Mapping Mountains – Hill Reclassifications – 100m Twmpau

Pt. 118.2m (SN 717 303) – 100m Sub-Twmpau addition

There has been confirmation of an addition to the list of the 100m 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 Pt. 118.2m (SN 717 303)

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

100m Twmpau – Welsh hills at or above 100m and below 200m in height that have 30m minimum drop, with an accompanying sub list entitled the 100m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 100m and below 200m 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. 

100m Twmpau by Myrddyn Phillips

The hill is being listed by the point (Pt. 118.2m) notation as an appropriate name for it either through local enquiry and/or historic research has not been found by the author, and it is adjoined to the Mynydd Du group of hills, which are situated in the southern part of South Wales (Region B, Sub-Region B5), and it is positioned with the A40 road to its north-west and a minor road to its immediate south-east, and has the village of Llangadog towards the south south-west.

When the original 100m 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. 

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

After the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-assessed and it was listed with an estimated c 26m of drop, based on an estimated c 117m summit height and an estimated c 91m bwlch height, with both heights based on interpolation of 5m contouring that appeared on the OS 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.

Therefore, the confirmation of the addition of this hill to 100m Sub-Twmpau status is due to LIDAR analysis, resulting in a 118.2m summit height and a 90.8m bwlch height, with these values giving this hill 27.4m of drop, which is sufficient for it to be classified as a 100m Sub-Twmpau. 

 

The full details for the hill are: 

Group:  Mynydd Du 

Name:  Pt. 118.2m 

OS 1:50,000 map:  146, 160

Summit Height:  118.2m (LIDAR) 

Summit Grid Reference:  SN 71731 30341 & SN 71732 30342 (LIDAR) 

Bwlch Height:  90.8m (LIDAR) 

Bwlch Grid Reference:  SN 71320 29901 (LIDAR) 

Drop:  27.4m (LIDAR) 

 

Myrddyn Phillips (April 2024)