Mapping Mountains – Hill Reclassifications – The 500-Metre Tops of England and Wales – Deweys

Twynwalter (SN 828 175) – Dewey deletion

This is one in a series of retrospective Hill Reclassification posts that detail hills whose status has altered in the listing of the Deweys and where I have had direct association with the status change.  These posts will tie in with a forthcoming Change Register giving detail to this list and its alterations since publication in the Mountain tables book.

LIDAR image of Twynwalter (SN 828 175)

The 500-Metre Tops of England and Wales are affectionately known after their hill list compiler; Michael Dewey.  This list mixes metric and imperial height in its criteria to bookend up to the 2000ft height band and takes in all hills in England, Isle of Man and Wales that are 500m and above and below 2000ft (609.6m) in height that have 30m minimum drop.

This list formed one of a number of lists that appeared in the Mountain tables book published by Constable in 1995 and at the time of publication comprised 373 hills with 164 in England, 5 in the Isle of Man and 204 in Wales.  The Deweys have undergone extensive revision since first publication with the initial stages forming the basis of this revision given below:

1995    Mountain tables published by Constable with 373 hills listed as Deweys.

April 2000    Strider (LDWA quarterly booklet) publishes contact details for David Purchase and Myrddyn Phillips who have found and list 24 and 14 possible new 500m tops respectively.

It was expanded versions of the above two lists that formed the basis of the next publication:

25^th May 2000    List of Possible 500 Metre Tops by Michael Dewey listing 44 hills.

David Purchase expands his Additional Dewey 500m Hills and Myrddyn Phillips produces lists of English 500m hills to measure and Welsh 500m hills to measure.

These lists formed the basis of the next publication:

29^th June 2000    Possible/Probable 500’s by Michael Dewey listing 77 hills.  Michael adopts following protocol; if one person proposes that a top should qualify as a 500 by personal survey, and is then confirmed by a second person, it should then be promoted to the main list.

April 2002    The 500+ Tops of England and Wales – The ‘New Deweys’ published in the Strider booklet and listing 66 new qualifying hills.

25^th May 2006    Rob Woodall republishes Michael’s main and possible/probable lists on the RHB Yahoo group file database. 

 

Mountaintables by Michael Dewey

The details for this deletion appear below:

The name the hill was listed by in the Deweys is Twynwalter, and it is adjoined to the Mynydd Du group of hills in the Brecon Beacons which are situated in south Wales, and it is positioned with the A4067 road to its east and south, and has the hamlet of Glyntawe towards the south-east and the village of Abercraf towards the south.

This hill was included in the original 1995 Constable publication, and listed with a 509m summit height which appears as a spot height on Ordnance Survey 1:25,000 Explorer maps and the Outdoor Leisure maps of the day.  Its drop value was later given as an estimated c 32m with its bwlch height an estimated c 477m based on interpolation of 10m contouring between 470m – 480m.

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

As the listed drop value was near the minimum 30m required for qualification to this list the hill was prioritised for a GNSS survey and this took place on the 10^th July 2014.  The summit of this hill was surveyed by Myrddyn Phillips using a Trimble GeoXH 6000.  However, this was the last of many surveys conducted during the day that included visiting the remotest spot in mainland Wales as well as one of the remotest hills in Wales and lack of daylight hours dictated that only the summit could be surveyed.  The survey resulted in a 502.1m summit height, which is 6.9m lower than the 509m spot height on the Ordnance Survey 1:25,000 Explorer map.

The Trimble GeoXH 6000 gathering data at the summit of Twynwalter (SN 828 175)

However, it was not until LIDAR became available that the details for the bwlch of 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.

LIDAR bwlch image of Twynwalter

The summit and bwlch heights for this hill were subsequently ascertained from LIDAR analysis initially conducted by Aled Williams and subsequently by Myrddyn Phillips, resulting in a bwlch height of 475.9m and when coupled with the 502.1m summit height from the Trimble GeoXH 6000 survey this gives the hill 26.25m of drop.

These details were forwarded to the list author; Michael Dewey and the hill was subsequently deleted from his list on 19^th February 2019.

 

The full details for the hill are:

Name:  Twynwalter

OS 1:50,000 map:  160

OS 1:25,000 map:  12

Summit Height:  502.1m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SN 82837 17506 (Trimble GeoXH 6000)

Bwlch Height:  475.9m (LIDAR)

Bwlch Grid Reference:  SN 82597 17917 (LIDAR)

Drop:  26.25m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Myrddyn Phillips (October 2020)

The 500-Metre Tops of England and Wales – the Deweys

The listing to The 500-Metre Tops of England and Wales appeared in Michael’s Mountain tables book which was published by Constable in 1995.  This list mixed metric and imperial height in its criteria to bookend up to the 2000ft height band and listed hills between 500m – 2000ft (609.6m) in height with 30m minimum drop.

Mountain tables by Michael Dewey

Since this publication there have been a number of amendments to this list, and Michael Dewey has confirmed the addition, deletion and reinstatement of the following three hills:

Dewey addition:

Cefn Cyfarwydd (SH 75201 63067) which was surveyed using a Trimble GeoXH 6000 by Myrddyn Phillips, with assistance from Aled Williams, and is situated in the great sweep of rock and heather bound hills that make up the higher north-eastern Carneddau in north Wales.

Summit: 501.7m at SH 75201 63067

Bwlch:  471.0m at SH 74708 62751

Drop:  30.7m

Cefn Cyfarwydd (SH 752 630)

Dewey deletion:

Twyn Walter (SN 82837 17506) is another hill surveyed with the Trimble GeoXH 6000 by Myrddyn Phillips, giving a summit height of 502.1m with its 475.9m col height relying on LIDAR analysis conducted by Aled Williams, and is situated in the limestone grasslands of Mynydd Du in south Wales.

Summit:  502.1m at SN 82837 17506

Bwlch:  475.9m at SN 82597 17917

Drop:  26.25m

The cairned summit of Twyn Walter (SN 828 175)

Dewey reinstatement:

Beefstand Hill (NT 821 143) has been reinstated by Michael Dewey based on communication with John Kirk who petitioned for this hill to be accepted back in to the Dewey ranks.  Having been included in the original list, it was subsequently deleted and has now been officially reinstated.  This reinstatement took place in January 2015.

Hello John,

Many thanks for your email on hill and mountain nationality. I think that your last paragraph sets it well ‘It is better to be inclusive rather than exclusive’.

Should anyone set a binding rule or a law, perhaps not!  However, I think that it should be the person who raised the list to make the decisions on the borderline tops that should or should not be included in any list.

Yes, I think that Beefstand Hill should be reinstated into English and Welsh 500 metre table (Dewey table). It makes sense when you look at the map.

Best regards,

Michael (January 2015)

The summit of Beefstand Hill.  Photo: John Kirk

Myrddyn Phillips (February 2019)

For the UKHillwalking article relating to these changes 

  

Mapping Mountains – Hill Reclassifications – 500m Twmpau

Twyn Walter (SN 828 175) - 500m Twmpau reclassified to 500m Sub-Twmpau

There has been a reclassification of a 500m Twmpau hill by surveying with the Trimble.   The hill is situated in the south-eastern lands of Y Mynydd Du in South Wales, and is positioned north-west of Glyntawe and the A4067 as it speeds its way between Pontsenni (Sennybridge) to the north and Ystradgynlais to the south.

These details are retrospective as the Trimble GeoXH 6000 survey that resulted in the reclassification of this hill from 500m Twmpau to 500m Sub-Twmpau was conducted on 10^th July 2014, in the company of Mark Trengove when we visited the remotest spot in mainland Wales, as well as the remotest hill in mainland Wales.

Access to the hill from the south-east of its summit is relatively easy as a broad path ascends from near to the Campsite entrance that is adjacent to Dan yr Ogof Showcaves.  As height is gained this path resembles a vehicle track and eventually heads north-west into the remote grasslands of Mynydd Du, on its way it passes within approximately 260 metres of the summit.

     

The hill is named Twyn Walter (written as Twynwalter on current Ordnance Survey maps) and its summit is positioned at SN 828 175.  The hill was listed with c 31m of drop based on a 509m summit spot height and an estimated bwlch height of c 478m.  The area of the bwlch has a number of sink holes on it which complicates pinpointing where the critical bwlch is positioned.  However, contouring suggests that there are two distinct positional possibilities for where this critical bwlch lies, these are at SN 82525 17584 and SN 82611 17986.

The survey with the Trimble GeoXH 6000 resulted in a 502.1m (converted to OSGM15) summit height, unfortunately daylight was quickly disappearing and this was the last survey of a long day on the hill and this dictated that the two options for the position of the bwlch were not surveyed.  However, the dramatic decrease in summit height from the 509m map height to the 502.1m (converted to OSGM15) surveyed height and the re-evaluated and estimated bwlch height from contour interpolation of c 476m gives this hill a drop value of only c 26m.

This now brings the overall total for the 500m Twmpau hills to 226, please click {here} to access the list and {here} for its detailed Introduction.

Since this reclassification was announced the height and position of this bwlch has been determined via LIDAR analysis conducted by Aled Williams, the details for which are given below. 

The full details for the hill are:

Group:  Mynydd Du

Name:  Twyn Walter

OS 1:50,000 map:  160

Summit Height:  502.1m (converted to OSGM15)

Summit Grid Reference:  SN 82837 17506

Bwlch Height:  475.9m (LIDAR)

Bwlch Grid Reference:  SN 82597 17917 (LIDAR)

Drop:  26.25m (Trimble summit and LIDAR bwlch)

Gathering data at the summit of Twyn Walter, which resulted in this hill being reclassified from a 500m Twmpau to a 500m Sub-Twmpau

For details on the survey that reclassified this hill from 500m Twmpau to 500m Sub-Twmpau please click {here}

Myrddyn Phillips (July 2014)

Mapping Mountains – Significant Height Revisions – Welsh Highlands - Uchafion Cymru and 500m Twmpau

Twyn Walter (SN 828 175)

There has been a Significant Height Revision initiated by a survey conducted with the Trimble GeoXH 6000 to the listing of the Yr Uchafion and the 500m Twmpau (thirty welsh metre prominences and upward), with these details being retrospective as the survey that resulted in this height revision was conducted on 10^th July 2014.

The criteria for these listings appear below:

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

500m Twmpau - All Welsh hills at or above 500m and below 600m in height with 30m minimum drop.  With the 500m Sub-Twmpau being all Welsh hills at or above 500m and below 600m in height with 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips.   

The name of the hill is Twyn Walter and it is situated in the Mynydd Du range of hills in south Wales, and the survey was conducted in the company of Mark Trengove on a lovely summer’s day when we visited the remotest point of mainland Wales as well as the remotest hill of mainland Wales.

The hill can be accessed from Glyntawe on a good path and track that ascends above the Dan-yr-Ogof Showcaves.  Heading west beyond the hill is some of the remotest land in the whole of Wales with the southern land of Y Mynydd Du comprising hills with limestone outcrops and a great wilderness of open grassland, a visit is highly recommended.

The summit height of this hill has been dramatically decreased from its current Ordnance Survey 1:25,000 Explorer map height of 509m, with the survey conducted with the Trimble GeoXH 6000 giving the height of the hill as 502.1m (converted to OSGM15).  Based on the 509m summit map height this hill used to be listed as a 500m Twmpau with over 30m of drop, however its height has now dramatically decreased and its drop value also re-evaluated giving this hill c 26m of drop and therefore it has been reclassified to a 500m Sub-Twmpau.

Therefore this hill’s new summit height is 6.9m lower than its previously listed height which came from the 509m spot height on current Ordnance Survey 1:25,000 Explorer maps and the Ordnance Survey enlarged mapping hosted on the Geograph website.

Since this height revision was announced the height and position of this hill's bwlch has been determined via LIDAR analysis conducted by Aled Williams, the details for which are given below.

The full details for the hill are:

Group:  Mynydd Du

Name:  Twyn Walter

OS 1:50,000 map:  160

Summit Height (New Height):  502.1m (converted to OSGM15)

Summit Grid Reference:  SN 82837 17506

  

Bwlch Height:  475.9m (LIDAR)

Bwlch Grid Reference:  SN 82597 17917 (LIDAR)

Drop:  26.25m (Trimble summit and LIDAR bwlch)

Gathering data from the summit of Twyn Walter which 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 (August 2015)

Mapping Mountains – Trimble Surveys – Mynydd Du

10.07.14  Cerrig Coegion (SN 790 176), Tyle Garw (SN 784 178), Disgwylfa (SN 815 178), Carreg Goch (SN 818 170) and Twyn Walter (SN 828 175).

Carreg Goch (SN 818 170)

To the south of the escarpment edge that gives the higher hills of Y Mynydd Du their beauty is a land unrivalled in the whole of Wales, as within its midst is the remotest hill and the remotest point from a paved public road in mainland Wales.  The sense of remoteness is relative, as by Scottish standards neither is exceptional, but for the country where the majority of my hill walks take place, both are without equal.

I wanted to do this walk for a number of years, ever since the maps were opened and studied and measurements taken and criteria adopted.  The map study culminated in a hill list named Y Pellennig (originally the Pellennigs) which was published on Geoff Crowder’s website in late 2011 and which is soon to be jointly produced with Aled Williams.

Initially I wanted to find the point in Wales that is farthest from a paved public road, I soon turned my attention to compiling a list of remote Welsh hills.  During compilation I wondered where the remotest spot and hill would be found, my first thoughts led me toward the great expanse of emptiness of the Elenydd, I was surprised to find that the southern lands of Y Mynydd Du included these two special places.

This walk was suggested to Mark a couple of months ago as a possibility as he wanted to visit south Wales to get better photographs for the 2^nd edition of Y Pedwarau that is planned for publication.  He also wanted a walk that combined Dewey and Pedwar hills, there are few possibilities in south Wales that give a good length walk with Dewey and Pedwar bagging, but todays walk is one of them.

We travelled south as the sun shone and the blue of the sky intimated a perfect day to venture in to such remote surroundings.  The ideal way to visit the five hills listed above is to traverse the mountain range, by doing so the hills of Carn Fadog (SN 767 171), Foel Fraith (SN 756 183) and Garreg Lwyd (SN 740 179) can also be visited.  Having only one car and no means to make the circuitous journey back, we opted for a there and back route. 

The easiest way toward this remote land from the east is to follow a good track from close to the Dan yr Ogof show caves in Glyntawe, this track bisects the three 500m Deweys and heads off in to the heart of wilderness.  As we planned to use this track for our outward journey we decided to ascend the lower southern ridge of Fan Hir and circumvent the three Deweys before joining the track and the remote land beyond.

Before getting our boots on we stopped to take photos of Cribarth (SN 831 143) before joining the hordes of school children and happy families as they descended upon the show caves, as most headed underground to admire the architecture that was carved out millions of years ago, we headed in to the café for coffee and cake!  Once nourished we drove to a car park opposite a pub brandishing a large ‘Closed’ sign which is on the A4067 a few hundred metres north of the show caves entrance.

The shapely profile of Cribarth (SN 831 143)

Adjacent to this car park is a path that forms part of the Beacons Way, which is a 152km (95 mile) linear walk across the Brecon Beacons National Park.  We soon gained height up the southerly ridge of Fan Hir above Cwm Haffes, to our north-east the rounded profile of Fan Gyhirych dominated the view, whilst further south the shapely mass of Cribarth overlooked the valley.

Fan Gyhirych (SN 880 191) the western outlier of Fforest Fawr

This route up relied on there being a path, or alternatively, easy ground, contouring around the upper part of the Afon Haffes, thankfully we picked up a good sheep track that led us toward a waterfall named Sgwd Ddu on the Ordnance Survey map.  On the way I found a hole to put my foot in and Mark plunged in to an unsavoury bog.

Heading toward Sgwd Ddu, a waterfall situated in a quiet area of Y Mynydd Du

A few kilometres beyond the horizon is the remotest land in mainland Wales

Mark making progress through the grassland with the slender cascade of Sgwd Ddu on the left of photo

Although this route in to the hills is not as easy as the track that bisects the three Deweys, it gave us the opportunity to see part of this land that is probably seldom visited, and as we looked across to Sgwd Ddu with its cascading water forever falling, a Heron silently appeared loping upstream toward the waterfall.  We crossed the Afon Haffes beyond the waterfall and headed west directly toward a large fenced off bog named Waun Fignen Felen.  We circumvented this on its northern side and smiled as we came across a foot stile directing walkers directly in to the morass of bog, we wondered if this had been put there by a Warden for an April fool’s joke!

Crossing the Afon Haffes

Beyond the bog we joined the track and came across a small party of youngsters who were traversing the hills as part of their silver award on the Duke of Edinburgh Award scheme.  As we chatted I looked west in to a large expanse of grassland, seemingly without fences, remarkably the only fence during nine hours of walking and surveying we came across was the one around the bog that we had just passed, otherwise this whole land is open for sheep and horses to roam and for the unwary walker to get lost.

The track passed one or two pools as it headed down to cross a stream, before heading uphill to cross the shoulder of Twyn Tal y Ddraenen, as height was gained we left the track and joined a sheep path heading south on an intermittent ridge, before venturing west in to a land of grass wilderness.  Even with the comfort of a hand-help GPS and a Trimble we kept checking the map and realising that the first hill we were aiming for was seemingly forever further on.

Disgwylfa (SN 815 178) rises above one of the small pools near to our inward track

The route from the intermittent ridge which is the southern part of descending land from Twyn Tal y Ddraenen took us directly toward the remotest point in the whole of mainland Wales, this is the spot of land that is farthest from any paved public road, this point is close to the apex of the northern ridge of Cerrig Coegion, to within a few metres its grid reference is SN 79220 18316.

Mark aims directly ahead toward the remotest point in mainland Wales

Mark led the way with his GPS in hand, striding out over the land like an intrepid traveller from a bygone age.  However, he was rather underwhelmed by the spot of land we reached, probably as he has so much experience of walking in Scotland, where the concept of Welsh remoteness would be a necessity to get to the majority of hills.  Once Mark had declared he had found the remotest point he stuck his walking poles in the ground and I then used the Trimble to hone in on the exact spot.  It had taken us three hours to get here, the customary photos were taken and I gathered five minutes of data with the Trimble, a new experience as this was neither a summit nor a bwlch, just a patch of land as far from a paved public road that one could get to in mainland Wales. 

Walking poles and Trimble mark the spot - the furthest point from a paved public road in mainland Wales

The Trimble GeoXH 6000 gathering data at the remotest spot in mainland Wales

Tyle Garw (SN 784 178) from the lower slopes of Cerrig Coegion

As the Trimble gathered data Mark headed up to the summit of our first hill of the day; Cerrig Coegion, I soon joined him.  Cerrig Coegion is the 3^rd remotest hill in mainland Wales, with only Foel Uchaf (SN 770 654) in the Elenydd and Tyle Garw (SN 784 178) surpassing it.  We gathered data on the high point at the position where the 474m spot height appears on the map; we then visited the trig pillar and gathered more data at the high point just to the west of the trig, as this looked like a contender for overall high point.  The whole summit area had limestone rocks scattered over it, with distant views across the Severn estuary to Devon and the south-westerly lands of England.

Mark heads off toward the first summit of the day; Cerrig Coegion

Mark on the summit of Cerrig Coegion, the 3rd remotest summit in mainland Wales

Gathering data on the summit of Cerrig Coegion

The 471m trig pillar is positioned just to the south of the summit of Cerrig Coegion

Our next hill was Tyle Garw; the remotest hill in mainland Wales.  We took a direct route past a pool and up to its summit, however unremarkable a spot when viewed as a singular summit; it was nonetheless a spot I had wanted to visit for a number of years.  As the Trimble gathered five minutes of data I looked out in all directions, all I could see were hills and open land, with one exception being to the south where England’s green and pleasant land could just be distinguished.  To the north a large bank of cloud over the higher Mynydd Du peaks was now heavier in colour and had descended upon the summit of Fan Brycheiniog, these higher hills had been bathed in shadow all day, whilst we had been on the periphery of the cloud bank in sunshine.

Heading toward Tyle Garw (SN 784 178), the remotest summit in mainland Wales

Mark on the summit of Tyle Garw - the remotest summit in mainland Wales

Gathering data at the summit of Tyle Garw

As we left the summit of Tyle Garw it was 5.45pm, we had been walking and surveying for five hours, we now had to retrace some of our inward route and get back on to the track that would take us up toward Disgwylfa and the three remaining Deweys.  By now the sun had lowered in the sky and those magical evening colours that are so sought after were just beginning to emerge.  As the open land of tussock and bog was crossed the lowering sun toward the bank of cloud had cast emerald on the grassland, we stopped for a moment to savour the colour as a Heron flew westward, effortless in flight with its distinguishable profile caught in memories eye with the browns and greens of the hills as backdrop.

Lowering sun highlighting the greens of  the southern lands of Y Mynydd Du

Heron caught mid-flight

Soon the two remote Pedwar hills disappeared from eye as we re-crossed the intermittent ridge of Twyn Tal y Ddraenen and re-joined the inward track, only stopping to watch a number of horses as they ran across the land.

Last view of Tyle Garw

Cerrig Coegion and Tyle Garw

One of many horses that roam the southern lands of Y Mynydd Du

The track led us up toward the last three summits of the day.  However, we had to leave the comfort of the track and branch right to slowly make our way up to the summit of Disgwylfa, a fine hill, with a limestone bouldered summit.  As the Trimble gathered data I looked out as evening light enhanced the glow of dark grey, white and blue in the sky.

Gathering data at the summit of Disgwylfa

Our next summit and penultimate of the day was Carreg Goch, a small path led the way past limestone outcrops down toward a large sink hole that splits the area of the bwlch in two.  At 558m on the map this hill was the highest of the day, it has a fine summit, again comprising an assortment of limestone boulders and rocks.  The Trimble sat on the highest, gathering data as we both took photos and looked down and across to the last summit of the day; Twyn Walter.

Mark taking a photo as the Trimble gathers data on the summit of Carreg Goch

The route from Carreg Goch to Twyn Walter does have an occasional sheep track to ease passage; otherwise it is pathless, but never difficult.  The magical hour of evening’s illuminated colour had gone by the time we reached its summit, replaced by the darkening silence of afterglow.  I removed the small summit cairn to place the Trimble on the highest point of the hill, and replaced the cairn after five minutes of data had been collected.

Gathering data at the summit of Twyn Walter, a hill that probably needs deleting from the Dewey list

We then re-joined the track and descended towards the valley as the full moon shone and the remaining cloud etched itself in pink, sometimes ablaze in shapely colour silhouetting a single small tree on the horizon. 

Evening's colour silhouetting a single small tree

The walk had taken nine hours and had covered 20.3km (12½ miles) with 715m (2,346ft) of ascent.  We arrived in Welshpool at 11.45pm where Mark had a quick rejuvenating cup of coffee before driving back home.  A great day! 

Survey Result:

Cerrig Coegion (significant name change)

Summit Height:  473.4m (converted to OSGM15, Trimble GeoXH 6000)  

Summit Grid Reference:  SN 79087 17673 (Trimble GeoXH 6000)

Bwlch Height:  415.4m (LIDAR)

Bwlch Grid Reference:  SN 79544 18696 & SN 79547 18693 & SN 79549 18689 (LIDAR)

Drop:  57.9m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Dominance:  12.24% (Trimble GeoXH 6000 summit and LIDAR bwlch)

Tyle Garw

Summit Height:  467.3m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SN 78499 17819 (Trimble GeoXH 6000)

Bwlch Height:  425.6m (LIDAR)

Bwlch Grid reference:  SN 78703 17366 & SN 78703 17363 (LIDAR)

Drop:  41.7m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Dominance:  8.92% (Trimble GeoXH 6000 summit and LIDAR bwlch) 

Disgwylfa

Summit Height:  543.5m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SN 81565 17897 (Trimble GeoXH 6000)

Bwlch Height:  c 503m (interpolation)

Bwlch Grid Reference:  SN 81562 17267 (interpolation)

Drop:  c 41m (Trimble GeoXH 6000 summit and interpolated bwlch) 

Dominance:  7.45% (Trimble GeoXH 6000 summit and interpolated bwlch)

Carreg Goch

Summit Height:  558.3m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SN 81887 17029 (Trimble GeoXH 6000)

Bwlch Height:  c 492m (interpolation)

Bwlch Grid Reference:  SN 81967 18317 (interpolation)

Drop:  c 66m (Trimble GeoXH 6000 summit and interpolated bwlch) 

Dominance:  11.82% (Trimble GeoXH 6000 summit and interpolated bwlch)

Twyn Walter

Summit Height:  502.1m (converted to OSGM15) (significant height revision)

Summit Grid Reference:  SN 82837 17506

Bwlch Height:  475.9m (LIDAR)

Bwlch Grid Reference:  SN 82597 17917 (LIDAR)

Drop:  26.25m (Trimble GeoXH 6000 summit and LIDAR bwlch) (500m Twmpau reclassified to 500m Sub-Twmpau) (Dewey deletion) (Dodd deletion)

Dominance:  5.23% (Trimble GeoXH 6000 summit and LIDAR bwlch)

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