Mapping Mountains – Summit Relocations – 30-99m Twmpau

 

Cae Pen y Cefn (SH 532 377) 

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 Cae Pen y Cefn (SH 532 377)

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 Cae Pen y Cefn and this was derived from the Tithe map, and it is adjoined to the Moel Hebog group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it is positioned with a minor road to its north and south, and the A497 road farther to its north, and has the town of Porthmadog towards the east 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 20m of drop, based on the 58m summit spot height that appears on the contemporary Ordnance Survey 1:25000 Explorer map and which is positioned at SH 53282 37746, and an estimated c 38m bwlch height, based on interpolation of 5m contouring between 35m – 40m. 

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 58.5m positioned at SH 53278 37755.  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 Cae Pen y Cefn (SH 532 377)

The height produced by LIDAR analysis to the highest remaining natural ground on this hill is 57.8m and this is positioned at SH 53267 37729, 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 highest remaining natural ground on this hill is 57.8m and is positioned at SH 53267 37729, this position is relatively close to where the spot height appears on the contemporary Ordnance Survey 1:25,000 Explorer map, and is approximately 26 metres south-westward from where the high point of the raised field boundary is positioned. 

 

The full details for the hill are: 

Group:  Moel Hebog 

Name:  Cae Pen y Cefn 

OS 1:50,000 map:  124

Summit Height:  57.8m (LIDAR) 

Summit Grid Reference (New Position):  SH 53267 37729 (LIDAR)               

Bwlch Height:  37.3m (LIDAR) 

Bwlch Grid Reference:  SH 53729 38357 (LIDAR) 

Drop:  20.5m (LIDAR) 

 

Myrddyn Phillips (May 2024)