UKTC Archive

RE: Water Demand of Cotoneaster

Subject: RE: Water Demand of Cotoneaster
From: Jim Quaife
Date: Sep 06 2017 06:11:47
There is some conjecture as to whether 4.2 should be used for 
back-calculation, although it seems to be so used regularly.  The foundation 
depths are all very precise, but the basis of them is rudimentary (and have 
been progressively increased), and the mature heights of the species are as a 
matter of course very modest.  It is all we have to go on and is regarded as 
factual data particularly if subject to litigation.
The faux accuracy of 4.2, RPAs and NJUG is intriguing, although I accept that 
in the absence of anything else we have to have some basis for decisions.  I 
return to my normal maxim that arboriculture is a matter of justification.
Heave is a factor that I have to explain to engineers (on a less regular 
basis nowadays - perhaps the message is getting through or maybe I just deal 
with the same people) and foundation design should be a matter of 
comprehensive site investigation.
The attention paid by building control officers generally errs on the side of 
caution (having peered into the trench, "another 500" is not an uncommon 
comment).  The big problem is PD construction, particularly conservatories 
when a 600 footing is frequently installed irrespective of site conditions 
and trees.  (I am going to another such case tomorrow).
Roots abstract water from a zone underneath them due to capillary action so 
roots which "stop" at the foundation depth can still present a risk.
With regard to heave there is a difference between annual soil volume 
variation with post-Christmas field capacity recovery, and a persistent 
moisture deficit.
Jim

-----Original Message-----
From: uktc-request@xxxxxx.tree-care.info 
[mailto:uktc-request@xxxxxx.tree-care.info] On Behalf Of Oisin
Sent: 05 September 2017 18:45
To: UK Tree Care
Subject: RE: Water Demand of Cotoneaster

<< Whether the soil is currently desiccated or not is not really a 
consideration>>

Yes it is. If there is no desiccation, the clay will not take up more water. 
It will pool or run-off.

When giving tree info for foundations calcs for felled trees, you need to 
compare tree height at time of removal v NHBC mature tree height and follow 
the guidance in Table 3a. Also see 4.2.9 if levels have changed.

Oisin
-----Original Message-----
From: uktc-request@xxxxxx.tree-care.info 
[mailto:uktc-request@xxxxxx.tree-care.info] On Behalf Of Bill Anderson
Sent: 05 September 2017 18:07
To: UK Tree Care <uktc@xxxxxx.tree-care.info>
Subject: Re: Water Demand of Cotoneaster

The heave risk ought to take account of future drought events and subsequent 
rainfall oughtn't it? Whether the soil is currently desiccated or not is not 
really a consideration. (I don't consider this to be shooting your hat off 
Andrew....) Bill.

On 5 September 2017 at 17:22, "Andrew Belson" <uktc@xxxxxx.tree-care.info>
wrote:

Dear Will and Collective,

I rarely put my head above the parapets as when I do, I usually get my 
hat shot off....

That said, here's my opinion.

You say the site is cleared.  In that case, all you need to know for 
the heave risk is: 'is the soil desiccated? (at or below foundation depth)'
Soil testing will tell you that.  The vegetation present is irrelevant 
(so far as heave calculation is concerned).

Heave = recovery; therefore, no desiccation = no volume to recover.

In relation to foundation design, if pushed for a 'water demand' for a 
Cotoneaster then I'd say 'medium' based on the fact that the NHBC have 
put most of the Rosaceae trees in that part of Table 12.

I'd put Pittosporum in 'Low' because of the (relatively) slow growth 
and hard leaves.  However, as others have pointed out, if you don’t 
know, you have to assume worst case for the NHBC to be happy.

The final point I want to make is that I think we should collectively 
avoid referring to roots 'below foundations'.  My preference being 'at 
foundation depth'.  This is because I think it perpetuates the 
layman's understanding of how trees cause damage.

Regards,

Andrew




-----Original Message-----
From: uktc-request@xxxxxx.tree-care.info [mailto:uktc-request@lists.
tree-care.info] On Behalf Of will ross
Sent: 05 September 2017 10:59
To: UK Tree Care <uktc@xxxxxx.tree-care.info>
Subject: RE: Water Demand of Cotoneaster

I agree with both answers in this case the site has been cleared and 
the engineer is trying to work out the so called water demand of the 
trees/shrubs that were there to design for potential  heave, in 
reality I agree with Jim as far as rooting depth and also general 
conditions including vitality of particular specimens.
Again many thanks , any further thoughts would be welcome.

Will

-----Original Message-----
From: uktc-request@xxxxxx.tree-care.info [mailto:uktc-request@lists.
tree-care.info] On Behalf Of Liam McKarry
Sent: 05 September 2017 10:46
To: UK Tree Care
Subject: RE: Water Demand of Cotoneaster

I've always thought 'Water Demand' was a silly term.

Plants remove water from the soil, anything that can root under 
foundations can therefore remove water from clay causing it to reduce 
in size meaning that foundations will move downward. Whether it's high 
demand or low demand seems a bit arbitrary.

If differential movement has occurred where the plant is and there are 
roots beneath the foundations it's a good bet that it's either the 
sole cause or a contributing factor (in combination with other 
trees/shrubs
nearby) to the clay shrinkage.



Liam McKarry
Arboricultural Officer (Planning) • Corporate and Place Services   •
Colchester Borough Council • www.colchester.gov.uk


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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: 05 September 2017 10:23
To: UK Tree Care <uktc@xxxxxx.tree-care.info>
Subject: RE: Water Demand of Cotoneaster

Water demand is a term that is understood and in common usage, but the 
trees with the higher WD are generally those better able to root 
deeply - coincidence eh??
I doubt that there are any data so if you need to be definite it would 
have to be a trial hole to discover the rooting depth profile.
I know that pyracantha is a bad boy in subs, but usually when grown 
against the wall.  I have no idea about cotoneaster.
Jim

-----Original Message-----
From: uktc-request@xxxxxx.tree-care.info [mailto:uktc-request@lists.
tree-care.info] On Behalf Of will ross
Sent: 05 September 2017 10:06
To: UK Tree Care
Subject: Water Demand of Cotoneaster

Hi,

    Does anyone have an idea of water demand for a cotoneaster, I am 
working from a third party report and the engineer is requesting 
further detail, the estimated height was 8m so I presume it was one of 
the large shrub/tree type such as waterii, also they have asked for 
the water demand of Pittosporum which I can't find. Any help would be 
welcome.



Will




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