Monday, 23 March 2020

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

Bryniau Gleision (SH 842 680) – 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 Ordnance Survey maps.

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 Bryniau Gleision, and it is adjoined to the Rhos group of hills which are situated in the northern part of North Wales (Region A, Sub-Region A2), and it is positioned with the B5113 road to its west and the A548 road to its south and east, and has the town of Llanrwst towards the south-west.

When the original 300m height band of Welsh P30 hills were published on Geoff Crowder’s 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. 

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 and it was listed with 20m of drop, based on the 333m spot height that appears on the Ordnance Survey 1:50,000 Landranger map and the 313m spot height that appears on the area of this hill’s bwlch on the Ordnance Survey 1:25,000 Explorer map.

Extract from the Ordnance Survey 1:50,000 Landranger 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 had many spot heights not on other publicly available Ordnance Survey maps, and also sometimes included 5m contouring.  As this mapping showed a small uppermost 335m ring contour the summit height of this hill was revised to an estimated c 335m.

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 used to appear on the online Vector Map Local.  This re-assessment resulted in the hill being listed with an estimated c 313m bwlch height with an interpolated position considered more accurate than the position of the 313m spot height, with this based on interpolation of 5m contouring between 310m – 315m.

Extract from the OS Maps website

Therefore, the addition of this hill to Sub-Trichant status is due to detail derived from contemporary Ordnance Survey maps, resulting in a c 335m summit height and a c 313m 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:  Rhos

Name:  Bryniau Gleision

OS 1:50,000 map:  116

Summit Height:  c 335m (interpolation)

Summit Grid Reference:  SH 84224 68029 (interpolation)

Bwlch Height:  c 313m (interpolation)

Bwlch Grid Reference:  SH 83865 68223 (interpolation)

Drop:  c 22m (interpolation)

Myrddyn Phillips (March 2020)

No comments: