Mapping Mountains – Hill Reclassifications – Y Trichant – The 300m Hills of Wales

 

Garth (SH 980 392) – Trichant reclassified to Sub-Trichant

There has been a reclassification to the list of 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 Garth (SH 980 392)

The criteria for the list that this reclassification 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 Garth, 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 A494 road to its north-west, a minor road to its south-west and the B4402 road to its south-east, and has the town of Y Bala towards the south-west. 

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, as it was considered not to meet the criteria then used for the main P30 category. 

When 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 29m of drop, based on an estimated c 307m summit height and an estimated c 278m bwlch height, with both heights based on interpolation of 10m contouring that appears on the Ordnance Survey 1:25,000 Explorer map. 

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

Since publication of the P30 lists of Geoff Crowder’s v-g.me website there have been a number of Ordnance Survey maps made available online, some of these are historic such as the series of Six-Inch maps on the National Library of Scotland website, whilst others are current and digitally updated such as the old Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map. 

The details for this hill were re-assessed when the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map became available online.  This mapping had many spot heights not on other publicly available maps and for this hill it had a 309m summit spot height positioned at SH 98123 39317, and when coupled with the estimated c 278m bwlch height gave this hill an estimated c 31m of drop and therefore it was reclassified to a Trichant. 

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. 

Therefore, the reclassification of this hill to Sub-Trichant status is due to LIDAR analysis, resulting in a 308.6m summit height and a 280.15m bwlch height, with these values giving this hill 28.5m of drop, which is insufficient for it to be classified as a Trichant. 

 

The full details for the hill are: 

Group:  Arenig 

Name:  Garth 

OS 1:50,000 map:  125

Summit Height:  308.6m (LIDAR)                                                           

Summit Grid Reference:  SH 98081 39259 (LIDAR) 

Bwlch Height:  280.15m (LIDAR) 

Bwlch Grid Reference:  SH 97706 38862 (LIDAR) 

Drop:  28.5m (LIDAR) 

 

Myrddyn Phillips (October 2021)