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Quality Assurance Prepared by WSP New Zealand Limited Revision History: Revision Author Reviewer Approved for Issue

Name Signature Name Signature Date

Issue 1 Brabhaharan, P Mason, D Brabhaharan, P 25 Sep 2020

Quality Information Document Title: Ngā Ūranga ki Pito-One Shared Path Project - Te Ara Tupua Natural Hazards and Resilience Version: Issue 1

Date: 25 September 2020 Prepared by: Brabhaharan, P Reviewed by: Mason, D

Approved by: Brabhaharan, P File Name: V.04 - Natural Hazards and Resilience Report - Issue 1 - 25 Sep 2020 Disclaimer This report (‘Report’) has been prepared by WSP exclusively for the Waka Kotahi NZ Transport Agency (‘Client’) in relation to obtaining approvals (‘Purpose’) and in accordance with the agreement for professional services dated 7 October 2019 under the Independent Professional Advisors (IPA) contract No 17 – 286. The findings in this Report are based on and are subject to the assumptions specified in the Report. WSP accepts no liability whatsoever for any reliance on or use of this Report, in whole or in part, for any use or purpose other than the Purpose or any use or reliance on the Report by any third party.

This report (‘Report’) has been prepared in support of the notices of requirement and applications for resource consent (‘Purpose’) for the Project made by Waka Kotahi NZ Transport Agency (‘Client’) under the COVID-19 Recovery (Fast-track Consenting) Act 2020 (COVID-19 Recovery Act). In particular, this report supports the assessment of the Project's effects on the environment as required by the COVID-19 Recovery Act. The requirements of the COVID-19 Recovery Act and an overall assessment of the effects of the Project on the environment are set out in the Assessment of Effects on the Environment.

In preparing the Report, WSP has relied upon data, surveys, analyses, designs, plans and other information (‘Client Data’) provided by or on behalf of the Client. Except as otherwise stated in the Report, WSP has not verified the accuracy or completeness of the Client Data. To the extent that the statements, opinions, facts, information, conclusions and/or recommendations in this Report are based in whole or part on the Client Data, those conclusions are contingent upon the accuracy and completeness of the Client Data. WSP will not be liable in relation to incorrect conclusions or findings in the Report should any Client Data be incorrect or have been concealed, withheld, misrepresented or otherwise not fully disclosed to WSP.

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Contents

Disclaimers and Limitations ...... 1

Summary ...... 2

Glossary ...... 9

Qualifications and Experience ...... 10

1 Introduction ...... 14

2 Project Objectives ...... 14

3 Project Description ...... 16

4 The Context ...... 18 4.1 Introduction ...... 18 4.2 Strategic transport network ...... 18 4.3 Government policy statement ...... 19 4.4 National resilience objectives ...... 20 4.5 Regional resilience objectives ...... 21

5 Resilience...... 22 5.1 Definition...... 22 5.2 Resilience of transport networks ...... 22 5.3 Route resilience ...... 22 5.4 Resilience from Redundancy and Connectivity ...... 24

6 Resilience Context ...... 27 6.1 Importance of context...... 27 6.2 Natural hazards ...... 27 6.3 Characterisation of resilience impacts ...... 27 6.4 Wellington region resilience context ...... 29

7 Natural Hazards ...... 34 7.1 Hazards context ...... 34 7.2 Storms ...... 34 7.3 Coastal erosion ...... 36 7.4 Landslides ...... 37 7.5 Earthquakes...... 37 7.6 Tsunami ...... 49 7.7 Sea level rise ...... 50

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8 Shared Path ...... 53 8.1 Description ...... 53 8.2 The Shared Path Bridge ...... 53 8.3 Shared path along harbour edge ...... 55 8.4 Rock revetment – concrete seawall ...... 55 8.5 Construction ...... 56

9 Resilience performance ...... 58 9.1 Overview ...... 58 9.2 Operational and maintenance events ...... 59 9.3 Frequent events ...... 59 9.4 Low impact high probability events ...... 60 9.5 High impact low probability events ...... 60 9.6 Progressive long period events ...... 63

10 Contribution of Project to Corridor Resilience ...... 65 10.1 Types of contribution to resilience ...... 65 10.2 Protection from sea to railway corridor...... 65 10.3 Redundancy from alternate shared path ...... 65 10.4 Emergency response access ...... 65 10.5 Quicker recovery of limited access after major event ...... 66 10.6 Operational resilience from improved access to fix the railway incidents ...... 66

11 Resilience of Honiana Te Puni Reserve Masterplan ...... 68

12 References ...... 69

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Disclaimers and Limitations This report (‘Report’) has been prepared by WSP exclusively for the Waka Kotahi New Zealand Transport Agency (‘Client’) in relation to obtaining approvals (‘Purpose’) and in accordance with the agreement for professional services dated 7 October 2019 under the Independent Professional Advisors (IPA) contract No 17 – 286. The findings in this Report are based on and are subject to the assumptions specified in the Report. WSP accepts no liability whatsoever for any reliance on or use of this Report, in whole or in part, for any use or purpose other than the Purpose or any use or reliance on the Report by any third party.

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Summary

The Project The Ngā Ūranga ki Pito-One Shared Path Project is a section of the Te Ara Tupua Programme (the Project) which aims to deliver a shared path between Wellington CBD and the Hutt Valley. This Project involves the construction of a shared path between Ngā Ūranga Interchange to just south of the Pito-One Railway Station and associated works.1 The primary objective of the Project is to provide safe walking and cycling infrastructure between Wellington and the Hutt Valley which will act as a catalyst for increased use of active transport modes. The Project will improve connections and integration with planned and existing walking and cycling infrastructure in Wellington City and Hutt City.

Resilience Objectives In providing a walking and cycling facility, the Project has considered transport resilience. This specialist report provides a natural hazards and resilience context for the Project, and the effect of the Project on the resilience of the Ngā Ūranga to Pito-One transport corridor and the wider region. It is important to emphasise that the primary objectives of the Project are:

• To provide safe walking and cycling infrastructure connecting Ngā Ūranga and Pito-One, that is a catalyst for increased walking and cycling between Wellington and the Hutt Valley; and

• In providing a walking and cycling connection, enhance the resilience of the transport corridor between Ngā Ūranga and Pito-One.

Natural Hazards Context The shared path will be located along the Ngā Ūranga to Pito-One transport corridor in the Wellington region, which has a high exposure to earthquake and climatic hazards, a steep terrain susceptible to landslides, and the location of the shared path along Te Whanganui-a-tara (Wellington Harbour) exposes it to earthquake liquefaction, coastal and sea level rise hazards.

The Ngā Ūranga to Pito-One transport corridor is located on a narrow coastal strip (and land reclamation) between the steep hillside and the seafront of the Wellington Harbour. The transport corridor comprises State Highway 2 (SH2) at the foot of the hills and the Hutt Valley Railway Line between SH2 and the Wellington Harbour (“railway”). A partial and narrow cycleway exists between the SH2 and the railway.

Currently SH2 is routinely affected by landslides and rockfall from the steep hillside and flooding and debris from the streams and gullies that drain from the hills towards Wellington Harbour.

The railway is affected by coastal erosion (particularly given the poor state of the sea revetment formed over a long period of time), storm surge, flooding, and to a lesser extent, landslides.

The corridor is also exposed to large landslides and liquefaction of the reclaimed ground and underlying marine sediments, from lower frequency, but moderate to large earthquake events affecting the region. Similarly, the corridor is exposed to tsunami hazards resulting from large earthquakes or submarine landslides. Over time, the transport corridor is also exposed to sea level rise due to the rise of global temperatures due to climate change, and regional subsidence of the region due to tectonic activity.

1 This report uses the preferred Te Reo spelling of “Ngā Ūranga” and “Pito-One” even where the official name may instead use “Ngauranga” or “Petone”.

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Natural hazards will vary in size from small events that occur regularly to large events that occur less frequently and the impacts of these will vary. The range of potential hazards are taken into consideration in understanding the resilience of our transport networks.

Resilience Resilience is the ability of network infrastructure to adapt to and recover rapidly from a range of significant disruptions and situations from natural disasters, operational incidents and the changing climate, demographics or economic shocks. In this context resilience is the ability to recover readily and return to functionality from adverse events such as storms, earthquakes or tsunami or the ability to adapt to changing conditions, such as sea level rise.

Resilience Context The National infrastructure plan, the Greater Wellington Long Term Plan and the Government Policy Statement all emphasise the need for our infrastructure, transport networks and society to be resilient.

The transport network in the Wellington region is highly vulnerable to natural hazards, and critical sections are vulnerable to short to moderate closures in moderate hazard events and major closures for many months in larger hazard events such as a local magnitude 7.5 earthquake (Opus, 2012, 2016), such as a characteristic earthquake on the Wellington Fault.

Waka Kotahi’s Wellington transport resilience business case (WSP, 2018) considered the resilience risks and interventions necessary to enhance the resilience of the land transport network. It identified and prioritised the resilience risks faced by the region based on their level of exposure and impact, as well as the importance of the routes exposed to these risks.

The business case identified the Ngā Ūranga to Pito-One transport corridor and the Ngā Ūranga interchange area to be the most critical resilience risks in the region with an extremely high priority for enhancement of resilience. This recognises the critical nature of this multi-modal link in providing day to day road, rail and cycling access for economic and social activity between Wellington City, and Hutt Valley and the Wairarapa. It also provides access from the Hutt Valley and Wairarapa to the regional hospital, airport and port as well as emergency service access and supply route to the Hutt Valley in the event of a major earthquake. The corridor is also shared by other critical utilities such as the bulk water supply main. It is also very vulnerable to natural hazards and has no close alternative access routes to provide redundancy in the event of closures due to natural hazards, operational incidents or even maintenance activities.

For the Ngā Ūranga to Pito-One transport corridor, the business case recommended that relocation of the railway and SH2 towards the Wellington Harbour would provide much needed enhanced resilience from landslides, flooding, coastal erosion and sea level rise.

The Wellington transport resilience programme business case provides an overarching strategy and a long-term programme of actions to enhance resilience of transport in the region and was endorsed by the board of Waka Kotahi in 2019.

Contribution of the Project to Resilience The primary purpose of the Project is to provide safe connectivity for walking and cycling along the transport corridor.

In doing so, it will also contribute toward enhancing the corridor’s resilience to some disruptive events caused by storm and sea surge. Also, the Project mitigates the effects of sea level rise which may affect the transport corridor and allows for future adaptation. The resilience of the railway to coastal hazards will be significantly improved. The shared path also provides another improved alternative mode for access between Wellington and the Hutt Valley.

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However, the Project has not been developed to provide ‘the’ resilience solution to the critical resilience needs of the Ngā Ūranga to Pito-One Transport corridor and the region. This is being considered separately through a revised Ngā Ūranga triangle study considering State Highways 1, 2 and 58 in a holistic manner.

Any resilience benefits that the shared path can provide will however be valuable for this corridor and the region.

Characterisation of resilience risks Natural hazards occur in a range of intensities, from very low intensity storms, tsunami, landslides or earthquake tremors (which occur frequently with a high probability) to very high intensity events (which occur with a low frequency or low probability) such as a major characteristic magnitude 7.5 earthquake event on the Wellington Fault. Other chronic hazards such as climate change and sea level rise are predicted to occur gradually over a long period of time.

Operational (i.e. vehicle incidents on SH2) and maintenance issues (i.e. full or partial road and/or rail closure for maintenance or repair) are also frequent events or actions that also impact on the resilience of the transport access.

To understand the range of resilience issues and risks along the Ngā Ūranga to Pito-One transport corridor it is useful to consider the range of scenarios that may affect access along this corridor:

1 Operational and maintenance Events (OM), which occur routinely.

2 Frequent events (FE) of a natural hazard nature, which occur very frequently (once every few months to few years).

3 Low impact high probability events (LIHP), which occur at a moderate frequency (once in 20 to 100 years).

4 High impact, low probability events (HILP), which occur infrequently (once in 500 to 1000 years) but have a disproportionately very large effect.

5 Progressive long period events (PLP), such as sea level rise, which gradually occur over a long period of time.

A similar approach was used in the Wellington transport resilience business case for Waka Kotahi (WSP, 2018).

Operational and Frequent events Frequent events include small slips, rockfall, localised flooding, coastal erosion, spills, accidents etc which only partially close SH2 or railway line, and often for an hour to part of a day. The northbound carriageways of SH2 are more exposed, being close to the steep hills. These occur many times in a year.

The shared path will provide some resilience benefits for operational or frequent events, as it will provide an alternate safe mode of travel for some people who are able to walk or cycle, in addition to using the rail or the road if one or the other is affected, or staying at work for longer where possible.

The shared path (while being safer from a transport accident sense) may not be able to be used safely or comfortably when exposed to high winds and associated sea spray, particularly strong southerlies, except for use by a small proportion of fearless and confident cyclists, particularly where the other road and rail modes of transport remain alternatives that are available. This would somewhat reduce the positive resilience benefits provided by the shared path in Operational and Frequent events.

Overall, the shared path will have positive resilience benefits for access along the Ngā Ūranga ki Pito- One corridor, by providing an alternate mode of access for some users.

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Low impact high probability events Low impact high probability (LIHP) events include modest storms, landslides, coastal erosion, moderate earthquakes and modest tsunami waves from distant events.

In such high probability events, the region’s socio-economy will remain nearly fully functional and therefore even restricted transport access will have a significant effect on socio-economic functionality.

Construction of the Project will enhance the resilience of transport access along the Ngā Ūranga ki Pito-One corridor in LIHP events.

This is primarily due to enhanced protection of the railway corridor from coastal erosion because it will be protected by the specifically designed seaside rock revetment, concrete seawalls and shared path formation, to be constructed as part of the Project. A significant 2013 event is discussed later in this report, when the railway was closed for a whole week after storm surge caused extensive coastal erosion of the aging revetment.

The railway corridor is also less likely to be affected or disrupted by storm surge events because the proposed rock revetment will dissipate wave energy, reducing sea spray effects. The shared path will also provide a buffer between the rail corridor and the sea during storm events.

A resilience benefit of the Project is that it will also provide an improved safe transport mode for users who are able to walk or cycle, where road or rail modes of transport are not able to be used.

SH2, and to a lesser extent the railway and the shared path, will continue to be affected by flooding and possibly debris from the upstream hill catchments to the west, where gully and Korokoro Stream (at the Pito-One end) flows are not able to be safely conveyed to the Wellington Harbour because of the inadequate capacity of the existing culverts under SH2 and the railway. However, such flooding is likely to be of relatively short duration of a few hours to a day or so.

Landslides from small to moderate storm or earthquake events are only likely to close the inner northbound lanes of SH2 and not the southbound lanes, railway or the shared path, but still cause extensive disruption of access between Wellington and the Hutt Valley.

While the shared path will provide an alternate mode of travel for people who have mode shifted to or are able to cycle, southbound lanes of SH2 and the railway corridor are likely to remain open and continue to provide other means of access. The recently installed median barrier gates on SH2 also provide the ability to provide contra-flow if one of the northbound or southbound lanes are closed. However, such events will still cause significant disruption to transport along the corridor, given the near fully functional socio-economy in an LIHP event.

Small tsunami events with low height waves of less than a metre or so from distant sources are not likely to affect the transport corridors significantly, although the shared path may be closed as a safety precaution. It is noted that open sea tsunami waves would be moderated by the geography of Wellington Harbour, thus reducing the tsunami wave heights and impacts along the shared path.

High impact low probability events High impact low probability events include major landslides, local-source tsunami and large earthquakes such as a major characteristic magnitude 7.5 earthquake on the Wellington Fault or other local faults in the region or subduction zone earthquakes. This might also include very major storms causing large landslides and debris flows, with recurrence intervals of 100 years or more.

The Project would provide little resilience benefits for transport access along this Ngā Ūranga ki Pito- One corridor in HILP events.

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In a large tsunami, all three transport modes will be affected due to large tsunami waves inundating the corridor. Such inundation may last for a few hours to a day or two. The receding waves often drag back debris towards the sea causing damage, but because of the lack of other buildings and other above ground infrastructure this is likely to be limited but could include trapped cars or rail carriages, and any erosion is likely to affect the path much more as it is closest to the sea. Because of the location of the Ngā Ūranga ki Pito-One corridor along the edge of the Wellington Harbour, tsunami waves are likely to be moderated and less destructive than if exposed to the open sea, and seiche effects in Wellington Harbour could last longer but are likely to be less destructive.

The Project will encourage more users along the 4.5 km stretch between the rail overbridge (the shared path bridge) north of Ngā Ūranga and the Wellington Rowing Association area. In a local tsunami event with only minutes warning, people are expected to self-evacuate after signs such as strong earthquake shaking. Given the 4.5 km stretch of shared path with the sea on one side and railway fence on the other, quick lateral evacuation from the shared path will only be possible near the shared path bridge. Users will need to evacuate to either end, and therefore users may not be able to evacuate in a timely manner. This risk would need to be mitigated by clear directions and signs along the shared path indicating the quickest evacuation routes that assist timely evacuation to high points at either end. Consideration could be given to remotely controlled gates along the section to facilitate escape of people from the shared path across the rail corridor to SH2 and higher ground. I understand from Waka Kotahi that discussions with KiwiRail indicate that they would be receptive to considering such options. As discussed in the report, gates are proposed along the fence to enable KiwiRail access to the railway line for maintenance purposes. Subject to alignment between KiwiRail and Waka Kotahi’s operational and safety requirements, detailed design can consider the opportunity to utilise these gates as part of the tsunami evacuation plan for users of the shared path. These responses require follow up and action during design.

Large earthquakes and associated landslides would likely devastate the transport corridor with debris inundating all lanes of SH2 along much of the length of the corridor, including the railway and the shared path in some places. Intense ground shaking is expected to give rise to:

• liquefaction of the existing reclamation fill and alluvial and marine sediments as well the end- tipped fill that will be placed behind the revetment to form the shared path; and

• lateral spreading of the reclamation causing severe damage to the shared path and railway line, making them unsuitable for emergency services access.

Although the proposed piled overbridge (shared path bridge) over the railway line (near the Ngā Ūranga end) is likely to remain functional and provide limited access to the shared path, the loss of the coastal section of the shared path would make it redundant for immediate emergency services access.

It is possible that the shared path formation could be recovered over time after such an event by forming a temporary 4 WD access along the waterfront with a rockfall barrier on the hillside, while SH2 and the railway remain closed for many months (i.e. a period greater than six months).

Progressive long period events Progressive events such as sea level rise due to climate change and regional land subsidence due to tectonic activity is predicted to occur over a period of decades and will pose an increasing risk to all three transport corridors (but mainly the shared path and railway line) due to the increased frequency and duration of storm surge and associated flooding from the sea.

The shared path will generally be at a level (300 mm to 600 mm) lower than the current railway formation along the Ngā Ūranga to Pito-One coastline. However, to provide for sea level rise, a 450 mm crest is provided for at the top of the rock revetment on the seaward side of the shared path. The level of this crest will bring the coastal edge to approximately the level of the existing railway

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formation, and along a 0.5 km long section up to 200 mm higher than the existing rail formation. The concrete vertical walls will have a similar crest level.

The factors below have been assessed to contribute to enhanced performance under the existing coastal hazards as well as when the sea level rises over the next 60 to 80 years:

• construction of the new rock revetment with a much flatter slope (2H:1V);

• incorporation of a 3 m wide bench at Elevation 0.8 m; and

• the selection of rock sizes.

A further appropriate response to such gradually increasing hazard is allowance for adaptation. The shared path has been configured to allow for raising of the sea wall / revetment as the sea level rises in the future. The bench configuration has been incorporated to allow for future adaptation of the rock revetment when this becomes necessary in the future.

The Project will therefore provide protection for some years of future sea level rise and a better opportunity to respond to sea level rise by adaptation through future raising of the sea wall revetment.

Operational and maintenance events Currently there is no lateral access into the railway corridor between Pito-One and Ngā Ūranga given the presence of SH2 on the western side and no space for access on the seaward side. This limits maintenance access or access to repair faults as the corridor needs to be shut down to gain access. The shared path will provide some resilience benefits by providing improved access to the eastern side of the railway corridor from the seaside (through planned gates along the fence) for operational incidents, fault repairs and routine monthly maintenance. This will enhance operational resilience for the railway.

Transport access also gets restricted by operational events such as mechanical and electrical faults (railway), accidents or spillage of hazardous substances or petroleum (Opus, 1999). These incidents are generally short term – and may affect access for an hour to a day or so. These events will continue to occur from time to time and affect SH2 and the railway. The shared path will enable some permanent mode shifting and will lead to positive resilience benefits as a proportion of the travel could still occur where the shared path is not affected. It will also provide another alternate mode of transport access for users, who are able to walk or cycle in the event of closure of the road or rail, which they would normally use. It is noted that the shared path would not provide access to commercial and heavy vehicles to facilitate economic activity.

There is the potential for further resilience improvements to be carried out as a separate project, to enhance the resilience of access between Ngā Ūranga and Pito-One, through a widened reclamation and moving the path, railway and state highway 2 away from the hillside cliffs, as recommended by the Wellington Transport Resilience PBC (WSP Opus, 2018).

Conclusion The Project will directly contribute toward enhancing the resilience of the Ngā Ūranga to Pito-One transport corridor.

The Project, through enabling mode shift, will lessen the effects of disruption on the road and rail corridor, where the shared path itself is not affected. It will also provide an improved alternate transport access mode, to users who are able to use this mode, in the event of the road or rail being closed due to small events, but the shared path being available.

It will provide a significant ancillary resilience benefit to the railway line through enhancing the protection of this corridor from coastal erosion (due to sea level rise and storm surge) and reducing

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disruption to rail services through buffering rail services from the coast. The Project will also provide enhanced access to the seaward side of the railway line for fault repairs and monthly maintenance without having to close the entire section of railway.

Overall, the Project provides positive resilience benefit for transport access along the Ngā Ūranga to Pito-One corridor in modest natural hazard events or operational incidents. This is achieved in part by facilitating mode shift, which will lessen the effects of disruption to road and rail services. More substantively it is achieved by significantly enhancing the protection of the railway line to coastal hazards including the effects of sea level rise.

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Glossary

AEE Assessment of Environmental Effects

HILP High Impact, Low Probability

LIHP Low Impact, High Probability

MHWS Mean High Water Spring

N2P Ngā Ūranga to Pito-One

NCTIR Northern Canterbury Transport Infrastructure Recovery

SH State Highway

Shared path The Ngā Ūranga ki Pito-One shared path

Te Ara Tupua Te Ara Tupua is the link being developed between Wellington CBD and Melling, made up of the 3 sections – Wellington CBD to Ngā Ūranga, Ngā Ūranga to Pito-One and Pito-One to Melling.

The Project Te Ara Tupua - The Ngā Ūranga ki Pito-One shared path, the associated use of part of Honiana Te Puni Reserve as a temporary construction yard, and the redevelopment and reinstatement of Honiana Te Puni Reserve including relocation and construction of an Integrated Clubs Building, construction of the Whare and other related cultural and community structures.

Waka Kotahi New Zealand Transport Agency

WSP WSP New Zealand Limited

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Qualifications and Experience

Qualifications My full name is Pathmanathan Brabhaharan.

I am National Technical Leader – Technical Director, Geotechnical & Earthquake Engineering, and Infrastructure Resilience at WSP New Zealand Limited ("WSP"). I am based in the Wellington Office of WSP.

I have the following qualifications and experience relevant to this report: 1) Bachelor of Science of Engineering with Honours, specialising in Civil Engineering, from the University of Peradeniya, Sri Lanka (1982). 2) Master of Science of Engineering in Foundation Engineering from the University of Birmingham, United Kingdom (1986). 3) Master of Business Administration from Deakin University, Australia (1998). 4) Chartered Professional Engineer in New Zealand.

Professional membership and roles I am a member of several relevant associations including: 1) Fellow of Engineering New Zealand; 2) Fellow of the New Zealand Society for Earthquake Engineering; 3) Member of the New Zealand Society for Risk Management; 4) Member of the New Zealand Geotechnical Society, affiliated to the International Society for Soil Mechanics and Geotechnical Engineering and the International Society for Rock Mechanics; 5) Member of the Structural Engineering Society; 6) Member of the IPWEA 7) Member of the NZ Society of Large Dams. I am also currently a member of the management committee of the NZ Society for Earthquake Engineering.

Experience 1) I have 38 years' experience in Geotechnical, Earthquake and Civil Engineering and Risk Management, in New Zealand, United Kingdom, Malaysia, Singapore and Sri Lanka. 2) I have been based in Wellington and have practised in New Zealand since 1989 (over the past 31 years), and during this period have provided geotechnical advice, design, investigations and construction monitoring for a variety of infrastructure projects, and in particular for motorways, expressways, highways, roads and bridges. 3) I was a member of the Learning from Earthquakes Team from the NZ Society for Earthquake Engineering that carried out reconnaissance of the damage to the built and natural environments in the Sichuan Province of China, as a result of the Richter Magnitude 8 Wenchuan Earthquake in May 2008, and Japan following the 2016 Kumamoto earthquake, and presented findings to the profession. 4) I was engaged by the New Zealand Transport Agency ("Transport Agency") to carry out field reconnaissance of damage to highways and bridges and to gather and report lessons on geotechnical aspects of the observed performance, following the 2010 Magnitude 7.1 Darfield Earthquake, the 2011 Magnitude 6.3 Christchurch Earthquake that affected Canterbury and the 2016 Kaikoura earthquake that affected the Kaikoura and Marlborough areas.

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5) I have been actively involved in the emergency response and recovery after the 2010-2011 Canterbury Earthquake Sequence, and the 2016 Kaikoura earthquake, and was involved in developing repair and reconstruction solutions. 6) I have carried out research and developed approaches to assess the resilience of transport networks and have over the past 20 years led the assessment of the resilience of the transport network in the Wellington Region, the national state highway network and other transport networks in New Zealand. 7) I led the Wellington Region Land Transport Business case for Waka Kotahi during 2016-2019, and assessed the resilience to various natural hazard events, prioritised the resilience risks and developed mitigation measures to enhance the resilience of the land transport system. 8) I am currently leading a theme on the performance of earthworks as a part of a 5-year research programme into earthquake induced landslides and other failures affecting the infrastructure in the 2016 Kaikoura Earthquake. 9) I led the earthquake hazard assessment studies, including liquefaction and slope failure hazards for the Wellington region (1992-1995), which resulted in the publication of earthquake hazard maps for the Wellington region. This included the Ngauranga to Petone area where the shared path will be constructed. 10) I have also led a number of studies to assess the resilience and develop risk management strategies for the State highways in the Wellington Region and the local authority road networks in Kāpiti Coast, Wellington City, Hutt Valley, Upper Hutt, and Porirua. The resilience of priority roads within the greater Wellington area under earthquake and / or storm conditions has been assessed as part of these studies. 11) I was involved in a study for the Transport Agency to identify critical sections along SH 1, SH 2 and SH 58 that would be affected in a major earthquake in the region, develop emergency response plans and in particular assess the likely time required to reopen the coastal route between Pukerua Bay and Paekakariki. 12) I have advised the Wellington Lifelines Group in the consideration of emergency access following a major earthquake in the region. 13) My experience includes a variety of highway projects in the Wellington, Nelson-Marlborough and other Regions, which have involved design and /or construction of large structures and earthworks in geological conditions similar to those encountered Ngauranga and Petone, including: a) Petone to Grenada scheme development, including a transport interchange at Petone, Horokiwi and Tawa and large cut and fill slopes. This included extensive geotechnical investigations and preliminary design concepts and mitigation of the liquefaction, landslide and fault rupture hazards. b) Transmission Gully expressway including 29 bridges (sand dunes and inter-dunal peat deposits at the north end, estuarine deposits at State Highway ("SH") 58, alluvium at the southern end and along the many stream valleys, and predominantly greywacke rock), for the preliminary geotechnical investigations and assessment, scheme assessment, development of designs for consents, assessment of environmental effects and preparation and presentation of evidence at the Board of Inquiry; and subsequently the development of tender design for a PPP consortium; c) Christchurch Southern Motorway (liquefiable and compressible alluvium), as reviewer for the scheme development, detailed design and construction stages; d) Peka Peka to Otaki Expressway (alluvium, sand and inter-dunal peat deposits), as lead geotechnical designer, for the scoping and scheme assessment stages, and preparation and presentation of evidence to the Board of Inquiry; e) SH6 Stoke Bypass – 7 km bypass along the sea waterfront between Nelson and Richmond, comprising embankments, cut slopes, retaining walls and bridges;

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f) SH2 Muldoon’s Corner realignment, as lead geotechnical engineer the scheme development, detailed design and construction monitoring of up to 60 m high cuttings, 45 m high embankments and slope stabilisation works. g) The Tunnel-Link project (alluvium and complex groundwater regime) of 1.2 km length between the south portal of the Terrace Tunnel and the west portal of the Mt Victoria Tunnel, for development of the scheme; my role included detailed assessment of the groundwater regime and its interaction with the proposed cut-and-cover tunnel structures, the bridge at the Basin Reserve area and associated retaining walls and earthworks; h) Wellington Inner City Bypass (alluvium and complex groundwater regime), for development of the scheme, detailed design, construction and maintenance management; my role included detailed assessment of the groundwater regime and its interaction with the road structures, development of solutions to mitigate any risks and monitoring during construction to demonstrate compliance; i) Mt Victoria Tunnel Strengthening and Duplication (fractured rock), involving strengthening of the portal structures, development of options for duplication of the Mt Victoria Tunnel as part of the Ngauranga to Airport Strategy Study, and peer review of the scoping study for the duplication of the tunnel; j) Newlands Interchange including overbridge (fill, alluvium and rock), as lead geotechnical designer, for concept, scheme assessment, detailed design and construction; k) Western Link Road including several bridges, between Raumati South and Waikanae (sand and inter-dunal peat deposits), for the design and consenting stages; l) Wellington East Girls College (fractured greywacke rock), seismic assessment and master planning project, and currently developing strengthening works at the school. m) I have also been involved in the seismic assessment and retrofit of bridges in New Zealand including development of innovative retrofit solutions for abutments, either as lead geotechnical engineer or peer reviewer, including: n) Thorndon Overbridge (preliminary assessment and then peer review);

Code of Conduct for expert witnesses I confirm that I have read the Code of Conduct for expert witnesses contained in the Environment Court Practice Note 2014. This assessment has been prepared in compliance with that Code. In particular, unless I state otherwise, this assessment is within my area of expertise and I have not omitted to consider material facts known to me that might alter or detract from the opinions I express.

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Figure 1-1 – Ngā Ūranga ki Pito-One shared path

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1 Introduction A new shared path (the Ngā Ūranga ki Pito-One Shared Path) is being planned between Ngā Ūranga (in Wellington) and Pito-One (in Lower Hutt), see Figure 1-1.

The shared path will be located along the Wellington Harbour on the seaward side of State Highway 2 (SH2) and the Hutt Valley - Wairarapa railway line.

Waka Kotahi NZ Transport Agency (Waka Kotahi) has commissioned WSP New Zealand Limited (WSP) to prepare an assessment of the Natural Hazards and Resilience in support of their application for Notice of Requirement (NOR) and resource consents for the Project.

This report has been prepared to support the Waka Kotahi application and the associated Assessment of Environmental Effects (AEE).

2 Project Objectives The objectives of the Project are:

1. To provide safe walking and cycling infrastructure connecting Ngā Ūranga and Pito-One, that is a catalyst for increased walking and cycling between Wellington and the Hutt Valley; and

2. In providing a walking and cycling connection, enhance the resilience of the transport corridor between Ngā Ūranga and Pito-One.

This specialist report provides a natural hazards and resilience context in which the shared path will be located and assesses the resilience benefits of this new facility to the Ngā Ūranga to Pito-One transport corridor and the wider region.

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Figure 3-1 Sectors along the shared path

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Sensitivity: General 3 Project Description The Ngā Ūranga ki Pito-One2 Shared Path Project (Project) is a section of the Te Ara Tupua Programme which aims to deliver a shared path between Wellington CBD and Hutt Valley. This Project involves the construction of a shared path from the Ngā Ūranga interchange to just south of the Pito-One Railway Station in the north and associated works as shown in Figure 3-1.

The Project will cater for active transport modes including cycling and walking and will provide an alternative to the existing State Highway 2 (SH2) cycle path located between the Hutt Valley Railway Line and the southbound SH2 carriageway. Works at Honiana Te Puni Reserve provide for the removal and replacement of the existing Wellington Rowing Association and Wellington Water Ski Club facilities at, and adjacent to, Honiana Te Puni Reserve and the introduction of new cultural facilities into the Reserve.

The primary objective of the Project is to provide safe walking and cycling infrastructure between Wellington and the Hutt Valley which will act as a catalyst for increased use of active transport modes. The Project will also provide increased transport resilience, improve connections and integration with planned and existing walking and cycling infrastructure in Wellington City and Hutt City and reconnect people with this long-inaccessible part of the Harbour’s edge.

The Project will provide a 4.5 km-long shared path between Ngā Ūranga and Pito-One featuring the following key elements:

a) A rail overbridge (shared path bridge) across the Hutt Valley Railway Line, connecting the shared path from Ngā Ūranga to the coastal edge;

b) A path with a 5 m surface width on existing and newly created land and coastal structures, on the seaward side of the Hutt Valley Railway Line;

c) A varied coastal edge which incorporates ūranga (landings), a rocky revetment the intermittent use of strategically placed seawalls along the path edge. The coastal edge treatment provides resilience, reflects the natural landscape, avoids sensitive habitat areas, provides for cultural expression and enhances amenity;

d) Construction of new offshore habitat for coastal avifauna;

e) Connections to the Pito-One to Melling (P2M) path and the Pito-One Esplanade;

f) Construction of a new integrated clubs building at the eastern end of Honiana Te Puni Reserve and an associated car parking area; and

g) A two-stage development of new cultural facilities at Honiana Te Puni Reserve, including:3

i. Construction of temporary Tāwharau Pods, consisting of three small building pods designed to accommodate a range of cultural or community uses, at the eastern end of Honiana Te Puni Reserve; and

ii. Post construction, the construction of the Whare to the west of Korokoro Stream, and permanent relocation of the Tāwharau pods to a site adjacent to the Project at the western end of Honiana Te Puni reserve.

2 For this project, Waka Kotahi uses the preferred Te Reo spelling of “Ngā Ūranga” and “Pito-One” even where the official name is “Ngauranga” and “Petone”. Te Whanganui a Tara refers to Wellington Harbour 3 Taranaki Whānui will determine whether these facilities, which are being consented as part of the Project, will be constructed.

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Sensitivity: General For description and assessment purposes in this report, the Project has been divided into three sectors (as shown in Figure 3-1). These are:

Sector 1 Ngā Ūranga Interchange and Bridge Crossing: The Southern Construction Yard and the connection from the Ngā Ūranga Interchange via the shared path bridge across the Hutt Valley Railway Line, to the coastal edge. Sector 2 Ngā Ūranga to Honiana Te Puni Reserve - Shared Path and ūranga: The typical shared path, rock revetment, ūranga, seawall structures and offshore habitats between Ngā Ūranga and Honiana Te Puni reserve; and Sector 3 Honiana Te Puni Reserve and Pito-One to Melling (P2M) Connection: Shared path connection to P2M adjacent to Honiana Te Puni Reserve, connections to Honiana Te Puni Reserve and Pito-One Esplanade, the Northern Construction Yard, integrated clubs building, associated car parking, the temporary and permanent Tāwharau Pods and Whare.

A full description of the Project including design and operation is provided in Chapter 3 Description of the Project in the Assessment of Effects on the Environment.

A description of the potential construction methodology that could be used to construct the Project is provided in Chapter 4 Construction of the Project of the Assessment of Effects on the Environment.

WSP has been engaged to undertake an assessment of effects on Natural Hazards and Resilience associated with the Project.

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Sensitivity: General 4 The Context

4.1 Introduction In carrying out an assessment of the natural hazards and resilience, the overarching transport and policy context has been considered, particularly in relation to resilience.

As described below the Ngā Ūranga ki Pito-One corridor is a strategic transport link in the region, and the national and regional policies require resilience be taken into consideration as key priorities in the development of transport infrastructure.

4.2 Strategic transport network The Ngā Ūranga ki Pito-One corridor is the primary (and only direct) land transport link between Wellington City and the Hutt Valley and comprises SH2 and the Wairarapa railway line. It forms part of one of only two highway and rail corridors connecting Wellington with the rest of the North Island, see Figure 4-1.

Pito-One

Ngā Ūranga

Figure 4-1: Transport Routes – One Network Road Classification (ONRC) (Note: Ngā Ūranga ki Pito-One corridor shown as dashed blue box)

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Sensitivity: General A key feature of the Ngā Ūranga ki Pito-One transport corridor is that it provides the only access (both road and rail) between Wellington and the Hutt Valley (comprising Hutt City and Upper Hutt City) and the Wairarapa area of the Wellington Region.

Further details are provided in Technical Report 1: Strategic Transport Assessment (WSP, 2020).

4.3 Government policy statement The Government Policy Statement (GPS) outlines the Government’s strategy to guide land transport investment over the next 10 years, see Figure 4-2. It also provides guidance to decision-makers about where the Government will focus resources. The GPS operates under the Land Transport Management Act 2003, which sets out the scope and requirements for the GPS. The GPS influences decisions on how money from the National Land Transport Fund (the Fund) will be invested across activity classes, such as state highways and public transport. It also guides Waka Kotahi and local government on the type of activities that should be included in Regional Land Transport Plans and the National Land Transport Programme.

Figure 4-2: Objectives in the Government Policy Statement 2018

The GPS of 2018 has the objective to achieve a land transport system that addresses issues that are important to the functioning of society.

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Sensitivity: General The four strategic priorities in the GPS as shown in Figure 4-2 are:

1. Access a) Increased access to economic and social opportunities b) Enables transport choice and access c) Is resilient 2. Safety 3. Environment 4. Value for money

Of these four priorities, Access and Safety are identified as Key Strategic Priorities. Therefore, providing resilient access is a key strategic priority of the GPS 2018.

4.4 National resilience objectives Resilience is one of the six guiding principles promoted by the National Infrastructure Plan (National Infrastructure Unit, The Treasury, 2011, 2015). The National Infrastructure Plan states that:

The concept of resilience is wider than natural disasters and covers the capacity of public, private and civic sectors to withstand disruption, absorb disturbance, act effectively in a crisis, adapt to changing conditions, including climate change, and grow over time.

That plan has a vision that by 2030 New Zealand's infrastructure is resilient and coordinated and contributes to economic growth and increased quality of life. Resilience is one of the six principles underpinning the Plan. This approach to resilience has been adopted by the National Programme Business Case of the New Zealand Transport Agency (2014). The above concept of resilience has five strands as summarised in Table 4.1.

Table 4-1: Relationship of resilience to National Infrastructure Plan

Relevance to resilience Strands of resilience Relevance to transportation routes assessment

1 Capacity to The resilience of routes to natural and Route Resilience – robustness withstand disruption technological hazards is important to of route to natural and withstand disruption to the route. technological hazards.

2 Capacity to absorb The ability of the network to absorb Network resilience from disturbance and function despite accidents, Redundancy and operational incidents, hazard impacts Connectivity – ability of the and maintenance closures is system to absorb the effects important for the network to absorb of closures and continue to the effects of such disturbance. function effectively.

3 Act effectively in a Emergency management and Have options available to re- crisis incident management preparedness. route and respond when incidents occur to minimise the impacts.

4 Adapt to changing Important that routes are able to Route Resilience - routes are conditions including function and don’t become more designed for changing risk climate change vulnerable as a result of changes in scape such as climate the environment, including climate change. change.

5 Grow over time Transport routes have flexibility and Capacity and adaptability to future proofing to enable them to grow over time. grow to cope with future needs.

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Sensitivity: General 4.5 Regional resilience objectives The Greater Wellington Long Term Plan 2012-2022 sets out five community outcomes which describe what Greater Wellington aims to achieve in order to improve the Wellington Region’s wellbeing over the long term.

These include:

1. Strong economy – a thriving, and diverse economy supported by high quality infrastructure that retains and grows business and employment. 2. Connected community – people are able to move around the region efficiently and our communications networks are effective and accessible. 3. Resilient community – a community that plans for the future, adapts to change and is prepared for emergencies. 4. Healthy environment – an environment with clean air, fresh water, healthy soils and diverse ecosystems that supports community needs. 5. Quality of life – an engaged community that takes pride in our region, values our urban and rural landscapes, and enjoys our amenities and choice of lifestyles. 6. The relevance of resilience of the road network in achieving these community outcomes are summarised in Table 4.2.

Table 4-2: Relationship to Greater Wellington’s community outcomes

Aims Community outcomes Relevance to resilience assessment

1 Strong A thriving and diverse economy A resilient transport network that economy supported by high quality provides confidence in its availability infrastructure that retains and grows is important to retain and grow business and employment. business and employment.

2 Connected People are able to move around the Moving around efficiently and community region efficiently and our effectively in spite of disruptive communications networks are events requires resilient transport effective and accessible. networks.

3 Resilient A community that plans for the The community needs to be able to community future, adapts to change and is rely on resilient transport networks prepared for emergencies. to ensure they can plan for and are prepared for emergencies.

4 Healthy An environment with clean air, fresh - environment water, healthy soils and diverse ecosystems that supports community needs.

5 Quality of life An engaged community that takes Resilient transport networks are vital pride in our region, values our urban for a community to take pride and and rural landscapes, and enjoys our enjoy the amenities. amenities and choice of lifestyles.

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Sensitivity: General 5 Resilience

5.1 Definition Resilience is the ability of network infrastructure to deal with a range of significant disruptions and situations from natural disasters and operational incidents to changing climate, demographics or economic shocks.

This wider view of resilience is consistent with the Government's National Infrastructure Plan.

5.2 Resilience of transport networks Both national and regional objectives emphasise the importance of resilient infrastructure including transportation networks.

In a transportation context, resilience comes from:

1) Resilience to unplanned disruptions from: a) natural hazard events, for example a storm, landslide, earthquake or tsunami b) technological hazards such as a petroleum or hazardous substances spill 2) Resilience to accidents, operational incidents or maintenance closures. It is the ability of the transportation network to rapidly recover and provide the necessary level of access, despite incidents, small or large.

When considering the resilience of access of the transport network as a whole, resilience depends on:

1) Route Resilience a) less vulnerable to failures in natural hazards b) ability to recover quickly after closures 2) Network Resilience from Redundancy and Connectivity a) Redundancy – availability of alternate routes or modes to cope with disruptions due to hazards, accidents or maintenance b) Connectivity – trip diversity and ability to move from one link to other to avoid blockage.

5.3 Route resilience Resilience is the ability to withstand or recover readily and return to its original form from adversity. It is the capacity to recover quickly from difficulties; i.e. toughness.

The Route Resilience of infrastructure lifelines such as roads is dependent on the loss of quality or serviceability, and the time taken to bring the route or service back into its original usage state after the reduction or loss of access due to an event.

Route Resilience depends on:

a) low vulnerability to failures in natural hazards

b) ability to recover quickly after closures due to natural hazards or technological hazards.

This is shown conceptually in Figure 5-1, after Brabhaharan (2006).

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Sensitivity: General

Figure 5-1: Resilience of infrastructure (after Brabhaharan, 2006)

The smaller the shaded green area, the more resilient is the route. The greater the area, the poorer is the performance.

It is important to recognise that enhancing resilience is not just about reducing the vulnerability of the route (making it more resilient), but also designing, constructing and operating it in a way that it can be quickly brought back into service (Brabhaharan, 2020). Therefore, it is important to enable a holistic achievement of resilience, through considering both vulnerability and ability to recover quickly.

“Performance States” or “Resilience States” representing the performance of the transport network have been developed to consider the impact of various natural hazards on the transportation network on a similar basis (Brabhaharan et al., 2006). These states are summarised in Tables 5-1 and 5-2. A single metric combining the availability state and outage state as disruption state is presented in Table 5-3.

Table 5-1: Availability State

Availability Level Availability State Availability Description

1 Full Full access (perhaps with driver care).

Available for slow access, but with difficulty by normal 2 Poor vehicles due to partial lane blockage, erosion or deformation.

Single lane access only with difficulty due to poor condition 3 Single Lane of remaining road.

4 Difficult Road accessible single lane by only 4x4 off road vehicles.

5 Closed Road closed and unavailable for use.

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Sensitivity: General

Table 5-2: Outage State

Outage Level Outage State Outage Description

1 Open No closure, except for maintenance

2 Minor Condition persists for up to 1 day

3 Moderate Condition persists for 1 day to 3 days

4 Short term Condition persists for 3 days to 3 weeks

5 Medium term Condition persists for 3 weeks to 3 months

6 Long term Condition persists for > 3 months

Table 5-3: Disruption State

Outage State and Level Disruption State Open Minor Moderate Short term Medium term Long term 1 2 3 4 5 6

Full 1 None None None None None None Level

& Poor 2 None Limited Limited Limited Moderate High

State Single lane 3 None Limited Limited Moderate High Severe

Difficult 4 None Limited Limited Moderate High Severe

Availability Availability Closed 5 None Limited Moderate High Severe Extreme

Natural hazards such as earthquakes and storms, as well as the potential for technological hazards, have an important effect on route resilience. This could be in major natural hazards such as a Wellington Fault earthquake, or in small to moderate storms or earthquakes.

An example of Route Resilience is the resilience of State Highway 3 through the Manawatu Gorge. Manawatu Gorge has failed repeatedly in the last 15 years, leading to closures. Given the geology and terrain, the route is susceptible to landslides and resulting closures. Also, it has taken very long periods to reopen the road, indicating a poor route resilience. This has led Waka Kotahi to close State Highway 3 through the Manawatu Gorge and develop a new alternate route over the hill to the north of the gorge.

5.4 Resilience from Redundancy and Connectivity Network resilience should also be considered when considering the resilience of a transport network.

Network Resilience comes from Redundancy and Connectivity

a) Redundancy – availability of alternate routes or modes in hazards, accidents or maintenance

b) Connectivity – trip diversity and ability to move from one link to other to avoid blockage.

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Sensitivity: General Taking the Manawatu Gorge example, when we consider the network as a whole, the network has a greater resilience than the Manawatu Gorge in isolation because of the presence of the alternative routes along Saddle Road and Pahiatua Track. The available redundancy gives greater network resilience than an individual isolated route, however the constraints and vulnerabilities along those alternative routes limit the total resilience of the network.

In Christchurch, although some routes were vulnerable and were closed after the Canterbury earthquakes of 2010-2011, the city has numerous routes, giving it ample redundancy. Its flat terrain has enabled the development of many alternative routes, and the transport network, as a whole, has good resilience, and access generally wasn’t a major issue after the earthquake. This was critical to emergency response and recovery after the earthquakes.

The recent November 2016 Kaikōura earthquake illustrates the effect of poor resilience and lack of redundancy of access on post-earthquake response and recovery even for a small town like Kaikōura. The consequences will be much greater for cities like Wellington and Lower Hutt.

The Ngā Ūranga to Pito-One corridor has no close alternative routes, and therefore no redundancy or connectivity. Therefore, the route resilience is much more critical to this corridor.

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Figure 6-2: Resilience of the Wellington region transport network in a large earthquake – availability state (after Opus, 2016)

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6 Resilience Context

6.1 Importance of context It is important to understand the resilience context of the Ngā Ūranga ki Pito-One route within the region and locally, to gain an appreciation of the resilience contribution of the Project.

Systematic studies of the resilience impacts of storm events and earthquakes on the SH2 and arterial local road network have been carried out (Opus, 2012, 2016a, 2016b), and therefore there is a much better understanding of these effects. These have been used to gain an understanding of the resilience context in the region.

6.2 Natural hazards The predominant natural hazards in the region are:

1) Storms 2) Coastal erosion 3) Landslides 4) Earthquakes 5) Tsunami 6) Sea level rise

Natural hazards occur in a range of intensities, from very low intensity storms, tsunami, landslides or earthquake tremors (which occur frequently with a high probability) to very high intensity events (which occur with a low frequency or low probability) such as a major characteristic magnitude 7.5 earthquake event on the Wellington Fault. The impacts of these hazards on the transportation system will also vary. Progressively larger events occur with lesser frequency, as shown in Figure 6-1.

Annual probability or frequency Intensity of hazard

Figure 6-1. Hazard intensity v annual probability

Sea level rise occurs gradually over a long period of time. The impact of a large earthquake on the transport infrastructure in the region is presented on Figure 6-2 and discussed further below in the Wellington Region Resilience context.

6.3 Characterisation of resilience impacts The resilience impacts of these events of different intensities will also vary enormously. Therefore, it is important for the range of potential hazards to be taken into consideration in understanding the resilience of our transport corridors. Not only do the resilience risks vary, the resilience expectations for transport routes will also vary depending on the size of the event and the overall performance of the built and natural environments. As it is not practical to consider every size or intensity of natural hazards, resilience studies have found it important to characterise natural hazards and understand their resilience impacts.

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Figure 6-3: Resilience of the Wellington region transport network in a large storm event (after Opus, 2016)

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The natural hazards have been characterised into the following scenarios to help understand the range of resilience issues:

1) Operational and maintenance (OM) events, which occur routinely.

2) Frequent events (FE) which occur very frequently (every few months to few years), which are managed by routine maintenance responses.

3) Low impact high probability events (LIHP), which occur at a moderate frequency (once in 20 to 100 years).

4) High impact, low probability events (HILP), which occur infrequently (once in 500 to 1000 years) but have a disproportionately very high impact.

5) Progressive long period events (PLP), such as sea level rise, which gradually occur over a long period of time.

This is similar to the approach used in the Wellington transport resilience business case. The impact of events with intermediate probabilities will have intermediate impacts, noting that the impacts don’t vary linearly between different frequency events.

Given the significant impact of HILP events on the transport corridor and other infrastructure lifelines and economic activity, there have been more studies carried out to better understand and characterise the impact from a HILP event, and to a lesser extent a LIHP event. There have also been studies to look at the impact of sea level rise. The results from these studies have been used to characterise the resilience issues in the region and also the Ngā Ūranga ki Pito-One corridor.

6.4 Wellington region resilience context

6.4.1 Redundancy and connectivity The Wellington Region has very limited redundancy and connectivity in its network outside the city centres. The Greater Wellington area comprises only two transport corridors providing road or rail access from outside the region, one along the western corridor (SH 1) and one from the east (SH 2). There are very few viable alternative arterial local roads, the only roads (Akatarawa Road, Paekakariki Hill Road) being very narrow and not appropriate for extended detour use or all vehicle types and thus having poorer resilience (Opus, 2012).

6.4.2 Resilience The transport network in the Wellington region is highly vulnerable to natural hazards, and critical sections are vulnerable to short to moderate closures in moderate hazard events and major closures for many months in larger hazard events such as a characteristic magnitude 7.5 earthquake on the Wellington Fault (Opus, 2012, 2016). The resilience of the network in terms of the resilience states is presented in Appendix A, and the availability state map is presented in Figure 6-2. This shows that in the event of a large earthquake (HILP) event, the region is expected to be cut off for many months from outside, and individual cities / towns cut off from each other.

The resilience of the transport network to a LIHP storm event is presented in Figure 6-3. This shows a lower impact on the transport network, but still a significant impact that would affect the socio- economic functionality of society.

These earthquake and storm resilience maps were developed for the local authorities in the greater Wellington area, Greater Wellington regional council and Waka Kotahi (Opus, 2012, 2016).

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Figure 6-4: Criticality of transport network resilience risks in the Wellington region

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6.4.3 Strategic case for resilience Waka Kotahi and the Greater Wellington Regional Council (GWRC) considered the strategic case for resilience in the Wellington Region in a 2014 report, and this is reported by Waka Kotahi (NZ Transport Agency 2014).

This report confirmed that the Wellington Region transport network is vulnerable to both “High Impact Low Probability” as well as “Low Impact High Probability” natural hazard events.

The report reached the following conclusions:

1) A more resilient regional network leads to improved recovery timeframes following a major event. 2) Investing in the improvement of the resilience of the transport corridors in this area would gain a Strategic Fit / Effectiveness rating of High/Moderate. 3) More resilient access into/out of the region would also reduce risk exposure to High Impact Low Probability events. 4) Addressing potential Low Impact High Probability events will minimise economic disruption and will lower ongoing emergency repair works and costs following storms and other more frequent events.

6.4.4 Transport resilience programme business case Recognising the significant resilience risks in the region, Waka Kotahi and GWRC jointly commissioned a transport resilience business case.

The Wellington Transport Resilience Programme Business Case (WSP, 2018) considered the resilience risks and interventions necessary to enhance the resilience of the land transport network. It identified and prioritised the resilience risks to transport links in the region based on their criticality. The criticality was based on the level of exposure and impact to transport modes (from earthquake, storm and tsunami hazards), as well as the importance of the routes. The impacts to other critical utilities were also considered.

The business case also developed potential interventions to enhance the resilience of critical journeys in the region and developed a long-term strategy for action.

6.4.5 Criticality of the Ngā Ūranga ki Pito-One corridor The critical resilience risks in the region including the Ngā Ūranga ki Pito-One corridor are presented on the map in Figure 6-4.

The corridor is also very vulnerable to natural hazards and has no close alternative access routes to provide redundancy in the event of closures due to natural hazards, operational incidents or maintenance activities.

For the Ngā Ūranga ki Pito-One transport corridor, there are no alternative routes available, other than distant road transport alternative via State Highway 1, State Highway 58 across Haywards hill and back via SH2 to Pito-One, which is a distance of 45 km, 9 times the direct Ngā Ūranga ki Pito-One link distance of 5 km.

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For the railway, the alternative will be even longer, from Wellington to Palmerston North, to Woodville via Manawatu Gorge, to Featherston through the Wairarapa, to Upper Hutt through the Remutaka rail tunnel and back down the Hutt Valley.

6.4.6 Resilience enhancement of the Ngā Ūranga ki Pito-One Corridor The Wellington transport resilience programme business case provides an overarching strategy and a long-term programme of actions to enhance resilience of transport in the region and was endorsed by the board of Waka Kotahi in 2019. The resilience enhancement actions from the business case are still to be considered and implemented.

The Ngā Ūranga ki Pito-One corridor is a critical resilience risk in operational, frequent, Low impact high frequency as well as High impact low frequency events, and both SH2 and the railway line are at risk from hillside landslide, flooding and coastal hazards.

The business case identified relocation of SH2 and railway away from cliff and protection of the seaward side of the railway, with a new seawall / revetment, which will address the range of hazards from operational and frequent events to high probability low impact events. The options to deal with this most critical resilience risk is being considered separately by Waka Kotahi.

The Ngā Ūranga ki Pito-One shared path will provide enhanced resilience to the railway from climate change including coastal hazards and sea level rise, and operational and maintenance events, as well as providing an alternate mode enhancing redundancy of transport modes of access.

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Flooding in the 1976 storm event

Figure 7-2: Flooding in Korokoro 1976 (Source: RNZ)

Figure 7-1: Flooding in the 1976 storm event Figure 7-3: Flooding in Korokoro 2015 (Source:RNZ)

Figure 7-4: Flooding Ngā Ūranga ki Pito-One corridor 2015 (Source: RNZ)

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7 Natural Hazards

7.1 Hazards context The Ngā Ūranga to Pito-One transport corridor is vulnerable to a range of natural hazards. In considering the resilience, it is important to understand the natural hazards that affect the corridor.

The predominant natural hazards that affect the corridor are:

1) Storms 2) Coastal erosion 3) Landslides 4) Earthquakes 5) Tsunami 6) Sea level rise

All these natural hazards vary in size from small events that occur regularly to large events that occur less frequently and the impacts of these will vary. Progressively larger events occur with lesser frequency, as shown in Figure 6-1. The natural hazards affecting the Ngā Ūranga to Pito-One transport corridor are discussed below and are illustrated using information that is readily available.

7.2 Storms

7.2.1 Storm Impacts The Wellington Region is prone to storms that can lead to the following consequences:

a) Flooding b) Strong winds c) Storm surge (coastal waves) d) Landslides induced by rainfall.

7.2.2 Flooding No systematic assessment of the flood hazards has been carried out for the Ngā Ūranga to Pito-One transport corridor. A map showing the approximate extent of the floods in the 1976 storm event is presented in Figure 7-1. This shows the flood hazard zone at the Pito-One end of the route. A photograph of the Pito-One end of the corridor in the 1976 event is shown on Figure 7-2.

The recent May 2015 and November 2016 storm events in the Wellington Region led to flooding in the Korokoro to Horokiwi area and affected the existing State Highway 2, see Figure 7-3 as well as further towards Ngā Ūranga, see Figure 7-4. These led to disruptions of half a day to a day.

The flood flows from the Korokoro Stream at the Pito-One end and other steep gullies that drain the western hills and is exacerbated by the culverts of inadequate capacity under state highway 2 and railway along this corridor.

In a large storm event, flooding of the Ngā Ūranga ki Pito-One transport corridor including the proposed shared path could be expected to be flooded for short periods of time.

7.2.3 Strong winds Strong winds can cause the failure of trees and overhead power lines and also induce storm surge. Overhead power lines may include the railway line electrification lines adjacent to the proposed shared path.

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7.2.4 Storm surge Storm tides within the Wellington Harbour have been assessed by Stephens et al (2009), and has been presented by Allis (2020), and this is reproduced in Table 7-1. Waves are expected to further increase the high sea level at the shoreline due to wave set-up. The joint probability of extreme sea level and wave setup have been assessed (Stephen et al 2011 and Lane et al 2012).

Table 7-2 Extreme storm tide sea levels for Wellington Harbour

Note: Results are in metres WVD-53, relative to a baseline MSL averaged from 1975-2008. ARI=Average Recurrence Interval, AEP=Annual Exceedance Probability (0–1 scale), C.I. =Confidence intervals of model fit.

For representative 1% AEP storm events, the high sea levels due to storm tides and wave setup has been assessed by them as 1.48 to 1.49 m WVD-53 datum for the Ngā Ūranga to Pito-One coastline.

7.2.5 Landslides Landslides are also caused by storm events but are generally of a smaller size than landslides caused by earthquakes but can fluidise in the presence of water and run out for greater distances. Storms cause different types of slope failures and debris flows where slope material and debris are mobilised by the storm runoff and increased groundwater pressures. Such debris flows are likely in some of the larger gullies draining the western hills to the west of the transport corridor. Figure 7-5 shows small slips that closed the northbound lanes at Horokiwi in 2006.

Generally, landslides caused by storm events are likely to be contained by the 4-lane state highway and two-line railway corridors. However, debris flows, and local flooding and runoff associated with such landslides can be expected to flow onto the Path corridor.

Figure 7-5: Landslide at Horokiwi along SH2 in 2006 Storm

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7.3 Coastal erosion Coastal erosion is an ongoing process but is often exacerbated by storms and associated waves and storm surge. The present coastline between the railway corridor and the sea is vulnerable to erosion. The existing coastal edge comprises a rock revetment protected by boulders, and concrete debris, and is of unknown construction that has evolved over the past century or more. Storm events have caused failure of this revetment and have impacted the railway line.

Wave runup and overtopping can cause damage to the coastal area, dependent on 3 factors (Allis, 2020):

1) Crest freeboard- the difference between the crest of the coastline structure and the mean water level during storms. This can become more critical with relative sea level rise (RSLR).

2) Coastal defence form – including profile (slope), offset, material composition (rock, gravels, concrete) and material roughness (e.g. rough rocks or smooth concrete).

3) Wave climate – larger waves cause greater overtopping. The waves in Wellington harbour are smaller than open coastlines and therefore the potential overtopping volumes are smaller, less hazardous and can be easily cleaned up.

The storm event of 20-22 June 2013 with wind speeds peaking at around 55 metres per second and wave heights reaching 4.1 metres led to erosion and failure of several sections of the coastal revetment along the railway line between Ngā Ūranga and Pito-One (T&T, 2013), see Figure 7-6. This led to closure of the railway line between 20 and 27 June 2013. Emergency works to reopen the railway line involved filling large cavities with rock and granular fill and re-armouring the slopes with concrete blocks and armour rock where the coastal revetment had failed. (T&T, 2015). Such storm events can be expected to occur more frequently as a result of climate change.

Figure 7-6: Coastal erosion along the Ngā Ūranga to Pito-One railway, July 2013 (Source: T&T, 2013)

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Other events on 16 August 1928, 14 February 1947, 9 April 1968 (the Wahine storm) also eroded the railway formation and disrupted rail services. On 22 Sep 2014 rail services were suspended due to waves and water on tracks.

7.4 Landslides The steep hillsides along the western side of the entire length of the Ngā Ūranga ki Pito-One corridor makes the corridor vulnerable to landslides. Landslides can occur without a trigger but are commonly triggered by storms or earthquakes and are therefore discussed in those sections.

7.5 Earthquakes

7.5.1 Hazards Earthquakes can be associated with the following hazards:

a) Fault rupture b) Ground shaking c) Liquefaction d) Landslides e) Tsunami

7.5.2 Seismicity The Ngā Ūranga to Pito-One transport corridor lies within the Wellington region, which is exposed to a high level of seismicity. The region has several major active faults and a subduction zone (Hikurangi trench) associated with the active plate boundary between the Pacific and Australian plates, see Figure 7-7. These structures can generate large earthquakes of magnitude 7.5 to 8+, and together these represent earthquake sources that contribute significantly to the seismic hazard in the Wellington region.

Figure 7-7: Pacific-Australia Plate Boundary (Source: GNS)

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Figure 7-8: Active Faults and Geology

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The principal active faults that lie within 20 km of the site are summarised in Table 7-1. Faults outside the region as well as unknown sources also contribute to the seismicity of the region, and these are taken into consideration in the development of the seismicity model and the relevant ground shaking parameters used for design.

In addition, the subduction interface between the Pacific and Australian plates has the potential to generate very large magnitude earthquakes (Mw 8.2-8.6) leading to strong ground shaking in the Wellington region (Holden and Zhao, 2011).

Table 7-1: Principal active faults

Characteristic Recurrence interval Distance from corridor Fault earthquake magnitude (years) (km)

Wellington Fault 7.5 800 - 1,100 0.2 (Pito-One)

Aotea Fault > 7 2,200 – 6,400 3 (Ngā Ūranga)

Moonshine Fault 7.1 11,150 - 12,540 5 (Pito-One)

Ohariu Fault 7.1-7.5 2,200 5 (Ngā Ūranga)

Wairarapa Fault 8.0-8.3 1,200 18 (Pito-One)

During the history since European settlement, major earthquakes have caused significant ground shaking in the Wellington-Lower Hutt area. These include the 1848 Marlborough earthquake, 1855 Wairarapa earthquake, and the 1942 Masterton earthquakes. In particular, the Wairarapa earthquake caused significant shaking in the area, including a major landslide as discussed below.

More recently, the 2013 Cook Strait earthquake, The Lake Grassmere earthquake and the 2016 Kaikōura earthquake caused ground shaking in the Wellington area, but caused no damage in the Ngā Ūranga to Pito-One transport corridor. These earthquakes only led to a modest 0.2g ground shaking on bedrock, but greater ground shaking in areas underlain by deep soils.

7.5.3 Fault Rupture The significant fault that has been mapped near the Ngā Ūranga to Pito-One transport corridor is the Wellington Fault, which is located offshore in the Wellington Harbour between Ngā Ūranga and Pito- One, see Figure 7-8.

The active Wellington fault is a southwest-northeast trending fault that has a recurrence interval of 800 years to 1,100 years, and ruptures in characteristic large earthquakes of magnitude 7.5 with typical fault displacements at the ground surface of 5 m horizontally and 1 m vertically (Little et al., 2010).

The location of the Wellington Fault is poorly constrained in the Pito-One and Wellington Harbour area. The 1:20,000 Wellington Fault Hazard Map (Wellington Regional Council, 1991) shows the fault to have two strands and suggests a wider fault zone. The northern strand runs closer to the section of State Highway 2 between Horokiwi and the Pito-One off-ramp, in a direction towards the northern end of the off-ramp. The southern strand runs parallel to the northern strand but about 550 m to the south, see Figure 7-7.

The 1:50,000 geological map (IGNS, 1996) and 1:250,000 QMap for Wellington (IGNS, 2000) show the fault broadly between the two strands shown on the 1991 map. Recent studies of the fault suggest that the area to the west of the fault could be comprised of a wider zone of discontinuous crushed, sheared and gouge zones (Begg et al., 2008).

These maps highlight the uncertainty around the location of the Wellington Fault, and the possible width of the fault zone.

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Recent geophysical surveys as part of geotechnical investigations carried out by Opus (2016) indicate that there may be two splinter fault strands associated with the Wellington Fault in Pito-One that may be located between the published map location of the Wellington Fault and the western hills at Korokoro, indicating that there may be strands of the Wellington Fault in the Ngā Ūranga to Pito-One area as indicated in the Wellington Regional Council (1991) fault map.

The Wellington Fault is located between 200 m and 600 m from the shared path and is nearest to the shared path near Rocky Point, see Figure 7-8. The bathymetry in the area indicates a shelf of shallow seabed extending 50 m to 100 m from much of the shared path alignment, which then becomes deeper to the east. This also suggests that the trace of the Wellington Fault is at a distance offshore from the alignment of the shared path.

Therefore, the likelihood of a Wellington Fault rupture (ground surface displacement) having an immediate ground surface rupture effect on the shared path alignment is low. However, there could be some ground cracking sympathetic to the fault rupture closer to or at the location of the shared path.

7.5.4 Ground shaking The fault, subduction zone and other earthquake sources give rise to a high seismicity for the Wellington region as discussed above. The ground shaking can be assessed using methods given in the Bridge Manual (NZTA, 2016) or NZS 1170.5 (Standards New Zealand, 2004).

AECOM (2019) present earthquake design accelerations derived from these sources which have been used for the preliminary seismic design of the facilities associated with the shared path.

There could be additional effects that could lead to a higher ground shaking along the shared path that arise from:

a) The proximity of the Wellington Fault and potential near-fault effects. b) The location along the edge of Wellington Harbour, leading to basin edge effects. The proximity of the Wellington Fault could lead to larger ground shaking effects than those considered to date and would need to be considered in the final design.

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Figure 7-9: Earthquake-induced liquefaction hazards (Source: Works Consultancy Services, 1992; Wellington Regional Council, 1993

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Significant basin edge edge-generated surface waves have been documented in past earthquakes such as the 1995 Kobe earthquake in Japan, in Santa Monica in the 1994 Northridge earthquake and in Seattle in the 2001 Nisqually earthquake in the USA.

Locally such basin edge effects have been observed in the Wellington area in the 2013 Cook Strait earthquake and the 2016 M7.8 Kaikōura earthquake. Such effects have been observed in the Thorndon basin and to a lesser extent in the Te Aro basin (Bradley et al., (2017; and 2018).

The Thorndon area is underlain by a deep subsoil basin with its northern boundary close to the Wellington Fault. This deep basin is in the northern part of Wellington CBD and is well away from the Ngā Ūranga to Pito-One corridor. The stronger ground motions attributed to basin edge effects were observed at strong motion stations such as PIPS, VUWS and TFSS which are at sites with deep bedrock depths of the order of 80 m to 250 m (Bradley et al., 2018). Given that bedrock is shallower along much of the Ngā Ūranga to Pito-One route and the path is located on the western side of the fault where bedrock is shallower, basin edge effects are not expected to be a significant issue.

7.5.5 Liquefaction Loose saturated cohesionless soils experience a loss of strength and stiffness due to a rise in porewater pressures during earthquake shaking, and this phenomenon is commonly known as liquefaction.

A liquefaction hazard study for the Wellington Region was carried out by Works Consultancy Services (now WSP) in 1992 and the results of the study were published (Wellington Regional Council, 1993 and Brabhaharan, 1994). The liquefaction-induced ground damage hazard in the Ngā Ūranga to Pito- One area is shown on Figure 7-9.

The map shows the potential for liquefaction along the shared path, and consequent lateral spreading of the liquefied ground towards the sea. The liquefaction hazard will be lower in the Horokiwi to Rocky Point area, where bedrock is exposed in the seabed and the existing reclamation may be underlain by shallow bedrock.

Geotechnical investigations carried out in 2019 for the Project and assessment have confirmed the potential for liquefaction and consequent lateral spreading of the reclamation soils present (AECOM, 2019). This indicated lateral displacements of the order of 500 mm.

Fill proposed to be placed to create new land to support the shared path and ūranga along the Project, is also likely to be subject to liquefaction given the current proposal to end or side tip fill materials into the sea to form the reclamation as described Chapter 4 of the AEE (2020). Observations of liquefaction and ground damage in the Centreport area following the 2016 Kaikōura earthquake have confirmed that end tipped gravelly fill materials are susceptible to liquefaction and consequent ground damage.

7.5.6 Earthquake-induced landslides An earthquake induced slope failure study carried out by Works Consultancy Services (Brabhaharan et al, 1993) identified the potential for earthquake induced landslides in the Wellington Region and this was subsequently published by the Wellington Regional Council (1995). An extract from this map showing the Ngā Ūranga to Pito-One corridor is presented in Figure 7-10.

The principal slope hazard is associated with the eroded Wellington Fault scarp along the corridor (Dellow, 1988). Large landslide blocks have also been identified in this area, such as the Ngā Ūranga - Horokiwi gravity slide, that includes Gold’s Landslide, which lies 0.5 km to the southwest of Horokiwi Quarry (Dellow, 1988), and possibly a block slide between Horokiwi and Pito-One off-ramp.

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Figure 7-10: Earthquake-induced slope failure hazards (Source: Works Consultancy Services, 1993; Wellington Regional Council, 1995)

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Historical earthquakes in the region have caused several landslides in the area, including large landslides (Brabhaharan et al, 1994). An example of such slides is the “Gold’s Slide” located near Horokiwi above the current State Highway 2, see Figure 7-11. This large landslide occurred along the Ngā Ūranga to Pito-One shoreline in the 1855 magnitude 8.1 Wairarapa earthquake, and the scarp of the landslide can still be seen in the landscape today.

Figure 7-11: Gold’s Slide in the 1855 Wairarapa earthquake

The map shows earthquake induced slope susceptibility, and an accompanying table indicates the potential sizes of landslides likely in three different earthquake scenarios.

GNS Science is leading a 5-year research programme to learn from earthquake induced landscape dynamics, with WSP leading a theme looking at the earthquake performance of earthworks and slopes and their impact on the resilience of infrastructure. This theme is led by the author (Brabhaharan) with research by Doug Mason. GNS Science has also led a project SLIDE to look at landsliding in Wellington, but this information has not been published or made available yet.

Preliminary information on research into landslide run-out based on the SLIDE project and early Kaikōura research, and analyses carried out for NCTIR as part of the Kaikōura recovery work (GNS, 2019), together with the local practical experience of WSP in managing landslide hazards in the Wellington region has been used to assess potential landslide run-outs along the Ngā Ūranga to Pito- One corridor.

The cross section in Figure 7-12 shows the relationship between the area of slope failure and the extent of landslide debris runout in relation to SH2, rail and shared path.

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Figure 7-12: Section showing Fahrböschung angle (F-angle) and runout zones

The highest hazard zone is closest to the slope, where the majority of debris is deposited. The Fahrböschung, or shadow, angle is the slope of a line from the crest of the landslide to the toe of the debris. This angle becomes shallower with increasing landslide volume and observed Fahrböschung angles derived for landslides triggered by the Kaikōura earthquake have been used to assess where the Ngā Ūranga to Pito-One corridor may be impacted by landslide debris in a local large earthquake.

It is noted that there were no observed landslides in the 2013 Cook Strait earthquakes and the 2016 Kaikōura earthquakes.

Figure 7-13 shows the potential earthquake induced landslides and runout along the Ngā Ūranga to Pito-One transport corridor in a moderate to large earthquake.

In a local large earthquake such as a M7.5 earthquake, larger landslides and runout can be expected as show on Figure 7-14 and 7-15.

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Figure 7-13: Landslide runout in a moderate to large earthquake

Figure 7-14: Earthquake induced landslide runout in a local large M7.5 earthquake

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Figure 7-15: Enlargement of landslide run out areas from Figure 7-14

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Figure 7-16: Tsunami hazard map

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7.6 Tsunami

7.6.1 Tsunami hazard zone Tsunami are long-period waves created by a physical disturbance to the sea. These can be generated by fault rupture and displacement of the sea floor during an earthquake, underwater volcanic eruption or subsea landslides.

The GWRC tsunami evacuation zones are shown in Figure 7-16. This shows that the entire Project area is exposed to tsunami hazards.

7.6.2 Tsunami characteristics Tsunami can be caused by two types of events:

a) A distant event b) A local event Depending on the size of the tsunami, the shared path is likely to be inundated by tsunami waves or seiche (from a seiching effect within the Wellington Harbour).

Tsunamis can lead to damage due to the impact of the large water waves, flooding and inundation, debris and erosion as the water recedes. The severity depends on the size of the waves, and the development in the area which contributes to debris generation.

7.6.3 Distant tsunami events Distant tsunami events are caused by disturbances of the sea from distant sources such as earthquake fault rupture, subsea volcanic eruption or subsea landslide.

Examples of such events are offshore earthquakes off the coast of South America or Indonesia. There is usually a longer warning time for such events as they typically take a longer time to arrive in the waters of New Zealand, and these are monitored by the Pacific Tsunami Warning centre or the local tsunami warning centre, via Geonet. Because of these advance warning and alert systems, there is generally time for evacuation of the areas affected. However, damage due to the tsunami will still occur.

7.6.4 Local tsunami event A local tsunami can occur due to a local event, such as a large earthquake involving a rupture on an offshore section of an active fault. Because the source of the tsunami is close by, generally there is little warning before the tsunami hits the area.

Two examples of past events are:

a) 1855 Wairarapa earthquake, where tsunami run up heights are reported to have reached 3 m to 4 m around the Wellington Harbour, especially in Evans Bay and Lyall Bay (Bell et al 2005). b) The 2016 Kaikōura earthquake is reported to have created tsunami waves of up to 1.6 m near Eastbourne foreshore. The travel time for tsunami waves from local events is short, and therefore there is usually no time for warning to be given and self-evacuation is encouraged. It is important that people know when and where to evacuate.

A local tsunami can potentially cause waves that inundate the path and transport corridor, and this could last several hours.

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7.6.5 Seiche In a body of water such as the Wellington Harbour, the form of such waves may be in the form of a seiche where the body of water oscillates in response to ground shaking. This is a possible mechanism which can also affect the path along the harbour coastline. This effect was observed in the Wellington Harbour for ~24 hours following the 1855 Wairarapa earthquake.

7.7 Sea level rise Climate change is expected to lead to sea level rise (SLR) due to the higher global temperatures and the associated melting of the ice shelves and the thermal expansion of sea water. Allis (2020) has assessed the coastal hazards relevant to the Project, including sea level rise, and this report draws heavily on his assessment.

The New Zealand Coastal Policy Statement requires coastal hazards including climate change hazards to be assessed for a period of over at least 100 years, and this would mean assessment for up to the year 2120.

The potential for sea level rise has been assessed and recommendations made for local authorities by the Ministry of the Environment (MfE, 2017). This recommends stress-testing infrastructure design for four scenarios to ensure sufficient flexibility is provided to enable adaptation of the design in the future depending on the future trajectory of sea level rise.

These scenarios are presented in Figure 7-17.

Figure 7-17: Four scenarios of Sea level rise projections for New Zealand

MfE (2017) also requires consideration of the local relative sea level rise (RSLR) where there is persistent ongoing land motion (rise or subsidence) due to New Zealand’s tectonic setting. Based on 10 years of continuous GPS data at several locations in the Wellington Region, it has been assessed that there is 2.7 mm / year subsidence from inter-seismic processes including slow slip (Bell et al 2018), which has increased from a previously assessed 2 mm / year in 2011 (Bevan and Litchfield, 2012).

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Extrapolating this rate linearly to 2120, a combined RSLR has been assessed and this is presented in Figure 7-18. Note that land subsidence exacerbates the relative sea level rise in Wellington.

The expected rise in sea level over the next 100 years (to 2120) varies between a low 0.6 m rise, to a high 1.4 m rise. Taking into consideration land subsidence, the RSLR varies up to 1.7 m in 2120.

Figure 7-18: Relative sea level rise scenarios for Wellington Region

MfE recommends that for major new infrastructure, the higher hazard scenario be adopted, which in this case would be about 1.4 m.

The ongoing SLR is expected to increase the frequency of wave overtopping and coastal inundation (MfE, 2017). In Wellington, just 0.3 m of SLR (occurring by 2030s to 2040s will lead to an increase in the frequency of a 100-year storm tide to a once per year event on average (PCE, 2015).

The Coastal Guidance advises sensitivity testing for coastal engineering projects for defining the coastal hazard exposure to 2100, using the following approach:

a) Range of future increases of 0 to 10% for storm surge

b) Range of future increases of 0 to 10% for extreme waves and swell

c) Changes in 99th percentile wind speeds with the relevant sea level rise scenarios to assess waves in limited fetch situations such as semi-enclosed harbours, sounds, fiords and estuaries.

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Figure 8-1: Shared Path between Ngā Ūranga and Pito-One

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8 Shared Path

8.1 Description The shared path will provide a 5 m wide dedicated shared path for walking and cycling, on the seaward side of the existing railway lines, between Ngā Ūranga and Pito-One, see Figure 8-1.

8.2 The Shared Path Bridge An overbridge just north of the Ngā Ūranga Interchange will provide access over the railway lines to the edge of Wellington Harbour, see Figure 8-2. The new architecturally designed bridge which provides for a consistent 5m width for the shared path, referred to as the shared path bridge, will provide access over the railway within Sector 1 of the Project. The bridge over the railway line is proposed to be founded on reinforced concrete bored piles supporting cast-in-situ piers, precast headstocks and the concrete beam and deck superstructure. A typical section showing an elevation of the bridge is presented in Figure 8-3. The length of the bridge including ramps in 273 m.

Figure 8-2: Shared path bridge

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Figure 8-4 Location of vertical concrete seawalls

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Figure 8-3: The shared path bridge over the railway lines

8.3 Shared path along harbour edge The shared path along the harbour edge in Sector 2 will be slightly below the level of the adjacent railway line by 0.3 m to 0.6m. The existing level of the railway formation in Sector 2 is between 3.12 m and 3.35 m between Chainage 1100 and 1500 m. The level is between 3.35 m and 4.5 m from Chainage 1500 m to 4500 m. The crest of the shared path formation will be a minimum on 3.35 m, and so will be up to 200 mm higher than the existing formation along a 500 m section.

8.4 Rock revetment – concrete seawall The new reclamation will be supported by a rock revetment on the seaward edge over much of the corridor, except for some sections where a vertical concrete seawall will be used to minimise occupation of the coastal marine area. The locations of the concrete walls are shown in Figure 8-4.

Figure 8-5 illustrates the shared path relative to the railway corridor and the rock revetment supporting the shared path.

Figure 8-5: Shared path supported by rock revetment

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The section of the shared path supported by concrete seawalls is shown on Figure 8-6. Please note that crest of the revetment is generally around the same level as the existing railway formation.

Some sections of the shared path will have ūranga with allowance for additional resting and recreational space, as shown on Figure 8-7.

Figure 8-6: Shared path supported by vertical concrete seawall

Figure 8-7: Shared path with ūranga

8.5 Construction The proposed construction envisages the rock revetment to be placed on the existing seabed and be allowed to settle over time. The general bulk fill is then proposed to be placed by either side tipping from rail wagons or end tipping from road trucks (see Chapter 4). This will result in a loose fill which will be allowed to consolidate over time. Above MHWS level, general fill will be placed and compacted.

It is understood that concrete retaining walls are proposed as sea walls along some sections of the route and will be constructed using precast concrete piles cast into pile holes drilled into the underlying seabed and bedrock. Precast concrete panels will be slotted between adjacent piles, and then backfilled.

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A cross section showing the construction of the shared path is shown in Figure 8-8.

Figure 8-8: Typical sea wall arrangement, rock revetment or concrete wall. Source: AECOM (2019).

Given that the walls are up to about 5 m in height, it is likely that the walls will require support in the form of anchors, and these would probably need to be socketed into the underlying bedrock, with careful consideration given to their durability in the corrosive marine environment.

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9 Resilience performance

9.1 Overview The resilience of the multi-modal Ngā Ūranga to Pito-One transport corridor is critical, and therefore the focus is on the transport corridor as a whole rather than the resilience of the Ngā Ūranga to Pito- One shared path in isolation. The resilience is considered for the event scenarios discussed earlier, in order to understand the resilience performance in events and in the range of natural hazards that can affect the corridor in different ways.

The overall resilience of the Ngā Ūranga to Pito-One transport corridor will be improved in operational and maintenance (OM) events as the Project provides an additional safe and comfortable access for people who are able to change their travel mode and walk or cycle when there is an incident causing disruption to the road (e.g. accident causing some lane closures and hence congestion) or rail (closed by a mechanical or electrical fault). The shared path would not significantly contribute to access for commercial use and hence would not appreciably improve economic functionality in such events. In addition, direct access to the railway line on the seaward side through gates from the shared path would facilitate faster access and repair of any railway faults along the line or maintenance and hence reduced disruption to rail travel.

In frequent hazard events (FE) that happen several to many times a year, the road or rail is unlikely to be completely closed, but lane closures for a few hours could cause disruption, and the shared path will be unaffected and again provides an alternate mode for those who are able to use this. The small slip on SH2 on 30 June 2020, which brought traffic to a halt and caused significant commuter delays, illustrates how a small disturbance can cause substantial disruption to travel in the Wellington Region. While the shared path would not eliminate the disruption, it would have allowed some people to walk home in addition to taking the trains to get home.

In low impact high probability events (LIHP), the Project will enhance resilience primarily by the protection provided by the shared path formation, rock revetment and seawalls to the railway corridor from erosion and storm surge in large storm events.

The shared path could also provide an alternate mode for people who are able to walk or cycle, except during the storm when the shared path could be closed by surge and sea spray or only be used by confident cyclists.

The exception is flooding in storm events which can affect all three transport modes – road, rail and the shared path. SH2 is unlikely to be fully closed, and closure of the lane or lanes on the northbound lanes at the foot of the hill due to landslides in large storm events could be managed by contraflow along the southbound lanes after quick clearance of any mud and before the landslide debris is cleared over a period of days. Also, in a moderate earthquake event, landslides are unlikely and limited rockfall on the northbound carriageways can be cleared quickly. In lower height distant tsunami events causing low wave heights of less than a metre, the road and rail may not be closed, but the shared path could be closed for safety reasons.

In high impact low probability earthquake events, the entire corridor is likely to be closed, the shared path and parts of the rail line would likely be damaged due to liquefaction and lateral spreading, and SH2 and the rail would likely be inundated from debris generated by large landslides. Landslides could also inundate parts of the shared path. Large low probability storms can also lead to landslides and debris flows with large runout causing inundation and closure of the highway, rail and shared path. So, in this case neither of the three modes would provide for emergency access or access in the short term until limited 4-wheel drive access can be formed.

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In progressive long period events, the shared path and associated rock revetment and seawall will substantially enhance the resilience of the railway line due to the less steep, rough and robust construction of the rock revetment and the vertical concrete seawalls with toe rock protection to dissipate energy from the seas. Without the shared path and with sea level rise, the existing steep and poor standard sea wall will be increasingly vulnerable to erosion and damage from storm, tide and coastal events. The shared path will also be better protected by the rock revetment from overtopping and erosion but will still be vulnerable to sea spray. The shared path has also been planned to allow for adaptation by providing the ability to raise the rock revetment after 60 to 80 years progressively on its seaward side. Adaptation is an appropriate strategy for such long period progressive hazards.

In summary, the Project will significantly enhance the resilience of the Ngā Ūranga to Pito-One transport corridor to higher frequency high probability low- moderate impact events, particularly by providing enhanced protection to the railway corridor to storm events and enabling faster access for fault repair of the railway line in operational incidents and for maintenance resulting in less disruption and faster recovery. The Project will also enable and facilitate mode shift for some corridor users, providing an alternate mode of access. This will improve transport corridor resilience to more frequent events, including operational incidences, disrupting road and/or rail corridor use, for people who are able to switch to walking or cycling.

In significant high impact lower probability events, like a large earthquake event, a very large storm event or a tsunami, the entire corridor is likely to be fully closed and may not be able to cater for the emergency response needs, and the poor resilience of the corridor will remain.

9.2 Operational and maintenance events There is currently very limited maintenance access to the Ngā Ūranga to Pito-One section of the Hutt Valley railway line from either the landward side, due to the presence of SH2, or the seaward side due to no space being available between the railway line and the sea along much of the route. Access to the corridor needs to be gained from either end by closing the railway line.

The Project will provide improved access along the seaward edge of the rail corridor, to fix any operational incidents affecting the railway line along this section, without closing the railway corridor. The shared path will also provide maintenance access through proposed gates in the fence between the railway line and the shared path. This will facilitate easier access to repair any faults along the line with shorter or partial closures. In addition, subject to alignment between KiwiRail and Waka Kotahi’s operational and safety requirements, detailed design can consider the opportunity to utilise these gates as part of the tsunami evacuation plan for users of the shared path.

The shared path will enable and facilitate mode shift to active transport modes for some corridor users, improving corridor resilience to disruptive road and rail operational and maintenance events (which do not impact the shared path). The shared path will also provide an alternate transport mode for people who are able to switch to walking or cycling, in the event the road or rail are closed. A more balanced distribution between rail, SH2 and the shared path may reduce the effect on society generally if one access route is compromised. The Project will therefore contribute toward enhancing the resilience of the Ngā Ūranga to Pito-One transport corridor in response to disruptive operational and maintenance incidents.

9.3 Frequent events For frequent natural hazard events, which may affect the road or rail corridor several times a year (i.e. storm events, small slippages) or once every few years (larger rock falls, flooding), the road or rail is typically affected for a few hours to half a day or so.

These events are largely due to storms, and the shared path may be unavailable due to sea spray from strong winds, particularly strong southerly gales.

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The Project will provide resilience benefits for frequent events, as it will provide an alternate safe mode of travel for people who are able to walk or cycle (except in strong southerly winds). It will enhance protection of the rail corridor from frequent events that that can disrupt rail services (i.e. sea spray or storm surge).

The disruption to the socio economy will largely remain the same as there is little alternate access to the Ngā Ūranga to Pito-One corridor.

9.4 Low impact high probability events Low impact high probability events include modest storms, landslides, coastal erosion, moderate earthquakes and modest tsunami waves from distant events.

Large storm events can close the road and/or rail corridors due to coastal erosion, landslides or flooding. An example of such an event for the railway is the 2013 storm, discussed above, that eroded the railway platform in many locations along this corridor and closed the railway line for a week. Such events have occurred regular over the past century and can be expected to occur with increasing frequency due to climate change and land subsidence and associated relative sea level rise.

The Project’s shared path protective rock revetment and seawall structures will be designed as Importance Level 3 (IL3) structures with a 100-year design life, to avoid structural damage in a 100- year ARI storm event. The shared path and its protective rock revetment and sea wall structures will provide protection to the Hutt Valley railway line from coastal erosion.

SH2, and to a lesser extent the railway and the shared path will continue to be affected by flooding and possibly debris from the upstream hill catchments to the west, where gully and Korokoro stream (at the Pito-One end) flows aren’t able to be safely conveyed to the harbour because of the inadequate capacity of the existing culverts under SH2 and the railway. However, such flooding, and disruption associated with debris deposition, is likely to be of relatively short duration of a few hours to no more than 1-2 days.

Landslides from small to moderate storm or earthquake events are only likely to close the inner northbound lanes of SH2 and not the southbound lanes, railway or the shared path.

While the Project’s shared path will provide an alternate mode of travel for people who have mode shifted to or are able to cycle, southbound lanes of SH2 and the railway corridor are likely to remain open. The recently installed median barrier gates on SH2 also provides the ability to provide contraflow if one of the northbound or southbound lanes are closed. However, such events will still cause significant disruption to transport along the corridor.

The shared path is likely to be closed due to storm surge, sea spray and flooding, but could provide alternate access for people able to switch to walking and cycling, after the flood recedes and clearing, in addition to switching to the rail.

Because the socio-economy will be functioning at near full capacity in a low impact event, there will be demand for near full access, and therefore the closure of SH2 will still lead to significant disruption to society.

9.5 High impact low probability events HILP events are low probability events but cause a disproportionately very high impact. In such events the socio economy will be seriously impacted and therefore there will not be the same demand for full access. However, access for emergency response, supply of food and medicine and other essential services is critical, and in this case Hutt Valley could be seriously affected by lack of land access as all access routes – Ngā Ūranga to Pito-One corridor, Remutaka Hill and State Highway 58 are all expected to be closed. Large earthquakes and associated tsunami could be the cause of such events, or perhaps a very large or major storm.

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The existing railway lines are understood to be underlain by loose to medium dense reclamation fill. In addition, the proposed granular bulk fill is planned to be placed by end tipping or side tipping of bulk fill. Therefore, both the existing reclamation fill under the railway and the proposed bulk fill under the cycleway are likely to be susceptible to liquefaction and consequent lateral spreading in earthquakes. Given that the proposed rock revetment is planned to be placed on the loose seabed materials, it can be expected to displace allowing lateral spreading, cracking and deformation of the shared path.

The geotechnical report (AECOM, 2019) suggests that the lateral displacement of the rock revetment and fill could be of the order of 500 mm not considering liquefaction induced lateral spreading. The lateral displacement could be larger with liquefaction of the retained soils and possibly the soils underlying the rock revetment. It should be noted that displacement and or failure of the rock revetment was observed in the Centre Port container yard area in the 2013 Cook Strait and 2016 Kaikōura earthquakes, where the fill was placed by similar end tipping methods. Therefore, the shared path could be severely damaged in such an earthquake event.

A large earthquake such as a magnitude 7.5 event on the Wellington Fault or one of the other faults or subduction zone beneath the region could result in large landslides from the eroded fault scarp cliff hillside to the west of SH2. Observation of the landslides along the Kaikōura coastal section of SH2 and the railway in the 2016 Kaikōura earthquakes suggests such landslides could lead to ‘runout’ of large volumes of rock and soil debris, which is likely to inundate both carriageways of SH2 in many places, and also may inundate some sections of the railway and the shared path furthest from the hill slopes, see Figure 9-1. However, it is likely that along much of the route, the landslide debris will be contained within SH2 and the railway corridor.

Figure 9-1: Closure of transport corridor due to runout from landslides

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In addition, ongoing aftershocks and fears for safety from rock fall and rock roll from the failed cliffs and accumulated landslide debris could lead to access being closed along the shared path.

The concrete retaining wall sections may be designed to resist the liquefaction and lateral spread loads from the reclamation fill behind them. However, this would require substantial walls with supports to resist these large loads. Should the debris from landslides run over sections supported by the concrete walls, then these could impose additional loads and lead to damage to these retaining walls. The design of these walls will be developed at the detailed design stage.

The combination of liquefaction and lateral spreading damage to the shared path, the likelihood of debris from the hillsides inundating the transport corridor including the shared path in places, and the safety concern from rock falls in aftershocks is likely to make the transport corridor being unavailable for general emergency response access after a large earthquake event. The earthquake resilience studies indicate that the transport corridor could be closed for many months to a year.

The shared path would not provide an enhanced resilience in a large earthquake event, ie HILP events, and is not expected to do so, and this will be addressed separately by Waka Kotahi.

The shared path is likely to be inundated by a tsunami from a local source with waves of few metres in height. The run-out of the tsunami waves could cause erosion of the shared path leading to severe damage. Depending on the vehicles or trains and associated “debris” on SH2 and the railway corridor, the “debris” may be dragged back onto the shared path as tsunami waves recede.

Cyclists and pedestrians would be more vulnerable to a tsunami wave than larger trains and vehicles depending on the size of the tsunami. A local tsunami created by the local offshore rupture of a fault could cause tsunami waves within minutes rather than hours giving no time for tsunami warnings. In such events, people are advised to self-evacuate in the event of a strong earthquake. A study of tsunami evacuation times in Wellington (GNS, 2018) shows the times required for people to evacuate to safety, see Figure 9-2. The map shows that currently people along the Ngā Ūranga ki Pito-One corridor would be able to generally evacuate within minutes of a warning. Construction of the shared path will increase the number of people potentially along the shared path depending on the time of the tsunami.

Given that a fence is proposed to be erected between the railway and the shared path along the entire 4.5 km coastal section, shared path users would need to run or cycle to either end of the Ngā Ūranga to Pito-One section to escape.

Waka Kotahi has discussed this with KiwiRail and agreed to consider enhancing potential escape paths away from the shared path, such as using remote unlocking of gates. Notices and signs showing shortest distance escape routes will be posted along the shared path. The bridges at either end of the route may provide a high location of temporary refuge for people escaping from a potential tsunami wave.

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Figure 9-2: Tsunami evacuation times in Wellington (Source: GNS Science, 2017)

9.6 Progressive long period events A progressive long period event would be relative sea level rise due to climate change and ongoing slow land subsidence due to the region’s location at the tectonic plate boundary.

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However, the construction of the new rock revetment with a much flatter slope (2H:1V), incorporation of a 3 m wide bench at Elevation 0.8 m, and the selection of rock sizes will all contribute to enhanced performance under the existing coastal hazards as well as when the sea level rises. The bench configuration has been incorporated to allow for future adaptation of the rock revetment when this becomes necessary in the future. Similarly, the vertical concrete sea wall will be designed so that it can be raised using a capping beam above it.

The impact of coastal processes including sea level rise has been considered in detail by the Coastal Processes Assessment, Allis (2020). This assessment indicates that the design of the shared path will provide a safe facility in 1-year ARI storm events for walking and cycling until to the 2080s at the earliest without the need to implement adaptive measures. This can be extended into the future with the implementation of adaptive measures. In larger 100-year ARI storm event, pedestrian discomfort and safety is likely to be exceeded and therefore would require proactive measures to close the shared path.

The proposed shared path will allow future adaptation by raising of the sea wall on the harbour side of the shared path, which would be difficult without the shared path, as there is currently no space available for the sea wall to be raised.

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10 Contribution of Project to Corridor Resilience

10.1 Types of contribution to resilience The Project will contribute to the resilience of the transportation system in several ways:

1) Providing protection to the railway lines through the new sea wall – revetment and a buffer zone from the sea.

2) Providing an alternate path and travel mode providing enhanced redundancy.

3) Potentially enabling emergency response access in the event of SH2 and the railway being closed in smaller more frequent events.

4) Providing improved operational accessibility to railway lines to repair faults or for regular maintenance.

The level of contribution is discussed below.

10.2 Protection from sea to railway corridor The construction of the Project, and its use of an integrated engineered rock revetment and sea wall along the length of the shared path’s coastal section (sector 2), will significantly improve the resilience of the Hutt Valley railway corridor. These will provide greater protection to the corridor from the effects of coastal erosion and storm surge, reduce wave overtopping and reduce the effects of sea spray disruption to rail services. The formed shared path will also provide an additional buffer between the rock revetment, or seawalls and the railway corridor, in the unlikely event of revetment and seawall failure, further enhancing the resilience of the railway line to the effects of coastal erosion.

10.3 Redundancy from alternate shared path Having a dedicated alternate shared path for cyclists and pedestrians will provide a level of transport mode redundancy for travel between Wellington and Hutt Valley.

In the event of closure of SH2 due to accidents, slips or flooding, or disruption to trains due to operational incidents, the shared path may be able to provide access as an alternate mode of travel, albeit in a limited way, in addition to the alternative rail or road access if the other is affected. This will enhance the resilience of access.

10.4 Emergency response access In the event of a major storm or earthquake closing SH2 and / or the railway due to landslides or flooding, the shared path will, where it remains functional, provide an alternate emergency response access route for pedestrians and cyclists, and for emergency response vehicles.

However, following a significant earthquake the shared path is likely to be damaged by liquefaction and lateral spreading of reclamation fills both from beneath the shared path formation itself, and from the adjacent KiwiRail land. This is expected to render the shared path unusable.

Landslides from the Wellington fault escarpment to the west of the shared path could potentially inundate the shared path in some locations due to the runout of debris from the hillside landslides. The shared path is therefore unlikely to provide emergency response access in large size earthquakes.

Where the landslides are smaller in magnitude and liquefaction induced lateral spreading is smaller in magnitude, the shared path may allow emergency response vehicles to pass slowly. But in such events some state highway lanes and railway are also likely to be available.

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In major events, the railway may be closed enabling temporary access over the railway lines at the Ngā Ūranga end. However, in moderate events where the railway is functional, emergency vehicles will be able to use the shared path bridge over the railway lines.

Discussions with the Wellington Regional Emergency Management office indicate that they realise that Ngā Ūranga to Pito-One access would be closed, and they are not expecting vehicle access to be available after a major earthquake event. Any limited access would therefore be an advantage.

10.5 Quicker recovery of limited access after major event The shared path being at a greater distance from the hillside, would potentially be able to be restored quicker after a major earthquake by clearing of the limited amount of debris and reinstating damage from liquefaction induced lateral spreading to provide 4WD access for recovery.

10.6 Operational resilience from improved access to fix the railway incidents The shared path would provide improved access to fix any operational incidents affecting the railway line along this section, without closing the full length of the railway corridor. Such access is currently not available as there is no space for access on the seaward side, and SH2 is on the landward side.

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Figure 11.1: Location of Wellington Fault and associated fault splays in the Honiana Te Puni reserve area

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11 Resilience of Honiana Te Puni Reserve Masterplan Buildings proposed for the Honiana Te Puni Reserve are located adjacent to or within the Wellington Fault zone and associated fault splays, see Figure 11.1.

In the event of an earthquake associated with rupture along the Wellington Fault where 4 m to 5 m of horizontal and 1 m to 1.5 m vertical displacement can occur, such buildings are likely to be severely damaged or destroyed. The recurrence interval of a characteristic rupture of the Wellington Fault is expected to be 800 to 1100 years, with a low annual probability of occurrence.

However, these buildings are not expected to be occupied most of the time and will be designed to an appropriate standard.

The Hutt district plan also restricts buildings within the Wellington Fault Special Study Area zone and this needs to be considered.

Where possible, it would be prudent to locate these buildings away from the fault zone. Given the complexity of the fault zone in the Honiana Te Puni reserve area, the 4 m to 5 m of typical ground surface rupture in a Wellington Fault earthquake may be distributed over a wider area, rather than concentrated on a single fault trace. Therefore, it would also be prudent to allow for ground surface deformation in the design of the buildings.

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12 References AECOM (2019). N2P Scheme Drawings.

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