Mapping Mountains – Hill Reclassifications – 200m Twmpau and 100m Twmpau

 

Cefn Cyfronydd (SJ 144 082) – 200m Twmpau reclassified to 100m Twmpau

There has been a reclassification to the list of 200m Twmpau and 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

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

200m Twmpau – Welsh hills at or above 200m and below 300m in height that have 30m minimum drop, with an accompanying sub list entitled the 200m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 200m and below 300m 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 200m Twmpau by Myrddyn Phillips

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. 

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 200m height band of Welsh P30 hills was published on Geoff Crowder’s v-g.me website, this hill was included in the main P30 list and listed with an estimated c 200m summit height, based on interpolation of its uppermost 200m ring contour that appears 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 image of Cefn Cyfronydd (SJ 144 082)

The result produced by LIDAR analysis gives this hill a 199.2m summit height, and as the summit has now been surveyed with the Trimble GeoXH 6000 it is this result that is being prioritised for listing purposes. 

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

Therefore, the reclassification of this hill from 200m Twmpau status is due to LIDAR analysis and a subsequent Trimble GeoXH 6000 survey, resulting in 45.5m of drop, with a 199.1m summit height and a 150.6m bwlch height, with the summit height confirming its 100m Twmpau status. 

 

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:  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)