Mapping Mountains – Hill Reclassifications – Y Trechol – The Dominant Hills of Wales

Pen y Crug (SO 029 303) – Lesser Dominant addition

There has been an addition to the list of the Y Trechol – The Dominant Hills of Wales, with the summit height, bwlch height and their locations, the drop, dominance and status of the hill derived from a Trimble GeoXH 6000 survey and LIDAR analysis conducted by Myrddyn Phillips. 

Pen y Crug (SO 029 303)

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

Y Trechol - The Dominant Hills of Wales - Welsh P30 hills whose prominence  equal or exceed half that of their absolute height.  With the criteria for Lesser Dominant status being those additional Welsh P30 hills whose prominence is between one third and half that of their absolute height.  The list is authored by Myrddyn Phillips with the Introduction to the start of the Mapping Mountains publication of this list appearing on the 3^rd December 2015, and the list is now available in its entirety on Mapping Mountains in Google Doc format. 

Y Trechol - The Dominant Hills of Wales by Myrddyn Phillips

The name the hill is listed by is Pen y Crug, and it is adjoined to the Mynydd Epynt group of hills, which are situated in the central part of South Wales (Region B, Sub-Region B1), and it is positioned with minor roads to its north and south-west, the B4520 road to its north-east and the A40 road farther to its south, and has the town of Aberhonddu (Brecon) towards the south-east.

When the original 300m 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 331m summit height, based on the spot height adjoined to a triangulation pillar that appears on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map. 

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-evaluated and it was listed with an estimated c 108m of drop, based on the 331m summit spot height and an estimated c 223m bwlch height, based on interpolation of 10m contouring between 220m – 230m, resulting in a dominance value of 32.63%, which was insufficient for Lesser Dominant status. 

The Trimble GeoXH 6000 gathering data at the summit of Pen y Crug

The summit of the hill was subsequently surveyed with the Trimble GeoXH 6000, resulting in a 331.2m height, which when combined with the amended bwlch height of an estimated c 222m, based on interpolation of 5m contouring then available on the OS Maps website, gave an estimated c 109m drop and 32.97% dominance value, which was still too low for Lesser Dominant status. 

LIDAR image of Pen y Crug (SO 029 303)

However, it was not until LIDAR became available that the bwlch 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 bwlch image of Pen y Crug

Therefore, the addition of this hill to Lesser Dominant status is due to a Trimble GeoXH 6000 summit survey and LIDAR bwlch analysis, resulting in a 331.2m summit height and a 219.9m bwlch height, with these values giving this hill 111.4m of drop and 33.62% dominance, which is sufficient for Lesser Dominant status. 

 

The full details for the hill are:

Group:  Mynydd Epynt

Name:  Pen y Crug

OS 1:50,000 map:  160

Summit Height:  331.2m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SO 02927 30312 (Trimble GeoXH 6000)

Bwlch Height:  219.9m (LIDAR)

Bwlch Grid Reference:  SO 02162 30880 (LIDAR)

Drop:  111.4m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Dominance:  33.62% (Trimble GeoXH 6000 summit and LIDAR bwlch)

 

Myrddyn Phillips (March 2024)