Wellington International Airport Runway Extension Coastal Processes Assessment

CONFIDENTIAL DRAFT

Draft for the purposes of stakeholder consultation only.

PPreparedrepared for Wellington International Airport Ltd.

DRAFTAugust 2015August 2015

1 September 2015 6.36 p.m.

Prepared by: R.G. Bell

For any information regarding this report please contact: Rob Bell Programme Leader: Hazards & Risk Coastal & Estuarine Processes +64-7-856 1742 [email protected]

National Institute of Water & Atmospheric Research Ltd PO Box 11115 Hamilton 3251

Phone +64 7 856 7026

NIWA CLIENT REPORT No: HAM2015-079 Report date: August 2015 NIWA Project: WIA15301

Quality Assurance Statement

Reviewed by: Dr C. Stevens DRAFTFormatting checked by: Approved for release by:

Image of Wellington International Airport in southerly swell on 25 June 2013. [Google Earth]

This report should be referenced in the style of this example: Brown, R.A., Green, C.D., White, C. (2014). Monitoring benthic communities in the Kaipara Harbour. NIWA Client Report HAM2012-083: 135 prepared for Company X.

© All rights reserved. This publication may not be reproduced or copied in any form without the permission of the copyright owner(s). Such permission is only to be given in accordance with the terms of the client’s contract with NIWA. This copyright extends to all forms of copying and any storage of material in any kind of information retrieval system.

Whilst NIWA has used all reasonable endeavours to ensure that the information contained in this document is accurate, NIWA does not give any express or implied warranty as to the completeness of the information contained herein, or that it will be suitable for any purpose(s) other than those specifically contemplated during the Project or agreed by NIWA and the Client.

1 September 2015 6.36 p.m.

Contents

Executive summary ...... 7

1 Background ...... 15

2 Description of the Project ...... 17

3 Assessment methodology ...... 19 3.1 Introduction ...... 19 3.2 Desk-top analysis ...... 20 3.3 Field surveys ...... 22 3.4 Modelling approach: coastal physical processes ...... 28 3.5 Assessment of effects criteria: policies/plans/statutes ...... 32

4 Existing environment ...... 35 4.1 Coastal and geomorphic setting ...... 35 4.2 Coastal geology, sediment processes and characteristics ...... 38 4.3 Marine discharges and water/sediment quality ...... 45 4.4 Winds ...... 47 4.5 HydrodynamicDRAFT and wave processes for existing environment ...... 49 5 Effects Assessment: Operation of Project ...... 59 5.1 Description of operational effects ...... 59 5.2 Assessment of operational effects ...... 60 5.3 Relevant assessments against statutory plans/policies or guidelines ...... 82

6 Effects assessment: Construction activities ...... 84 6.1 Description of construction effects ...... 84 6.2 Assessment of construction effects ...... 85 6.3 Assessment against statutory plans/policies or technical criteria and guidelines . 87

7 Mitigation and monitoring ...... 89 7.1 Overview of effects on coastal physical processes ...... 89 7.2 Mitigation or avoidance measures ...... 90 7.3 Suggested coastal monitoring conditions ...... 90

8 Summary and conclusions ...... 92

Wellington International Airport Runway Extension: Coastal Processes 1 September 2015 6.36 p.m.

9 Acknowledgements ...... 93

10 Glossary of abbreviations and terms ...... 94

11 References ...... 96

Tables Table 3-1: Locations (WGS-84) and 2014 deployment information for the Lyall Bay instruments. 26 Table 5-1: Change in predicted wave heights locally at site P1 near The Corner as a result of the runway extension. 67 Table 5-2: Change in predicted wave heights locally at site P4 in the centre of inner Lyall Bay as a result of the runway extension. 68

Figures Figure 2-1: General layout for the south runway extension into Lyall Bay to develop a 2300 m Take Off Runway Available (TORA). 17 Figure 3-1: Sea-bed sediment sampling sites in Lyall Bay, Wellington. Contaminant sampling sites were 1, 3, 5, 8, 10, 11 and 12. 24 Figure 3-2: Extent of Lyall Bay infill bathymetry survey (black dashed line) shown against grey area collected from previous surveys. 25 Figure 3-3: Site map showing oceanographic instrument locations overlying the seabed bathymetry to WVD-53. 27 Figure 3-4: Delft3D-WAVE model grid (red) of south Wellington coast superimposed on DRAFTtop of the Delft3D-FLOW model grid (black) that also includes Wellington Harbour. 29 Figure 3-5: ARTEMIS finite-element model grid resolution in the area around the runway extension (left) existing runway; (right) proposed runway reclamation. 31 Figure 3-6: ARTEMIS model predicted surface water level as a result of a 1.5 m wave at the Cook Strait boundary with a wave period of 12 seconds (LEFT). Google Earth image of Lyall Bay taken on 24 July 2014 for a wave height of 1–1.5 m and a period ~10 seconds (RIGHT). 32 Figure 3-7: Areas of Conservation Value in Lyall Bay area (Tarakena Bay and Tauputeranga Island) in the Regional Coastal Plan. 33 Figure 4-1: Aerial photograph looking north on completion of the airport construction (21 Jan 1959). 36 Figure 4-2: Geomorphic features in Lyall Bay incl. the 1941 shoreline. 37 Figure 4-3: Multi-beam bathymetric data at 0.5 m resolution off the existing runway in Lyall Bay obtained by NIWA (Mackay and Mitchell, 2014). 38 Figure 4-4: Surface sea-bed sediments of Lyall Bay and Wellington south coast (from Arron & Lewis 1993). 39 Figure 4-5: Sand cover (cm) and the edge of bedrock estimated from an early geophysical survey of eastern Lyall Bay in 1971. 40 Figure 4-6: Historic bathymetric changes in Lyall Bay. 41

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Figure 4-7: Aerial photograph of the beach at Moa Point showing the beach slope profile locations (transects #1-12). 43 Figure 4-8: (Right): Western end of Moa Point beach with coastal cliffs at top right; (Left): Central area of exposed rock dividing the beach into two shallow-indented coves, looking along the cuspated beach from the southern/eastern cove. 44 Figure 4-9: Wind roses for the Wellington area. 48 Figure 4-10: Wind rose derived from hourly records of wind speed and direction at Wellington Airport from 1962–2004. 48 Figure 4-11: Present-day tide marks at Wellington relative to WVD-53. 49 Figure 4-12: Alignment of the as-built Lyall Bay outfall (white line) and sites for the Baring Head NIWA wave buoy and a recording current meter (RCM) in Lyall Bay in September 1989. 51 Figure 4-13: Lyall Bay and Moa Point circulation zones during an ebb tide (top) and a flood tide (bottom). 52 Figure 4-14: Wave refraction and diffraction patterns during a southerly-swell event on 29 April 2015. 53 Figure 4-15: Surfing waves at The Corner viewed from the stormwater outlet adjacent to the eastern carpark (30 June 2015). 54

Figure 4-16: Significant wave height (Hs) vs mean zero-crossing wave period (Tz) distribution as a % of the entire 15-year Waverider buoy record off Baring Head. 55

Figure 4-17: Hs distributions (top) full distribution (in total days per year, i.e. number of 30 minute estimates in each 0.25 m Hs bins divided by 48, with a semi-log10 scale) and (bottom) partial cumulative distribution (proportion) showing that e.g. 99% of the time waves have a Hs<4.0 m. 56 Figure 4-18: Wave conditions averaged over the 55-day SWAN simulation, in Lyall Bay. 58

Figure 4-19: Distribution of Hs from 55-day simulation (top panel) and wave roses (joint DRAFToccurrence distributions for mean wave direction and height) (bottom panel) at sites 4, 6, 15. 59 Figure 5-1: Residual (net) current circulation in Lyall Bay over the ~7-week field deployment period. 62 Figure 5-2: Current circulation at mid-flood tide (HW-3 hrs) for strong southerly winds (top) and northerly winds (bottom) for the existing situation (left panels) and the proposed runway extension (right panels). 64 Figure 5-3: Lyall Bay bathymetry plots showing the point extraction sites (P1–P8) for assessment of changes in wave heights. 66 Figure 5-4: For a boundary incident wave height of 1.5 m with a wave period of 8 seconds: (Top) Spatial variability of wave height for existing situation (left) and with the proposed runway extension (right), and (bottom) map of changes in wave height after the extension relative to present. 71 Figure 5-5: For a boundary incident wave height of 1.5 m with a wave period of 12 seconds: (Top) Spatial variability of wave height for existing situation (left) and with the proposed runway extension (right), and (bottom) map of changes in wave height after the extension relative to present. 72 Figure 5-6: For a boundary incident wave height of 3 m with a wave period of 8 seconds: (Top) Spatial variability of wave height for existing situation (left) and with the proposed runway extension (right), and (bottom) map of changes in wave height after the extension relative to present. 73

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Figure 5-7: For a boundary incident wave height of 3 m with a wave period of 12 seconds: (Top) Spatial variability of wave height for existing situation (left) and with the proposed runway extension (right), and (bottom) map of changes in wave height after the extension relative to present. 74 Figure 5-8: Predicted changes in seabed height for the existing situation over the ~7-week field period in 2014. 78 Figure 5-9: Predicted changes in seabed height for the proposed runway situation over the ~7-week field period in 2014. 78 Figure 5-10: Net or relative change in the response of sea-bed heights with the proposed runway in place over the ~7-week simulation. 80 Figure 6-1: Schematics of a NW decant discharge location (top) and a SW discharge location (bottom) in the perimeter rock dyke and options for associated fill operations. 85

DRAFT

Wellington International Airport Runway Extension: Coastal Processes 1 September 2015 6.36 p.m.

Executive summary Wellington International Airport Limited (WIAL) propose to extend the runway to 2300 m Take Off Runway Available to further enable long-haul flights, including Code E aircraft (e.g., Boeing 777 or Airbus A320) and the ensuing economic benefits for the Wellington region. After evaluating options for extending north and south, WIAL is proceeding with a 350-m extension of the runway south in to Lyall Bay (”the Project”).

Coastal environmental assessments are required to support applications for coastal permits and consents and Notices of Requirement (NOR) for the Airport runway upgrade in the coastal marine area (CMA). NIWA were engaged by WIAL in 2014 to undertake technical studies and an assessment of effects of the extended runway on coastal physical processes.

This AEE Report covers the assessment of effects on coastal physical processes of the extended runway into Lyall Bay, focused on coastal hydrodynamic and coastal sediment processes. It draws on comprehensive information from field and model studies in the Technical Report on Coastal Hydrodynamics and Sediment Processes in Lyall Bay (Prichard et al., 2015), the report on sediment characteristics and sediment contaminant levels (Depree et al., 2015), an analysis of the existing wave climate off Baring Head (Section 4.5) and an additional site survey of the cove east of the runway extension (covered in Section 4.2).

As effects of the runway extension on inshore waves were highlighted early on in the AEE investigations, surfing and recreational-related effects are given greater scrutiny when assessing the degree of coastal environmental impacts, with a more detailed, complementary assessment provided by DHI (2015). Consequently, this Report only describes likely changes in wave patterns, but the effects of these changes on water-contact recreation activities such as surfing and swimming are covered by DHI.DRAFT Other than for describing the existing environment, this AEE Report also does not cover assessments of coastal-hazard extremes (e.g., waves, tsunami, storm-tide) or climate-change effects, such as sea- level rise, which are considered in the Engineering Report (URS Ltd., 2015).

Assessment methodology used For this assessment, the main coastal physical processes considered in terms of potential effects from the Project are:

° Coastal hydrodynamics (changes in tidal and wind-driven currents)

° Coastal wave heights and wave refraction patterns

° Sediment transport and coastal geomorphology (storm-scale changes to Lyall Bay and Moa Point beaches)

° Water quality (turbidity and any subsequent sedimentation from suspended-sediment discharges and potential for contaminant release arising from sea-bed disturbances from construction sites).

There are no quantitative assessment criteria for assessing the degree of effects on hydrodynamic, wave and sediment processes and sub-tidal geomorphology from reclamation and construction effects. Therefore the assessments in this AEE Report rely on a blend of expert appraisal, supported by comprehensive field observations and modelling, as well as understanding the analogue of how

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the existing runway reclamation has influenced physical processes. The assessments are underpinned by the following considerations:

° Within inner Lyall Bay, the effects on waves of the runway extension are likely to be considerably more sensitive than the change in current velocity patterns, as tidal currents are generally weak.

° Surfing amenity of waves within Lyall Bay are potentially sensitive to changes in wave refraction patterns caused by the proposed runway extension. Therefore surfing and recreational-related effects are given greater scrutiny when assessing the degree of coastal environmental impacts, with a more detailed, complementary assessment provided by DHI (2015).

° Modelling of combined coastal hydrodynamic and geomorphic/sediment processes continues to be challenging and at the forefront of ongoing research, particularly over longer multi-timescales, and the considerable natural variability that is invariably present. Therefore reliance is placed on using the models as tools, with sufficiently robust physics, to assess the relative changes before and after the runway extension is in place, backed up by field data when modelling the existing situation;

° Given the predominance of sands on the sea bed in Lyall Bay with minimal fine sediments and low contamination, discharge simulations for assessing the effect of turbidity are focused on de-watering discharges from the construction operations associated with the imported fill (which may contain fine sediments), rather than modelling sea-bed disturbances that may arise from using controlled ground- treatment techniques or rock placement for the dyke. The effects onDRAFT coastal physical processes are also assessed in line with requirements of the Resource Management Act (RMA), the NZ Coastal Policy Statement (NZCPS) and the operative Wellington Regional Coastal Plan (19 June 2000).

Existing coastal environment Lyall Bay is a semi-circular, open bay on the Wellington south coast between the rocky headlands of Te Raekaihu to the west and Hue te Taka (Moa Point) to the east that is exposed to southerly swell from the Cook Strait. Lyall Bay formed when a tombolo connected the Miramar Peninsula (to the east of the Airport) to the hills to the west of Kilbirnie after four uplift events in the past 7000 years.

The construction of Wellington Airport at Rongotai from 1952–1959 reclaimed 14 hectares of the eastern Lyall Bay for an 850 m runway extension, connecting with a rocky outcrop towards Moa Point beach, which formerly acted as a natural breakwater. The reclamation at that stage extended to the spur groyne (breakwater) placed on the submerged natural rock outcrop from the headland and permanently occupied about a quarter of the inner Bay coastal marine area.1 The runway reclamation was subsequently extended by 180 m to its present shoreline configuration in 1971– 1972, to allow operation of DC-8s, with 10-tonne akmon units placed along the periphery for coastal- wave protection (now has 12-tonne akmons along the southern edge after storm damage in 1973).

1 inner Bay here defined as the environment inshore of an east-west line through the spur breakwater (groyne) at the end of the original runway reclamation

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Locally, around the terminus of the existing runway and spur-groyne, the seabed bathymetry is dominated by the submerged extension of the former rocky reef (that was reclaimed) and gravelly deposits, whereas most of Lyall Bay comprises surface sediments of fine sand (median size of 0.15 mm) or rocky platforms along the periphery of the outer Bay. The area north of spur-groyne (breakwater) and to the west of the original runway reclamation, has accreted since the reclamations, forming a shoal that provides good-quality surfing waves in The Corner. The western side of inner Lyall Bay has an extensive naturally-occurring shoal, with diminished wave energy.

In terms of the geomorphic setting and associated hydrodynamic processes, the existing environment in the eastern side of Lyall Bay has been considerably modified by the existing reclamations. The historic placement of a seawall along the back beach of Lyall Bay and associated carparks and road has also considerably modified the natural beach processes by permanently fixing the shoreline.

The morphology of Lyall Bay Beach is largely-shaped by sequences of southerly-wave events (especially in winter), resulting in temporary landward retreat of the shoreline, with the sediment removed forming an offshore bar. There tends to be a reversal of this process in summer. The cove on the east side of the runway (Moa Point beach) is sandy with a coarser surface veneer of pebbles, but the relatively-shallow beach sand cover is generally perched on an underlying rock platform. The longer-term morphological response of Lyall Bay, to climate cycles such as El Niño-Southern Oscillation episodes and longer 20–30 year Pacific-wide climate cycles, is largely unknown. There has been no routine beach-profile monitoring of Lyall Bay Beach (Dr Iain Dawe, GWRC, pers. com.) from which to understand long-term effects (e.g., from the existing runway reclamations, or from climate variability), apart from a 1979 study by the then NZ Oceanographic Institute (Pickrill, 1979).

Lyall Bay receives stormwater through shoreline outfalls from five neighbouring catchments and a marine outfall off the entrance to Lyall Bay discharged treated effluent from the Wellington City wastewater treatmentDRAFT plant (adjacent to the Airport). Despite these discharges, the water quality is generally very good and is mirrored in the quality of the seabed-sediment samples tested, which produced very low contaminant levels.

Winds are dominated by either southerlies or northerlies, with a long-term average wind speed of 27 km/hr based on the Airport wind-station record. Southerlies can generate a substantial wind sea which is usually accompanied by swell from the long fetches to the south, whereas the local sea generated by northerlies is severely limited by the short fetch (although may be coincident with a residual swell from the south).

The tide range for Wellington is relatively low compared with the rest of New Zealand, with an average range of just over 1 m. Only around 11% of the water volume of Lyall bay is exchanged on an average tide, which explains why the tidal currents are very weak (negligible) within the inner confines of Lyall Bay. Currents near the spur-groyne are typically less than 0.1 m/s with low to moderate winds, but currents reached 0.32–0.37 m/s during two southerly gales during the 2014 field deployment. Modelling shows wind-driven currents tend to flow down-wind along the shallower margins of the Bay, and into the wind through the middle of the Bay— although for strong southerlies a clockwise eddy develops in the northern section and an anti-clockwise eddy in the southern section joining to drive a flow to the westerly quarter from the spur-groyne area.

The wave climate of the south Wellington coastline and outer Lyall Bay is well described, given the long 15-year wave-buoy record off Baring Head and shorter deployments in outer Lyall Bay. The

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majority of waves are relatively low (<1 m) and short period (3–7 seconds), while the more highly- publicized southerly wave events of over 5 m are only episodic. Significant wave heights exceeding 3 m and 5 m occur on average for a cumulative time period of 14 days and 1 day per year respectively. From the ~7-week deployment off the spur-groyne and wave modelling during the AEE investigations, there is evidence of attenuation in wave height within the confines of inner Lyall Bay, for both average conditions and larger events e.g., 80 km/hr southerly gale of 22-September 2014 produced a significant wave height of 4.7 m compared with 6.1 m in outer Lyall Bay.

High-resolution wave modelling of the existing situation shows that wave refraction, as the wave shoals in shallower water, and wave diffraction around the spur-groyne, produce a wide range of wave directions within the inner Bay, whereas the approaching wave trains in the outer Bay are tightly constrained around due South. The spur-groyne and associated submerged rock outcrop, acts as a hydraulic control on wave patterns in The Corner area to the west of the existing runway.

Assessment of effects of the proposed 350-m runway extension was undertaken through modelling primarily, looking at the changes relative to the existing environment as the baseline (which includes previous runway reclamations).

Operational effects on coastal physical processes Currents— Delft2D model simulations indicate that there would be little change in Lyall Bay wind- driven circulation during strong northerly winds, other than minor localised changes around the runway embankment area. Circulation during northerly winds would remain largely unaffected in the Bay by the proposed extended runway.

During strong southerly winds, the before-and-after model simulations indicate that the proposed runway extension would slightly weaken the wind-driven current through the central area of Lyall Bay that passes off the existing-runway terminus. This westerly current, which would presently pass across the endDRAFT of the existing runway, would be partially intercepted by the proposed runway extension by steering the current to double back into the wind in order to pass around the longer extension, thereby weakening the flow into the central Bay. The southerly-wind simulations also suggest that the runway extension would somewhat weaken wind-driven currents over a broader convergence zone between the two eddy systems, relative to the existing situation, but would only have a minor effect on the wind-driven hydrodynamics of the central Bay and is unlikely to affect morphological change or flushing of the inner Bay. The local re-steering of the downwind flow off Moa Point beach would also produce slightly faster velocities across the end of the extended runway than presently occurs at the same location 350–400 m off the present runway terminus, as would be expected.

Waves— The high-resolution ARTEMIS wave model used reproduces the spatial wave-crest patterns in Lyall Bay shown on vertical satellite images, as the incident wave-train is refracted and diffracted, particularly in shoaling waters of the inner Bay. Results from modelling the before and post- construction situations, indicate that the proposed runway extension has the potential to have a more than minor effect on some combinations of wave height and period in some parts of the Bay, mainly on the eastern side of Lyall Bay near the existing runway revetment and more localised along the western and eastern sides of the proposed extended runway.

In the north-eastern sector in the lee of the spur groyne, 1.5 m incident waves of 8-second period propagating into Lyall Bay from Cook Strait could be attenuated by a further 0.2 to 0.6 m in a zone extending out ~250 m west from the existing runway revetment. The greatest wave-height reduction

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in this sector would be 80–100 m NW of the spur groyne, and conversely, a very localised increase in these 8-second wind waves immediately behind the spur groyne through diffraction. In The Corner, the wave-height reduction would be somewhat less at 0.2 to 0.4 m for the 1.5 m incident waves. The model also predicts an increase in wave heights: i) locally around the spur groyne (breakwater) and adjacent submerged rock outcrop; ii) slight increases in a narrow central part of the inner Bay of the main Beach; and iii) in a patch close to the beach towards the eastern end of Lyall Bay Beach near The Corner. This latter area arises due to the reduced wave height offshore from this part of the Beach, with waves able to propagate (shoal) slightly further inshore than is the case for the existing situation, given the same offshore wave height and period.

The largest reduction in wave height overall would occur adjacent to the west-side rock dyke of the extended-runway, as the wave peels along the rock dyke subject to dissipation by friction (drag) exerted by the accropode units and also the influence of a subtle wave-sheltering effect as the runway extension alignment of ~183°S is slightly west of the predominant wave-approach direction from due south.

Predicted changes for the same-height (1.5 m), but incident swell of 12-second period, after the runway is extended, would show a similar spatial pattern of wave height change to the shorter 8- second waves. The main differences would be a somewhat smaller reduction in wave height as the swell peels along the western side of the extended-runway rock dyke and a wider shadow zone in eastern part of Lyall Bay with reductions of 0.3 to 0.6 m. The eastern-most swath of propagating swell, parallel with and ~50 m west of the existing runway revetment, is predicted to be slightly narrower and around 0.2–0.4 m lower in wave height than for the existing situation for a surfing combination of 1.5 m incident swell height of 12 seconds. The increase in wave height around the spur groyne (breakwater) and adjacent rock outcrop would cover less area for the longer swells compared to an 8-second wave, given the same incident wave height. The height of DRAFTwave-trains reaching the central part of Lyall Bay Beach are likely to be only slightly affected by the runway extension, otherwise elsewhere in the Bay, including the western side, the changes will be negligible.

The cove east of the runway (Moa Point beach) will also exhibit a reduction in wave height as a result of the proposed extension. This reduction in wave height is more appreciable inshore and in the NW corner immediately adjacent to the eastern side of the existing runway. There is also likely to be more resonant or wave-sloshing behaviour within the cove after the extension has been constructed, arising from the more-enclosed basin.

These results indicate the predicted scale of changes in waves, relative to the existing situation, using a high-resolution wave model. The implications and down-stream effects of these predicted changes in wave patterns and heights, such as the effects on surfing quality and safety of recreational users, are described in the Surfing and Recreational Users Report by DHI (2015).

Coastal morphology — Introducing waves as well as tide and wind-driven forcing into a sediment- transport model, showed the predicted net change in sea-bed heights, following the construction of the 350-m runway extension, would be no more than minor over seasonal timescales over much of Lyall Bay, including the nearshore area off Lyall Bay Beach and the eastern cove (Moa Point beach). The morphology of Lyall Bay beach will still be dominated by cut and fill along an on/offshore seabed profile governed by southerly storm events, with any effects of the proposed runway extension on seasonal morphological timescales likely to be second-order influences.

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Localised changes in sea-bed heights, within 50 m around the extended runway, are likely to be minor, particularly after the existing sea-bed topography has adjusted to the presence of the rock dyke and the associated wave interaction with the structure. The local morphological adjustments off the end of the proposed runway dyke will occur through some erosion of sand seaward of the rock apron, adjacent to the rock/accropode dyke, and depositing the sand further offshore, especially to the south, to form a new equilibrium seabed profile. However, this is likely to be a “dynamic equilibrium” depending on varying seasonal weather conditions and swell frequency or persistence.

Based on the limited beach-profile dataset of Pickrill (1979), most of the seabed height variability occurred within about 600 m of the shoreline, which indicates that any morphological effects of the runway-extension Project are likely to be driven by changes in waves and currents northwards of the existing spur-groyne and associated submerged rock outcrop. Indeed, the wave modelling has demonstrated that this existing groyne (breakwater) on the rock outcrop, is acting as a critical hydraulic control on wave refraction and diffraction processes north of this structure, and to some extent on current flows as well.

The predicted wave patterns for the proposed runway configuration in the Technical Report on Hydrodynamic and Sediment Processes (Pritchard et al., 2015), show that largely within the nearshore zoneDRAFT off Lyall Bay Beach, the overall spatial pattern of wave refraction and diffraction is similar to the existing situation, albeit with reduced wave heights preferentially on the eastern side. Given the wave refraction and diffraction patterns and wave crest orientations are likely to be similar to the existing situation, then long term, the gradual shoaling of the NE corner of the Bay arising from the original runway reclamation and spur groyne (which governs the current wave climate in The Corner), is likely to continue with only minor effects from the proposed runway extension further offshore. There may however be some subtle changes in the shoaling rate as it adjusts to the reduced wave heights on average after the runway extension is in place.

A fixed-term beach-profile monitoring programme could be implemented to provide more quantitative information on how the nearshore morphology responds to storm sequences over a period of a few years. However, because of the more dominant response of the nearshore-beach system to natural climate variability and southerly-storm sequences, it would be difficult to isolate the effect of the proposed runway extension (in deeper water) from the ongoing morphological response associated with the historic runway reclamation and spur groyne (breakwater) and the seawalls that limit the back-beach response along Lyall Bay Beach during storm-cut cycles.

Water quality and clarity — Other than operational stormwater discharges, the permanent runway extension would have negligible effects on turbidity and hence water quality and clarity. Local changes in waves and swell during storms around the runway extension may slightly alter resuspension of finer seabed sediments, but usually turbidity increases in Lyall Bay are ubiquitous during strong wind and/or wave events, so any changes in turbidity post-construction would not be

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detectable. Operational stormwater discharges from the additional runway extension are covered elsewhere in the Engineering Report (URS Ltd, 2015).

Construction effects Water quality and clarity — During construction of the extended runway, de-watering discharges during the embankment fill phase have the potential to introduce high-turbidity plumes into the receiving waters of Lyall Bay if a fine-sediment fraction is present in the fill material. The main source of turbidity in the water column would be from any fine sediments (clays, muds, silts) present in the fill material, even if they are only a small percentage of material by volume.

Two alternative location options for a weir (or decant discharge outlet) in the dyke walls were assessed on the western side of the airport runway extension at the NW and SW corners of the dyke. Options were also considered for undertaking the fill operation, including truck dumps (NW discharge only), barge entry (NW discharge only) or piped dredged-sediments as a slurry from an anchored barge (either of the discharge locations). Based on a fine-sediment load of 1 kg/sec (which can be scaled), maximum suspended-sediment concentrations (SSC) of 5 mg/L above background levels would extend within a relatively constrained area of up to 500 m around the discharge point, or further if the sediment discharge rate was higher (e.g., double the sediment discharge rate will double the extent of the plume area with a maximum of 5 mg/L above background). A additional SSC of 1–2 mg/L above background in the wider area is unlikely to be detected within the accuracy of a turbidity sensor, with an even higher threshold of SSC for any potential effects on marine ecology (Marine Ecology AEE Report, 2015).

With a mainly freshwater-based sediment discharge (e.g., from rainfall run-off based on a truck- dumping fill operation), the turbid plume would disperse in the upper water column, while more- slowly mixing downward, as well as settling processes, so initial dilution in the near-field could be considerably lessDRAFT resulting in higher SSC. Results show that due to the slow currents, advection/transport of the plume is minimal as indicated by the small footprints of the simulated plumes e.g. for a maximum SSC of 5 mg/L above background (for a 1 kg/sec source), especially for the NW discharge location. Rather the main dispersion process is likely to be turbulent mixing by waves or lateral spreading of the plume along with the slow settling of the medium silt particles.

Due to low contaminant concentrations in Lyall Bay surficial sediments, any mobilisation of seabed sediments by disturbance activities, such as excavation and hole boring, are not expected to result in any significant increase in sediment-contaminant concentrations in surrounding areas (Depree et al., 2015). Therefore the risk of any adverse effects on the water column from transient sediment suspension/disturbance events during construction is very low given that water column concentrations, even after allowing for reasonable mixing, are estimated to be at least two-orders of magnitude lower than default ANZECC water quality trigger values (Depree et al., 2015).

Further, erosion and soil control measures to be built into the construction methodology e.g., containment of drilling and placement of stone columns, trenching during calmer-wave periods etc, will further reduce the environmental risk from sea-bed disturbances.

Monitoring conditions and mitigation of potential effects A set of monitoring conditions associated with coastal physical processes is put forward, mainly documenting start of construction and changes to the coastal marine area, encouraging the use of

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clean fill material that has as low a fraction of silts, and the use of best-practice sediment and erosion control measures to control discharges to the CMA “at source” from the infill operations.

Other than the effect of the runway extension on reducing waves in some parts of the Bay, all other effects on coastal physical processes are assessed as being minor or negligible. Mitigation of the effects of changes in wave patterns arising from the extended runway is covered in the Surfing and Recreational Users Report by DHI (2015).

DRAFT

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1 Background Wellington International Airport operates on a constrained footprint in the coastal suburb of Rongotai. The Airport has a single runway of 1945 m Take Off Runway Available (TORA) with 90 m safety areas at each end of the runway.

Wellington International Airport Limited (WIAL) propose to extend the runway to 2300 m TORA to further enable long-haul flights, including Code E aircraft (e.g., Boeing 777 or Airbus A320) and the ensuing economic benefits for the Wellington region.

WIAL engaged URS Ltd. (now AECOM) to provide Engineering Services in the development of engineering design options and the proposed specimen design carried forward through the environmental assessment and consenting process. The URS component also includes incorporating all aspects of hazard risk (wave overtopping, tsunami, storm-tide), climate-change, marine geology and earthquake faulting into the final specimen design. This information is covered in the Engineering Report (URS Ltd., 2015).

The approximate additional 350 m extension, after initial engineering and economic feasibility studies considering both Evans Bay and Lyall Bay, is proposed to be to the south into Lyall Bay.

An initial scoping investigation was carried out and reported in October 2013 (AES/NIWA, 2013) and a number of work streams identified which would involve further field work and modelling as part of an Assessment of Effects (AEE) for the proposed runway-extension project.

This work has now been completed and a description of the existing coastal processes in Lyall Bay, covering tides, currents, waves, sediment transport, coastal morphology and sediment discharges (during construction) together with predicted level of changes as a result of the runway extension, has been preparedDRAFT based on existing and new information (Pritchard et al., 2015). A separate technical report was prepared by Depree et al. (2015) on seabed sediment characteristics and the level of in-situ contamination of these sediments. New work undertaken as part of this assessment has included:

° Deployment of moorings in Lyall Bay for ~7 weeks to gather information on waves, currents, and physical characteristics of the water column (light, turbidity, temperature, salinity)

° Bathymetric surveys of Lyall Bay to support modelling and engineering investigations (Mackay & Mitchell, 2014)

° Modelling of the potential impacts of the extended runway structure on waves, currents, sediment transport and coastal morphology for the ongoing impacts of the reclamation

° Modelling of the potential impacts of sediment-plume discharges during construction of the runway structure and associated fill operations on in-situ turbidity of Lyall Bay

° Site survey of the intertidal beach of the cove east of the runway (referred to as Moa Point beach alongside Moa Point Road).

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Coastal environmental assessments are required to support applications for coastal permits and consents and Notices of Requirement (NOR) for the Airport runway extension in the coastal marine area (CMA).

This Report covers the assessment of effects on coastal physical processes of the extended runway into Lyall Bay, focused on coastal hydrodynamic and coastal sediment processes. It draws on detailed information from field and model studies in the Technical Report on Coastal Hydrodynamics and Sediment Processes in Lyall Bay (Prichard et al., 2015), the report on sediment characteristics and sediment contaminant levels (Depree et al., 2015) and an additional site survey of the cove east of the runway extension (covered in Section 4.2). As effects of the runway extension on inshore waves were highlighted early on in the AEE investigations, surfing and recreational-related effects are given greater scrutiny when assessing the degree of coastal environmental impacts, with a more detailed, complementary assessment provided by DHI (2015). Consequently, this Report only describes likely changes in wave patterns, but the effects of these changes on water-contact recreation activities such as surfing and swimming are covered by DHI (2015).

Other than for describing the existing environment, this Report does not cover assessments of coastal-hazard extremes (e.g., waves, tsunami, storm-tide) or climate-change effects, such as sea- level rise.

A separate report on the assessment of coastal ecological effects was prepared by James et al. (2015). DRAFT

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2 Description of the Project Wellington International Airport Limited (WIAL) propose to extend the runway to 2300 m TORA to further enable long-haul flights, including Code E aircraft (e.g., Boeing 777 or Airbus A320).

WIAL are very aware of concerns about a reclamation for a runway extension and the potential effects on the environment and have commenced planning for this extension with the first phase being preparation of resource consent applications. As yet the final engineering design of the extension has not been confirmed but based on geotechnical work, and consideration of options to the north and south, a decision has been made to reclaim land to the south into Lyall Bay.

Providing for this increased capacity of aircraft will involve an extension of the runway and taxiway of approximately 350 m into Lyall Bay2, as shown in Figure 2-1.

DRAFT

Figure 2-1: General layout for the south runway extension into Lyall Bay to develop a 2300 m Take Off Runway Available (TORA). [Source: URS Ltd.].

The key elements of the Project, which could potentially affect physical processes in the coastal marine area (CMA), either during construction and/or during the operational lifetime, are:

1. Sea-bed ground treatment (e.g., stone columns), if required, to ensure sufficient strength to support the extended embankment into Lyall Bay [construction effect];

2 with an additional ~35–45 m length underwater for the revetment batter and toe rock apron in approximately 13 m water depth (MSL)

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2. Perimeter rock dyke constructed on the sea bed to contain the runway embankment [construction & operational effects];

3. Wave protection armour on the seaward side of the rock dyke using various size/weight of accropode units, which are unreinforced concrete objects that interlock and better resist the action of waves on breakwaters and coastal structures [construction & operational effects];

4. Placement of gravel/sand fill material within the rock dyke to form the runway platform reclaimed from the sea – either through pumping from barges or tipped from trucks, with a de-watering discharge to the CMA of supernatant containing suspended fine sediment [construction effect];

5. Construction of runway and taxiway bridges over Moa Point Road, which currently circumvents the southern end of the present runway [construction effect].

The source of the reclamation fill material is yet to be finalized but is likely to consist of material from a quarry and/or possibly from dredging predominantly sand material from the entrance to the Harbour or elsewhere along the south Wellington coast.

Further details on the construction of the specimen runway-extension design are provided in the Construction Methodology Report (URS Ltd, 2015). DRAFT

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3 Assessment methodology

3.1 Introduction This AEE Report describes both the existing coastal environment of Lyall Bay focusing on coastal physical processes, sediments and the potential effects on these processes that may arise from construction and long-term operation of the reclamation to form the ~350 m runway extension.

For this assessment, the main coastal physical processes considered in terms of potential effects from the Project are:

° Coastal hydrodynamics (changes in tidal and wind-driven currents)

° Coastal wave heights and wave refraction patterns

° Sediment transport and coastal geomorphology (storm-scale changes to Lyall Bay and Moa Point beaches)

° Water quality (turbidity and any subsequent sedimentation from suspended-sediment discharges and potential for contaminant release arising from sea-bed disturbances from construction sites).

Coastal processes will also have the potential to impact on the Project, particularly in this case from wave impacts, tsunami and longer-term, from climate change. These processes are factored into the overall design of the Project in order satisfy the requirement under the RMA to consider the effects of coastal hazards and climate change, over a period of at least 100 years as stipulated in the NZ Coastal Policy Statement. These aspects are covered in the Engineering Report (URS Ltd, 2015) and the AEE.

Effects on coastalDRAFT ecology are discussed in the Marine Ecology Assessment Report (James et al., 2015).

There are no quantitative assessment criteria for assessing the degree of effects on hydrodynamic, wave and sediment processes and sub-tidal geomorphology from reclamation and construction effects. Therefore the assessments in this Report rely on a blend of expert appraisal, supported by field observations and modelling, as well as understanding the analogue of how the existing runway reclamation has influenced physical processes. The assessments are underpinned by the following considerations:

° Modelling of combined both coastal hydrodynamic and geomorphic/sediment processes continues to be challenging and at the forefront of ongoing research, particularly over longer multi-timescales, not to mention the considerable natural

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variability that is invariably present. Therefore reliance is placed on using the models as tools, with sufficiently robust physics, to assess the relative changes before and after the runway extension is in place, without resorting to intensive field programmes to support very detailed calibration and verification when modelling the existing situation;

° Given the predominance of clean sands on the sea bed in Lyall Bay, discharge simulations for assessing the effect of turbidity are focused on de-watering discharges from the construction operations associated with the imported fill (which may contain fine sediments), rather than modelling sea-bed disturbances that may arise from using controlled ground-treatment techniques or rock placement for the dyke.

The effects on coastal physical processes are also assessed in line with requirements of the Resource Management Act (RMA), the NZ Coastal Policy Statement (NZCPS) and the operative Wellington Regional Coastal Plan (19 June 2000).

The investigations and assessment of effects on coastal physical processes of the proposed extended runway into Lyall Bay were undertaken through a mix of:

° desk-top review of previous reports, field data and satellite imagery. The review was previously undertaken for WIAL in 2013 by Aquatic Environmental Sciences Ltd and NIWA (2013);

° field investigations and surveys focused on bathymetric surveys, seabed sediment/contaminant sampling and deployment of in-situ instruments in Lyall Bay to measure waves, currents and turbidity;

° numerical modelling of the effects of the runway extension, relative to the existing DRAFTsituation, for waves, currents, sub-tidal geomorphic change and suspended-sediment discharges during construction;

° expert appraisal of potential effects of the Project (both construction and operational) from the simulated changes from modelling investigations, informed by the above analyses, information and the response to the historic runway extension. Potential effects are aligned with requirements in relevant statutory instruments to assess whether effects are minor or otherwise, and whether mitigation or remediation is possible and some suggested monitoring conditions.

3.2 Desk-top analysis The desk-top analysis undertaken for WIAL (Aquatic Environmental Sciences Ltd. & NIWA, 2013) for the existing coastal environment, both Lyall Bay and Evans Bay, included a review of the following information sources:

° Previous bathymetric and seabed geological surveys.

° Past oceanographic field deployments and analyses, primarily for AEE investigations for the ocean outfall in Lyall Bay that discharges from the Wellington City wastewater treatment plant adjacent to the Airport;

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° Modelling of currents and plume dispersion in that late 1980s (e.g., Beca Carter– Caldwell Connell, 1980; Bell, 1989) and 2013 (for Opus Consultants Ltd. and Capacity Infrastructure Services Ltd.) to assess the water quality effects of the main Wellington ocean outfall in outer Lyall Bay;

° Research papers or reports on coastal physical processes, such as sediment transport pathways and beach response for Lyall Bay specifically or more generally along the south Wellington coast.

° Long-term monitoring data for winds (Met Service station at the Airport) and waves (NIWA buoy at Baring Head operated on behalf of Greater Wellington Regional Council-GWRC).

° Synthesis on past investigations on coastal hazards (winds, waves, tsunami, storm-tide and climate-change impacts);

° Marine ecological studies, fisheries models and research papers in both bays.

The desk-top review of previous investigations highlighted gaps in the available data and knowledge, which then formed the basis for implementing additional field and modelling work in 2014 to support the environmental assessment of coastal physical processes.

Studies required to fill information gaps on coastal physical processes that were identified in the desk-top review are listed below, excluding items on coastal hazards and engineering requirements, which are covered in the Engineering Report (URS Ltd., 2015). Succeeding actions are listed in italics after each item.

3.2.1 Relevant gaps - Sediments/Geology ° DRAFTContamination remobilisation potential from disturbed sediments – collection of grab or core samples and analysis for specific chemical species and sediment grain-size and settling/floc characteristics. [Reduced sea-bed sediment sampling grid undertaken only in Lyall Bay, given contamination levels were assumed to be low (Depree et al., 2015).]

° Establish a before (baseline) and after-construction beach-profile monitoring programme on the Lyall Bay Beach if a southern option is preferred, to monitor any changes due to reclamation and wave refraction/diffraction. [This aspect could be part of a coastal-permit monitoring condition, but it would be difficult to isolate any specific effects of the extended runway from any ongoing morphological adjustment of historical shoreline modifications and reclamations and climate variability.]

3.2.2 Gaps - Hydrodynamics ° Complete full multi-beam bathymetric mapping coverage of western Lyall Bay; improve compatibility of existing multi-beam coverage in Evans and Lyall Bays undertaken in different surveys to produce a consistent dataset. [Completed in both Bays in January 2014 – see Mackay & Mitchell, 2014).]

° High-resolution wave modelling in Lyall Bay or Evans Bay, with and without reclamation options to assess changes in wave patterns and description of the extreme wave climate in Lyall and Evans bays to inform engineering design. [Wave modelling

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undertaken for this assessment in Lyall Bay only – the extreme wave analysis on Baring Head wave buoy data was performed by URS Ltd. for the Engineering Report.]

° Assessment of any changes in potential tsunami propagation in Lyall and Evans Bays as a result of reclamation and assessment of tsunami wave amplitude to consider for engineering design. [Tsunami was a consideration in the engineering design of the runway extension by URS Ltd.]

° Assess the extent of turbid-plume dispersion using existing models. [Plume modelling undertaken for this assessment in Lyall Bay only.]

3.3 Field surveys Based largely on the gap analysis in the desk-top review outlined above, the necessary field data requirements for the preferred Lyall Bay option were focused on:

° collecting a representative range of sea-bed sediment characteristics and surficial- sediment contaminants;

° high-resolution sea-bed bathymetry obtained from multi-beam sounding surveys;

° background turbidity and water column clarity measurements, which are covered in the Marine Ecology AEE Report (James et al., 2015);

° an additional field deployment for at least 1 month of wave and current-meter gauges at two sites in Lyall Bay to provide additional calibration data for modelling, especially DRAFTfor waves.

3.3.1 Sea-bed sediment and contaminant characteristics

Sea-bed sampling Broad-scale sea-bed sediment mapping in Lyall Bay was undertaken for grain-size analyses and contaminants in such a way as to complement the use of the same sites for the companion marine biological sampling (MacDiarmid et al., 2015). Short-core sediment extrusions underwent laboratory analysis. The analyses determined grain-size and also total organic carbon and contaminants (see below) that were also undertaken for the companion marine ecological studies.

The gridded survey plan included a total of 13 sampling sites in Lyall Bay (Figure 3-1) from which surficial sediments (0–5 cm) and subsurface sediments (typically less than 20 cm) were collected. Water depths of the sites ranged from approximately 5 to 15 m. These sites were identical to the sites also sampled for benthic biological communities. Specific sampling sites for contaminant analysis included sediments adjacent to (sites 1, 3, 5 and 8) and within the proposed area of the runway extension (sites 10, 11 and 12), a total of seven sites (Figure 3-1).

Grain-size analyses Grain-size distributions in the sediment samples were measured using a Beckman Coulter LS13-320 dual-wavelength laser-particle sizer that measures grain-sizes in the 0.04–2000 μm size range with

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3 3 1% reproducibility. An approximate volume of 0.5 cm of sediment was re-suspended in distilled water and then washed through a 2 mm sieve into the laser-sizer where it was analysed.

Standard statistics (mean, sorting, skewness and kurtosis) on the grain-size distributions measured were calculated for each core sample from the ‘percent by volume’ laser data and matched to standard sediment textural descriptions using the Folk and Ward (1957) classification scheme. Although continuous grain-size distributions are produced from the laser-particle sizer output, grain- sizes are presented primarily as percent gravel (over 2 mm diameter), sand (0.063–2 mm), mud (<0.063 mm), silt (0.002–0.063 mm) and clay (<0.002 mm).

Contaminant analyses Samples from surficial sediments and the last depth fraction to the bottom of the core (typically less than 20 cm penetration due to the sandy nature of the seafloor sediments) were double-bagged in labelled zip-lock plastic bags, chilled and shipped overnight to the NIWA Hamilton laboratory for further processing. Both whole (<2 mm size) and fine (<0.063 mm) sediment particle size-fractions were prepared for analysis of contaminants.

The samples were analysed for a range of contaminants, based on previous and ongoing Greater Wellington Regional Council (GWRC) and Wellington City Council (WCC) monitoring in Wellington Harbour. Analyses conducted on these samples included Total Organic Carbon (TOC), heavy metals and DDT-derived organochlorine pesticides. Further analyses were undertaken for sites 10 and 11 (proposed runway extension), where deeper cores were sampled in 5 cm increments to 20 cm and 0– 10 cm and 10–20 cm depth composites were used for elutriate testing (mobilisation/solubilisation of contaminants from sediments to overlying water). These elutriate sediment depth fractions at these two sites were also analysed for heavy metals.

Outputs Grain-size informationDRAFT was used to develop a picture of grain size distributions within Lyall Bay and complement previous studies of sediment characteristics and sea-bed morphology. From this grain- size information, settling velocities for suspended-sediment plume modelling of sea-bed disturbances, especially fine sediment fractions, could be determined, although no modelling was undertaken for disturbances due to the small fraction of fine material and limited disturbance- generating activities required (Construction Methodology Report, URS Ltd., 2015). Note: the primary source of fine sediments in de-watering discharges comes from the fines in imported fill material.

Sediment contaminant analyses enabled the spatial distribution of contaminants within in Lyall Bay to be determined and assessed. The results were assessed with ANZECC and other guidelines.

3 μm = micro-metres or 0.001 mm

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DRAFT

Figure 3-1: Sea-bed sediment sampling sites in Lyall Bay, Wellington. Contaminant sampling sites were 1, 3, 5, 8, 10, 11 and 12. Other sampling sites shown were analysed for sediment grain-sizes. Seds = Sediment analyses, Contam = Contaminant analyses, Elutriates = Elutriation experiments (see Depree et al., 2015 for details). The location of the Lyall Bay ocean outfall is also shown as a red line. Bathymetric data are from Wright et al. (2006) and Mackay & Mitchell (2014).

3.3.2 Hydrodynamic processes

Bathymetric surveys In January 2014, NIWA carried out a bathymetric survey of parts of Lyall Bay and Evans Bay on behalf of WIAL (Mackay & Mitchell, 2014). The vessel used for the hydrographic survey was the 14-m survey

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launch Ikatere, owned and operated by NIWA Vessels. Previous bathymetric surveys have been undertaken in Lyall Bay (e.g., Wright et al, 2006), so the focus was on sounding the area enclosed by the black dashed line in Figure 3-2. For engineering and geo-technical purposes, a survey was also undertaken immediately to the south of the present runway (Mackay & Mitchell, 2014; Figure 2) covering the proposed runway extension footprint and reached within 10 m of the akmon coastal protection units.

A Kongsberg EM-3002D shallow water multi-beam echo sounder was used to obtain near-complete coverage of the seabed in the survey areas, although limited to narrower swathes in shallow water 25-m apart. Depths shallower than ~2 m below Chart Datum were not able to be surveyed due to draught restrictions. Also the shallower waters along the eastern and western periphery of outer Lyall Bay were also not able to be surveyed due to submerged rocky outcrops. The results were processed according to hydrographic best practice and tidally corrected based on tidal measurements in Lyall Bay relative to surveyed benchmarks in Wellington Vertical Datum-1953.

The same gridded-dataset at 25 m spacing was supplied to the hydrodynamic/wave modellers at both NIWA and DHI. DRAFT

Figure 3-2: Extent of Lyall Bay infill bathymetry survey (black dashed line) shown against grey area collected from previous surveys. Background image: ESRI World Imagery.

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Hydrodynamic/wave deployments Given the importance in quantifying the effects of changes in waves from the proposed Wellington Airport runway extension, a field deployment of instruments was undertaken in Lyall Bay over a ~7- week period from August to October 2014 to provide observational data to validate both wave and tidal models.

Figure 3-3 shows the locations occupied during the instrument deployment in Lyall Bay. The details of what instruments were deployed at each of the sites and over which period are in shown in Table 3-1.

Table 3-1: Locations (WGS-84) and 2014 deployment information for the Lyall Bay instruments.

Location Latitude Longitude Instrument Deployment Depth Mean (S) (E) (parameter measured) Period below water Water depth Surface (m) (m)

Site 1 41˚ 20.197 174˚ 48.140 ADCP (currents and waves) 18-Aug 14:00 to 11.0 11.0 (inshore) 09-Oct 09:00

Site 2 41˚ 20.932 174˚ 47.933 ADCP (currents and waves)4 N/A (offshore) DWG (waves) 04-Sep 11:00 to 7.6 19.0 09-Oct 09:00

Current velocities in the Lyall Bay were measured using Acoustic Doppler Current Profilers (ADCP). ADCPs measureDRAFT currents in “bins” throughout the water column, thus providing the user with a velocity profile over the entire water column.

ADCPs were deployed on the sea bed facing the water surface, which is known as a bottom-mounted upward-looking configuration. ADCP acoustic transducers were nominally positioned 0.4 m above the sea bed.

5 Significant wave height (Hs), mean spectral period (Tm) and, where possible, peak direction of wave propagation (Dp) were measured using an ADCP and a DOBIE Wave Gauge.

The outer ADCP at Site 2 broke free during a southerly gale on or around 22 September 2014 and was not found on subsequent searches. Fortunately, a DOBIE Wave Gauge was moored adjacent to the ADCP at Site 2, so some wave information was collected (excluding wave direction).

Winds prior to 1 January 2013 were obtained from the Automatic Weather Station at Wellington airport operated by the NZ Met Service (NIWA Climate Database; Agent No. 3455). The station at Wellington airport is located 4 m above mean sea level. Winds for Lyall Bay after 1 January 2013 were obtained from NIWA’s meteorological forecasting model (EcoConnect) as nowcasts (i.e.,

4 The ADCP at Site 2 was lost to a storm during the deployment. No current data is available at Site 2.Wave data at Site 2 comes from the DWG. 5 Defined as the average of the top 33% (1/3) of wave heights over the measurement cycle

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current conditions at or a few hours ahead of the forecast time), as access to NZ Met Service data is now restricted.

Further details are provided in Section 2 of the Technical Report on Coastal Hydrodynamics and Sediment Processes in Lyall Bay (Prichard et al., 2015).

DRAFT

Figure 3-3: Site map showing oceanographic instrument locations overlying the seabed bathymetry to WVD-53. The black polygon outlines the approximate area covered by the proposed runway extension.

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3.4 Modelling approach: coastal physical processes

3.4.1 Approach to hydrodynamic and sediment-transport modelling The integrated Deltares Delft3D modelling suite was used in the investigations of the changes before and after construction of the extended runway on the tide, wind and wave-driven dynamics of Lyall Bay and on the before-and-after effect of changes in current circulation and waves on sediment transport and morphology in the Bay (Coastal Processes Technical Report, Pritchard et al., 2015). The modelling approach adopted was based on the following components:

• For this present application to the south Wellington coast and Wellington Harbour, the Delft3D modelling system was used in depth-averaged (2-D) mode. The use of the depth- average 2-D mode, which still incorporates all the main forcing mechanisms, can be justified as outlined in Section 3 of the Coastal Processes Technical Report, alongside run- time constraints on running the entire model in 3-D (which included part of the deep Cook Strait waters and Wellington Harbour as shown in Figure 3-4)

• The model were primarily used as a comparative tool to determine the effects on hydrodynamics after the runway extension is constructed, relative to the present situation.

° Residual hydrodynamic circulation in Lyall Bay was investigated using forcing from tides at the open-sea boundary in Cook Strait and local wind speed and directions applied over the sea-surface of the model. The simulations were run for the same time frame as the field observational period of approximately 7 weeks in 2014.

• Combined tide and wind-driven circulation investigations in Lyall Bay focused on isolating the wind response to currents (leaving aside waves) and were forced by a sequence of 3- day wind events peaking at a speed of 22 m/s (strong gale), directed from the prevailing southDRAFT and north directions. The winds were superimposed on a background of a repeating mean (average) tide applied as a boundary condition on the open-sea boundary to better isolate the change in wind-driven response in currents (before and after the runway extension).

• For assessing sediment transport and morphological change, the 2-D hydrodynamic model was forced with tide (multiple constituents), local wind speed and directions and coupled with a SWAN wave model6 on the same grid for the south Wellington coast (red–coloured grid in Figure 3-4). The simulations also covered the same time frame as the ~7-week field- measurement period. Sand transport in shallow coastal areas is a complex interaction between waves, which primarily re-suspended seabed sediments into the water column, which are then subsequently transported by currents until the sediment particles settle again. In nearshore waters, including the surf-zone, non-linear wave dynamics along can also transport re-suspended sediments, especially if waves propagate towards the nearshore zone at an oblique angle to the beach. The Delft3D-SED and Delft3D-MOR modules incorporate tidal and wind-driven hydrodynamics from the Delft2D simulation coupled with waves simulated by the SWAN spectral-wave model to combine these wave- current interactions with mobile sediments on the seabed. The sediment-transport modelling, based on fine sand with a median grain size of 0.15 mm, was then used to determine the before and after changes in sand deposition or scour within Lyall Bay.

6 SWAN is a spectral wave model developed by Delft Hydraulics, that is widely used globally for broader-scale wave climate studies

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• The spatial variability of wave climate for the existing environment of Lyall Bay was also appraised using the SWAN model and compared to the field measurements on waves at Sites 1 and 2 (Figure 3-3).

• Investigation of the intensity and extent of suspended-sediment plumes from de-watering discharges during construction was supported by simulations using the 2-D hydrodynamic model coupled to a non-cohesive sediment-transport and settling model. This assumed that the water in the discharge is the same density as water in the bay, which would be the case for barged fill material sourced from dredging the seabed or from discharging wave- overtopping waters. In this case, there would be no buoyancy effect in the water column associated with the sediment plume. For discharges with substantial freshwater from stormwater runoff, further model simulations will be required to include plume-buoyancy effects, through coupling with a near-field mixing model for the discharge.

Further details of the model grids and implementation of the modelling simulations are described in the Coastal Processes Technical Report. DRAFT

Figure 3-4: Delft3D-WAVE model grid (red) of south Wellington coast superimposed on top of the Delft3D- FLOW model grid (black) that also includes Wellington Harbour.

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3.4.2 High-resolution wave modelling to predict changes post runway-extension In order to locally resolve wave patterns around a structure such as the Wellington International Airport runway extension into Lyall Bay, a high-resolution wave model is required that incorporates local changes in wave processes particularly:

° Refraction – process by which the direction of a wave moving in shallow water at an angle to the seabed contours is changed (e.g., the part of the wave in shallower water moves more slowly than the part still advancing in deeper water). Refraction explains why swell and longer-period wind waves straighten up across inner Lyall Bay, even if the waves approach the outer Bay slightly to the east or west of a southerly direction.

° Diffraction – where wave energy is transmitted laterally along a wave crest, when part of a train of waves is interrupted by a barrier such as a rock revetment or breakwater of a comparable physical scale to the wave length. Diffraction is the "spreading" of waves into the sheltered region within the barrier's geometric shadow. This currently occurs in the lee of the spur groyne and associated rocky outcrop on the western side of the existing runway revetment.

° Reflection– part of an incident wave that is returned seaward when a wave impinges on a steep beach, rocky outcrop, rock revetment or other reflecting structure. This would potentially occur on the end of the extended runway revetment. However, porous multi-layer rock armour layers and akmons or accropodes provide substantial absorption of wave energy, thereby reducing reflection, which is controlled in models by a reflection coefficient. ° DRAFTWave breaking – depth-induced steepening and eventual breaking of waves as they shoal into shallower water, and depends on the wave period how far offshore they break e.g., swell waves feel the bottom in greater depths than wind sea.

There are a number of high-resolution phase-resolving7 models available globally – NIWA selected the ARTEMIS8 model (Aelbrecht, 1997), which is part of the widely-applied TELEMAC–MASCARET modelling system developed by Laboratoire National d'Hydraulique (Electricite de France).

ARTEMIS model runs on a finite element or triangular grid to solve the extended elliptic mild-slope wave equation with additional dissipative terms (Booji, 1981). It is used to describe the combined effects of diffraction, refraction, reflection and wave breaking for water waves propagating over bathymetry and due to interactions with lateral boundaries—like breakwaters and coastlines.

The resolution of the Lyall Bay ARTEMIS grid zoomed in on the immediate area around the end of the present runway and proposed runway reclamations is shown in Figure 3-5 to show the degree of grid resolution at around grid-cell scales of 5 m. The extent of the entire Lyall Bay grid out to the entrance in Cook Strait is shown in the Coastal Processes Technical Report (Section 5).

ARTEMIS was used for the Project to compare wave patterns in Lyall Bay with the existing runway revetment to the wave patterns and heights predicted for the proposed extended runway

7 Phase resolving means there are sufficient model grid nodes or cells to fully resolve a single wave, including the crest and trough. SWAN on the other hand operates on coarser grids as it is only resolving spatial changes in wave spectral energy (and excludes diffraction). 8 Agitation and Refraction with Telemac on a MIldSlope http://www.opentelemac.org/index.php/presentation?id=19

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revetment. The results in the Coastal Processes Technical Report (Pritchard et al., 2015) were presented as a change in significant wave height relative to the existing runway situation, which is in line with assessment of effects relative to the existing environment.

In consideration of post-extension changes on the range of waves in Lyall Bay used by surfers, the Coastal Processes Technical Report focused mainly on wave heights of 1–3 m for longer period wind waves (e.g., 8 seconds) and the 10 – 15 second swell wave spectrum. Surfing is undertaken at ‘The Corner’ which is located to the eastern end of Lyall Bay (Figure 4-2) and also in the central part of the Bay.

DHI have undertaken complementary wave modelling and assessment specifically addressing effects on surfing-wave quality and public safety of beach recreational users (DHI, 2015).

DRAFT

Figure 3-5: ARTEMIS finite-element model grid resolution in the area around the runway extension (left) existing runway; (right) proposed runway reclamation. Depths are scaled according to colour shading (red shallowest, blue deepest). [Horizontal grid: NZTM].

A visual validation of the ARTEMIS wave model is shown in Figure 3-6 comparing spatial wave-crest patterns and breaking zones throughout Lyall Bay from a historic aerial photo archived in the Google Earth software. This visual comparison with the vertical view of the predicted wave fields for similar incident waves, shows a close match with a number of features, including the extent of surf zones (white areas in Figure 3-6), zones of refracting shoaling waves turning into both coasts of the outer

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Bay, more quiescent areas in coves and the western side of the Bay and a particularly close match with the overall refracting and diffracting wave crest patterns including in The Corner area adjacent to the existing runway revetment. There are some slight local differences in the wave-crest pattern in the predicted wave field at the tip of the spur groyne – an area of rapidly changing bathymetry associated with the rock outcrop.

Results from the ARTEMIS wave model suggest that for 1 and 1.5 m regular waves applied at the outer-Bay boundary, the wave attenuation between the two field mooring sites (Site 1–inner ADCP and Site 2, located in Figure 3-3) is between 0.03 and 0.05 m, which is within the limits of measurable accuracy of the instruments.

DRAFT

Figure 3-6: ARTEMIS model predicted surface water level as a result of a 1.5 m wave at the Cook Strait boundary with a wave period of 12 seconds (LEFT). Google Earth image of Lyall Bay taken on 24 July 2014 for a wave height of 1–1.5 m and a period ~10 seconds (RIGHT). Wave measurements for the latter were derived from the Baring Head wavebuoy.

3.5 Assessment of effects criteria: policies/plans/statutes

3.5.1 Wellington Regional Coastal Plan (2000) The Regional Coastal Plan (RCP), which has been operative from June 2000, provides objectives, policies and rules for managing activities in and above the coastal marine area (CMA), which is the marine waters and inter-tidal land below Mean High Water Springs (MHWS).

The RCP also specifies designated areas around the Wellington region of either significant or important conservation value. The only conservation areas in the general vicinity of Lyall Bay area are Tarakena Bay (Figure 3-7) to the west of Hue te Taka Peninsula and east of West Ledge Reef, which is an Area of Important Conservation Value (AICV) marking an important waka landing place and the area around Taputeranga Island off Island Bay (Figure 3-7).

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Planning Map 8D in the RCP designates water quality classes in the Wellington area, with the waters throughout Lyall Bay managed for water-contact recreation and the nearshore waters around Te Raekaihau Point and Hue te Taka Peninsula in outer Lyall Bay also managed for shellfish gathering (see Figure 4-2 for locations).

Figure 3-7: Areas of Conservation Value in Lyall Bay area (Tarakena Bay and Tauputeranga Island) in the Regional Coastal Plan. Source: Planning Map 2H, Regional Coastal Plan, GWRC. DRAFT 3.5.2 NZ Coastal Policy Statement (NZCPS) The policies and objectives of the NZCPS most relevant to coastal physical processes are:

° Objective 1: “… maintaining or enhancing natural biological and physical processes in the coastal environment and recognising their dynamic, complex and interdependent nature …”

° Policy 3(1): “Adopt a precautionary approach towards proposed activities whose effects on the coastal environment are uncertain, unknown or little understood, but potentially adverse.”

° Policy 10(1–2) on reclamation: For 10(1), “Where a reclamation is considered to be a suitable use of the coastal marine area, in considering its form and design have particular regard to [Policy 10(2)]: …

c) the use of materials in the reclamation, including avoiding the use of contaminated materials9 that could significantly adversely affect water quality …. in the coastal marine area;

9 Suspended-sediments or turbidity generate from discharges or disturbances can be regarded as a contaminant (RMA Section 2 definition)

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e) the ability to remedy or mitigate adverse effects on the coastal environment;

g) the ability to avoid consequential erosion and accretion, and other natural hazards.”

° Policy 23 (Discharge of contaminants) – covered in the Marine Ecology AEE Report (James et al., 2105).

° Policy 24 (Coastal hazards and climate change) – considered as part of the Engineering Report (URS Ltd, 2015).

3.5.3 Resource Management Act (RMA) 1991 Relevant aspects of the RMA in relation to coastal physical processes are outlined below.

Under section 3, actual or potential effects includes any positive or adverse effect, temporary or permanent effect, any past10, present or future effect and any cumulative effects. In this Report, actual or potential effects have been assessed as:

° Negligible

° Minor11

° Major effect

Central to the purpose of the Act (section 5) is sustainable management in managing the use, development and protection of natural and physical resources which enables communities to provide for social, economic and cultural wellbeing, while …. (c) avoiding, remedying or mitigating any adverse effectsDRAFT of activities on the environment. Section 6 (Matters of national importance) and section 7 (Other matters) in general relation to coastal processes are covered in the AEE and the Marine Ecology AEE Report (James et al., 2015) and the Natural Character and Landscapes AEE Report (Boffa Miskell, 2015)

Based on section 105, the consent authority must, in addition to matters in section 104(1), have regard to: a) the nature of the discharge and the sensitivity of the receiving environment to adverse effects (covered in the Marine Ecology AEE Report); b) the applicant’s reasons for the proposed choice; and c) possible alternatives methods of discharge, including discharge into any other receiving environment. These latter two matters are addressed in the AEE and in the Construction Methodology Report.

Section 107 for assessing discharge permits, outlines that after allowing for reasonable mixing, the discharged contaminant (suspended sediment in this case) should not produce any conspicuous change in colour or visual clarity. This aspect is largely covered in the Marine Ecology AEE Report (James et al., 2015).

10 Past and any continuing effects from the historic runway reclamation on the CMA are not considered in this Report, as reclamations are granted in perpetuity and become land. 11 Minor is a comparative word meaning lesser or comparatively small in size or importance (Bethwaite v. Christchurch City Council (CO85/93)19

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4 Existing environment This section provides a description of the existing coastal environment, relative to which the effects of introducing the proposed extended-runway reclamation are assessed. It covers the geomorphic and geographical setting followed by a description of coastal physical processes that currently operate in Lyall Bay based on previous studies and new data collected during the present AEE investigations for the runway extension.

4.1 Coastal and geomorphic setting Lyall Bay is a semi-circular, open bay on the Wellington south coast between the rocky headlands of Te Raekaihu to the west and Hue te Taka (Moa Point) to the east that is exposed to southerly swell from the Cook Strait (Figure 3-3).

Pillans & Huber (1992) provide evidence that there has been at least four uplift events of the Miramar Peninsula area over the Holocene epoch in the last 7000 years, probably relating mainly to activity on the Wairarapa Fault. Lyall Bay formed when a tombolo connected the Miramar Peninsula (to the east of the Airport) to the hills to the west of Kilbirnie. The growth of the tombolo has occurred within the last 900 years. Māori history identifies the Miramar Peninsula as a separate island (Motu-Kairangi or Miramar Island) some 900 years ago (Raukura Consultants, 2014), but the area has since been subject to tectonic uplift by two events in more recent geological time. Uplift of ~3 m occurred from an end of 15th century earthquake event 520–470 years before present (Pickrill, 1979; Pillans & Huber, 1992; Clark et al., 2015) and ~2 m in the 1855 Wairarapa earthquake (Pickrill, 1979). Sediment from the shelf in Cook Strait and to a lesser extent flanking cliffs, have progressively extended the tombolo southwards until it attained its present-day width (Pickrill, 1979).

The construction of Wellington Airport at Rongotai from 1952–1959 reclaimed 14 hectares of the eastern Lyall BayDRAFT for an 850 m runway extension, connecting with a rocky outcrop towards Moa Point beach, which formerly acted as a natural breakwater (Figure 4-1). The reclamation at that stage extended to the spur groyne (breakwater) placed on the submerged natural rock outcrop from the headland and occupied about a quarter of the inner Bay coastal marine area (i.e., inshore of an east- west line through the spur-groyne).

The runway reclamation was subsequently extended by 180 m to its present shoreline configuration Figure 4-2 in 1971–1972, to allow operation of DC-8s, with 10-tonne akmon units placed along the periphery for coastal-wave protection (Webby, 1984). During a storm in May 1972, a substantial number of akmons were displaced, so heavier 12-tonne units were placed along the southern edge and the bund crest raised by 2 m in August 1973 (Webby, 1984). There is no documented evidence of the effects that the additional 180-m runway extension has had on coastal processes, but is likely to have been modest, given the hydraulic control on waves in particular by the spur groyne (breakwater) and that it was a short extension.

Wellington International Airport Runway Extension: Coastal Processes 35 1 September 2015 6.36 p.m.

Figure 4-1: Aerial photograph looking north on completion of the airport construction (21 Jan 1959). Source Ref: WA-49119-F. Alexander Turnbull Library.

The original 1941 shoreline of Lyall Bay and the former rocky outcrop are shown in Figure 4-2, along with other features mentioned in this Report, including The Corner where surfing is popular.

The bathymetry of Lyall Bay (Figure 3-3) reflects the Pleistocene geological history, with the former steep-sided valley infilled with sands and reworked by wave activity to form a flat seabed gently sloping seaward (Pickrill, 1979). Inshore of the present Airport runway embankment, the Bay is asymmetrical,DRAFT with a deeper trough extending down the eastern side and a wide shallow sandy platform extending from the western shoreline (Figure 3-3), which greatly influences the wave refraction patterns from east to west off Lyall Bay Beach.

Locally, around the terminus of the existing runway and spur-groyne, the seabed bathymetry is dominated by the submerged extension of the former rocky reef (that was reclaimed) and gravelly deposits, with the sandy bed shoaling to the north of the groyne, as shown in Figure 4-3. More recently in 2014, NIWA carried out additional multi-beam sounding surveys for the Project to cover gaps from previous bathymetric surveys and another high-resolution survey off the end of the existing runway (see Section 3.3.2).

Lyall Bay is 1.3 km wide at the southern entrance narrowing to 1.1 km in the inner Bay (post-runway extension in 1959) and is 2 km in total length over a north-south orientation. Lyall Bay encompasses a depth range from 25-30 m (MSL) beyond Hue te Taka Peninsula, 12-13 m deep in the central section before shoaling to the intertidal beach at the northern head of the Bay.

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DRAFT

Figure 4-2: Geomorphic features in Lyall Bay incl. the 1941 shoreline. Blue line shows the approx. 1941 shoreline (from Pickrill, 1979) and green dotted line the rock outcrop in 1941 that joined the submerged rock outcrop the spur groyne currently sits on. [Background image: Google Earth, 8 October, 2014].

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DRAFT Figure 4-3: Multi-beam bathymetric data at 0.5 m resolution off the existing runway in Lyall Bay obtained by NIWA (Mackay and Mitchell, 2014). Background imagery is sourced from ESRI http://services.arcgisonline.com/arcgis/rest/services/World_Imagery/MapServer

4.2 Coastal geology, sediment processes and characteristics

Sediments and geology Surface sediments in Lyall Bay are predominantly well sorted, fine sands overlying coarser gravels that can form exposed aprons of mega-ripples, especially in the vicinity of the rocky substrates (greywacke bedrock) that form the headlands (e.g., Arron and Lewis, 1993; Carter and Lewis, 1995). The upper sandy deposits are mobile under fair- and storm-wave activity, with pebble gravels also able to be transported under extreme wave conditions, even at water depths of 60 m (Nodder, 1991, 1994; Carter and Lewis, 1995). Offshore, in the vicinity of Hue te Taka (Moa Point), greywacke basement or boulder-sized materials associated with the basement lithologies may be within about 2 m of the sea-floor, although there are localised incidences of the upper sandy and gravel deposits being at least 7-10 m below the sediment surface (Nodder and Smits, 1994). In outer Lyall Bay, the depth to greywacke basement might be as much as 70-80 m (Davey, 1971; Rogers, 1971; Grant- Taylor et al., 1974).

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The spatial distribution of sea-bed sediments in Lyall Bay is shown in the map extract in Figure 4-4, comprising predominantly well-sorted fine sands (light shade in Figure 4-4) overlying coarser gravels and gravelly-sands (stippled shade) that can form exposed aprons on the seabed especially in the vicinity of the rocky substrates (greywacke bedrock- red shade) that form the two enclosing headlands Te Raekaihau on the west and Hue te Taka on the east (Arron and Lewis, 1993).

In the wider context of the south Wellington coast, Lyall Bay contains the largest area of surficial sands on the seabed followed by neighbouring Houghton Bay (Figure 4-4). Recent sampling of seabed sediments in association with the seabed contaminant survey (Depree et al., 2015) at sites shown in Figure 3-1 showed that the seabed sediments in Lyall Bay comprise moderately to well-sorted, very fine to fine sands (except for two subsamples from sites 8 and 12 which were very fine gravelly sands). Across all sites (Figure 3-1), the average sand content was 97.4% (±0.7, 1 standard deviation), with 0.1% (±0.3) gravel, 2.5% (±0.7) silt and 0% clay. The median grain-size (D50) for all sand samples was 0.154 (±0.013) mm diameter, which is categorized as fine sand.

These grain-size data obtained by Depree et al. (2015) confirm previous work undertaken in Lyall Bay and along the Wellington south coast, with well-sorted fine sands forming a uniform sandy veneer that overlies pebbly gravels, which are often exposed as aprons around many of the submerged rocky reefs along the Wellington south coast (e.g., Arron and Lewis, 1993; Carter and Lewis, 1995; Wright et al. 2006). These very gravelly sediment substrates were not sampled by the recent AEE field study, since the focus was on the sandy substrates and their association with potential contaminantsDRAFT and infauna that might be affected by the proposed runway extension.

Figure 4-4: Surface sea-bed sediments of Lyall Bay and Wellington south coast (from Arron & Lewis 1993). Light-shade (fine sands); stippled shade (gravels and gravelly-sands) and red shade (bedrock).

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Since long sediment cores were unable to be obtained as part of the present study (Depree et al., 2015), the thickness of the uppermost fine sandy sediment is not known precisely in Lyall Bay. Previous studies suggest that the fine sand veneer is of the order of 1–2 m thick (Nodder, 1991, 1994; pers. obs.; Nodder and Smits, 1994), thinning closer to the coast where coarse-grained gravels and rocky outcrops are exposed eventually (e.g., Arron and Lewis, 1993). Figure 4-5 shows the results in sand cover estimates (in cm) from an early geophysical survey in eastern Lyall Bay by the then DSIR Geophysics Division (Davey, 1971; also cited in Rogers, 1971), that Dr Scott Nodder (NIWA) considered in the above estimate of the sand veneer. Further information is described in the Engineering Report (URS Ltd., 2015) based on recent boreholes in Lyall Bay for the Project.

DRAFT

Figure 4-5: Sand cover (cm) and the edge of bedrock estimated from an early geophysical survey of eastern Lyall Bay in 1971. Note: North is to the left of the image. Source: Davey (1971), Rogers (1971).

In terms of sediment mobility, Carter and Lewis (1995) have showed that fine sand (less than 0.25 mm diameter) will be typically stirred by wave activity at water depths less than 30 m for almost 50% of the time, especially in autumn through to spring, based on wave data from Lyall Bay by Pickrill (1979). Furthermore, under extreme swell wave conditions, even pebble-sized gravels (greater than 4 mm diameter) will be mobilised over water depths up to 60 m (Nodder, 1994).

Morphology of inner Lyall Bay The morphology of inner Lyall Bay was investigated by Pickrill (1979), covering long-term bathymetric changes and shoreline modifications (e.g. the runway extension) – information and aerial photos from which the 1941 shoreline was plotted in Figure 4-2.

Following the reclamation for the existing runway in 1959, shoaling occurred north of the spur groyne and adjacent to the revetment, with the largest accretion of 3–5 metres in waters which were deepest prior to reclamation as shown in Figure 4-6 (Pickrill, 1979). The map of accretion since construction of the runway reclamation (bottom panel) also indicates that the spur groyne and

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associated submerged rock outcrop is acting as a wave and hydraulic control, as there is no apparent accretion immediately behind (north) of the groyne/outcrop and the accretion thickness tapers off towards it. The modern bathymetry (Figure 3-3) also shows the shoal pinches in close to the runway revetment (e.g., dashed 5 m contour) about 150 m to the north of the groyne, matching the shadow wave diffraction zone (Figure 5-4 to Figure 5-7).

The beach and nearshore morphology and temporal changes in the morphology are a direct response to the wave climate, with the largest changes to the beach system taking place in the high-energy centre of the beach, with smaller changes (over and above the eastern shoaling) occurring at the more sheltered ends of the Beach (Pickrill, 1979). During periods of calm or low energy (including northerlies), the beach develops low berms, midway up the nearshore profiles, which is replaced by a concave planar profile during southerly storms. In winter, Pickrill (1979) observed landward retreat of the shoreline, with sediment removed forming an offshore bar, which grows and moves seaward. There tends to be a reversal of this process in summer. The annual sand budget was estimated to be at least 106,000 m3 by Pickrill (1979), with more than half of this sand accounted for by seasonal changes in morphology. The sediment-transport modelling at seasonal timescales undertaken for the Project, which incorporated one southerly-gale event, was able to mimic this offshore transport and bar formation in Lyall Bay (see Section 5.2.3). DRAFT

Figure 4-6: Historic bathymetric changes in Lyall Bay. A. Changes between 1903 Penguin and 1950 Lachlan surveys; B. Changes between 1950 and a NZ Oceanographic Institute survey in 1977. [Source: Pickrill (1979)].

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Over the last 100 years, the coastal environment has been modified considerably – coastal dunes have been replaced by housing, roading, a seawall built at the head of the beach, and the eastern part of the crenulate-shape beach reclaimed for the airport runway (Pickrill, 1979). A carpark also occupies the eastern coastal margin near the runway embankment. These modifications of the backshore have altered the planform shape of Lyall Bay Beach, and reduced the natural sediment buffering capacity, causing past issues with erosion of the seawall and overwash or wind-blown sand deposits during southerly storms. While the original vegetation is long cleared, revegetation of stretches along the foreshore and environs carried out by Wellington City Council and interest groups, provides a mosaic vegetation cover that is establishing slowly given the difficult climatic conditions (Boffa Miskell, 2015).

Eastern cove morphology A beach survey was undertaken by Nodder & Gerring (2015) on 5-February 2015 of the eastern cove (Moa Point beach) between the existing runway and Hue te Taka Peninsula (adjacent to Moa Point Road). The survey straddled one hour either side of low tide at 1335 h (NZDT), with fine weather conditions, slightly cloudy and a 20–25 knot northerly wind.

Beach slope profiles were measured using a surveyor theodolite and extendable measuring pole at twelve locations along the Moa Point beach that were either 20 m (transects #1-8) or 40 m apart (transects #8-12) as shown in Figure 4-7. At the lowest possible position on the lower beach-face, typically at or below the low-tide mark, a 1.5 m long steel probe, with a diameter of 20 mm, was hammered into the beach sediments using a fence-post rammer. The depth at which the probe could not penetrateDRAFT any further was noted.

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DRAFT

Figure 4-7: Aerial photograph of the beach at Moa Point showing the beach slope profile locations (transects #1-12). Source: NIWA field report (Nodder & Gerring, 2015)

The Moa Point beach is located in a small, west-facing pocket bay (cove) indented at the start of Moa Point proper (Hue te Taka) and east of the present airport runway. The natural geomorphology and backshore is modified to some extent by: the presence of the coastal road; the buried Lyall Bay marine outfall pipeline, which comes onshore at the northern/western end of the beach; and two sets of storm water discharge pipes.

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Moa Point beach can be divided into two coved sections north and south of the rocky outcrop (Figure 4-7).

Along the northern/western end of the eastern bay, the beach is backed by 2–3 m-high vertical “cliffs” in late Quaternary gravels and modern infill rubble that diminish in height along the beach to less than 1 m near the central part of the beach Figure 4-8. Here, the eroded gravels and rubble cliffs are replaced by low-lying sandy to pebbly gravel dunes covered in marram grass that extend up to the road. The eroded cliffs probably represent erosion only by the most extreme waves that occur episodically in Lyall Bay.

Figure 4-8: (Right): Western end of Moa Point beach with coastal cliffs at top right; (Left): Central area of exposed rock dividing the beach into two shallow-indented coves, looking along the cuspated beach from the southern/eastern cove. [Credit: P. Gerring, S. Nodder].

In the central part of the bay, a 40 m-wide area of exposed rocks extends offshore from the lower beach-face andDRAFT includes several small stacks that are exposed sub-aerially, even at high tide (Figure 4-8; right panel). The central rock outcrops effectively separate the bay into two smaller, shallow- indented coves; the cove at the western end is about 200 m long (transects #1-8; Figure 4-7) and that at the eastern end is about 120 m long (transects #10-12). Offshore, these rocks form part of a more extensive area of subtidal reef that extends out to at least 5 m water depth along the coastline of the entire northern/western embayment (Figure 4-7).

The Moa Point beach itself comprises medium to coarse sand (0.25–2 mm diameter) and well- rounded, pebble to cobble gravel-sized sediments (>2 mm, up to ~250-260 mm diameter). The sands and gravels on beach-face form a series of beach cusps where the gravels are arranged in lobate “horns” that point seaward and finer sand-sized particles occur in the intervening “embayments” (Figure 4-8; left panel), with larger and probably coarser cusps found north of the central rock outcrop than those to the south.

Penetration depths through the surficial sediments of the lower beach-face ranged from 0.1 to 0.8 m. Shallowest penetration depths of 0.1 and 0.2 m were encountered in the vicinity of the central rocky outcrops in the middle of the bay (transects #8 and 9; Figure 4-7). The probe measurements are only indicative (as probe resistance can be affected by single boulders, consolidated gravels, as well as bedrock. However, they show that the unconsolidated mobile sediments in this eastern cove generally occupy a relatively shallow veneer on the surface, with areas of bedrock acting as a control on any excessive beach erosion. Within the beach cusps, it appears that the pebble-cobble gravels that form the cusp “horns” are a veneer that may be only a single particle thick (i.e., perhaps from ~5

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to up to 25 cm-thick since most of the gravels are pebble- to cobble-sized). This veneer overlies the underlying medium-coarse sands.

4.3 Marine discharges and water/sediment quality Lyall Bay receives stormwater from the Lyall Bay catchment, the southern parts of the Miramar Golf Course and Wellington Airport and part of Moa Point Wastewater Treatment Plant. The approximately 280 ha catchment comprises 5 urban sub-catchments, namely (WCC, 2014; Depree et al., 2015):

• Lyall Bay West (118 ha), fully developed and outer residential, 4 major stormwater outfalls and one constructed overflow (sewage).

• Lyall Bay East (29 ha), fully developed and outer residential, 2 major stormwater outfalls.

• Airport South (57 ha), airport land, 1 major stormwater outfall.

• Strathmore Park South (57 ha), fully developed and outer residential, 1 major stormwater outfall.

• Moa Point (16 ha), fully developed and outer residential, wastewater treatment discharge.

The catchments discharge through a series of outfalls at Lyall Bay Beach, Moa Point, and near the breakwater at the south end of the airport runway. The discharge zone is therefore spread along a large exposed beach, breakwater and rocky coast, all of which are subject to relatively high energy from waves. Stormwater loads of contaminants (zinc, copper, lead and PAHs) are estimated to be around 5% of the total load from Wellington City (catchment comprises 4% of the total area). Despite some sourcesDRAFT of waste water (i.e., occasional partially-treated overflows), water quality is generally very good with respect to aesthetics and human health (WCC 2014). Chemical contaminants have not been previously assessed, but because of the high dilution and dispersion of the area, contaminants are not considered to have any significant effects in Lyall Bay (WCC 2014).

Outer Lyall Bay receives treated wastewater (and occasional partially-treated overflows following heavy rainfall) from the Moa Point Wastewater Treatment Plant that treats wastewater from most areas of Wellington City (except the Karori catchment). Treated and UV-disinfected wastewater is discharged into the marine receiving environment in Cook Strait via an outfall pipe that enters the CMA (buried initially) just to the east of the existing runway revetment. The outfall diffuser is located 1.9 km offshore, SSW of the existing Wellington Airport runway embankment in a water depth of 22 m (MSL), providing substantial initial dilution once the buoyant plume surfaces (Bell, 1989; WCC, 1990).

Despite sources of stormwater and wastewater (i.e., overflows), water quality is generally very good with respect to aesthetics and human health (WCC, 2014). Chemical contaminants have not been previously assessed, but because of the high dilution and dispersion of the area, contaminants are not considered to have any significant effects on marine organisms (WCC 2014).

The main findings from the recent AEE field investigation and laboratory analyses (Depree et al, 2015) of contaminants in the surficial sediments of Lyall Bay were:

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• Total extractable heavy metals (and arsenic) concentrations were consistent with background soil/rock for the Wellington region, with no measurable anthropogenic ‘foot print’ observed in the Lyall Bay surficial sediments.

• Total extractable heavy metal concentrations of arsenic, cadmium, chromium, copper, nickel, lead, zinc and mercury in Lyall Bay sediments (<2 mm fraction) were all well below ANZECC interim sediment quality ISQG guideline trigger (‘low’) values.

• Heavy metal concentrations at sites 10 and 11 (Figure 3-1) within the proposed runway extension area appear to be homogenously distributed to at least a depth of 0.2 m. Over this depth range, it is assumed that organic concentrations, similarly do not change (i.e., increase) markedly.

• DDT and associated analogues were the main organochlorine pesticides present in the surficial sediments of Lyall Bay, but the average concentration (±1 standard deviation) of 0.24 ± 0.15 µg/kg is 6-times lower than the current ANZECC ISQG ‘low’ trigger value of 1.6 µg/kg and below the pending revised ANZECC trigger value of 1 µg/kg.

• PAH concentrations ranged from 30 to 150 µg/kg in Lyall Bay sediments, with an average concentration (±1 s.d.) of 84±37 µg/kg, which is around 50-times lower than the ANZECC ISQG ‘low’ trigger value of 4,000 µg/kg and below the pending revised ANZECC trigger value of 10,000 µg/kg.

Contaminant concentrations in Lyall Bay surficial sediments are therefore very low and uniformly distributed across the study area, including at sites most likely to be disturbed by construction activities, namely, sites 10 and 11 in the area to be reclaimed (Depree et al., 2015). Mobilisation of sediment from 0–0.2 m depths from within the area of the proposed runway extension is not expected to resultDRAFT in any significant increase in sediment contaminant concentrations in surrounding areas.

From a contaminant perspective, the risk of adverse effects on the water column from transient sediment suspension/disturbance events during construction is very low given that water column concentrations, even after allowing for reasonable mixing, are estimated to be at least two-orders of magnitude lower than default ANZECC water quality trigger values (Depree et al., 2015).

The 5-week deployment of a mooring in Lyall Bay during the AEE investigations during September 2014 provided an assessment of the dynamics in optical water quality and estimates of total suspended sediment from turbidity over the early-spring month (MacDiarmid et al., 2015). The deployment captured calm periods and several storm events, with corresponding reduction in visibility range.

This 5-week snapshot showed that the waters were typical of clear water with a blue-green hue with more of browner colour during storm events due to sediment runoff (and re-suspension of bottom sediments by wave orbital motions). During the deployment reduced visibility (20–30 m down to <1 m) corresponded to storm events. Although limited to a snap-shot in time, this time-series provides a realistic range of conditions likely to be experienced in Lyall Bay (MacDiarmid et al., 2015; James et al., 2015). Total suspended sediment concentrations from grab water samples taken at the mooring site varied from 0.46 to 2.9 mg/L, corresponding to a turbidity of 0.3 to 2.2 NTU and secchi disc depth 5 to 11.5 m.

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An earlier study of water clarity and underwater light attenuation in Lyall Bay (Bell et al., 1992; Beca Carter-Caldwell Connell, 1980) for the marine outfall investigations at sites 1.8 and 2.5 km offshore (former is present outfall diffuser site), showed that significant penetration of short-wavelength visible light occurs in the Bay down to about 9–12 m, approaching quite clear ocean-type waters.

4.4 Winds Long-term wind and barometric pressure measurements have been collected from the following stations in the region around Wellington International Airport:

° main weather station at the Airport operated by NZ MetService since 1960 (Agent #3445)

° a newer automatic weather station (AWS) at the south end of the runway operated by NZ MetService (Agent #10331)

° Beacon Hill above Breaker Bay, operated by Port of Wellington from 1969 to 2004 (Agent #3440)

° Baring Head operated by NIWA since 1969 (Agent #18234).

The main Airport wind-gauge dataset now extends to a 54-year record and at Baring Head, a 45–year record. Wind roses from the earlier part of these records along with other Wellington wind gauges is shown in Figure 4-9, illustrating the spatial variability in distribution of wind directions.

Wind flows across central New Zealand are concentrated through Cook Strait and blow across the Wellington area almost always from either north/north-west or south/south-east, depending on location in theDRAFT Harbour (Figure 4-9). At Wellington International Airport and in Lyall Bay, winds are further influenced by local topography to be either northerly or southerly winds. Winds from the northerly quarter, which often includes when prevailing south-westerly flows occur over NZ, are more frequent than those from the south, especially in spring and summer, but many of the most severe storms have been southerlies (Quayle, 1984). Strong southerlies tend to be more frequent in winter.

A more up-to-date wind rose for Wellington Airport, covering a 43-year period up to 2004, was produced by Gorman et al. (2006) as shown in Figure 4-10. The average wind speed (based on an average speed for 10-minutes) over this long-term record was 7.4 m/s or 27 km/hr.

The maximum recorded 10-minute wind speed is 40 m/s or 145 km/hr, which occurred during ex- tropical cyclone Gisele (aka “Wahine Storm”) on 10 April 1968 from a SSW direction. Sustained winds above 110 km/hr blew for nearly 8 hours. A recent southerly gale on 20 June 2013 reached 101 km/hr, causing damage around Wellington, closure of the Airport and generated waves that matched those during Gisele.

Calm periods with winds <1 m/s occur for just under 3% of the time.

Waves in Lyall Bay are strongly influenced by the predominant bi-modal distribution of winds, from either the south or the north, with the latter generating much smaller short-period wind waves than the waves and swell that propagate into the Bay from the south.

Wellington International Airport Runway Extension: Coastal Processes 47 1 September 2015 6.36 p.m.

Figure 4-9: WindDRAFT roses for the Wellington area. Source: Quayle (1984).

Figure 4-10: Wind rose derived from hourly records of wind speed and direction at Wellington Airport from 1962–2004. Note: direction is in meteorological convention of where the wind blows from. [Source: Gorman et al. (2006)]

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4.5 Hydrodynamic and wave processes for existing environment

4.5.1 Tides, sea-level variability and volumes Wellington has a relatively small tidal range compared to other areas of New Zealand, with a spring tidal range of 1.36 m, 1.06 m average tide range and a neap-tide range of 0.76 m (Nautical Almanac, 2015/16). Lyall Bay has a slightly smaller tidal range than Wellington Port - about 0.02-0.04 m less for the average tide range (Walters et al., 2010).

Present-day tide-marks extracted from the Queens Wharf record at Wellington Port are shown in relative to WVD-1953 (Bell & Hannah, 2012). The present-day MSL is nearly 0.2 m above WVD-53, based on the average from the recent record 2006 to 2011.

DRAFT

Figure 4-11: Present-day tide marks at Wellington relative to WVD-53. Note: MHWS-10 is the level exceeded by 10% of all high tides; MLWS-10, low tide mark at which 10% of all low tides descend below, and MSL is the present mean level of the sea for period 2006-2011 [Source: Bell & Hannah (2012)].

Sea-level also varies at widely-different time scales, spanning:

° hourly to daily from weather influences including storm surge and seiching;

° monthly to annual for seasonal climate effects on sea level; and

° multi-year to decadal effects from longer-term climate cycles such as El Niño–Southern Oscillation of ENSO (2–4 year episodes) and the 20–30 year Inter-decadal Pacific Oscillation (IPO), both of which generate changes in sea level across the entire Pacific.

For Wellington, storm surges could reach over 0.7–0.8 m above the predicted tide. Variability of MSL on a monthly basis from seasonal to decadal climate influences can range from -0.16 to +0.20 m based on an analysis period 1945 to 2011 (Bell & Hannah, 2012). Higher than normal sea levels occur during La Niña episodes and the negative phase of the IPO (which we have been in since 1999). Conversely, monthly sea levels are lowest during El Niño episodes combined with a positive phase of the IPO.

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Wellington Harbour has experienced an average rise in relative sea level of 2.03 ±0.15 mm/year or 0.2 m in the last 100 years, which is relative to the inner-city landmass (Bell & Hannah, 2012).

The estimated average volume of water within Lyall Bay is around 27.19 Mm3 relative to WVD-53 (calculated from the ARTEMIS wave model grid area in Figure 3-6) covering a surface area of approximately 2.99 Mm2. Based on an average tide range,12 the proportion of seawater volume each tidal-cycle entering and exiting Lyall Bay to the total average volume of the Bay is only 11%, which reflects the relatively small role tides play in circulation of the Bay, particularly in Zone 1 (Figure 4-13).

4.5.2 Tidal and wind-generated currents

Previous relevant studies Previous information on hydrodynamic and wave processes from several studies have provided a reasonable sound basis for understanding the coastal physical processes that operate in the Lyall Bay environs (AES/NIWA, 2013). Much of the present knowledge on tides and currents along the south Wellington coast has been derived from environmental investigations in the 1980s associated with options for a long ocean outfall, to replace the shoreline outlet discharge into Lavender Bay, from the Moa Point Wastewater Treatment Plant and for the Hutt Valley outfall a Tunnel Point on the opposite side of the Harbour Entrance (locations in Figure 4-12).

For the Wellington outfall study, current meters at 2 m and 14 m above the sea-bed were deployed 1.5 km offshore in Lyall Bay in September 1989 (see location RCM in Figure 4-12), to support hydrodynamic and plume modelling for the Fitzroy and Lyall Bay outfall study by Bell (1989) for Wellington City Council and the then Hutt Valley Drainage Board. The measured currents and tide levels from this deployment were used to calibrate the hydrodynamic model for the present AEE (Pritchard et al.,DRAFT 2015). The median current speeds out beyond Hue te Taka Peninsula at the RCM site were reasonably modest at 0.075 m/s and 0.09 m/s respectively at the bottom and top mooring, reaching a maximum during wind events of 0.25-0.3 m/s. The main ebb-tide flow was NW towards Te Raekaihau at the upper mooring but more westerly nearer the seabed, which also aligns with the residual or deployment-average flow directions arising from the slightly stronger ebb-tide flows than the easterly flood-tide currents heading for the Harbour Entrance.

An earlier report on the oceanography of the area was undertaken by Beca Carter – Caldwell Connell (1980), based on drogues and dye-tracing studies to determine water circulation patterns in outer Lyall Bay and from current-meters moored off Lavender Bay and around West Ledge for a longer Lavender Bay outfall option. An even earlier report in 1971 on the feasibility of extending the Airport runway by the Ministry of Works & Development Central Laboratories, showed through drogue tracking that current velocities in inner Lyall Bay were weak (0.02–0.09 m/s), and mainly generated by surface winds, with the observation that tidal currents only seem to occur outside the Bay (Rogers, 1971).

A schematic of the tidal-current circulation in Lyall and Lavender Bays was developed in WCC (1990) from the information from these two previous 1980 and 1989 oceanographic studies and is reproduced in Figure 4-13 for ebb-tide flows (top panel) and incoming flood-tide flows (bottom panel). Tidal currents weaken considerably once inside the confines of Lyall Bay marked as Zone 1 in Figure 4-13.

12 averaging spring and neap ranges for Wellington- NZ Nautical Almanac 2015/16 and subtracting 3 cm for Lyall Bay

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A recent 2013 project for Opus Consultants and Capacity infrastructure Services Ltd. on the Lyall Bay outfall discharge was based on modelling the hydrodynamics of the south Wellington coast including Lyall Bay using a depth-averaged Delft 3D model grid that also included Wellington Harbour. This hydrodynamic model was further refined as part of the present Project, with new bathymetry from Lyall Bay (Mackay & Mitchell, 2014) included in a higher-resolution grid and a SWAN wave model grid by Pritchard et al. (2015) as shown above in Figure 3-4. The generally low currents within inner Lyall Bay, where regular tidal currents are very weak, explained why plume dispersion from the Lyall Bay marine outfall is more influenced by lateral mixing and spreading rather than dominated by transport processes such as stretching and shearing from higher currents and spatial gradients in velocity.

DRAFT

Figure 4-12: Alignment of the as-built Lyall Bay outfall (white line) and sites for the Baring Head NIWA wave buoy and a recording current meter (RCM) in Lyall Bay in September 1989. Image source: Google Earth.

AEE investigations Measurements from the ADCP current meter moored during the 2014 field programme at Site 1 near the spur groyne (Figure 3-3) indicated that tidal currents were statistically inseparable from back ground noise in the velocities measured. Hence, tidal currents were basically not able to be detected within the accuracy performance of the ADCP.

Further out near the outer entrance to Lyall Bay, where the tidal currents of Cook Strait are stronger (average of 0.1–0.3 m/s), the comparisons between the observed and predicted tidal currents by the hydrodynamic model indicated good agreement, indicating the hydrodynamic model is performing well.

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A summary of the current circulation zones in Lyall Bay from an earlier study for the marine outfall is shown in Figure 4-13, which still largely applies with the new current-meter data now available from inner Lyall Bay near the runway.

DRAFT

Figure 4-13: Lyall Bay and Moa Point circulation zones during an ebb tide (top) and a flood tide (bottom). Solid back lines represent ocean outfall options for the 1990 wastewater treatment plant study. Source: From Fig. 5.3 of Wellington City Council (1990) after Bell (1989).

Current-meter observations from Site 1 (Figure 3-3) during the 2014 field programme show that substantial wind-driven currents can be generated within Lyall Bay, in comparison with the weak tidal currents, especially during strong winds (Pritchard et al., 2015). Currents at Site 1 were typically less than 0.1 m/s, but during the two southerly-gale events, currents reached 0.32–0.37 m/s. There was a considerable degree of scatter in current directions with time and with depth through the 10-

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m water depth, which are probably influenced by the proximity to Site 1 of the submerged rock outcrop off the spur groyne (Figure 3-3).

Wind fields during the 2014 field deployment were more dominated by southerly winds, with one event reaching 80 km/hr. However, the longer term climatic records of the area (Section 4.4 above) show that strong northerly winds also occur with similar or higher frequencies.

To investigate wind-driven circulation inside Lyall Bay, a time series of idealised northerly- and southerly-directed winds peaking at 80 km/hr were modelled for both the existing and the proposed runway extension scenarios, superimposed on a repeating average lunar tide cycle to focus more on wind circulation. The circulation patterns of wind-driven currents for both strong southerly and northerly winds is discussed in Section 5.2.1. Of particular note is the strongest wind-driven currents are downwind along the shallower waters around the periphery of Lyall Bay with a slower, but broader return flow upwind in the deeper central waters of the Bay, although the southerly-wind case generates a more complex twin eddy-circulation system (Figure 5-2).

4.5.3 Waves and swell Lyall Bay and the southern terminus of the Airport runway is very exposed directly to the south and hence can be subjected to large waves generated by southerlies in the Greater Cook Strait region through to long-period swell from remote storms in the Southern Ocean (e.g., Figure 4-14). A recent example was the damaging swell in Lyall Bay on 15–16 June 2015 on a fine sunny day, generated by a deep low-pressure system well to the southeast of New Zealand. Complex wave patterns occur locally around the existing runway embankment and the associated spur groyne, with wave diffraction occurring around the latter (Figure 4-14) and wave refraction further bending the shoaling waves into TheDRAFT Corner area.

Figure 4-14: Wave refraction and diffraction patterns during a southerly-swell event on 29 April 2015. [Credit: DigitalGlobe (2015), Google Earth].

When swell is present, surfing is popular in Lyall Bay, particularly in The Corner (Figure 4-15) but also off the middle of Lyall Bay Beach, depending on wave conditions.

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DRAFT Figure 4-15: Surfing waves at The Corner viewed from the stormwater outlet adjacent to the eastern carpark (30 June 2015). [Credit: Dave Allen, NIWA].

Long-term wave climate for south Wellington Coast NIWA operates a Datawell Waverider buoy off Baring Head on behalf of the Harbourmaster at GWRC. The buoy is moored in 45 m water depth approximately 1.6 km offshore from Baring Head (Figure 4-12). A buoy has been operating in this location since 1999 apart from some brief periods of equipment failure, and has provided a 15-year record of wave conditions at the Baring Head.

13 Wave statistics: significant wave height (Hs), mean zero-crossing period (Tz), and the maximum individual wave height (Hmax), have been derived for 30 minute intervals from the 20-minute measurement bursts during the 15-year Baring Head record. While the Waverider at Baring Head is 10 km from the southern end of the runway, both locations have similar exposure to southerly swell, but the airport site is more protected from swell with any easterly component. The significant wave height (Hs) versus wave period (Tz) distribution (Figure 4-16) shows that the majority of waves measured off Baring Head are relatively low (0.1–1 m) short-period (3–7 secs) waves and that the more highly publicized wave events of over 5 m are relatively rare.

13 Hs or significant wave height is a derived representative value related to the variance of the wave height and is the average of the top 33% of waves measured each 20-min period. One can expect occasional individual waves of as much as 2×Hs, perhaps every few hours.

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Figure 4-16: Significant wave height (Hs) vs mean zero-crossing wave period (Tz) distribution as a % of the entire 15-year Waverider buoy record off Baring Head. [Credit: Craig Stevens, NIWA]

Focusing on significant wave height (Figure 4-17), although distorted by the vertical log scale, it is clear that the majority of waves are in the range where Hs<2.0 m and significant wave heights exceeding 3 m and 5 m only occur on average for a cumulative time periods of 14 days and 1 day per year (3.8% and 0.3% of the time) respectively as shown in bottom panel (Figure 4-17). Note that individual wavesDRAFT up to twice this height will occasionally appear. Persistence of calmer wave conditions will be an important consideration for construction windows at critical phases of the runway-extension reclamation. An analysis of the wave dataset from off Baring Head shows there are on average 4–5 events with significant wave height remaining below 1.5 m (arbitrary threshold) over a 5-day window or longer every quarter. However, there is an identifiable reduction in number of occasions when waves are below a wave-height threshold in the winter and early spring quarter (July–September).

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Lyall Bay wave climate Some shorter records provide further insights on the wave climate within Lyall Bay in comparison.

The then Ministry of Works & Development Central Laboratories deployed two Waverider buoys for ~20 months from October 1978 through to mid-1980 in outer Lyall Bay (near the site marked RCM in Figure 4-12) and further to the east near the end of West Ledge. Some of the data is reported in Beca Carter–Caldwell Connell (1980; Fig 7-6) – and a summary of the deployment in a Central Laboratories report (Valentine, 1980). Significant wave height (Hs) in outer Lyall Bay was above 1.48 m for 50% of the time (median) and exceeding just under 3.0 m for 5% of the time and exceeding 4.1 m for 1% of the time (Valentine, 1980). Comparing these more limited outer Lyall Bay measurements with the frequency-wave height from the long-term Baring Head record (Figure 4-17; e.g., 0.95 is just under 3 m and 0.99 is 4.1 m) shows that wave heights in outer Lyall bay are similar in general to waves at the Baring Head buoy site. Zero-crossing wave periods also show similar distributions with significant wave height at both sites.

For extreme wave heights, significant wave height reached was 7 m in outer Lyall Bay (on 3–4 January 1980 during the deployment in 1978–80), and over 9 m in the much longer Baring Head for the 20 June 2013 event, with a maximum wave height of 15 m for the same storm (Pritchard et al., 2015). Such high waves would break before reaching the end of the existing runway, with physical

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model studies showing the highest waves would reach 5–5.5 m based on a wave period of 11.5 seconds (Webby, 1984).

A recent ~7-week deployment of an ADCP to the SW of the spur groyne (breakwater) and a wave- pressure gauge further out in the Bay (Figure 3-3) for the present AEE investigations from August to

Oct 2014 (Pritchard et al., 2015). At Site 1 (Figure 3-3) off the runway, significant wave heights (Hs) were above 2 m on seven occasions due to the preponderance of southerly-wind events, with a maximum significant wave height of 4.7 m and mean wave period of 11 seconds (i.e. swell) recorded on 22-Sept-2014 during a southerly gale reaching 80 km/hr wind speeds (Pritchard et al., 2015). During northerly winds, the significant wave height generally dropped to <0.5 m, but sometimes a ground swell from the south overrides the local wind sea e.g., significant wave height reached 2.5 m in Lyall Bay on 25-Sept-2014 during a northerly wind of 20-35 km/hr. Wave direction at Site 1 were almost completely dominated (90%) by wave from due South with a smaller proportion of measured waves from the SSE direction. Assessment and subsequent wave modelling (e.g., Figure 4-18) and aerial images indicate that there is around an 8° bias towards the east in the measured wave- direction, as waves at Site 1 tend to arrive in a very narrow directional window from due south or slightly west of south (Pritchard et al., 2015).

Further out in Lyall Bay at Site 2 (Figure 3-3), the same southerly gale on 22-Sept-2-14 produced higher significant wave heights peaking at 6.1 m at a similar wave period, and compared more closely with concurrent measurements at the Baring Head wave buoy of over 6 m (6.5 m peak). By inference comparing the peak waves during the southerly gale at Sites 1 and 2, the wave heights attenuate somewhat as they propagate and shoal within the inner part of Lyall Bay.

As part of the AEE investigations, wave modelling using SWAN was undertaken for a 55-day period covering the 2014 instrument deployment (Section 3.4.1). Detailed results of the spatial distribution of wave heights and period are provided in Section 4 of the Coastal Processes Technical Report (Pritchard et al.,DRAFT 2015), but a summary of the main wave patterns in Lyall Bay are repeated here. Wave statistics output from the SWAN model were averaged over the 55-day simulation period in

2014. While a simple time average was taken for significant wave height to produce a mean Hs over this period, a mean value of mean wave direction was obtained by vector averaging, weighted by wave height. The spatial pattern of average significant wave height and direction are shown in Figure 4-18, which shows a similar pattern of spatial variability in wave height to what was seen in the two strong southerly events during the field deployment. Attenuation of wave heights is more pronounced on the western side of the bay where depths are shallower, with a smaller degree of attenuation through the deeper waters to the area off the existing runway, as discussed above. The SWAN model results also show localised amplification of average wave height off the spur groyne and submerged rock outcrop, as frequently observed. The waves in the cove on the eastern side of the runway are substantially dampened and refracted as they approach the curved shoreline.

Normally to establish a long-term wave climate, several years data is required. For Lyall Bay, the 55- day wave model simulation undertaken is shorter than would be required to produce long-term wave climate statistics for Lyall Bay. However, the 55-day field deployment produced a wide range of wave conditions including an infrequent southerly-gale event, plus we have the benefit of comparing with the long-term wave climate from the Baring Head wave buoy. Therefore summary wave statistics from the 55-day simulation primarily illustrate spatial variability within Lyall Bay, if not a full representation of longer-term temporal variability.

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Significant wave height and mean wave direction are shown in Figure 4-19 from three representative sites in Lyall Bay (shown in Figure 4-18), out of the 18 sites presented in the Coastal Processes Technical Report (Pritchard et al., 2015). These results show a shift in significant wave height distribution at inner Bay sites (6–mid inner Bay, 15- off runway) by about a 0.25 m histogram bin relative to the location in the outer Bay (site 4), due to attenuation of wave in the confines of the Bay. Mean wave directions vary spatially as a result of wave refraction processes e.g. wave trains have a more SSW wave approach off the runway than from due south further west in Lyall Bay off the spur groyne (also in Figure 4-14).

Wave refraction and diffraction patterns for the existing situation in Lyall Bay are presented in Section 5.2.2.

4 DRAFT

Figure 4-18: Wave conditions averaged over the 55-day SWAN simulation, in Lyall Bay. Mean significant wave height is shown by the colour scale, and contours at 0.1 m intervals. Black arrows show mean wave direction. Sites marked in grey relate to the next Figure. [Credit: Richard Gorman, NIWA].

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Figure 4-19: Distribution of Hs from 55-day simulation (top panel) and wave roses (joint occurrence distributions for mean wave direction and height) (bottom panel) at sites 4, 6, 15. Sites marked in Figure 4-18 – Site 4 is same site where the outer wave instrument was deployed. [Credit: Richard Gorman, NIWA]. 5 Effects Assessment: Operation of Project

5.1 Description of operational effects It is proposed that the reclamation works for the runway extension will be undertaken in several steps, as detailedDRAFT in the Construction Methodology Report (URS Ltd, 2015). The permanent aspects of the works relevant to coastal physical processes:

° Stone blanket (or filter) of approximately 5 m width on the seafloor around the outer periphery of the wave–protection structure to protect the structure from toe scour and provide a transition between the large rock and accropode elements and the natural mobile sediments of the adjacent seabed. The outer perimeter of the permanent works is approximately shown in Figure 2-1.

° Toe structure approximately 15 m wide and 1–2 m thick between the sloping revetment and stone blanket comprising larger rocks in the outer section transitioning to smaller accropodes at the base of the main revetment.

° A 1:1.5 sloping revetment (or dyke) and topped off with an approximately 10 m berm comprising large accropodes. This structure will act as the main protection against large breaking waves and absorb much of the incident wave energy.

° The lineal distance offshore of the proposed reclamation is approximately 350 m south into Lyall Bay from the present wave-protection revetment, with an additional ~35– 45 m length underwater for the revetment batter and toe rock apron in approximately 13 m water depth (MSL).

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° The orientation of the runway-extension reclamation will be slight west of south at approximately 183°S, compared to the predominant wave-approach direction from due South.

The 3-D profile of these structural elements surrounding the proposed reclamation have been incorporated into the fine-resolution grid used for wave modelling (right-hand panel; Figure 3-5) and to a lesser extent resolved by the schematized grids used for assessing changes to flows and sediment transport patterns.

The estimated water volume of Lyall Bay displaced by the proposed extended reclamation is around 995,000 m3, based on a comparison of the volume for the two ARTEMIS model grids (Figure 3-6) before and after the extension relative to WVD-53, which is around 3.5% of the still-water volume of Lyall Bay out to the end of the rock outcrop off Te Raekaihu Point.

Following completion of construction of the Project, these elements of the overall structure, particularly the footprint and 3-D profile shape of the outer “surfaces” acting as an obstacle to flows and waves, will lead to permanent (operational) effects of varying degrees on coastal physical processes. Any ongoing effects of the present runway and wave-protection revetment are not considered, as these elements form part of the existing environment.

The permanent effects of the Project on coastal physical processes considered were changes in (relative to the existing situation):

° Tidal current-flow patterns

° Flow circulation by wind-generated currents

° Spatial wave and swell patterns

° DRAFTSediment transport (short-term and seasonal) and associated morphological response

° Long-term morphological change for Lyall Bay Beach

As the potential effects on inshore wave patterns were highlighted early in the AEE investigations, surfing and recreational-related effects are given greater scrutiny when assessing the degree of coastal environmental impacts. Subsequently, a more detailed, complementary assessment has been provided by DHI (2015). This AEE Technical Report only describes likely changes in wave patterns, but the effects of these changes on water-contact recreation activities such as surfing, kite-surfing and swimming and possible mitigation options are covered by DHI (2015).

This Report also does not cover assessments of the effects of the Project on coastal-hazard extremes (e.g., waves, tsunami, storm-tide) or climate-change effects, such as sea-level rise, which a covered in the Engineering Report (URS Ltd) and the AEE.

5.2 Assessment of operational effects The follow sub-sections outline the key findings from the Technical Report on Coastal Hydrodynamics and Sediment Processes in Lyall Bay (Prichard et al., 2015) and determine the degree of effects in each case.

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5.2.1 Tidal and wind-driven currents The 350-m extension of the proposed reclamation will jut out further into Lyall Bay than the present runway which blends in more with the coast along the cove to the east adjacent to Moa Point Road (Figure 4-2). Consequently, the extended reclamation will partially block current flows locally potentially affecting local circulation.

The hydrodynamic modelling of the before and after runway extension simulations highlighted the following predicted changes to current flows.

Tides only Within inner Lyall Bay, the predicted tidal currents by the model are very weak both for the existing situation, mirroring the measurements at Site 1, and for the proposed extension. Consequently, the proposed runway extension will have negligible effect on tidal currents (excluding the wind component).

Residual circulation (winds and tides) Residual or net current circulation is the current pattern remaining after the to and fro tidal and wind-generated movements have been averaged out, and is indicative of flushing and general circulation within an embayment such as Lyall Bay. The residual is generated by vector-averaging the predicted velocities spatially across the model domain (taking into account both speed and direction) over a given period – in this case the ~7-week field deployment period from August to October in 2014 (Section 3.3). This period included a strong southerly gale of 80 km/hr on 22 September, but less stronger northerlies.

The modelled magnitude and direction of residual circulation within Lyall Bay both before and after the proposed runway construction is presented in Figure 5-1. The circulationDRAFT in the outer part of Lyall Bay beyond the end of Hue te Taka Peninsula and Te Raekaihu Point is governed by the stronger ebb-tidal currents that start to enter the Bay and exit back out into Cook Strait on the west side (Figure 5-1). The residual (net) current analysis indicates the existence of two weak residual eddy-like circulation patterns within Lyall Bay with small net- current amplitudes of order <0.06 m/s.

In the mid-section of the Bay (up to the end of the present runway), a residual anti-clockwise circulation occurred for the sequence of winds (mainly southerly) and tides during the field deployment period. This residual current pathway heads towards Moa Point and the eastern shoreline before turning west at the end of the present runway embankment (Panel A; Figure 5-1). The introduction of the proposed runway extension (panel B; Figure 5-1) would partially interrupt and re-direct this westerly net flow inshore beside the present runway, given the same set of tidal and wind conditions, and would form two more quiescent zones (negligible net currents) either side of the proposed runway extension. This would provide less general flushing of the cove east of the proposed runway extension, but given it is still open and exposed to waves, this effect on coastal physical processes would be minor.

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Figure 5-1: Residual (net) current circulation in Lyall Bay over the ~7-week field deployment period. Existing environment (A) and proposed runway extension included (B).

Further inshore, off Lyall Bay Beach, a weak residual clockwise circulation occurs, generating a weak north-eastwards net transport in the nearshore towards The Corner and southwards along the existing runway embankment for the field deployment period (Panel A; Figure 5-1). Along with wave diffraction around the spur groyne and rock outcrop (covered later), this albeit weak net drift towards the NE corner of the Bay could partially explain the overall seabed accretion that has occurred in the eastern side of the Bay adjacent to the runway embankment (Figure 2; Pickrill, 1979). The proposed runway extension would have a negligible effect on this inner Bay circulation cell (panel B; FigureDRAFT 5-1). The inter-comparison of results from these net (residual) circulation simulations indicate that overall the proposed runway extension is likely to have only a minor localised effect on the residual circulation within the middle section of Lyall Bay and a negligible effect on residual circulation in the nearshore area off Lyall Bay Beach.

Strong-wind current circulation The current-meter observations show that substantial wind-driven currents can be generated within Lyall Bay, relative to tidal currents, especially during strong winds.

Wind fields during the 2014 field deployment were more dominated by southerly winds, with one event reaching 80 km/hr. However, analysis of the longer term climatic records of the area show that strong northerly winds also occur for similar frequencies (Section 2; Pritchard et al, 2015).

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In response to strong southerly-wind conditions, the most intense wind-driven currents flow north (down-wind) in the shallow water along the periphery of both the western and eastern shores of Lyall Bay – more so on the former (top-left panel; Figure 5-2). At the head of the Bay, the currents then turn clockwise and flow eastwards along nearshore zone, then south along the existing-runway embankment before being deflected WSW by the spur groyne and rock outcrop into the centre of the Bay. This clockwise eddy then converges with counter-clockwise eddy that extends from the eastern shore of the outer Bay at Moa Point and westwards across the end of the existing runway out into the central Bay. This mid-bay eddy would be partially intercepted by the proposed runway extension (top-right panel; Figure 5-2) that forces the down-wind drift into the cove at Moa Point to turn into the wind around the runway extension, weakening the flow into the central Bay.

Based on a visual comparison of the modelled southerly-wind scenario for before and after the runway is extended (top panels; Figure 5-2), there is likely to be only relatively localised effects on the wind-generated current flows during southerlies caused by the extended runway embankment from local re-steering of the downwind flow along the eastern Bay and slightly faster velocities across the end of the extended runway than presently occur at the same location. A stone blanket on the seabed around the periphery of the proposed revetment will protect any mobilising of seabed sediments due to this slight higher wind-generated current across the southern end in proximity to the structure.

DRAFT

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DRAFT

Figure 5-2: Current circulation at mid-flood tide (HW-3 hrs) for strong southerly winds (top) and northerly winds (bottom) for the existing situation (left panels) and the proposed runway extension (right panels).

In response to strong northerly-wind conditions, the most intense wind-driven currents flow south (down-wind) in the shallow water along the periphery of both the western and eastern shores of Lyall Bay – more so on the unimpeded western side (bottom-left panel; Figure 5-2).

The down-wind outflows along the eastern and western sides of the Bay cause waters to be drawn in from Cook Strait through the central Bay to maintain water volume equilibrium. This is seen as a tongue of inflowing water directed up-wind to the north. At the head of Lyall Bay, the inflowing tongue of water then bifurcates and forms a dipole circulation. The flow on the west side of the Bay turns counter-clockwise and merges with the wind-driven southerly outflow, and the flow on the eastern side forms a clockwise eddy that eventually converges with the northerly inflow in the central Bay. The eastwards flow into The Corner area (see location in Figure 4-2), is in the same direction as for southerly winds, although considerably weaker, thus both northerly and southerly winds contribute to the easterly residual current in the NE corner of the Bay. This pattern fits with

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the seabed accretion that has occurred in this area since the runway was extended into Lyall Bay in the late 1950s (Figure 2; Pickrill, 1979).

Summary of effects on wind-driven current patterns The Delft2D model simulations indicate that there would be little change in Lyall Bay wind-driven circulation during strong northerly winds, other than minor localised changes around the runway embankment area, comparing both bottom panels in Figure 5 2. Circulation during northerly winds would remain largely unaffected in the Bay by the proposed extended runway.

During strong southerly winds, the simulations indicate that the proposed runway extension would slightly weaken the counter-clockwise eddy-driven outflow through the central area of Lyall Bay that passes off the existing-runway terminus. This mid-bay eddy would be partially intercepted by the proposed runway extension that would force the down-wind drift into the cove at Moa Point beach to double back in order to pass around the extension, thereby weakening the flow into the central Bay. The simulations suggest that the extension would somewhat weaken wind-driven currents over a broader the convergence zone between the inner-bay clock-wise eddy and mid-bay eddy, relative to the existing situation. This slightly weaker and broader flow convergence zone would only have a minor effect on the wind-driven hydrodynamics of the central Bay and is unlikely to affect morphological change or flushing of the inner Bay. The local re-steering of the downwind flow along the eastern Bay would also produce slightly faster velocities across the end of the extended runway than presently occurs at the same location 350–400 m off the present runway terminus, as would be expected.

5.2.2 Waves and swell: spatial changes Chapter 5 of the Technical Report on Coastal Hydrodynamics and Sediment Processes in Lyall Bay (Prichard et al., 2015) describes in detail the various effects of the proposed Wellington International Airport runwayDRAFT extension on Lyall Bay wave patterns from the modelled results, focusing on the changes relative to the present shoreline and runway configuration. The following sub-section outlined the main results for assessing effects on waves from the proposed runway extension.

Changes at locations within inner Lyall Bay Results from the ARTEMIS wave model were initially extracted from 8 point locations (“P”) throughout the Bay as shown in Figure 5-3.

These results provide predictions of changes in wave height at a limited set of locations, but across the full range of wave heights and wave periods applied to the outer Cook Strait boundary of the model, to compare before-and-after construction wave scenarios. The majority of locations were focused on the eastern side of the Bay, including near The Corner (“P1”). However, as will be shown below, extracting results from specific points only provides part of the picture – which complements the analysis of the full spatial changes in wave heights for a sub-set of four particular wave conditions.

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Figure 5-3: Lyall Bay bathymetry plots showing the point extraction sites (P1–P8) for assessment of changes in wave heights. Lines show the extraction transects (T1–T8) discussed in Coastal Hydrodynamics and Sediment Processes technical report.

Table 5-1 and Table 5-2 shows the absolute change in significant wave height locally for site P1 (near the corner) and P4 in the centre of inner Lyall Bay. The Tables are ordered as matrix (rows and columns) of waveDRAFT period and wave height applied at the outer-Bay boundary (not the local wave height), with the contents of the matrix listing the change in wave height at the specific location after the runway extension is in place, relative to the existing situation. The changes have been colour- coded according to the scale on the right-hand side. A negative value for change implies a reduction in wave height by that amount listed in the Table.

At site P1 (near The Corner) the proposed airport runway extension would result in the greatest change on wave heights (Table 5-1) for incident significant wave heights of 3–5 m and periods of 5– 13 seconds (i.e., mainly steep wind-sea or medium-range swell), with reductions of over 0.4 m in wave height for these combinations. The relative change at P1 for these combinations would be around 22 to 40% percentage reduction of the wave height relative to the existing situation. For surfing wave conditions of 1–3 m wave heights at 10–15 second periods, the reduction is slightly lower, with a 16–17% reduction for incident waves of 1–1.5 m at P1 for those wave periods. The highest reduction at P1 in significant wave height from the runway extension is 0.78 m or a 40% reduction locally compared to the existing wave height, for the scenario of an incoming steep 5- metre wind wave of only 5 seconds period at the entrance to Lyall Bay.

At site P4, in the middle of inner Lyall Bay (Figure 5-3), there is no appreciable change predicted in wave heights as a result of the proposed airport runway extension, across the range of incident wave heights and periods applied at the offshore boundary of the model (Table 5-2).

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Overall, the main changes in wave height predicted for the eight selected locations (Figure 5-3) occur for sites near or “downstream” of the proposed runway extension, with smaller changes in wave heights across the wider inner Bay for wind-waves but less so for swell.

Table 5-1: Change in predicted wave heights locally at site P1 near The Corner as a result of the runway extension. Axes list the wave period and wave height applied at the Cook Strait boundary of the model. Negative change is a reduction in wave height.

DRAFT

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Table 5-2: Change in predicted wave heights locally at site P4 in the centre of inner Lyall Bay as a result of the runway extension. Axes list the wave period and wave height applied at the Cook Strait boundary of the model. Negative change is a reduction in wave height.

Changes in wave heights spatially within Lyall Bay This sub-section focuses on the overall spatial pattern of changes in wave heights and refraction and diffraction of DRAFTwave crests. A limited set of results is presented for the more common sets of waves, covering incident wave heights of 1.5 and 3 m and periods of 8 and 12 seconds, spanning wind-waves (period 8 seconds) and the combination of 1.5 m and 12-second swell that represents a surfable wave, and a higher 3-m swell.

Spatial plots of the wave heights (Figure 5-4 to Figure 5-7) are presented side-by-side to compare the ARTEMIS model results for the existing environment with those for the proposed runway extension in place (top panels), followed underneath by a spatial map of the differences in wave heights that are predicted to arise from the extended runway, relative to present.

Figure 5-4 shows the spatial variability in wave height comparing present versus runway extension and the predicted change in wave height for a 1.5 m boundary incident wave height with a period of 8 seconds. The main features of the spatial wave pattern for this combination for the existing environment (left-hand top panel) are:

° the zone of highest waves inshore occur in the central part of the Bay and the beach (between transect lines marked T1 and T2), with little attenuation in wave height from the southern entrance to the Bay

° high attenuation in wave height through refraction in the western part of inner Lyall Bay, where depths shoal quickly (blue and yellow areas of Figure 5-4)

° in the eastern sector north of location P2, including The Corner, the wave field spreads out behind the spur groyne and rock outcrop due to both diffraction and refraction,

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with attenuation of wave heights e.g., 0.7 to 1.2 m for an incident offshore wave of 1.5 m

° substantial attenuation of wave heights within the cove adjacent to Moa Point Road to the east of the existing runway (e.g., location P5) in the wave shadow of Hue te Taka reducing 1.5 m incident wave heights to around 0.1 to 0.5 m.

These same features are also evident in the spatial pattern of the mean significant wave height simulated by the SWAN model for the 2014 field-deployment period in Figure 4-18 described in Section 4.5.3 of this Report.

Turning to the spatial wave patterns predicted after the runway has been extended, the main changes shown for a 1.5 m incident wave height and 8-second period are (mainly bottom panel of Figure 5-4):

° the zone of highest waves in the central part of Lyall Bay and the beach (between transect lines T1 and T2) would largely be unaffected – with only small differences due to the runway extension, but with some patches of increases wave height for the given scenario (grey areas of Figure 5-4).

° the greatest change from the existing situation would be a reduction of 0.7–0.8 m in wave height along the western revetment of the runway extension through to the existing spur groyne, which is due to: a) the frictional (drag) effects on the wave trains as they pass alongside the accropodes protecting the extension, and b) a partial shadow zone created by the slightly-west of south alignment of the runway revetment.

° in the eastern sector of the Bay north of the spur groyne, the waves would be attenuated by a reduction of 0.2 to 0.6 m in a zone extending out ~250 m from the DRAFTexisting runway revetment. The greatest wave-height reduction would be 80–100 m NW of the spur groyne, with a local increase (relative to present) in these 8-second wind waves immediately behind the spur groyne through diffraction. In The Corner, the wave-height reduction would be somewhat less at 0.2 to 0.4 m.

° a localised increase in wave height around the spur groyne (breakwater) and submerged rock outcrop (grey areas of Figure 5-4)

° a patch of increased wave height (relative to present) near the beach towards the eastern end of Lyall Bay Beach (grey area of Figure 5-4 near The Corner). This arises due to the reduced wave height offshore from this part of the Beach, able to propagate (shoal) slightly further inshore than is the case for the existing situation, given the same wave height and period offshore.

° reduction in wave heights within the cove immediately adjacent to the east side to the extended-runway revetment

° negligible changes in wave height in the rest Lyall Bay including the western side, outside the proximal areas near the runway (existing and proposed extension).

Figure 5-5 shows the spatial variability in wave height comparing present versus runway extension and the predicted change in wave height for a 1.5 m boundary incident swell with a longer period of

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12 seconds. The differences in features of the spatial wave pattern for this swell combination for the existing environment (left-hand panel), compared with the 8-second wind waves are:

° the zone of highest waves in the central part of the Bay and the beach exhibits a wider spread than for the 8-second wave trains (top-left panel; Figure 5-4)

° comparatively higher waves propagate into The Corner than for shorter-period wind waves, with a 60-65 m swath of higher waves propagating into The Corner parallel and some 50 m off the existing runway revetment, east of location P1 (Figure 5-5)

° swell is refracted and diffracted around the lee of the spur groyne and associated rock outcrop, leading to less of a shadow zone than for shorter-period wind waves.

The bottom panel of Figure 5-5 shows the predicted changes, after the runway is extended, would show a similar spatial pattern of changes in wave heights as for the 8-second waves (Figure 5-4). The main differences would be a somewhat smaller reduction in wave height as swell peels along the western side of the extended revetment and a wider shadow zone in eastern part of inner Lyall Bay with reductions of 0.2 to 0.6 m. The eastern most swath of propagating swell, adjacent to the existing runway revetment, is predicted to be slightly narrower and around 0.2–0.4 m lower in wave height than for the existing situation for a 1.5 m incident wave height. There would also be a wider area of lower wave heights centred on site P1 (Figure 5-5). The patches where wave heights are predicted to increase, would cover a smaller area around and in the lee of the spur groyne, but a slightly wider area in the central inner-Bay area and in the nearshore Beach area just off the breaker zone (grey areas in Figure 5-5).

Figure 5-6 shows the spatial variability in wave height comparing present versus runway extension and the predicted change in wave height for a higher 3 m boundary incident swell with a period of 8 seconds. TheDRAFT spatial wave pattern for this higher wind-wave combination for the existing environment is similar to that predicted for the 1.5 m wave of the same wave period (Figure 5-4). The only obvious difference is the breaking zone is further offshore as expected for higher waves.

The predicted spatial changes in wave height arising from the runway extension are also similar to the smaller 8-second wave (compare lower panels of Figure 5-4 with Figure 5-6), but with a smaller increase in wave heights immediately behind the spur groyne for the higher waves.

Figure 5-7 shows the spatial variability in wave height comparing present versus runway extension and the predicted change in wave height for a 3 m boundary incident swell height with a period of 12 seconds. Again, the spatial pattern of changes in wave height is similar to that predicted for the 1.5 m wave of the same wave period (Figure 5-5), apart from breaking further offshore and less of an increase in wave height immediately behind the spur groyne.

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DRAFT

Figure 5-4: For a boundary incident wave height of 1.5 m with a wave period of 8 seconds: (Top) Spatial variability of wave height for existing situation (left) and with the proposed runway extension (right), and (bottom) map of changes in wave height after the extension relative to present. For changes, positive values (grey) represent an increase in wave height, negative values (green) are a decrease in wave height.

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DRAFT

Figure 5-5: For a boundary incident wave height of 1.5 m with a wave period of 12 seconds: (Top) Spatial variability of wave height for existing situation (left) and with the proposed runway extension (right), and (bottom) map of changes in wave height after the extension relative to present. For changes, positive values (grey) represent an increase in wave height, negative values (green) are a decrease in wave height.

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DRAFT

Figure 5-6: For a boundary incident wave height of 3 m with a wave period of 8 seconds: (Top) Spatial variability of wave height for existing situation (left) and with the proposed runway extension (right), and (bottom) map of changes in wave height after the extension relative to present. For changes, positive values (grey) represent an increase in wave height, negative values (green) are a decrease in wave height.

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DRAFT

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Overview of spatial variability of effects on wave heights

The high-resolution ARTEMIS wave model reproduces the spatial wave-crest patterns in Lyall Bay shown in vertical satellite images, as the incident wave-train is refracted and diffracted, particularly in shoaling waters of the inner Bay. Results from modelling the before and post-construction situations, indicate that the proposed runway extension has the potential to have a more than minor effect on some combinations of wave height and period in some parts of the Bay, mainly on the eastern side of Lyall Bay near the existing runway revetment and more localised along the western and eastern sides of the proposed extended runway.

In the north-eastern sector in the lee of the spur groyne, 1.5 m incident waves of 8-second period propagating into Lyall Bay from Cook Strait would be attenuated by a further 0.2 to 0.6 m in a zone extending out ~250 m from the existing runway revetment. The greatest wave-height reduction in this sector would be 80–100 m NW of the spur groyne (breakwater), and conversely, a local increase in these 8-second wind waves immediately behind the spur groyne through diffraction. In The Corner, the wave-height reduction would be somewhat less at 0.2 to 0.4 m. The model also predicts an increase in wave heights: i) locally around the spur groyne (breakwater) and adjacent submerged rock outcrop; ii) slight increases in a narrow central part of the inner Bay of the main Beach; and iii) in a patch close to the beach towards the eastern end of Lyall Bay Beach near The Corner. This latter area arises due to the reduced wave height offshore from this part of the Beach, with waves able to propagate (shoal) slightly further inshore than is the case for the existing situation, given the same offshore wave height and period.

The largest reduction in wave height overall would occur adjacent to the west side of the extended runway, as the wave peels along the revetment subject to dissipation by friction (drag) exerted by the accropode units and also the influence of a subtle wave-sheltering effect as the runway extension alignment of ~183DRAFT°S is slightly west of the predominant wave-approach direction from due south. After the runway is extended, predicted changes for the same-height (1.5 m), but incident swell of 12-second period, would show a similar spatial pattern of wave height change to the shorter 8- second waves. The main differences would be a somewhat smaller reduction in wave height as the swell peels along the western side of the extended revetment and a wider shadow zone in eastern part of Lyall Bay with reductions of 0.3 to 0.6 m. The eastern most swath of propagating swell, parallel with and 50 m off the existing runway revetment, is predicted to be slightly narrower and around 0.2–0.4 m lower in wave height than for the existing situation for a surfing combination of 1.5 m incident swell height of 12 seconds. The increase in wave height adjacent to and in the lee of the spur groyne would cover less area for the longer swells compared to an 8-second wave, given the same incident wave height.

The height of wave-trains reaching the central part of Lyall Bay Beach are likely to be only slightly affected by the runway extension, otherwise elsewhere in the Bay, including the western side, the changes will be negligible.

The cove east of the runway (Moa Point beach) will also exhibit a reduction in wave height as a result of the proposed extension. This reduction in wave height is more appreciable inshore and in the NW corner immediately adjacent to the existing runway. There is also likely to be more resonant or wave- sloshing behaviour within the cove after the extension has been constructed, arising from the more- enclosed basin.

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The above results indicate the predicted scale of changes in waves, relative to the existing situation, using a high-resolution wave model. The implications and down-stream effects of these predicted changes in wave patterns and heights, such as the effects on surfing quality and safety of recreational users, are described in the Surfing and Recreational Report by DHI (2015).

5.2.3 Sediment transport and associated morphological change

Short-to-seasonal timescales Sand transport in shallow coastal areas is a complex interaction between waves, which primarily re- suspend seabed sediments into the water column, which are then subsequently transported by currents until the sediment particles settle again. In nearshore waters, including the surf-zone, non- linear wave dynamics along can also transport re-suspended sediments, especially if waves propagate towards the nearshore zone at an oblique angle to the beach. The Delft3D-SED and Delft3D-MOR modules incorporate tidal and wind-driven hydrodynamics from the Delft2D simulation coupled with waves simulated by the SWAN spectral-wave model (at a less finer resolution than the ARTEMIS model grid) to combine these wave-current interactions with mobile sediments on the seabed.

To provide some context in the Lyall Bay situation, the fine sand largely present on the seabed of median diameter of 0.15 mm, would require a current of ~0.16 m/s acting alone to mobilise these sediments. Based on the currents measured at Site 1 (Figure 3-3), only the two highest southerly events over the ~7-week field programme would have been capable of mobilising sediments in the absence of waves. On the other hand, wave orbital velocities are more efficient at mobilising these fine sands, and increases dramatically as the wave height and wave period increases. Taking the example of a 1 m wave height, sands in Lyall Bay would be mobilised in water depths up to 24, 31 and 35 m for wave periods of 8, 10 and 12 seconds. Sediment transport from one location to another only occurs whenDRAFT mobilised sand, usually by waves, is carried along by a current – often in a series of short steps or hops, before it re-settles on the seabed when wave conditions abate.

In this section we present results in context of the relative change between the start and end of the ~7 week instrument deployment period in August to October 2014, which included a strong southerly gale of 80 km/hr that would have generated substantial sediment transport and morphological change through wave processes, besides other southerly events during the field- monitoring programme. Such an event would be at a recurrence interval of a season through to an annual time scale. Northerly winds are unlikely to generate any substantial sediment transport acting alone, leaving aside the higher currents of 0.4–0.5 m/s along the rocky west coast and outer east coast of the Bay (lower panels; Figure 5-2) and wave energy is much more subdued at short wave periods (e.g., 2-4 seconds) with a very short fetch. Consequently, under northerly-wind conditions, re-suspension of sand by wave orbital motions is limited, even though northerly winds can produce wind-generated currents in the Bay that could otherwise transport wave-suspended sands.

The Delft3D-SED model was forced by tide, wind and SWAN wave boundary conditions (Chapter 4; Technical Report on Hydrodynamic and Sediment Processes; Pritchard et al., 2015) derived for the field deployment period in 2014 and applied equally to both the pre and post runway extension bathymetry in Lyall Bay to ascertain the difference in morphological response over the ~7-week period, including the southerly gale event.

Sediment-transport and associated morphological models require intensive field measurements of seabed changes and bed shear stress thresholds for erosion and deposition under a wide range of

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wave and current combinations, to calibrate the various model parameters to best match the time- varying sea-bed changes. The required fieldwork would have been a costly and extensive undertaking and in our opinion is unwarranted when comparing the before and after construction situation, where widely-used sediment transport formulae can suffice for determining relative change. We have therefore not undertaken an exact sediment-transport calibration, but have used an un- calibrated sand-transport model to approximate the relative morphological change both with and without the proposed runway extension.

The default values for sediment transport for the median sand size in Lyall Bay (fine sand of 0.15 mm median grain size) in the Delft3D-SED model were invoked, which are based on the widely-applied sediment-transport formulations of van Rijn (1984a; 1984b). So while the adoption of this sediment- transport formulae may not necessarily have reproduced the exact seabed erosion and accretion changes that would have occurred over the field-deployment period, applying the same formulae, parameters and all other model forcing (waves, winds, tides) to both existing and post runway extension situations, sets up a comparable pair of simulations where the relative changes between the simulations is directly related to the effects of the runway extension.

Sea-bed response comparing pre and post runway extension The results of running the coupled Delft3D-SED and Delft3D-MOR modules, including waves from the SWAN model embedded in Delft3D-SED, over the ~7-week simulation period are presented in Figure 5-8 for the existing situation and Figure 5-9 for the proposed runway extension bathymetry included (with all other aspects of the model simulation kept the same). The plots show the areas of net erosion, net deposition or negligible change over the ~7-week period, rather than numerical changes in sea-bed height. In most cases the seabed height of erosion of deposition is of the order of cm down to mm, but could be decimetres where cross-shore processes such as storm-cut and offshore bar formation occurs. Since the sediment-transport model uses generally-applicable sediment- transport parameters,DRAFT the absolute magnitudes of sea-bed height changes predicted by each model run may not be accurate for the local conditions, but we focus instead on the relative change in deposition and erosion patterns with and without runway extension using the same default sediment-transport parameters in both before and after simulations.

Both simulations shown below predict that over the 2014 field-deployment period for both pre- and post-runway extension, an erosional storm cut occurs close inshore at Lyall Bay Beach with sand migrating offshore and depositing further offshore in the form of a sand bar.

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Figure 5-8: Predicted changes in seabed height for the existing situation over the ~7-week field period in 2014. CategorizedDRAFT as erosion (E), deposition (D) or negligible change (0).

Figure 5-9: Predicted changes in seabed height for the proposed runway situation over the ~7-week field period in 2014. Categorized as erosion (E), deposition (D) or negligible change (0).

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The erosion band in shallow water adjacent to, and including, the lower beach was mainly due to near-bed wave orbital velocity and current-wave interaction increasing bed shear stress, particularly during the strong southerlies, especially the southerly gale on 22–23 September 2014, when the significant wave height reached 4.7 m, with a mean period of 11 seconds off the spur groyne (Section 2; Technical Report on Hydrodynamic and Sediment Processes; Pritchard et al., 2015). Furthermore, the incident wave field for the ~7-week simulation was mainly from the south and propagated inshore into Lyall Bay, frequently having the energy to mobilise the seabed.

Wind-generated currents during southerlies mainly play a transporting role for wave re-suspended sediments, particularly along the eastern and western perimeters of Lyall Bay where higher currents are predicted as shown in the top panels of Figure 5-2. The predicted erosion areas along the western and outer eastern perimeters by the sediment-transport model (Figure 5-8 and Figure 5-9) can be explained by the combination of wave re-suspension and transport by both wind-generated currents and non-linear wave motions in the shallow near-shore waters. The simulated effect of forcing with a northerly wind alone, coupled with local wave generation through the SWAN model (not presented), on sand transport throughout Lyall Bay was negligible. This is largely due to the very limited fetch within inner Lyall Bay and then only limited to local wind wave generation (i.e., no residual southerly swell included), which can only mobilise seabed sediments in shallow waters.

A shore-parallel band of deposition further offshore from Lyall Bay Beach is indicative of the development of an offshore bar 150–250 m from the shoreline, which was built by sand eroding from the nearshore zone in the sediment model and migrating further offshore during the ~7-week period of mainly southerlies. This cut and fill behaviour of the beach profiles at Lyall Bay was also observed in a previous study by Pickrill (1979), especially in winter when southerly swells are more frequent, with a bar forming between 200–250 m offshore. Therefore there is some confidence in the sediment-transport model predictions that the overall behaviour of the seasonal storm cut and fill pattern off LyallDRAFT Bay Beach is being reasonably replicated for an active southerly-wind period with the attendant energetic wave dynamics.

The relative change in erosion or deposition patterns is shown in Figure 5-10 where the sea-bed heights predicted for the runway-extension were subtracted from the sea-bed heights for the existing situation. In Figure 5-10, erosion (E) means the sea bed would have eroded more than for the existing situation, and deposition (D) means the sea bed would have accreted more than for the existing situation, white areas (0) mark areas predicted to have negligible or undetectable change to seabed heights with the runway extension in place.

The predicted net change in sea-bed heights, following the construction of the runway extension, would be small over much of Lyall Bay (Figure 5-10), particularly within the inner Lyall Bay, the main beach, the eastern cove (Moa Point beach) and the areas along the western and outer-eastern perimeter of the Bay. The main changes in sea-bed heights are localised around the extended- runway, where the existing sea-bed has to adjust to the presence of the rock dyke and the associated wave interaction with the structure, which it does by eroding sand from adjacent to sections the dyke and depositing the sand further offshore, especially to the south, to form a new equilibrium sea-bed profile.

Under the seasonal time scales and environmental conditions that were simulated, the model predicts that there may be some localised deposition on the SW and SE corners of the dyke. This is not to say that over much longer periods, varying seasonal weather conditions and swell frequency that such sand deposits next to the runway-extension rock dyke will not re-mobilise and move e.g., a

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cut and offshore fill response or alongshore drift around the end of the revetment, given the high wave exposure of this area.

The model also predicts narrow bands of both increased erosion and deposition in the order of cm to the SW of the extended runway, which are likely to be due to changes in wind-generated current patterns during southerlies (e.g., right-hand top panel of Figure 5-2) transporting wave re-suspended sediment, rather than changes in waves (which are shown to be minimal in this area as shown by the high-resolution ARTEMIS modelling discussed above).

DRAFT

Figure 5-10: Net or relative change in the response of sea-bed heights with the proposed runway in place over the ~7-week simulation. Categorized as erosion (E), deposition (D) or negligible change (0) for the proposed runway extension compared to the existing situation.

Overall predicted seasonal morphological changes (summary) Introducing waves as well as tide and wind-driven forcing into a sediment-transport model, showed the predicted net change in sea-bed heights, following the construction of the runway extension, would be no more than minor over seasonal timescales over much of Lyall Bay, including the nearshore area off Lyall Bay Beach and the eastern cove (Moa Point beach). The morphology of Lyall Bay beach will still be dominated by cut and fill along an on/offshore seabed profile governed by southerly storm events, with any effects of the runway extension on seasonal morphological timescales likely to be second-order influences.

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Under the seasonal time scales and environmental conditions that were simulated, the sediment- transport model predicts that there may be some localised deposition on the SW and SE corners of the dyke. This is not to say that over much longer periods, varying seasonal weather conditions and swell frequency that such sand deposits next to the runway-extension rock dyke will not re-mobilise and move, given the high wave exposure of this area. Note: the terminus of the existing runway revetment is positioned in an area of submerged rock outcrop (Figure 3-3) so the existing in-situ morphological analogue of the local seabed response built up over decades is not easily transferable to the local seabed south of the extended runway dyke, where a mobile sand cover will be present without surface rock outcrops. However, this will be a local effect and any resulting scour effect on the structure can be managed by transitioning to natural seabed with rock aprons in front of the rock dyke.

Long-term morphological effects The longer-term morphological response of Lyall Bay, to climate cycles such as El Niño-Southern Oscillation episodes and longer 20–30 year Pacific-wide climate cycles, is largely unknown.

For assessing any changes to longer-term beach-nearshore morphology, it is not feasible or meaningful to scale up the sediment–transport and morphology model results to longer timescales than seasonal without having the benefit of a multi-year beach profiling dataset for Lyall Bay (confirmed by Dr Iain Dawe, GWRC, pers. com.). However an indication of the likely long-term effects of the additional runway extension in deeper water can be based on both the existing analogue of the present runway embankment and associated spur groyne (breakwater) still having the dominant control on nearshore morphology on the eastern side of the inner Bay, along with the wave and morphological model results for seasonal timescales (which incorporates the changes in wave heights). Based on the DRAFTlimited beach-profile dataset of Pickrill (1979), most of the seabed height variability occurred within about 600 m of the shoreline, which indicates that any morphological effects of the runway-extension Project are likely to be driven by changes in waves and currents northwards of the existing spur-groyne and associated submerged rock outcrop. Indeed, the wave modelling has demonstrated that this existing groyne on the rock outcrop, is acting as a critical hydraulic control on wave refraction and diffraction processes north of this structure, and to some extent on current flows as well.

The predicted wave patterns for the proposed runway configuration (Figure 5-4 to Figure 5-7) and further plots on the free surface elevations of wave crests and troughs in Chapter 5 of the Technical Report on Hydrodynamic and Sediment Processes (Pritchard et al., 2015), show that largely within the nearshore zone off Lyall Bay Beach, the overall spatial pattern of wave refraction and diffraction is similar to the existing situation, albeit with reduced wave heights preferentially on the eastern side. Given the wave refraction and diffraction patterns and wave crest orientations are likely to be similar to the existing situation, then long term, the gradual shoaling of the NE corner of the Bay arising from the original runway reclamation and spur groyne (which governs the current wave climate in The Corner), is likely to continue with only minor effects from the proposed runway further offshore. There may however be some subtle changes in the shoaling rate as it adjusts to the reduced wave heights on average after the runway extension is in place.

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system to natural climate variability and southerly-storm sequences, it would be difficult to isolate the effect of the proposed runway extension (in deeper water) from the ongoing morphological response associated with the historic runway reclamation and spur groyne (breakwater) and the seawalls that limit the back-beach response along Lyall Bay Beach during storm-cut cycles.

5.2.4 Water quality and clarity Other than operational stormwater discharges, the permanent runway extension would have negligible effects on turbidity and hence water quality and clarity. Local changes in waves and swell during storms around the runway extension may slightly alter resuspension of finer seabed sediments, but usually turbidity increases in Lyall Bay are ubiquitous during strong wind and/or wave events, so any changes in turbidity post-construction would not be detectable. Operational stormwater discharges from the additional runway extension are covered elsewhere in the Engineering Report (URS Ltd, 2015).

5.3 Relevant assessments against statutory plans/policies or guidelines For the level of operational effects described above for coastal physical processes, changes in wave heights is the only effect where there is potential in some parts of Lyall Bay for more than minor effects, with other “downstream” effects on recreational activities such as surfing and swimming, which are appraised in the AEE Report by DHI (2015).

For completeness, the operational effects on coastal physical processes are assessed against the relevant elements of plans, policies and the RMA, as outlined in Section 3.5.

Regional Coastal Plan: Conservation Areas The only conservationDRAFT area in the general vicinity of Lyall Bay area is at Tarakena Bay (Figure 3-7) to the west of Hue te Taka Peninsula and east of West Ledge Reef, which is an Area of Important Conservation Value (AICV) in the Regional Coastal Plan (RCP) for Wellington. The operational effects on coastal physical processes, including waves, will be undetectable at this Conservation site.

Similarly, operational effects on turbidity will be negligible on the waters throughout Lyall Bay managed for water-contact recreation and the nearshore waters around Te Raekaihau Point and Hue te taka Peninsula in outer Lyall Bay managed for shellfish gathering.

NZCPS The policies and objectives of the NZCPS (underlining added for emphasis) relevant to be considered in relation to coastal physical processes are (and the degree of effects):

° Objective 1: “… maintaining or enhancing natural biological and physical processes in the coastal environment and recognising their dynamic, complex and interdependent nature …”. [Overall the dynamic functioning of physical processes in Lyall Bay such as tides, currents, flow circulation, sediment transport and wave refraction patterns will be largely unaffected, but locally in the area around the runway extension in the NE area of the Bay, there will be changes around the extended runway, there will be only negligible or minor changes apart from more than minor changes to wave heights localised around the proposed runway extension and extending into the NE corner of the Bay.]

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° Policy 3(1): “Adopt a precautionary approach towards proposed activities whose effects on the coastal environment are uncertain, unknown or little understood, but potentially adverse.” [Through numerical modelling of the before-and-after situations, assessing the existing analogue of the historic runway extension and expert opinion, the effects of coastal physical processes are reasonably understood and known. DHI (2015) cover the assessment of effects of changes in wave heights and uncertainties on water- contact recreational users.]

° Policy 10(2) on reclamation: For Policy 10(1), “Where a reclamation is considered to be a suitable use of the coastal marine area, in considering its form and design have particular regard to: …

c) the use of materials in the reclamation, including avoiding the use of contaminated materials that could significantly adversely affect water quality …. in the coastal marine area; [Not an issue for the operation of the extended runway – fine sediments (the main contaminant) and turbidity and the low levels of contaminants in the seabed sediments are covered in the next Chapter under construction effects.]

e) the ability to remedy or mitigate adverse effects on the coastal environment; [DHI (2015) consider measures to mitigate or remedy the potential effects on water-contact recreational users.]

g) the ability to avoid consequential erosion and accretion, and other natural hazards.” [There will only be minor changes on seabed erosion and accretion in proximity to the proposed runway extension, with the design provision of the rock aprons around the periphery the revetment structure, mitigating any DRAFTpotential effects from adjacent seabed scour and undermining the works. The NW corner of the cove to the east of the runway extension is likely to accrete somewhat (rather than erode), as this area will become less exposed to waves and the wind-generated currents from strong southerlies will no longer flow west across this area as they do now. Changes in erosion and accretion processes in the nearshore area of Lyall Bay Beach are likely to be minor and negligible in the western half of the Beach, which must be appraised in the context of a highly-modified shoreline environment with possibly slow morphological adjustment ongoing.]

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6 Effects assessment: Construction activities The two potential phases of construction where effects (other than occupation of the sea bed and reclamation) may arise are:

° Discharges of decant water from the infill operations for the embankment within the rock dyke, likely to contain a fraction of fine sediment resulting in dispersing suspended-sediment plume

° Disturbances of the seabed in the CMA from ground improvement activities, including trenching for the dyke, drilling and installation of stone columns or other similar in- ground strengthening works and placement of the peripheral rock apron on the seabed. These activities have the potential to release any resident contamination present in the seabed sediments or fine sediments themselves, leading to turbidity plumes.

This Chapter outlines the assessment of these two types of effects during the construction phase, based generally on the methods proposed in the Construction Methodology Report (URS Ltd, 2015).

6.1 Description of construction effects Decant discharges from the infill operations During the construction of the extended runway, de-watering discharges during the embankment fill phase have the potential to introduce high-turbidity plumes into the receiving waters of Lyall Bay if a fine-sediment fraction is present in the fill material. The main source of turbidity in the water column would be from any fine sediments (clays, muds, silts) present in the fill material, even if they are only a small percentage of material by volume. The alternativeDRAFT location options for a weir (or decant discharge outlet) in the dyke walls on the western side of the airport runway extension are shown in Figure 6-1. Also shown are options for undertaking the fill operation, including truck dumps (NW discharge only), barge entry (NW discharge only) or piped dredged-sediments as a slurry from an anchored barge (either of the discharge locations).

The potential dispersal footprint of suspended-sediment discharges from each of these two outlets during the construction phase were modelled using the Delft3D-SED cohesive sediment module. This assumes that the decant water is saltwater from pumped dredged or barged fill and/or sourced from wave overtopping. Additional near-field mixing simulations using the CORMIX plume model would be needed if significant freshwater was part or all of the decant discharge (e.g., if quarry fill was to be used).

No definitive information is available at this stage on the characteristics of any fine sediment in the fill material (sources of which are yet to be finalised) nor the rate of discharge of decant water over the weir at the discharge location. Therefore a generic fine-sediment discharge of 1 kg/sec within a saltwater discharge has been simulated assuming all the sediment is medium silt (grain size = 15 µm).

Silts in the water column are well known to cause persistent turbidity plumes due to the slow settling rates compared with say sand particles. A representative settling velocity of the suspended sediment in the receiving waters was set for medium silt particles. The suspended-sediment concentration (SSC) results can later be linearly scaled when the sediment discharge over the weir is known, or for setting sediment concentration limits for monitoring at any sensitive receiving water site, which then

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relate back to a silt sediment discharge rate that shouldn’t be exceeded by the contractor to meet that SSC or turbidity limit.

The hydrodynamic conditions for the plume modelling were also generalised to a repeating mean M2 tide (given tidal currents are very low within the inner Bay) over a 30-day period interspersed with two southerly and one northerly wind events as used for isolating the effect of winds versus tidal hydrodynamics in Lyall Bay in the Hydrodynamic and Sediment Processes Technical Report (Pritchard et al., 2015).

DRAFT

Figure 6-1: Schematics of a NW decant discharge location (top) and a SW discharge location (bottom) in the perimeter rock dyke and options for associated fill operations. Source: URS Ltd. (2015).

Releases from disturbances from the initial seabed activities To be updated from the updated Construction methodology Report (URS Ltd., 2015)

6.2 Assessment of construction effects Model simulations of suspended sediment plume footprints during runway construction phase utilised the Delft3D-SED cohesive sediment transport module. This allows the input of fine suspended particles (fine clay, silts, muds) from fixed discharge points. The model parameters were set to a constant discharge flux of 1 kg/s at both alternative discharge sites, a settling velocity (based on Stokes settling velocity computations) of 0.13 mm/s.

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Delft3D-SED is a far-field dispersion model, so doesn’t adequately predict the near-field dilution and mixing processes within 10’s of metres of the discharge point. The maximum SSC within the initial model cell in which the discharge is injected will be diluted and averaged over the cell, therefore SSC will be higher than modelled in close proximity to the discharge point. For scale reference, the cells into which the discharge is injected are around 35×35 m in size.

The outputs from the suspended-sediment plume simulations for each of the discharge locations is provided as a composite envelope of the maximum suspended-sediment concentration (SSC) that occurs in each model cell at any time during the 30-day simulation (so is not an instantaneous snapshot of the plume SSC). However, the temporal variability in predicted SSC out in the Bay from a constant sediment load is relatively small, so the maximum values are not too much higher than the mean SSC (Pritchard et al., 2015). The results are based on a turbid saltwater discharge that mixes relatively quickly with the ambient coastal waters.

The predicted SSC from the plume modelling is over and above the background SSC or turbidity level. Background SSC levels from limited water samples during the 2014 field deployment period taken at the mooring sites varied from 0.46 to 2.9 mg/L, with more continuous measurements of visibility distance ranging 20–30 m down to <1 m and euphotic depth ranging from 40–50 m to <10 m, with the lower values occurring during southerly-storm events when the water appearance became more of a brown hue (James et al., 2015; MacDiarmid et al., 2015). Maximum SSC values of 5 mg/L above background would extend within a relatively constrained area of up to 500 m around the discharge point, or further if the sediment discharge rate was higher (e.g., double the sediment discharge rate will double the extent of the plume area with a maximum of 5 mg/L above background). With a mainly freshwater-based sediment discharge (e.g., from rainfall run-off based on a truck-dumping fill operation), the turbid plume would disperse in the upper water column, while mixing more-slowly downward, as well as settling processes, so initial dilution in the near-field could be considerably less and thereforeDRAFT higher SSC. The highest of the predicted maximum SSC is around 10–11 mg/L (for a 1 kg/sec source) above background levels, in the area of the discharge point for both discharge locations. As mentioned previously, the SSC will be locally higher within the near-field of the discharge e.g., within 35–50 m.

Results show that due to the slow currents, advection/transport of the plume is minimal as indicated by the small footprints of the plume e.g., with a maximum SSC of 5 mg/L above background (for a 1 kg/sec source), especially for the NW discharge location. Rather the main dispersion process is likely to be turbulent diffusion by waves or lateral spreading of the plume along with the slow settling of the medium silt particles.

Further plume modelling is to be undertaken after refinement of the construction methodology, including the key role of erosion and sediment control measures to reduce the turbidity in the discharge “at source” before entering the receiving environment.

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Disturbances Contaminant concentrations in Lyall Bay surficial sediments are very low and uniformly distributed across the study area, including at sites most likely to be disturbed by construction activities, namely, sites 10 and 11 in the area to be reclaimed by the runway extension (Depree et al., 2015). Mobilisation of surface sediment to a depth of at least 0.2 m from within the area of the proposed runway extension is not expected to result in any significant increase in sediment-contaminant concentrations in surrounding areas (Depree et al., 2015).

From a contaminant perspective, the risk of any adverse effects on the water column from transient sediment suspension/disturbance events during construction is very low given that water column concentrations, even after allowing for reasonable mixing, are estimated to be at least two-orders of magnitude lower than default ANZECC water quality trigger values (Depree et al., 2015).

6.3 Assessment against statutory plans/policies or technical criteria and guidelines

6.3.1 Sea-bed disturbances The two conservation areas designated in the Regional Coastal Plan (RCP) in the general vicinity of Lyall Bay area – Tarakena Bay and Taputeranga Island, off Island Bay (Figure 3-7) – are unlikely to be affected by water-borne contaminants from seabed activities during construction, which will be limited to theDRAFT area of the reclamation off the present runway due to the low in-situ contaminant levels in the surface sediment and substantial settling in the near field of any fine-sediment fraction present.

Planning Map 8D in the RCP designates the water quality class in the waters throughout Lyall Bay to be managed for water-contact recreation, with the nearshore waters around Te Raekaihau Point and Hue te Taka Peninsula in outer Lyall Bay also managed for shellfish gathering. As water quality for both these types of activity relate primarily to the presence of water-borne pathogens in relation to public health of users, sea-bed disturbances in the limited area of construction for the proposed runway extension would not expose these waters to any additional public-health risks.

Policy 10(2)(c) of the NZCPS states having particular regard to the use of materials in the reclamation, including avoiding the use of contaminated materials that could significantly adversely affect water quality in the coastal marine area. This mainly relates to fill material – covered in the next sub- section in regard to turbidity. Management of sea-bed and introduced material associated with ground-treatment and trenching methods is covered in the Construction Methodology Report (URS Ltd., 2015).

6.3.2 Turbidity and discharges to the CMA With contaminant risks to the CMA negligible, the remaining environmental risk from construction activities associated with the runway extension into the CMA is the generation of suspended- sediment discharges, which could potentially result in excessive turbidity locally, if not managed effectively at source.

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Section 107 of the RMA for assessing discharge permits, outlines that after allowing for reasonable mixing, the discharged contaminant (suspended sediment in this case) should not produce any conspicuous change in colour or visual clarity, nor any significant adverse effects on aquatic life. Numerical modelling of suspended-sediment plume dispersion (Section 6.2) can predict the magnitude and extent of turbidity above background levels for a range of discharge location and sediment-load scenarios. However, to assess the effects of discharges to the CMA, as per section 107 of the Act, requires a determination of what constitutes a conspicuous change in colour or visual clarity in the Lyall Bay environment, and also the upper threshold in-situ turbidity levels before adverse effects occur on fauna and flora. These aspects are covered in the Marine Ecology AEE Report (James et al., 2015), but need to be in tandem with best-practice sediment and erosion control measures (including fill-material specification and settling techniques) during construction – particularly the infilling operation once the rock dykes are in place.

Policy 10(2)(c) of the NZCPS states having particular regard to the use of materials in the reclamation, including avoiding the use of contaminated materials that could significantly adversely affect water quality in the CMA. This encourages the use of clean fill material that has as low a fraction of silts and clays as practically possible and minimal chemical-contaminant levels and a consent condition could specify, for example:

° All imported fill material to be used in the reclamations, rock dykes, groynes and temporary fill/surcharge shall be in accordance with the Ministry for the Environment “cleanfill” definition, as detailed in Publication ME418 “A Guide to the Management of Cleanfills, 2002”.

Based on the construction methodology put forward (URS Ltd., 2015), there are no other potential effects arising from construction that would cause greater than minor effects on coastal processes, other than the reclamation itself removing a small portion of the water compartment of Lyall Bay and any extreme wave-stormDRAFT that could damage and move sections of the rock dyke (which would need to repaired quickly anyway for construction to proceed).

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7 Mitigation and monitoring This Section outlines the effects on coastal physical processes and therefore may require an assessment of on-site or off-site measures to mitigate or remedy the effects, with very limited options for avoidance (given the spatial extent of the proposed reclamation of the CMA).

7.1 Overview of effects on coastal physical processes Waves–During the operational (permanent) phase of the extended runway south into the CMA of Lyall Bay, the only assessed change in coastal physical processes that is potentially more than minor is the reduction in some combinations of wave heights and period in parts of Lyall Bay, particularly in the NE area of Lyall Bay adjacent to the existing runway revetment, and to a lesser extent on the cove (Moa Point beach) east of the runway extension.

In the north-eastern sector in the lee of the spur groyne, 1.5 m incident waves propagating into Lyall Bay from Cook Strait would be attenuated by a further 0.2 to 0.6 m (8-second wave) and 0.2 to 0.4 m (12-second wave) than present in a zone extending out ~250 m from the existing runway revetment. The greatest wave-height reduction in this sector would be 80–100 m NW of the spur groyne, and conversely, a slight local increase in these 8-second wind waves immediately behind the spur groyne (breakwater) through diffraction.

The wave model also predicts slight increases in wave heights for the following areas: i) adjacent to and in the lee of the spur groyne and submerged rock outcrop; ii) slight increases in a narrow central part of the inner Bay of the main Beach; and iii) in a patch close to the beach towards the eastern end of Lyall Bay Beach near The Corner. However, these effects of increased wave heights from the runway extension on wave heights are likely to be minor and not readily distinguishable against the background day-to-day up to storm variability in wave conditions. The largest reductionDRAFT in wave height overall would occur adjacent to the west-side rock dyke of the extended runway, as the wave peels along the rock dyke being subject to dissipation by friction (drag) exerted by the accropode units and also the influence of a subtle wave-sheltering effect as the runway extension alignment of ~183°S is slightly west of the predominant wave-approach direction from due south. However, the effects of this reduction will only have minor effects on seabed sediment transport and morphology change outside the peripheral rock aprons.

The cove east of the runway (adjacent to Moa Point Road) will also exhibit a reduction in wave height as a result of the proposed extension. This reduction in wave height is more appreciable inshore and in the NW corner immediately adjacent to the existing runway. There is also likely to be more resonant or wave-sloshing behaviour within the more-enclosed cove after the extension has been constructed, creating a more-enclosed basin in this area. However this cove, which will be more enclosed than present, will still be dynamically flushed, but less vigorously than present as it will still be exposed to refracting waves and southerly-wind directed currents directed into the cove.

Turbidity – the exact sedimentary characteristics of the fill for the reclamation are not known. So will need to be an adaptive management approach to monitoring the turbidity generated by the decant

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discharges e.g., 100 m from the discharge point and managing sediment and erosion control measures within the infill work area.

7.2 Mitigation or avoidance measures The implications and down-stream effects of the predicted changes in wave patterns and heights, such as the effects on surfing quality and safety of recreational beach hazards, are described in the Surfing and Recreational Users Report by DHI (2015).

Sediment and erosion control measures to mitigate seabed disturbances and turbid discharges to the CMA are outline in the Construction Methodology Report (URS Ltd., 2015).

7.3 Suggested coastal monitoring conditions The following coastal monitoring conditions are recommended to:

• Gather additional data to document physical changes to the existing environment (e.g., bathymetry, beach profiles), which should be analysed to attribute changes where possible and a report provided;

• Best-practice construction or post-construction house-keeping;

• Visual observations to ensure effects are no more than minor as works proceed (especially in relation to the decant discharges during construction);

• Compliance monitoring as part of an adaptive management approach e.g., to ensure changes to turbidity (after reasonable mixing) are within acceptable limits.

For example, monitoring conditions for coastal physical processes could include: C.1 – WIAL shallDRAFT provide to the Greater Wellington Regional Council (GWRC), plans and drawings (including dimensioned, cross sections, elevations and site plans of all areas of proposed reclamation (including associated permanent and temporary CMA occupation), permanent structures and temporary structures) at least XX working days before the proposed date of commencement of the construction of the reclamation or temporary structures.

C.2 – Construction in the CMA of Lyall Bay shall be undertaken generally in accordance with the construction methodology detailed in the application, specifically the Engineering Technical Report, Construction and Methodology Report and the Erosion and Sediment Control Plan. The construction methodology shall include:

(a) xx;

(b) xx;

C.3 – The WIAL shall notify the Greater Wellington Regional Council in writing within 10 working days of the completion of each discrete area of ground-treatment works, reclamation, structures and revetments.

C.4 – The WIAL shall supply to the Greater Wellington Regional Council and the LINZ Hydrographic Services Office and LINZ Topographic Services Office (Chief Hydrographer, National Topo/Hydro Authority, Land Information New Zealand, Private Box PO Box 5501, Wellington 6145), a complete

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set of “as built” plans, final topographic and bathymetric data, and appropriate certification confirming that the new reclamations, structures, revetment works have been built in accordance with sound engineering practice, within 60 working days of the completion of the reclamation works.

C.5 – The WIAL shall maintain the site in good order and shall, as far as practicable, remedy all damage and disturbance caused by plant, vehicles and equipment to the foreshore during construction, to the satisfaction of the Greater Wellington Regional Council.

C.6 – The WIAL shall ensure the, remove removal of all equipment, erosion and sediment control measures, surplus soil, sediment and construction materials from the CMA within XX working days following the completion of the construction works, to the satisfaction of the Greater Wellington Regional Council.

C.7 – Cleanfill: All imported fill material to be used in the reclamations, rock dykes, groynes and temporary fill/surcharge shall be in accordance with the Ministry for the Environment “cleanfill” definition, as detailed in Publication ME418 “A Guide to the Management of Cleanfills, 2002” or subsequent updates.

C.8 – The WIAL shall maintain a log recording the source of fill material imported onto each reclamation or temporary and permanent occupation site. This log shall be made available to the Greater Wellington Regional Council for inspection on request.

C.9 – Repeat bathymetric survey in eastern Lyall Bay 2 years after construction of the rock dyke. Hydrographic survey report to compare with the 2014 survey and ascertain any anomalous changes in seabed heights or accretion/deposition patterns. A copy of the Report to be supplied to GWRC.

DRAFT

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8 Summary and conclusions [To be completed at the end of the consultative period based on Exec Summary]

DRAFT

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9 Acknowledgements This report summarises material from a number of sources, particularly NIWA technical reports prepared by my colleagues for WIAL to support the AEE.

I especially acknowledge the input of Craig Stevens (Baring Head wave climate) and Scott Nodder and Peter Gerring (Moa Point beach survey), along with other NIWA colleagues who contributed material and carried out modelling and field studies (Pritchard et al., 2015; Depree et al., 2015; MacDiarmid et al., 2015).

Thanks to Dr Mark James (Aquatic Environmental Sciences) who coordinated the coastal environmental studies on behalf of WIAL and provided insightful comments on the report.

DRAFT

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10 Glossary of abbreviations and terms ADCP Acoustic Doppler Current Profiler – measures currents throughout the water depth and waves. AEE Assessment of Effects Report (accompanies applications for consents) accropodes A single-layer artificial heavy armour unit developed by SOGREAH in 1981, later modified by chipping away excess materials and adding friction features in the form of small pyramids to increase interlocking. akmons Heavy unreinforced pre-cast concrete shapes that interlock to form a robust coastal-wave protection layer, as used at the southern end of the existing runway into Lyall Bay ANZECC guidelines Australia NZ Environment Conservation Council produced guidelines on freshwater and marine water quality in 2000 (http://www.mfe.govt.nz/freshwater/tools-and-guidelines/anzecc-2000-guidelines) ARTEMIS A high-resolution phase-resolving wave model that is part of the TELEMAC model suite Coastal environment Includes elements of coastal areas influenced by coastal processes on land above MHWS, as well as the CMA, as defined in Policy 1 (NZCPS) CMA Coastal marine area – as defined in s. 2 of the RMA Delft3D The widely-used Deltares hydrodynamic, sediment and water quality suite of models (Deltares, 2011) GWRC DRAFTGreater Wellington Regional Council mean spectral wave Average of all wave periods in a time-series representing a certain sea state

period (Tm) mean wave direction The average wave direction, which is defined as the mean of all the individual wave directions in a time-series representing a certain sea state MHWS Mean High Water Spring – the average high-tide level during spring tides MSL Mean Sea Level – the actual mean level of the sea (rather than a datum) NZCPS NZ Coastal Policy Statement (2010) – the mandatory coastal policy statement required under s. 56–58 of the RMA peak direction of wave Direction of travel for waves at the wave period at which the wave energy is

propagation (Dp) highest (maybe for wind sea or a swell component of a mixed sea) Phase-resolving wave A wave model with grid cells of high enough resolution that have several cells model resolving a single wave length, and therefore resolve refraction and diffraction processes. Usually based on the wave mild-slope algorithm and waves applied at the seaward boundary are usually monochromatic (waves of constant height and period with time).

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RMA Resource Management Act 1991 and subsequent amendments significant wave height The average of the highest 1/3 of wave heights over a measured or simulated

(Hs) period. Akin to the average an observer would perceive, which is usually biased towards noticing the larger waves. SSC Suspended-sediment concentration SWAN A widely-used Deltares spectral wave model (Deltares, 2011) swell Generally waves with periods greater than 8–10 seconds for medium-distance swells and above 10 seconds for longer-distance ground swells, reaching up to 20 seconds for trans-Pacific swell. wave diffraction Diffraction is the process by which the waves are bent around into the lee zone behind a structure or barrier (e.g., rock revetment or groyne) by energy transmitting laterally along the wave crests. wave refraction Process where wave crests arriving at an angle (rather than parallel) to the seabed contours in shallow water are changed, with the part of the wave in shallower water moving more slowly than the part still advancing in deeper water. A consequence of this is that the wave fronts tend to become aligned with the depth contours as they shoal. WCC Wellington City Council WIAL Wellington International Airport Ltd WVD-53 Wellington Vertical Datum–1953 (regional vertical survey datum) Zero-crossingDRAFT mean Average of wave period analysing wave water-surface measurements extracting wave period (Tz) times between the up-crossing (when the water surface just rises above the average sea level) and the next down-crossing (when water surface dips below the sea level). Usually lower than the mean spectral wave period, due to the large number of short-period, low-energy waves.

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Davey, F.J. (1971). Seismic surveys in Wellington Harbour. A. Seismic refraction measurements in eastern Lyall Bay. B. A re-interpretation of the Point Howard seismic

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