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

 

Ffridd (SH 953 451) 

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 Ffridd (SH 953 451)

The criteria for the list this height revision affects 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 and this was derived from the Tithe map, 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 the A5 road to its north-east, the B4501 road to its west and a minor road to its south, and has the village of Llangwm towards the east south-east. 

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 Hills to be surveyed sub list with a summit height of 361m, based on the spot height that appears on the Ordnance Survey 1:50,000 Landranger map, with the Ordnance Survey 1:25,000 Explorer map just having an uppermost 360m ring contour without any spot height. 

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 analysis gives the summit height of this hill as 363.6m 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, this hill’s new listed summit height is 363.6m and this was derived from LIDAR analysis, this is 2.6m higher than the previously listed summit height of 361m which appears as a spot height on the contemporary Ordnance Survey 1:50,000 Landranger map. 

 

The full details for the hill are: 

Group:  Arenig 

Name:  Ffridd 

OS 1:50,000 map:  116

Summit Height New Height):  363.6m (LIDAR)                                                           

Summit Grid Reference:  SH 95302 45157 (LIDAR) 

Bwlch Height:  338.5m (LIDAR) 

Bwlch Grid Reference:  SH 94841 45316 (LIDAR) 

Drop:  25.1m (LIDAR) 

 

Myrddyn Phillips (June 2021)