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

Broughton Burrows (SS 413 927)

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 hill’s height, drop and dominance confirmed by LIDAR analysis conducted by Myrddyn Phillips.

LIDAR image of Broughton Burrows

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

30-99m Twmpau – Welsh hills at or above 30m and below 100m in height that have a minimum 30m of 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.

 

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 addition Welsh P30 hills whose prominence is 33.33% or more and below 50% 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.

The name of the hill is Broughton Burrows, and it is adjoined to the Gŵyr group of hills, which are situated in the western part of South Wales (Region C, Sub-Region C1), and it is positioned at the western end of the Gŵyr, and has the small community of Llangynydd towards the south-east.

Although the summit of this hill is not a part of open access land, and as such permission to visit should be sought, there is general acceptance for people to visit, with the nearest public footpath encircling the summit of the hill which comprises a dune system.

When the original Welsh 30-99m P30 list was published on Geoff Crowder’s v-g.me website, this hill was listed with a 49m summit height which appears as a spot height on the Ordnance Survey 1:25,000 Explorer map.

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

When interpolated height and also drop values were added to these lists, this hill was listed with c 32m of drop based on the 49m spot height and an interpolated bwlch height of c 17m based on what was thought to be bwlch contouring between 15m – 20m as indicated on the 1:25,000 Explorer map.  However, as this hill is a part of a dune system this map did not show continuous contours on either the summit or bwlch area of this hill.

Prior to LIDAR analysis this hill was analysed using the 5m contouring on OS Maps, which is the recent replacement for OS Get-a-map.  The bwlch height was confirmed as being between 15m – 20m and an interpolated height of c 18m the listed.  However, this mapping showed a number of 60m continuous ring contours for the summit area of this hill and therefore LIDAR was examined, with the summit height produced being 61.9m and this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

Extract from OS Maps

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 summit height is 61.9m and this was produced from LIDAR analysis, this is 12.9m higher than its previously listed height of 49m which appears as a spot height on the Ordnance Survey 1:25,000 Explorer map, however this new height is in accordance with the 5m contouring on OS Maps.

LIDAR summit image of Broughton Burrows

ills of Wales, and are reproduced below@

Close up LIDAR summit image of Broughton Burrows

The full details for the hill are:

Group:  Gŵyr

Name:  Broughton Burrows

OS 1:50,000 map:  159

Summit Height (New height):  61.9m (LIDAR)

Summit Grid Reference:  SS 41391 92781 (LIDAR)

Bwlch Height:  17.4m (LIDAR)

Bwlch Grid Reference:  SS 41739 92663 (LIDAR) 

 

Drop:  44.5m (LIDAR)

Dominance:  71.95% (LIDAR)

Myrddyn Phillips (December 2018)

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

Burry Holms (SS 398 926)

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 hill’s height, drop, dominance and status confirmed by LIDAR analysis conducted by Myrddyn Phillips.

LIDAR summit image of Burry Holms

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

30-99m Twmpau – Welsh hills at or above 30m and below 100m in height that have a minimum 30m of 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.

 

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 addition Welsh P30 hills whose prominence is 33.33% or more and below 50% 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.

The name of the hill is Burry Holms, and as this name implies the hill is a part of an island, and it is adjoined to the Gŵyr group of hills, which are situated in the western part of South Wales (Region C, Sub-Region C1), and is positioned at the western end of the Gŵyr, with the small community of Llangynydd towards the east south-east.

Although the island is not a part of open access land, and as such permission to visit should be sought, there is general acceptance for people to visit, with the nearest public footpath leading to the beach and island to the east on the western part of Broughton Burrows.

When the original Welsh 30-99m P30 list was published on Geoff Crowder’s v-g.me website this hill was listed with a 35m summit height based on information from David Purchase who had noted a 35m spot height on the Ordnance Survey 1:10,000 map.

Prior to LIDAR analysis the uppermost 30m ring contour on contemporary Ordnance Survey maps had been interpolated, giving an estimated summit height of c 33m.  However, even though the 1:10,000 mapping is prioritised over this interpolated summit height, the 35.1m height produced by LIDAR analysis still comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

Extract from the Ordnance Survey Interactive Coverage Map hosted on the Geograph website

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 summit height is 35.1m and this was produced from LIDAR analysis, this height is only 0.1m higher than the previously listed height of 35m which was derived from the Ordnance Survey 1:10,000 map, but it is 2.1m higher than the interpolated height of c 33m taken from contemporary Ordnance Survey maps.

LIDAR bwlch image of Burry Holms

ills of Wales, and are reproduced below@

The full details for the hill are:

Group:  Gŵyr

Name:  Burry Holms

OS 1:50,000 map:  159

Summit Height (New height):  35.1m (LIDAR)

Summit Grid Reference:  SS 39863 92603 (LIDAR)

Bwlch Height:  0.3m (LIDAR)

Bwlch Grid Reference:  SS 40173 92525 (LIDAR) 

 

Drop:  34.8m (LIDAR)

Dominance:  99.02% (LIDAR)

Myrddyn Phillips (December 2018)

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

Ynys Deullyn (SM 844 340)

There has been a Significant Height Revision to a hill that appears in the following lists; 30-99m Twmpau and Y Trechol – The Dominant Hills of Wales, with the hill’s height, drop, dominance and status confirmed by LIDAR analysis conducted by Myrddyn Phillips.

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

30-99m Twmpau – Welsh hills at or above 30m and below 100m in height that have a minimum 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.

The name of the hill is Ynys Deullyn and as its name implies it is an island, or more strictly speaking a tidal island that is attached to mainland Wales at low tide.  The hill is adjoined to the Carn Llidi group of hills, which are situated in the south-western part of Mid and West Wales (Region B, Sub-Region B4), with the island being positioned on the northern part of the Pembrokeshire coast, and it has the small community of Abercastell towards its west south-west.

If wanting to visit the island permission to do so should be sought as it is not a part of designated open access land, for those wishing to do so caution is advised as the easiest approach will probably necessitate some form of scramble.

This hill did not appear in the main P30 list or the accompanying Hills to be surveyed sub list when the original Welsh P30 hills were published on Geoff Crowder’s v-g.me website, as it was thought not to have 30m of drop and did not meet the criteria then used for the sub category; however this sub list has now been standardised including the addition of interpolated drop and height values.

This hill was included as a P30 shortly after the Ordnance Survey Interactive Coverage Map became available on the Geograph website, and prior to LIDAR analysis it was listed with 30m of drop based on the 30m summit spot height that appears on this map.

Extract from the Ordnance Survey Interactive Coverage Map hosted on the Geograph website

The summit height produced by 2m DSM LIDAR analysis is 32.6m, this is not a dramatic height revision when 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:

2m DSM LIDAR image of Ynys Deullyn (SM 844 340)

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 by LIDAR analysis, 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 summit height is 32.6m and this was produced from LIDAR analysis, this is 2.6m higher than its previously listed height of 30m which appears on the Ordnance Survey Interactive Coverage Map hosted on the Geograph website.

The full details for the hill are:

Group:  Carn Llidi

Summit Height (New Height):  32.6m (LIDAR)

Name:  Ynys Deullyn

OS 1:50,000 map:  157

Summit Grid Reference:  SM 84479 34095 (LIDAR) 

  

Drop:  30.5m (LIDAR)

Dominance:  93.51% (LIDAR) 

Myrddyn Phillips (September 2018)

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

Fegla Fach (SH 638 153)

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, drop, dominance and status of the hill confirmed by a combination of LIDAR analysis and a Trimble GeoXH 6000 survey conducted by Myrddyn Phillips.

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

30-99m Twmpau – Welsh hills at or above 30m and below 100m in height that have a minimum 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.

The name of the hill is Fegla Fach and it is adjoined to the Cadair Idris group of hills, which are situated in the south-western part of North Wales (Region A, Sub-Region A3), with the hill being positioned between the Afon Mawddach to its north-west and the A 493 road to its south-east, and has the village of Y Friog (Fairbourne) to the south-west.  

As the hill is not a part of designated open access land permission to visit should be sought, for those wishing to do so access to its summit can be found from the confines of a camp site which is situated at the base of the hill to its south-west.

Prior to LIDAR analysis and the Trimble survey this hill was listed with 25m of drop based on the 28m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and the 3m bwlch spot height that appears on the Ordnance Survey Interactive Coverage Map hosted on the Geograph website.

Extract from the Ordnance Survey Interactive Coverage Map hosted on the Geograph website

The summit height produced by LIDAR analysis is 31.5m, this is not a dramatic height revision when 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:

LIDAR image of Fegla Fach (top right of photograph) and showing the Arthog bog

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 summit height is 31.5 and this was produced by LIDAR analysis, this is 3.5m higher than its previously listed height of 28m which appears as a spot height on the Ordnance Survey 1:25,000 Explorer map.

The full details for the hill are:

Group:  Cadair Idris

Summit Height (New Height):  31.5m (LIDAR)

Name:  Fegla Fach

OS 1:50,000 map:  124

Summit Grid Reference:  SH 63818 15311 (LIDAR)   

Drop:  30.0m (LIDAR summit and Trimble bwlch)

Dominance:  95.37% (LIDAR summit and Trimble bwlch)

The summit of Fegla Fach (SH 638 153)

For details on the survey and on-site visit that significantly revised the summit height of this hill

Myrddyn Phillips (August 2018)

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

Fegla Fawr (SH 629 146)

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, drop and dominance of the hill confirmed by a Trimble GeoXH 6000 survey and LIDAR analysis conducted by Myrddyn Phillips.

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

30-99m Twmpau – Welsh hills at or above 30m and below 100m in height that have a minimum 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.

The name of the hill is Fegla Fawr and it is adjoined to the Cadair Idris group of hills, which are situated in the south-western part of North Wales (Region A, Sub-Region A3), with the hill being positioned between the Afon Mawddach to its north-west and north and the A 493 road to its south-east, and has the village of Y Friog (Fairbourne) to the south-west.  

As the hill is not a part of designated open access land permission to visit should be sought, however there are paths leading toward its summit which is an indicator that local concession exists to visit it summit.

Prior to LIDAR analysis and the Trimble survey this hill was listed with c 55m of drop based on an estimated c 57m summit height with the hill having an uppermost 50m ring contour on contemporary Ordnance Survey maps, and a bwlch height of 2m based on the spot height that appears on the Ordnance Survey Interactive Coverage Map hosted on the Geograph website.

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

LIDAR image of Fegla Fawr

The summit height produced by the Trimble GeoXH 6000 survey is 59.5m (converted to OSGM15), this is not a dramatic height revision when 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 summit height is 59.5m (converted to OSGM15) and this was produced by the Trimble GeoXH 6000 survey, this is 2.5m higher than its previously listed height of c 57m which was estimated from the uppermost 50m ring contour on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map.

The full details for the hill are:

Group:  Cadair Idris

Summit Height (New Height):  59.5m (converted to OSGM15)

Name:  Fegla Fawr

OS 1:50,000 map:  124

Summit Grid Reference:  SH 62966 14665  

 

Drop:  57.6m (Trimble summit and LIDAR bwlch)

Dominance:  96.81% (Trimble summit and LIDAR bwlch)

Gathering data at the summit of Fegla Fawr (SH 629 146) 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 (August 2018)

Mapping Mountains – Significant Height Revisions – Y Trichant and Y Trechol – The Dominant Hills of Wales

Upper Park (SJ 189 052)

There has been a Significant Height Revision to a hill that is listed in the Y Trichant and Y Trechol – The Dominant Hills of Wales, and which was initiated by a survey with the Trimble GeoXH 6000, with the survey that confirmed this height revision being conducted on the 7^th January 2018.

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

Y Trichant - Welsh hills at and above 300m and below 400m in height that have 30m minimum drop. 

Y Trechol - The Dominant Hills of Wales - These are the Welsh P30 hills whose prominence  equal or exceed half that of their absolute height.  With the criteria for Lesser Dominant status being those addition Welsh P30 hills whose prominence is 33% or more and below 50% of their absolute height.

The name of the hill is Upper Park and it is situated in the Carnedd Wen range of hills which are in the south-eastern part of North Wales (Region A, Sub-Region A4), and it is positioned between the A 458 road to its north and the A 483 road to its south-east, and has the town of Y Trallwng (Welshpool) to its north-east.

As the summit of the hill is not on designated open access land and is part of a private estate permission to visit should be sought, for those wishing to do so there are a number of options for an ascent, all of which use tracks through forested plantations.

Prior to the survey with the Trimble GeoXH 6000 the height of the hill was originally listed as 352m, with this taken from the spot height that appears on the Ordnance Survey 1:25,000 Explorer map, latterly the hill has been listed with an estimated c 353m summit height.

The 354.0m (converted to OSGM15) summit height produced by the Trimble GeoXH 6000 is not a dramatic increase from the 352m spot height, but 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 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, and also hill’s that do not possess a summit spot height and whose estimated summit height has a 2m or more discrepancy when compared to data produced either by the Trimble or by LIDAR.  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 summit height is 354.0m (converted to OSGM15) which is 2.0m higher than the 352m spot height that appears on the Ordnance Survey 1:25,000 Explorer map.

The full details for the hill are:

Group:  Carnedd Wen

Summit Height (New Height):  354.0m (converted to OSGM15)

Name:  Upper Park

OS 1:50,000 map:  125

Summit Grid Reference:  SJ 18980 05270 

        

Drop:  177.0m (converted to OSGM15)

Dominance:  49.998%

The Trimble GeoXH 6000 gathering data at the summit of Upper Park (SJ 189 052) 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 (February 2018)