Wednesday, 28 March 2018

Mapping Mountains – Hill Reclassifications – 200m Twmpau

Ffridd Tyddyn Mawr (SH 654 140) – 200m Sub-Twmpau addition

There has been a confirmation of an addition to the 200m Twmpau with the summit height, drop and status of the hill confirmed by a survey with the Trimble GeoXH 6000, which was conducted by Myrddyn Phillips and took place on the 17th February 2018, and LIDAR analysis for the bwlch.

The criteria for this listing are:

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.

The hill did not appear in the original Welsh P30 lists on Geoff Crowder’s website as it did not meet the criteria then adopted for the Hills to be surveyed sub list.  The hill was subsequently listed in the sub category after this was standardised and interpolated drop values added, and was included when the updates to the 200m Welsh P30s were published for the Cadair Idris group of hills on Mapping Mountains on the 7th July 2014.

Prior to the survey with the Trimble GeoXH 6000 the hill was listed with 20m of drop, based on the 274m summit spot height and 254m bwlch spot height that appear on the Ordnance Survey Interactive Coverage Map hosted on the Geograph website.

The bounded land where the summit of this hill is situated is named Ffridd Tyddyn Mawr and it is adjoined to the Cadair Idris group of hills, which is situated in the south-western part of North Wales (Region A, Sub-Region A3), and is positioned above the double lakes of Llynnau Cregennan which are to its north north-east and the small community of Arthog which is to its west north-west.

As the upper section of the hill is a part of designated open access land permission to visit does not need to be sought, for those wishing to visit the hill it can be approached from the lakeside car park adjacent to Llynnau Cregennan where a series of gates give access from one walled and bounded ffridd to the next.

The confirmation that Ffridd Tyddyn Mawr is a 200m Sub-Tumpau was due to the survey with the Trimble GeoXH 6000 and LIDAR analysis, resulting in a 273.2m (converted to OSGM15) summit height and a 251.2m (LIDAR) bwlch height, with these values giving the hill 22.0m of drop which is sufficient for its classification to this sub list.

The full details for the hill are:

Group:  Cadair Idris

Summit Height:  273.2m (converted to OSGM15)

Name:  Ffridd Tyddyn Mawr

OS 1:50,000 map:  124

Summit Grid Reference:  SH 65486 14081  
Drop:  22.0m (Trimble summit and LIDAR bwlch)

Ffridd Tyddyn Mawr (SO 654 140) now confirmed as a 200m Sub-Twmpau addition

Myrddyn Phillips (March 2018)

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