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

 

Coed Gaer (SH 799 808) 

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 a Trimble GeoXH 6000 summit survey and LIDAR bwlch analysis conducted by Myrddyn Phillips. 

Coed Gaer (SH 799 808)

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 Coed Gaer, 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 B5115 road to its north, the A470 road to its west and minor roads to its south and 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 non-interpolated c 130m summit height, with the prioritised summit position given as SH 802 810, and with an accompanying note stating; Two points of same height – other at SH799808. 

The Trimble GeoXH 6000 gathering data at the summit of Coed Gaer

However, it was not until the survey with the Trimble GeoXH 6000 that an accurate height could be ascertained for one of these points and not until LIDAR became available that the details for these two points could be 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 summit image of Coed Gaer (SH 799 808)

LIDAR analysis gives the highest ground close to the old prioritised summit as 131.1m positioned at SH 80216 80952, whilst the survey with the Trimble GeoXH 6000 gives the height of the recognised summit as 134.0m positioned at SH 79924 80840, and when compared to the original prioritised summit position 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 the Trimble GeoXH 6000 survey to the recognised summit is 134.0m and is positioned at SH 79924 80840, this position is given an uppermost 130m ring contour on the contemporary Ordnance Survey 1:25,000 Explorer map, and is approximately 290 metres south-westward from the position of the old prioritised summit. 

 

The full details for the hill are: 

Group:  Mynydd Hiraethog 

Name:  Coed Gaer 

OS 1:50,000 map:  115

Summit Height:  134.0m (converted to OSGM15, Trimble GeoXH 6000) 

Summit Grid Reference (New Position):  SH 79924 80840 (Trimble GeoXH 6000) 

Bwlch Height:  60.0m (LIDAR) 

Bwlch Grid Reference:  SH 81486 81889 (LIDAR) 

Drop:  74.0m (Trimble GeoXH 6000 summit and LIDAR bwlch) 

Dominance:  55.25% (Trimble GeoXH 6000 summit and LIDAR bwlch) 

 

Myrddyn Phillips (April 2024)