5837 and topo surveys

[sloth]

Just out of interest, when doing 5837 surveys on small scale residential developments do you insist on a full topo survey prior to carrying out any tree survey?

I'd be interested too in any current or former TOs opinions on the matter.

 

It says in 5837 4.2.1 "An accurately measured topographical survey should be undertaken showing all relevant features."

('should', not 'must')

 

In my experience, on these small developments there is rarely an accurate professionally produced topo available, or if there is it was produced prior to any kind of arb input and therefore is often missing relevant trees. How do you work around these situations? I tend to measure from significant fixed points and add the trees in myself; obviously this won't be 'pro topo' accuracy, but accurate enough in most cases. Where a tree is obviously (by several or many meters) away from potential impacts I am happy with this, otherwise I will obviously say so, and in any case I mention this is how I have produced the AIA etc and that it has been a limitation. Up until now, this has never been an issue for me - to be honest the site owner in this case really should have got a topo produced anyway (as he had been advised to by the LA planning dept.), so I was just working with what I had been provided with, however there is one tree in particular which has prompted this query.

Perhaps I should refuse to carry out any survey in future until an accurate topo has been produced, but I suspect for many of the small household extension type jobs (which make up a good portion of my 5837 work) this would lose me work...

Bit of a rambling post, sorry, I'm tired and it's been long day already!

[Gary Prentice]

I can't answer from the TO point of view, but generally for missing trees, I do the same as you - triangulate from other fixed objects to plot it.

 

To date, fortunately, I've always had topo's supplied or arranged to get them done for the client. If, for an extension as your example, none was forthcoming I think I'd look at OS mapping to plot the trees on and explain how any plans had then been drawn.

 

Sorry, not much help really, am I?

[sloth]

Helpful in as much as knowing I'm not the only one doing it that way!

[Gary Prentice]

I guess that it isn't wrong if whatever is produced is acceptable as being suitable by the planning authority.

 

If the client understands that it may not be, in the absence of a topo, then they assume the risk if they don't want to pay for the land survey.

[Andrew McEwan]

NTM mapping overlaid on an aerial photo will help you get accurate canopy outlines, but obviously not stem position.

[Gary Prentice]

Andrew, I had a quick look at that - looks terrifying!

 

Kevin. Do you use any GIS/GPS hardware? It's all 'dark arts' to me ATM but I wonder if the accuracy of what's available (at a reasonable cost) is sufficient to plot onto downloaded OS maps.

 

Paul Barton organised something a yr or two back with CAS, keysoft solutions and a really good speaker on GIS whose name escapes me. The GIS part was a bit above my head, but it's pretty remarkable.

[sloth]

As long as you make it clear in your report that trees missed from the 'topo'/site plan have been plotted manually with a degree of error of + or - 3m or similar then there shouldn't be a problem. I would also add which trees had been plotted in this way.

 

BS 5837 is guidance/recommendations, not the law. As it says in the Standard; Its recommendations are expressed in sentences in which the principal auxiliary verb is “should”.

My thoughts too. If you're having to argue your case down to metre or two being the difference between too close and OK, it's probably a bit contentious anyway!

 

Kevin. Do you use any GIS/GPS hardware? It's all 'dark arts' to me ATM but I wonder if the accuracy of what's available (at a reasonable cost) is sufficient to plot onto downloaded OS maps.

 

Paul Barton organised something a yr or two back with CAS, keysoft solutions and a really good speaker on GIS whose name escapes me. The GIS part was a bit above my head, but it's pretty remarkable.

 

I do use a GPS data logger, which I think is accurate to about 2m, but this can vary depending on the weather/canopy cover/high buildings/number of available satellites etc... Which is fine for safety surveys (with tags to be sure sometimes), and for using with topos with tree positions added.

Sub meter or less equipment is a big price jump, and producing your own topo from scratch is different job entirely and not something for a lowly arb! Using a mastermap is fine for small sites with no topo ime, if you can measure from a fixed point (like a building being extended) so it's all relative. However OS mastermaps are quite limited for planning use I think - they don't have many important site features and buildings aren't always true to shape/size/orientation etc. Also they vary in accuracy of data points depending on the scale by +/-1m up to many meters (see https://www.ordnancesurvey.co.uk/business-and-government/help-and-support/products/topography-layer.html tab 'how accurate is OS mastermap topography layer?') which makes the sub meter accuracy GPS equipment kind of pointless; unless you have been provided a pro produced site topo, but then you'd expect to see the trees plotted anyway!

I don't use gis, but as I understand it that's more like clicking a point on a map and being presented with data relative to that point (a tree for example). In that respect I think it's more suited to LA TPO maps online, as opposed to a written report and plan on paper.

Would the speaker have James England? He helped me decide when looking at GPS gear options, vary knowledgeable chap with arbcentric experience...

[Gary Prentice]

Hi Kevin, yes James England. His surname came to mind last night.

 

I've used OS maps for basic surveys (with tree tags), but was wondering about their use in place of topographicals. Considering the inaccuracies in OS mapping I see daily on council websites you're almost certainly right:biggrin:

 

Which data logger are you using? I'm sick of manually inputting site data into CAD, then again into the report. I do need to be better informed though before such a major purchase.

[sloth]

I'm using a getac ps236, it's pretty old now, but fairly indestructible and fully waterproof! It's essentially a Windows mobile device, but rugged and with a GPS receiver, using pocketgis for mapping. I think you can get all sorts of options now, including android rather than Windows. Ultimately I went for pear because it was didn't involve an autocad licence and learning that, the pear mapper is pretty intuitive and there support is second to none. They can, while on the phone, take over your map programme and talk you through things even. The time saved in not having to type out hand taken surveys into Excel makes it so worthwhile! A survey of 20 or 30 trees might take me a few hours by the time I've gone back and double checked it all, with the gadget I plug it in and it's there in minutes, which is nice. The full pear package cost me a couple of grand I think (several years ago now) at a time when I really debated if I could afford/justify it, it was worth every penny...

[sloth]

Oh, it also automatically plots all the trees/RPAs etc too, which saves time, and time is money...