18.03.14 and 08.04.14
Bryn y Beili (SJ 235 643)
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Bryn y Beili (SJ 235 643)
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And what a dramatic day this turned out to
be! It had started with a visit to Moel
Ffagnallt (SJ 189 700) a rather unimposing small hill above the hamlet of
Rhes-y-cae. I was with Mark Trengove who
had suggested a day spent looking for ‘new’ P30’s, Moel Ffagnallt was the first
possibility (it just failed with 27.2m of drop). The second possibility was Bryn y Beili (Bailey
Hill in English).
At the top of Bryn y Beili is an impressive
motte and bailey built on an old glacial mound, just below the summit is a
bowling green which has a 135m spot height on it on the Ordnance Surveyed
enlarged Geograph map. It also has a
small recreational area with a slide, and a stone gorsedd circle where John,
Graham and I filmed one of the introductory videos to the survey of
Tryfan. We used the upright stones to
demonstrate how we planned to survey Adam or Eve.
The rise from the bowling green to the top of
the motte is steep; we estimated it as a minimum of 5m, placing the height of
the summit at approximately 140m (+/- 2m).
The critical bwlch for the hill lies in the cobweb of roads near to the
centre of Mold with the northerly valley to valley contour making its way up
(south) Ffordd Pennant until it reaches the junction with Gwernaffield Road. Just east of this road junction is Park
Avenue, which is the opposing road on the valley to valley traverse that makes
its way up (north) until it reaches the junction with Gwernaffield Road. This latter road junction has a 111m spot
height on the Ordnance Survey enlarged Geograph map.
We parked on Ffordd Pennant and assessed the
area of the bwlch as we walked into town for a relaxing hour in a pub with
dinner time grub. Whilst walking from
the car down (or should that be up) Gwernaffield Road we realised that we would
probably need two data sets from the road as it seems quite flat for 200 metres
or so. From one direction it seemed to
be going up and when looking back at the previously sighted point from the
point of upness it also seemed to be going up.
We debated this predicament and assessed the upness from a number of
points. During lunch we struck upon a
cunning plan and decided that a shop in Mold must sell a surveying implement
that may solve the ‘upness’ problem. The
surveying implement was found in a joke shop, it cost £2.50 (money well
spent!), with the theory being that when the newly bought, expensive surveying
implement was placed on the ground it would roll downhill. Unfortunately it was a little windy and the
technicalities of the surveying procedure quickly got out of hand as the
surveying implement kept being blown uphill.
This resulted in a number of giggles and the thought of what John and
Graham would think about the whole thing!
A photograph of the expensive surveying implement appears below.
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Mark proudly holds the expensive surveying implement
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Once we were fed we walked back to the area of
the bwlch and visited the car to pick up all necessary gear, we deposited the
football in the boot as its surveying life was probably not a lengthy one. Our next stop was the junction of Gwernaffield
Road and Park Avenue, this is where the 111m spot height appears on the OS
enlarged Geograph map. The Trimble was
placed on the pavement near to the road and whilst it gathered its ten minutes
of data Mark headed south to assess the bwlch from that direction, and I kept
my eye fixed on all traffic as I didn’t want the Trimble to end up as road
kill. We then headed further down / up
Gwernaffield road to the second point where we wanted to gather prospective
bwlch data from.
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At the junction of Gwernaffield Road and Park Avenue - gathering data next to roads can be highly dangerous for Trimbles
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Again the Trimble was positioned on the pavement
near to the road, we stood about four metres away, sufficiently close to grab
it if any rogue car decided to try and squash it, but also sufficiently far
away from it that we wouldn’t disrupt satellite coverage. It took quite some time to get toward the
required 0.1m accuracy before starting to ‘Log’ data; this was due to it having
cars passing it every few seconds.
During this time Mark and I chatted and waited patiently. I remember looking to my right and being
shocked to see a car on the pavement, having cut the corner of the road
junction, at that stage I remember being quite horrified as its front wheel had
already passed the Trimble by inches, but its rear wheel was on a collision
course with a very expensive bit of surveying equipment.
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DON'T SQUASH THE TRIMBLE!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
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I shouted in desperation for the driver to
stop and then watched as he drove straight over the Trimble. The car’s rear wheel went straight over the
centre of the Trimble and kicked it up slightly from the pavement. I expected to see it completely crushed and
splintered across the pavement, remarkably it sat there in one piece. Hard little beasts these Trimbles! The driver realised that something was amiss
because of me dashing towards his car shouting just before he tried to kill
it. He stopped and got out and was very
apologetic, we spoke for two or three minutes, he apologised profusely, and as
it was still in one piece and I was probably more concerned with its immediate
welfare than anything else, I didn’t think about asking or swapping insurance
details. After a few minutes he got back
in to his car and drove off. I inspected
the Trimble and the only external damage seemed to be on the outer casing on
the back, where the force of the impact had scuffed the black surround. Slight external damage is one thing but it is
the prospect of internal damage that is the concern.
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Battered
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| Bruised |
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| But still intact |
On our way to the top of Bryn y Beili we chatted
about the incident. Once on top we set
the Trimble up, firstly on the floor operating with its internal antenna, and
secondly on its 2m pole, operating with its external antenna. On both occasions it didn’t reach its
required 0.1m accuracy, therefore we did not ‘Log’ any data. The nearest it reached was 0.12m with its
external antenna. The reason for this
may be because of the mature tree coverage around the summit area. But of course it may be because the Trimble
was in a state of unrepairable shock.
Mark suggested we take a data set on a field close
to his house, which we did. The accuracy
of 0.1m was reached; it gathered data and this was then post-processed with no
seeming problem. I then gathered a data
set from a datum point outside my bungalow later that night and post-processed
the data the following morning. The
standard deviation was o.6 which is very poor and the height was 0.5m below the
usual measurement. This latter data set
coupled with the screen showing signs of flickering when trying to gather data
at the top of Bryn y Beili is a sign for concern.
The Trimble will have to be looked at by the
experts at KOREC UK. This has been
organised and I await their assessment.
I suspect there will be no more Trimbling for a few weeks. Hopefully when looked at/ repaired/ replaced
we can come back to Bryn y Beili and survey its summit. But until then the GeoXH 6000 is in the
Trimbe hospital being assessed.
I handed the Trimble over to Martyn Palmer at a
service station off the M54 near to Telford.
He set it running next to a new 7series Trimble, operating each machine
in sync with the other, his first assessment was encouraging as he said he
would be amazed if there was any internal damage. After a coffee and a good chat Martyn took
the Trimble off to the workshop at KOREC UK in Huntington.
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Can I have the nice pretty new one on the right please sir?
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Martyn Palmer assessing the XH 6000 against the new 7series
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Two weeks later it was delivered back to me with
a clean bill of health, quite remarkable considering a car tried to squish it
to smitherines. Bryn y Beili awaited and
it had to be surveyed with Mark. We
decided upon this evening, a lovely early spring day with blue sky, a slight
breeze and daylight hours extending to just beyond 8.00pm.
I parked in Mold and by 5.00pm I was on top of
the hill, having paid my respects to the scene of the crime. Mark was due to meet me at 6.00pm. I first tried the Trimble on the high point
using its internal antenna whilst on the ground. It achieved 0.12m accuracy, but never the
0.1m required to start logging data; pesky tree coverage was to blame.
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The scene of the crime with Bryn y Beili in the background
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I’d brought my old measuring staff as the
bowling green on the south of the motte has a 135m spot height on it on the
Ordnance Survey enlarged Geograph map, it also has good clear sky above it, so
if the tree coverage hampered data gathering at the summit, we could at least
gather data on the bowling green and then survey from this point to the summit using
my old staff.
Although the Trimble didn’t achieve its required
0.1m accuracy it was great to be out with it again. I then decided to try it at the gorsedd
circle just to the north of the motte, if I could get data from here we could use
the old staff to measure up to the high point.
Twenty minutes later and it still hadn’t reached the required accuracy;
it slowly crept down toward 0.1m but kept bouncing back up when reaching
0.15m. When this happens experience has
taught me to be patient, as each time it creeps back toward the required
accuracy it seems to get closer before bouncing back up again. But after the third or fourth time of this
happening I decided to visit the Bowling Green and its view of clear sky.
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The view of the motte from the gorsedd stone circle
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I
paced out the bowling green and put the Trimble where I imagined the spot
height appeared on the map. It was 5.50pm by the
time the Trimble attained 0.1m and I celebrated by quickly pressing ‘Log’. A few minutes later and Mark appeared in his
trendy surveying threads. We gathered
data at the bowling green for 20 minutes and then line surveyed from this point
to the summit; the height difference came to 26½ft / 8.1m. We’d already estimated that if this figure
came to 7m or more Bryn y Beili would probably be a new P30. But we really needed to get a good data set
from the summit.
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Gathering data on the bowling green with the motte behind the trees in the background
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One last try and this
time we set the Trimble up on its 2m pole, pushing this in to the ground for
extra stability whilst also using its bipod.
The distance from bottom of antenna to the ground was measured and input
as a measurement offset and we then waited and hoped that the magical 0.1m would
appear on the screen. Every few minutes
I checked it and every few minutes the figure crept down; 0.19, 0.15, 0.13 and
then 0.11m, the closest yet. A few
minutes later and there it was – 0.1m – at last!
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| Mark watches for rogue cars as the Trimble GeoXH 6000 eventually attains its 0.1m required accuracy |
It only took a road accident, over three
weeks and four goes on the summit to get the required accuracy. Once ‘Log’ was pressed I joined Mark and we
waited until over 30 minutes of data had been collected. All that was left was to pack everything away
and visit a pub for an evening meal, an excellent way to end a very fulfilling
evening’s survey.
Survey Result:
Bryn y Beili
Summit Grid Reference: SJ 23544 64367
Bwlch Height: 111.5m (converted to OSGM15)
Bwlch Grid Reference: SJ 23251 64429
The survey on the bowling green
came to 135.276m (converted to OSGM15), the height from this point to the summit using the old staff
was measured as 8.077m. Therefore the absolute height of the hill from this back-up survey is 143.4m. Whilst doing the survey
Mark asked me the margin of uncertainty associated with using the old measuring
staff over the distance and terrain from the bowling green to the summit, I
estimated +/- 1ft / 0.3m.
For further details please
consult the Trimble survey spreadsheet click {here}
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