Mapping Mountains – Summit Relocations – 100m Twmpau

 

Cefn Cyfronydd (SJ 144 082) 

There has been a Summit Relocation to a hill that is now listed in the 100m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill confirmed by LIDAR analysis and a subsequent Trimble GeoXH 6000 survey conducted by Myrddyn Phillips. 

Cefn Cyfronydd (SJ 144 082) on the left of photo

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

100m Twmpau - Welsh hills at or above 100m and below 200m in height with 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. 

The 100m Twmpau by Myrddyn Phillips

The name the hill is listed by is Cefn Cyfronydd and this was derived from local enquiry, and it is adjoined to the Carnedd Wen group of hills which are situated in the south-eastern part of North Wales (Region A, Sub-Region A4), and it is positioned with a minor road to its north, the B4389 road to its north-west, the A458 road to its south-west and the B4392 road to its east, and has the small town of Llanfair Caereinion towards the west south-west. 

When the original Welsh 200m P30 list was published on Geoff Crowder’s v-g.me website the height of the prioritised summit of this hill was estimated as c 200m and positioned at SJ 146 084, with an accompanying note stating; Two points of same height – other at SJ 144 083, with both heights based on interpolation of the two uppermost 200m ring contours that appear on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map. 

Extract from the Ordnance Survey 1:25,000 Explorer 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 summit image of Cefn Cyfronydd

The result produced by LIDAR analysis confirms the summit of this hill as under 200m in height and gives the previously listed non-prioritised summit as the higher, and as this summit has now been surveyed with the Trimble GeoXH 6000 it is this result that is being prioritised for listing purposes, 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 hill’s high point is found to be positioned; in a different field, to a different feature such as in a conifer plantation, placed within a different map contour, to a different point where a number of potential summit positions are within close proximity, or 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 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. 

The Trimble GeoXH 6000 gathering data at the summit of Cefn Cyfronydd

Therefore, the summit height produced by the Trimble GeoXH 6000 survey is 199.1m and this is positioned at SJ 14459 08297, this is approximately 190 metres south-westward from where the previously prioritised summit is positioned. 

 

The full details for the hill are: 

Group:  Carnedd Wen 

Name:  Cefn Cyfronydd 

OS 1:50,000 map:  125

Summit Height:  199.1m (converted to OSGM15, Trimble GeoXH 6000)                                                           

Summit Grid Reference (New Position):  SJ 14459 08297 (Trimble GeoXH 6000) 

Bwlch Height:  150.6m (LIDAR) 

Bwlch Grid Reference:  SJ 14997 08587 (LIDAR) 

Drop:  48.5m (Trimble GeoXH 6000 summit and LIDAR bwlch) 

 

Myrddyn Phillips (July 2021)