Mapping Mountains – Significant Height Revisions – 30-99m Twmpau and Y Trechol – The Dominant Hills of Wales

 

Penllwyngwyn Mawr (SN 549 007) 

There has been a Significant Height Revision to a hill that is listed in the 30-99m 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 derived from LIDAR analysis conducted by Myrddyn Phillips.               

LIDAR image of Penllwyngwyn Mawr (SN 549 007)

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

30-99m Twmpau – Welsh hills at or above 30m and below 100m in height that have 30m minimum drop, with an accompanying sub list entitled the 30-99m Sub-Twmpau, with the criteria for this sub category being all Welsh hills at or above 30m and below 100m 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. 

30-99m Twmpau by Myrddyn Phillips

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. 

Y Trechol - The Dominant Hills of Wales by Myrddyn Phillips

The name the hill is now listed by is Penllwyngwyn Mawr and this was derived from the Tithe map, and it is adjoined to the Mynydd Sylen group of hills, which are situated in the southern part of South Wales (Region B, Sub-Region B5), and it is positioned with the B4297 road to its immediate north and to its south, and has the town of Llanelli towards the west.

When the original 30-99m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was included in the main P30 list with a 72m summit height, based on the spot height positioned at SN 55146 00863 that appears on the contemporary Ordnance Survey 1:25,000 Explorer map. 

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

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 47m of drop, based on an estimated c 75m summit height positioned at SH 54904 00700 and an estimated c 28m bwlch height, based on interpolation of 5m contouring between 25m – 30m.  With the caveat that the uppermost 75m ring contour had been missed when the details for this hill were first compiled and published.

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. 

LIDAR summit image of Penllwyngwyn Mawr (SN 549 007)

The summit height produced by LIDAR analysis is 76.8m and is positioned at SN 54907 00706, and this 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 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, the new listed summit height of this hill is 76.8m and this was derived from LIDAR analysis, this is 4.8m higher than the originally listed summit height of 72m, which was based on the spot height that appears on the contemporary Ordnance Survey 1:25,000 Explorer map.

 

ills of Wales, and are reproduced below@

The full details for the hill are:

Group:  Mynydd Sylen 

Name:  Penllwyngwyn Mawr 

OS 1:50,000 map:  164, 178

Summit Height (New Height):  76.8m (LIDAR) 

Summit Grid Reference:  SN 54907 00706 (LIDAR)               

Bwlch Height:  25.0m (LIDAR) 

Bwlch Grid Reference:  SN 53996 01771 (LIDAR) 

Drop:  51.8m (LIDAR) 

Dominance:  67.44% (LIDAR)

 

Myrddyn Phillips (October 2024)

Mapping Mountains – Hill Reclassifications – 30-99m Twmpau

 

Ffridd (SN 708 986) – 30-99m Sub-Twmpau addition 

There has been confirmation of an addition to the list of 30-99m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Ffridd (SN 708 986)

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

30-99m Twmpau – Welsh hills at or above 30m and below 100m in height that have 30m minimum drop, with an accompanying sub list entitled the 30-99m Sub-Twmpau, with the criteria for this sub category being all Welsh hills at or above 30m and below 100m 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. 

30-99m Twmpau by Myrddyn Phillips

The name the hill is now listed by is Ffridd, and this was derived from the Tithe map, and it is adjoined to the Banc Llechwedd Mawr group of hills, which are situated in the northern part of South Wales (Region B, Sub-Region B1), and it is positioned with the A487 road to its west and a minor road to its east, and has the town of Machynlleth towards the north-east.

When the original 30-99m 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, as it was considered not to meet the criteria then used for this sub category.

After 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 21m of drop, based on the 98m summit spot height that appeared on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map and an estimated c 77m bwlch height, based on interpolation of 10m contouring between 70m – 80m. 

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 30-99m Sub-Twmpau status is due to LIDAR analysis, resulting in a 97.6m summit height and a 74.5m bwlch height, with these values giving this hill 23.1m of drop, which is sufficient for it to be classified as a 30-99m Sub-Twmpau. 

 

The full details for the hill are: 

Group:  Banc Llechwedd Mawr 

Name:  Ffridd 

OS 1:50,000 map:  135

Summit Height:  97.6m (LIDAR) 

Summit Grid Reference:  SN 70875 98692 (LIDAR)               

Bwlch Height:  74.5m (LIDAR) 

Bwlch Grid Reference:  SN 71072 98917 (LIDAR) 

Drop:  23.1m (LIDAR) 

 

Myrddyn Phillips (October 2024)

 

 

 

 

Mapping Mountains – Significant Height Revisions – Y Trichant – The 300m Hills of Wales

Crugiau Dwy (SN 171 311) 

There has been a Significant Height Revision to a hill that is listed in the Y Trichant – The 300m Hills of Wales, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Crugiau Dwy (SN 171 311)

The criteria for the list that this height revision 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 13^th May 2017, and the Introduction to the Mapping Mountains publication of the list appearing on the 1^st January 2022. 

Y Trichant - The 300m Hills of Wales by Myrddyn Phillips

The name the hill is listed by is Crugiau Dwy, and it is adjoined to the Mynydd Preseli group of hills, which are situated in the south-western part of South Wales (Region B, Sub-Region B1), and it is positioned with minor roads to its north and south-east, and the A478 road to its east, and has the village of Crymych towards the north 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 included in the main P30 list with a 359m summit height, based on the spot height that appears on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map. 

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

After 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 38m of drop, based on the 359m summit spot height and an estimated c 321m bwlch height, based on interpolation of 5m contouring between 320m – 325m.

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. 

LIDAR summit image of Crugiau Dwy (SN 171 311)

The summit height produced by LIDAR analysis is 360.3m and is positioned at SN 17129 31154 and SN 17133 31187, and this 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 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, the new listed summit height of this hill is 360.3m and this was derived from LIDAR analysis, this is 1.3m higher than the previously listed summit height of 359m, which was based on the spot height that appears on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map. 

 

The full details for the hill are: 

Group:  Mynydd Preseli 

Name:  Crugiau Dwy 

OS 1:50,000 map:  145

Summit Height (New Height):  360.3m (LIDAR)                                                           

Summit Grid Reference:  SN 17129 31154 & SN 17133 31187 (LIDAR) 

Bwlch Height:  321.5m (LIDAR) 

Bwlch Grid Reference:  SN 16431 30609 & SN 16432 30606 (LIDAR) 

Drop:  38.8m (LIDAR) 

 

Myrddyn Phillips (October 2024)

 

 

 

  

Mapping Mountains – Trimble Surveys – Arenig Fawr

28.07.24  Pen Tyrau (SH 837 382) 

The early morning start provided negligible respite from the summer heat.  I stood forlornly upon the bank of Llyn Arenig Fawr as I eyed up the steep sections of the arm that would take me to Bwlch Blaen Nant.  The anxiety lapsed as I took in the beauty of the scene; abstract reflections of a rugged mountain framed by a cloudless sky, the calm intercepted momentarily by the shrieking calls of peregrine falcons.

The morning view from Llyn Arenig Fawr.  Photo: Aled Williams 

Ahead lay Pen Tyrau, which was the surveying objective of the day, having recently been deleted as a P10 Sub-Top within The Welsh Highlands list.  Analysis of LIDAR data indicated that the prominence of the hill only reached 9.7m, which is 30cm short of the qualifying threshold of 10m.  Armed with Myrddyn’s Trimble GeoXH 6000, my intention was to confirm the hill’s status by obtaining an accurate value for its drop.

Looking toward the summit area of Pen Tyrau.  Photo: Aled Williams 

Despite its modest credentials as a separate hill, the top caps an extensive crag-rimmed plateau that forms the north-eastern projection of Arenig Fawr.  This promontory is known locally as Pen Tyrau, a name that has suffered slippage on OS maps over the years.  Its elevated position is a wild place consisting of moorland dappled with small pools and dotted with rough outcrops and small glacial erratics. Having traversed through the bogs of Blaen Nant, I soon found myself standing beside the summit cairn where data was to be collected.

The view from the summit of Pen Tyrau.  Photo: Aled Williams

Surveying was not made easy by the clouds of midges that were swarming the plateau.  Having completed the first survey, I begrudgingly decided to take another set of measurements from a nearby rock that the Abney level had deemed to be close in height to the cairned high point.  As I waited for the Trimble to complete its measuring, I looked out to Arenig Fach and noted the similarities between the character and topography of that hill to that of Pen Tyrau.

The Trimble GeoXH 6000 gathering data at the summit of Pen Tyrau.  Photo: Aled Williams

I headed to the hill’s bwlch for the final survey of the day.  A characteristic of such places is the tricks they play on the eyes, with ups looking like downs and vice versa depending on where one stands.  This bwlch proved to be no exception and I unashamedly used the Trimble as a hand-held GPS to bring me to the point LIDAR had determined to be both the trough in the hill-to-hill line and the crest in the valley-to-valley traverse.

Gathering data at the bwlch of Pen Tyrau.  Photo: Aled Williams

The end of the surveying brought a sudden end to the veritable feast that the midges were enjoying.  I escaped via my inward route to Bwlch Blaen Nant and stopped atop the crags of Y Castell to admire the view down into the waters of Llyn Arenig Fawr.  Behind me towered the upper ridge of Arenig Fawr, which the midday sun would not entice me to visit.

Arenig Fawr from the descent of Pen Tyrau.  Photo: Aled Williams

Aled Williams (July 2024)

 

Survey Result: 

 

Pen Tyrau

Summit Height:  697.4m (converted to OSGM15)

Summit Grid Reference:  SH 83737 38250

Bwlch Height:  687.4m (converted to OSGM15)

Bwlch Grid Reference:  SH 83601 38142

Drop:  10.0m (Welsh Highland Sub addition)

Dominance:  1.44%

 

For further details please consult the Trimble Survey Spreadsheet

 

 

 

  

Mapping Mountains – Significant Height Revisions – The Fours – The 400m Hills of England

The Heart’s Toe (NT 766 069) 

There has been a Significant Height Revision to a hill that is listed in the The Fours – The 400m Hills of England, with the summit height, col height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of The Heart's Toe (NT 766 069)

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

The Fours – The 400m Hills of England - English hills at or above 400m and below 500m in height that have 30m minimum drop, accompanying the main list is a sub list entitled the Sub-Fours, the criteria for which are all English hills at or above 400m and below 500m in height that have 15m or more and below 30m of drop.  The list is co-authored by Myrddyn Phillips and Aled Williams and is available to download in Google Doc format from the Mapping Mountains site.

The Fours - The 400m Hills of England by Myrddyn Phillips and Aled Williams

The name the hill is listed by is The Heart’s Toe, and it is adjoined to the the Thirl Moor group of hills, which are situated in Northumberland, and it is positioned with the A68 road to its south and a minor road to its south-east, and has the village of Byrness towards the south.

When the Introduction to the first group of hills for the updated and revised listing of the The Fours – The 400m Hills of England was published by Mapping Mountains on the 10^th September 2022, it was announced that the accompanying sub lists were being revised with the two 390m categories dispensed with and the criteria and name of the 400m Sub-Fours revised.  The one accompanying sub list is now named the Sub-Fours with its criteria being all English hills 400m and above and below 500m in height that have 15m and more and below 30m of drop.

Prior to this revision this hill was listed with 16m of drop, based on the 449m summit spot height and the 433m col spot height that appear 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. 

LIDAR summit image of The Heart's Toe (NT 766 069)

LIDAR analysis gives the height of this hill as 450.1m positioned at NT 76665 06926, and when compared to its originally listed summit height of 449m this 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 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, the new listed summit height of this hill is 450.1m and this was derived from LIDAR analysis, this is 1.1m higher than its originally listed 449m summit height, which appears as a spot height on the contemporary Ordnance Survey 1:25,000 Explorer map. 

 

The full details for the hill are:

Group:  Thirl Moor

Name:  The Heart’s Toe

OS 1:50,000 map:  80

Summit Height (New Height):  450.1m (LIDAR)

Summit Grid Reference:  NT 76665 06926 (LIDAR)

Col Height:  434.1m (LIDAR)

Col Grid Reference:  NT 76452 06833 & NT 76462 06833 (LIDAR)

Drop:  16.0m (LIDAR)

 

Myrddyn Phillips and Aled Williams (October 2024)