Mapping Mountains – Summit Relocations – 100m Twmpau and Y Trechol – The Dominant Hills of Wales

Bryn Pydew (SH 810 789) 

There has been a Summit Relocation to a hill that is listed in the 100m Twmpau 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. 

LIDAR image of Bryn Pydew (SH 810 789)

The criteria for the two listings that this summit relocation applies to are:

100m Twmpau - Welsh hills at or above 100m and below 200m in height that have 30m minimum drop, with an accompanying sub list entitled the 100m Sub-Twmpau, with the criteria for this sub category being all Welsh hills at or above 100m and below 200m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

100m Twmpau 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 Bryn Pydew, and it is adjoined to the Mynydd Hiraethog group of hills, which are situated in the northern part of North Wales (Region A, Sub-Region A2), and it is positioned with the A470 road to its west, a minor road to its immediate south and the A55 road to its south-east, and has the town of Llandudno towards the north-west. 

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

When the original Welsh 100m P30 list was published on Geoff Crowder’s v-g.me website, this hill was listed with a 128m summit height, based on the spot height positioned at SH 81095 79015 which appears on the contemporary Ordnance Survey 1:50,000 Landranger map. 

Extract from the Ordnance Survey 1:50,000 Landranger 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.

LIDAR analysis gives the highest ground on this hill as 130.0m positioned at SH 81103 78989.  However, this is to the top of a covered reservoir and protocols dictate that as this is deemed a relatively recent man-made construct such ground is discounted from the height of a hill.

LIDAR summit image of Bryn Pydew (SH 810 789)

The height produced by LIDAR analysis to the natural summit of this hill is 128.5m and is positioned at SH 81097 78986, 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 height produced by LIDAR analysis to the natural summit of this hill is 128.5m and is positioned at SH 81097 78986, this position is relatively close to where the spot height appears on the contemporary Ordnance Survey 1:50,000 Landranger map, and is approximately 6 metres south-westward from the high point of the covered reservoir. 

 

The full details for the hill are: 

Group:  Mynydd Hiraethog 

Name:  Bryn Pydew 

OS 1:50,000 map:  116

Summit Height:  128.5m (LIDAR) 

Summit Grid Reference (New Position):  SH 81097 78986 (LIDAR) 

Bwlch Height:  13.15m (LIDAR) 

Bwlch Grid Reference:  SH 80308 80155 (LIDAR) 

Drop:  115.4m (LIDAR) 

Dominance:  89.77% (LIDAR) 

 

Myrddyn Phillips (April 2024)