Mapping Mountains – Hill Reclassifications – Y Pellennig – The Remotest Hills of Wales

Twll y Gwyddel (SM 705 225) – Pellennig addition

There has been an addition to the listing of Y Pellennig – The Remotest Hills of Wales, with the summit height, bwlch height and their locations, the drop and status of the hill confirmed by LIDAR analysis conducted by Aled Williams.

Twll y Gwyddel (SM 705 225)

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

Y Pellennig – The Remotest Hills of Wales - Welsh hills whose summit is at least 2.5km from the nearest paved public road and the hill has a minimum 15m of drop, the list is a joint compilation between Myrddyn Phillips and Aled Williams and is available as a downloadable e-booklet or print-booklet version on Mapping Mountains Publications with the up-to-date master list available on the Mapping Mountains site in Google Doc format.

This hill is a stack and it is found in Twll y Gwyddel and is adjoined to the Carn Llidi group of hills which are situated in the south-western part of Mid and West Wales (Region B, Sub-Region B4), and it is positioned with the southern part of Ynys Dewi to its north and Ynys Cantwr to its south.

This hill was not included when the original list of Pellennig hills was compiled as contemporary Ordnance Survey 1:25,000 Explorer maps do not give it any contour ring.  The lack of contour rings is also applicable to the Ordnance Survey Vector Map Local hosted on the Geograph website which is entitled the Interactive Coverage Map.

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

Extract from the Ordnance Survey Vector Map Local hosted on the Geograph website

The details for this area were re-assessed when the OS Maps website became available online.  This is the replacement for OS Get-a-map and has 5m contour intervals.  But even this map does not show this hill as having any contour rings.

Extract from 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.

LIDAR DSM image of the stack found in Twll y Gwyddel.  1m contour (black), 10m contour (red) and sea level (yellow).

LIDAR DSM image of the stack found in Twll y Gwyddel.  Black lines represent 1m contours, yellow lines represent sea level below which is coloured dark blue.  Coloured shading represents land between 1m contours.  Red line denotes the valley-to-valley traverse through the boulders which are found between the stack and Foel Fawr to the north

The addition of this hill to Pellennig status is due to LIDAR analysis, resulting in a 16.4m summit height and a 0.8m bwlch height, with these values giving this hill 15.6m of drop, and with the distance between its summit and the nearest paved public road being 3.300km, it gives this hill sufficient remoteness and drop for Pellennig status.

The full details for the hill are:

Group:  Carn Llidi

Name:  Twll y Gwyddel

OS 1:50,000 map:  157

Summit Height:  16.4m (LIDAR)

Summit Grid Reference:  SM 70552 22500 (LIDAR)

Bwlch Height:  0.8m (LIDAR)

Bwlch Grid Reference:  SM 70545 22512 (LIDAR)  

 

Drop:  15.6m (LIDAR)

Remoteness:  3.300km

For the additions and deletions to Y Pellennig – The Remotest Hills of Wales reported on Mapping Mountains please consult the following Change Register:

Y Pellennig – The Remotest Hills of Wales

Myrddyn Phillips and Aled Williams (July 2019)

© Crown: CHERISH PROJECT 2019. Produced with EU funds through the Ireland Wales Co-operation Programme 2014-2020. All material made freely available through the Open Government Licence.