Mapping Mountains – Hill Reclassifications – 200m Twmpau

Foel Tyddyn y Berllan (SH 634 051) – 200m Sub-Twmpau reclassified to 200m Twmpau

There has been a reclassification to the listing of 200m Twmpau due to LIDAR analysis conducted by Myrddyn Phillips and subsequently confirmed via a survey with the Trimble GeoXH 6000 which took place on the 14.05.18, with the criteria for this list being:

200m Twmpau - Welsh hills at or above 200m and below 300m in height with 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.

Prior to LIDAR analysis this hill was listed in the Hills to be surveyed sub list when the original Welsh P30 hills were published on Geoff Crowder’s v-g.me website, and after this sub list was standardised with interpolated heights and drop values also included it was initially listed with an estimated c 31m of drop and later changed to 28m of drop, based on the 233m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and the 205m bwlch spot height that appears on the Ordnance Survey Interactive Coverage Map hosted on the Geograph website.

Extract from the Ordnance Survey Interactive Coverage Map hosted on the Geograph website

The locally known name of the hill is Foel Tyddyn y Berllan and it is adjoined to the Tarennydd range of hills which are situated in the south-western part of North Wales (Region A, Sub-Region A3), and it overlooks the Dyffryn Dysynni to its north-west, and has the small community of Anertrinant towards its east and Bryn-crug towards its south-west. 

Foel Tyddyn y Berllan (SH 634 051)

As the summit of the hill is not a part of designated open access land permission to visit should be sought, for those wishing to do so a public footpath towards the east of the summit can gain the eastern ridge of the adjacent hill which is positioned towards the south, and from here it is only a short distance to the summit of this hill.

The reclassification of Foel Tyddyn y Berllan to 200m Twmpau status is due to LIDAR analysis conducted by Myrddyn Phillips.  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 Foel Tyddyn y Berllan

The 1m DTM LIDAR analysis gives the hill the following details:

Name:  Foel Tyddyn y Berllan

Summit Height:  232.3m

Summit Grid Reference:  SH 63480 05160

Bwlch Height:  200.5m

Bwlch Grid Reference:  SH 63493 04962

Drop:  31.8m

Therefore, the 232.3m LIDAR analysis for the summit position at SH 63480 05160 and the 200.5m LIDAR analysis for the bwlch position at SH 63493 04962 gives this hill 31.8m of drop, which is sufficient for it to be classified as a 200m Twmpau, with the details from the Trimble GeoXH 6000 survey being 232.8m (converted to OSGM15) summit at SH 63481 05158 and 200.3m (converted to OSGM15) bwlch at SH 63494 04961, giving this hill 32.5m of drop. 

The full details for the hill are:

Group:  Tarennydd

Name:  Foel Tyddyn y Berllan

OS 1:50,000 map:  124

Summit Height:  232.8m (converted to OSGM15)

Summit Grid Reference:  SH 63481 05158

Bwlch Height:  200.3m (converted t0 OSGM15)

Bwlch Grid Reference:  SH 63494 04961

Drop:  32.5m

The Trimble GeoXH 6000 gathering data at the summit of Foel Tyddyn y Berllan

For details on the survey that confirmed this hill’s reclassification to 200m Twmpau status

Myrddyn Phillips (August 2018)