On 04 January 2005 11:29, Cameron Gibson wrote:
If I have the right incident, I think it was 2 x 250 yr old
Beech. The
report was in the Daily Mail yesterday. The Chief Inspector of the
Police commented that the trees had been inspected regularly
and that it
was a freak accident. The report also stated that the winds
reached up
to 60mph. I didnt think that this, on its own, was sufficient to blow
over a mature Beech in a woodland but I guess this comment
may open up a
can of worms and put me to rights.
60mph is a lot of wind (force 10), and I've seen 70mph (force 11) quoted
in places. <http://www.stormfax.com/beaufort.htm> has some nice little
pictures illustrating the effects of these winds. At force 10 the tree
in the picture is in three pieces, the flag pole has snapped and the
roof has blown off the house. By force 11 the whole house is on its way
out, which seems a little extreme, but basically, it's a lot of wind.
Elsewhere, I've seen force 10 described as "Seldom experienced inland;
trees uprooted; considerable structural damage occurs."
Since the tree presumably hit the ground I would be inclined not to
assume it was actually in woodland. A woodland edge tree perhaps. And
since two of them came down, a freak localised gust seems plausible.
Furthermore, the strength of gusts needs context. I don't know the area,
but say we are talking about a relatively sheltered lowland site. If
those gust strengths are measured at the site, then this is an amount of
wind that the trees will not be used to withstanding. A tree on an
exposed upland site may routinely be hit by 60mph (well not that
routinely, as I said, it's a lot of wind) and have adapted to that. In
this context, wind direction is also relevant.
--
Chris Hastie
Strategy Officer (Arboriculture)
Warwick District Council
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