Mapping Mountains – Hill Reclassifications – 100m Twmpau

Pen y Foel (SN 000 381) – 100m Twmpau reclassified to 100m Sub-Twmpau

There has been a reclassification to the list of 100m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Pen y Foel (SN 000 381) 

The criteria for the list that this reclassification applies to are:

100m Twmpau – Welsh hills at or above 100m and below 200m in height that have 30m minimum drop, with an accompanying sub list entitled the 100m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 100m and below 200m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

The 100m Twmpau by Myrddyn Phillips

The name the hill is listed by is Pen y Foel, and it is adjoined to the Mynydd Preseli group of hills, which are situated in the south-western part of South Wales (Region B, Sub-Region B1), and it is positioned with a minor road to its west, and the A487 road to its south-east, and has the town of Abergwaun (Fishguard) towards the west south-west.

When the original 100m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was included in the main P30 list, as the contemporary Ordnance Survey 1:25,000 Explorer map gives this hill an uppermost 110m contour and bwlch contouring between 75m – 80m, resulting in this hill having a minimum of 30m of drop.

After the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-assessed and it was listed with an estimated c 31m of drop, based on an estimated c 110m summit spot height and an estimated c 79m bwlch height, with both heights based on interpolation of 5m contouring that appears on the Ordnance Survey 1:25,000 Explorer map. 

Extract from the Ordnance Survey 1:25,000 Explorer map

The details for this hill were re-assessed when the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map became available online.  This mapping had many spot heights not on other publicly available Ordnance Survey maps and for this hill it had a 109m summit spot height which resulted in the drop value of this hill being amended to an estimated c 30m.

However, it was not until LIDAR became available that the details for this hill could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales.

Therefore, the reclassification of this hill to 100m Sub-Twmpau status is due to LIDAR analysis, resulting in a 108.5m summit height and an 80.1m bwlch height, with these values giving this hill 28.4m of drop, which is insufficient for it to be classified as a 100m Twmpau. 

 

The full details for the hill are: 

Group:  Mynydd Preseli 

Name:  Pen y Foel 

OS 1:50,000 map:  145, 157

Summit Height:  108.5m (LIDAR) 

Summit Grid Reference:  SN 00073 38103 (LIDAR) 

Bwlch Height:  80.1m (LIDAR) 

Bwlch Grid Reference:  SN 00179 37983 (LIDAR) 

Drop:  28.4m (LIDAR) 

 

Myrddyn Phillips (March 2023)

 

 

 

 

 

 

 

 

  

Mapping Mountains – Trimble Surveys – Carnedd Wen

 

04.02.21  Pen y Foel (SJ 179 058) and Y Golfa (SJ 182 070, previously Trimbled)

Y Golfa (SJ 182 070)

Hill walking is a wonderful way to spend a few hours.  I rarely arrive back home unfulfilled.  It gives solace and with good company can bring laughs a plenty with stunning countryside as a backdrop. 

Today I was out with Linda, with two hills planned to visit; Pen y Foel and Y Golfa.  The former is a small, unobtrusive hill squeezed between the higher Upper Park to its south-east and Y Golfa towards its north, with the latter proving a delightful hill to visit during lock down.  One that gives excellent extended views and a variety of routes for its ascent and descent. 

We met at 8.30am outside The Raven and followed public footpaths across muddied fields parallel with the Llanfair Caereinion road, from where the hum of morning traffic meandered across the land. 

It was only after an hour or so of our walk up valley that we emerged in to morning sunshine.  The sun had been lost behind the Upper Park ridge with us walking in shade whilst it tantalised us across the intervening brook springing out of the Black Pools with bright coloured conditions on the opposing hillside.  The sunshine highlighted the rusted winter colour of brackened slopes on Y Golfa and accentuated those wonderful winter greens of grazed pasture. 

The beautiful morning gave way to increasing cloud and patchy rain in the afternoon

The footpath soon turned to a track making its way toward Talyrnau and Upper Talyrnau farms, where slurried walkways led past ever so cute calves looking out at us from their pens. 

Blue skies dominated the horizon, but with forecast cloud banks and the possibility of rain later in the day we enjoyed the fresh colour that was now with us.  Beyond Upper Talyrnau we wandered across expansive greened fields to a lane that gave access to the track leading to Pen y Foel.  We used this for a short distance before contouring the upper hillside to the area of the summit. 

Pen y Foel (SJ 179 058)

Prior to our visit I had LIDARed this hill for height and position of both summit and bwlch, and this gave an indication for Trimble summit placement.  The summit of Pen y Foel looked impressive and especially so to a person that due to lockdown restrictions was now used to the gentle mid Wales landscape having kept my walks local.  The remains of its ancient hill fort circled the upper hill, and whilst Linda relaxed sitting beside a fence I set the Trimble up on the highest part of its earthen embankment.  This was the first hill that I had surveyed during any of the three lock downs that Wales has experienced over the last 11 months.  I wondered if this constituted work, recreation or exercise.  As I felt knackered at the end of the walk I decided it couldn’t be classified as recreation! 

LIDAR image of Pen y Foel

I took two data sets, the first from the high point of the ancient embankment and the second from what I judged to be the high point beside the fence, with each looking similar in height. 

Gathering data at one of two positions surveyed for the summit of Pen y Foel

From here we skirted the near wood using its periphery to make our way around to a sharp, steep decline and a barb wired fence, which gave access down a large field to a gate.  Ahead of us over a couple of intervening fields was the small community of Castell Caereinion, which nestled into the landscape against the surrounding green pastured hills. 

Castell Caereinion

From here we had a rail and road crossing before the next uphill.  Once we had gained a semblance of height we sat on brackened slopes and enjoyed the last throngs of winter sunshine, as the westerly and southerly emerging cloud banks were forever pushing our way. 

Winter greens

Leaving the sun behind us we continued uphill following a public footpath toward the Golf Club.  Here we sat at a picnic table where Linda thoughtfully produced two beakers for a welcome warmed coffee each. 

Approaching Y Golfa from Pen y Foel

Beyond the Golf Club the skies turned grey and by the time we arrived beside the trig pillar atop Y Golfa the first windblown flecks of rain were falling.  We didn’t linger and headed down the easterly ridge toward Llanerchydol.  The rain increased and kept with us for 30 minutes or so, never too much for me to put my Goretex on, but sufficient to dampen proceedings. 

Heading for the summit of Y Golfa

At the summit of Y Golfa with the weather closing in

We sheltered under a number of trees and continued our conversational topics.  By the time we set off again the last of the rain had blown northward leaving dulled skies but dry conditions.  It was only a short distance down Llanerchydol drive to The Raven passing banks of white dotted Snowdrops on the way. 

Snowdrops beside the Llanerchydol drive

After washing our wellies I left Linda with an elbow bump and waved my bi bi’s.  All that remained was a slow plod back through the empty streets of Welshpool and the ever welcome canal tow path leading me home.  The walk proved a wonderful way to spend a few hours. 

 

Survey Result: 

 

Pen y Foel

Summit Height:  284.1m (converted to OSGM15, Trimble GeoXH 6000) (two points surveyed giving 284.137m and 284.136m respectively, with only 1mm difference both positions are given below) 

Summit Grid Reference:  SJ 17893 05893 and SJ 17916 05895 (Trimble GeoXH 6000) 

Bwlch Height:  194.2m (LIDAR)

Bwlch Grid Reference:  SJ 18505 05867 (LIDAR)

Drop:  89.97m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Dominance:  31.66% (Trimble GeoXH 6000 summit and LIDAR bwlch)

 

 

Y Golfa

Summit Height:  341.4m (converted to OSGM15, from previous Trimble GeoXH 6000 survey) 

Summit Grid Reference:  SJ 18247 07086 (from previous Trimble GeoXH 6000 survey) 

Bwlch Height:  175.1m (LIDAR)

Bwlch Grid Reference:  SJ 16645 06017 (LIDAR)

Drop:  166.3m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Dominance:  48.72% (Trimble GeoXH 6000 summit and LIDAR bwlch)

 

 

For details on the survey of Y Golfa

For details on the 2^nd visit to Y Golfa

For details on the 3^rd visit to Y Golfa

For details on the 4^th visit to Y Golfa

 

For further details please consult the Trimble Survey Spreadsheet

 

 

Mapping Mountains – Hill Reclassifications – Y Trechol – The Dominant Hills of Wales

 

Pen y Foel (SH 425 844) – Lesser Dominant reclassified to Dominant

There has been a reclassification to the listing of Y Trechol – The Dominant Hills of Wales, with the summit height, bwlch height and their locations, the drop, dominance and status of the hill derived from a Trimble GeoXH 6000 summit survey and analysis of partial LIDAR bwlch coverage conducted by Myrddyn Phillips. 

Pen y Foel (SH 425 844)

The criteria for the list that this reclassification applies to are: 

Y Trechol – The Dominant Hills of Wales – Welsh P30 hills whose prominence equal or exceed half that of their absolute height.  With the criteria for Lesser Dominant status being those additional Welsh P30 hills whose prominence is between one third and half that of their absolute height.  The list is authored by Myrddyn Phillips with the Introduction to the start of the Mapping Mountains publication of this list appearing on the 3^rd December 2015, and the list is now available in its entirety on Mapping Mountains in Google Doc format. 

Y Trechol - The Dominant Hills of Wales by Myrddyn Phillips

The name the hill is listed by is Pen y Foel and it is adjoined to the Ynys Môn group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it has the B5111 road to its north-west and south, and has the village of Llannerch-y-medd towards the south-west. 

When the original 100m height band of Welsh P30 hills published on Geoff Crowder’s v-g.me website were standardised and interpolated heights and drop values also included, this hill was listed with an estimated c 59m of drop and 48.36% dominance, based on an estimated c 122m summit height and an estimated c 63m bwlch height, with each based on interpolation of 5m contouring that appears on the Ordnance Survey 1:25,000 Explorer map. 

Extract from the Ordnance Survey 1:25,000 Explorer map

The details for this hill were re-assessed when the Ordnance Survey Vector Map Local hosted on the Geograph website and which is entitled the Interactive Coverage Map became available online.  This mapping had many spot heights not on other publicly available Ordnance Survey maps and gave a 123m summit spot height and a 62m spot height on the area of the bwlch for this hill, which increased its drop value to 61m and its dominance to 49.59%. 

The summit of this hill was subsequently surveyed with the Trimble GeoXH 6000 resulting in a 122.5m height positioned at SH 42575 84415.  This resulted in its dominance amended to 49.40%. 

The Trimble GeoXH 6000 gathering data at the summit of Pen y Foel

However, it was not until LIDAR became available that the details for this hill could again be re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales. 

Extract from the Ordnance Survey 1:25,000 Explorer map showing the bwlch of Pen y Foel

LIDAR does not cover the actual bwlch position of this hill, but there is sufficient coverage of the area of this hill’s bwlch for a better interpolated height compared to the position and height of the 62m spot height previously used for the drop and dominance values of this hill. 

LIDAR bwlch image of Pen y Foel

LIDAR bwlch image of Pen y Foel

Therefore, the reclassification of this hill from Lesser Dominant status is due to a Trimble GeoXH 6000 summit survey and analysis of partial LIDAR bwlch coverage, resulting in a 122.5m summit height and an estimated c 61m bwlch height, with these values giving this hill an estimated c 62m of drop and 50.21% dominance, which is sufficient for it to be classified as a Dominant hill. 

 

The full details for the hill are:

Group:  Ynys Môn

Name:  Pen y Foel 

OS 1:50,000 map:  114, 115

Summit Grid Reference:  SH 42575 84415 (Trimble GeoXH 6000)

Summit Height:  122.5m (converted to OSGM15, Trimble GeoXH 6000)

Bwlch Grid Reference:  SH 44053 82788 (interpolation)

Drop Summit to Bwlch:  c 62m (Trimble GeoXH 6000 summit and interpolation of partial LIDAR bwlch coverage)

Drop Bwlch to ODN:  c 61m (interpolation of partial LIDAR coverage)

Dominance:  50.21% (Trimble GeoXH 6000 summit and interpolation of partial LIDAR bwlch coverage)

 

Myrddyn Phillips (March 2021)

Mapping Mountains – Trimble Surveys – Mynydd Twr

28.10.18  Pen y Foel (SH 425 844)  

Pen y Foel (SH 425 844)

Pen y Foel was my fourth P30 of the morning and if time and surveying inclination permitted I hoped to visit another four P30s during the remainder of the day.  The hill is positioned overlooking the small community of Llannerch-y-medd on Ynys Môn and is crowned by the remains of the Llwydiarth Tower; which is a squat red bricked structure.

A public footpath heads northward from the periphery of Llannerch-y-medd and confidently strikes out toward the summit of the hill.  Today the edges of the green track which constitutes the footpath were slightly overgrown, but not so much as to lessen my pace or dampen my enthusiasm for another new hill.

The way to the hill

The green track soon led to an open grazing field where the remains of one forlorn looking house stands, with the Llwydiarth Tower situated just beyond perched on the summit of the hill, and which soon came in to view as I gained height.

The Llwydiarth Tower at the summit of Pen y Foel

Arriving at the summit I quickly judged where the high point of the hill was situated and soon had the Trimble in position and as the equipment was now placed beside the brick structure I decided that a ten minute data set should be taken.

The Trimble set-up position at the summit of Pen y Foel

Once the Trimble was activated to gather data I stood away from it and looked out across the island and beyond the Menai Strait to the elongated spine of Wales’ highest mountains on the mainland of this wonderful and beautiful country where I just happen to live.

Gathering data at the summit of Pen y Foel

Once data were gathered and stored I packed the Trimble away and followed my inward route back to my car.  I now wanted to head further north and visit four more hills over two walks and take data from the summit of the 178m map heighted Yr Arwydd (SH 472 854) and the 177m map heighted Mynydd Eilian (SH 472 917), with the former the recognised high point of Ynys Môn (outside of Mynydd Twr on Ynys Gybi) and the listed Marilyn.

Survey Result:

Pen y Foel 

Summit Height:  122.5m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SH 42575 84415 (Trimble GeoXH 6000)

Bwlch Height: c 61m (interpolation)

Bwlch Grid Reference:  SH 44053 82788 (interpolation)

Drop:  c 62m (Trimble GeoXH 6000 summit and interpolated bwlch)

Dominance:  50.21% (Trimble GeoXH 6000 summit and interpolated bwlch) (Lesser Dominant reclassified to Dominant)

For further details please consult the Trimble Survey Spreadsheet