26.07.18 Great Rhos (SO 182 638, bwlch only [SO 177
718]) and Pegwn Mawr (SO 023 812, bwlch only [SN 926 800])
It was only a short walk
down a vehicle track heading toward the rail line through the parched land of a
field to where I wanted to gather Trimble data from. Thankfully all was quiet as I went about my
business; I had consulted the timetable before deciding which bwlch to survey
first and no trains were planned to use this track for the next 80 minutes. However, as I placed the Trimble atop my
rucksack to give it elevation above its immediate surrounds and measured the
offset between its internal antenna and the ground below, I was conscious that
I should not linger.
 |
| The vehicle track leading down toward the rail line |
Thankfully the Trimble
attained its 0.1m accuracy level before data should be logged in the customary
quick way, and once it was activated to gather data I stood back and counted
the seconds to when the allocated five minutes of data were collected and
stored. I then switched the equipment
off, took a number of photographs from different directions and packed the
Trimble away, gathered up my rucksack, and opened the gate giving me access
back in to the field leading toward my car.
 |
| Gathering data at what proved to be the critical bwlch of Great Rhos |
Once on the minor lane I
walked past my car and up the track toward Maylord farm as I wanted to gather a
data set from where the current listed position of this bwlch is given, and
even though this was visually much higher on the hill to hill traverse it would
complete all necessary surveys for this bwlch position.
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| The Trimble set-up position for the second survey at the southerly bwlch |
The critical point of
this higher position is placed beside the gravel track leading to Maylord farm,
and as the Trimble beeped away in the morning sunshine I gained height to its
north-east and took a series of photographs looking back down on its position,
that of my car and the rail line below.
Once five minutes of data were gathered I closed the Trimble down,
packed it away and headed back to my car for the drive north to the outskirts
of Llangurig where the northerly bwlch is placed.
 |
| Gathering data for the second position at the southerly bwlch |
LIDAR covers this
northerly bwlch although its analysis is not as easy as many other bylchau I
have looked at over recent months, the reason for this is that the A 470 road has
elevated the ground it is built on and the disused railway has created a
cutting. However, extensive LIDAR
analysis led me to believe that the natural bwlch is still intact and I came
prepared with three ten figure grid references and their respective heights
produced by LIDAR analysis.
 |
| LIDAR image of the northern bwlch |
The first position to
survey was where LIDAR places the natural bwlch, the second is a remaining
natural bwlch that is higher on the hill to hill traverse and therefore not the
natural bwlch, with this second point having been recently terra-formed by the
introduction of wide gravelled tracks, and the third position is where the
valley to valley traverse meets in the railway cutting.
I parked on the wide
gravelled track which heads up toward Maesgwyn farm, from here a public
footpath heads across the field to where the natural bwlch is positioned, as I was
entering the field a large wagon chugged its way down the gravel track and
stopped beside my car and the diver shouted over that it was best that I park
in the near lay-by as vehicles would be using the track during the next few
hours, I duly moved my car and proceeded to walk back on the road to gain
access to the gate leading in to the field.
By now the sun was
increasing in strength and even though all I did was walk on relatively level
ground it brought beads of sweat to my brow, the blue of the sky was radiant
above and as I went about this next series of surveys, cars hurtled past on the
A 470, all blissfully unaware of the unusual proceedings being conducted in the
field next to the road!
The ten figure grid
reference produced by LIDAR analysis zeroed me in to the critical and natural
bwlch and once the Trimble had been set up I gathered 11 minutes of data. I was not the only one in the field as a herd
of cows were slowly grazing their way toward where the Trimble was placed,
thankfully none came too close and the survey proceeded without any difficulty.
 |
| Gathering data at what proved to be the intact natural and critical bwlch of Pegwn Mawr |
LIDAR analysis also
indicates that there is another remaining natural bwlch that is higher on the
hill to hill traverse and therefore not the natural bwlch, and whilst here I
thought I should also gather data from this second point, which I duly
did. This second point is where ground
has recently been disturbed through the construction of either a new track or
the widening of existing tracks, and another five minutes of data were gathered
from this position.
 |
| Gathering data for the second position at the northerly bwlch |
All that remained was to
gather a data set from the disused rail cutting; thankfully a gate gives easy
access to this from the main road close to where my car was parked. And again the ten figure grid reference obtained
from LIDAR analysis directed me to the critical point, as this was deep in an
overgrown cutting I decided that 15 minutes of data should be gathered, and
whilst the Trimble did its stuff I tried to persuade one of three grazing cows
that it did not want to eat the Trimble, thankfully once it had taken a few
unwelcome steps toward it my encouragement not to come any closer seemed to do
the trick and it gently backed away to continue chomping on grass.
 |
| The Trimble being eyed up by an inquisitive cow in the overgrown remains of the railway cutting |
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| Gathering data for the third position at the northerly bwlch |
As the Trimble gathered
this last data set of the day I sat on a grassed hummock and watched the three
cows whilst luxuriating myself in the warmth of the morning. Once 15 minutes of data were gathered and
stored I headed back to my car and called on good friends in Llanidloes; Eryl
and Rita, to sit in the sun for a number of hours catching up with conversation
and enjoying a lovely lunch, an excellent end to a good morning’s surveying.
Survey Result:
Great Rhos
Summit Height: 659.9m (converted to OSGM15, from subsequent Trimble GeoXH 6000 survey)
Summit Grid Reference: SO 18213 63896 (from subsequent Trimble GeoXH 6000 survey)
Bwlch Height: 281.3m (converted to OSGM15)
Bwlch Grid Reference: SO 17776 71803
Drop: 378.6m
Dominance: 57.38%
Pegwn Mawr
Summit Height: 585.3m (converted to OSGM15, average of two subsequent Trimble
GeoXH 6000 surveys)
Summit Grid Reference: SO 02391 81239 (from subsequent Trimble GeoXH 6000 survey)
Bwlch Height: 285.9m (converted to OSGM15, natural bwlch)
Bwlch Height: 283.8m (converted to OSGM15, disused rail cutting)
Bwlch Grid Reference: SN 92693 80074 (natural bwlch)
Bwlch Grid Reference: SN 92601 80035 (disused rail cutting)
Drop: 299.3m (natural bwlch)
Drop: 301.5m (disused rail cutting bwlch)
Dominance: 51.14% (natural bwlch)
Dominance: 51.51% (disused rail cutting bwlch)
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