What damage can skyscraper air turbulence do?

A Study prepared for The Vauxhall Society

What’s one thing we can’t do without, is there to enjoy and yet can harm our environment and hurt or even kill us?

Answer: air. A cooling breeze on a hot day brings a smile to the face. But moving air can also become a ferocious, unseen force, pushing, shoving, and tugging at our clothing. Even that kind of air can be bracing, say at the coast and overlooking the open sea.

However, there are wind factors that trouble aerodynamicists, wind farm engineers, architects and others. These factors are the energy and the force to which wind can subject people and buildings. With its invisible might, wind can and does destroy both. These are matters that should concern you if you live, work or are responsible for people and services in Vauxhall and much of Wandsworth.

When wind and skyscrapers meet

Skyscrapers can be slender, elegant marvels of engineering and design. Designers subject model skyscrapers to wind-tunnel tests to see what effect real wind might have on a real structure.

If the designers get things wrong or do not look deep enough, there could be real trouble.

It quickly became clear that designers got the Millennium Bridge wrong. No lives were lost, and it was relatively simple if expensive and time-consuming to rectify.

Tall buildings are different from low bridges. Once built, skyscrapers are much harder to put right. So is the damage that such buildings can do, to people, to property and even to whole neighbourhoods.

Take Canary Wharf, a grandiose development to which the Mayor’s Vauxhall, Nine Elms & Battersea Opportunity Area is often compared. When it’s windy it can be very unpleasant on the streets of Canary Wharf, such is the wind turbulence the tall buildings create at ground level.

Luckily, Canary Wharf’s shops were built underground.

But this turbulence is not confined to the surrounding streets. The downwind area affected by these tall buildings extends along the River Thames. Few seem to know for how far, or how strong the effects.

Never mind rainchecks, let’s have wind checks

How thorough, then, are checks on the impact of a tall building on wind conditions to the lee side in the building’s immediate vicinity, let alone around clusters of such buildings or in communities some distance away? Answer, these checks may not be as thoroughgoing as you might think.

Wind is volatile, tricky, and tall buildings make it even more so. Conditions in a given area will change depending on the speed of any surrounding wind or winds. Patterns of wind may move around and interact in surprising ways.

The overall extent (or reach) of tall-building wind turbulence can extend well beyond the immediate surroundings of any one structure or group. A kind of wind ‘shadow’ or ‘plume’ can be generated, invisible to the eye unless accompanied by dust storm.

A place in the lee of a tall building may be calm when the wind is moderate, but should wind-speed change, conditions can veer from calm to unpleasant and even threatening. Gales and storms are hardly unknown, even in Vauxhall.

Whirling pollen may increase health and allergy risks. Air quality suffers as pockets turbulence trap pollutants and fine particulate matter. Trees shed branches or just keel over.

All these things can and do happen, often at a distance from the buildings that create or exacerbate the necessary wind conditions. Wind turbulence in the form of swirls, gusts and high- speed-wind valleys is caused by the mass, orientation and shape of a building interacting with the prevailing wind directions and speeds.

But what if there’s more than one skyscraper?

What happens if we have other tall structures near that building?

Well, each structure introduces a down-wind effect of its own; they then all interact and combine in some way. That effect can be disruptive, if not damaging, to buildings and roofing. Leisure spaces may become unwelcoming. Pedestrians may be buffeted or blown over and injured, or hurt by falling debris such as roof tiles.

Such things may have been unknown before the arrival of a tall-building cluster.

Is anybody telling you what effects such a cluster could have over what size area as the Vauxhall riverside disappears under skyscrapers?

Does anybody really know?

If so, they have yet to come forward.

Trouble waiting to happen in Vauxhall and beyond?

There is, I suggest, trouble waiting to happen in Vauxhall, indeed throughout London. This is because UK planning policy for tall structures does NOT require any assessment of the impact on the area down-wind, except in the immediate vicinity. Today’s town planners give priority to ‘pedestrian comfort’ in the street below; the well-being of the community beyond is rarely considered.

This continuing failure to require an adequate assessment of the ‘bigger picture’, the effect on the extended area, ignores the potentially-disastrous combined impact of the addition of one tall building to an existing structure – let alone, as in Vauxhall, a cluster of them.

Planning policy, I suggest, must include better-informed and fairer expectations, guidelines and research requirements. We need to know a design proposal’s total ‘urban wind effect’.

As far as I know (and I would welcome being corrected if I’m wrong) the wind-assessment reports prepared for planning proposals today are limited to assessing only the impact on resident and pedestrian ‘comfort’ not much further than the other side of the street.

Do planners ask for thorough wind-speed assessments?

Yet even here, you’re lucky if a real wind-speed assessment is done at the proposed construction site. Wind-speed data is gathered, but may be presented to (and accepted by) local authority planners in a form convenient to investors and developers. Peak wind speeds (as in gusts) may be excluded. Questionable assumptions may be made as to the condition of the wind as it approaches a tall-building site.

Yet tall structures can affect wind conditions far beyond their own neighbourhood, especially during seasonal gales.

As things stand, however, the science of urban wind engineering and tall structures is so little-consulted that makers of planning policy can afford to ignore or work around it.

The consequences for an area such as Vauxhall, as we have seen at Canary Wharf, will be unsettling, to say the least.

The ‘downwind community’ of the Vauxhall Cross/Nine Elms skyscraper clusters, for example, could well include the Kia Oval cricket ground, which stands a mere 500 metres from the nearest proposed tall structure. This is the 32-story block proposed for 30-60 South Lambeth Road, opposite (and shading) Vauxhall Park and its massive trees.

There are many other planning applications under consideration for tall structures within far less than 500 metres of 30-60 South Lambeth Road.

Building risks into skyscraper clusters

Until wind-effect assessment for tall buildings becomes more thorough and less selectively self-serving, we are building risks into skyscraper clusters. Everything may turn out right. But what if it doesn’t?

Who might suffer, where, when and how? What architect, builder, developer, investor or local-authority official would be held liable?

Few people, it seems, are pausing to ask, let alone answer such questions. Skyscrapers = ‘regeneration’, and ‘regeneration’ = ‘recovery’, so we’re told ‘upwards’ =‘onwards’.

We should not be so ‘blindly led’ that future generations see us as ‘the fools that followed’.

Community groups should start asking questions of the tax-funded planning bureaucracy, the councillors and Mayor of London too.

The Mayor’s London Plan is the policy framework behind all these ‘regeneration’ schemes that, like ours in Vauxhall, is based upon attaining increased urban residential density through clusters of tall buildings.

Yet the London Plan bysteps the impact of such clusters on the broader, urban wind environment and the effects on communities such as ours.

How can community groups respond?

  • Begin by demanding a comprehensive urban wind-impact assessment for each and every proposed building more than five floors high and for an area of at least a mile
  • The study should take into account the overall impact on wind conditions in the entire area that exists, downwind of the site of the proposed tall building
  • Planning policy and planning applications require extensive evaluation of the impact on views, especially heritage views. Yet there is no assessment of altered wind conditions on the broader community. We should expect the same standard of assessment for the living conditions and environment of people living in that view, downwind of any group of tall buildings
  • Developers and planners should be required to measure wind-speeds accurately, during all four seasons, on location and over an extensive area
  • Studies should take into account the condition of wind as it approaches grouped buildings, as well as of wind conditions downwind of a proposed construction site
  • Push your representatives in local and central government to ferret out the facts on high building-induced wind turbulence, make those facts widely available, and to enforce a planning system in which fairness to people is not in inverse proportion to the distance they live from tall buildings.

That’s how you put wind effect at the centre of planning policy on skyscrapers.

Brian Vos

At the time of writing, neither the author nor The Vauxhall Society has received the courtesy of a reply from any official, planner or professional organisation approached for help with the preparation of this paper.

NOTES

WHAT CAN HAPPEN WHEN WIND-SPEED MEASUREMENTS ARE SKIMPED

West Yorkshire, 1965, three of Ferrybridge C power station’s eight cooling towers vibrate then collapse and the other five are wrecked in 85mph gusts. The towers had been designed to withstand higher wind speeds, but were tested for average wind speeds over one minute, neglecting shorter gusts The grouping of the cooling towers funnelled westerly winds into the towers themselves to create a vortex. Nobody hurt.

INTERNATIONAL ACADEMIC RESEARCH – WHY NOT TAKE A LOOK AT VAUXHALL?

International academic research institutions actively study wind in towns overseas.

An opportunity may exist to propose Vauxhall as a good site for such research.

Vauxhall presents unique characteristics that condition the wind before it reaches the cluster of tall buildings built or proposed for Vauxhall Cross/Nine Elms.

The direction of prevailing winds aligns with the widely-fluctuating level of the tidal River Thames, an approximate 220m-wide basin of cold water, varies in depth with the tides by about 5.5m.

THE NEW US EMBASSY: AT RISK FROM TALL BUILDINGS?

The relocation of the United States embassy to Nine Elms within about 1 km of Vauxhall Cross raises security questions for any development nearby.

There is a case for designating each tall building a security risk, and for assessing them individually and as a group.

The risk to be assessed is that, in providing access to high-points near the ‘Embassy Quarter’ and within that area’s prevailing winds, that tall buildings nearby could become a target for terrorist attack, or worse still, a platform for releasing toxic contaminant into the atmosphere.

For a report on what can happen within 1km: Atmospheric Dispersion from Releases from Releases in the Vicinity of Buildings – C. Walsh & J. A. Jones, June 2002 (ISBN 0 85951 487 0)

National Radiological Protection Board

ACADEMIC/SCIENTIFIC RESEARCH

Tokyo Polytechnic University
Tall Buildings and Urban Habitat
:

UK GOVERMENT abolished the Commission for the Built Environment and the London Development Agency, reassigning their responsibilities to, among others, the Greater London Authority.

The Localisation Act devolves responsibilities from central & regional to more local authorities, such as the GLA. The ensuing political disruption may present an opportunity to influence Planning Policy, with regard to the importance of Tall Buildings and Urban Wind Impact, presently not considered as having much importance, if at all.

SOME ORGANISATIONS

RWDI – Consulting Engineers – ‘The science of buildings, structures and environment’ – Authors of 30-60 South Lambeth Road Wind Assessment report, WES affiliates
WES – UK Wind Engineering Society

WES is affiliated to the Institution of Civil Engineers
See also profile

WES is also affiliated to the International Association for Wind Engineering

The American Association for Wind Engineering
Council on Tall Buildings and Urban Habitat
Working Group – Wind Engineering

UK AUTHORITIES

Note the trend towards limiting the scope of wind impact to the immediate vicinity for ‘pedestrian comfort’, no consideration of broader impact on areas downwind of a tall building or group of tall buildings.

UK Government Select Committee on Tall Buildings 2001/2
CABE – Commission for Architecture and the Built Environment – (abolished 2011)
London Development Agency – (abolished March 2012):
Greater London Authority – the Mayor and London Plan

SOME USEFUL DEFINITIONS

Downdraft – the wind that flows down and around the face of the structure, causing a ‘Wind Tunnelling’, high-speed winds around the base of the building.

Eddy, eddies – small, relatively speaking, swirls of air, in a turbulent flow.

Laminar flow – smooth and even airflow

Leeward – Downwind of any structure or location point

Turbulence – Unstable flow of air, experienced as buffeting or gusts

Vortex – a volume of air that may be swirling

Wind shear – changes in wind speeds and directions in a 3d spatial volume (a space)

Wind wake – the effect of wind in the area downwind of a structure. The character of the area depends upon factors such as wind direction/speed, and whether the approaching wind is turbulent or not

Wind channelling – this happens when the wind is accelerated between two buildings or along streets with buildings along either side.

Wind Valley – similar to a channel, but wider