Radar expert reviews ground-penetrating radar report

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Sean Freeman, an arborist who has commented on this blog and who is part of the Veteran Tree Group, was kind enough to refer me to a ground-penetrating radar expert to have a look at GBG’s investigation in Laman Street. I needed this because I was – I was about to say confused but I think incredulous is more to the point – astounded at the information given out to the attendees at the charette that the roots we can all see on the report are reflections in the minerals in the bitumen.

Mr Richard Yelf is from Georadar which is the most experienced GPR company in Australia, with 25 years of experience behind them. I sent him an email giving him my take on what has happened in Laman Street and he looked at the radar report and wrote back to me within hours. He said,

‘I have read GBG’s report on their GPR survey for mapping tree roots at Laman Street.
 
I know GBG well and familiar with the standard and style of their work. I think they have done a reasonable job under the circumstances. They would not show roots on the drawings unless they actually saw them, so these features are real.
 
The interpretation has been complicated the 330 mm of crushed rock slag used as levelling fill and road base. The slag contains sintered carbon, and this adversely affects the radar. However the tree roots are visible on the radargrams and my comment as above is that these features (the tree roots) are real. They extend over multiple lines, and are non-linear as is typical of tree roots.
 
I think we can trust their interpretation. There would be many other roots, both smaller than 50 mm and also those roots that could not be detected, which are also present. GBG have not reported on these, they only report on what they can definitely see.
 
 He concluded with
‘In my opinion, having read the GBG report and being considered an expert in the field of GPR, my conclusion is that the tree roots which they have mapped are real features, and their interpretation is correct.’
Of course, the response to this may be NCC saying that the trenching failed to show roots so it presumably doesn’t matter to them what the radar shows, but it matters to residents.
 
Video footage should have been taken of the trenches and shown at the charette. If you seriously want to convince the community that you are giving them all the available information, this is the sort of evidence and the sort of occasion when this would have been perfect. Photographs were taken by council staff, if the footage seen on NBN news is to be believed – where are these?
 
More importantly, instead of spending  three days and lots of staff overtime digging yet more holes around these poor trees, which deserve better treatment, council should have asked a radar expert to review the report.
 
No- let’s use new-fangled technology when it suits us but resort to older methods when it doesn’t. And when the evidence doesn’t fit our theory or plans let’s ignore it.
And on a completely different topic –
if you have had a chance to read some of the earlier posts on this site you will have noticed my gripes about tree risk assessment. I worry because it seems so subjective and obviously varies depending on the expertise and experience of the professional givung the opinion. If one company gives an assessment that scares a government body we all suffer.
 
I just found the most wonderful quote  from Mike Ellison, a QTRA expert (and architect? I’ll have to look that up) about assessing the risk of tree safety:(from the qtra.co.uk website, in the public discussion section)
The issue of error [in quantifying tree risk] is currently being considered, but we do not operate to an absolute prescriptive threshold and any outcome that contradicts intuition can be reassessed and refined if necessary.
 The risk assessment of the trees in Laman Street is a great example of something that contradicts intuition.
Show me someone who would refuse to walk down Laman Street for fear of the trees falling on them.     Home
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3 Responses to “Radar expert reviews ground-penetrating radar report”

  1. Ali Says:

    Thanks for your tenacity and thoroughness Caity, this is very informative and encouraging.

  2. Jacqueline Says:

    I thank Mr Sean Freeman from Veteran Tree Group & Mr Richard Yelf from Georadar for helping you. This was enormously kind of them. It is also good to get confirmation that the roots are real.

  3. Ali Says:

    Hear Hear. My thankyou’s also, such input is incredibly valuable and much appreciated.

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