Mapping Mountains – Significant Height Revisions – Y Trechol - The Dominant Hills of Wales, Welsh Highlands - Uchafion Cymru and 600m Twmpau

Mynydd yr Hewyrch (SH 816 150)

There has been a Significant Height Revision to a hill that is listed in the Yr Uchafion, 600m Twmpau and Y Trechol - The Dominant Hills of Wales, and which was initiated by a survey with the Trimble GeoXH 6000 and a survey with the Leica RX1250, with the survey that resulted in this height revision being conducted on the 2oth October 2016 in good, clear and calm conditions in the company of Alan Dawson. 

The criteria for the three listings that this height revision affects are:

Yr Uchafion - All Welsh hills at or above 500m in height that have 15m minimum drop.  The list is co-authored by Myrddyn Phillips and Aled Williams.

600 Twmpau - These are the Welsh hills at or above 600m and below 700m in height that have a minimum drop of 30m.  The word Twmpau is an acronym for thirty welsh metre prominences and upward, and the list is authored by Myrddyn Phillips. 

Y Trechol - The Dominant Hills of Wales - These are the Welsh P30 hills whose prominence  equal or exceed half that of their absolute height.  The list is authored by Myrddyn Phillips.

The name that the hill is currently listed by is Mynydd yr Hewyrch and it is situated in the hills of the Rhwng Dyfi a Dulas range which have been referred to as the Bryniau Dyfi and which are situated in the south-western part of north Wales, with the survey of this hill conducted during the late afternoon in the company of Alan Dawson, who had suggested the walk and also surveyed the hill with his Leica RX1250, and it is the result from the Leica equipment that is being used for this hill's data.

The hill is situated between the Afon Cerist and the A 470 road to its north and the conifer plantation of the Dyfi Fforest (Dovey Forest) to its south and is positioned above the small community of Dinas Mawddwy to its east, and the hill can be easily accessed from a lane leading to a path that heads for the summit via the escarpment edge above Craig Maesglase, or via the north-eastern ridge that heads straight for the summit of its adjacent top; Maen Du.

Prior to the survey with the Leica RX1250 and the Trimble GeoXH 6000 the height of the hill was listed as 676m based on the summit spot height on the Harvey 1:40,000 Britain Mountain Map.  However, the summit of Mynydd yr Hewyrch only has a 670m uppermost contour on Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps with the adjacent summit of Maen Du at SH 822 151 being given a 674m spot height, because of this the summit of Maen Du was previously listed as that for the hill, and the higher summit of Mynydd yr Hewyrch is therefore a recent addition and first noted by Tim Jones who reported that he believed this summit to be higher to John and Anne Nuttall in 1996.

Three points were surveyed for summit position using the Trimble GeoXH 6000 and the Leica RX1250, each position being close in height and taken to ground consisting of moorland peat hags rising above a shapely large pool which is positioned on the summit area.

The 678.5m (converted to OSGM15) height produced by the Leica RX1250 is 2.5m higher than the previously listed height of 676m, which was based on the Harvey British Mountain Map spot height, and 8.5m higher than the uppermost contour on Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps and therefore comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revision applies to any listed hill whose 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, also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble.  As heights on different scaled Ordnance Survey maps are not consistent the height given on the 1:25,000 map is being prioritised in favour of the 1:50,000 for detailing these revisions.

The summit of this hill consists of ground at the top of a moorland peat hag, and therefore this hill’s new summit height as surveyed by Alan Dawson with the Leica RX1250 is 678.5m (converted to OSGM15) which is 2.5m higher than its previously listed height of 676m which appears on the Harvey 1:40,000 British Mountain Map and 8.5m higher than the uppermost 670m contour ring on Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps.

The full details for the hill are:

Cardinal Hill:  Mynydd yr Hewyrch

Summit Height (New Height):  678.5m (converted to OSGM15, Leica RX1250)

Name:  Mynydd yr Hewyrch

OS 1:50,000 map:  124, 125

Summit Grid Reference:  SH 81697 15003 

 

Drop:  318.0m (converted to OSGM15, Trimble GeoXH 6000 bwlch)

Dominance:  46.87%

The Trimble GeoXH 6000 gathering data at one of the three positions surveyed atop Mynydd yr Hewyrch which when coupled with the Leica RX1250 survey resulted in this hill's significant height revision

For details on the survey that significantly revised the summit height of this hill

Myrddyn Phillips and Aled Williams (November 2016)

Mapping Mountains – Trimble Surveys – Bryniau Dyfi

20.10.16  Cribin Fawr (SH 794 152), Waun Oer (SH 785 147) only bwlch surveyed), Craig Portas (SH 801 141), Mynydd Gartheiniog (SH 807 142), Mynydd yr Hewyrch (SH 816 150) and Maen Du (SH 822 151)

Cribin Fawr (SH 794 152)

Bwlch Oerddrws is one of the gateways between the east and its gentle sloping hills and the ruggedness of the west at it plunges toward the coast, and at over 360m it is also a convenient starting point to tackle the Aran ridge to its north or part of Bryniau Dyfi to its south.  It was the latter Alan and I visited today, this was the second day out with the Leica and Trimble and I was enthusiastic to see how my right knee dealt with the rigours of two consecutive days in the hills after I twisted it a number of weeks ago.

By the time we parked the Dyfi hills were clear of cloud and the forecast for the remainder of the day was good with only an occasional shower predicted to meander across the country.

I’d only ascended Cribin Fawr once from this high starting point and then used a zig zagging path that takes an almost direct route onto the hill’s northern ridge, today we decided to explore the path that skirts the hill’s eastern ridge and continues westward to gain the ridge north of the summit.

I set off first and toiled in the overly warm conditions as little breeze was present, but progress was made, as it always is, and as I plodded up the final slopes toward the ridge, Alan appeared in front having taken a path directly up the eastern ridge, and by the time I joined him on the summit of Cribin Fawr he had assembled his Leica RX1250 and it was gathering data.

Alan beside the Leica RX1250 at the summit of Cribin Fawr

When on a part of the Berwyn yesterday we’d used a surveying method with the Leica gathering data for approximately 20 minutes, followed by the Trimble set up over the same point for five minutes, and whilst the latter gathered data Alan headed toward the next survey point to set up his Leica and I would later join him to set up my Trimble, this method worked extremely well and we used it again today.

Gathering data with the Trimble GeoXH 6000 at the summit of Cribin Fawr

Once Leica and then Trimble data were gathered I followed the wet path beside a fence past a number of oozing black peat channels and continued south-eastward down to the first bwlch of the day.  We planned on surveying three main bylchau with each having map contours between 550m – 560m, and therefore their respective hills may swap dependent upon which is higher or lower.

By the time I arrived the Leica was gathering another 21 minute data set, this we listed as the critical bwlch for Waun Oer; a 670m map heighted hill to the south-west of Cribin Fawr.  These meetings at each summit and bwlch gave an opportunity to chat and relax as the equipment gathered its data.

Relaxing at the bwlch of Waun Oer

Gathering data with the Trimble GeoXH 6000 at the critical bwlch of Waun Oer

Looming above us were the steep slopes of Craig Portas which is a 605m map heighted Simm, Dewey and Twmpau, and after Alan had packed the Leica away he headed up as I assembled the Trimble, a few minutes later and with data stored I followed him up to the hill’s featureless summit.  During the first few hours of the walk the sky remained a dulled light grey and the ever present threat of rain pervaded as showers were breaking out further west and north, and occasional spits of rain fell our way on the light breeze that ebbed across the hills, but thankfully no persistent rain or heavy shower materialised during the day on the hills we visited.

Craig Portas (SH 801 141)

The summit of Craig Portas is one that must be usually bi-passed unless visited by a bagger as the main path skirts its upper northern cwm, leaving its summit lonely and tussock ridden, today it was surveyed with both the Leica RX1250 and Trimble GeoXH 6000.  After Alan headed off toward the next bwlch, I remained at the summit and waited for the Trimble to gather its customary five minutes of data and stood looking west toward the higher peaks radiating out from Cadair Idris, whose profile always stands out from the Dyfi ridge.

Alan beside the Leica RX1250 at the summit of Craig Portas

Waun Oer (SH 785 147) from the summit of Craig Portas

I soon joined Alan at the next bwlch, this we listed as the critical one for Craig Portas, the bwlch is a tight affair with a few rogue conifers to its immediate south, and a fence and plunging drop to its immediate north, Alan had set his Leica on an extended pole and after it had gathered 20 minutes of data I placed the Trimble on the top of the Leica antenna and noted a 1.12m measurement offset between its internal antenna and the critical point of the bwlch, and the two of us waited for five minutes of data to be gathered.  As the equipment beeped away gathering its individual data points an occasional flash of sunlight brightened the land giving colour to the otherwise dulled surrounds.

Alan setting the Leica RX1250 up at the critical bwlch of Craig Portas, with Mynydd Gartheiniog in the background

Alan beside the Leica RX1250 at the bwlch of Craig Portas

The Trimble GeoXH 6000 gathering data perched on top of the Leica RX1250 at the bwlch of Craig Portas

The next summit along the ridge is another that must usually be bi-passed unless visited by a bagger as its high point is positioned away from the path which continues toward the high point of these hills; Mynydd yr Hewyrch.  We both visited its top, and as I set the Trimble up Alan continued toward the next bwlch.  This hill is a part of Mynydd Gartheiniog and is listed as such in the 500m Twmpau, whilst Michael uses the name of Craig Portas – East Top in his listing of Deweys.  Its summit consists of soft tussocks with a slight path of sorts leading toward its high point.

Ascending Mynydd Gartheiniog from Craig Portas

Dramatic cloud out to the west

Gathering data at the summit of Mynydd Gartheiniog

As I joined Alan at the next bwlch the western sky started showing signs of late afternoon light as dramatic clouds built up out to the west, this late light remained with us for the remainder of the walk giving beautiful conditions over Cadair Idris and succulent autumnal colours on the high Aran.

As data were gathered at the last of the three main bylchau Alan spotted two people near the summit of Craig Portas, they continued toward Mynydd Gartheiniog and eventually disappeared into the day.  Beyond this bwlch lay a fence line heading toward the summit of Mynydd yr Hewyrch; the high point of Bryniau Dyfi, and as the Trimble gathered the last of its allotted 300 datum points I watched Alan make progress up the slope, beside the fence line and disappearing beyond view.

The Trimble GeoXH 6000 gathering data at the critical bwlch of Mynydd Gartheiniog

Looking toward Cadair Idris from the ascent of Mynydd yr Hewyrch

The summit of Mynydd yr Hewyrch consists of a large watery puddle with four grassed peat hags vying for its high point; it is an unusually attractive place and is one that we spent a great amount of time at, as three points were each surveyed with the Leica and Trimble, with each having been Distoed by Alan.

The Leica RX1250 gathering data at one of the three points surveyed atop Mynydd yr Hewyrch

Late afternoon light above Cadair Idris

The Leica RX1250 gathering data at one of the three points surveyed atop Mynydd yr Hewyrch

The Leica RX1250 gathering data at one of three points surveyed atop Mynydd yr Hewyrch

The Trimble GeoXH 6000 gathering data at one of three points surveyed atop Mynydd yr Hewyrch

The Leica RX1250 gathering data at one of three points surveyed atop Mynydd yr Hewyrch

The Trimble GeoXH 6000 gathering data at one of three points surveyed atop Mynydd yr Hewyrch

As the Leica was set up at the third summit point I headed off toward Maen Du, the 674m map heighted top further east which for many years was the recognised high point of the hill.  As I followed the narrow peaty path colour cascaded down across the hills, it was radiant and piecing in its intensity, giving brilliance to the autumnal colour.  I stopped and soaked in the scene as grey shadowed summits were edged against the glowing greens, oranges and autumnal yellows.

On my way toward Maen Du I stopped and surveyed its connecting bwlch with Mynydd yr Hewyrch and then continued to its summit, where Alan joined me a few minutes later.  The summit of Maen Du was the eleventh survey with the Trimble during the day and once data were gathered and the equipment packed away we followed the path southward around the edge of Craig Maesglase and its impressive plunging waterfall.

Long shadows and autumnal colours at the bwlch of Maen Du

Aran Fawddwy

Gathering data at the summit of Maen Du

By now the colour was intense as the last of the days light illuminated Aran Fawddwy, this late intensity of colour only lasts for a few short minutes as the sun sinks ever lower and once gone it was replaced by a subdued light that crept ever onward toward darkness.

Our route down following the escarpment edge above Craig Maesglase

Aran Fawddwy illuminated in late afternoon light

Succulent autumnal colour illuminating Aran Fawddwy

Maen Du with the high Aran in the background

We arrived back at the awaiting car at 6.55pm in dimmed light, having followed the path down onto a lane with the ever present upper reaches of the cwm nestling the Nant Maesglase at its heart, giving us a wonderful darkened and almost silhouetted view up to the ridge line that we had just followed down.

Survey Result:

Cribin Fawr

Summit Height:  658.7m (converted to OSGM15, Trimble GeoXH 6000) 658.8m (Leica RX1250)

Summit Grid Reference:  SH 79452 15285

Bwlch Height:  566m (spot height)

Bwlch Grid Reference:  SH 78954 15066 (spot height)

Drop:  93m (Leica RX1250 summit and spot height bwlch)

Dominance:  14.09% (Leica RX1250 summit and spot height bwlch)

 

Waun Oer

Summit Height:  670m (triangulation pillar)

Summit Grid Reference:  SH 78556 14786 (hand-held GPS via DoBIH)

Bwlch Height:  549.4m (converted to OSGM15, Trimble GeoXH 6000) 549.6m (Leica RX1250)

Bwlch Grid Reference:  SH 80115 14398

Drop:  120m (triangulation pillar summit and Leica RX1250 bwlch)  

         

Dominance:  17.97% (triangulation pillar summit and Leica RX1250 bwlch)

  

Craig Portas

Summit Height:  603.8m (converted to OSGM15, Trimble GeoXH 6000) 604.2m (Leica RX1250)

Summit Grid Reference:  SH 80154 14120

Bwlch Height:  549.7m (converted to OSGM15, Trimble GeoXH 6000) 550.0m (Leica RX1250)

Bwlch Grid Reference:  SH 80530 14218

Drop:  54.2m (Trimble GeoXH 6000) 54.2m (Leica RX1250)  

       

Dominance:  8.97% (Leica RX1250 summit and bwlch)

 

Mynydd Gartheiniog

Summit Height:  586.3m (converted to OSGM15)

Summit Grid Reference:  SH 80794 14282

Bwlch Height:  552.8m (converted to OSGM15, Trimble GeoXH 6000) 553.1m (Leica RX1250)

Bwlch Grid Reference:  SH 80951 14527

Drop:  33.3m (Trimble GeoXH 6000 summit and Leica RX1250 bwlch) (Dewey and 500m Twmpau status confirmed)

Dominance:  5.67% (Trimble GeoXH 6000 summit and Leica RX1250 bwlch)

 

Mynydd yr Hewyrch

Summit Height:  678.3m (converted to OSGM15, Trimble GeoXH 6000)  678.5m (Leica RX1250) (significant height revision)

Summit Grid Reference:  SH 81697 15003

Bwlch Height:  360.5m (converted to OSGM15, from previous Trimble GeoXH 6000 survey)

Bwlch Grid Reference:  SH 80208 17001 (from previous Trimble GeoXH 6000 survey)

Drop:  318.0m (based on Trimble GeoXH 6000 bwlch and Leica RX1250 summit)

Dominance:  46.87% (based on Trimble GeoXH 6000 bwlch and Leica RX1250 summit) (Lesser Dominant status confirmed) 

 

Maen Du

Summit Height:  675.0m (converted to OSGM15)

Summit Grid Reference:  SH 82237 15172

Bwlch Height:  667.8m (converted to OSGM15)

Bwlch Grid Reference:  SH 81910 15043

Drop:  7.2m

Dominance:  1.07% 
 

For details on the bwlch survey of Mynydd yr Hewyrch

For further details please consult the Trimble Survey Spreadsheet

Mapping Mountains – Trimble Surveys – Aran and Bryniau Dyfi

08.03.14  Pen y Brynfforchog  (SH 817 179), Pt. 564.3m (SH 809 172) and Mynydd yr Hewyrch (SH 816 150), only bwlch surveyed

Pt. 564.3m (SH 809 172)

Spring is here!  The winter storms seem to be over and the sun is finally making an appearance as a predicted high pressure system is stabilising over the country.  However, high pressure systems can also bring murk and gloom, and so it was this morning, with the forecast of sunshine by midday.  Therefore I pottered about doing a variety of things before waiting for the first glimpse of the bright stuff before heading west to park at Bwlch Oerddrws (SH 802 170).

Two hills were on today’s agenda; Pen y Brynfforchog which is the most southerly of the Aran 2,000ft’s and Pt. 564.3m which is listed in Michael Dewey’s 500m list by a part invented name of Pen Ochr y Bwlch.

Bwlch Oerddrws is situated at the top of the A470 as it heads west from Dinas Mawddwy to Dolgellau and has a fairly large car park at its highest point.  To the north of this road rises a steep grassed slope with a helpful fence indicating the way up.  As progress is made up this slope the upper section of wire in the fence has been used as an aid in uphill momentum!

I was surprised to find a brisk breeze at the bwlch and as height was gained this turned into a buffeting wind.  Thankfully the strength of the wind was being funnelled up the hillsides and across the bylchau, so at least it wasn’t constant.

After the initial steep section is overcome a path contours around the bulk of Pt. 564m and heads towards its connecting bwlch with Pen y Brynfforchog.  This gave easy access to the latter hill and 90 minutes after leaving the car I was placing the Trimble close to the small summit cairn to gather data.

Pen y Brynfforchog (SH 817 179)

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

Between this summit and the higher Aran is a conifer plantation that can be circumvented when heading toward Aran Fawddwy, but for those wishing to connect this hill up with the 600.5m summit of Y Gribin (SH 843 177) and the 541.9m summit of Foel Benddin (SH 853 165) (both heights are from surveys conducted by Alan Dawson with the blog author in attendance) a forest path is the most convenient way between the respective summits.  The conifer plantation has now largely been felled, with only haphazard pockets of trees remaining.  So the onward route to Y Gribin and Foel Benddin will now have views and hopefully the path hasn’t been destroyed by the tree felling.

Pen y Brynfforchog has an interesting listing history as its lower 656m summit at SH 818 185 had been designated the top in a number of published hill lists.  This was only rectified in 1974 when Phil Cooper listed the higher 685m summit at SH 817 179 in his single ring contour unpublished list.  The first published list to assign the higher 685m summit being in 1984 by Terry Marsh.

Once the Trimble had been packed away I headed back down beside the fence to the bwlch that connects Pen y Brynfforchog with Pt. 564m, I took data sets at two points.  The lower of the two and the one at the critical bwlch is nearer to the latter hill.

Gathering data at the first option for the bwlch of Pt. 564.3m

Gathering data at the second option for the bwlch of Pt. 564.3m

I then visited the summit of Pt. 564.3m which consists of an almost flat narrow ridge of grass which is rather unusual; I viewed this from opposing angles and chose my spot for the Trimble to be placed.  This hill was not included in Michael’s original 500-Metre Tops of England and Wales list and only entered the listing after a 115ft (35.1m) basic levelling survey I conducted for drop on the 28^th April 2000.  If memory serves me right I proposed the name of Ochr y Bwlch to Michael as this name appears on the OS map (although the hill is not known locally as this) and it was Rob Woodall who suggested adding the ‘Pen’ part to designate that the name applied to the ‘top’ of the hill, apologies to Mr Woodall if my memory is not wholly factual. 

  

The summit of Pt. 564.3m (SH 809 172)

As the Trimble gathered its data I looked out toward Cadair Idris to the west and down the A470 as it follows the course of the Afon Cerist toward Dinas Mawddwy.  Above this rose Mynydd yr Hewyrch, grand in its bulk and profile.

Cadair Idris from the southern Aran

Mynydd yr Hewyrch (SH 816 150) from the southern Aran

The downward route on the steep slope back to the car proved a little quicker than the upward slog.  Adjacent to the car park is the critical bwlch for Mynydd yr Hewyrch, the Ordnance Survey map has a 363m spot height on the road, but the bwlch is lower than the road and if not for a slightly raised section of land next to a fence that heads toward the next hill of Cribin Fawr (SH 794 153) the whole area would be a wet bog.  This raised section has the beginnings of a water course on its immediate west and another one a few metres away on its east; I placed the Trimble on the eastern edge of the raised section of land trying not to submerge it in the bog in the process.  Once ten minutes of data were collected I packed it away and headed up to Nantlle for the weekend.

Survey Result:

Pen y Brynfforchog

Summit Height:  685.0m (converted to OSGM15)

Summit Grid Reference:  SH  81776 17959

Bwlch Height:  614m (spot height)

Bwlch Grid Reference:  SH 82207 18618 (spot height)

Drop:  71m (Trimble GeoXH 6000 summit and spot height bwlch)

Dominance:  10.36% (Trimble GeoXH 6000 summit and spot height bwlch)

 

Pt. 564.3m

Summit Height:  564.3m (converted to OSGM15)

Summit Grid Reference:  SH 80957 17269

Bwlch Height:  530.5m (converted to OSGM15)

Bwlch Grid Reference:  SH 81133 17386

Drop:  33.8m (Dodd, Dewey and 500m Twmpau status confirmed)

Dominance:  5.99%

Mynydd yr Hewyrch

Summit Height:  678.3m (converted to OSGM15, from subsequent Trimble GeoXH 6000 survey) 678.5m (from subsequent Leica RX1250 survey) (significant height revision)

Summit Grid Reference:  SH 81697 15003

Bwlch Height:  360.5m (converted to OSGM15)

Bwlch Grid Reference:  SH  80208 17001

Drop:  318.0m (based on Trimble GeoXH 6000 bwlch and Leica RX1250 summit)

Dominance:  46.87% (based on Trimble GeoXH 6000 bwlch and Leica RX1250 summit) (Lesser Dominant status confirmed) 

The basic levelling survey conducted on the hill known as Pt. 564.3m in April 2000 gives good accordance with the data produced by the Trimble as Pt. 564.3m has 33.8m of drop (35.1m from the basic levelling survey), whilst current Ordnance Survey data has a bwlch spot height of 533m (enlarged Geograph map) and a summit spot height of 564m, giving a drop of 31m.

For details on the summit survey of Mynydd yr Hewyrch

For further details please consult the Trimble Survey Spreadsheet