 1 Introduction Beca has been engaged by Panuku Development Auckland (Panuku) to carry out the coastal processes assessment for