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

Mapping Mountains – Summit Relocations – 100m Twmpau

Bryn Bach (SS 903 875)

There has been confirmation of a Summit Relocation to a hill that is listed in the 100m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill being confirmed by LIDAR analysis conducted by Myrddyn Phillips.

LIDAR image of Bryn Bach

The criteria for the list that this summit relocation applies to are:

100m Twmpau - Welsh hills at or above 100m and below 200m in height with 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 name of the hill is Bryn Bach, and this was derived from the Ordnance Survey One-Inch ‘Old Series’ map and it is this name that the hill is now listed by, 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 is positioned with the A4063 road and the Afon Llynfi to its south-west and the A4064 road and the Afon Garw to its south-east, and has the small community of Betws towards the south. 

When this hill was originally listed in the 100m height band of Welsh P30 hills on Geoff Crowder’s v-g.me website, its summit was listed at SS900871 and it appeared with an accompanying note stating; Two points of same height – other at SS903875, with these details being taken from the Ordnance Survey 1:25,000 Explorer map.

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

Prior to LIDAR analysis this hill was listed with an estimated c 31m of drop, based on the 164m summit spot height that appears on the Ordnance Survey Vector Map Local hosted on the Geograph website and which is entitled the Interactive Coverage Map.  This spot height appears beside a field boundary at SS 90354 87551.

Extract from the Ordnance Survey Vector Map Local hosted on the Geograph website

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.  

The height produced by LIDAR analysis is 167.0m positioned at SS 90364 87531, and is in a different field and not beside the field boundary compared to the position of the 164m spot height, and confirms this land is higher than the prioritised position originally given in the 100m P30 list of Geoff Crowder’s v-g.me website, and as such comes within the parameters of the Summit Relocations used within this page heading, these parameters are:

The term Summit Relocations applies to any listed hill whose summit meets the following criteria; where there are a number of potential summit positions within close proximity and the highest point is not where previously given, or a relocation of approximately 100 metres or more in distance from either the position of a map spot height or from where the summit of the hill was previously thought to exist, or when the summit of the hill is in a different field compared to where previously given, or when the natural and intact summit of a hill is confirmed compared to a higher point such as a raised field boundary that is judged to be a relatively recent man-made construct.  As heights on different scaled Ordnance Survey maps are not consistent the height given on the 1:25,000 Explorer map is being prioritised in favour of the 1:50,000 Landranger map for detailing these relocations.

LIDAR summit image of Bryn Bach

Therefore, the height produced by LIDAR analysis is 167.0m to what is constituted natural ground and this is positioned at SS 90364 87531, this position is not given a spot height on Ordnance Survey maps and is approximately 600 metres north-eastward from where the prioritised listed summit was originally given and is positioned in a different field to where the 164m spot height appears on the Ordnance Survey Vector Map Local hosted on the Geograph website.

The full details for the hill are:

Group:  Cymoedd Morgannwg

Name:  Bryn Bach

OS 1:50,000 map:  170

Summit Height:  167.0m (LIDAR)

Summit Grid Reference (New Position):  SS 90364 87531 (LIDAR)

Bwlch Height:  135.2m (LIDAR)

Bwlch Grid Reference:  SS 90511 87849 (LIDAR)

Drop:  31.9m (LIDAR)

Myrddyn Phillips (June 2019)

Mapping Mountains – Significant Height Revisions – 100m Twmpau

Bryn Bach (SS 903 875)

There has been a Significant Height Revision to a hill that is now listed in the 100m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill confirmed by LIDAR analysis conducted by Myrddyn Phillips.

LIDAR image of Bryn Bach

The criteria for the list that this height revision applies to are:

100m Twmpau - Welsh hills at or above 100m and below 200m in height with 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 name of the hill is Bryn Bach, and this was derived from the Ordnance Survey One-Inch ‘Old Series’ map and it is this name that the hill is now listed by, 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 is positioned with the A4063 road and the Afon Llynfi to its south-west and the A4064 road and the Afon Garw to its south-east, and has the small community of Betws towards the south. 

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 Hills to be surveyed sub list that accompanied the main P30 list, as it did not meet the criteria then used. 

When the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated and it was listed with an estimated c 31m of drop, based on an estimated summit height of c 164m and an estimated bwlch height of c 133m, with both heights based on interpolation of 10m contouring 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 became available online; this mapping is entitled the Interactive Coverage Map.  This mapping gives a 164m summit spot height and as it has 5m contour intervals it enabled a better assessment for an interpolated value for the height of the bwlch.  It also has a 133m spot height at a junction of roads at the area of this hill’s bwlch, with interpolation favouring a different position for the critical bwlch and an estimated height of c 133m, with these values giving this hill c 31m of drop.

Extract from the Ordnance Survey Vector Map Local hosted on the Geograph website

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.  

The summit height produced by LIDAR analysis is 167.0m, this is not a substantial revision compared to some revised heights, but it does come within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revisions applies to any listed hill whose interpolated height and Ordnance Survey or Harvey map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or analysis of data produced via LIDAR, also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble or by LIDAR analysis.  As heights on different scaled Ordnance Survey maps are not consistent the height given on the 1:25,000 Explorer map is being prioritised in favour of the 1:50,000 Landranger map for detailing these revisions.

Therefore, this hill’s new listed summit height is 167.0m and this was produced by LIDAR analysis, this is 3m higher than the 164m spot height that appears on the Ordnance Survey Vector Map Local hosted on the Geograph website and which is entitled the Interactive Coverage Map.

ills of Wales, and are reproduced below@

The full details for the hill are:

Group:  Cymoedd Morgannwg

Name:  Bryn Bach

OS 1:50,000 map:  170

Summit Height (New height):  167.0m (LIDAR)

Summit Grid Reference:  SS 90364 87431 (LIDAR)

  

Bwlch Height:  135.2m (LIDAR)

Bwlch Grid Reference:  SS 90511 87849 (LIDAR)

Drop:  31.9m (LIDAR)

Myrddyn Phillips (June 2019)

Mapping Mountains – Significant Name Changes – 100m Twmpau

Bryn Bach (SS 903 875)

There has been a Significant Name Change to a hill that is listed in the 100m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill confirmed by LIDAR analysis conducted by Myrddyn Phillips.

LIDAR image of Bryn Bach

The criteria for the list that this name change applies to are:

100m Twmpau - Welsh hills at or above 100m and below 200m in height with 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 hill 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 is positioned with the A4063 road and the Afon Llynfi to its south-west and the A4064 road and the Afon Garw to its south-east, and has the small community of Betws towards the south. 

This hill was first listed in the original Welsh 100m P30 list published on Geoff Crowder’s v-g.me website, under the partly invented and transposed name of Bryn Betws, with an accompanying note stating; Name from village at summit.

Bryn Betws

160c

SS900871

170

166

Two points of same height - other at SS903875. Name from village at summit.

During my early hill listing I thought it appropriate to either invent a name for a hill, or use a name that appeared near to the summit of the hill on Ordnance Survey maps of the day.  My preference was to use farm names and put Pen, Bryn or Moel in front of them or as in this instance use a name of what I presumed to be a village and add the word Bryn to it.  This is not a practice that I now advocate as with time and inclination place-name data can be improved either by asking local people or by examining historic documents, through this form of research an appropriate name for the hill can usually be found.

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

Since publication of these P30 lists on Geoff Crowder’s v-g.me website there have been a number of Ordnance Survey maps made available online, some of these are historic such as the series of Six-Inch maps on the National Library of Scotland website, whilst others are current and digitally updated such as the Vector Map Local hosted on the Geograph website and which is named the Interactive Coverage Map.  One of the historic maps now available is the Ordnance Survey One-Inch ‘Old Series’ map and it is this map that formed the basis for the change in this hill’s listed name.

The One-Inch ‘Old Series’ map was the first map that the Ordnance Survey produced, and their publication culminated from the whole of Britain being surveyed between 1791 and 1874 and the detail gathered therein produced at a scale of one inch to the mile and published in sheet format between 1805 and 1874.  The One-Inch ‘Old Series’ maps for the whole of Wales are now available online; they are also available in map format as enlarged and re-projected versions to match the scale and dimensions of the Ordnance Survey 1:50,000 Landranger series and are published by Cassini.  This series of maps form another important part in the study of Welsh upland place-names and bridge the timeframe leading up to the production of the Ordnance Survey base map of the Six-Inch series, and importantly for this hill and its listed name, it is this map that names the hill as Bryn Bach.

Extract from the Ordnance Survey One-Inch 'Old Series' map

Therefore, the name this hill is now listed by in the 100m Twmpau is Bryn Bach, and this was derived from the Ordnance Survey One-Inch ‘Old Series’ map.

The full details for the hill are:

Group:  Cymoedd Morgannwg

Name:  Bryn Bach

Previously Listed Name:  Bryn Betws 

OS 1:50,000 map:  170

Summit Height:  167.0m (LIDAR)

Summit Grid Reference:  SS 90364 87531 (LIDAR)

Bwlch Height:  135.2m (LIDAR)

Bwlch Grid Reference:  SS 90511 87849 (LIDAR)

 

Drop:  31.9m (LIDAR)

Myrddyn Phillips (June 2019)