Saturday, 6 May 2017

Mapping Mountains – Hill Reclassifications – 200m Twmpau

Moelfryn (SH 569 511) – 200m Twmpau reclassified to 200m Sub-Twmpau

There has been a reclassification to the listing of Twmpau (thirty welsh metre prominences and upward) hills due to analysis of LIDAR data by Aled Williams.  The hill was listed in the 200m height band of P30 Twmpau hills and it has now been reclassified to a 200m Sub-Twmpau, with the criteria for 200m Twmpau status being all Welsh hills at or above 200m and below 300m in height with 30m minimum drop, and the 200m Sub-Twmpau being all Welsh hills at or above 200m and below 300m in height with 20m or more and below 30m of drop.

The hill was originally listed in the sub list that accompanied the P30 lists when published on Geoff Crowder’s website under the title of ‘Hills to be surveyed.’  When this list was re-evaluated the hill was reclassified to a P30 with c 30m of drop based on its 277m summit spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps and an estimated bwlch height of c 247m.  However, the 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 unsighted and blanketed in trees.

The hill is situated in the north-eastern part of the Beddgelert Forest and is adjoined to Crib Nantlle and the Moel Hebog group of hills, with its Cardinal Hill being Pt. 734m (SH 525 502) and is placed in the Region of North Wales (Region A, Sub-Region A1), and is situated between the small communities of Rhyd-ddu to its north and Beddgelert to its south south-east.

As the hill is immersed in conifer plantation any ascent may prove problematical, but forest tracks are marked on the map to the north-east and south-west of the summit, with the former indicated as giving nearer access.

The name of the hill is Moelfryn and its reclassification to a 200m Sub-Twmpau is due to the analysis of LIDAR data by Aled Williams.  LIDAR (Light Detection & Ranging) is highly accurate height data that is now freely available for much of England and Wales.

Aled’s analysis of LIDAR data gives the hill the following details:


Summit Height:  269.0m

Summit Grid Reference:  SH 56900 51151

Bwlch Height:  246.1m

Bwlch Grid Reference:  SH 56416 51301

Drop:  22.9m

Therefore, the 269.0m LIDAR data produced for the summit position at SH 56900 51151 and the 246.1m LIDAR data produced for the bwlch position at SH 56416 51301 gives this hill 22.9m of drop.  However as the DTM model may have struggled to model the summit hillock the detail from the Ordnance Survey Six-Inch map is being taken for the summit.

The full details for the hill are:

Cardinal Hill:  Pt. 734m (SH 525 502)

Summit Height:  275m (height rounded up from Six-Inch map)

Name:  Moelfryn

OS 1:50,000 map:  115

Summit Grid Reference:  SH 56900 51151  

Drop:  29m (summit height from Six-Inch map and bwlch height from LIDAR data)

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

Myrddyn Phillips (May 2017)

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