Mapping Mountains – Hill Reclassifications – 200m Twmpau

Craig y Castell (SH 694 173) – 200m Sub-Twmpau reclassified to 200m Twmpau

There has been confirmation of a reclassification to the 200m Twmpau list due to LIDAR analysis conducted by Myrddyn Phillips, with the criteria for this list being:

200m Twmpau - Welsh hills at and 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 and above 200m and below 300m in height with 20m and more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward.

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 as it did not meet the criteria then used for the main P30 list; however this list has now been standardised and interpolated heights and drop values also included, resulting in this hill being listed with an estimated c 33m of drop, based on the 297m summit spot height that appears on Harvey maps and an estimated bwlch height of c 264m based on bwlch contouring between 260m – 270m.  The details for this hill were later amended when the Ordnance Survey Interactive Coverage Map hosted on the Geograph website became available online and it was then listed with 34m of drop based on the 298m summit and 264m bwlch spot heights that appear on this map.

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

The name of the hill is Craig y Castell and it is adjoined to the Cadair Idris group of hills, which are situated in the south-western part of North Wales (Region A, Sub-Region A3), and the hill is positioned overlooking the A 493 road to its north-west and has the town of Dolgellau towards its east.

As the upper section of the hill is a part of designated open access land an ascent from most directions is feasible, with a minor road towards its south-east and a public footpath towards its north probably giving the easiest option for ascent.

The confirmation of the reclassification of Craig y Castell 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. 

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

Name:  Craig y Castell

Summit Height:  297.1m

Summit Grid Reference:  SH 69405 17302

Bwlch Height:  263.5m

Bwlch Grid Reference:  SH 69186 17218

Drop:  33.6m

LIDAR image of Craig y Castell

Therefore, the 297.1m LIDAR analysis for the summit position at SH 69405 17302 and the 263.5m LIDAR analysis for the bwlch position at SH 69186 17218 gives this hill 33.6m of drop, which confirms its reclassification to 200m Twmpau status.

The full details for the hill are:

Group:  Cadair Idris

Name:  Craig y Castell

OS 1:50,000 map:  124

Summit Height:  297.1m (LIDAR)

Summit Grid Reference:  SH 69405 17302 (LIDAR)

Bwlch Height:  263.5m (LIDAR)

Bwlch Grid Reference:  SH 69186 17218 (LIDAR)

Drop:  33.6m (LIDAR)

Myrddyn Phillips (May 2018)