Mapping Mountains – Summit Relocations – Y Trichant – The 300m Hills of Wales

Graig Orddle (SN 998 935) 

There has been a Summit Relocation to a hill that is listed in the 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 LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Graig Orddle (SN 998 935)

The criteria for the list that this summit relocation 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 Graig Orddle, and it is adjoined to the Pumlumon group of hills, which are situated in the northern part of South Wales (Region B, Sub-Region B1), and it is positioned with the A470 road to its north-east, a minor road to its west and the B4569 to its south, and has the village of Caersŵs towards the south-east.

When the original 300m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was included under the name of Foel y Belan with a 352m summit height, based on the spot height that appears on the Ordnance Survey 1:25,000 Explorer map and which is positioned at SN 994 933. 

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

The details for this hill were re-assessed when the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map became available online.  This mapping had many spot heights not on other publicly available Ordnance Survey maps and for this hill it had a twin 352m spot heighted summit named Graig Orddle and which is positioned at SN 998 935.

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. 

LIDAR image of Foel y Belan (SN 994 933) and Graig Orddle (SN 998 935)

The summit height produced by LIDAR analysis for Graig Orddle is 351.8m positioned at SN 99841 93587, whilst the summit height produced by LIDAR analysis for Foel y Belan is 351.3m positioned at SN 99411 93331, and this comes within the parameters of the Summit Relocations used within this page heading, these parameters are:

The term Summit Relocations applies when the high point of the hill is found to be positioned; in a different field, to a different feature such as in a conifer plantation,  within a different map contour, to a different point where a number of potential summit positions are within close proximity, when natural ground or the natural and intact summit of a hill is confirmed compared to a higher point such as a raised field boundary or covered reservoir that is judged to be a relatively recent man-made construct, or a relocation of approximately 100 metres or more in distance from either the position of a map spot height or from where the summit of the hill was previously thought to exist.

Therefore, the summit height produced by LIDAR analysis is 351.8m and this is positioned at SN 99841 93587, this position is not given a spot height on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map, and is approximately 500 metres north-eastward from where the originally listed summit is positioned. 

 

The full details for the hill are:

Group:  Pumlumon 

Name:  Graig Orddle 

OS 1:50,000 map:  136

Summit Height:  351.8m (LIDAR)                                                           

Summit Grid Reference:  SN 99841 93587 (LIDAR) 

Bwlch Height:  272.8m (LIDAR) 

Bwlch Grid Reference:  SN 98777 93951 (LIDAR) 

Drop:  79.0m (LIDAR) 

 

Myrddyn Phillips (November 2022)