UKTC Archive

Re: critical wind-speeds for tree failure

Subject: Re: critical wind-speeds for tree failure
From: Wayne Tyson
Date: Oct 12 2017 14:55:20
Here in the US, many trees are often left standing (albeit shorn of their
leaves and some of the smaller branches amidst the rubble of buildings
destroyed by a tornado--and some are down.

Wayne

On Thu, Oct 12, 2017 at 7:28 AM, Jim Quaife <jq@xxxxxxxxxxxxxxxxx.co.uk>
wrote:

I attach the Land-based Beaufort Scale as an appendix.

-----Original Message-----
From: uktc-request@xxxxxx.tree-care.info [mailto:uktc-request@lists.
tree-care.info] On Behalf Of Paul Muir
Sent: 12 October 2017 15:22
To: UK Tree Care
Subject: RE: critical wind-speeds for tree failure

...and I was suggesting that it is preferable to use the observable signs
one would expect to see during a Force 8 storm event (if that's what you've
settled on to advise your client with) rather than the equivalent wind
speeds, or even the term "force 8" for exactly the reasons you state
Jim...because what does force 8 mean to the layman? They might take the
quoted wind speeds and struggle with translating that to an action...with
many pitfalls available in the process.



Paul Muir
Senior Arboricultural Consultant / Contracts Administrator Treework
Environmental Practice
Mobile: 07966 XXXXXX
Head Office:  0117 XXX XXXX
www.treeworks.co.uk

Monarch House, 1-7 Smyth Road, Bedminster, Bristol, BS3 2BX


Treework Environmental Practice Covers the UK

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– Wales – Manchester and North

Treework Environmental Practice is the trading name of Treework Services
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-----Original Message-----
From: uktc-request@xxxxxx.tree-care.info [mailto:uktc-request@lists.
tree-care.info] On Behalf Of Jim Quaife
Sent: 12 October 2017 14:43
To: UK Tree Care
Subject: RE: critical wind-speeds for tree failure

Just bear in mind folks the recipient of a report.  He, she or it will
read the report but the first question is - so what?  They want to know
what to do in laymen's terms and the Beaufort Scale is designed for lay
people.  It is for guidance.
We arbs need to understand all we can, but there is no need to over-think
things for clients. Force 8 has never been challenged as a benchmark and it
is clear.  If we bung in a long paragraph explaining all the variables -
none of which are predictable - are we actually  answering the "so what"
question?
Don't get me wrong, the uktc discussion are useful, but the only reason
any of us is here (even TOs) is because someone is paying us to provide a
reasoned and understandable opinion and course of action.  I settled on
Force 8 a long time ago to avoid the arm-waving.
Jim

-----Original Message-----
From: uktc-request@xxxxxx.tree-care.info [mailto:uktc-request@lists.
tree-care.info] On Behalf Of Paul Muir
Sent: 12 October 2017 14:24
To: UK Tree Care
Subject: RE: critical wind-speeds for tree failure

Given the descriptive origins of the Beaufort scale, the fact that a
particular part of the scale is equivalent to a range of wind speeds, not a
particular speed, and that a description of a particular wind event in
relation to the wind profile adjacent to a tree is pretty complex and open
to all sorts of errors and misunderstandings I'd tend to steer clear of
setting any specific wind speed in this context.

All wind events are defined by an average and a gust speed, so whilst the
Beaufort Scale doesn't list the gust speeds in the table, there will be a
gust speed associated with the averages that are presented. Actually a
storm event will have different average and gusts speeds as it travels
across a land mass from the sea (there's a wind zone map in BS6399-2 1997,
and I'm sure foresters are familiar with this, or similar zone maps), and
both the average and gust speeds are further affected by the roughness
category of the land preceding the object within the path of the wind
event. All of which means that there's a lot of uncertainty about the
relationship of the wind speed that is measured at a measuring station,
what it will be at a site, and how this relates to the weather event on a
national or regional scale.

All of which means that the text that is at the core of the Beaufort
Scale, describing the observable effects on trees and tree crowns, seem far
more appropriate and useful, and far less likely to be open to significant
errors or misinterpretation. Setting Force 8 as a threshold means one
closes a site when the winds are strong enough to break twigs. For this
observable outcome to occur at a sheltered site in comparison to an exposed
site would require different wind speeds at your nearest weather station.
I'd say the observable signs were more important in relation to the
likelihood of tree failure.



Paul Muir
Senior Arboricultural Consultant / Contracts Administrator Treework
Environmental Practice
Mobile: 07966 XXXXXX
Head Office:  0117 XXX XXXX
www.treeworks.co.uk

Monarch House, 1-7 Smyth Road, Bedminster, Bristol, BS3 2BX


Treework Environmental Practice Covers the UK

London and South East  – Birmingham and Midlands – Bristol and South West
– Wales – Manchester and North

Treework Environmental Practice is the trading name of Treework Services
Ltd.
Registered Office & Place of Registration: Treework Services Ltd, Monarch
House, 1-7 Smyth Road, Bedminster, Bristol, BS3 2BX

Reg No.: 1621606
VAT No.: 397 XXXX XX

This email including attachments is intended for the addressed recipient
only.  It may contain confidential information and may be subject to legal,
professional or other privilege. It must not be copied, disclosed or used
by any other person.  If you are not the intended recipient, please notify
the sender and then delete from your system immediately.

Treework Environmental Practice does not guarantee the attachments or
enclosures are secure or virus-free.

-----Original Message-----
From: uktc-request@xxxxxx.tree-care.info [mailto:uktc-request@lists.
tree-care.info] On Behalf Of Jim Quaife
Sent: 12 October 2017 12:12
To: UK Tree Care
Subject: RE: critical wind-speeds for tree failure

For many years now we have indicated Force 8 on the land-based Beaufort
Scale (handy because many of the indicators refer to trees) as being a
speed which should prompt a check of trees we have identified.  This was a
benchmark arrived at by a consensus of a gaggle of arbs over a few years,
but of course it doesn't account for gusts, and nor can it possibly take
account of the actual individual vulnerability of a tree or its oscillation
movements.
In short Force 8 is probably "wrong", but it is rather more useful to a
client than the vagueness of "have a butcher's if it's a bit windy"
approach.
We have never been challenged about it, but then again how many trees blow
over or fracture?  We have our standard caveat paragraph which I have
published on and off for 20 years or so, so I may as well paste it below.
(Before the howls of derision start I did construe it with a QC's opinion -
and that wasn't cheap!). Please bear in mind that legally it - using the
words of the QC - isn't worth the paper it is written on, but it sets the
scene and provides guidance and perspective to the client.  In the event of
a court claim the court would decide what is a reasonable duration period
for my opinions - I can't divest myself of my legal responsibilities just
by saying so!
Jim
The statements made in this Report do not take account of the effects of
extremes of climate, vandalism or accident, whether physical, chemical or
fire.  Quaife Woodlands cannot therefore accept any liability in connection
with these factors, nor where prescribed work is not carried out in a
correct and professional manner in accordance with current good practice.
The authority of this Report ceases at any stated time limit within it, or
if none stated after two years from the date of the survey or when any site
conditions change, or pruning or other works unspecified in the Report are
carried out to, or affecting, the Subject Tree(s), whichever is the sooner.
-----Original Message-----
From: uktc-request@xxxxxx.tree-care.info [mailto:uktc-request@lists.
tree-care.info] On Behalf Of Alastair Durkin
Sent: 12 October 2017 11:58
To: UK Tree Care
Subject: RE: critical wind-speeds for tree failure

Hi Rupert

This was from the 2017 AA amenity conference in Exeter:

https://www.trees.org.uk/Amenity-Conference/Wednesday-Speakers-2017

-----Original Message-----
From: uktc-request@xxxxxx.tree-care.info [mailto:uktc-request@lists.
tree-care.info] On Behalf Of Rupert Baker
Sent: 12 October 2017 11:23
To: UK Tree Care
Subject: critical wind-speeds for tree failure

Hi collective,

I googled this term when puzzling over a request to suggest a critical
wind speed above which a woodland should be closed;  it came up with

https://www.trees.org.uk/Trees.org.uk/media/Trees-org.
uk/Documents/Conferenc
e17/WED-08-Prof-Steffen-Rust.pdf which appear to be a powerpoint
presentation from this year.  Now the main address is the AA;  anyone know
which seminar or W.H.Y. this came from?

The authors/presenters are Steffen Rust, Lothar Gocke (with an umlaut on
the
o) and Franziska Jachning



All the best



Rupert




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