UKTC Archive

How much special surface

Subject: How much special surface
From: Chris Hastie
Date: Dec 20 2002 14:12:56
I'm trying to reach a suitable compromise with all the other people
involved (highways design, highways maintenance, urban design, landscape
artichokes etc) over the nature of surfacing in a redevelopment of part
of Nottingham. This scheme is particularly significant because it will
apparently form the blue print for future street scene design briefs for

Naturally, I want a porous surface. With a tree friendly sub base,
probably something like Amsterdam soil, may be held in place using a geo
web (I'm told that the combination of geoweb and Amsterdam soil will
take a fair bit of heavy traffic).

Engineers want sealed York stone laid on a concrete slab.

If we were to compromise and have the porous surface only around trees -
how far should this extend? Companies marketing Amsterdam soil or
similar seem to indicate a figure of 5m³ of AS per tree (assuming newly
planted trees I think), to a depth of 1m. This gives a surface area of
5m², which equates to a 2.23m square, or a circle of radius 1.26m. This
doesn't seem a lot to me. Has any one any other suggestions?

I'd also be interested to hear of any existing, successful schemes
involving mixing paving and trees, whether existing trees or newly
planted. I'm particularly interested in Formpave Aquaflow blocks and
similar SUDS systems. One objection that has been raised to SUDS style
systems is the alleged need to replace surfaces after around 5 years
because of silting up. This seems like a ridiculous constraint to me,
and other people I've spoken to have been less than complimentary about
the person who raised this point! Anyone out there got any experience of
SUDS systems? I here they're more popular in Scotland - perhaps some
friendly Scottish subscriber could quiz their highways people for me.

My phoning round entirely partial people so far has also produced the
anecdotal comment that use of AS reduces root disruption. Apparently,
the provision of a good rooting environment tends to lead to the
proliferation of smaller roots and reduces the tendency of trees to
develop larger diameter roots heading off along kerb edges in search of
moisture (to anthropomorphise a bit). Any one know anything of this? And
what of the implications on stability?

Chris Hastie
Arboricultural Officer

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