Friday, 18 September 2015

Mapping Mountains – Trimble Surveys – Bannau Brycheiniog

18.08.15  Pen y Fan (SO 012 215, only bwlch surveyed [SH 931 000])  

The critical bwlch of Pen y Fan (SH 931 000)

There can be a perverse sense of fulfilment and enjoyment in surveying bylchau, this is not something that is always evident when tackling summits.  Although the high point of a hill can sometimes be found in the most unusual of places, bylchau are prone to be situated in land that can be thought of as rather esoteric.

There’s also the added excitement of making forays onto ground that is private, permission to do so should of course be sought, but occasionally circumstance necessitates a clandestine visit, assessing the ground as quickly and as accurately as time allows and getting back onto the relative safety of common or public ground as quickly as possible.

A number of today’s bylchau fitted the scenario as outlined above, with the first and the only one this blog post deals with, in a field on the outskirts of Talerddig, which is situated beside the A470 between Caersws and Glantwymyn (Cemmaes Road).

Depending upon one’s inclination this particular bwlch is one of two that are the most important in Wales, as it spits the Regional mass of North Wales from that of Mid and West Wales.  This point is also the critical bwlch for Pen y Fan, and the association between summit and critical bwlch can also be rather perverse as in this instance the former is the highest point in South Wales and dominates the skyline with its distinctive profile, whilst the latter is almost forgotten except by the occasional passing bwlch connoisseur who enjoys this kind of thing!

The critical bwlch of Pen y Fan can be found in a field on the outskirts of the small community of Talerddig, which according to many on-line entries is a small village in Mid-Wales, however topographically the village is split between the Regions of North Wales and that of Mid and West Wales.  This Regional split will be detailed in a later blog post and will form an intrinsic part of a hill list co-authored with Aled Williams. 

The area of this critical bwlch has a 218m spot height at SH 93198 00039 on Ordnance Survey maps, this spot height is placed on the A470.  Centralising the hill to hill contours suggests that the critical bwlch is placed just to the south of this road; this is backed up by driving around the area in a Google Car which suggests that the critical bwlch is placed somewhat below this road to the south in a field.  The bwlch area also has a railway cutting to its west; this cutting is substantial and formed part of the line between Newtown and Machynlleth, which was closed during the Beeching cuts.  This cutting is 37m (120ft) deep and when completed in 1862 it was the deepest railway cutting in the world, but as I was looking for the natural bwlch the old railway line and its cutting could wait for another day for a person a little more adventurous than me.

I set off relatively early from Welshpool and once in Talerddig I parked just off the A470 and walked back up the road to examine the lay of the land.  A quick inspection confirmed what I had seen when whizzing around in the Google Car as the ground fell away from the road to its south.  However, once in one of the fields I wondered where exactly the critical bwlch lay as there was a vegetated water channel running the length of a near hedge and a land bridge of earth and grass crossing it to gain access into the adjacent field through a gate.  The land then continued toward a house, it was this land that formed part of the valley to valley traverse, as with most bylchau the hill to hill traverse is relatively easy to ascertain but the valley to valley traverse can be problematic to pinpoint when doing so without the aid of an optical implement and a grid of flags.

Between me and the house was a hedge, gate and another open field with very little coverage to camouflage proceedings, thankfully the bedroom curtains of the house were still closed, so I went about my business as quickly and quietly as I could, it seemed that the valley to valley highpoint was through the gate and in the adjacent field, so within a couple of minutes I had positioned the Trimble on top of my rucksack and measured a 0.44m offset between the ground at its base and the internal antenna in the Trimble.  Before starting to log data I wandered up the field to assess the lay of land from a different direction, happy with the Trimble’s placement I pressed ‘Log’ and it started gathering data.

The Trimble GeoXH 6000 placed were I deemed the critical bwlch of Pen y Fan to be situated

The view down the field toward the Trimble with the continuation of the hill to hill traverse toward the mast in the background and on the left of this photograph

During the time that the Trimble gathered data I stood behind a hedge in the opposing field and hoped the bedroom curtains would not be thrown open for the occupant to be confronted by a mysterious blue rucksack that had an equally mysterious yellow and black object perched on top of it.  Thankfully by the time that five minutes of data were collected the village still remained quiet and I packed the equipment away and walked back up the field and onto the road.

I just hoped that the bedroom curtains weren't going to open

As I headed towards my car I looked back across the field toward where the Trimble had been placed, the adjacent house was now almost directly in front of me and the lay of land seemingly gently rising up part of the valley to valley traverse to the position where the Trimble had been placed, happy with the morning’s activities I got back into my car and drove south to examine the second of these Regional bylchau.

From this direction the low point of the hill to hill traverse is better seen and this is where the Trimble was placed

Survey Result:

Pen y Fan

Bwlch Height:  214.4m (converted to OSGM15)

Bwlch Grid Reference:  SH 93152 00006

Drop:  671.3m (converted to OSGM15)

Dominance:  75.79%

For the summit survey of Pen y Fan

For further details please consult the Trimble survey spreadsheet click {here}

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