Mapping Mountains – Significant Height Revisions – Y Trichant – The 300m Hills of Wales

 

Pen Llwyn Uchel (SN 517 387) 

There has been a Significant Height Revision to a hill that is listed in the Y Trichant – The 300m Hills of Wales, 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 Pen Llwyn Uchel (SN 517 387)

The criteria for the list that this height revision applies to are:

Y Trichant – The 300m Hills of Wales – 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, and the Introduction to the Mapping Mountains publication of the list appearing on the 1^st January 2022. 

Y Trichant - The 300m Hills of Wales by Myrddyn Phillips

The name the hill is listed by is Pen Llwyn Uchel and it is adjoined to the Mynydd Pencarreg group of hills, which are situated in the south-western part of South Wales (Region B, Sub-Region B1), and it is positioned with a minor road to its immediate north, the A485 road to its west and the B4337 road to its east, and has the town of Llanybydder towards the north. 

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

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 accompanying Hills to be surveyed sub list with a 381m summit height, based on the twin 381m spot heights that appear on the Ordnance Survey 1:25,000 Explorer map, with an accompanying note stating; Two tops of same height (SN517388 is 383m on 1985 1:50000 map). 

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

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 summit image of Pen Llwyn Uchel (SN 517 387)

The summit height produced by LIDAR analysis is 383.45m and is positioned at SN 51750 38783 and SN 51757 38784, and this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revisions applies to any listed hill whose interpolated height and Ordnance Survey or Harvey map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or analysis of data produced via LIDAR, also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble or by LIDAR analysis.

Therefore, the new listed summit height of this hill is 383.45m and this was derived from LIDAR analysis, this is 2.45m higher than the previously listed summit height of 381m, which was based on the spot height that appears on the Ordnance Survey 1:25,000 Explorer map. 

 

The full details for the hill are: 

Group:  Mynydd Pencarreg 

Name:  Pen Llwyn Uchel 

OS 1:50,000 map:  146

Summit Height (New Height):  383.45m (LIDAR)                                                           

Summit Grid Reference:  SN 51750 38783 & SN 51757 38784 (LIDAR) 

Bwlch Height:  359.6m (LIDAR) 

Bwlch Grid Reference:  SN 52370 38728 (LIDAR) 

Drop:  23.8m (LIDAR) 

 

Myrddyn Phillips (September 2023)