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

 

Yr Oerfa (SJ 101 191) – Sub-Trichant addition

There has been confirmation of 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 and LIDAR analysis conducted by Myrddyn Phillips. 

Yr Oerfa (SJ 101 191)

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, and the Introduction to the Mapping Mountains publication of the list appearing on the 1^st January 2022. 

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

The name the hill is listed by is Yr Oerfa, and it is adjoined to the Foel Cedig group of hills, which are situated in the southern part of North Wales (Region A, Sub-Region A3), and it is positioned with minor roads to its north, west and south, and the B4393 road to its south-east, and has the town of Llanfyllin 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.

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 25m of drop, based on the 377m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and an estimated c 352m bwlch height, based on interpolation of 10m contouring between 350m – 360m. 

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

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 addition of this hill to Sub-Trichant status is due to detail on contemporary maps produced from Ordnance Survey data and LIDAR analysis, resulting in a 377.3m summit height and an estimated c 352m bwlch height, with these values giving this hill an estimated c 25m of drop, which is sufficient for it to be classified as a Sub-Trichant. 

 

The full details for the hill are: 

Group:  Foel Cedig 

Name:  Yr Oerfa 

OS 1:50,000 map:  125

Summit Height:  377.3m (LIDAR)                                                           

Summit Grid Reference:  SJ 01051 19181 (LIDAR) 

Bwlch Height:  c 352m (interpolation) 

Bwlch Grid Reference:  SJ 10156 19505 (interpolation) 

Drop:  c 25m (LIDAR summit and interpolated bwlch) 

 

Myrddyn Phillips (July 2022)