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

 

Ffridd Felen (SH 855 388) 

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 initially conducted by Aled Williams and subsequently by Myrddyn Phillips. 

LIDAR image of Ffridd Felen (SH 855 388)

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. 

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

The name the hill is listed by is Ffridd Felen, and it is adjoined to the Arenig group of hills, which are situated in the central part of North Wales (Region A, Sub-Region A3), and it is positioned with a minor road to its north-east and the A4212 road to its north-west, and has the town of Y Bala towards the east 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 not included in the Hills to be surveyed sub list, as it was considered not to meet the criteria then used for this sub category. 

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 21m of drop, based on the 392m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and an estimated c 371m bwlch height, with the latter based on interpolation of 10m contouring between 370m – 380m that appear on the Ordnance Survey 1:25,000 Explorer map. 

Extract from the Ordnance Survey 1:25,000 Explorer 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 analysis gives the summit height of this hill as 395.0m 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 summit 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 395.0m and this was derived from LIDAR analysis, this is 3.0m higher than the previously listed summit height of 392m which appears as a spot height on the contemporary Ordnance Survey 1:25,000 Explorer map. 

 

The full details for the hill are: 

Group:  Arenig 

Name:  Ffridd Felen 

OS 1:50,000 map:  124, 125

Summit Height (New Height):  395.0m (LIDAR)                                                           

Summit Grid Reference:  SH 85563 38821 (LIDAR) 

Bwlch Height:  372.0m (LIDAR) 

Bwlch Grid Reference:  SH 85597 38395 (LIDAR) 

Drop:  23.0m (LIDAR) 

 

Myrddyn Phillips (December 2021)