Mapping Mountains – Summit Relocations – 30-99m Twmpau

30-99m Twmpau – Summit Relocations

The 30-99m Twmpau (thirty welsh metre prominences and upward) are the Welsh hills at or above 30m and below 100m in height that have 30m minimum drop.  Accompanying the main list are two sub lists entitled the 30-99m Sub-Twmpau with the criteria being all Welsh hills at or above 30m and below 100m in height with 20m or more and below 30m of drop, and the Double Sub-Twmpau with the criteria being all Welsh hills at or above 20m and below 30m in height with 20m or more and below 30m of drop.

The list is authored by Myrddyn Phillips and the posts that have appeared on Mapping Mountains detailing the Summit Relocations to the main P30 list and the sub lists appear below presented chronologically in receding order.

Mapping Mountains - Summit Relocations - 30-99m Twmpau

Pen y Coed (SN 569 049) - 36th summit relocation

Hill Reclassifications post for Pen y Coed

Significant Name Changes post for Pen y Coed

 

There has been a Summit Relocation to a hill that is listed in the 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 Pen y Coed (SN 569 049)

The criteria for the list that this summit relocation 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 Pen y Coed and this was drived 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 B4306 road to its north-east, a minor road to its south-west, and the M4 motorway to its south-east, and has the town of Pontarddulais towards the south-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 20m of drop, based on the 88m summit spot height positioned at SN 56954 04958 that appears on the contemporary Ordnance Survey 1:25,000 Explorer map and an estimated c 68m bwlch height, based on interpolation of 5m contouring between 65m – 70m. 

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 analysis gives the highest ground on this hill as 89.3m positioned at SN 56988 04938 and SN 56989 04939.  However, this is a part of a raised field boundary and protocols dictate that as this is deemed a relatively recent man-made construct such ground is discounted from the height of a hill. 

LIDAR summit image of Pen y Coed (SN 569 049)

The height produced by LIDAR analysis to the highest remaining natural summit of this hill is 89.2m and this is positioned at SN 56986 04941, and this comes within the parameters of the Summit Relocations used within this page heading, these parameters are:

The term Summit Relocations applies when the high point of the hill is found to be positioned; in a different field, to a different feature such as in a conifer plantation,  within a different map contour, to a different point where a number of potential summit positions are within close proximity, when natural ground or the natural and intact summit of a hill is confirmed compared to a higher point such as a raised field boundary or covered reservoir that is judged to be a relatively recent man-made construct, 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.

Therefore, the height produced by LIDAR analysis to the remaining natural summit of this hill is 89.2m and is positioned at SN 56986 04941, this position is relatively close to where the spot height appears on the Ordnance Survey 1:25,000 Explorer map and is approximately 3 metres north-westward from where the high point of the raised field boundary is positioned. 

 

The full details for the hill are: 

Group:  Mynydd Sylen 

Name:  Pen y Coed 

OS 1:50,000 map:  159

Summit Height:  89.2m (LIDAR) 

Summit Grid Reference (New Position):  SN 56986 04941 (LIDAR)               

Bwlch Height:  68.0m (LIDAR) 

Bwlch Grid Reference:  SN 56691 04800 (LIDAR) 

Drop:  21.2m (LIDAR)