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

 

Y Gyrn (SH 641 359) – 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 derived from detail on contemporary maps produced from Ordnance Survey data. 

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 13^th May 2017. 

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

The name the hill is listed by is Y Gyrn, and it is adjoined to the Rhinogydd group of hills, which are situated in the western part of North Wales (Region A, Sub-Region A3), and it is positioned with a minor road to its north-west and the A496 road to its west, and has the village of Harlech 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, 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 21m of drop, based on the 349m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and an estimated c 328m bwlch height, based on interpolation of 10m contouring between 320m – 330m that appear on the Ordnance Survey 1:25,000 Explorer map. 

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

The details for this hill were subsequently re-assessed against the mapping on the OS Maps website.  This is the replacement for OS Get-a-map and until recent times had contours at 5m intervals which were proving consistently more accurate compared to the 5m contours that sometimes appear on the Ordnance Survey 1:25,000 Explorer map and used to appear on the online Vector Map Local.  This mapping had bwlch contouring between 325m – 330m, with interpolation giving an estimated bwlch height of c 327m.  This re-assessment resulted in the drop value being amended to an estimated c 22m. 

Therefore, the addition of this hill to Sub-Trichant status is due to detail on contemporary maps produced from Ordnance Survey data , resulting in a 349m summit height and an estimated c 327m bwlch height, with these values giving this hill an estimated c 22m of drop, which is sufficient for it to be classified as a Sub-Trichant. 

 

The full details for the hill are: 

Group:  Rhinogydd 

Name:  Y Gyrn 

OS 1:50,000 map:  124

Summit Height:  349m (spot height)                                                           

Summit Grid Reference:  SH 64172 35969 (spot height) 

Bwlch Height:  c 327m (interpolation) 

Bwlch Grid Reference:  SH 64353 35812 (interpolation) 

Drop:  c 22m (spot height summit and interpolated bwlch) 

 

Myrddyn Phillips (December 2021)