Mapping Mountains – Hill Reclassifications – 200m Twmpau

Moelfryn (SH 568 511) – 200m Twmpau reclassified to 200m Sub-Twmpau

There has been a reclassification to the list of 200m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis initially conducted by Aled Williams and subsequently by Myrddyn Phillips.

LIDAR image of Moelfryn (SH 568 511) 

The criteria for the list 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.  The list is authored by Myrddyn Phillips, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward.

200m Twmpau by Myrddyn Phillips

The name the hill is now listed by is Moelfryn, and it is adjoined to the Moel Hebog group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it is positioned with a the B4418 road to its north-west and the A4085 road to its east,  and the A488 road to its south-east, and has the village of Beddgelert towards the south south-east.

When the original 200m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was included in the accompanying Hills to be surveyed sub list, with a summit height of 277m, based on the spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map.

Extract from the Ordnance Survey 1:50,000 Landranger map

After the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated and it was listed with an estimated c 30m of drop, based on the 277m summit spot height and an estimated c 247m bwlch height, based on interpolation of 10m contouring between 240m - 250m.

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

Since the original publication of the Welsh P30 lists on Geoff Crowder’s v-g.me website there have been a number of maps made available online.  Some of these are historic such as the series of Six-Inch maps on the National Library of Scotland website.  Whilst others were digitally updated such as the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map, whilst others are current and digitally updated such as the interactive mapping on the Magic Maps and WalkLakes websites.

The Ordnance Survey series of Six-Inch maps formed the base map Ordnance Survey used for many decades leading to the production of the 1:10,000 Series of maps, both have now been superseded by the digitised Master Map.  The Six-Inch maps suggest the contemporary 277m spot height may be erroneous as this summit is immersed in conifer plantation and the only spot height preceding it that has appeared on Ordnance Survey maps is the imperial height of 901ft (274.6m) which originated on the Six-Inch series.  Therefore, there seems no evidence to support how a spot height has changed by 2.4m when the summit is immersed in trees.

Extract from the Ordnance Survey series of Six-Inch maps

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.

Therefore, the reclassification of this hill from 200m Twmpau status is due to LIDAR analysis, resulting in a 274.7m summit height and a 246.1m bwlch height, with these values giving this hill 28.6m of drop, which is sufficient for it to be classified as a 200m Sub-Twmpau. 

The full details for the hill are: 

Group:  Moel Hebog 

Name:  Moelfryn 

OS 1:50,000 map:  115

Summit Height:  274.7m (LIDAR) 

Summit Grid Reference:  SH 56888 51162 (LIDAR) 

Bwlch Height:  246.1m (LIDAR) 

Bwlch Grid Reference:  SH 56415 51302 (LIDAR) 

Drop:  28.6m (LIDAR) 

My thanks to Aled Williams for sending the details of this hill to me

Myrddyn Phillips (May 2017)