APPENDIX 11 WIND EFFECTS ASSESSMENT

Transcription

1 APPENDIX 11 WIND EFFECTS ASSESSMENT Summerset Villages (Lower Hutt) Ltd District Plan Change Request Prepared by Urban Perspectives Ltd 17 September

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3 Opus Research Report D84.00 Wind Assessment of the Proposed Boulcott Retirement Village, Lower Hutt 343

4 Opus Research Report D84.00 Wind Assessment of the Proposed Boulcott Retirement Village, Lower Hutt Prepared By Neil Jamieson Research Leader - Aerodynamics Opus Research 33 The Esplanade, Petone PO Box , Lower Hutt 5040 New Zealand Reviewed By Telephone: Paul Carpenter Facsimile: Wind Engineering Consultant Date: 4 August 2014 Reference: 529D84.00 Status: Final

5 Opus Research Report D84.00 i Contents 1. Introduction The Site, Area and Proposed Development Existing Wind Conditions Effects of the Proposed Development on Wind Conditions General Northerly Winds Southerly Winds Building Entrances Concluding Comments D August

6 Opus Research Report D CLIENT CONTACT Summerset Retirement Village (Lower Hutt) Ltd c/- Summerset Group Holdings Ltd P.O Box 5187 Lambton Quay Wellington Mr Vaughan Bell 1. Introduction This wind assessment describes the expected effects of the proposed Boulcott Retirement Village in Lower Hutt on wind conditions likely to be experienced by residents, neighbours and pedestrians in its vicinity. While a wind assessment or wind tunnel test is not generally required for new buildings in this area of Lower Hutt under the District Plan, this assessment is intended to form part of the assessment of environmental effects that make up the private plan change request documentation and/or application for resource consent. Its main objectives are to (1) address the questions on wind issues raised at public meetings during the consultation process, and (2) provide design advice on wind mitigation and improvement of the overall amenity, and that of specific areas for residents and visitors. The assessment report was prepared at the request of Mr Vaughan Bell on behalf of Summerset Retirement Village (Lower Hutt) Ltd. Our assessment of the expected wind effects of the proposed development is based on our wide experience of assessing wind conditions in for new buildings and additions in urban areas. No wind tunnel testing has been performed on the proposal for this assessment. A visit to the site was made on Thursday 25 th July 2013, during a period of light to moderate northerly winds. 2. The Site, Area and Proposed Development The Boulcott Retirement Village development site is located south of the new Hutt River stopbank, and is between the Boulcott s Farm Heritage Golf Course to the north, and the adjacent residential area to the south. It extends around in a rough arc between the northern end of Boulcott Street and the northern end of Military Road, and is currently largely vacant. Figure 1 shows an aerial view of the area immediately around the site. Included on this figure are the direction sectors for the prevailing wind directions in Lower Hutt shown in red, and an approximate layout for the proposed development. Figure 2 shows views of the existing situation. It can be seen from these figures that the golf course area to the north is relatively open, with trees and other vegetation being the main obstructions to the wind. To the south the buildings are generally residential houses of one or two storeys, with the most significant buildings in terms of size being those of Boulcott Primary School to the south of the site. Figure 1 shows that the anticipated development can be roughly split into two areas, one to the east of the narrow pinch point near the centre of the site, and one to the west. The area to the east of this midpoint will comprise of residential blocks made up of one and two storey elements. The area to the west of the midpoint will comprise of larger elements, both in terms of height and area, with these ranging up to four storeys in height and in close proximity to the north boundary. These will step up in height towards the centre of this space, with the four-storey blocks being opposite the Boulcott Primary School playing fields. These blocks are approximately square in plan, and are comprised of ground level carparking with three levels of apartments/care facilities above. An 529D August

7 Opus Research Report D internal driveway will which connect through to Boulcott Street and Military Road. There is also a pedestrian walkway connecting the site through to Hathaway Ave. 529D August

8 Opus Research Report D Figure 1. Aerial view of the site and the surrounding area (also shows (1) the prevailing wind directions for strong winds, (2) the location of the development site and its main building elements, and (3) the storey heights of these elements) 529D August

9 Opus Research Report D (a) View looking approximately west from near the Military Rd end of the site (b) View looking northeast from near the Boulcott St end of the site Figure 2. Views of the existing situation 529D August

10 Opus Research Report D Existing Wind Conditions Prevailing strong winds over Lower Hutt are dominated by flows from either approximately northerly or southerly directions. Wind flows are similar to those over the Wellington region in general, with the addition of significant sheltering and channelling effects. The hills that line the west side of the Hutt Valley provide considerable shelter from northerly winds. The hills on both sides of the valley channel northerly winds to some degree, but have more impact on southerly winds. Lower Hutt itself is relatively exposed to southerly wind flows. While northerlies usually occur more frequently than southerlies for light to moderate winds, the highest wind speeds generally occur with about the same frequency for both direction sectors. Strong southerly winds are usually noticed more by pedestrians because they are often also cold and wet. Local pedestrian level wind conditions in this part of Lower Hutt are primarily determined by a combination of four factors. The most significant of these are: (1) the sizes and locations of open spaces, e.g. the golf course, and (2) the sizes, locations, orientations, and heights, of the buildings in the immediate area. The other secondary factors are (3) the alignment of streets relative to the prevailing wind directions, and (4) the local topography, primarily the new stopbank. With reference to Figure 1, the development site is relatively exposed to winds from the north, receiving only very limited shelter from the existing trees on the golf course and from the new raised stopbank. It generally receives somewhat more shelter from southerly winds from the residential buildings and associated trees, other lower plantings, and fences. These shelter effects are lower around the Boulcott St end of the site, and adjacent to the Boulcott Primary School playing fields. 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, as described in Table 1. Typically they are highest in the larger open spaces, around the windward corners of the more exposed buildings, and through some of the narrower gaps between buildings. Generally, the ranges of wind speeds and the overall average wind speeds are expected to be higher for northerly winds than southerly winds because of the shelter effects described above. Table 1: Gust Wind Speed Range Descriptions Wind Speed Range 11m/s and below 12-14m/s 15-17m/s 18-20m/s 21-23m/s 24-26m/s 27m/s and above Description very low low moderate moderately high high very high extremely high 529D August

11 Opus Research Report D Effects of the Proposed Development on Wind Conditions 4.1 General New buildings, as well as changes and additions to existing buildings, can have a significant impact on wind conditions in the surrounding areas. New buildings or additions to buildings 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. They can also be 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 deteriorate. 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. These effects can be particularly significant when a new building occupies a vacant or largely vacant site, as is the case here. The following assessment of the effects of the proposed development on wind conditions has been divided into sections relating to northerly winds and southerly winds, and further divided into those areas outside the site, i.e. the neighbouring residential areas and the golf course, and the area of the site itself. 4.2 Northerly Winds Areas outside the site Eastern Section of the Site In northerly winds the effects on wind conditions in areas outside the site are generally expected to be small. The one and two storey blocks that make up the eastern section of the development will actually provide some additional shelter for the neighbouring properties. This should be further enhanced by any proposed planting in this area, and if there is also a more or less continuous line of fencing between the development and the neighbouring properties to the south. Western Section of the Site Most of the buildings making up the western section of the site are both larger in plan, and taller in height, than the buildings on the eastern section. Consequently, it would usually be expected that they could potentially have a much greater impact on wind conditions in properties to the south of the site. The taller buildings have been concentrated in the centre of this western section, with the lower buildings being the ones that are located closer to the nearby residential buildings. Lower buildings typically have less impact on pedestrian wind speeds than taller buildings of the same plan area. Other factors will also contribute to ameliorating the potential wind effects for neighbouring properties, depending on how they are included in the final design. The internal link road provides some separation between the taller buildings of the development and the neighbouring houses, 529D August

12 Opus Research Report D which is beneficial in that the effects of buildings on the wind diminish with distance. Any planting that is included along the southern edge of the internal link road and around the development buildings will also be beneficial, with the potential benefits generally increasing with higher density of planting, and being generally greater if the trees and shrubs are evergreen. Similarly, creating a largely consistent line of fencing around 1.8m to 2m high between the site and the neighbouring properties would also provide additional shelter. For most wind directions and wind conditions, the size and bulk of the taller buildings on the western section of the site should provide overall more shelter for downstream areas, including neighbouring properties, than currently exists. However, as noted above, there are likely to be some limited effects that could be substantially ameliorated or mitigated through refinement of the design. The Golf Course There will be no impact on wind conditions on the neighbouring golf course (despite the proximity of 4 storey buildings), as this area is located upstream of the development, and is also somewhat separated from it by the raised stopbank On-site areas Eastern Section of the Site Wind conditions around the buildings on the eastern section of the site will be mostly similar to those currently experienced by the existing residential blocks adjacent to the golf course. They could be improved by planting and fencing in the areas between the new buildings and the stopbank. Western Section of the Site There are elements in the development design that could be refined or incorporated to improve the amenity for residents and visitors to the site. These relate more to external landscaping, screening and fencing, rather than changes to the building configurations. The first area to consider is the space between the stopbank and the buildings. The greater the height and density of the landscaping (trees, shrubbery and fencing) in this area the more shelter will be afforded to both the pedestrians and the buildings. The next area to consider is around the windward corners of the buildings, which is where wind speeds around buildings are generally highest. There are some building design options that could potentially help to reduce wind speeds in these areas. However often the simplest and most effective option is to use planting, screening, or a combination of these or similar elements, to keep people away from the windward building corners. Following this are the areas between the buildings. Northerly wind flows will be channelled between them. Accordingly, screening or planting could be used to provide shelter in these spaces. This could be spread out, in an attempt to shelter the entire area, or it could be more targeted to provide shelter for selected areas or pedestrian routes. The area along the southern sides of the larger buildings, adjacent to the internal link road has the potential to be reasonably well sheltered with the combination of shelter from the buildings, and any proposed landscaping. 529D August

13 Opus Research Report D Southerly Winds Areas outside the site In southerly winds the development is not expected to have any major significant detrimental effect on wind conditions in any of the residential areas to the south of the site, as these areas are upwind of the proposed buildings. Further amelioration could be achieved through fences 1.8m to 2m high along the site boundary in this area, together with trees and other shrubbery. The users of the golf course and/or people potentially walking along the stopbank to the north of the development are unlikely to notice any change in the amenity of this area. This is because: the new buildings on the eastern section of the site are one and two storey blocks, which are similar in height and plan to the existing residential buildings to the south, the taller buildings on the western section of the site should actually provide some additional overall shelter for the adjacent areas of the golf course and stop bank, and the new raised stopbank also helps to offset some of the effects around the corners of the new buildings On-site areas Many of the comments and suggestions made for improving the amenity and providing additional wind shelter that were made for northerly winds also apply for southerly winds. This includes (1) landscaping the areas adjacent to the internal driveway as much as is practical, (2) keeping people away from the windward corners of the buildings, if possible, and (3) landscaping the areas between the taller buildings according to use and pedestrian routes. 4.4 Building Entrances The entrances to the taller buildings on the western section of the site deserve some design consideration. Entrances are where people transition from a calm internal space, potentially to the full effects of the weather outside. This is particularly important in this situation, where the larger proportion of people will be older, and potentially less able to deal with strong wind gusts. Where possible, entrances should be positioned on the more sheltered eastern and western sides of the buildings, and the northern and southern ends and corners avoided. Recessing of entrances can also provide a more gradual transition from internal to exterior spaces. If it is not possible to avoid placing entrances on the northern and southern sides of the buildings then the following options could be considered: sheltering the doors with external screens or landscaping, using automatic sliding doors rather than swing doors, or using two sets of separated automatic doors to create a wind lobby. These options could also be used for entrances on the eastern and western sides of the buildings to improve the usability of these spaces. 529D August

14 Opus Research Report D Concluding Comments (1) Existing wind speeds in the immediate area around the site range from low to high, with many of the higher winds speeds being a consequence of the exposed nature of the site to northerly winds. (2) The layout of the proposed development has included some intelligent design choices with respect to wind effects. These include the positioning of lower rise elements close to the adjacent residential areas, and the massing of the taller buildings mostly away from residential areas. (3) In northerly winds the proposed development should have a net beneficial effect on wind conditions in adjacent residential properties, by providing additional shelter to these areas. (4) In southerly winds, the proposed development should have minimal impact on wind conditions in the adjacent residential properties, given it is located downstream of these areas. (5) Users of the neighbouring golf course and stop bank areas should not notice any deterioration on the overall amenity of this area. (6) The above conclusions would also generally apply to other potential site layout options consistent with the storey heights referred to and the District Plan Change prepared by Summerset. (7) Suggestions have been made about how the effects of the development on wind conditions, both internal and external to the site, could be ameliorated or improved through the refinement of elements already included in the design. These include planting (trees and shrubbery), screens and fencing, and the location and design of the building entrances. Authored by: Reviewed by: Neil Jamieson Research Leader Aerodynamics Paul Carpenter Wind Engineering Consultant 529D August

15 Opus Research 33 The Esplanade, Petone PO Box , Lower Hutt 5040 New Zealand t: f: w: 355

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