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

Pen Gallt y Llyn (SH 619 504) – Sub-Trichant addition

There has been an addition 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 confirmed by LIDAR analysis conducted by Myrddyn Phillips.

LIDAR image of Pen Gallt y Llyn (SH 619 504)

The criteria for the list that this addition 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 13th May 2017.

The name the hill is listed by is Pen Gallt y Llyn and it is adjoined to the Yr Wyddfa group of hills which are situated in the north-western part of North Wales (Region A, Sub-Region A12), and it is positioned with the Afon Glaslyn and the A498 road to its south-east and Llyn Dinas towards its south, and has the village of Beddgelert 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 not included in the Hills to be surveyed sub list that accompanied the main P30 list, as it was considered not to meet the criteria then used for this sub 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 17m of drop, based on the 309m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and an estimated bwlch height of c 292m based on contouring between 290m – 300m.

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

The details for this hill were re-examined when the Ordnance Survey Vector Map Local hosted on the Geograph website and which is entitled the Interactive Coverage Map became available online.  This mapping has many spot heights not on any other publicly available Ordnance Survey map and gives a second 309m spot height on the summit area of this hill.  This spot height is also shown on Ordnance Survey data that appears on the Magic Maps website.  As this mapping did not have any additional spot heights at the bwlch area of this hill its listed drop remained as c 17m.

Extract from the Magic Maps website

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 image of Pen Gallt y Llyn (SH 619 504)

The addition of Pen Gallt y Llyn to Sub-Trichant status is due to LIDAR analysis, resulting in a 309.1m summit height and a 289.0m bwlch height, with these values giving this hill 20.1m of drop which is sufficient for it to be classified as a Sub-Trichant.

The full details for the hill are:

Group:  Yr Wyddfa

Name:  Pen Gallt y Llyn

OS 1:50,000 map:  115

Summit Height:  309.1m (LIDAR)

Summit Grid Reference:  SH 61964 50400 (LIDAR)

Bwlch Height:  289.0m (LIDAR)

Bwlch Grid Reference:  SH 61833 50330 (LIDAR)

Drop:  20.1m (LIDAR)

Myrddyn Phillips (January 2020)