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

 

Pen y Bryn Mawr (SN 705 732) 

There has been confirmation of a Summit Relocation to a hill that is listed in the Y Trichant – The 300m Hills of Wales and Y Trechol – The Dominant Hills of Wales, with the summit height, bwlch height and their locations, the drop, dominance and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

The forested summit of Pen y Bryn Mawr (SN 705 732)

The criteria for the two listings 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. 

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

Y Trechol – The Dominant Hills of Wales – Welsh P30 hills whose prominence equal or exceed half that of their absolute height.  With the criteria for Lesser Dominant status being those additional Welsh P30 hills whose prominence is between one third and half that of their absolute height.  The list is authored by Myrddyn Phillips with the Introduction to the start of the Mapping Mountains publication of this list appearing on the 3^rd December 2015, and the list is now available in its entirety on Mapping Mountains in Google Doc format. 

Y Trechol - The Dominant Hills of Wales by Myrddyn Phillips

The name the hill is listed by is Pen y Bryn Mawr and it is adjoined to the Elenydd group of hills which are situated in the western part of Mid and West Wales (Region B, Sub-Region B2), and it is encircled by minor roads with the A4120 road farther to its north, the B4340 road farther to its west and the B4343 road farther to its east, and has the village of Pont-rhyd-y-groes towards the east. 

When the original 300m height band of Welsh P30 hills was published on Geoff Crowder’s v-g.me website, this hill was listed under the name of Cefn Blewog with a 341m summit height based on the spot height that appears on the Ordnance Survey 1:25,000 Explorer map and which is positioned at SN 70556 72711. 

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

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 115m of drop and 33.72% dominance, based on the 341m summit spot height and an estimated c 226m bwlch height, based on interpolation of 10m contouring between 220m – 230m that appears on the Ordnance Survey 1:25,000 Explorer map. 

The details of this hill were later re-examined and its summit position relocated to Pen y Bryn Mawr, this hill is due north of Cefn Blewog and although it does not possess a summit spot height on contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps, its uppermost 340m ring contour is larger than that given Cefn Blewog and therefore Pen y Bryn Mawr was listed with an estimated c 342m summit height, and when coupled with an emended c 224m bwlch height, these values gave Pen y Bryn Mawr an estimated c 118m of drop and 34.50% dominance. 

LIDAR image of Pen y Bryn Mawr (SN 705 732) and Cefn Blewog (SN 705 727)

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. 

The summit height produced by LIDAR analysis for these two hills is given below:

 

341.619m at SN 70567 73222 for Pen y Bryn Mawr

 

340.660m at SN 70552 72709 for Cefn Blewog

 

This comes within the parameters of the Summit Relocations used within this page heading, these parameters are: 

The term Summit Relocations applies when the hill’s high point is found to be positioned; in a different field, within a different map contour, to a different feature such as in a conifer plantation, to a different point where a number of potential summit positions are within close proximity, 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, or when natural ground or the natural and intact summit is confirmed compared to a higher point such as a raised field boundary that is judged to be a relatively recent man-made construct. 

The Trimble GeoXH 6000 at the summit of Pen y Bryn Mawr

Therefore, the listed summit height of this hill is 341.6m and its new position is SN 70567 73222, 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 northward from where the previously listed summit is positioned. 

 

The full details for the hill are:

Group:  Elenydd

Name:  Pen y Bryn Mawr 

OS 1:50,000 map:  135, 147

Summit Height:  341.6m (LIDAR)                                                           

Summit Grid Reference (New Position):  SN 70567 73222 (LIDAR) 

Bwlch Height:  222.8m (LIDAR) 

Bwlch Grid Reference:  SN 72170 73551 (LIDAR) 

Drop:  118.8m (LIDAR) 

Dominance:  34.77% (LIDAR) 

 

Myrddyn Phillips (September 2021)