Mapping Mountains – Hill Reclassifications – Marilyns

Coed y Bwnydd (SO 366 069) – Submarilyn addition

This is one in a series of retrospective Hill Reclassification posts that detail hills whose status has altered in the listing of the Welsh Marilyns.  These reclassification posts will give details of hills where I have had direct association with their change of status, and they will tie in with a forthcoming Change Register giving detail to this list and its alterations since publication in the TACit Tables booklet

The listing of Welsh Marilyns was published in booklet format by TACit Tables in February 1997 and entitled The Hewitts and Marilyns of Wales.  The Marilyns were originally listed as an all British compilation and were published by Cicerone Press in 1992 in the book entitled The Relative Hills of Britain.  The list compiler for the Marilyns is Alan Dawson.

When the Welsh Marilyns list was published in booklet format there were 156 qualifying hills with a further 27 Welsh Submarilyns also included.  The criteria for Marilyn status being any hill that has a drop of at least 150m, irrespective of their height, with the criteria for Submarilyn being any hill that has 140m or more and below 150m of drop.

The Hewitts and Marilyns of Wales by Alan Dawson

The details for the hill reclassification appear below:

The name of the hill is Coed y Bwnydd, and it is situated in the Mynyddoedd Duon group of hills in the south-eastern part of Wales, and is positioned with the Afon Wysg (River Usk) and the B4598 road to its west, the A40 road to its north and the A449 road to its east, and has the village of Raglan towards the east north-east and the town of Brynbuga (Usk) towards the south south-east.

Extract from the Ordnance Survey 1:25,000 Explorer map showing detail for Trostrey Hill

Prior to the reclassification of this hill to Submarilyn status it was listed by the name of Clytha Hill with an estimated c 68m of drop based on the 196m spot heights that appear on the Ordnance Survey 1:25,000 Explorer map at SO 36831 06935 and the Ordnance Survey Vector Map Local hosted on the Geograph website and which is entitled the Interactive Coverage Map at SO 36738 06931, and an estimated bwlch height of c 128m based on bwlch contouring between 125m – 130m.

Extract from the Ordnance Survey 1:25,000 Explorer map showing detail for Coed y Bwnydd

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 Coed y Bwnydd (SO 366 069)

The result produced by LIDAR analysis also affects the adjoining Trostrey Hill (SO 369 051), with LIDAR giving Coed y Bwnydd as higher and therefore the bwlch position for each hill are swapped.  The swapping of bylchau has also altered the drop value for each hill, with the caveat that the drop value for the higher hill; Coed y Bwnydd has also been amended as there is a road cutting on the hill to hill traverse.  The LIDAR heights for each summit and bwlch are given below:

Coed y Bwnydd: 

201.4m summit at SO 36613 06919

59.4m bwlch at SO 39308 08901

142.0m drop

Trostrey Hill

199.3m summit at SO 36920 05188

129.1m bwlch at SO 37462 05935

70.2m drop  

LIDAR analysis for Coed y Bwnydd was conducted by Myrddyn Phillips resulting in a summit height of 201.4m positioned at SO 36613 06919 with this position to an embankment that is a part of an ancient hill fort, and the bwlch height is 59.4m positioned at SO 39308 08901 with this position to a road cutting, and the ground of both meets the criteria used within this list.

LIDAR bwlch image of Coed y Bwnydd

The addition of this hill to Submarilyn status was accepted by the list author; Alan Dawson, and its new classification augmented in to the listing of Marilyns in April 2019.

The full details for the hill are:

Name:  Coed y Bwnydd

OS 1:50,000 map:  161

OS 1:25,000 map:  13

Summit Height:  201.4m (LIDAR)

Summit Grid Reference:  SO 36613 06919 (LIDAR)

Bwlch Height:  59.4m (LIDAR)

Bwlch Grid Reference:  SO 39308 08901 (LIDAR)

Drop:  142.0m (LIDAR)

Myrddyn Phillips (March 2020)

Mapping Mountains – Significant Height Revisions – 200m Twmpau and Y Trechol – The Dominant Hills of Wales

Coed y Bwnydd (SO 366 069)

There has been a Significant Height Revision to a hill that is listed in the 200m 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 Coed y Bwnydd (SO 366 069)

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

200m Twmpau – Welsh hills at or above 200m and below 300m in height that have 30m minimum drop, with an accompanying sub list entitled the 200m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 200m and below 300m in height with 20m or more and below 30m of drop.

200m 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 listed by is Coed y Bwnydd and it is adjoined to the Mynyddoedd Duon group of hills which are situated in the eastern part of South Wales (Region C, Sub-Region C3), and it is positioned with the Afon Wysg (River Usk) and the B4598 road to its west, the A40 road to its north and the A449 road to its east, and has the village of Raglan towards the east north-east and the town of Brynbuga (Usk) towards the south south-east.

When the original 100m 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 under the name of Clytha Hill and listed with a 196m summit height, based on the spot height that appears on the Ordnance Survey 1:25,000 Explorer map at SO 368 069.

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 second 196m spot height on the summit area of this hill and positioned at SO 367 069.  This additional 196m 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. 

                                        

LIDAR summit image of Coed y Bwnydd (SO 366 069)

The summit height produced by LIDAR analysis is 201.4m positioned at SO 36613 06919, this is a relatively substantial revision compared to some revised heights, 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, the new listed summit height of this hill is 201.4m and this was produced by LIDAR analysis, this is 5.4m higher than its previously listed height of 196m which was based on the spot height that appears on the Ordnance Survey 1:25,000 Explorer map and the online Vector Map Local.

The full details for the hill are:

Group:  Mynyddoedd Duon

Name:  Coed y Bwnydd

OS 1:50,000 map:  161

Summit Height (New Height):  201.4m (LIDAR)

Summit Grid Reference:  SO 36613 06919 (LIDAR)

Bwlch Height:  59.4m (LIDAR)

Bwlch Grid Reference:  SO 39308 08901 (LIDAR)

Drop:  142.0m (LIDAR)

Dominance:  70.50%

Myrddyn Phillips (February 2020)

Mapping Mountains – Significant Name Changes – 200m Twmpau and Y Trechol – The Dominant Hills of Wales

Coed y Bwnydd (SO 366 069)

There has been a Significant Name Change to a hill that is listed in the 200m Twmpau and the 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 Coed y Bwnydd (SO 366 069)

The criteria for the two listings that this name change applies to are:

200m Twmpau - Welsh hills at or above 200m and below 300m in height with 30m minimum drop, with an accompanying sub list entitled the 200m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 200m and below 300m 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.

200m 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 which is now available in its entirety on Mapping Mountains in Google Doc format.

Y Trechol - The Dominant Hills of Wales by Myrddyn Phillips

The hill is adjoined to the Mynyddoedd Duon group of hills which are situated in the eastern part of South Wales (Region C, Sub-Region C3), and it is positioned with the Afon Wysg (River Usk) and the B4598 road to its west, the A40 road to its north and the A449 road to its east, and has the village of Raglan towards the east north-east and the town of Brynbuga (Usk) towards the south south-east.

When the original 100m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website this hill was listed under the name of Clytha Hill, which is a prominent name that appears on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map close to what was thought to be the summit of this hill.

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

LIDAR analysis has relocated the summit position of this hill from a 196m point that was given as two spot heights that are positioned close to where the name of Clytha Hill appears on contemporary Ordnance Survey maps to a higher 201.4m summit positioned at SO 36613 06919.  This higher summit is situated in woodland that is named on the map as Coed y Bwnydd.  This name appears on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and its position in relation to the summit of this hill is substantiated via the Ordnance Survey series of Six-Inch maps.

LIDAR summit image of Coed y Bwnydd (SO 366 069)

Extract from the Ordnance Survey series of Six-Inch maps

Therefore, the name this hill is now listed by in the 200m Twmpau and Y Trechol – The Dominant Hills of Wales is Coed y Bwnydd, and this name was derived from contemporary Ordnance Survey maps and its position in relation to the summit of this hill substantiated via the Ordnance Survey series of Six-Inch maps.  

The full details for the hill are:

Group:  Mynyddoedd Duon

Name:  Coed y Bwnydd

Previously Listed Name:  Clytha Hill 

  

OS 1:50,000 map:  161

Summit Height:  201.4m (LIDAR)

Summit Grid Reference:  SO 36613 06919 (LIDAR)

Bwlch Height:  59.4m (LIDAR)

Bwlch Grid Reference:  SO 39308 08901 (LIDAR)

Drop:  142.0m (LIDAR)

Dominance:  70.50% (LIDAR)

Myrddyn Phillips (February 2020)

Mapping Mountains – Summit Relocations – 200m Twmpau and Y Trechol – The Dominant Hills of Wales

Coed y Bwnydd (SO 366 069)

There has been a Summit Relocation to a hill that is listed in the 200m 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 Coed y Bwnydd (SO 366 069)

The criteria for the two listings this summit relocation affects are:

200m Twmpau – Welsh hills at or above 200m and below 300m in height that have 30m minimum drop, with an accompanying sub list entitled the 200m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 200m and below 300m in height with 20m or more and below 30m of drop.

200m 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 3rd 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 listed by is Coed y Bwnydd and it is adjoined to the Mynyddoedd Duon group of hills which are situated in the eastern part of South Wales (Region C, Sub-Region C3), and it is positioned with the Afon Wysg (River Usk) and the B4598 road to its west, the A40 road to its north and the A449 road to its east, and has the village of Raglan towards the east north-east and the town of Brynbuga (Usk) towards the south south-east.

When the original 100m 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 under the name of Clytha Hill and listed with a 196m summit height, based on the spot height that appears on the Ordnance Survey 1:25,000 Explorer map at SO 368 069.

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 second 196m spot height on the summit area of this hill and positioned at SO 367 069.  This additional 196m 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. 

                                        

LIDAR summit image of Coed y Bwnydd (SO 366 069)

The summit height produced by LIDAR analysis is 201.4m positioned at SO 36613 06919.  The above detail comes within the parameters of the Summit Relocations used within this page heading, these parameters are:

The term Summit Relocations applies to any listed hill whose summit meets the following criteria; where there are a number of potential summit positions within close proximity and the highest point is not where previously given, or a relocation of approximately 100 metres or more in distance from either the position of a map spot height or from where the summit of the hill was previously thought to exist, or when the summit of the hill is in a different field compared to where previously given, or when it is positioned to a different feature such as in a conifer plantation, or when the high point of the hill is placed within a different map contour compared to its previous listed position, or when the natural and intact summit of a hill is confirmed compared to a higher point such as a raised field boundary that is judged to be a relatively recent man-made construct.

Therefore, the summit height produced by LIDAR analysis is 201.4m positioned at SO 36613 06919, this position is to an embankment that is a part of an ancient hill fort and this ground meets the criteria used within this list, and is approximately 120 metres westward from where the previous listed summit is positioned.

The full details for the hill are:

Group:  Mynyddoedd Duon

Name:  Coed y Bwnydd

OS 1:50,000 map:  161

Summit Height:  201.4m (LIDAR)

Summit Grid Reference (New Position):  SO 36613 06919 (LIDAR)

Bwlch Height:  59.4m (LIDAR)

Bwlch Grid Reference:  SO 39308 08901 (LIDAR)

Drop:  142.0m (LIDAR)

Dominance:  70.50%

Myrddyn Phillips (February 2020)

Mapping Mountains – Hill Reclassifications – Y Trechol – The Dominant Hills of Wales

Coed y Bwnydd (SO 366 069) – Lesser Dominant reclassified to Dominant

There has been a reclassification to the list of the 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 Coed y Bwnydd (SO 366 069)

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

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, with the Introduction to the Mapping Mountains publication of this list appearing on the 3rd 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 listed by is Coed y Bwnydd and it is adjoined to the Mynyddoedd Duon group of hills which are situated in the eastern part of South Wales (Region C, Sub-Region C3), and it is positioned with the Afon Wysg (River Usk) and the B4598 road to its west, the A40 road to its north and the A449 road to its east, and has the village of Raglan towards the east north-east and the town of Brynbuga (Usk) towards the south south-east.

When the original 100m 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 under the name of Clytha Hill and listed with a 196m summit height, based on the spot height that appears on the Ordnance Survey 1:25,000 Explorer map at SO 368 069.

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

When the P30 lists were 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 68m of drop based on the 196m summit height and an estimated bwlch height of c 128m.  These details were transferred to the Dominants list when first compiled, with these values giving this hill 34.69% dominance.

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 second 196m spot height on the summit area of this hill and positioned at SO 367 069.  This additional 196m 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. 

LIDAR summit image of Coed y Bwnydd

LIDAR bwlch image of Coed y Bwnydd

Therefore, the reclassification of this hill from Lesser Dominant status is due to LIDAR analysis, resulting in a 201.4m summit height and a 59.4m bwlch height, with these values giving this hill 142.0m of drop and 70.50% dominance.  With the 201.4m summit height taken to the remains of an embankment which forms a part of an ancient hill fort and the 59.4m bwlch height taken to a road cutting, and as ancient summit structures deemed permanent in nature and the depth of road and rail cuttings qualify under the criteria used within this list the dominance is sufficient for this hill to be reclassified to Dominant status.

The full details for the hill are:

Group:  Mynyddoedd Duon

Name:  Coed y Bwnydd

OS 1:50,000 map:  161

Summit Height:  201.4m (LIDAR)

Summit Grid Reference:  SO 36613 06919 (LIDAR)

Bwlch Height:  59.4m (LIDAR)

Bwlch Grid Reference:  SO 39308 08901 (LIDAR)

Drop:  142.0m (LIDAR)

Dominance:  70.50% (LIDAR) 

Myrddyn Phillips (February 2020)