Monday, 20 January 2020

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

Pt. 316.1m (SH 608 479) – 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 by LIDAR analysis conducted by Myrddyn Phillips.

LIDAR image of Pt. 316.1m (SH 608 479)

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 hill is being listed by the point (Pt. 316.1m) notation as an appropriate name for it either through local enquiry and / or historic research has not been found by the author, and it is adjoined to the Moelwynion group of hills which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it is positioned with the Afon Glaslyn and the A498 road to its north and west, and has the village of Beddgelert towards the 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 an estimated c 19m of drop, based on the 315m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and an estimated bwlch height of c 296m based on interpolation of contouring between 290m – 300m.

The details for this hill were re-assessed 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 other publicly available Ordnance Survey maps.

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.  These re-assessments resulted in the hill remaining with an estimated drop of c 19m.

Extract from the OS Maps website

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 LIDAR analysis, resulting in a 316.1m summit height and a 296.0m bwlch height, with these values giving this hill 20.1m of drop which is sufficient for it to be classified as a Sub-Trichant.

The full details for the hill are:

Group:  Moelwynion

Name:  Pt. 316.1m

OS 1:50,000 map:  115

Summit Height:  316.1m (LIDAR)

Summit Grid Reference:  SH 60849 47935 (LIDAR)

Bwlch Height:  296.0m (LIDAR)

Bwlch Grid Reference:  SH 60963 47863 (LIDAR)

Drop:  20.1m (LIDAR)

Myrddyn Phillips (January 2020)

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