Mapping Mountains – Hill Reclassifications – Y Trichant

Pen Rhiw Warren (ST 214 904) – Trichant addition

There has been an addition to the list of the Y Trichant, with the summit height, bwlch height and their locations, the drop and status of the hill confirmed by LIDAR analysis conducted by Myrddyn Phillips.

LIDAR image of Pen Rhiw Warren (ST 214 904)

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

Y Trichant – Welsh hills at or above 300m and below 400m in height that have 30m minimum drop, with an accompanying sub list entitled the Sub-Trichant with the criteria for this sub category being all Welsh hills at or above 300m and below 400m in height with 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips, with the Introduction to the list and the renaming of it appearing on Mapping Mountains on the 13^th May 2017.

The name of the hill is Pen Rhiw Warren and its present state is the result of mine spoil, and it is adjoined to the Cymoedd Gwent group of hills, which are situated in the eastern part of South Wales (Region C, Sub-Region C2), and is positioned with the A468 road and the Afon Rhymni (Rhymney River) to its south, the B4251 and A467 roads and the Afon Sirhywi (Sirhowy River) towards the north, and has the town of Caerffili (Caerphilly) towards the west south-west.

This hill was not included in the main P30 list or the accompanying Hills to be surveyed sub list when the original Welsh 300m P30 hills were published on Geoff Crowder’s v-g.me website, as it was considered not to meet the criteria then used for this list.  This list has now been standardised and interpolated heights and drop values also included in the main P30 and the accompanying sub list.

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

The details for this hill were re-examined when the OS Maps website became available online.  This is the replacement for OS Get-a-map and has contours at 5m intervals and for the majority of land comprising old mine and quarry workings, and rail and road cuttings it shows present day continuous contours, as opposed to the broken contours on contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps.  The mapping on OS Maps shows this hill as having eight continuous 5m contour rings, implying that the hill has at least 35m of drop.

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.

The addition of this hill to Y Trichant status is due to LIDAR analysis, resulting in a 350.5m summit height and a 313.9m bwlch height, with these values giving this hill 36.6m of drop which is sufficient for it to be classified as a Trichant.

The inclusion of this hill to Trichant status is dependent upon using the present-day height of the hill, which has been terra-formed by man’s intrusion and is the result of raised mine spoil.  As the hill in its present form is considered solid and stable its inclusion as a Trichant is accepted as a present-day representation of the land.

 

The full details for the hill are:

Group:  Cymoedd Gwent

Name:  Pen Rhiw Warren

OS 1:50,000 map:  171

Summit Height:  350.5m (LIDAR)

Summit Grid Reference:  ST 21463 90441 (LIDAR)

Bwlch Height:  313.9m (LIDAR)

Bwlch Grid Reference:  ST 21869 90427 (LIDAR)

 

Drop:  36.6m (LIDAR)

Myrddyn Phillips (August 2019)