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

Mynydd Pencarreg (SN 575 432) – Lesser Dominant deletion

There has been a deletion 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 summit survey conducted by Myrddyn Phillips and LIDAR bwlch analysis initially conducted by Aled Williams and subsequently by Myrddyn Phillips. 

The summit area of Mynydd Pencarreg (SN 575 432)

The criteria for the list that this deletion 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 Mynydd Pencarreg and it is the highest point in its own grouping of hills, which are situated in the south-western part of South Wales (Region B, Sub-Region B1), and it is positioned with the B4337 road to its south-west and the A482 road to its north-east, and has the town of Llanbedr Pont Steffan (Lampeter) towards the north. 

Extract from the Ordnance Survey 1:50,000 Landranger map

After the original 400m height band of Welsh P30 hills published on Geoff Crowder’s v-g.me website were standardised and interpolated heights and drop values also included, this hill was listed with an estimated c 138m of drop, based on the 415m summit spot height adjoined to a triangulation pillar that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and an estimated c 277m bwlch height, based on interpolation of 10m contouring between 270m – 280m, with these values giving this hill 33.25% dominance. 

Extract from the Ordnance Survey 1:25,000 Explorer map showing the area of the bwlch

The summit of this hill was subsequently surveyed with the Trimble GeoXH 6000, resulting in a 414.9m height and with the bwlch having been analysed via 2m LIDAR, resulting in a 276.2m height, these values gave this hill 138.7m of drop and 33.43% domiance, which was sufficient for it to be classified as a Lesser Dominant hill. 

The Trimble GeoXH 6000 gathering data at the summit of Mynydd Pencarreg

However, it was not until the latest 1m 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 bwlch image of Mynydd Pencarreg

Therefore, the deletion of this hill from Lesser Dominant status is due to LIDAR bwlch analysis coupled with the summit height derived from the Trimble GeoXH 6000 survey, resulting in a 414.9m summit height and a 276.7m bwlch height, with these values giving this hill 138.2m of drop and 33.32% dominance, which is insufficient for Lesser Dominant status. 

 

The full details for the hill are:

Group:  Mynydd Pencarreg

Name:  Mynydd Pencarreg

OS 1:50,000 map:  146

Summit Height:  414.9m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SN 57560 43115 (Trimble GeoXH 6000)

Bwlch Height:  276.7m (LIDAR)

Bwlch Grid Reference:  SN 60000 44090 (LIDAR)

Drop:  138.2m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Dominance:  33.32% (Trimble GeoXH 6000 summit and LIDAR bwlch)

 

Myrddyn Phillips (July 2024)