Mapping Mountains – Hill Reclassifications – 200m Twmpau

Gwastad Meirionydd (SH 589 071) – 200m Sub-Twmpau addition

There has been an addition to the 200m Twmpau 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.

Prior to LIDAR analysis this hill was listed with 19m of drop based on the 214m summit spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and the bwlch spot height of 195m that appears on the Ordnance Survey 1:25,000 Explorer map.

Extract from the Ordnance Survey 1:25,000 Explorer map

The name of the hill is Gwastad Meirionydd 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 between the coast to its north-west and the Afon Dysynni to its south-east and has the small communities of Llwyngwril to the north and Llanegryn to the south-east.

If wanting to visit the hill permission to do so should be sought as it is not a part of designated open access land, however the track to its west and north is a bridleway and is not too far from the high point of the hill.

The addition of Gwastad Meirionydd to 200m Sub-Twmpau status is due to LIDAR analysis of the bwlch conducted by Myrddyn Phillips, with the summit of the hill not covered by LIDAR.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales. 

The 2m DTM LIDAR analysis gives the hill the following details:

Gwastad Meirionydd

Summit Height:  214m

Summit Grid Reference:  SH 589 071

Bwlch Height:  191.5m

Bwlch Grid Reference:  SH 59229 08003

Drop:  23m

LIDAR image of Gwastad Meirionydd

Therefore, the 191.5m LIDAR analysis for the bwlch position at SH 59229 08003 when coupled with the 214m summit height gives this hill 23m of drop, which is sufficient for 200m Sub-Twmpau status.

The full details for the hill are:

Group:  Cadair Idris

Name:  Gwastad Meirionydd

Summit Height:  214m

Summit Grid Reference:  SH 589 071

Bwlch Height:  191.5m (LIDAR)

Bwlch Grid Reference:  SH 59229 08003 (LIDAR)

OS 1:50,000 map:  124

Drop:  23m

Myrddyn Phillips (May 2018)