VALID Tree Risk Here’s the tree at the junction of South Ealing Road and Little Ealing Lane getting blown
Updated with some photos and commentary.
Picked up this London Plane pollard fall into the road dashcam footage through a Facebook post (hat tip to Linda Saretok). The dashcam footage is here.
Here's Google Maps street view, with the timeline function turned on for those of you who want to have a look around.
The photos show the changes in hard standing going back to 2008 from Google Street View.
The main resurfacing was between 2008 - 2012.
Half the surfacing at the structural roots changes to black stuff between 2012 - 2014
An additional rectangle of black stuff is added shop-side between 2016 - 2017
Then some crops of the uprooted tree.
From the dashcam footage it looks like it's rotated by about 90 degrees when it fell. The decayed roots at about 9 O'Clock are what were facing South Ealing Road - the direction the fell.
The most intact roots, with the root hairs, looks like it's come from under the most recent black topdressing between 2016-17
I was asked about how this would’ve been risk assessed by VALID. Here's my take on it with VALID's Tree Risk-Benefit Management Strategy. It's based on the dashcam footage and Google street view images and is made with those limitations.
This a 'Very High' level of occupancy (on average more than one person. Or more than one vehicle. Or more than person and more than one vehicle). It would've been managed by Active and Passive Assessment. There are three levels of Active Assessment. Basic, Detailed, and Advanced.
Passive Assessment - Risk is Acceptable
If you walked or drove past this tree, there's no obvious tree risk feature to trigger taking a closer look.
Active Assessment
Basic Assessment - Risk is Acceptable
On foot. There are no obvious tree risk features. It looks there has been no recent major infrastructure work within the structural root zone to warrant any concern. I can't see a trigger to go beyond a Basic Assessment to a Detailed level. New surface dressing in structural root zone would’ve encouraged a tap at the root collar.
Detailed Assessment - Risk is Acceptable
I'm not sure a Detailed Assessment, triggered because some decay was picked up by a sounding hammer, would've revealed the extent of decay in the roots. There's some uncertainty about this, but the buttressing looks like it's nicely developed for a tree of this size, age, and management history.
Advanced Assessment - Risk is Not Acceptable
I think only an Advanced Assessment, involving a Static Load Test, would've established that the tree had a Safety Factor of less than 1.0. But I can't see a trigger to reasonably justify this.
It wasn't THAT windy on Sunday in South Ealing. I wonder whether primary failure happened with the storms we had earlier (or last year), and it's only as the tree's come into full foliage, 3-4 years (?) into its pollard cycle, that the moderate wind load intercepted by the canopy hit the critical point.
Of course, it could be a 'black swan'. Generally, the chances of regularly pollarded London Plane, with no obvious tree risk features, and no obvious recent root damage, falling are incredibly low.
It now presents an interesting problem for the council. That paving specification at pedestrian crossings might be of concern given how long ago it was done and the root system resembles that of spring onion.
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