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

Mynydd Glan Llyn y Forwyn (SH 686 238) – 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 Mynydd Glan Llyn y Forwyn, and it is adjoined to the Y Llethr group of hills, which are situated in the western part of North Wales (Region A, Sub-Region A2), and it is positioned with the A496 road to its south and the A470 road to its east, and has the village of Ganllwyd towards the 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, with the caveat that its twin 378m map heighted summit positioned at SH 68596 23970 was given priority summit status, with an accompanying note stating; Two points of same height – other at SH687238. 

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 378m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and an estimated bwlch height of c 357m based on interpolation of 10m contouring between 350m – 360m. 

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

Since the original publication of the Welsh P30 lists on Geoff Crowder’s v-g.me website there have been a number of 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 were digitally updated such as the Ordnance Survey Vector Map Local that was hosted on the Geograph website and which was entitled the Interactive Coverage Map, whilst others are current such as the interactive mapping on the Magic Maps and WalkLakes websites. 

One of the resources recently available online is the mapping on the OS Maps website and the details for this hill were subsequently re-assessed against this mapping.  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 355m – 360m, with interpolation placing the height of the bwlch as an estimated c 356m. 

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 378m summit height and an estimated c 356m 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:  Y Llethr 

Name:  Mynydd Glan Llyn y Forwyn 

OS 1:50,000 map:  124

Summit Height:  378m (spot height)                                                           

Summit Grid Reference:  SH 68660 23806 (hand-held GPS via DoBIH) 

Bwlch Height:  c 356m (interpolation) 

Bwlch Grid Reference:  SH 68637 23856 (interpolation) 

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

 

Myrddyn Phillips (January 2022)