Mapping Mountains – Hill Reclassifications – 500m Twmpau

Drum Ddu (SH 931 167) – 500m Sub-Twmpau deletion

There has been a deletion of a hill in the listing of the 500m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill confirmed by detail on contemporary maps produced from Ordnance Survey data

The summit of Drum Ddu (SH 931 167)

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 the hill is listed by is Drum Ddu, and it is adjoined to the Y Berwyn group of hills, which are situated in the south-eastern part of North Wales (Region A, Sub-Region A4), and it is positioned with the A470 road to its west, the A458 road to its south and the B4393 road to its north-east, and has the town of Dinas Mawddwy towards the west south-west. 

When the list that later became known as the 500m Twmpau was first compiled this hill was listed with c 25m of drop based on the 538m summit spot height and an estimated bwlch height of c 513m based on bwlch contouring between 510m – 520m that appear on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps.

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

However, as Drum Ddu has an adjacent hill named Tapiau y Gell (SH 927 168 [refer to Y Pellennig – The Remotest Hills of Wales by Aled Williams and Myrddyn Phillips]) of similar height that has no spot height on either the Ordnance Survey 1:50,000 Landranger or the 1:25,000 Explorer map, it was noted that if Tapiau y Gell is higher, it would also be the qualifying hill for the 500m Sub-Twmpau.

ills of WalesHillThe details for this hill were re-evaluated when the WalkLakes interactive map became available online.  This map originated from the Ordnance Survey Open Data programme and has many spot heights not on other publicly available Ordnance Survey maps and gives a 539m spot height on the summit area of Tapiau y Gell.

Extract from the WalkLakes website

Therefore, the deletion of Drum Ddu from 500m Sub-Twmpau status is due to detail on contemporary maps produced from Ordnance Survey data with this hill given a 538m summit spot height as opposed to the 539m summit spot height given to Tapiau y Gell.  Therefore, the position of the bylchau for these hills are swapped resulting in Drum Ddu now being listed with a 538m summit height and c 523m bwlch height, with these values giving this hill c 15m of drop, which is insufficient for it to be classified as a 500m Sub-Twmpau.

The full details for the hill are:

Group:  Y Berwyn

Name:  Drum Ddu

OS 1:50,000 map:  125

Summit Height:  538m (spot height)

Summit Grid Reference:  SH 93180 16796 (hand-held GPS via DoBIH)

Bwlch Height:  c 523m (interpolation)

Bwlch Grid Reference:  SH 93019 16980 (interpolation)

Drop:  c 15m (spot height summit and interpolated bwlch)

Myrddyn Phillips (June 2020)

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

THIS HILL HAS SUBSEQUENTLY BEEN DELETED FROM THE DEWEY LIST

Foel Cynfal (SH 749 395) – Dewey addition

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.

Foel Cynfal (SH 749 395)

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. 

 

Mountain tables by Michael Dewey

The details for this addition appear below:

The name the hill is listed by in the Deweys is Foel Cynfal, and it is adjoined to the Arenig group of hills which are situated in the central part of North Wales, and it is positioned with the B4391 road to its north, the A470 road to its west and the A4212 road to its south, and has the village of Trawsfynydd towards the south-west.

This hill was not included in the original 1995 Constable publication, with no summit spot height on the publicly available Ordnance Survey maps and with an uppermost 540m ring contour and bwlch contouring between 510m – 520m that appear on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map, this hill was noted as an outside possibility for a potential new Dewey.

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

The above detail was noted by Myrddyn Phillips who then conducted a basic levelling survey (BLS) of this hill on the 15^th July 2000, resulting in 93½ft / 28.5m of drop.  These details were forwarded to the list author; Michael Dewey along with other recent results produced from basic levelling surveys.

Although surveyed as having less than the minimum 30m of drop required to enter this list, the hill was inadvertently included by Michael Dewey.  Its inclusion was subsequently noted during proof reading when an updated copy of the list was received by Myrddyn Phillips.  Although its inclusion in this list was an error, it was for a short period of time listed as a Dewey and therefore the details of this hill are appearing in this Hill Reclassification post and the forthcoming Change Register.

The Trimble GeoXH 6000 gathering data at the summit of Foel Cynfal

The Trimble GeoXH 6000 gathering data at the bwlch of Foel Cynfal

As the margin of uncertainty for the BLS method of surveying over terrain such as that on this hill is approximately +/- 2m and as the resulting 28.5m of drop was near the minimum 30m qualifying drop value, this hill was prioritised for a GNSS survey, and this took place on the 1^st July 2017.  The summit and bwlch of this hill were surveyed by Myrddyn Phillips and Aled Williams using a Trimble GeoXH 6000, resulting in a 545.5m summit height and a 517.4m bwlch height, with these values giving this hill 28.1m of drop, and confirming its non-Dewey status.

The full details for the hill are:

Name:  Foel Cynfal

OS 1:50,000 map:  124

OS 1:25,000 map:  18

Summit Height:  545.5m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SH 74998 39546 (Trimble GeoXH 6000)

Bwlch Height:  517.4m (converted to OSGM15, Trimble GeoXH 6000)

Bwlch Grid Reference:  SH 74884 39528 (Trimble GeoXH 6000)

Drop:  28.1m (Trimble GeoXH 6000)

Myrddyn Phillips (June 2020)

Mapping Mountains – Significant Height Revisions – 100m Twmpau and Y Trechol – The Dominant Hills of Wales

Chepstow Hill (ST 355 905)

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

LIDAR image of Chepstow Hill (ST 355 905)

The criteria for the two listings 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.

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.

The name the hill is listed by is Chepstow Hill and it is adjoined to the Gwent Is Coed group of hills which are situated in the south-eastern part of South Wales (Region C, Sub-Region C3), and it is positioned with the Afon Wysg (River Usk) to its north-west, the M4 motorway to its south and the A449 road to its east, and has the city of Casnewydd (Newport) towards the 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 listed with a 111m summit height based on the spot height 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 gives a 114m spot height on the summit area of this hill and positioned at ST 356 905.  This 114m spot height also appears on Ordnance Survey data available on the Magic Maps website.

Extract from the Magic Maps 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 116.6m positioned at ST 35547 90567, this is a substantial height revision compared to the original 111m listed summit height, and it comes 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 summit 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. 

Therefore, this hill’s new listed summit height is 116.6m and this was produced by LIDAR analysis, this is 5.6m higher than its original listed height of 111m that appears as a spot height on the Ordnance Survey 1:25,000 Explorer map, and 2.6m higher than that of the online Vector Map Local.

ills of Wales, and are reproduced below@

The full details for the hill are:

Group:  Gwent Is Coed

Name:  Chepstow Hill

OS 1:50,000 map:  171

Summit Height (New Height):  116.6m (LIDAR)

Summit Grid Reference:  ST 35547 90567 (LIDAR)

Bwlch Height:  63.2m (LIDAR)

Bwlch Grid Reference:  ST 36979 90843 (LIDAR)

Drop:  53.4m (LIDAR)

Dominance:  45.76% (LIDAR)

Myrddyn Phillips (June 2020)

Mapping Mountains – Hill Reclassifications – Y Trichant – The 300m Hills of Wales

Pt. 369.4m (SJ 047 509) – Sub-Trichant addition

There has been confirmation of an addition to the list of Y Trichant – The 300m Hills of Wales, with the summit height and its location confirmed by LIDAR analysis conducted by Myrddyn Phillips, and the bwlch height and its location, the drop and status of the hill derived from detail on contemporary maps produced from Ordnance Survey data.

LIDAR image of Pt. 369.4m (SJ 047 509)

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

Y Trichant – The 300m Hills of Wales – Welsh hills at or above 300m and below 400m in height that have 30m minimum drop, with an accompanying sub list entitled the Sub-Trichant with the criteria for this sub category being all Welsh hills at or above 300m and below 400m in height with 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips, with the Introduction to the list and the renaming of it appearing on Mapping Mountains on the 13th May 2017.

The hill is being listed by the point (Pt. 369.4m) notation as an appropriate name for it either through local enquiry and / or historic research has not been found by the author, and it is adjoined to the Mynydd Hiraethog group of hills which are situated in the north-eastern part of North Wales (Region A, Sub-Region A2), and it is positioned with the B5105 road to its north and minor roads to it immediate west and south-east, with the A494 road further to its south-east, and has the village of Clawddnewydd towards the east north-east.

When the original 300m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website this hill was not included in the Hills to be surveyed sub list that accompanied the main P30 list, as it was considered not to meet the criteria then used for this sub category. 

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 29m of drop, based on an estimated c 370m summit height and the 341m bwlch spot height that appears on the Ordnance Survey 1:25,000 Explorer map.

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

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 confirmation of the addition of this hill to Sub-Trichant status is due to LIDAR analysis which only covers the summit area and detail derived from contemporary maps produced from Ordnance Survey data, resulting in a 369.35m summit height and a 341m bwlch height, with these values giving this hill 28m of drop, which is sufficient for it to be classified as a Sub-Trichant.

The full details for the hill are:

Group:  Mynydd Hiraethog

Name:  Pt. 369.4m

OS 1:50,000 map:  116

Summit Height:  369.4m (LIDAR)

Summit Grid Reference:  SJ 04708 50996 (LIDAR)

Bwlch Height:  341m (spot height)

Bwlch Grid Reference:  SJ 04933 51669 (spot height)

Drop:  28m (LIDAR summit and spot height bwlch)

Myrddyn Phillips (June 2020)

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

Twr Pen-cyrn (SO 202 144) – Dewey deletion

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 publication of this list there have been a number of status changes to it. In recent years this has involved independent surveyors and the use of LIDAR.  Both have enabled an accurate re-assessment of many of the hills included in Michael’s list.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales. 

LIDAR summit image of Twr Pen-cyrn (SO 202 144)

The details for this hill were forwarded to Michael Dewey in February 2017.  These details were produced by LIDAR analysis conducted by Aled Williams:

Dewey deletion:

Name:  Twr Pen-cyrn

OS 1:50,000:  161

Summit Height:  528.4m

Summit Grid Reference:  SO 20283 14511

Bwlch Height:  499.6m

Bwlch Grid Reference:  SO 18452 15398

Drop:  28.8m

Subsequent LIDAR analysis conducted by Myrddyn Phillips produced the following result:

Name:  Twr Pen-cyrn

OS 1:50,000:  161

Summit Height:  528.9m

Summit Grid Reference:  SO 20281 14491

Bwlch Height:  499.7m

Bwlch Grid Reference:  SO 18531 15394

Drop:  29.3m

As this hill has a large ancient cairn positioned a few metres in distance from a triangulation pillar, the discrepancy in the summit height and position given above in the two evaluations is dependent upon where natural ground is judged to be positioned, with the caveat that higher natural ground may exist under the ancient cairn.  However, this was judged not to influence this hill’s demotion from Dewey status.  The difference in bwlch position is given as 2mm by LIDAR with the slightly lower position on the hill to hill traverse presented in the latter evaluation.

LIDAR bwlch image for Twr Pen-cyrn

Michael has now been consulted regarding this hill, and this has resulted in him confirming the deletion of Twr Pen-cyrn from Dewey status.

Aled Williams and Myrddyn Phillips (June 2020)