Mapping Mountains – Hill Reclassifications – 500m Twmpau

Mynydd Pen y Cae (SN 887 032) – 500m Sub-Twmpau deletion

There has been a deletion of a hill that is listed in the 500m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill confirmed by a survey with the Trimble GeoXH 6000 conducted by Myrddyn Phillips with assistance from Aled Williams which took place on the 22^nd June 2019.

Mynydd Pen y Cae (SN 887 032)

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

500m Twmpau - Welsh hills at or above 500m and below 600m in height with 30m minimum drop, with an accompanying sub list entitled the 500m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 500m and below 600m 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 name of the hill is Mynydd Pen y Cae, and it is adjoined to the Cymoedd Morgannwg group of hills, which are situated in the central part of South Wales (Region C, Sub-Region C2), and it is positioned with the A465 road and Cwm Nedd (Vale of Neath) to its north-west and the A4061 road to its east, and has the small town of Glyn-nedd (Glynneath) to the north. 

Prior to the survey with the Trimble GeoXH 6000 this hill was listed with an estimated c 20m of drop based on the 573m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and an estimated bwlch height of c 553m based on 10m contouring between 550m – 560m.

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 became available online; this mapping is entitled the Interactive Coverage Map and as its summit spot height and bwlch contouring remained the same, so did the estimated c 20m drop value.

The area taking in this hill was re-examined when the OS Maps website became available online.  This is the replacement for OS Get-a-map and has contours at 5m intervals.  This mapping shows the bwlch contouring between 555m – 560m with interpolation placing the bwlch height as an estimated c 557m which when coupled with the 573m summit spot height on the 1:25,000 Explorer map gives this hill c 16m of drop.

Extract from the OS Maps website

The deletion of Mynydd Pen y Cae from 500m Sub-Twmpau status is due to a survey with the Trimble GeoXH 6000, resulting in a 574.6m summit height and a 557.0m bwlch height, with the latter in accordance with the 5m contouring on the OS Maps website, with these values giving this hill 17.6m of drop which is insufficient for its continued classification as a 500m Sub-Twmpau.

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

The Trimble GeoXH 6000 gathering data at the bwlch of Mynydd Pen y Cae

The full details for the hill are:

Group:  Cymoedd Morgannwg

Name:  Mynydd Pen y Cae

OS 1:50,000 map:  170

Summit Height:  574.6m (converted to OSGM15)

Summit Grid Reference:  SN 88743 03214

Bwlch Height:  557.0m (converted to OSGM15)

Bwlch Grid Reference:  SN 89494 03481

Drop:  17.6m

For details on the survey of this hill

Myrddyn Phillips (September 2019)

Mapping Mountains – Trimble Surveys – Cymoedd Morgannwg

22.06.19  Bryn Bach (SN 905 004), Mynydd Pen y Cae (SN 887 032) and Craig y Llyn (SN 906 031)

Craig y Llyn (SN 906 031)

Today comprised eight hours following forest tracks and visiting three hills in increasingly warm conditions under a radiant and piercing blue sky in south Wales.  For me, two of these were new hills, whilst the three were all new for Aled, including the highest; Craig y Llyn.

We were parked at the beginning of a forest track adjacent to the A4061 road as it descends south toward Treherbert and Treorci and ready to walk at 9.35am.  It was already warm with wisps of high cloud and a beautiful blue sky above giving clarity of colour that remained with us all day.

The access / forest track leading to the hills

Since my last visit to Craig y Llyn the hill now has an extensive wind farm on it, and the forest and access tracks would lead us to and between each of the three hills in a circuitous route, with only minimum doubling back from Bryn Bach toward our onward route to Mynydd Pen y Cae.

Where once there was open hillside, there is now forestry and wind turbines

Leaving the car the wide access track led to a crossroads where the main substation for the turbines is situated, here we turned left and headed south toward what we thought would be a relatively easy visit to the summit of our first hill of the day; Bryn Bach.  Unfortunately the person with the map (me) wasn’t paying heed to the tracks, time and mileage and was immersed in conversation and therefore we walked straight over the summit of Bryn Bach without realising it and only stopped a mile further south when we reached what we thought was the top.  The ten figure grid reference in the Trimble and a quick study of the map told us our (my) mistake and we turned around and walked back the mile to the top we had already passed over!

Heading south from the sub-station

The summit position produced by Aled’s LIDAR analysis led us to the high point of Bryn Bach which is easily reached in forestry adjacent to the track.  I set the Trimble up without much expectation of gathering data and so it proved as the accuracy level before data should be logged was not attained.  Having rested in the shade I packed the Trimble away and we left the summit on a near forest break taking us back to the track and headed toward the hill’s connecting bwlch which was positioned in felled forestry with new planted saplings already taking hold.  We assessed the area of the bwlch from opposing directions on the hill to hill traverse, chose the spot for Trimble placement and rested in the sun as it gathered its customary five minutes of data. 

The summit of Bryn Bach

Gathering data at the bwlch of Bryn Bach

Leaving the bwlch we headed back to the sub-station where we turned left and continued following the wide and greyed track around the head of Cwm Corrwg; an extensive valley which before the forestry was planted must have been a beautiful place.

The large sub-station between Bryn Bach and Craig y Llyn

By now the heat had increased and although welcome after the recent wet weather I started to wilt under its intensity.  We sat and rested on large rocks above the thin thread of the Afon Corrwg with it forever tricking downward as occasional bird song wafted from the trees.

The view down Cwm Corrwg

We now followed forest tracks westward before joining a good path that headed direct to the summit ridge of our second hill of the day; Mynydd Pen y Cae.  When the path reached a fence we veered right and followed its continuation to the high point of the hill and sat with midges as company whilst the Trimble beeped away gathering summit data.

The path leading to the summit ridge of Mynydd Pen y Cae

Gathering data at the summit of Mynydd Pen y Cae

I was now flagging and slowly followed Aled over a bog to join another main forest track where the view north-west in to Cwm Nedd opened up.  We followed this track eastward toward the connecting bwlch where an inordinate amount of time was spent wandering in a forest break and the near trees assessing the lay of land before we chose the spot for Trimble placement.

The distant peaks of Bannau Brycheiniog

Gathering data at the bwlch of Mynydd Pen y Cae

Once data were taken I joined Aled on the escarpment path that led to the viewpoint overlooking Llyn Fach.  By now any stop was welcome as the heat had battered me.  We continued on the path to the marker post signalling the divergence of paths with a turning right leading to the summit of Craig y LLyn.  Before heading toward its trig pillar we sat and rested.  I felt as if I could easily stay here for an hour, recovering from the day’s exertions, and found the process of standing and getting my legs to work as legs should, a disconcerting process, but once a few steps were taken I followed Aled toward the trig where I activated the Trimble to be met with a blank screen.  So the summit of Craig y Llyn was not Trimbled, which was a shame.

Llyn Fach

Leaving the summit we followed the path down to an intersecting forest track and turned left and continued down to our inward route which took us back to my awaiting car.  All that remained was to change and stop at the near viewpoint on the A4061 for a well-earned ice cream before the drive to Caersŵs where Aled’s car was parked for his onward journey back to Porthmadog.

Survey Result:

Bryn Bach

Summit Height:  533.2m (LIDAR)

Summit Grid Reference:  SN 90574 00441 (LIDAR)

Bwlch Height:  518.0m (converted to OSGM15)

Bwlch Grid Reference:  SN 90572 01251

Drop:  15.2m (LIDAR summit and Trimble bwlch) (Uchaf status confirmed)

Dominance:  2.84% (LIDAR summit and Trimble bwlch)

Mynydd Pen y Cae

Summit Height:  574.6m (converted to OSGM15)

Summit Grid Reference:  SN 88743 03214

Bwlch Height:  557.0m (converted to OSGM15)

Bwlch Grid Reference:  SN 89494 03481

Drop:  17.6m (500m Sub-Twmpau deletion)

Dominance:  3.06%

Craig y Llyn

Summit Height:  600m (triangulation pillar)

Summit Grid Reference:  SN 90685 03150 (triangulation pillar)

Bwlch Height:  208m (spot height)

Bwlch Grid Reference:  SN 94284 06208 (spot height)

Drop:  392m

Dominance:  65.33%

For further details please consult the Trimble Survey Spreadsheet