appendix 9 - wind assessmentappendix 9: wind assessment opus research report 15-529f31.00 wind...

Boffa Miskell Ltd | Wellington Airport – New Control Tower | Resource Consent Application and Assessment of Environmental Effects 1

Appendix 9: Wind Assessment

Opus Research Report 15-529F31.00

Wind Assessment: Proposed Wellington Airport Control Tower

Opus Research Report 15-529F31.00

Wind Assessment:

Proposed Wellington

Airport Control Tower

© Opus International Consultants Ltd 2015

Prepared By Opus International Consultants Ltd

Neil Jamieson Opus Research

Research Leader - Aerodynamics 33 The Esplanade, Petone

PO Box 30 845, Lower Hutt 5040

New Zealand

Reviewed By

Telephone: +64 4 587 0600

Paul Carpenter Facsimile: +64 4 587 0604

Wind Engineering Consultant

Date: 19 February 2015

Reference: 529F31.00

Status: Final

Opus Research Report 15-529F31.00 i

529F31.00 19 February 2015 Opus International Consultants Ltd

Contents

1 Introduction ....................................................................................................... 2

2 The Site, Area and Proposed Development ......................................................... 2

3 Wellington City Council Wind Rules................................................................... 5

4 Existing Wind Conditions ................................................................................... 5

5 Effects of the Proposed Development on Wind Conditions ................................. 7

5.1 General ................................................................................................................................... 7

5.2 Northerly and Southerly Winds ........................................................................................... 7

5.3 Wind Mitigation .................................................................................................................... 7

5.4 Overall Assessment ............................................................................................................... 8

6 Concluding Comments ....................................................................................... 9

Opus Research Report 15-529F31.00 2


CLIENT Airways New Zealand

P.O Box 14131

Christchurch

CONTACT Peter Rivers

PROJECT MANAGERS Boffa Miskell

P.O Box 11 340

Wellington

CONTACT Jaimee Semmens/Hamish Wesney

ARCHITECTS StudioPacific Architecture

P.O Box 11517

Wellington

CONTACT Evzen Novak

1 Introduction

This wind assessment report describes the expected effects of the proposed new control tower at

Wellington Airport on wind conditions likely to be experienced by pedestrians in its vicinity. It is

intended to address the reporting requirements of District Plan Change 73 (DPC 73) of the

Wellington City Council District Plan for wind effects. The assessment report for this development

was prepared at the request of Boffa Miskell on behalf of Airways New Zealand.

Our assessment of the expected wind effects of the proposed control tower development is based on

our wide experience of assessing wind conditions in urban areas in the Wellington region. This

review was carried out to determine the existing wind speed levels, and assess the likely levels of

wind speed changes. No wind tunnel testing has been performed on the proposal for this assessment.

A site visit was made on Wednesday 17th December, during a period of mostly light northerly. Plans

of the proposed control tower development were provided by Boffa Miskell on 11th December 2014.

Updated landscape plans were provided by StudioPacific Architecture on 17th February 2015.

2 The Site, Area and Proposed Development

The site of the proposed new control tower for Wellington Airport is located in an area immediately

to the east of Tirangi Road, and a short distance north of George Bolt Street in Lyall Bay. It lies

outside the Wellington Airport security perimeter, and occupies part of the carparking area for the

existing Wellington Airport Retail Park. Figure 1 shows a high level view of the site location, while

Figure 2 shows a closer aerial view of the immediate area. Also shown on Figure 2 is the site for the

planned extension of the Airport Retail Park, on the space to the immediate north of the existing

Retail Park. This extension has resource consent, but construction has not yet started, and the site is

currently vacant.



Figure 1 shows that the site of the new control tower sits approximately in the middle of an area of

retail, industrial, commercial and airport buildings, some of which sit inside the airport security

perimeter. These range in size and height, although the maximum height of these is around 10-12m.

Figure 1: High level aerial view showing the new control tower location

Figure 2: Close aerial view (LINZ, 2014) of the site and surrounding area (also shows

the Airport retail park extension site (outlined in red) and the prevailing wind

direction sectors)



It can be seen from Figure 2 that the site of the proposed new control tower sits in the middle of an

open area formed by the surrounding carpark and the adjacent road (Tirangi Rd).

The proposed new control tower is a relatively slender structure, with a rectangular planform

approximately 10m by 13m, sloping back towards the north, with a capping element and “cab” taking

the total height to slightly over 32m. The building is proposed to be located approximately 4m from

Tirangi Road, and approximately 14m from George Bolt Street. Also included in the design are hard

landscaping elements around the base of the tower. These include (1) structured bunds constructed

from concrete, steel or stone, (2) plantings of coastal shrubs and grasses, and (3) a palisade perimeter

fence of tubular steel of varying heights. The main entrances to the tower are located on its northern

and southern sides. Figure 3 shows the tower inserted into a photographic view of the site.

Figure 3. Photo montage of the proposed control tower from Tirangi Rd



3 Wellington City Council Wind Rules

This wind assessment has been prepared in accordance with the wind rules in District Plan Change

73 (DPC 73) of the Wellington City District Plan. While the wind rules in DP73 do not apply to the

Airport Zone, they provide helpful guidance for assessing the wind effects resulting from a building

which does not comply with the maximum height standard in the Airport Zone (12 metres). The

following assessment compares the effects of the proposed control tower development to the existing

situation. It also considers (1) the likely effects of the planned extension of the retail park, and (2)

the design of the tower with reference to Wellington City Council’s Design Guide for Wind (2000).

This design guide outlines in non-scientific terms the basics of wind effects caused by buildings and

shows how particular relationships can cause or alleviate problems.

4 Existing Wind Conditions

Over Wellington the prevailing strong winds are dominated by north to north-westerly and south to

south-westerly wind flows, as shown in Figure 2. Northerly winds typically occur more frequently

than southerly winds for light to moderate winds. However, the highest wind speeds occur with

around the same frequency for both direction sectors. Strong southerly winds are often noticed more

by pedestrians because they are often also cold and frequently accompanied by rain.

In this area of Wellington the pedestrian wind environment is largely determined by three major

factors, these being (1) the orientation of the streets to the prevailing wind directions, (2) the sizes,

locations and heights of the buildings, and (3) the sizes and locations of open spaces. Strong

horizontal wind flows, particularly southerly flows coming off the open expanse of Lyall Bay,

currently occur along those streets and open spaces aligned more parallel to the prevailing wind

directions. There include both Tirangi Rd and Cochrane St. There are also limited contributions from

horizontal wind flows blowing out of those “side” streets aligned more normal to the prevailing wind

directions. As most of the buildings are of relatively similar size and height, there are only limited

effects where vertical wind flows are deflected down the windward faces of the taller or more exposed

buildings. However, the buildings do deflect and channel the horizontal wind flows making the street

intersections, and the areas around the corners of buildings, quite windy for particular wind

directions.

When assessing the wind effects of buildings in urban areas, where specific data from wind tunnel

studies is either unavailable or limited, we recommend the use of the wind speed descriptions as

listed in Table 1.

Table 1: Gust Wind Speed Range Descriptions

Wind Speed Range Description

11m/s and below

12 - 14m/s

15 - 17m/s

18 - 20m/s

21 - 23m/s

24 - 26m/s

27m/s and above

very low low

moderate

moderately high

high

very high

extremely high



Based on the results of wind tunnel studies in similar areas, where the exposure is comparable and

the buildings are similar in size and height, e.g. close to The Esplanade in Petone, gust wind speeds

in the pedestrian areas around and close to the site are assessed to currently range from very low in

sheltered areas to high in more exposed locations. Typically they are highest in the larger open spaces

(including Retail Park carpark area), around the windward corners of the more exposed buildings,

and through some of the narrower gaps between buildings. For example, some of the higher wind

speeds occur in the space between the two existing elements of the Retail Park in northerly winds,

where these two elements, which site approximately at right angles, channel wind flows through this

narrow gap. Generally, the ranges of wind speeds and the overall average wind speeds are expected

to be somewhat higher for southerly winds than northerly winds because of the proximity of the site

to the open expanse of Lyall Bay.



5 Effects of the Proposed Development on Wind

Conditions

5.1 General

New buildings, as well as changes and additions to an existing building, can have a significant impact

on wind conditions in the surrounding pedestrian areas. They will occupy space and force wind that

would normally flow through this space to take other paths. Wind flows can be deflected down from

higher levels into adjacent areas, or channelled through gaps between buildings, or accelerated

around corners. Some of the worst wind conditions occur where these vertical and horizontal wind

flows combine, most often around the windward corners and sides of a building. However, new

buildings or additions will not always cause local wind conditions to get worse. New buildings can

often provide increased shelter to some areas, generally those immediately downwind. They can also

potentially keep wind flows away from pedestrian areas, either by deflecting them into lesser used

areas, or well above ground level. Accordingly, new building developments can cause wind speeds

to increase in some areas, and to decrease in other areas.

5.2 Northerly and Southerly Winds

Given the design of the building, its orientation, and similar immediate exposure to both northerly

and southerly winds, the effects for both northerly and southerly direction sectors were also expected

to be generally similar.

With a height of around 32m, and being located in an open carparking area, the new control tower

represents a significant physical change from the existing situation. Typically, a building of this

height in a relatively open area, surrounded by much lower buildings, could potentially have a

significant impact on the local wind environment for the reasons described above. However, at

13m by 10m in plan at ground floor level, the building presents a relatively small footprint and

slender aspect to the wind. This means that the vertical wind flows usually expected for a building

of this height will not be fully realised at ground level, with a significant proportion of the vertical

wind flows being generated being able to spill around the sides of the tower before reaching the

ground. However, some vertical wind flows will still reach ground level, and combined with the

deflection of horizontal wind flows around the windward corners of the building, would normally

make the areas around these windward corners quite windy locations. The hard landscaping

elements included around the base of the tower, have the potential to not only mitigate some of the

effects created by the tower, but also to keep people further away from the corners of the building,

most notably around the north side, and to provide some shelter for the entrance on the north side

of the building. It is also important to note that neither the adjacent Tirangi Road footpath, nor

this part of the carpark, are particularly high usage pedestrian areas. There will be some areas of

localised shelter on the leeward sides of the tower in northerly and southerly winds, but these will

mostly be of benefit for the tower users.

5.3 Wind Mitigation

As mentioned above, the hard landscaping elements included in the design are expected to provide

some mitigation of the wind effects created around the windward corners of the new control tower,

although mostly around the northern side of the building. The overall benefits of these elements

could be improved if the porosity of the palisade fence was reduced, either by reducing the spacing



of the tubing, or by incorporating other elements into the fence, e.g. climbers or trellis. If the

landscaping elements are removed from the design, or they are significantly scaled back in size,

alternative options for wind shelter should be included around the windward corners of the building.

This could take the form of planting (trees and shrubbery), or vertical screens or fences.

The primary pedestrian entrance to the tower is located at the centre of the south side to the building,

and there is also a second entrance to the adjacent FAP/Valve room. Accordingly, in southerly winds

these will be quite exposed, and the doors may at times be difficult to open, both from the inside and

outside. It would be beneficial if some additional shelter could be provided for at least the main

central doors, either as an integral part of the hard landscaping elements, or perhaps separate

screening. Alternatively, consideration could be given to moving the main doors to the east side of

the building.

5.4 Overall Assessment

The net effect of the proposed control tower development on wind conditions in pedestrian areas is

expected to be a small deterioration in the immediate wind environment, localised to small areas

around the windward corners of the building. The hard landscaping elements can be used to mitigate

most of the expected effects of the tower, or exclude people from the windier areas. However, the

benefits will depend on their final locations and size.



6 Concluding Comments

(1) Existing wind speeds in the immediate area around the site generally range from very low to

high. Overall, wind speeds are higher in southerly winds than northerlies because of the

different exposure of the site to direct wind flows.

(2) The effects of the control tower development are expected to be generally similar in both

northerly and southerly winds. Although the control tower is relatively slender, some vertical

wind flows will be deflected down the windward faces to combine with the incident horizontal

flows. The hard landscaping elements around the base of the tower will mitigate most of these

effects and also keep people away from the windier areas around the corners of the building,

provided they are retained in the final design at a similar size and extent.

(3) Reducing the porosity of the palisade fence around the building would provide additional

benefits.

(4) It would be useful to consider some form of shelter for the building entrances, particularly

those on the south side of the building. This could be included as part of the proposed

landscaping elements, or as separate screening specifically for the doors.

Authored by: Reviewed by:

Neil Jamieson Paul Carpenter

Research Leader Wind Engineering Consultant

Aerodynamics

Opus International Consultants Ltd Opus Research 33 The Esplanade, Petone PO Box 30 845, Lower Hutt 5040 New Zealand t: +64 4 587 0600 f: +64 4 587 0604 w: www.opus.co.nz

appendix 9 - wind assessmentappendix 9: wind assessment opus research report 15-529f31.00 wind...

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