Mapping Mountains – Summit Relocations – 200m Twmpau

 

Cae Twyn Pellaf (SN 935 497) 

There has been a Summit Relocation to a hill that is listed in the 200m 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 Twyn Pellaf (SN 935 497)

The criteria for the list that this summit relocation applies to 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, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

200m Twmpau by Myrddyn Phillips

The name the hill is now listed by is Cae Twyn Pellaf and this was derived from the Tithe map, and it is adjoined to the Drygarn Fawr group of hills, which are situated in the central part of South Wales (Region B, Sub-Region B1), and it is positioned with the A483 road to its north, and minor roads to its west, south and south-east, and has the village of Beulah towards the north-west.

When the original 200m 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 232m summit height, based on the spot height that appears on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and which is positioned at SN 93557 49739.

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 35m of drop, based on the 232m summit spot height and an estimated c 197m bwlch height, based on interpolation of 10m contouring between 190m – 200m. 

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 233.7m positioned at SN 93535 49743.  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 Twyn Pellaf (SN 935 497)

The height produced by LIDAR analysis to the natural summit of this hill is 233.3m positioned at SN 93547 49747 and SN 93549 49748 and SN 93548 49750, and this position in relation to the raised field boundary 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 considered 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 summit height produced by LIDAR analysis is 233.3m and this is positioned at SN 93547 49747 and SN 93549 49748 and SN 93548 49750, this is close to where the 232m spot height is positioned and is approximately 12 metres eastward from the high point of the raised field boundary. 

 

The full details for the hill are: 

Group:  Drygarn Fawr 

Name:  Cae Twyn Pellaf 

OS 1:50,000 map:  147

Summit Height:  233.3m (LIDAR) 

Summit Grid Reference (New Position):  SN 93547 49747 & SN 93549 49748 & SN 93548 49750 (LIDAR) 

Bwlch Height:  199.1m (LIDAR) 

Bwlch Grid Reference:  SN 93427 49480 (LIDAR) 

Drop:  34.2m (LIDAR) 

 

Myrddyn Phillips (June 2024)