13.06.17
Fan Brycheiniog (SN 824 220, only bwlch surveyed)
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| Gathering data at the bwlch of Fan Brycheiniog |
Standing beside an A
road watching cars and lorries thunder past a small piece of surveying
equipment could be thought of as an unusual pastime, to many it undoubtedly is,
but there is a satisfaction to such a thing, albeit an unusual one.
Having visited Mynydd y
Drum and the Nant Helen Opencast Mine and with a small walk above Llanfair-ym-Muallt
(Builth Wells) pencilled in for later in the day I thought I’d better survey
the critical bwlch of Fan Brycheiniog; one of south Wales’ highest
mountains. This bwlch is positioned on
or beside the A 4067 as it heads southward from Sennybridge toward
Ystradgynlais, it was a bwlch I drove over earlier in the day and when doing so
I tried to judge where its critical point lay.
Thankfully the road has
a number of large pull-ins close to the area of the bwlch and once out of my
car I went to work. This work consisted
of bending over, kneeling and sometimes lying on the ground assessing where the
uphill from the valley to valley traverse meets the downhill from the hill to
hill traverse. When doing this it is
advantageous to gain height for an overall view of the scene, unfortunately the
ground to the east of the road is steep and therefore I used a conveniently
placed ladder stile to stand on top of and gain a little elevation to assess
the lay of land.
It proved easy to judge
where the upper part of the northern valley lay as the reed grass and wet
surrounds of the Blaen-crai was positioned beside the ladder stile, which was
only a few metres from the road. I
marched back to the lay-by where my car was parked and proceeded to kneel on
the grass verge to look at the uphill part of the road, there seemed to be two
points where the high point may lie, with a slight dip in the road between.
I ummed and aghed for
ten minutes or so wondering which out of these two points to gather data from,
on the eastern side of the road a drainage ditch beside the grass verge helped
in judging where the downward southern land lay, however as drainage ditches
aren’t necessarily consistent in their depth I decided only to treat this as an
indicator of where the critical point may lie.
During this process
vehicles sped past, one thing was certain the Trimble was not going to be
set-up on the road, perhaps if this bwlch was on a country lane it would be all
right to do so, but a busy A road was asking for trouble. Deciding on my point I set the Trimble up on
my rucksack and measured a 0.42m offset between the equipment’s internal
antenna and the ground at the base of the rucksack and waited until the 0.1m
accuracy level was attained before data should be logged.
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| The Trimble set-up position at the bwlch of Fan Brycheiniog |
During data collection I
made a note of how many vehicles whizzed past heading south, the total amounted
to eight cars and four Lorries, all within five minutes; hopefully the data set
won’t be compromised by this activity.
Once the allotted five
minutes of data collection were up, I switched the equipment off, packed it
away and headed north to the outskirts of Llanfair-ym-Muallt (Builth Wells) and
the joys of Garth (SO 053 506), a hill I’d wanted to visit for many a year.
Postscript:
Since this survey took place the details for the bwlch of this hill have been ascertained from LIDAR analysis conducted by Aled Williams, and these details are being prioritised in favour of those produced by the Trimble GeoXH 6000.
Survey Result:
Fan Brycheiniog
Summit Height: 802.7m (converted to OSGM15, Trimble GeoXH 6000)
Summit Grid Reference: SN 82435 22060 (Trimble GeoXH 6000)
Bwlch Height: 378.5m (LIDAR)
Bwlch Grid Reference: SN 87056 19547 (LIDAR)
Drop: 424.2m (Trimble GeoXH 6000 summit and LIDAR bwlch)
Dominance: 52.84% (Trimble GeoXH 6000 summit and LIDAR bwlch)
Dominance: 52.84% (Trimble GeoXH 6000 summit and LIDAR bwlch)
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