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

Mynydd Deulyn (SH 756 609) – 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 via map spot height and contour interpolation.

Mynydd Deulyn (SH 756 609) and its higher northerly summit

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.

The name the hill is listed by is Mynydd Deulyn and it is adjoined to the Carneddau group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it is positioned between Llyn Crafnant to its west and Llyn Geirionydd to its east, with the A5 road to its south and the B5106 road, the Afon Conwy and the A470 road to its east, and has the village of Capel Curig towards the south-west and the town of Llanrwst 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 that accompanied the main P30 list, as it did not meet the criteria then used for this sub category. 

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

When the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated.  Its details were also 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.

The details for this hill were also re-assessed when the OS Maps website became available online.  This is the replacement for OS Get-a-map and has contours at 5m intervals which are proving consistently more accurate compared to the 5m contours that sometimes appear on Ordnance Survey 1:25,000 Explorer maps and the online Vector Map Local.  These re-assessments resulted in the hill being listed with an estimated c 20m of drop.

Extract from the OS Maps website

Therefore, the addition of this hill to Sub-Trichant status is due to the summit spot height and interpolation of bwlch contouring resulting in a 382m summit height based on the spot height that appears on the Ordnance Survey 1:25,000 Explorer map and an estimated bwlch height of c 362m based on interpolation of bwlch contouring between 360m – 365m on the OS Maps website, with these values giving this hill c 20m of drop, which is sufficient for it to be classified as a Sub-Trichant.

The full details for the hill are:

Group:  Carneddau

Name:  Mynydd Deulyn

OS 1:50,000 map:  115

Summit Height:  382m (spot height)

Summit Grid Reference:  SH 75657 60903 (spot height)

Bwlch Height:  c 362m (interpolation)

Bwlch Grid Reference:  SH 75760 61053 (interpolation)

Drop:  c 20m

Myrddyn Phillips (November 2019)